EP4635312A1

EP4635312A1 - Plant and method for the production of filter tubes

Info

Publication number: EP4635312A1
Application number: EP25171373.1A
Authority: EP
Inventors: Fausto Mengoli; Alessandro CAPPELLI
Original assignee: GD SpA
Current assignee: GD SpA
Priority date: 2024-04-19
Filing date: 2025-04-17
Publication date: 2025-10-22

Abstract

A plant (1) for the production of filter tubes, comprising feed means for feeding a succession of hollow tubular elements and a filter tip attachment machine (N) for combining, at a combiner drum (E), at least one filter segment with each hollow tubular element so as to form a respective group of segments. The plant (1) comprises an applicator device (G) operatively positioned downstream of the combiner drum (E) and configured to receive a web (S) unwound from an unwinding unit (A), to divide the web (S) into connecting strips and to apply each connecting strip in a flag-like manner on a respective group of segments. The plant (1) comprises an embossing unit (100), disposed at a position interposed between the unwinding unit (A) and the applicator device (G) along a feed path of the web (S) to print an embossing on said web (S).

Description

The present invention relates to the field of smoking articles and the object thereof is a plant and a method for the production of filter tubes.
The expression "filter tubes" is commonly used for smoker articles (in other words, articles pf the tobacco industry) characterized by a hollow tubular element rigidly connected to a filtering segment by the application of a paper connecting strip, typically of the "cork" type, rolled onto both elements. Filter tubes are sold with the tubular element empty, thus allowing the consumer to fill them autonomously with a mixture of tobacco or other smokable materials, according to their preferences. The diffusion thereof is mainly in contexts where users desire more control over the composition and intensity of their smoking experience.
In the pertinent field of the present invention, plants for the production of filter tubes are known. Such plants comprise a machine for the production of a succession of hollow tubular elements (commonly called maker machine) and a machine for applying at least one filter segment to each hollow tubular element (commonly called filter tip attachment machine) so as to form a respective group of segments. Known plants further comprise an unwinding unit configured to receive at least one roll from which a paper web is unwound which is cut to form a plurality of connecting strips used to wrap and stabilize the respective groups of segments.
Conventionally, the paper employed as connecting strip has a graphic design printed on the surface.
Moreover, in order to give the connecting strips a more pleasant texture for the smoker, the paper web is often embossed beforehand. In other words, a plurality of ridges and recesses is made on the paper web according to a predetermined pattern.
In other words, the unwinding unit of the known plants is configured to operate with rolls in which the paper web has already undergone an embossing process and which, therefore, already have the aforesaid plurality of ridges and recesses.
The Applicant has found that although it is operable, the plant described above has some drawbacks, making it improvable.
Firstly, rolls with a pre-embossed web occupy a larger space than rolls with a smooth web (i.e., not embossed), length of the web wound on the roll being equal. This can result in difficulty in storing the rolls in the limited spaces of warehouses, as well as in the movement thereof during the internal and external transport.
For the same reason, the aforesaid plants are to be capable of handling large rolls (wound web being equal). Alternatively, assuming rolls with smaller dimensions are wanted (which results in a shorter length of the wound web), the rolls will require frequent changes.
A further problem relates to the possibility of the web pre-embossing being ruined during the storage in rolls, compromising the quality of the end product. Indeed, if the pre-embossing is damaged during storage, for example, due to excessive pressures, humidity or incorrect handling, the web could lose its structural integrity, compromising the end product.
Therefore, in such a context, it is the technical task of the present invention to provide a plant and a method for the production of filter tubes which are free from the drawbacks of the prior art.
It is therefore the object of the present invention to provide a plant and a method for the production of filter tubes which are improved in terms of operating efficiency and structural efficiency.
