Method and device for heating an embossing roll in an embossing-laminating apparatus

Abstract

The invention provides an embossing device and an embossing method, which employ an electromagnetic induction device (19, 20) in order to induce eddy currents mainly on the outer surface of an embossing roller (4, 5). The eddy currents mainly heat the outer surface of the embossing roller.

Description

TECHNICAL FIELD

[0001] The present invention relates to improvements in the method and apparatus for heating an embossing roll suitable for producing a multi-ply cellulosic web material. BACKGROUND

[0002] In the field of tissue paper production and processing, in order to obtain products such as rolls of toilet paper, kitchen paper, napkins and facial tissues, it is known to unwind a plurality of cellulosic fibrous plies from one or more parent reels and to process these plies into semi-finished or finished products comprising two or more plies bonded to each other.

[0003] The bonding of the cellulosic fibrous plies for producing a multi-ply web material is usually carried out using glue or by mechanical ply bonding, i.e. by pressing one ply against another under high pressure. For this purpose, at least one of the cellulosic fibrous plies is embossed by an embossing roll and a pressure roll, which is usually coated with an elastically yielding material. By embossing, the cellulosic fibrous ply is permanently deformed, so that embossing protrusions are formed. While the cellulosic fibrous ply is still adhering to the embossing cylinder, glue is applied to the embossing protrusions. Subsequently, a second ply is superimposed on the embossed cellulosic fibrous ply and the two plies are pressed against each other in the areas where the glue is received, so that they adhere to each other.

[0004] The two or more plies, at least one, part or all of which are embossed, are then bonded to form a multi-ply web material. The web material can be wound to form a roll, or cut and folded to form facial tissues, napkins, etc.

[0005] In addition to enabling the cellulosic material plies to adhere to each other, embossing has the purpose of improving the quality of the multi-ply paper product. For example, in the case where one or more cellulosic material plies are wound into a roll, the thickness of each single ply can be increased in order to obtain an increase in the bulk or diameter of the finished product. In other cases, the mechanical strength, i.e. the ultimate tensile strength, of the plies can be increased, or the absorbency or softness can be increased.

[0006] For these reasons, a number of methods and machines for embossing cellulosic material plies have been developed, as described in EP 1075387, EP 1855876, US 3556907, EP 1239079, EP 1319748, US 6746558.

[0007] To further improve the characteristics of the layer of cellulosic material, an improved embossing technology has been developed, which uses a heated embossing roll. This technology is described in patent IT MI 1995 A001 197, in which a layer of cellulosic material is moistened and passed through a nip formed by a pair of steel embossing rolls provided on the surface with embossing protuberances, in which the protuberances of the two rolls are arranged in contact with each other under pressure according to the "end-to-end" mode, and in which the two steel rolls are heated during embossing to dry the layer.

[0008] To heat the aforementioned embossing rolls (and, in general, for all calendering systems provided with smooth heated rolls, for example in the case of forming paper layers), systems for recirculating heat-conducting oil, steam or water located inside the embossing rolls are used. These systems are very expensive, energy-intensive and very inefficient, and are dangerous for the operators who need to work near the heating devices and the embossing rolls.

[0009] The heating of the embossing rolls achieved by recirculation of fluids also requires a long heating time, since the heat supplied internally by the fluid must heat the entire roll before it reaches the outer surface, i.e. the working surface for processing the layer of cellulosic material.

[0010] Furthermore, heating systems with recirculating fluids are dangerous for the operators, since they are generally pressurized in the pipes that go from the heating boiler to the embossing rolls. A breakage of one of the pipes or a leak of hot fluid from one of the pipes, or simply contact with these pipes, can cause serious burns to the operators. Therefore, there is a need to improve the heating technology, in particular the heating technology of embossing rolls, i.e. to adopt a system that is more energy-efficient, heats the rolls more quickly and is safer for the operators who need to work with embossing machines with heated rolls. SUMMARY

[0011] These and other objects are achieved by the embossing-laminating device according to the appended claim 1 and by the method for the electromagnetic heating of an embossing roll in an embossing-laminating device according to claim 31, which will be more apparent hereinafter.

[0012] Before showing the characteristics of the various embodiments of the method, device and products obtained thereby, some definitions should be provided.

[0013] In this text, the term "embossing" relates to a process of permanent deformation of a portion of a cellulosic structure, such as a layer or a multi-layered sheet, perpendicular to the plane in which it lies, by which the cellulosic structure is permanently deformed, thereby forming protrusions or elevations that protrude from the normal plane in which the cellulosic structure lies (for example, in the case of embossing on a multi-layered material, the plane in which the layer or multi-layered web material lies).

[0014] The embossing device generally refers to a device that performs the embossing process on at least one layer and, if necessary, binds two or more layers to each other by lamination, for example, using glue that is applied to at least one of the layers, preferably to the top surface of at least some of the embossing protrusions formed on one or more layers.

[0015] The "outer surface" of the embossing cylinder refers to the entire area of the front surface including the embossing protrusions, the side surface of the embossing protrusions, and the surface of the plane in which the roller lies outwardly protruding with the embossing protrusions.

[0016] The aim of the present invention is to obtain an improved embossing device with a heated roller that solves the problems of the prior art, more particularly, to obtain a device with a roller that is heated by electromagnetic induction for uniformly heating the outer surface of the roller.

[0017] The aim of the present invention is also to obtain an embossing device with a heating system for a roller that is efficient, quickly reaches the outer temperature of the embossing roller and quickly cools the outer temperature of the embossing roller in order to reduce the downtime of the machine, and is an overall smaller and economical system compared to the systems of the prior art. In practice, by heating mainly the outer surface of the embossing roller, i.e. the working part of the roller that embosses the web material, energy waste is prevented that would be caused by heating the entire roller. Only the energy needed to bring the minimum working part of the roller to the desired temperature is used, and the energy needed to maintain the desired temperature is supplied.

