WO2023186952A1

WO2023186952A1 - Embossing-laminating device and method

Info

Publication number: WO2023186952A1
Application number: PCT/EP2023/058081
Authority: WO
Inventors: Andrea Petrone; Matteo GALOPPINI
Original assignee: Körber Tissue S.p.A.
Priority date: 2022-03-30
Filing date: 2023-03-29
Publication date: 2023-10-05

Abstract

The embossing-laminating device comprises a first embossing roller provided with first embossing protuberances forming a first embossing pattern. The first embossing roller co-acts with a first pressure roller forming, with the first embossing roller, a first embossing nip. The embossing-laminating device further comprises a second embossing roller provided with second embossing protuberances forming a second embossing pattern. The second embossing roller co-acts with a second pressure roller defining, with the second embossing roller, a second embossing nip. A heating device heats the first embossing roller to make the first embossing roller achieve, in use, a first temperature higher than a second temperature of the second embossing roller. The first embossing pattern and the second embossing pattern are so configured as to be in phase with each other when the first embossing roller is at the first temperature and the second embossing roller is at the second temperature.

Description

EMBOSSING-LAMINATING DEVICE AND METHOD

DESCRIPTION

TECHNICAL FIELD

[0001] The present invention relates to the field of paper converting machines, particularly tissue paper converting machines, or machines for converting other products in ply or web form, for example non-woven fabric or the like. Embodiments disclosed herein relate to novel engraving patterns of the embossing rollers for embossing devices, especially for embossing-laminating devices, used for embossing plies of cellulose material, synthetic material, or thermoplastic material, or combinations thereof, to form an embossed multi -ply web material.

BACKGROUND ART

[0002] In tissue paper producing and converting industry, to produce products like rolls of toilet paper, kitchen towels, napkins, handkerchiefs, interfolded wipes and towels and the like, it is well known to unwind a plurality of plies of cellulose fibers from one or more master rolls, and to convert the cellulose plies into a semi-finished or finished product comprising one or more plies bonded together, for example by gluing or mechanical ply-bonding.

[0003] Typically, before bonding the plies together, one or both plies are embossed, i.e. subjected to an operation of permanent deformation, by making the ply pass through an embossing nip between an embossing roller, having a plurality of embossing protuberances, and a pressure roller. The pressure roller can be smooth and provided with an elastically yielding coating layer, made for example of natural or synthetic rubber. In other cases, the pressure roller is engraved with an engraving pattern which is complementary to the pattern of the embossing protuberances.

[0004] The heat embossing technique, i.e. embossing by heating the embossing roller and the ply of web material driven around it, has been well known for a long time. Examples of heat embossing systems are disclosed in US2013/220151, JP2007136861, US6913673. Heat embossing devices and methods, using a heating system that is innovative and more efficient than the prior art systems, are disclosed in WO2021/205255. [0005] In embossing and embossing-laminating devices with two embossing rollers, several drawbacks may arise when heat embossing operations are carried out, due to the differential thermal expansions of the embossing rollers.

[0006] There is therefore the need for embossing and embossing-laminating devices that completely or partially overcome these drawbacks.

SUMMARY OF THE INVENTION

[0007] According to an aspect, an embossing-laminating device is disclosed herein, comprising a first embossing roller provided with first embossing protuberances forming a first embossing pattern, and a first pressure roller forming, with the first embossing roller, a first embossing nip. The embossing-laminating device further comprises a second embossing roller provided with second embossing protuberances forming a second embossing pattern, and a second pressure roller forming, with the second embossing roller, a second embossing nip. A heating device is also provided, adapted to heat the first embossing roller to make the first embossing roller achieve, in use, a first temperature higher than a second temperature of the second embossing roller. The first embossing pattern and the second embossing pattern are so configured as to be in phase with each other when the first embossing roller is at the first temperature and the second embossing roller is at the second temperature.

