Method and device for heating embossing roller in embossing / laminating device

Abstract

An embossing apparatus and an embossing method using an electromagnetic induction device (19, 20) for selectively inducing eddy currents on the outer surface of an embossing roller (4, 5). The eddy currents are currents that selectively heat the outer surface of the embossing roller.

Description

[Technical field]

[0001] The present invention relates to an improved method and apparatus for heating an embossing roller adapted for the production of multi-ply cellulosic web materials. [Background technology]

[0002] In the tissue paper manufacturing and converting art, it is known to unwind a plurality of cellulosic fiber plies from one or more parent reels and convert them into a semi-finished or finished product consisting of two or more plies bonded together to obtain roll products such as toilet paper, kitchen towels, napkins, facial tissue, and the like.

[0003] Cellulosic fiber plies are often bonded together to produce a multi-ply web material using adhesives or mechanical ply bonding, i.e., by pressing one ply against the other ply with high pressure. For this purpose, at least one of the cellulose fiber plies is embossed, usually by means of an embossing roller and a pressure roller coated with a resilient, flexible material. The embossing process permanently deforms the cellulose fiber ply and forms embossed projections. While the cellulose fiber ply is in close contact with the embossing cylinder, glue is applied to the embossing projections. A second ply is then superimposed on the embossed cellulose fiber ply and the two plies are pressed together at the adhesive-received areas, adhering them to each other.

[0004] Two or more plies, at least one of which is partially or fully embossed, are then adhered together to form a multi-ply web material which may be wound to form a roll or cut and folded to form facial tissues, napkins, and the like.

[0005] In addition to allowing the plies of cellulosic material to adhere to each other, embossing can also be used to improve the quality of multi-ply paper products: for example, when one or more plies of cellulosic material are wound into a roll, it is possible to increase the thickness of each single ply so as to increase the volume or diameter of the final product, or in other cases to increase the mechanical strength, i.e. ultimate tensile strength, of the ply, or to improve its absorbency or flexibility.

[0006] For the reasons stated above, many methods and apparatus have been developed for embossing plies of cellulosic material, such as those described in EP 1075387, EP 1855876, U.S. Pat. No. 3,556,907, EP 1239079, EP 1319748, and U.S. Pat. No. 6,746,558.

[0007] To further improve the characteristics of the cellulosic material plies, an improved embossing technique using heated embossing rollers has been developed, as disclosed in patent ITMI-1995-A001197, in which the cellulosic material plies are moistened and passed through a nip formed by a pair of steel embossing rollers with embossing projections on their surfaces, the projections of the two rollers being arranged in contact under pressure according to a "tip-to-tip" pattern, and the two steel rollers being heated to dry the ply during embossing.

[0008] For the heating of the aforementioned embossing rollers (and generally for all calendering systems with smooth heated rollers, such as for forming paper plies), systems of recirculating diastere oil, steam or water placed inside the embossing roller are used. These systems are very costly, energy intensive, very inefficient and also involve dangers for workers, since they have to work close to the heating equipment and the embossing roller.

[0009] Heating the embossing roller by circulating a fluid requires long heating times because the heat supplied to the interior by the fluid must heat the entire mass of the roller before it can reach the outer surface of the roller, i.e. the working surface for treating the cellulosic material ply.

[0010] In addition, heating systems that circulate fluids are generally dangerous to workers because the piping from the heating boiler to the embossing rollers is typically pressurized. If the piping breaks, hot liquid leaks, or even if workers just touch the piping, they can suffer severe burns. There is therefore a need to improve heating technology, especially for embossing rollers, by adopting a system that is more energy efficient, heats the rollers more quickly, and is safer for workers who have to work with embossing devices that have heated rollers. Summary of the Invention

[0011] These and other objects which will become apparent hereinafter are achieved by an embossing and laminating apparatus according to claim 1 and a method for electromagnetically heating an embossing roller in an embossing and laminating apparatus according to claim 31 of the accompanying claims.

[0012] Before describing the features of various embodiments of the present method, apparatus, and resulting products, some definitions are provided.

[0013] As used herein, the term "embossing" refers to a process in which a portion of a cellulosic structure, such as a ply or multi-ply sheet, is permanently deformed in a direction perpendicular to the plane in which it lies, through which the cellulosic structure becomes When embossing is performed on the normally flat surface on which the cellulosic structure lies, such as a multi-ply material, the ply or multi-ply web material is permanently deformed with a number of projections or ridges that protrude out of the plane on which it lies.

[0014] Generally, an embossing machine refers to a machine that embosses at least one ply and, if necessary, laminates two or more plies together using an adhesive applied to the upper surface of at least a portion of the embossed projections formed on at least one of the plies, and preferably one or more of the plies.

[0015] The "outer surface" of the embossing cylinder means the entire area consisting of the front faces of the embossing projections, the sides of the embossing projections, and the planar surface on which the roller rests from which the embossing projections project outwardly.

[0016] It is an object of the present invention to provide an improved embossing apparatus with heated rollers which overcomes the problems of the prior art, and more particularly, an apparatus with a roller heated by electromagnetic induction for uniformly heating the outer surface of the roller.