[0018] The object of the present invention is to obtain an embossing device comprising a first path for a first layer of web material, a first pressure roller cooperating with a first embossing roller defining a first embossing nip for the first layer of web material along the first path. The first embossing roller comprises embossing protrusions. The embossing device further comprises at least a first electromagnetic induction device externally associated with the first embossing roller to mainly heat the outer surface of the first embossing roller, wherein the first electromagnetic induction device is connected to a first generator device to supply the first electromagnetic induction device with an electromagnetic induction current adapted to generate an electromagnetic flux directed towards the first embossing roller, and wherein the operating frequency of the electromagnetic induction current is such as to generate an eddy current on the first embossing roller so as to mainly follow the profile of the outer surface of the first embossing roller.

[0019] The object of the present invention is also to form an embossing device wherein the eddy current only or mainly follows the protrusions of the first embossing roller. Preferably, the operating frequency of the electromagnetic induction current ranges between 500 Hz and 100 kHz, preferably between 1 kHz and 100 kHz, even more preferably between 5 kHz and 100 kHz, more preferably between 10 kHz and 60 kHz. The induction-heated embossing device has an eddy current so as to have a minimum power density value equal to at least 30% of the maximum power density value, the minimum value being detected within a thickness measured from the outer surface of the first embossing roller equal to at least 0.6 mm, preferably at least 0.4 mm. In other words, at least 70% of the current density is included within a thickness equal to at least 0.7 mm, preferably 0.5 mm.

[0020] Preferably, the method can comprise a machine stop step comprising the steps of: 1) moving the first pressure roller away from the first embossing roller; 2) keeping the first induction-heated embossing roller rotating at low speed; 3) powering the induction device so as to keep the temperature of the embossing roller within a range around a given embossing operating temperature.

[0021] In general, a machine stop is defined as a condition in which the machine, i.e. the embossing device, has to stop for safety reasons, for example due to a malfunction, a breakage of the paper layer, or a maintenance, and also as a condition in which the machine has to remain ready to start again during a stop caused by non-safety reasons. In the case of safety, it can be necessary to cool the heated embossing roll if the operator needs to operate in the vicinity of the heated embossing roll. In the case of a machine stop due to production problems, in which the machine has to be ready to start again quickly, the embossing roll has to remain hot. Similarly, a machine stop can also mean a condition in which the machine is simply switched off, i.e. not running. In this case, the embossing roll has to be heated from room temperature to the operating temperature, or close to the operating temperature. BRIEF DESCRIPTION OF DRAWINGS

[0022] The application will be better understood with the following description and the appended drawings, which show non-limiting examples of embodiments of the application. More particularly, in the drawings:

[0023] Figure 1 shows a side view of an embossing-laminating device comprising an electromagnetic induction device;

[0024] Figure 1A and 1B shows a detail of Figure 1 ;

[0025] Figure 2 shows an isometric view of an embossing roll associated with the electromagnetic induction device;

[0026] Figure 3 shows a cross-sectional view of Figure 2 according to a plane perpendicular to the axis of the roll;

[0027] Figure 4 shows a detail of an embodiment of the application;

[0028] Figure 5A shows a first simulation of the distribution of the power density induced on the embossing protuberances; and

[0029] Figure 5B shows a second simulation of the distribution of the power density induced on the embossing protuberances. DETAILED DESCRIPTION

[0030] In the illustrated embodiment, the embossing-laminating device 1 has a carrying structure, indicated as a whole with 2. The carrying structure can comprise two lateral side panels 3.

[0031] In some embodiments, a first embossing roll 4 and a second embossing roll 5 can be arranged between the two lateral side panels 3 of the carrying structure 2. The first embossing roll 4 can be provided with embossing protuberances 4P, as Figure 1Aas shown in the enlarged detail of Fig. 2, while the second embossing roller 5 can be provided with embossing protrusions 5P, as shown in the enlarged detail of Fig. 3. The bottom surface of the embossing rollers 4, 5 can be defined as the surface of the rollers separating the bases of the embossing protrusions 4P, 5P, and is denoted by 4F and 5F. Typically, the surfaces 4F, 5F are smooth. In case the embossing protrusions have two heights, the bottom surface of the embossing roller is considered to be the bottom surface separating the bases of the tips having the smaller height. Figure 1B

[0032] The first embossing roller 4 can cooperate with a first pressure roller 6. In some embodiments, the pressure roller 6 can be coated with an outer layer 6A made of a yielding material, preferably an elastically yielding material, such as rubber. The second embossing roller 5 can cooperate with a second pressure roller 7. In some embodiments, the pressure roller 7 can also be coated with an outer layer 7A made of a yielding material, in particular an elastically yielding material.

[0033] The reference numerals 4X, 5X, 6X and 7X denote the rotation axes of the two embossing rollers 4, 5 and the two pressure rollers 6, 7, respectively. These axes are substantially parallel to each other.

[0034] The first embossing roller 4 and the first pressure roller 6 form a first embossing nip 8 therebetween, through which the first layer V1 passes to be embossed by the protrusions 4P of the first embossing roller 4. When the pressure roller 6 is provided with a yielding outer coating 6A, the protrusions 4P are pressed against the first pressure roller 6 and penetrate the yielding coating 6A, thereby permanently deforming the layer V1.

[0035] The second embossing roller 5 and the second pressure roller 7 form a second embossing nip 9, through which the second layer V2 passes. Due to the protrusions 5P of the second embossing roller 5 being pressed against the second pressure roller 7, the second layer V2 is embossed in a similar manner as the first layer V1. If an elastically yielding coating 7A is provided, the embossing protrusions 5P penetrate the yielding coating and cause the layer V2 to be permanently deformed.