It is a further object of the present invention to provide a plant and a method for the production of filter tubes which ensure a satisfactory finished product in terms of quality.
The technical task specified and the objects specified are substantially achieved by a plant for the production of filter tubes having the technical features outlined below. The technical task specified and the objects specified are substantially achieved by a method for the production of filter tubes, which is preferably performed by means of the aforesaid plant.
The plant comprises feed means for feeding a succession of hollow tubular elements. In the context of the present invention, the expression "hollow tubular element" refers to the part of the filter tube product intended to contain, in use, the smoking material. This hollow tubular element is an internally empty cylinder usually made of paper.
The plant comprises a filter tip attachment machine for applying at least one filter segment to each hollow tubular element. The expression "filter segment" refers to the part of the filter tube product which consists of filtering material. This segment is usually made of cellulose acetate fiber or other porous materials and/or having a filtering effect (such as, for example, preferably crimped paper or cellulose), i.e., designed to trap some particles present in the smoke during the combustion of the product. The filter tip attachment machine comprises a downfeed line configured to feed a succession of filter segments.
The filter tip attachment machine comprises a combiner drum in which each filter segment is combined with at least one hollow tubular element to form a group of segments. In an embodiment, each (double-length) filter segment in the combiner drum is combined with a pair of tubular segments obtained from cutting a double-length hollow tubular element.
The plant comprises an unwinding unit configured to receive at least one roll and to unwind from it a web, preferably of paper.
Preferably, such a web is smooth (i.e., it is not pre-embossed).
Preferably, the web has a substantially smooth surface, i.e., without ridges and/or recesses.
The filter tip attachment machine comprises an applicator device operatively positioned downstream of the combiner drum and configured to receive the web unwound from the unwinding unit, to divide (preferably cut) the web into connecting strips and to apply each connecting strip in a flag-like manner on a respective group of segments.
The plant comprises web guide means for guiding the web along a feed path that preferably extends between the unwinding unit and the applicator device.
The expression "feed path" means the movement path along which the web is fed, which starts from the unwinding of the web from the respective roll and ends with the application of each connecting strip on the respective group of segments.
The filter tip attachment machine therefore comprises a rolling device, positioned downstream of the applicator device and configured to wrap the aforesaid connecting strip round the respective group of segments.
According to an aspect of the present invention, the plant comprises an embossing unit, located along the feed path of the web in position interposed between the unwinding unit and the applicator device. The embossing unit is configured to print an embossing on the web.
Preferably, the embossing unit is configured to print a plurality of recesses and ridges on the surface of the web according to a predefined pattern.
Advantageously, the Applicant has found that the employment of an embossing device operatively disposed in the production line, introduced in order to obtain filter tubes with an embossed connecting strip without employing a pre-embossed web (due to all the drawbacks described above), ensures a plurality of advantages.
Firstly, by eliminating the pre-embossing from the web itself, the space required to store and transport the rolls is reduced. This is because non-pre-embossed rolls (web length being equal) occupy less space than the pre-embossed ones, allowing increased efficiency in exploiting the storage spaces and simplifying the movement during the internal and external transport.
Moreover, the addition of the pre-embossing device to the feed line allows increased flexibility in adapting to production needs. Since the pre-embossing occurs in real time during the production process, it is possible to easily adjust the intensity of the embossing based on the specifications required by the end product or the client's preferences. This level of control can result in increased accuracy in the quality of the embossing, thus ensuring an improved use experience for the final consumer.