[0008] According to a further aspect, a method is disclosed for producing an embossed web material comprising at least a first ply, embossed with a first embossing pattern, and a second ply, embossed with a second embossing pattern, bonded together; the method comprising the following steps: feeding the first ply through a first embossing nip formed between a first embossing roller, provided with first embossing protuberances that form a first embossing pattern, and a first pressure roller, and embossing the first ply in the first embossing nip; wherein the first embossing roller is kept at a first temperature; feeding a second ply through a second embossing nip formed between a second embossing roller, provided with second embossing protuberances that form a second embossing pattern, and a second pressure roller; wherein the second embossing roller is at a second temperature, lower than the first temperature; bonding together the first ply, provided with a first embossed pattern generated by the first embossing protuberances, and the second embossed ply, provided with a second embossed pattern generated by the second embossing protuberances, with the first embossed pattern in phase with the second embossed pattern.

[0009] The first embossing pattern and the second embossing pattern are so configured to be in phase with each other when the first embossing roller is at the first temperature and the second embossing roller is at the second temperature, and out of phase with each other when the first embossing roller and the second embossing roller are at the same temperature.

[0010] Further features and embodiments of the method and the embossinglaminating device are described below.

BRIEF DESCRIPTION OF THE DRAWING

[0011] The invention will be better understood by following the description below and the attached drawing, showing a non-limiting embodiment of the invention. More specifically, in the drawing:

Fig. 1 shows a schematic of an embossing-laminating device;

Figs. 2A and 2B schematically show an enlargement of portions of the embossing rollers of the embossing-laminating device of Fig. 1;

Figs. 3 and 4 are schematic views of a surface portion of the first embossing roller and of the second embossing roller when they are at the same temperature;

Figs. 5 and 6 show views similar to those of Figs. 3 and 4 when the first embossing roller is at a temperature higher than the temperature of the second embossing roller;

Fig. 7 is a schematic view of the embossing patterns, generated by the first embossing roller and the second embossing roller, put over each other;

Fig. 8 is a schematic cross-section of a portion of web material; and

Fig. 9 shows a diagram of the first embossing roller and the related bearings. DETAILED DESCRIPTION

[0012] In the description below reference will be made, just by way of example, to an embossing-laminating device producing a multi-ply web material, that is a web material comprising at least two plies bonded together. Each ply is composed of one or more layers of cellulose material. However, novel features disclosed herein can be used also in more complex embossing-laminating devices, with a larger number of paths for the plies to be embossed and/or a different number of embossing rollers and pressure rollers.

[0013] Embodiments described herein refer to a so-called nested embossinglaminating device. However, it should be understood that the embossing rollers described herein and the related engraving methods can be also used in different types of embossing-laminating devices, for example tip-to-tip or embossing-gluing (“goffra-incolla”) devices.

[0014] Moreover, in this description reference is specifically made to the embossing of cellulose plies. However, this is just by way of non-limiting example, as the embossing described herein can be used also for ply or web materials of different kind, as mentioned in the introduction. Typically, the ply and/or the web material obtained with one or more plies can be composed of, or can comprise, one or more layers of non-woven fabric, either consolidated or not. The non-woven fabric can be consolidated, for example, thermally, chemically, mechanically, hydraulically or through combinations of these techniques.

[0015] With reference to the drawing, in the embodiment illustrated in Fig. 1, an embossing device 1 (more precisely an embossing-laminating device) has a bearing structure 2, that, in turn, comprises two flanks 3, between which the rollers and the paths for the cellulose plies are arranged, as described below.

[0016] In some embodiments, a first embossing roller 4 and a second embossing roller 5 are provided between the two flanks 3 of the bearing structure 2. The first embossing roller 4 is provided with first embossing protuberances 4P, schematically shown in Fig. 2A. The first embossing protuberances 4P form a first embossing pattern. The second embossing roller 5 is provided with second embossing protuberances 5P, schematically shown in Fig. 2B. The second embossing protuberances 5P form a second embossing pattern.

[0017] The protuberances 4P and 5P can have any shape. They can be, for example, simple protuberances of truncated-conical or truncated-pyramidal shape. In other embodiments, the protuberances 4P and/or 5P are more complex and form more complex patterns, formed by sets of protuberances of variable shapes and sizes. The protuberances 4P and/or 5P may be, for example, linear and/or may have sides with different inclinations and/or different heights or other variants known in the art.

[0018] The first embossing roller 4 co-acts with a first pressure roller 6. In some embodiments, the pressure roller 6 is coated with an outer layer 6A made of a yielding material, preferably an elastically yielding material, for example rubber. The second embossing roller 5 co-acts with a second pressure roller 7. In some embodiments, also the pressure roller 7 is coated with an outer layer 7A made of a yielding material, preferably an elastically yielding material.