[0017] It is also an object of the present invention to provide an embossing apparatus having a roller heating system that is efficient and rapidly reaches the external temperature of the embossing roller and rapidly cools it, thereby reducing machine downtime and providing a system that is smaller in overall size and more economical than prior art systems. In fact, by focusing the heating on the external surface of the embossing roller, i.e., the working portion of the roller that embosses the web material, energy is avoided from being wasted in heating the entire roller. Only the energy required to bring the least active portion of the roller up to the required temperature is used, and only the amount of energy required to maintain the desired temperature is provided.

[0018] It is an object of the present invention to provide an embossing device having a first path for a first ply of web material along which a first pressure roller is arranged to cooperate with a first embossing roller to define a first embossing nip for the first ply of web material, the first embossing roller being provided with embossing projections, and having at least a first electromagnetic induction device externally associated with the first embossing roller for selectively heating an outer surface of the first embossing roller, the first electromagnetic induction device being connected to a first generator supplying the first electromagnetic induction device with an electromagnetic induction current adapted to generate an electromagnetic flux directed towards the first embossing roller, the operating frequency of the electromagnetic induction current being such that eddy currents are generated on the first embossing roller that selectively follow the profile of the outer surface of the first embossing roller.

[0019] It is also an object of the present invention to manufacture an embossing device in which the eddy currents follow only or predominantly follow the projections of the first embossing roller. Preferably, the operating frequency of the electromagnetic induction currents is in the range of 500Hz-100kHz, preferably 1kHz-100kHz, even more preferably 5kHz-100kHz, more preferably 10kHz-60KHz. The induction embossing device has eddy currents with a minimum value of power density equal to at least 30% of the maximum value of power density, the minimum value being detected in a thickness measured from the outer surface of the first embossing roller at least equal to 0.6mm, preferably at least 0.4mm. In other words, at least 70% of the current density is contained within a thickness at least equal to 0.7mm, preferably at least 0.5mm.

[0020] Preferably, the method can include a machine shut-down step comprising the steps of: 1) moving the first pressure roller away from the first embossing roller, 2) maintaining the first inductively heated embossing roller rotating at a slow speed, and 3) supplying power to the induction device to maintain the temperature of the embossing roller in a range around a predetermined embossing operating temperature.

[0021] Machine downtime is generally defined as a state in which the machine, i.e. the embossing machine, must be stopped for safety reasons, e.g. due to a malfunction, a broken paper ply or for maintenance, but also as a state in which the machine must remain capable of restarting during a stoppage that is not due to safety reasons. In the case of safety, if an operator needs to work close to the heated embossing roller, this roller may need to be cooled. In the case of a production-related stop of the machine, the embossing roller needs to be kept at a high temperature in order to be able to start again quickly. Similarly, machine downtime may also mean that the machine is simply switched off, i.e. inactive. In this case, the embossing roller needs to be heated from room temperature to or close to the operating temperature. The invention will be better understood by following the description and the accompanying drawings which show non-limiting examples of embodiments of the invention. [Brief description of the drawings]

[0022] [Figure 1] FIG. 2 is a side view of an embossing / laminating device equipped with an electromagnetic induction device. [Figure 1A] FIG. 2 is an enlarged view showing a detail of FIG. [Figure 1B] FIG. 2 is an enlarged view showing a detail of FIG. [Diagram 2] FIG. 2 is a perspective view of an embossing roller associated with an electromagnetic induction device. [Diagram 3] 3 is a cross-sectional view of FIG. 2 taken along a plane perpendicular to the axis of the roller. [Figure 4] FIG. 2 is a diagram showing details of an embodiment of the present invention. [Figure 5A] FIG. 13 shows a first simulation of the power density distribution induced in the embossed protrusions. [Figure 5B] FIG. 13 shows a second simulation of the power density distribution induced in the embossed protrusions. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] In the embodiment shown, the embossing and laminating device 1 comprises a load-bearing structure, generally designated 2. The load-bearing structure may comprise two lateral side panels 3.

[0024] In some embodiments, a first embossing roller 4 and a second embossing roller 5 may be arranged between two lateral side panels 3 of the load-bearing structure 2. The first embossing roller 4 may be provided with a number of embossing projections 4P, as shown in the enlarged detail of FIG. 1A, and the second embossing roller 5 may be provided with a number of embossing projections 5P, as shown in the enlarged detail of FIG. 1B. The bottom surfaces of the embossing rollers 4 and 5 may be defined as the roller surfaces separating the bases of the embossing projections 4P and 5P, and are indicated by the references 4F and 5F. Generally, the bottom surfaces 4F and 5F are smooth. In the case of embossing projections with two heights, the surface separating the bases of the tips with the smaller height is taken as the bottom surface of the embossing cylinder.

[0025] The first embossing roller 4 may cooperate with a first pressure roller 6. In some embodiments, said pressure roller 6 may be covered with an outer layer 6A made of a yielding material, such as rubber, preferably an elastically yielding material. The second embossing roller 5 may cooperate with a second pressure roller 7. In some embodiments, the pressure roller 7 may also be covered with an outer layer 7A made of a yielding material, in particular an elastically yielding material.

[0026] The references 4X, 5X, 6X and 7X respectively denote the rotation axes of the two embossing rollers 4 and 5 and of the two pressure rollers 6 and 7. These axes are substantially parallel to one another.