Again, by eliminating the pre-embossing, the risk of damage to the pre-embossing itself when the rolls are stored and moved is reduced. Indeed, without the need to manage pre-embossed rolls, which are more delicate, the probability of damaging the rolls during the loading, unloading and transport operations is reduced.
Overall, the implementation of rolls with a non-pre-embossed web (i.e., smooth) in combination with an embossing device on the feed path of the web can lead to increased efficiency in exploiting warehouse spaces, increased production flexibility, an improved end product in terms of quality, and increased overall efficiency of the production process.
According to an aspect of the present invention, the embossing unit can be employed in a plant for the production of filter tubes ad hoc designed or can be retrofittable or retrofitted in a pre-existing plant for the production of filter tubes originally devoid of the possibility of embossing the web.
In the context of the present invention, the expression "retrofit" means the functional integration of an embossing unit in a pre-existing plant for the production of filter tubes, originally devoid of such a functionality, without requiring significant structural modifications to the plant itself. As will become increasingly apparent below, the embossing unit is designed to be operatively compatible with existing plants, allowing the addition of the embossing function via minimum mechanical and functional connections. The retrofit, thus defined, allows the production capacity of the plant to be enriched, improving the operating efficiency and quality of the finished product without the need to replace or redesign the basic infrastructure.
Advantageously, especially in the case of retrofitting installation, the embossing unit can be integrated in a relatively easy manner in a pre-existing plant for the production of filter tubes, thus providing the possibility of enriching the production process without the need to invest in a complete and new plant.
Preferably, the embossing unit comprises a containing frame and an embossing device supported by the containing frame. Preferably, the embossing unit comprises further operating elements (a web entraining device, guide rollers, tensioners, and so on) supported by the containing frame. According to a preferred embodiment, said embossing unit is of the stand-alone type, i.e., suitable to employ in any zone of the working area outside the filter tip attachment machine.
Some non-exclusive embodiments of the embossing unit retrofitted in a plant for the production of filter tubes of the known type are introduced below. Clearly, according to the generality of the invention, the following technical features can be applied also to an ad hoc designed plant for the production of filter tubes.
According to a first embodiment, the embossing unit is separate from said filter tip attachment machine and the web unwinding unit. "Separate" means physically detached from, and independent of the unwinding unit and the filter tip attachment machine.
For example, the filter tip attachment machine comprises a main frame and the unwinding unit comprises a secondary frame. According to an embodiment, the embossing unit is interposed between the main and secondary frames but separate from them. According to such an example, the feed path of the web starts at the secondary web, passes through the embossing unit, and ends at the main frame.
Alternatively, in an example similar to the one above, the embossing unit is again interposed between the main and secondary frames along the feed path of the web, but it is firmly fixed (physically connected) to the secondary frame and/or it is integrated in the secondary frame. Also, according to such an example, the feed path of the web starts at the secondary frame, passes through the embossing unit and ends at the main frame.
According to a further different embodiment, the unwinding unit is reincluded (integrated) in the main frame. In this case, the embossing unit can be physically separate from the main frame, and external to it, or it can be physically connected to the main frame.
Further features and advantages of the present invention will become more apparent from the indicative, and therefore non-limiting, description of three embodiments of a plant for the production of filter tubes, as well as a method for the production of filter tubes, which is preferably performed by the aforesaid plant, according to the invention.
Such a description will be presented below with reference to the accompanying drawings, provided by way of mere and thus non-limiting indication, in which:

Figure 1 shows a diagrammatic view of a first embodiment of a plant for the production of filter tubes in accordance with the present invention;
Figure 2 shows a diagrammatic view of a second embodiment of a plant for the production of filter tubes in accordance with the present invention;
Figure 3 shows a diagrammatic view of a third embodiment of a plant for the production of filter tubes in accordance with the present invention;
Figure 4 shows an embodiment of an embossing unit employable in the context of the present invention.

According to the accompanying drawings, reference numeral 1 indicates a plant for the production of filter tubes. In the continuation, a method for the production of filter tubes according to the present invention is also described, which is preferably performed by means of the aforesaid plant 1.
According to the present invention, plant 1 comprises feed means for feeding a succession of hollow tubular elements.
According to a preferred embodiment, the feed means comprise a maker machine "M", configured to make hollow tubular elements, and transfer means for transferring said hollow tubular elements from the maker machine "M" to the filter tip attachment machine "N" (described below). The maker machine "M" is of the known type and therefore, its structure is not described in detail. Preferably, the maker machine "M" is configured to make a succession of double-length hollow tubular elements, in particular obtained by cutting a continuous tubular element.
According to an embodiment variant, alternatively to the maker machine "M", the feed means can comprise a containment hopper for containing a plurality of hollow tubular elements and transfer means (preferably at least one drum) for transferring said hollow tubular elements from the containment hopper to the filter tip attachment machine "N" (described below).
Plant 1 further comprises a filter tip attachment machine "N" for applying at least one filter segment to each hollow tubular element. In other words, the filter tip attachment machine "N" receives the succession of hollow tubular elements from the feed means (for example, from the maker machine "M") and is configured to combine at least one filter segment with a respective hollow tubular element, preferably a double-filter segment with two tubular segments obtained from cutting a respective double-length hollow tubular element, thus obtaining a group of segments. The expression "to combine" means arranging the hollow tubular element and the filter segment side-by-side, with the respective longitudinal extension axes axially aligned. Preferably, the expression "to combine" means arranging the hollow tubular element and the filter segment mutually abutting (i.e., with a respective end disposed in contact). Alternatively, a space or another segment could be positioned between said hollow tubular element and the filter segment.
In detail, the filter tip attachment machine "N" comprises a downfeed line "D" configured to feed a succession of filter segments.
Preferably, the filter tip attachment machine "N" comprises a downfeed line "D" configured to feed a succession of double-length filter segments.
The filter tip attachment machine "N" therefore comprises a combiner drum "E" in which each filter segment is combined with at least one hollow tubular element to form a group of segments.
According to the preferred embodiment in which the feed means comprise a maker machine "M" and transfer means for transferring said hollow tubular elements from the maker machine "M" to the filter tip attachment machine "N", the transfer means are disposed at a transfer station "B" in which the hollow tubular elements advanced in a longitudinal direction (i.e., parallel to the extension axis of the hollow tubular elements) at the maker machine "M" are deflected from the longitudinal path thereof and advanced in a direction transverse to the extension axis thereof at the filter tip attachment machine "N".
Preferably, the maker machine "M" is configured to make double-length hollow tubular elements and the downfeed line "D" is configured to feed a succession of double-length filter segments.
In such an embodiment, the filter tip attachment machine "N" comprises a cutting and spreading station "C" configured to cut and spread each of said double-length hollow tubular elements so as to obtain two respective single-length hollow tubular elements which are spaced from each other. Moreover, the combining drum "E" is configured to place a respective double-length filter segment between said two single-length hollow tubular elements.
Therefore, the double-length hollow tubular elements are transferred into the cutting and spreading station "C" where they are cut so as to obtain single-length hollow tubular elements which are spaced from one another. Then, the single-length hollow tubular elements thus spaced are conveyed towards the combiner drum "E". The double-length filter segments are also conveyed, for example, through a succession of drums, from the downfeed line "D" up to the combiner drum "E". Each double-length filter segment on the combiner drum "E" is interposed (i.e. inserted in the space) between two respective hollow tubular elements. Thereby, the combiner drum "E" forms a succession of groups of segments, each comprising a double-length filter segment and, abutting on opposite ends of the filter segment and coaxial to the filter segment, two single-length hollow tubular elements.