[0019] The references 4X, 5X, and 6X, 7X indicate respectively the rotation axes of the two embossing rollers 4, 5 and of the two pressure rollers 6, 7. These axes are substantially parallel. In some embodiments, the axes 4X, 6X are adjustable so as to be arranged slightly skewed, i.e. not parallel, to change the conditions of, and to balance any non-uniformity in, the mutual contact between the central area and the end areas of the rollers 4, 6. Similarly, the axes 5X, 7X are adjustable so as to be arranged slightly skewed, i.e. not parallel, to change the conditions of, and to balance any non-uniformity in, the mutual contact between central area and end areas of the rollers 5, 7.

[0020] A first embossing nip 8 is formed between the first embossing roller 4 and the first pressure roller 6; through the nip 8, a first feed path Pl extends, along which a first ply VI moves forward for being embossed by the embossing protuberances 4P of the first embossing roller 4. If the pressure roller 6 has an outer yielding coating 6 A, the embossing protuberances 4P are pressed against the first pressure roller 6 and penetrate into the yielding coating 6A, thus permanently deforming the ply VI. The pattern formed by the first embossing protuberances 4P generates, in the ply VI, a first embossed pattern, constituted by embossed projections of the material, cellulose or other material, of which the ply VI is made. [0021] A second embossing nip 9 is formed between the second embossing roller 5 and the second pressure roller 7; through the nip 9, a second feed path P2 extends, along which a second ply V2 moves forward. The second ply V2 is embossed in a way analogous to that of the first ply VI, i.e. through the protuberances 5P of the second embossing roller 5 that are pressed against the second pressure roller 7. If the second pressure roller 7 is provided with an elastically yielding coating 7A, the embossing protuberances 5P penetrate into the yielding coating 7A, thus permanently deforming the ply V2. The pattern formed by the second embossing protuberances 5P generates, in the ply V2, a second embossed pattern, constituted by embossed projections of the material, cellulose or any other material, of which the ply V2 is made.

[0022] To exert the necessary pressure between the pressure rollers 6, 7 and the respective embossing rollers 4, 5, a first actuator 23 is provided for the first pressure roller 6 and a second actuator 24 is provided for the second pressure roller 7. In practical embodiments, the first pressure roller 6 is supported by a pair of arms 25 hinged to the flanks 3 and loaded by the first actuator 23, and the second pressure roller 7 is supported by a pair of arms 26 hinged to the flanks 3 and loaded by the second actuator 24.

[0023] The actuators 23, 24 are hydraulic cylinder-piston actuators or other suitable actuators. Instead of arms hinged to the flanks 3, other movable support members can be provided, allowing the movement of the pressure rollers 6, 7 toward and away from the embossing rollers 4, 5.

[0024] In some embodiments, not shown, the two embossing rollers 4 and 5 are so configured as to work tip-to-tip, i.e. with at least some of the embossing protuberances 4P and 5P pressed against one another or anyway arranged so that the mutual distance between the heads of the protuberances is smaller than the thickness of the plies, in a nip 10 formed between the two embossing rollers 4, 5. In this case, the nip 10 constitutes a lamination nip. In this case, the embossing protuberances 4P and 5P are in phase with each other, i.e. the protuberances 4P and the protuberances 5P (or at least some of them) face one another in the lamination nip 10.

[0025] In other embodiments, as shown in Fig. 1, the embossing-laminating device 1 comprises a marrying roller 11, pressed against the first embossing roller 4 and forming, with the first embossing roller, a lamination nip 12. In this way, the two plies VI and V2 are laminated between the first embossing roller 4 and the marrying roller 11. In the nip 10, formed between the embossing rollers 4, 5, these latter are slightly spaced from each other, and/or the embossing protuberances 4P, 5P of the embossing rollers 4,5 are not phased with each other. In this case, the embossing device generates a material embossed according to the so-called nested technique, i.e. with embossing protuberances of the ply V2 nested, i.e. entering, between embossing protuberances of the ply VI, and vice versa. In this case, the embossing protuberances 4P and 5P are in phase with one another, i.e. the embossing projections generated by the embossing protuberances 5P of the embossing roller 5 in the ply V2, or the majority thereof, nest between the protuberances 4P of the embossing roller 4 (and therefore between the embossed projections generated by the embossing roller 4 in the ply VI) in the lamination nip 12.