[0027] The first embossing roller 4 and the first pressure roller 6 form a first embossing nip 8 between them through which the first ply V1 passes and is embossed by the protrusions 4P of the first embossing roller 4. If the pressure roller 6 is provided with a yielding outer layer 6A, the protrusions 4P are pressed against the first pressure roller 6 and penetrate the yielding outer layer 6A, permanently deforming the ply V1.

[0028] The second embossing roller 5 and the second pressure roller 7 form a second embossing nip 9 through which the second ply V2 passes. The second ply V2 is embossed in the same way as the first ply VI by pressing the projections 5P of the second embossing roller 5 against the second pressure roller 7. If provided with an elastically yielding outer jacket 7A, the embossing projections 5P penetrate the yielding jacket and cause a permanent deformation of the ply V2.

[0029] The two pressure rollers 6 and 7 may be supported by arms or other members that allow them to move towards or away from the respective embossing rollers 4 and 5 for purposes described below. An actuator (not shown), for example a piston-cylinder type actuator, may be used to press the pressure roller 6 against the first embossing roller 4 and the second pressure roller 7 against the second embossing roller 5.

[0030] In some embodiments, the two embossing rollers 5 and 6 may be configured to operate end-to-end, i.e. with their protrusions 4P and 5P pressed against each other within the nip 10 formed between the two embossing rollers 4 and 5.

[0031] In another embodiment, the embossing and laminating device 1 may have a laminating roller 11 which is pressed against the embossing roller 5 and forms a laminating nip 12 therewith. In this way, the two plies V1 and V2 may be laminated between the second embossing roller 5 and the laminating roller 11. In the nip 10, the embossing rollers 4 and 5 are slightly spaced apart from each other so that the two plies V1 and V2 do not come into contact. In this case, the embossing device may produce an embossed material according to a nesting technique, in which the embossing projections of ply V2 are nested between the embossing projections of ply V1, or vice versa.

[0032] In some embodiments, the embossing and laminating device 1 may be configured to operate according to a tip-to-tip technique, i.e. alternately according to a nesting technique. For this purpose, the embossing rollers may for example be moved parallel and orthogonal to their axes and the laminating rollers may be moved alternately between an active and a non-active position.

[0033] The embossing and laminating device 1 may have a functional fluid dispenser 13. The functional fluid dispenser 13 is a device adapted to dispense a liquid or gaseous fluid onto the ply V2. For example, the functional fluid dispenser 13 may dispense saturated or unsaturated steam to promote the pressure-induced adhesion of the plies V1 and V2. In a preferred embodiment of the present invention, as shown in FIG. 1, the functional fluid dispenser 13 may have a liquid fluid source 14, a first patterned or anilox roller 15 that picks up liquid from the liquid fluid source 14, and a second cliché or applicator roller 16 that receives liquid from the anilox roller 15 and distributes the liquid fluid onto the portion of the embossed ply V2 attached to the second embossing roller 5. Generally, the liquid fluid is applied to at least some of the tips of the embossing projections 5P provided on the embossing roller 5 in the portion of the ply embossed by the embossing projections 5P. The liquid fluid may be water or an adhesive. When the fluid is water, bonding of the plies is achieved exclusively by mechanical pressure.

[0034] In an advantageous embodiment, the first embossing roller 4 and the second embossing roller 5 must be made of a ferromagnetic material, a metal, for example steel. Said metal may also be subjected to a surface hardening treatment. The embossing projections 4P and 5P of the embossing rollers 4 and 5 may be produced in any suitable manner, for example by chemical etching, laser etching, chip removal by means of a tool or another suitable method. The hardening treatment may be performed only on the embossing projections 4P and 5P.

[0035] When the embossing and laminating device 1 is in operation, the first ply V1 and the second ply V2 move towards the embossing roller according to the arrows fl and f2 and are embossed separately between the pairs of rollers 4 and 6 and 5 and 7. The embossed plies are bonded and laminated between the embossing roller 5 and the laminating roller 11, so as to form a multi-ply web material N, which moves towards a downstream station, e.g. a rewinding device (not shown), according to the double arrow fN. ​​The pressure roller 7 presses against the embossing roller 5, while the pressure roller 6 presses against the embossing roller 4 and the laminating roller 11 presses against the embossing roller 5, so as to obtain the bonding of the plies V1 and V2.

[0036] In some embodiments the functional fluid dispenser unit 13 is mounted on a slide block or support member 17 which can move according to the double arrow f17, for example along a guide 18 supported by an element of the fixed structure 2. The movement according to the double arrow f17 can be controlled by a suitable actuator, for example a piston-cylinder actuator, an electric motor or any other suitable actuator not shown.

[0037] In an advantageous embodiment, an electromagnetic induction device 19 and 20 is associated with at least one of the embossing rollers 4 and 5 in order to induce eddy currents in the outer surface of the embossing rollers 4 and 5 which are heated by the Joule effect. In effect, the induced eddy currents circulate locally on the surface of the embossing rollers 4 and 5 and generate heat proportional to the electrical resistance of the embossing roller and the square of the induced eddy currents.