Plant 1 comprises an unwinding unit "A" configured to receive at least one roll from which a web "S", preferably made of paper (either paper-based or cellulose-based), is unwound. The unwinding unit "A" has an architecture that is known in the prior art and in particular, it comprises at least one support for a roll.
Preferably, web "S" is smooth. In other words, web "S" is not pre-embossed.
Preferably, web "S" has a substantially smooth surface, i.e., without ridges and/or recesses.
The paper web "S" is fed to the filter tip attachment machine "N".
Plant 1 comprises guide means for web "S", interposed between the unwinding unit "A" and an applicator device "G" of the filter tip attachment machine "N". The guide means for the web "S" are configured to guide web "S" along a feed path "L". The feed path "L" of web "S" starts at the unwinding unit "A" and ends at the applicator device "G".
In particular, one or more unwinders of web "S" and/or tensioners of web "S" and/or at least one rubberizing device for applying an adhesive (or glue) on web "S" are provided along the feed path "L"; such unwinders, tensioners and rubberizing device are not illustrated in the drawings and are of the known type, therefore, they are not further detailed.
The applicator device "G" is operatively positioned downstream of the combiner drum "E" and configured to receive web "S", to divide (preferably cut) web "S" into connecting strips and to apply each connecting strip in a flag-like manner on a respective group of segments (in particular, consisting of a filter segment and at least one hollow tubular element).
To this end, the applicator device "G" preferably comprises a support drum and a blade cutting drum, tangent to each other and operating in a known manner to divide web "S" into connecting strips.
In other words, the roll of web "S" is unwound and web "S" is continuously fed along the feed path "L"; then, web "S" is cut into portions (connecting strips) so that each portion (connecting strip) is wrapped round a group of segments to fix in-between a hollow tubular element with a filter segment. In such a circumstance, downstream of the combiner drum "E", during the advancement of the hollow tubular elements combined with the respective double-length filter segment, each connecting strip is applied in a "flag-like manner" to a respective group of segments and then rolled (wrapped) round the group of segments so as to obtain a double-length filter tube. To this end, the filter tip attachment machine "N" comprises a rolling device "I", positioned downstream of the applicator device "G" and configured to wrap each connecting strip round a respective group of segments. In particular, as is known, the rolling device "I" has a rolling drum which acts in conjunction with a rolling bed.
Preferably, the filter tip attachment machine "N" further comprises, downstream of the rolling device "I", a cutting station "H" in which the double-length filter tubes are cut so as to obtain single-length filter tubes, forming two parallel flows.
Preferably, the filter tip attachment machine "N" comprises, downstream of the cutting station "H", an overturning station "R" in which the filter tubes of one of the two aforesaid flows are overturned so as to form a single flow of single-length filter tubes having the same orientation. Preferably, a laser station for making perforations at the filter tubes can be provided downstream of the overturning station "R".
According to an aspect of the present invention, plant 1 comprises an embossing device 110, located along the feed path "L" of the web in position interposed between the unwinding unit "A" and the applicator device "G". The embossing device 110 is configured to print an embossing on the web.
Figure 1 shows a first embodiment of the invention.
In such an embodiment, the filter tip attachment machine "N" comprises a main frame 10 and the unwinding unit "A" comprises a secondary frame 20. The two frames 10, 20 are separate from, and independent of each other. In other words, the two frames 10, 20 are physically detached.
Therefore, this results in the unwinding unit "A" being outside the main frame 10.
Plant 1 further comprises an embossing unit 100, also positioned outside the main frame 10 and detached therefrom. Moreover, in said specific embodiment, the embossing unit 100 is separate from and independent of the unwinding unit "A".
In greater detail, the embossing unit 100 comprises a respective containing frame 101 which supports an embossing device 110, of the type with opposed rollers, for example.
Figure 4 shows an embodiment of the embossing unit 100.
With reference to Figure 4, the embossing unit 100 comprises, mounted on the containing frame 101 (i.e., supported by the containing frame 101), an entraining device 140 having the function of pulling web "S", a tensioner 150 (for example, an oscillating arm tensioner) and guide rollers 160, 170 forming part of the guide means.
According to a further embodiment, the embossing unit 100 can comprise a pre-unwinding device 180 (Figure 4), positioned upstream of the aforesaid entraining device 140, for example. Moreover, the embossing unit 100 can comprise further tensioners 190 (Figure 4). Such an embodiment of the embossing unit 4 is particularly advantageous when applied downstream of an unwinding unit "A" in which the respective roll is only braked but not motorized. For example, such an embodiment of the embossing unit 100 can be applied advantageously to the embodiment of plant 1 according to Figure 3, which is described in the continuation of the present description.