[0026] In some embodiments, the embossing-laminating device 1 is so configured as to alternatively operate according to the tip-to-tip technique or to the nested technique. To this end, the embossing rollers 4, 5 are movable, relative to each other, parallel or orthogonally to their axes, and the marrying roller is alternatively movable between an active position and an idle position. To this end, the marrying roller 11 is supported by arms 27 hinged to the flanks 3, and is associated with an actuator 28 that either moves the marrying roller 11 away from the first embossing roller 4, or presses it (if necessary, with variable pressure) against the first embossing roller 4.

[0027] The embossing-laminating device 1 comprises a functional fluid applicator 13 associated with the first embossing roller 4. The functional fluid applicator 13 is a device adapted to apply a fluid, preferably for example a water-based liquid, to the ply VI, the fluid being adapted to promote, facilitate or perform mutual adhesion of the plies VI and V2.

[0028] The functional fluid applicator 13 comprises a source 14 for the liquid, for instance a glue, or water with chemical compounds adapted to promote the adhesion of the plies through formation of hydrogen bonds or the like, a screened roller or anilox roller 15, taking the liquid from the liquid source 14, and a plate roller or application roller 16, receiving the liquid from the screened roller 15 and distributing it onto portions of the embossed ply VI adhering to the first embossing roller 4. The liquid is generally applied, at at least some heads of the embossing protuberances 4P, with which the first embossing roller 4 is equipped, on the portions of ply VI when this latter is still engaged to the surface of the embossing roller 4. The liquid may be simply water with no adhesive matters. If the liquid is water, the adhesion of the plies is performed mainly through mechanical pressure.

[0029] In some embodiments, the functional fluid applicator 13 is mounted on a slide or carriage 17 movable according to the double arrow fl 7, for example along guides 18 carried by an element of the bearing structure 2. The movement according to the double arrow fl 7 is controlled by a suitable actuator, for example a cylinderpiston actuator, an electric motor, or any other suitable actuator. A pinion 17A is schematically shown in Fig. 1, which engages a rack integral with the guides 18 and is driven into controlled rotation by an electric motor 17B, integral with the slide or carriage 17.

[0030] When the embossing-laminating device 1 is operating, the first ply VI and the second ply V2 move forward according to the arrows fl and f2 along the first feed path Pl and along the second feed path P2 towards the embossing rollers 4, 5 and the embossing nips 8, 9, to be separately embossed between the pairs of rollers 4, 6 and 5, 7, to generate embossed patterns formed by respective embossed projections that are in turn generated by the embossing protuberances 4P and 5P. The embossed plies VI, V2 are bonded together and laminated between the embossing roller 4 and the marrying roller 11, thus forming an embossed web material N (in the illustrated example a multi-ply web material) that moves forward according to the arrow fN along an exit path towards a downward station, for example a rewinding station or an interfolding machine, not shown.

[0031] For embossing the two plies V2 and VI, the pressure roller 7 is pressed against the embossing roller 5, the pressure roller 6 is pressed against the embossing roller 4, respectively, and the marrying roller 11 is pressed against the embossing roller 4 to bond the plies VI, V2 together.

[0032] The marrying roller 11 can be made of steel, preferably with a smooth outer surface, or coated with a hard material. The coating can be made, for example, of rubber, usually harder than the yielding material 6A, 7A which coats the pressure rollers 6 and 7. In other embodiments, preferably when an embossed web material N shall be produced without using glue, the marrying roller 11 is composed of a series of smooth or engraved small rollers made of steel, constituting so-called mechanical ply-bonding wheels.

[0033] In the embodiment illustrated in Fig. 1, the first embossing roller 4 is associated with a heating device 40. In the illustrated embodiment, the heating device 40 is provided outside the first embossing roller 4. However, the heating device 40 can be even provided inside the embossing roller 4, or it can comprise heating members arranged both inside and outside the embossing roller 4.

[0034] In advantageous embodiments, the heating device 40 comprises an electromagnetic device for heating by induction. Embodiments of electromagnetic heating devices usable in this context are disclosed, for example, in WO2021/205255.