[0038] As shown in Fig. 1, the electromagnetic induction device 19 associated with the embossing roller 4 is preferably arranged in the area between the contact point with the pressure roller 6 and the nip 10 for reasons related to the overall dimensions. It is clear that in other embossing and laminating devices with different configurations, the electromagnetic induction device can be arranged in a different position, for example between the contact point with the pressure roller 6 and the nip 10. Similarly, the electromagnetic induction device 20 associated with the embossing roller 5 (shown in dashed lines in Fig. 1) can be arranged instead between the contact point with the pressure roller 7 and the cliche roller 16, or between the contact point with the pressure roller 7 and the laminating nip 12, or between the cliche roller 16 and the nip 10. The choice of one or more of these positions is made depending on the different embossing and laminating devices with different configurations and arrangements of rollers present on the market.

[0039] Associated with each of the induction devices 19 and 20 is a respective generator or inverter 23 and 24 capable of directing an appropriate current towards the induction devices to obtain the desired heating. In a preferred arrangement of the invention, a closed loop control system is arranged to regulate the desired temperature at the surface of the embossing rollers 4 and 5, i.e. the operating temperature. The control system comprises at least one temperature sensor 21 and 22 of any type, such as a thermocouple, pyrometer, thermal camera or another suitable device, associated with each roller, the embossing device 4 and 5, and connected to a control unit 25 which controls the inverters 23 and 24 to stabilise the desired temperature at the outer surface of the embossing rollers 4 and 5 based on a suitable control algorithm as will be explained in more detail below. The control device may be a PLC, an industrial computer, a microprocessor, a computer network or other similar known device.

[0040] The generators 23, 24 may be inverters that operate at a particular operating frequency that is approximately the same as the resonant frequency of the electric circuit that the electromagnetic induction devices 19 and 20 form at the output of the inverters.

[0041] The regulation of the operating temperature of the embossing roller with which the inductor is associated can be performed as follows: the inductor is adjusted to supply maximum power; this power is maintained until the desired operating temperature (or a temperature just below it, for example at least 3 / 4 of that temperature) is reached; then a PID (proportional integral derivative) controller (associated with the inductor and with the unit 25) is activated to keep the temperature constant, i.e. to regulate and compensate for the heat absorbed by the paper. By operating the PID controller after the desired target temperature is reached, the heating time can be reduced (compared to operating the PID controller from the start of heating). In practice, the PID controller adjusts the power of the inductor so that the temperature detected by the sensor minus the "target" temperature (operating temperature) is zero or close to zero. It is understood that other types of temperature regulation different from the above regulation method are possible without departing from the object of the invention.

[0042] In a preferred embodiment of the invention, the embossing rollers 4 and 5 are kept rotating at a low speed during the heating step, i.e. to bring them from room temperature to the operating temperature. In this step, the embossing rollers can be heated both when the paper ply is wrapped around them and when the paper ply is completely released. In the first case, the pressure roller is preferably open, i.e. not in contact with the embossing roller, allowing the embossing pressure roller to rotate rubbing against the paper wrapped around it. In this case, no paper is fed towards the downstream station, thus avoiding the waste of a large amount of paper.

[0043] 2 and 3, the induction devices 19 and 20 may include a single coil 26 of conductive material, such as copper or other suitable material, disposed generally parallel to the axes 4X and 5X of the embossing rollers 4 and 5. In other configurations, the induction devices 19 and 20 may include multiple coils.

[0044] In one embodiment, the coil 26 of conductive material may be supported by a frame 27 that moves so that the coil 26 can be moved towards or away from the outer surfaces of the embossing rollers 4 and 5. In a preferred embodiment, the frame 27 pivots around a pivot 29 according to the arrow f29. The pivoting movement of the frame 27 towards or away from the embossing rollers can be obtained via an actuator 28 connected to the end 27A of the frame 27. The actuator 28 may be a pneumatic piston controlled by a solenoid valve (not shown) connected to the control unit 25. In this case, by extending and retracting the rod of the piston, the guide device 19 can be moved away from and towards the outer surfaces of the embossing rollers 4 and 5. In another embodiment, the actuator 28 may be an electric motor.

[0045] Other alternative embodiments for the movement of the frame 27 equivalent to those described above can be manufactured. For example, the frame 27 can be mounted on a slide block that slides on guides and can be moved towards and away from the embossing rollers 4 and 5 via actuators such as pneumatic pistons or electric motors.

[0046] The position of the coil 26 is preferably radially symmetrical with respect to the embossing rollers 4 and 5, at least when the coil 26 is in the operating position, preventing one of the two conductor branches forming the coil 26 from being closer to the embossing rollers 4 and 5 than the other. In some cases, the two conductor branches of the coil 26 remain radially symmetrical even in positions different from the operating position.

[0047] In a particularly advantageous embodiment, as in the case of FIG. 4, the part of the frame 27 supporting the coil 26 can be formed by an electromagnetic flux focusing element 27A adapted to direct the electromagnetic flux more efficiently towards the outer surface of the roller. Preferably, the electromagnetic flux focusing element 27A is E-shaped, completely surrounding the coil 26 but leaving the side facing the embossing rollers 4 and 5 free. This reduces the leakage of the electromagnetic waves and allows the induction device to supply a smaller current for the same heating, since the waves are concentrated on the outer surface of the embossing rollers 4 and 5. The electromagnetic flux focusing element 27A can be formed of a pack of ferrite or non-conductive ferromagnetic laminations, the high magnetic permeability of which allows the electromagnetic field lines to be directed towards the free side of the coil facing the embossing rollers 4 and 5. It is also possible for the electromagnetic flux focusing element to have, for example, a rectangular or C-shaped or other shape. FIG. 4 shows only a part of the coil 26 and the electromagnetic flux focusing element 27A, which in a preferred embodiment is wound around the coil over its entire length.