[0036] The two pressure rollers 6, 7 can be supported by arms or other members that allow them to be moved towards or away from the respective embossing rollers 4, 5, the purpose of which will be explained below. Actuators (not shown), such as piston-cylinder actuators, can 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.

[0037] In certain embodiments, the two embossing rollers 5, 6 can be configured to operate in tip-to-tip fashion, i.e. with their protrusions 4P, 5P being pressed against each other in a nip 10 formed between the two embossing rollers 4, 5.

[0038] ​In other embodiments, the embossing-laminating device 1 can comprise a laminating roller 11 which is pressed against and forms a laminating nip 12 with the embossing roller 5. In this way, the two layers V1 and V2 can be laminated between the second embossing roller 5 and the laminating roller 11. In the nip 10, the embossing rollers 4, 5 are slightly spaced apart from each other so that the two layers V1, V2 do not come into contact. In this case, the embossing device can generate embossed material according to the nest technique, in which the embossing protrusions of the layer V2 are nested between the embossing protrusions of the layer V1, or vice versa.

[0039] In certain embodiments, the embossing-laminating device 1 can be configured to optionally operate according to the end-to-end technique or according to the nest technique. To this end, the embossing rollers can be moved, for example, parallel and perpendicular to their axis, and the laminating roller can be optionally moved into an active position and an inactive position.

[0040] The embossing-laminating device 1 can comprise a functional fluid distributor 13. The functional fluid distributor 13 is a device adapted to distribute a fluid, liquid or gas on the layer V2. For example, the functional fluid distributor 13 can distribute saturated or unsaturated steam to promote the adhesion of the layers V1 and V2 by pressure. In a preferred embodiment of the invention, as shown in Figure 1 the functional fluid distributor 13 can comprise a source of liquid fluid 14, a first pattern roller or anilox roller 15 which takes up the liquid from the source of liquid fluid 14, and a second cliché or applicator roller 16 which receives the liquid fluid from the anilox roller 15 and distributes it on the portion of the embossed layer V2 adhered to the second embossing roller 5. Typically, the liquid fluid is applied on the portion of the layer embossed by the embossing protrusions 5P at least to some ends of the embossing protrusions 5P provided by the embossing roller 5. The liquid fluid can be water or glue. In the case where the fluid is water, the adhesion of the layers occurs mainly by mechanical pressure.

[0041] 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. The metal can be subjected to a surface hardening treatment. The embossing protrusions 4P and 5P of the embossing rollers 4 and 5 can be produced in any suitable manner, for example by chemical etching, laser etching, chip removal by means of a tool, or in another suitable manner. The hardening treatment can be performed only on the embossing protrusions 4P and 5P.

[0042] When the embossing-laminating device 1 is in operating condition, the first and second layers V1 and V2 are moved according to the arrows f1 and f2 towards the embossing rollers to be embossed individually between the pairs of rollers 4, 6 and 5, 7. The embossed layers are glued and laminated between the embossing roller 5 and the laminating roller 11 and thus a multilayer web material N is formed which is moved according to the double arrow fN towards a downstream station, for example a rewinder not shown. The pressure roller 7 is pressed against the embossing roller 5 while the pressure roller 6 is pressed against the embossing roller 4 and the laminating roller 11 is pressed against the embossing roller 5 to obtain the joining of the layers V1, V2.

[0043] In some embodiments, the functional fluid distributor units 13 are mounted on a sliding block or carriage 17 which can be moved according to the double arrow f17, for example along a guide 18 carried by elements 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, by an electric motor or by any other suitable actuator (not shown).

[0044] In an advantageous embodiment, electromagnetic induction devices 19, 20 are associated with at least one of the embossing rollers 4, 5 to induce eddy currents on the outer surface of the embossing rollers 4, 5, heating said outer surface by Joule effect. In fact, the induced eddy currents circulate locally on the surface of the embossing rollers 4, 5 and generate heat proportional to the electrical resistance of the embossing rollers and to the square of the induced eddy currents.

[0045] As shown in Figure 1 For reasons related to the overall dimensions, the electromagnetic induction device 19 associated with the embossing roller 4 is preferably positioned in the area between the contact point with the pressure roller 6 and the nip 10. Obviously, in other embossing-laminating devices having a different configuration, the electromagnetic induction device can be positioned differently 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 (marked by a dashed line in Figure 1 between the contact point with the pressure roller 7 and the plate cylinder 16 or between the contact point with the pressure roller 7 and the laminating nip 12 or between the plate cylinder 16 and the nip 10. The choice of one or more of these positions depends on the different embossing-laminating devices present on the market which can thus have different configurations and arrangements of the rollers.

[0046] A corresponding generator or inverter 23, 24 is associated with each electromagnetic induction device 19, 20, which is able to drive a suitable current towards the induction device in order to obtain the desired heating. In the preferred configuration of the present application, in order to regulate the desired temperature, i.e. the operating temperature, on the surface of the embossing rollers 4, 5, a closed loop control system is generated, which comprises at least one temperature sensor 21, 22 of any type, such as a thermocouple, a pyrometer, a thermal camera or another suitable device, associated with the corresponding roller (embossing device 4, 5) and connected to a control unit 25, which controls the inverters 23, 24 on the basis of a suitable control algorithm in order to stabilize the desired temperature on the outer surface of the embossing rollers 4, 5, as will be explained in greater detail below. The control unit can be a PLC, an industrial computer, a microprocessor, a computer network or any other similar known device.

[0047] The generators 23, 24 can be inverters, which operate at a specific operating frequency, which is approximately the same as the resonance frequency of the circuit formed by the electromagnetic induction device 19, 20 and the output of the inverter.