[0035] Generally, the embossing-laminating device 1 has a heating device 40 also for the second embossing roller 5. However, the novel features disclosed herein are particularly useful when, in use, one of the embossing rollers is heated and the other one is not heated, i.e. it is at room temperature, or at temperatures slightly higher than the room temperature due to the thermal effects resulting from co-action between the members of the embossing-laminating device, especially the co-action between embossing roller and pressure roller, and the indirect heat from the heating device 40 through the embossing roller 4.

[0036] In the illustrated embodiment, the heating device 40 is associated with the first embossing roller 4, because this allows better effects in heat embossing. However, a single heating device can also be used, associated with the embossing roller 5 instead of the embossing roller 4.

[0037] Two heating devices can be also used, one for each embossing roller 4, 5, so controlled as to keep the two embossing rollers 4, 5 at different operating temperatures.

[0038] In some embodiments, the temperature to which the embossing roller 4 is heated is several tens of degrees higher than the operating temperature of the embossing roller 5. Typically, the difference in temperature is comprised between 50°C and 200°C.

[0039] This difference in temperature results in a differential expansion of the two embossing rollers 4, 5. In detail, the first embossing roller 4 is subject to a thermal expansion in both radial and axial direction, whilst the second embossing roller 5 is not subject to significant expansions, as it remains approximately at room temperature, or at a slightly higher temperature. As the radial dimensions of the embossing rollers are definitely lower than the axial dimensions, the difference in thermal expansion between the two embossing rollers 4, 5 is particularly significant in axial direction.

[0040] Usually, when the two embossing rollers 4, 5 operate at substantially equal temperature, for examples because they both are heated, the thermal expansions in axial and radial directions are substantially the same for the two embossing rollers. Thus, the embossing patterns of the two embossing rollers expand in the same way in both axial and radial direction, and therefore the operating temperature does not affect the phase between the two patterns.

[0041] However, if one of the two embossing rollers (the embossing roller 4 in the illustrated example) is heated by the heating device 40, whilst the other embossing roller is not heated, or is only incidentally heated due to the heat transferred from the heated roller and to the mechanical friction, the difference in thermal expansion (above all in axial direction) can result in the embossing patterns being mutually shifted, so that the embossed patterns generated on the two plies VI, V2 of the web material N are no longer in phase.

[0042] Similar problems arise even when both embossing rollers 4, 5 are heated by respective heating devices, if they are heated up to substantially different temperatures.

[0043] Particularly, if the embossing-laminating device 1 is configured for tip-to- tip embossing, a thermal expansion of the first embossing roller 4 relative to the second embossing roller 5 may bring the embossing protuberances 4P in shifted position relative to the embossing protuberances 5P, so that, in the nip 10 between the embossing rollers 4, 5 there is no longer correspondence between the heads of the embossing protuberances 4P and the heads of the embossing protuberances 5P. If this occurs, the two plies VI, V2 are not bonded together, resulting in a waste product. The problem also arises if only some protuberances are mutually shifted, for example the protuberances near an end of the embossing rollers 4, 5, where there is the larger axial shift due to the thermal expansion, assuming that the other end is constrained in fixed position relative to a bearing structure. In this case, devices can be also provided for adjusting, and therefore restoring, the right mutual distance between the rollers so as to make the embossing points 4P and 5P operate again in the right tip-to- tip configuration, thus balancing also the radial expansion.

[0044] Similar problems due to the differential thermal expansion can arise in case of nested embossing or of double embosser sincronizer lamination (DESL). In these cases, the differential thermal expansions of the two embossing rollers 4, 5 results in a phase shift (i.e. an out-of-phase) between the pattern embossed on the ply VI and the pattern embossed on the ply V2. This phase shift occurs in the lamination nip 12.

[0045] Under correct operating conditions, the embossed projections formed in the ply V2 by the embossing protuberances 5P nest between the embossed projections formed in the ply VI by the embossing protuberances 4P. More precisely, as the two plies are bonded together through lamination in the lamination nip 12, the embossed projections formed in the ply V2 shall be nested between embossing protuberances 4P of the embossing roller 4 in the lamination nip 12, where the ply VI is still in contact with the first embossing roller 4. If the embossing roller 4 expands more than the embossing roller 5, there is an out-of-phase and the embossed projections formed in the ply V2 end up over the embossing protuberances 4P and are pressed by the marrying roller 11, with consequent damage to the finished product, which shall be rejected.