In further reference to Figure 4, the embossing unit 100 is configured to allow the feeding of web "S" along a first path that guides web "S" through the embossing device 110, or along a second path in which web "S" circumvents the embossing device 110 without passing through it.
Preferably, the containing frame 101 is equipped with lower support elements 102 for defining a positioning which is independent of the embossing unit 100 with respect to the main frame 10. This gives the embossing unit 100 an independent structure.
According to the embodiment in Figure 1, the containing frame 101 is interposed between the main frame 10 and the secondary frame 20. In such an embodiment, the containing frame 101 is separate from and independent of both main and secondary frames 10, 20.
In such an embodiment, therefore, the feed path "L" of the web starts at the secondary frame 20, crosses the containing frame 101 and ends at the main frame 10.
Figure 2 shows a second embodiment of the invention that is described below.
In such an embodiment, the containing frame 101 of the embossing unit 100 is separate from, and independent of the main frame 10 but mechanically connected to the secondary frame 20. In other words, as clearly shown in Figure 2, the containing frame 101 is coupled to the secondary frame 20.
In such an embodiment, therefore, the feed path "L" of the paper web starts at the secondary frame 20, crosses the containing frame 101 ( by crossing an interface zone in the joint between secondary frame 20 and containing frame 101). Then, the feed path "L" of web "S" extends towards the main frame 10, and the web "S" is conveyed outside the frames 10, 20, 101 (preferably above the frames 10, 20, 101).
To this end, the guide means can comprise a portion that guides the web in the stretch outside the frames 10, 20, 101. According to Figure 2, said portion of the guide means is only diagrammatically depicted as a channel 200 positioned outside the frames 10, 20, 101. It is understood that the drawing is diagrammatic.
Said portion guiding the web in the stretch outside the frames 10, 20, 101 can be employed also in the plant depicted in Figure 1, in the event of different mutual positioning between unwinding unit "A" and embossing unit 100, and/or it could be omitted in the plant depicted in Figure 2, in the event of a different mutual positioning between unwinding unit "A" and embossing unit 100.
Also, in the embodiment of Figure 2, the embossing unit 100 can be made as shown in Figure 4.
Figure 3 shows a third embodiment of the plant of the present invention, which is described below.
In such an embodiment, the unwinding unit "A" is disposed on, or integrated in the main frame 10.
In such an embodiment, the containing frame 101 of the embossing unit 100 can be stand-alone (as shown in Figure 3) or connected outside the main frame 10 (solution not illustrated). In other words, the containing frame 101 can be separate from and independent of the main frame 10, or it can be coupled thereto.
In such an embodiment, the feed path "L" of web "S" starts at the main frame 10 (at the unwinding unit "A"), it crosses the containing frame 101 and returns to the main frame 10.
According to the embodiment illustrated, the feed path "L" of web "S" passes through the frames 10, 101 from above.
To this end, the guide means comprise a portion that guides the web in the stretch outside the frames 10, 101. According to Figure 3 (and to what was already indicated for Figure 2), said portion of the guide means is only diagrammatically depicted as a channel 200 positioned outside the frames 10, 101. It is understood that the drawing is diagrammatic.
Also, in the embodiment in Figure 3, the embossing unit 100 can be made as shown in Figure 4.
The present invention achieves the intended purposes by eliminating the drawbacks highlighted in the prior art.
To this end, it is worth noting, firstly, that plant 1 and the method, as described and claimed, ensure increased operating and structural efficiency. Such a result is particularly achieved by employing an embossing device 110, interposed between the feeding unit "A" and the applicator device "G" of the filter tip attachment machine "N". Indeed, the presence of an embossing device 110 allows employing webs without pre-embossing and therefore, less voluminous than those regularly employed in the prior art. Advantageously, such a technical feature allows rolls having a longer web (roll volume being equal) to be employed.
It is also worth noting that plant 1 and the method, as described and/or claimed, ensure an improved finished product in terms of quality. Such a result is particularly achieved by employing an embossing device 110, interposed between the feeding unit "A" and the applicator device "G" of the filter tip attachment machine "N", configured to perform the embossing during the production steps of the filter tubes. By embossing the web directly in plant 1, the risk that the embossing is damaged when the rolls are stored is eliminated, thus ensuring a production of articles with no defects nor inferior quality.
It is also worth noting that the embossing device 110 as described and claimed is installable on plants for the production of filter tubes in a highly advantageous manner. Advantageously, thereby, there is no need to make ad hoc plants 1, but it is possible to modify an existing plant 1, resulting in considerable economic and time savings.