[0048] The regulation of the operating temperature of the embossing rollers associated with the induction devices can be carried out in the following way. The induction devices are regulated to supply maximum power. This power is maintained until the desired operating temperature is reached (or just below this temperature, for example at least 3 / 4 of this temperature). A PID (Proportional-Integral-Derivative) controller is then activated (associated with the induction devices and the unit 25) in order to keep the temperature constant, i.e. to regulate and compensate for the heat absorbed by the paper. By activating the PID controller after the desired target temperature has been reached, a faster heating time is obtained (compared to the case in which the PID controller is activated from the start of heating). In fact, the PID controller regulates the power of the induction devices so that the temperature detected by the sensor minus the "target" temperature (operating temperature) is equal to zero or close to zero. It should be understood that other types of temperature regulation different from the aforementioned regulation method are also possible without departing from the object of the present application.

[0049] In the preferred embodiment of the present application, during the heating step, i.e. during the heating of the embossing rollers 4, 5 from room temperature to the operating temperature, the embossing rollers are kept rotating at low speed. In this step, the embossing rollers can be heated both when the paper layer is wound around the embossing rollers and when the embossing rollers are completely free of the paper layer. In the first case, the pressure rollers are preferably open, i.e. not in contact with the embossing rollers, thus allowing the embossing rollers to rotate in order to rub on the paper wound around them. In this case, the paper is not fed towards the downstream stations in order to avoid discarding large amounts of paper.

[0050] AsFigure 2 and Figure 3 As schematically shown, sensing devices 19, 20 may include a single coil 26 made of a conductive material (such as copper or any suitable material), the single coil 26 being positioned approximately parallel to the axes 4X, 5X of the embossing rollers 4, 5. In other configurations, sensing devices 19, 20 may include more than one coil.

[0051] In one embodiment, the conductive material coil 26 may be supported by a frame 27 that moves to allow the coil 26 to move toward or away from the outer surface of the embossing rollers 4, 5. In a preferred embodiment, the frame 27 rotates about a pivot 29 according to arrow f29. Rotational movement of the frame 27 toward or away from the embossing rollers can be achieved by an actuator 28 connected to an end 27A of the frame 27. The actuator 28 may be a pneumatic piston controlled by a solenoid valve (not shown) connected to a control unit 25. In this case, by extending or retracting the piston rod, the sensing device 19 can be moved away from and toward the outer surface of the embossing rollers 4, 5 accordingly. In other embodiments, the actuator 28 may be an electric motor.

[0052] Other alternative embodiments equivalent to those described above can be used to generate movement for frame 27. For example, frame 27 can be mounted on a slider that slides on a guide to move frame 27 toward and away from embossing rollers 4 and 5 by means of an actuator (such as a pneumatic piston or an electric motor).

[0053] At least when coil 26 is in the operating position, the position of coil 26 is preferably radially symmetrical with respect to embossing rollers 4, 5 to prevent one of the two conductor branches forming coil 26 from being closer to embossing rollers 4, 5 than the other. In some cases, the two conductor branches of coil 26 also remain radially symmetrical in positions different from the operating position.

[0054] In particularly advantageous embodiments, such as in Figure 4In the case of a portion of the support coil 26, the frame 27 can be formed by an electromagnetic flux concentrator element 27A adapted to more effectively direct the electromagnetic flux towards the outer surface of the roller. Preferably, the electromagnetic flux concentrator 27A is E-shaped, completely surrounding the coil 26, but leaving the side facing the embossing roller 4, 5 free. In this way, the leakage of electromagnetic flux is reduced and the electromagnetic flux is concentrated towards the outer surface of the embossing roller 4, 5, thus obtaining a smaller supply current of the induction device at the same heating. The electromagnetic flux concentrator 27A can be made of ferrite or by a group of non-conductive ferromagnetic laminations, and, due to its high magnetic permeability, it forces the electromagnetic field lines to be directed towards the free side of the coil facing the embossing roller 4, 5. The electromagnetic flux concentrator can also have other shapes, for example rectangular or C-shaped or other shapes. Figure 4 Only a portion of the coil 26 and of the electromagnetic flux concentrator 27A is shown, in the preferred embodiment, the electromagnetic flux concentrator 27A is wound around the entire length of the coil.

[0055] In a preferred variant of the application, the embossing-laminating device 1 can be provided with one or more sensors (not shown in the figures) to detect the breakage of the paper and any accumulation of the layers V1, V2 on the embossing rollers 4, 5. A video camera, a high-speed video camera, a video camera with observation, a photocell, a photocell array or a laser sensor can be used for this purpose. In the case of pressure rollers 6, 7 adjacent to the respective embossing roller 4, 5, the accumulation signal of the layers V1 or V2 can be generated with an air piston, detecting the pressure peaks on the piston. In other words, the accumulation of the layers V1 or V2 around the embossing roller 4, 5 increases the pressure exerted by the pressure rollers 6, 7 and by the embossing rollers 4, 5. When the sensors for detecting the breakage of the paper generate an accumulation signal to the control unit 25 to which they are connected, this control unit 25 immediately controls the movement of the frame 27 away from the embossing rollers 4, 5 to prevent damage to the embossing rollers and to the induction device, and puts the machine in emergency mode.

[0056] In a particularly advantageous embodiment, more than one induction device can be used for each embossing cylinder, in order to obtain a surface temperature as uniform as possible. In this case, the induction devices can be powered by the same inverter, or each induction device can be powered by a respective inverter controlled by the central control unit 25 according to the temperature of the outer surface of the embossing roller 4, 5 detected by one or more temperature sensors.