[0046] To avoid these problems, the following is characteristically provided for. The embossing protuberances 4P of the first embossing roller 4 form a first embossing pattern and the embossing protuberances 5P of the second embossing roller 5P form a second embossing pattern. The first embossing pattern and the second embossing pattern are so configured as to be in phase with each other when the first embossing roller and the second embossing roller are at different operating temperatures, i.e., under conditions of differential thermal expansion.

[0047] The term “in phase”, when used with reference to the embossing protuberances 4P and 5P of the embossing rollers 4, 5, can have a different meaning depending upon the type of embossing. As mentioned above, in the case of tip-to-tip embossing, the embossing patterns formed by the protuberances 4P and 5P are in phase when, in the lamination nip 10 between the embossing rollers 4, 5, the protuberances 4P and the protuberances 5P are opposite each other, with consequent mutual pressure between the plies VI and V2 at the embossed projections formed in the two plies VI, V2.

[0048] Vice versa, in the case of nested or DESL embossing, the two embossing rollers 4, 5 are in phase with each other when, in the lamination nip 12, the embossed projections formed in the ply V2 nest between the embossed projections formed in the ply V 1.

[0049] For better illustrating what described above, Figs. 3 and 4 show a plan view of a portion of the embossing rollers 4 and 5, respectively, the embossing protuberances of which are indicated with 4P and 5P. In Figs. 3 and 4, the two embossing rollers 4, 5 are at the same temperature, for example at room temperature. It should be noted that the pattern on the embossing roller 4 is smaller than the pattern on the embossing roller 5.

[0050] When the two embossing rollers 4, 5 are brought to the operating temperature, they expand differentially, in particular only the first embossing roller 4 expands, while the dimensions of the embossing roller 5 remain approximately constant. Consequently, the two embossing patterns formed by the embossing protuberances 4P and 5P expand in differential way, in particular one remains almost the same (embossing roller 5) whilst the other significantly expands (embossing roller 4).

[0051] Practically, if the embossing roller 5 operates without being heated (except for the heat due to the frictions and to the heat transferred from the embossing roller 4), the embossing pattern thereof remains substantially unchanged, as it is clearly apparent by comparing Figs. 4 and 6. Vice versa, if the embossing roller 4 is heated by the heating device 40, the pattern thereof expands, as it is clearly apparent by comparing Figs. 3 and 5. The patern formed by the protuberances 4P remains the same in shape, but has expanded substantially uniformly in all directions.

[0052] As clearly apparent from Figs. 3 and 4, if the two embossing rollers have the same temperature, the two embossing patterns formed by the protuberances 4P and 5P are mutually out of phase, that is the position of the protuberances 4P is completely random relative to the position of the protuberances 5P, i.e. the protuberances 4P cannot nest between the protuberances 5P, and vice versa.

[0053] On the contrary, if the embossing rollers 4, 5 are brought to the operating temperature and the embossing roller 4 has expanded more than the embossing roller 5 (which can be at room temperature, therefore not expanded), the embossing paterns formed by the protuberances 4P and 5P are in phase with each another. This is clearly apparent by putting the two patterns of Figs. 5, 6 over each other.

[0054] In Fig.7, the two embossing patterns, which have been subjected to a differential thermal expansion, are superposed. The embossing protuberances 5P of the second embossing roller 5 nest between the embossing protuberances 4P of the first embossing roller 4, because in this example the embossing pattern is a nested pattern.

[0055] In practice, this phasing between the embossing protuberances 4P and 5P results in the mutual phase between the patterns embossed on the plies VI and V2, that are bonded together by lamination in the lamination nip 12. In practice, Fig. 7 can be understood as the superimposition of the embossed patterns, formed by embossed projections generated in the two plies VI, V2, once the plies VI and V2 have been superposed and bonded together.