[0048] In a preferred variant of the invention, the embossing and laminating device 1 may be provided with one or more sensors, not shown, for detecting breaks in the paper and any accumulation of plies V1 and V2 on the embossing rollers 4 and 5. Video cameras, high-speed video cameras, viewing video cameras, photocells, photocell arrays or laser sensors, etc. may be used for this purpose. When the pressure rollers 6 and 7 are adjacent to the respective embossing rollers 4 and 5, a pneumatic piston may detect a pressure peak in the piston and generate an accumulation signal of plies V1 or V2. In other words, the accumulation of plies VI or V2 around the embossing rollers 4 and 5 increases the pressure exerted by the pressure rollers 6 and 7 and the embossing rollers 4 and 5. When the sensors detecting the break in the paper generate an accumulation signal towards the control unit 25 to which they are connected, the control unit 25 controls the movement of the frame 27 to immediately move away from the embossing rollers 4 and 5, preventing damage to both the embossing rollers and the guide device and putting the device into emergency mode.

[0049] In a particularly advantageous embodiment, in order to make the surface temperature as uniform as possible, two or more induction devices can be used for each embossing cylinder, in which case the induction devices can be powered by the same inverter or by respective inverters controlled by the central control unit 25 depending on the outer surface temperatures of the embossing rollers 4 and 5 detected by one or more temperature sensors.

[0050] The induction device 19 may be cooled by known means, for example by running cooling water through the inside of the induction device 19, in which case the induction device 19 may be made of copper pipe or other conductive material.

[0051] In an operating step, a coil 26 made of a conductive material is supplied with alternating currents I1 and I2 and is placed in an operating range at a distance d from the outer surfaces of the embossing rollers 4 and 5. This generates a time-varying magnetic field B penetrating the outermost periphery of the embossing rollers 4 and 5, inducing eddy currents Ip that heat the embossing rollers 4 and 5 by the Joule effect, as explained above. The distance d can be varied to adjust the gap and optimize the magnetic flux, and can be between 1 mm and 8 mm.

[0052] In some cases, more than one temperature sensor may be used for a single embossing cylinder, and more typically, more than one temperature sensor of different types may be used for each embossing cylinder, e.g., one or more thermocouples, pyrometers and / or thermographs. Typically, the sensors are located on the outside of the embossing rollers 4 and 5, but in some cases, the sensors may be inserted inside the cylinders. For example, multiple thermocouples may be placed at different depths inside the embossing rollers 4 and 5 to monitor the temperature of the rollers in the radial direction, i.e. along the inside of the rollers.

[0053] The use of thermography is preferred over other sensors since it allows a more complete overview of the temperature distribution on the surface of the embossing rollers 4 and 5. For example, the embossing protrusions may be at a higher temperature relative to the bottom surface of the embossing roller or vice versa, and therefore the frequency of the electromagnetic induction currents I1 and I2 supplied by the inverters 23 and 24 to the induction devices 19 and 20 must be modified and generally suitably controlled. The eddy currents induced on the outer surface of the embossing rollers 4 and 5, generated by the time-varying magnetic field, have a penetration depth into the rollers that depends on the magnetization frequency of the induction devices 19 and 20.

[0054] In practice, as is known, the induced eddy currents are calculated by the following formula: TIFF0007633613000001.tif84159

[0055] In an advantageous embodiment, the temperature profile of the outer surface of the embossing rollers 4 and 5 can be detected and any temperature difference between the embossing projections 4P and 5P and the bottom surface 4F and 5F, and any temperature anomaly between the outer surface of the roller and the innermost part of the embossing rollers 4 and 5 can be highlighted. In this case, the central control unit 25 can control the inverters 23 and 24 to modify the frequency and / or the intensity of the electromagnetic induced currents I1 and I2 to obtain an optimal temperature profile, i.e. a temperature profile in which only the outer surface of the embossing roller is at the desired temperature. Advantageously, the operating frequency can be in the range of 500Hz-100kHz, preferably 1kHz-100kHz, even more preferably 5kHz-100kHz, more preferably 10kHz-60KHz, i.e. a frequency range in which the induced eddy currents Is are mostly confined on the embossing projections 4P and 5P.

[0056] As shown in Fig. 5A, by supplying the induction device 19 with electromagnetic induction currents I1 and 12 at an operating frequency of the order of 1000 Hz, it is possible to obtain a power density distribution focused along one of the outer surfaces SE of the embossing projections 4P and 5P. In other words, the thickness S of the embossing rollers 4 and 5, measured starting from the outer surface SE, includes a minimum power density value equal to at least three-quarters of the maximum power density value. The thickness S can vary from one tenth of a millimeter to five tenths of a millimeter. In the case of Fig. 5A, the thickness is equal to 0.4 mm and includes a minimum power density value corresponding to approximately three-fifths of the maximum power density value.