[0057] The induction device 19 can be cooled with known devices. For example, a coolant can be made to flow inside the induction device 19, in which case the induction device 19 can be made of copper tubes or another electrically conductive material.

[0058] In an operating step, the electrically conductive material coil 26 is supplied with alternating current I1, I2 and placed in an operating area at a distance d from the outer surface of the embossing rollers 4, 5. This generates a magnetic field B that penetrates the outermost part of the embossing rollers 4, 5, inducing eddy currents I p As previously mentioned, the eddy currents I p The embossing rollers 4, 5 are heated by the Joule effect. The distance d can be variable to adjust the gap and optimize the magnetic flux and can be between 1 mm and 8 mm.

[0059] In some cases, more than one temperature sensor associated with a single embossing cylinder can be used, and even more generally, more than one different type of temperature sensor can be used for each embossing cylinder, for example, one or more thermocouples, pyrometers and / or thermal cameras. Typically, the sensors are positioned outside the embossing rollers 4, 5, but in some cases, these sensors can be inserted inside the cylinder. For example, several thermocouples can be positioned inside the embossing rollers 4, 5 at different depths to monitor the temperature of the rollers along the radial direction, i.e. the direction inside the rollers.

[0060] The thermal camera can be preferably used with respect to the other sensors, since it is able to provide a more complete overview of the temperature distribution on the surface of the embossing rollers 4, 5. For example, with respect to the bottom surface of the embossing rollers, the embossing protrusions can be at a higher temperature, and vice versa, so the frequency of the electromagnetic induction current I1, I2 supplied to the induction devices 19, 20 by the inverters 23, 24 must be changed and, in general, must be properly controlled. The eddy currents induced on the outer surface of the embossing rollers 4, 5 generated by the time-varying magnetic field have a penetration depth inside the rollers that is a function of the magnetization frequency of the induction devices 19, 20.

[0061] In fact, it is known that the induced eddy current is calculated according to the following formula:

[0062] I P (x) = I0·e -δ / x

[0063] where:

[0064] I P (x) is the density modulus of the induced eddy current, which is a function of the penetration depth

[0065] I0is the current density modulus at x = 0

[0066] is the penetration thickness,

[0067] where:

[0068] f is the frequency of the magnetizing current.

[0069] μ0 is the relative permeability of the material.

[0070] σ is the resistivity of the material.

[0071] In an advantageous embodiment, the temperature distribution on the outer surfaces of the embossing rollers 4, 5 can be detected, thereby highlighting any temperature differences between the embossing protrusions 4P, 5P and the bottom surfaces 4F, 5F, as well as any temperature anomalies between the outer surfaces of the rollers and the innermost portions of the embossing rollers 4, 5. In this case, the central control unit 25 can control the inverters 23, 24 to modify the frequency and / or intensity of the electromagnetically induced currents I1, I2, and to obtain an optimal temperature distribution, i.e., where only the outer surfaces of the embossing rollers are at the desired temperature distribution. Advantageously, the operating frequency range can be between 500Hz and 100kHz, preferably between 1kHz and 100kHz, even more preferably between 5kHz and 100kHz, and even more preferably between 10kHz and 60kHz, i.e., where the induced eddy currents I1, I2, and I2 are within the range of 500Hz to 100kHz, preferably between 1kHz and 100kHz, and even more preferably between 5kHz and 100kHz, and even more preferably between 10kHz and 60kHz, i.e., where the induced eddy currents I1, I2, and I2 are within the range of 10kHz to 60kHz. s The frequency is mainly limited to the embossed protrusions 4P and 5P.

[0072] like Figure 5A As shown, by supplying electromagnetic induction currents I1 and I2 with an operating frequency of approximately 1000 Hz to the sensing device 19, a power density distribution primarily along the outer surface SE of one of the embossing protrusions 4P and 5P can be obtained. In other words, the thickness S of the embossing rollers 4 and 5, measured from the outer surface SE, contains at least three-quarters of the minimum power density value equal to the maximum power density value. The thickness S can vary between one-tenth of a millimeter and five-tenths of a millimeter. Figure 5A In this case, the thickness is equal to 0.4 mm, and it contains a minimum power density of approximately three-fifths of the maximum power density value.

[0073] Figure 5B An example is shown of supplying electromagnetic induced currents I1 and I2 with an operating frequency of approximately 10,000 Hz to the sensing device 19. In this case, the eddy currents, and therefore the power density distribution, mainly follow the outer surface SE and thus its contour. In this case, within a thickness S of approximately 0.1 mm, the minimum power density is equal to one-third of the maximum power density value.

[0074] In other words, using frequencies, for example, above 500 Hz, more preferably above 5 kHz, at least 50% or more of the current density is limited within a thickness of 0.5 mm. By increasing the frequency, 60% or even 70% or more of the current density can be limited within a thickness of 0.4 mm or less.

[0075] The two examples shown concern the induced eddy currents I s Examples of how they must preferably circulate in the vicinity of the outer surface SE of the embossing rollers 4, 5. In other words, they must be mostly confined within a limited thickness S of the outermost portion of the roller embossing device 4, 5. Advantageously, the distribution of the power density makes it possible to take into account the induced eddy currents I mainly on the embossing projections 4P, 5P and on the bottom surface, i.e. the outer surface of the roller separating each embossing projection 4P, 5P s .

[0076] In other embodiments, which can also depend on the embossing pattern, i.e. the size, shape and distribution of the embossing projections 4P, 5P, the embossing-laminating device 1 can be adjusted to keep the embossing projections 4P, 5P at a higher temperature with respect to the bottom surface 4F, 5F. Advantageously, the control unit 25 controls the inverters 23, 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 surface of the embossing rollers 4, 5.