Claims

A plant (1) for the production of filter tubes, comprising:
- feeding means for feeding a succession of hollow tubular elements;

- a filter tip attachment machine (N) for applying at least one filter segment to each hollow tubular element;

wherein the filter tip attachment machine (N) comprises a downfeed line (D), configured to feed a succession of filter segments and a combiner drum (E) in which each filter segment is combined with at least one hollow tubular element to form a group of segments;
- an unwinding unit (A) configured to receive at least one roll and to unwind from it a web (S), preferably of paper;

- guide means for the web (S) for guiding the web (S) along a feed path (L);

wherein the filter tip attachment machine (N) comprises:
- an applicator device (G) operatively positioned downstream of the combiner drum (E) and configured to receive the web (S), to divide the web (S) into connecting strips and to apply each connecting strip in flag-like manner on a respective group of segments;

- a rolling device (I), positioned downstream of the applicator device (G) and configured to wrap the connecting strip round the respective group of segments;

wherein the plant (1) is characterized in that it comprises an embossing unit (100), located along said feed path (L) at a position interposed between the unwinding unit (A) and the applicator device (G) and configured to print embossing on said web (S).
The plant (1) according to claim 1, wherein said filter tip attachment machine (N) comprises a main frame (10) defining a supporting structure of the filter tip attachment machine (N) and wherein said embossing unit (100) is separate from said main frame (10) and is positioned outside the main frame (10).
The plant (1) according to claim 2, wherein the feed path (L) extends at least partly outside the main frame (10).
The plant (1) according to claim 2 or 3, wherein the embossing unit (100) comprises a containing frame (101) and an embossing device (110), which is preferably equipped with a pair of rollers, at least one of which is provided with embossing ridges, and which is supported by the containing frame (101).
The plant (1) according to claim 4, wherein the embossing unit (100) comprises an entraining device (140) having the function of pulling the web (S), supported by the containing frame (101) and preferably positioned upstream of the embossing device (110).
The plant (1) according to any one of claims 2 to 5, wherein the unwinding unit (A) comprises a secondary frame (20) and means for supporting the at least one roll; preferably said secondary frame (20) being separate from the main frame (10).
The plant (1) according to any one of claims 1 to 6, wherein the embossing unit (100) and the unwinding unit (A) are stably connected to define a rigid, unwinding and embossing unit.
The plant (1) according to claims 4, 6 and 7, wherein the secondary frame (20) and the containing frame (101) are rigidly fixed to each other.
The plant (1) according to claim 1, wherein said filter tip attachment machine (N) comprises a main frame (10) defining a supporting structure of the filter tip attachment machine (N) and wherein said embossing unit (100) is mounted on said main frame (10).
The plant (1) according to any one of claims 2 to 5 or according to claim 9, wherein said unwinding unit (A) is mounted on said main frame (10).
The plant (1) according to any one of the preceding claims, wherein the feed means comprise a maker machine (M), configured to make hollow tubular elements, and transfer means for transferring said hollow tubular elements from the maker machine (M) to the filter tip attachment machine (N).
The plant (1) according to claim 11, wherein:
said maker machine (M) is configured to make double-length, hollow tubular elements and wherein said downfeed line (D) is configured to feed a succession of double-length filter segments;

said filter tip attachment machine (N) comprises a cutting and spreading station (C) configured to cut and spread each of said double-length, hollow tubular elements so as to obtain two respective single-length hollow tubular elements which are spaced from each other;

said combining drum (E) is configured to place a respective double-length filter segment between said two single-length hollow tubular elements.
The plant (1) according to any one of the preceding claims, wherein said embossing unit (100) is retrofitted or retrofittable into an existing plant without an embossing unit.
A method for making filter tubes, preferably implemented by a plant (1) according to any one of the preceding claims, comprising the following steps:
- feeding a succession of hollow tubular elements;

- feeding a succession of filter segments;

- combining each filter segment with at least one hollow tubular element to make a respective group of segments;

- feeding a web (S), preferably of paper, along a feed path (L);

- dividing the web (S) into connecting strips and applying each connecting strip in flag-like manner on a respective group of segments;

- wrapping each connecting strip round a respective group of segments;
wherein the method is characterized in that it comprises a step of embossing the web (S), carried out before the step of dividing the web (S) into connecting strips.
The method according to claim 14, wherein the step of feeding a succession of hollow tubular elements comprises the step of making hollow tubular elements by means of a maker machine (M) and transferring said hollow tubular elements from the maker machine (M) to a filter tip attachment machine (N) in which each filter segment is combined with a hollow tubular element to make a respective group of segments.
The method according to claim 14 or 15, wherein:
the step of feeding a succession of hollow tubular elements comprises feeding a succession of double-length, hollow tubular elements;

the step of feeding a succession of filter segments comprises feeding a succession of double-length filter segments;

the step of combining each filter segment with at least one hollow tubular element comprises the following steps: cutting and spreading each of said double-length, hollow tubular elements so as to obtain two respective single-length hollow tubular elements which are spaced from each other;

placing a respective double-length filter segment between said two single-length hollow tubular elements;

the step of dividing the paper web (S) into connecting strips and applying each connecting strip in flag-like manner on a respective group of segments comprises dividing the paper web (S) into double-length connecting strips.