[0057] 5B shows an embodiment in which the induction device 19 is supplied with electromagnetic induction currents I1 and I2 at an operating frequency of about 10,000 Hz. In this case, the eddy currents, and therefore the power density distribution, mostly follow the outer surface SE and thus its profile. In this case, within a thickness S of about 0.1 mm, the minimum value of the power density is equal to 1 / 3 of the maximum value of the power density.

[0058] In other words, for example, by using a frequency of 500 Hz or more, more preferably 5 kHz or more, at least 50% or more of the current density can be confined within a thickness of 0.5 mm. By increasing the frequency, it is possible to confine 60% or 70% or more in a thickness of 0.4 mm or less.

[0059] The two illustrated embodiments relate to examples of how the induced eddy currents Is must preferably circulate in the vicinity of the outer surface SE of the embossing rollers 4 and 5. In other words, they must be largely confined to a limited thickness S of the outermost periphery of the roller embossing devices 4 and 5. Advantageously, the power density distribution is such that the induced eddy currents Is can be considered to be prevalent not only on the embossing projections 4P, 5P but also on the bottom surface, i.e. the outer surface of the roller separating each embossing projection 4P, 5P.

[0060] Depending on the embossing pattern, i.e. also the size, shape and distribution of the embossing projections 4P and 5P, in other embodiments the embossing and laminating device 1 can be adjusted to keep the embossing projections 4P and 5P at a higher temperature relative to the bottom surfaces 4F and 5F. Advantageously, the control unit 25 controls the inverters 23 and 24 to keep only a very small surface thickness S at the desired temperature in order to reduce the energy required for heating and to obtain a rapid cooling of the outer surfaces of the embossing rollers 4 and 5.

[0061] The embossing machine may have a cooling system 30 (for example as shown in FIG. 1) for the embossing rollers 4 and 5 with associated induction devices 19 and 20. This cooling system 30 is configured to cool the heated embossing rollers during machine shutdowns, in case an operator needs to work in close proximity to the hot embossing rollers. Access to the machine is only allowed under safe conditions, that is, when all rollers are stopped and braked, and, in the case of hot rollers, a predetermined temperature is not exceeded.

[0062] The cooling system 30 may comprise a device for discharging cooling air towards the embossing roller to be cooled, which may consist, for example, of an air blade type cooling device (i.e. a distributor with a nozzle having an elongated slot, discharging an air flow having an elongated, i.e. linear, discharge front, preferably at least equal to the axial length of the embossing roller to be cooled), or of a vortex tube type cooling device, also known by the name "Rank-Hirsch vortex tube".

[0063] On the other hand, when the embossing device has to be stopped due to production needs and therefore not due to a breakdown, malfunction, maintenance etc. that requires the operator to be present in the vicinity of the embossing roller, it is necessary to prevent a decrease in the heating of the embossing roller, so the induction device is kept in operation to heat the roller (or rollers). A complete stop would result in only the part facing the induction heating device being heated, which would obviously lead to uneven expansion and unacceptable local overheating. This uneven heating defect would lead to an imbalance of the rollers when the embossing device is started again, which would result in vibrations, with the result that the embossing quality of the paper would be reduced, or the line would have to be run at a slower speed until the rollers are heated uniformly, with the risk of breakdowns and reduced production. Therefore, during a stop where the embossing device is to be started again immediately, it is necessary to ensure that the embossing roller (or both embossing rollers) is uniformly heated to the desired temperature. To achieve this, it is first necessary to reduce the power of the supply current of the induction device (or devices), since with the line stopped, the heat is no longer subtracted by absorption by the paper. Next, the embossing roller (or rollers) must continue to rotate so that the induction device can continue to heat the rollers evenly. To keep the embossing rollers rotating without tearing the paper, each pressure roller must be moved away an appropriate amount, slightly loosening the tension on the paper around the pressure and embossing rollers as necessary. This allows the embossing roller to rotate at a very slow speed with the paper wrapped around it. The friction between the paper and the roller is very low, and no problems such as ply breakage occur. In practical terms, this procedure allows the paper ply to rub against the circumference of the embossing roller without tearing. Of course, if there are multiple embossing and pressure rollers, as in the example shown in the drawings, this logic applies to all the rollers.

[0064] In summary, with the embossing device stopped, 1) Moving the pressure rollers (both pressure and optionally laminating) away from the embossing roller, moving the paper away from the embossing roller and reducing tension / pulling on the paper; 2) maintaining the induction heated embossing roller rotating at a slow speed; 3) Power is supplied to the induction device to maintain the temperature approximately constant and at or slightly below the operating temperature, for example 3 / 4 of the operating temperature, or in any case within a predetermined temperature range close to the operating temperature, i.e. the embossing temperature (which can be set depending on the type of embossing). For example, if the operating temperature is H, the range is between temperatures corresponding to H+l / 4×H and Hl / 4×H.

[0065] A slow rotation of the embossing roller may mean a speed lower than one tenth of the operating speed of the roller during the embossing step, more preferably a speed lower than one twentieth of the operating speed, and even more preferably a tangential speed of the embossing roller in the range of 1 m / min to 10 m / min.