[0077] The embossing device can comprise a cooling system 30 (for example shown in Figure 1 ) for the embossing rollers 4, 5 associated with the induction device 19, 20. This cooling system 30 is configured to cool the heated embossing rollers during machine stoppage in the event that the operator needs to work in the vicinity of the hot embossing rollers. Access to the machine is allowed only under safety conditions: all the rollers must be stopped, any brakes must be activated, and in the case of hot rollers, these hot rollers must not exceed a given temperature.

[0078] The cooling system 30 can comprise means for discharging cooling air towards the embossing roller to be cooled, said means comprising for example air-knife type cooling means, i.e. a distributor with nozzles with elongated slots discharging an air flow with an elongated, i.e. linear, discharge front preferably at least equal to the axial length of the embossing roller to be cooled, or vortex tube type cooling means, also known as "Ranque-Hilsch vortex tube".

[0079] Differently, when the embossing device has to be stopped for production needs, and not for malfunction, breakdown, maintenance or other reasons requiring the operator to operate in the proximity of the embossing rolls, it is necessary to prevent the heating of the embossing rolls from decreasing, and therefore to keep the induction devices operating to heat the roll(s). If the embossing device is completely stopped, only the part of it facing the induction devices will be heated, with a clearly uneven expansion and unacceptable local overheating. Once the embossing device resumes operation, this uneven heating defect will cause unbalance and vibrations of the rolls, with consequent poor embossing quality on the paper and the risk of breakdowns or reduced production rates, since the line has to be run at a lower speed until the rolls are again heated evenly. Therefore, during a stop requiring the embossing device to be restarted immediately, the embossing roll (or the two embossing rolls) must be kept uniformly heated at the desired temperature. To this end, it is necessary to first reduce the power of the supply current of the induction devices (or of the induction devices), since in the case of a stop of the line the heat is no longer dissipated by the absorption of the paper. Secondly, the embossing roll (or the embossing rolls) must continue to rotate so that the induction devices can continue to keep the roll uniformly heated. In order to keep the embossing roll rotating without breaking the paper, it is necessary to move the corresponding pressure roll away by a suitable amount, and if necessary to slightly relax the tension of the paper around the pressure roll and the embossing roll. In this way, the embossing roll can rotate at a very low speed, while the paper continues to wind around it. The friction between the paper and the roll is very low and does not create problems or breaks of the ply. In fact, by this process it is possible to make the ply rub on the outer surface of the embossing roll without breaking. Naturally, in the case of more than one embossing roll and pressure roll, as in the example shown in the attached figures, the logic applies to all the rolls.

[0080] In summary, in the case of a stop of the embossing device: 1) the pressure rolls (pressing rolls and optionally laminating rolls) are moved away from the embossing rolls so as to release the paper from the embossing rolls and reduce the tension / tension of the paper, 2) the embossing rolls heated by induction are kept rotating at low speed, 3) the induction devices are powered so as to keep the temperature approximately constant and equal to the operating temperature, or slightly lower (for example 3 / 4 of the operating temperature), or in any case within a given temperature range around the operating temperature, said operating temperature being the embossing process temperature (settable depending on the type of embossing process). For example, given H as the value of the operating temperature, the range is between the temperature value equal to H + 1 / 4 x H and the temperature value equal to H - 1 / 4 x H.

[0081] The low speed rotation of the embossing roll can refer to a speed lower than a value equal to one tenth of the operating speed of the roll during the embossing step, more preferably lower than a value equal to one twentieth of the operating speed, even more preferably a tangential speed of the embossing roll between 1 m / min and 10 m / min.

[0082] Similarly, when the heated embossing roller needs to be cooled: 1) the pressure rollers (pressing and optionally laminating) are moved away from the embossing roller so as to release the paper from the embossing roller and reduce the tension / tension of the paper, 2) the embossing roller is kept rotating at low speed, 3) the induction device is switched off. In this way, the low speed rotation of the embossing roller allows its entire outer surface to be gradually and repeatedly in contact with the cooling system 30 so as to reduce the cooling time and obtain a uniform cooling on the entire surface of the roller.

[0083] Therefore, the embossing device comprises machine stopping means which allow the embossing roller and the pressure roller and / or the laminating roller to be moved away from each other and allow the embossing roller to rotate at low speed. These means are of known type and are not described in detail again and can for example comprise relative movement mechanisms or devices of the axes of the embossing roller and of the pressure roller and / or laminating device so that there is no pressure or there is a limited pressure between the rollers. The cooling device of the embossing roller can be associated with these means and with the procedures for operating the induction device facing the embossing roller rotating at low speed.

[0084] Similarly, when one or more embossing rollers need to be heated from room temperature to operating temperature: 1) the embossing roller is rotated at low speed, 2) the induction device is powered. In this step, the paper layer can or can not be wound around the embossing roller. If the paper is wound around the embossing roller, the pressure roller is preferably kept disconnected, i.e. not in contact with the embossing roller being heated.

[0085] The above-described embodiments refer to an embossing-laminating device which has been taken as a non-limiting example of the present invention. In fact, the person skilled in the art knows that there are many different types of embossing-laminating devices which can differ in the number of embossing rollers, their arrangement and naturally in the type of treatment they perform on the paper layer, without departing from the principles, concepts and teachings of the present invention. For example, the present invention can also be applied to embossing devices comprising only one embossing roller and therefore not requiring laminating means.