[0056] Fig.8 schematically shows a cross-section of a web material N formed by the plies VI, V2. The ply VI has embossed projections SI formed by the embossing protuberances 4P, whilst the ply V2 has embossed projections S2 formed by the embossing protuberances 5P. C indicates a glue or other functional fluids that, applied to the head of the embossed projections SI, is used to bond the two plies VI, V2 together. If the plies are bonded in nested way, the glue C, applied to at least some embossing protuberances 4P, adheres to the bottom of the ply V2, i.e. in areas where an embossing protuberance had not been generated. Typically, even if not strictly necessary, the embossing protuberances 5P are at the same level as, or at a lower level than, the embossing protuberances 4P.

[0057] To allow the embossing roller 4 to thermally expand in axial direction, the one or the other of the two bearings of the embossing roller 4 allow movements in axial direction, i.e. parallel to the rotation axis of the roller. Fig. 9 schematically shows the embossing roller 4 with bearings 42, 44 supporting the roller in the flanks

3. Either bearing can be configured to allow a thermal expansion of the embossing roller 4 in axial direction. The references fTl and fT2 indicate two axial displacements of the two ends of the embossing roller 4. In practical embodiments, it is sufficient, and can be preferable, that only one of the two bearings 42, 44 allows the axial displacement, while the other bearing defines a fixed position of the corresponding end of the embossing roller 4. For example, the bearing 42 defines a fixed unchangeable position of the left (in the drawing) end of the embossing roller

4, whilst the bearing 44 allows translations according to the double arrow fTl of the right (in the drawing) end of the embossing roller 4 following the thermal expansion due to the heating of the embossing roller. In some cases, it can be provided for both the bearings to allow, theoretically, an axial displacement, but for the embossing roller 4 to be subjected to a mechanical constraint preventing an end thereof from moving, so that the whole displacement is performed by the other end.

[0058] In this case, when the first embossing roller 4 and the second embossing roller 5 are at the same temperature, the first embossing pattern formed by the first embossing protuberances 4P, and the second embossing pattern, formed by the second embossing protuberances 5P, are in phase with each other at a first axial end of the first embossing roller 4 and of the second embossing roller 5 and have a phase shift increasing from the first axial end towards the second axial end of the first embossing roller 4 and of the second embossing roller 5. Due to the fact that the first embossing roller 4 is supported at the first axial end by a bearing fixed relative to the flanks 3 of the bearing structure, and the second bearing is movable relative to the bearing structure, when the embossing roller 4 expands, the right end thereof moves until to bring the first embossing pattern in phase with the second embossing pattern.

[0059] It is easily understood that each point of the surface of the first embossing roller 4 displaces (in this example to the right) by an entity that is proportional to the increase in temperature and to the distance from the (left) end axially constrained by the fixed bearing 42. Therefore, when not heated, the difference in phase between the two embossing patterns is not the same along the whole axial extension of the embossing rollers 4, 5, but it decreases from a null phase shift at the fixed (non- translatable) end of the embossing roller 4 to a maximal phase shift at the opposite end.

[0060] In other embodiments, if both bearings 42, 44 allow axial displacements of the first embossing roller 4, the first embossing pattern and the second embossing pattern are so configured that, when the first embossing roller and the second embossing roller are at the same temperature, the first embossing pattern and the second embossing pattern are in phase with each other in a central position, between a first axial end of the embossing rollers and a second axial end of the embossing rollers. The two embossing patterns have a phase shift increasing from the central position towards the first axial end and the second axial end of the first embossing roller and of the second embossing roller. The phase shift becomes null when the first embossing roller 4 thermally expands with a substantially symmetrical elongation in the two directions fTl and fT2 of both the ends of the embossing roller 4.

[0061] In both cases, the result is achieved, of embossing the two plies VI, V2 with phased patterns (tip-to-tip, nested, DESL or other required phase) even when the embossing rollers are kept at substantially different operating temperatures.

Claims

1. An embossing-laminating device comprising: a first embossing roller provided with first embossing protuberances forming a first embossing pattern; a first pressure roller forming, with the first embossing roller, a first embossing nip; a second embossing roller provided with second embossing protuberances forming a second embossing pattern; a second pressure roller forming, with the second embossing roller, a second embossing nip; a heating device adapted to heat the first embossing roller to make the first embossing roller achieve, in use, a first temperature higher than a second temperature of the second embossing roller; wherein the first embossing pattern and the second embossing pattern are so configured as to be in phase with each other when the first embossing roller is at the first temperature and the second embossing roller is at the second temperature.