[0066] Similarly, if the heated embossing roller needs to be cooled, 1) Moving the pressure rollers (both the press and optionally the laminating) away from the embossing roller, moving the paper away from the embossing roller and reducing tension / pulling on the paper; 2) Keep the embossing roller rotating at a slow speed; 3) Turn off the induction device. In this manner, the slow rotation of the embossing roller allows its entire outer surface to be gradually and repeatedly brought into contact with the cooling system 30, shortening the cooling time and providing uniform cooling over the entire roller surface.

[0067] The embossing device is therefore equipped with device stopping means for moving the embossing roller, the pressure roller and / or the laminating roller away from each other and allowing the embossing roller to rotate at a slower speed. These means are of known type and will not be described in detail, for example comprising mechanisms or devices for relative movement of the shaft of the embossing roller with the shaft of the pressure roller and / or the shaft of the laminating device, so that there is no pressure or only limited pressure between the rollers. A cooling device for the embossing roller may be associated with these means and also with a program for operating a guide device facing the embossing roller rotating at a slower speed.

[0068] Similarly, if one or more embossing rollers need to be heated from room temperature to operating temperature, 1) Rotate the embossing roller at a slow speed. 2) Provide power to the induction device. In this step, the paper ply may or may not be wrapped around the embossing roller, and if the paper is wrapped around it, the pressure roller is preferably kept open, i.e., not in contact with the heated embossing roller.

[0069] The above-described embodiment relates to one type of embossing and laminating device taken as a non-limiting example of the present invention. In fact, those skilled in the art will recognize that there are many different types of embossing and laminating devices that may differ in the number of embossing rollers, their arrangement, and of course the type of processing performed on the paper plies, without departing from the principles, concepts and teachings of the present invention. For example, the present invention is also applicable to an embossing device that has only one embossing roller and therefore does not require a ply bonding device.

[0070] Some examples of the embodiments of the present invention have been described in detail with reference to the drawings. Those skilled in the art will understand that many modifications, variations, additions and omissions are possible without departing from the principles, concepts and teachings of the present invention as defined in the appended claims. Therefore, the scope of the present invention should be determined purely based on the broadest interpretation of the appended claims, and includes such modifications, variations, additions and omissions. The terms "comprise", "have" and their derivatives do not exclude the presence of other elements or steps than those specifically recited in the claims. The definite article "a" or "an" preceding an element, means or feature in a claim does not exclude the presence of a plurality of such elements, means or features. When an apparatus claim recites a plurality of "means", some or all of these "means" may be embodied by a single component, member or structure. The recitation of certain elements, features or means in separate dependent claims does not exclude the possibility that such elements, features or means may be combined with each other. When a method claim recites a sequence of steps, the order in which these steps are recited is not binding and may be changed unless a specific order is indicated as binding. Any reference signs in the accompanying claims are provided to facilitate the reading of the claims with reference to the description and the drawings and do not limit the scope of protection represented by the claims.

Claims

1. - a first path for a first ply of web material; a first pressure roller cooperating with a first embossing roller about which paper is wrapped along said first path, said first embossing roller and said first pressure roller defining a first embossing nip for a first ply of web material, said first embossing roller being provided with embossing protrusions; at least one first electromagnetic induction device external to the first embossing roller for heating the surface of the first embossing roller, the first electromagnetic induction device being connected to a first generator which supplies the first electromagnetic induction device with an electromagnetic induction current adapted to generate an electromagnetic flux towards the first embossing roller, the operating frequency of the electromagnetic induction current being such that eddy currents are generated on the first embossing roller that primarily follow the profile of the outer surface of the first embossing roller; and a device stop means for moving said first pressure roller away from said first embossing roller while maintaining rotation of said first embossing roller at a speed which allows the paper to rub against the outer surface of said first embossing roller without tearing the ply of paper, said paper remaining wrapped around said first embossing roller; An embossing device comprising:

2. The operating frequency of the electromagnetic induction current is in the range of 500 Hz to 100 kHz.

2. An embossing device according to claim 1.

3. The first electromagnetic induction device includes an electromagnetic flux focusing member.

3. An embossing device according to claim 1 or 2.

4. adapted to detect the temperature of the first embossing roller with which the first electromagnetic induction device is associated A first temperature sensor; a central control unit communicatively connected to the first temperature sensor; The embossing device according to any one of claims 1 to 3, further comprising:

5. The first generator is controlled by the central control device in response to the temperature detected by the first temperature sensor to vary the operating frequency and / or the intensity of the electromagnetic induction current.

5. An embossing device according to claim 4.

6. a second pass for a second ply of web material; and a second pressure roller cooperating with the second embossing roller along said second path; Equipped with The second embossing roller and the second pressure roller define a second embossing nip for a second ply of web material.

2. An embossing device according to claim 1.

7. at least one bonding device for bonding the first and second plies together, the bonding device cooperating with the second embossing roller; the bonding device and the second embossing roller define a lamination nip; The coupling device comprises a roller.

7. An embossing device according to claim 6.

8. The first and second electromagnetic induction devices are associated with the first embossing roller and / or the second embossing roller, respectively.

7. An embossing device according to claim 6.

9. First and second temperature sensors are associated with the first and second embossing rollers and adapted to detect temperatures of the first and second embossing rollers with which the first and second electromagnetic induction devices are associated.