[0086] The embodiments described above and illustrated in the drawings have been discussed in detail as examples of embodiments of the present application. 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 application as defined in the appended claims. Therefore, it is intended that the scope of the application be determined by the broadest interpretation of the appended claims (including modifications, variations, additions and omissions as therein included) and that the specification be construed as merely a exemplification of the preferred embodiments. The term "comprising" and its derivatives do not exclude the presence of elements or steps other than those listed in a given claim. The term "a" or "an" preceding an element, device or feature does not exclude the presence of a plurality of such elements, devices or features. When the apparatus claim recites "a," "an," or "the" article followed by "device," "member," "means" or "structure," such "a," "an" or "the" article is used in the sense that it refers to one or more than one of the referenced item. When the device claim recites a plurality of "means," one or more of those "means" can be implemented by one or more corresponding components, members or structures. The use of the terms "first," "second" and other such terms does not imply any particular order, but they are used for purposes of nomenclature. The use of the term "or" in the claims is used to mean "and / or" unless explicitly indicated to refer to an exclusive "or". Any reference signs in the claims should not be construed as limiting the scope of the claims.

Claims

1. An embossing device, comprising: - First path for the first layer of web material; - A first pressure roller along the first path, the first pressure roller working in conjunction with a first embossing roller, wherein the first layer of web material is wound around the first embossing roller, the first embossing roller and the first pressure roller defining a first embossing roller gap for the first layer of web material, the first embossing roller including embossing protrusions; - At least a first electromagnetic induction device, the at least first electromagnetic induction device being externally associated with the first embossing roller to heat the surface of the first embossing roller; wherein the first electromagnetic induction device is connected to a first generator device to supply an electromagnetic induction current to the first electromagnetic induction device, the electromagnetic induction current being adapted to generate an electromagnetic flux directed toward the first embossing roller, and wherein the operating frequency of the electromagnetic induction current causes eddy currents to be generated on the first embossing roller so as to follow primarily the contour of the outer surface of the first embossing roller. - A machine stop device configured to move the pressure roller away from the first embossing roller while maintaining the first embossing roller at a low speed, thereby causing the first layer of web material to rub against the outer surface of the first embossing roller without breaking, wherein the first layer of web material continues to wrap around the first embossing roller.

2. The embossing device according to claim 1, characterized in that, The operating frequency of the electromagnetic induced current is in the range of 500 Hz to 100 kHz.

3. The embossing device according to claim 1, characterized in that, The operating frequency of the electromagnetic induced current is in the range of 1 kHz to 100 kHz.

4. The embossing device according to claim 1, characterized in that, The operating frequency of the electromagnetic induced current is in the range of 5 kHz to 100 kHz.

5. The embossing device according to claim 1, characterized in that, The operating frequency of the electromagnetic induced current is in the range of 10 kHz to 60 kHz.

6. The embossing device according to claim 1, characterized in that, The electromagnetic induction device includes an electromagnetic flux concentrator.

7. The embossing device according to claim 1, comprising: - At least a first temperature sensor, the at least first temperature sensor being adapted to detect the temperature of the first embossing roller associated with the at least first electromagnetic induction device; -A central control unit that is communicatively connected to the first temperature sensor.

8. The embossing device according to claim 7, characterized in that, The central control unit controls the generator based on the temperature detected by the first temperature sensor, thereby changing the operating frequency and / or intensity of the electromagnetic induction current.

9. The embossing apparatus of claim 1, comprising a second path for a second layer of web material, a second pressure roller along the second path, the second pressure roller cooperating with a second embossing roller, the second embossing roller and the second pressure roller defining a second embossing roller gap for the second layer of web material.

10. The embossing apparatus according to claim 9, comprising at least one connecting device for the first layer web material and the second layer web material, the connecting device working together with the first embossing roller or the second embossing roller, the connecting device and the first embossing roller or the second embossing roller defining a lamination roller gap, the connecting device being a single roller or a series of coaxial rollers.

11. The embossing device according to claim 9, characterized in that, The first electromagnetic induction device and the second electromagnetic induction device are respectively associated with the first embossing roller and / or the second embossing roller.

12. The embossing device according to claim 11, characterized in that, A first temperature sensor and a second temperature sensor are associated with the first embossing roller and the second embossing roller, and the first temperature sensor and the second temperature sensor are adapted to detect the temperature of the first embossing roller and the second embossing roller associated with the first electromagnetic induction device and the second electromagnetic induction device.

13. The embossing device according to claim 12, characterized in that, The first temperature sensor and the second temperature sensor are communicatively connected to the central control unit.

14. The embossing device according to claim 12, characterized in that, The temperature detected by the first temperature sensor and / or the second temperature sensor is the temperature of the outer surface of the first embossing roller and / or the second embossing roller.

15. The embossing apparatus of claim 10, further comprising a functional fluid distributor that interacts with the first embossing roller to distribute fluid onto at least some of the protrusions of the first embossing roller over which the first layer of web material travels.

16. The embossing device according to claim 15, characterized in that, The fluid may optionally be glue, water, steam, or a combination thereof.

17. The embossing device according to claim 10, characterized in that, The at least first electromagnetic induction device is positioned between the first embossing roller gap and the lamination roller gap.

18. The embossing device according to claim 15, characterized in that, The first electromagnetic induction device is positioned between the first embossing roller gap and the functional fluid distributor.

19. The embossing device according to claim 15, characterized in that, The electromagnetic induction device is positioned between the functional fluid distributor and the lamination roller gap.

20. The embossing device according to claim 9, characterized in that, The first electromagnetic induction device is associated with a motion device to move from an operating area close to and next to the first embossing roller to a non-operating area at a certain distance from the first embossing roller.

21. The embossing device according to claim 20, characterized in that, The operating area is equal to a distance between 1 mm and 10 mm.

22. The embossing device according to claim 21, characterized in that, The operating area is equal to a distance between 2 mm and 6 mm.

23. The embossing device according to claim 9, characterized in that, The electromagnetic induction device is longitudinally adjacent to the first embossing roller and has a length equal to the axial length of the first embossing roller and / or the second embossing roller.