2. The embossing-laminating device of claim 1, wherein, in use, the first temperature is between 50°C and 200°C higher than the second temperature.

3. The embossing-laminating device of claim 1 or 2, wherein, when the first embossing roller and the second embossing roller are at the same temperature, the first embossing pattern and the second embossing pattern are in phase with each other at a first axial end of the first embossing roller and of the second embossing roller and have a phase shift increasing from the first axial end towards the second axial end of the first embossing roller and of the second embossing roller; wherein the first embossing roller is supported, at the first axial end, by a first bearing and, at the second axial end, by a second bearing; and wherein the first bearing is fixed with respect to a bearing structure, and the second bearing is movable with respect to the bearing structure, to follow an axial elongation of the first embossing roller caused by a thermal expansion of the first embossing roller, when the first embossing roller is heated.

4. The embossing-laminating device of claim 1 or 2, wherein, when the first embossing roller and the second embossing roller are at the same temperature, the first embossing pattern and the second embossing pattern are in phase with each other in a central position between a first axial end of the first embossing roller and of the second embossing roller and a second axial end of the first embossing roller and of the second embossing roller and have a phase shift increasing from the central position towards the first axial end and the second axial end of the first embossing roller and of the second embossing roller; wherein the first embossing roller is supported, at the first axial end, by a first bearing and, at the second axial end, by a second bearing; and wherein the first bearing and the second bearing are movable with respect to a bearing structure to follow a symmetrical thermal expansion of the first embossing roller, with symmetrical displacements of the first axial end and of the second axial end, when the first embossing roller is heated.

5. A method for producing an embossed web material comprising at least a first ply, embossed with a first embossing pattern, and a second ply, embossed with a second embossing pattern, bonded together; the method comprising the following steps: feeding the first ply through a first embossing nip formed between a first embossing roller, provided with first embossing protuberances that form a first embossing pattern, and a first pressure roller, and embossing the first ply in the first embossing nip; wherein the first embossing roller is kept at a first temperature; feeding a second ply through a second embossing nip formed between a second embossing roller, provided with second embossing protuberances that form a second embossing pattern, and a second pressure roller; wherein the second embossing roller is at a second temperature, lower than the first temperature; bonding together the first ply, provided with a first embossed pattern generated by the first embossing protuberances, and the second embossed ply, provided with a second embossed pattern generated by the second embossing protuberances, with the first embossed pattern in phase with the second embossed pattern; wherein the first embossing pattern and the second embossing pattern are so configured to be in phase with each other when the first embossing roller is at the first temperature and the second embossing roller is at the second temperature, and out of phase with each other when the first embossing roller and the second embossing roller are at the same temperature.

6. The method of claim 5, wherein the first temperature is between 50°C and 200°C higher than the second temperature.

7. The method of claim 5 or 6, wherein, when the first embossing roller and the second embossing roller are at the same temperature, the first embossing pattern and the second embossing pattern are in phase with each other at a first axial end of the first embossing roller and of the second embossing roller and have a phase shift increasing from the first axial end towards the second axial end of the first embossing roller and of the second embossing roller; wherein the first embossing roller is supported, at the first axial end, by a first bearing and, at the second axial end, by a second bearing; and wherein the first bearing is fixed with respect to a bearing structure, and the second bearing is movable with respect to the bearing structure, to follow an axial elongation of the first embossing roller caused by a thermal expansion of the first embossing roller, when the first embossing roller is heated.

8. The method of claim 5 or 6, wherein, when the first embossing roller and the second embossing roller are at the same temperature, the first embossing pattern and the second embossing pattern are in phase with each other in a central position between a first axial end of the first embossing roller and of the second embossing roller and a second axial end of the first embossing roller and of the second embossing roller and have a phase shift increasing from the central position towards the first axial end and the second axial end of the first embossing roller and of the second embossing roller; wherein the first embossing roller is supported, at the first axial end, by a first bearing and, at the second axial end, by a second bearing; and wherein the first bearing and the second bearing are movable with respect to a bearing structure to follow a symmetrical thermal expansion of the first embossing roller, with symmetrical displacements of the first axial end and of the second axial end, when the first embossing roller is heated.