9. An embossing device according to claim 8.

10. The temperature detected by the first and / or second temperature sensor is the temperature of the outer surface of the first and / or second embossing roller.

10. An embossing device according to claim 9.

11. a functional fluid dispenser associated with the second embossing roller, the functional fluid dispenser dispensing fluid onto at least some of the protrusions of the second embossing roller over which the second ply travels; An embossing device according to any one of claims 6 to 10.

12. The fluid is optionally an adhesive, water, steam or a combination thereof.

12. An embossing device according to claim 11.

13. The first electromagnetic induction device is disposed between the first embossing nip and the lamination nip.

8. An embossing device according to claim 7.

14. A cooling system for cooling the first embossing roller with which the first electromagnetic induction device is associated, The cooling system is adapted to operate to cool the first embossing roller during a stop of the embossing apparatus. An embossing device according to any one of claims 1 to 13.

15. The cooling system comprises at least one device for directing cooling air towards the first embossing roller to be cooled.

15. An embossing device according to claim 14.

16. The device stopping means is configured to also move the bonding device away from the first embossing roller while maintaining rotation of the first embossing roller.

8. An embossing device according to claim 7.

17. The device stopping means if it is necessary to continue to heat the first embossing roller, while the first embossing roller is rotating, maintaining the first electromagnetic induction device opposite the first embossing roller in a state in which it is operated with an induction power such as to maintain the temperature of the first embossing roller at an embossing temperature; If the first embossing roller needs to be cooled, the cooling system according to claim 14 or 15 is used to cool the first embossing roller while it is rotating.

17. An embossing device according to claim 16.

18. The device stopping means If an initial heating step is required from a temperature state below the operating temperature of the first embossing roller to an operating temperature state, - maintaining rotation of the first embossing roller with the first pressure roller and / or the bonding device spaced apart from the first embossing roller; activating the first electromagnetic induction device opposing the first embossing roller while the first embossing roller is rotating to heat the first embossing roller from a temperature state below the operating temperature to a temperature state at the operating temperature; 17. An embossing device according to claim 16.

19. A first pressure roller having embossing projections and cooperating with a first embossing roller having paper wrapped thereon provides a first path for a first ply of web material defining a first embossing nip for the first ply of web material; an electromagnetic induction device for generating a time-varying electromagnetic flux toward the outer surface of the first embossing roller to induce eddy currents in the first embossing roller that generate heat by Joule effect; A method for electromagnetically heating a first embossing roller in an embossing device, comprising providing an electromagnetic induction current generator, generating said electromagnetic flux at an operating frequency such as to generate eddy currents in said first embossing roller that primarily follow the profile of an outer surface of said first embossing roller; The method further comprises a step of shutting down the device; The device stopping step includes: - spacing the first pressure roller from the first embossing roller; - maintaining rotation of the first embossing roller at a speed that allows the ply of paper to rub on the outer surface of the first embossing roller without tearing, while the paper remains wrapped around the first embossing roller; have A method comprising:

20. The operating frequency of the electromagnetic induction current is in the range of 500 Hz to 100 kHz.

20. The method of claim 19 .

21. The electromagnetic induction device includes an electromagnetic flux focusing member.

21. The method according to claim 19 or 20.

22. A temperature sensor communicatively connected to a central control device for detecting an external temperature of the first embossing roller is provided.

20. The method of claim 19 .

23. The method of claim 22, wherein the electromagnetic flux is controlled in response to a temperature of the outer surface of the first embossing roller detected by the temperature sensor.

23. The method of claim 22.

24. A central control device controls the electromagnetic induction current generator to vary the frequency and / or intensity of the electromagnetic induction current, the electromagnetic induction current being supplied by the electromagnetic induction current generator to the electromagnetic induction device.

24. The method according to any one of claims 19 to 23.

25. The method of claim 25, wherein the central controller controls movement of the electromagnetic induction device from a first operating area along the first embossing roller toward a non-operating area away from the first embossing roller when a first sensor adapted to detect breakage of the first ply of the web material notifies the central controller of the breakage of the first ply.

23. The method of claim 22.

26. The first sensor is a photocell, a photocell array, a laser sensor, a video camera, a high speed video camera, or a vision system.

26. The method of claim 25.

27. ​​The temperature sensor detects a temperature of the protrusions of the first embossing roller and a temperature of a bottom surface of the first embossing roller; The central control unit controls an electromagnetic induction current generator in response to the temperature difference between the protrusion and the bottom surface.

23. The method of claim 22.

28. The method of claim 27, further comprising the steps of: supplying power to the electromagnetic induction device such that the temperature of the first embossing roller is maintained at an embossing temperature; and - turning off the electromagnetic induction device and cooling the first embossing roller by a cooling device; Selectively include 28. The method of claim 27.

29. The cooling device comprising at least one device for directing cooling air towards the first embossing roller to be cooled.

29. The method of claim 28.

30. Initially heating the first embossing roller from a temperature condition below an operating temperature to an operating temperature condition, comprising: - maintaining rotation of the first embossing roller; - activating the electromagnetic induction device to heat the first embossing roller; The method includes the steps of:

30. The method according to any one of claims 19 to 29.

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