24. The embossing apparatus of claim 20, comprising at least one sensor for detecting breakage of the first or second web material, the at least one sensor being communicatively connected to a central control unit.

25. The embossing device according to claim 24, characterized in that, If the sensor detects a breakage in the first or second layer of web material, the central control unit controls the electromagnetic induction device to open from the operating area to the non-operating area.

26. The embossing apparatus of claim 24, comprising a cooling system for cooling at least one of the first embossing roller and the second embossing roller associated with at least one heating system, the cooling system being adapted to operate during machine stops to cool at least one of the first embossing roller and the second embossing roller.

27. The embossing device according to claim 26, characterized in that, The cooling system includes at least one discharge device for discharging cooling air toward at least one of the first embossing roller and the second embossing roller to be cooled.

28. The embossing device according to claim 10, characterized in that, The machine stopping device is configured to move the connecting device away from the first embossing roller while maintaining the first embossing roller rotating at a low speed.

29. The embossing device according to claim 28, characterized in that, The machine stopping device: When the first embossing roller needs to be kept heated, the sensing device facing the first embossing roller is kept operating at a certain sensing power during the low-speed rotation of the first embossing roller, so as to keep the temperature of the first embossing roller within a range close to the given embossing operation temperature. - When the first embossing roller needs to be cooled, the first embossing roller is cooled by the cooling system of the embossing apparatus according to claim 26, the cooling system being adapted to function at least during the low-speed rotation of the first embossing roller.

30. The embossing device according to claim 29, characterized in that, In the initial heating step where it is necessary to heat the first embossing roller from a temperature below the operating temperature to the operating temperature, the machine stop device: - Keep the first embossing roller rotating at a low speed, wherein the pressure roller moves away from the first embossing roller. - The sensing device facing the first embossing roller is operated during the low-speed rotation of the first embossing roller to heat the first embossing roller from a temperature state below the operating temperature state to the operating temperature state.

31. The embossing device according to claim 30, characterized in that, The connecting device also moves away from the first embossing roller while maintaining the first embossing roller rotating at a low speed.

32. A method for electromagnetically heating an embossing roller in an embossing device, comprising the following steps: -Providing a first path for a first layer of web material, wherein a first pressure roller acting in conjunction with a first embossing roller defines a first embossing roller gap for the first layer of web material, the first embossing roller including embossing protrusions, the first layer of web material being wound around the first embossing roller; - Provide an electromagnetic induction device to generate an electromagnetic flux that varies with time toward the outer surface of the first embossing roller, thereby inducing eddy currents on the first embossing roller, the eddy currents generating heat through the Joule effect; - Electromagnetic induction current generator; The electromagnetic flux is generated at an operating frequency to generate eddy currents on the first embossing roller, the eddy currents mainly following the contour of the outer surface of the first embossing roller. The method further includes a machine stopping step, which comprises the following steps: -Move the first pressure roller away from the first embossing roller. - Keep the first embossing roller, which is induction heated, rotating at a low speed, so that the first layer of web material rubs against the outer surface of the first embossing roller without breaking, wherein the first layer of web material continues to wrap around the first embossing roller.

33. The method according to claim 32, characterized in that, The operating frequency of the electromagnetic induction current is in the range of 500 Hz to 100 kHz.

34. The method according to claim 33, characterized in that, The operating frequency of the electromagnetic induced current is in the range of 1 kHz to 100 kHz.

35. The method according to claim 34, characterized in that, The operating frequency of the electromagnetic induction current is in the range of 5 kHz to 100 kHz.

36. The method according to claim 35, characterized in that, The operating frequency of the electromagnetic induced current is in the range of 10 kHz to 60 kHz.

37. The method according to claim 32, characterized in that, The electromagnetic induction device includes an electromagnetic flux concentrator.

38. The method of claim 33, further comprising at least one temperature sensor for detecting the external temperature of the first embossing roller, the at least one temperature sensor being communicatively connected to a central control unit.

39. The method according to claim 38, characterized in that, The electromagnetic flux is controlled based on the temperature detected by the temperature sensor on the outer surface of the first embossing roller.

40. The method according to claim 38, characterized in that, The central control unit controls the electromagnetic induction current generator to change the frequency and / or intensity of the electromagnetic induction current, which is supplied to the electromagnetic induction device by the electromagnetic induction current generator.

41. The method according to claim 32, characterized in that, When at least a first sensor adapted to detect the breakage of the first layer web material notifies the first central control unit of the breakage of the first layer web material, the first central control unit controls the movement of the electromagnetic induction device from a first operating area next to the first embossing roller toward a non-operating area away from the first embossing roller.

42. The method according to claim 41, characterized in that, The at least first sensor is a photovoltaic cell or photovoltaic cell array or laser sensor or camera or high-speed camera or vision system.

43. The method according to claim 38, characterized in that, The at least one temperature sensor detects the temperature of the protrusions of the first embossing roller and the temperature of the bottom surface of the first embossing roller, and wherein the central control unit controls the electromagnetic induction current generator based on the temperature difference between the protrusions and the bottom surface.

44. The method of claim 43, optionally comprising the following steps: - Power the electromagnetic induction device to maintain the temperature of the first embossing roller within a range near the given embossing operating temperature. - Turn off the electromagnetic induction device and cool the first embossing roller through the cooling system.

45. The method according to claim 44, characterized in that, The cooling system includes at least one device for discharging cooling air toward at least one of the first embossing rollers to be cooled.

46. ​​The method of claim 32, further comprising an initial heating step of heating the first embossing roller from a temperature state below the operating temperature to the operating temperature state, the initial heating step comprising the following steps: - Keep the first embossing roller rotating at a low speed. - Power the electromagnetic induction device to heat the first embossing roller.

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