Method and embosser with temperature controlled pressure roller

Abstract

A method for producing an embossed cellulosic web includes the steps of: (a) directly heating the outside surface of a pressure roller, and (b) embossing the web between an embossing roller and the pressure roller. Additional web(s), some or all of which may be embossed, may be combined with the embossed web to produce a product. The interior of the pressure roller may be cooled to produce a temperature gradient between the exterior and the interior of the pressure roller.

Description

[0001] METHOD AND EMBOSSER WITH TEMPERATURE CONTROLLED PRESSURE ROLLER

[0002] RELATED APPLICATION DATA

[0003] This application claims priority benefit to US provisional app. ser. no. 63 / 611265, filed December 18, 2023, the disclosure of which is incorporated by reference herein. BACKGROUND

[0004] In the production of cellulosic ply products, such as bathroom tissue rolls, kitchen towel rolls, paper handkerchiefs, napkins, and similar items, it is frequent to process a ply of web material by means of embossing - meaning passing the ply through an embossing nip station formed by a pair of embossing rollers or by a pair comprised of an embossing roller and a pressure roller covered with rubber. A roller with a metallic (typically steel) core which is covered with rubber may be referred to generally as a non-metallic pressure roller. The embossing roller, typically steel, has a pattern of protuberances that deform the elastic cover of the pressure roller. The embossing roller is typically engraved to form the protuberances. The pressure exerted between the embossing roller and the pressure roller causes permanent deformation of the cellulosic material ply which passes through the embossing nip formed between the embossing roller and the pressure roller, forming embossments in the ply. Two or more plies of web, at least one, some, or all of which are embossed in one or more embossing stations, may be brought together to form a multi-ply web material. The web material may be wound to form rolls of bathroom tissue or kitchen towels, or it can be cut and folded to form handkerchiefs, napkins, or similar. Each ply may in turn consist of one or more layers of cellulose or other material.

[0005] The embossing pattern is for decorative and functional purposes. From a functional point of view, embossing serves to create limited areas to which water or adhesive is applied to bond multiple plies that form the web material to one another. Embossing is also used to increase the overall thickness of the web material for maximum web bulk (unit volume per unit mass), increase its softness and absorption capabilities, and for other functions known in the field.

[0006] An embossing-laminating device is generally defined as a device that performs an embossing process on at least one ply and bonds two or more plies together by lamination, possibly using a binding agent such as water or an adhesive applied to at least one of the plies, preferably with the binding agent applied to the protruding surfaces of at least some of the embossing protuberances formed on one or more plies. US 3556907 discloses an embossing-laminating device which is in many ways still representative of the current state of the art. US 5294475 discloses tangential passage of each ply between its respective embossing roller and pressure roller (neither the embossing roller nor the pressure roller are wrapped by any web, and only contact the web at the embossing nip). US 7584698 discloses an embossing-laminating device representative of the current state of the art, with an improvement over the device shown in US 3556907 being the open adhesive fountain and the transfer rollers are replaced by an adhesive distributing assembly comprising an enclosed adhesive chamber, a gravure roller, and an applicator roller.

[0007] The heated embossing technique, i.e. embossing by heating the embossing roller and the ply of web material driven around it, has been well known for a long time, with various theories proposed to explain its benefits. Moisture-enhanced embossing, i.e. adding moisture to the web in the form of water or steam, has been well known for at least as long as heated embossing. The positive impacts of heat and moisture manifest themselves in various ways. It is known that, for some grades of paper, it is advantageous to run parent rolls as soon as possible after they were produced. It is also known that, for some grades of paper, it is advantageous to run parent rolls in the order in which they were produced. Further, it is known that, for some grades of paper, it is advantageous to locate the converting line in a climate-controlled environment.

[0008] The prior art proposes various theories to explain the benefits of heated embossing and moisture-enhanced embossing.

[0009] US 1946838 discloses "paper to be embossed is advantageously moist in order better to take the embossing."

[0010] US 2890540 discloses "it has been discovered if the paper to be embossed is exceptionally dry that no amount of heat or pressure could satisfactorily impress the pattern of the present invention on the paper web. Moreover, if the paper is too damp, the pattern, though impressed into the surface will soon be lost because the paper will straighten out after it has passed through the embossing rolls and reflectance contrast will be slight." US 4994144 discloses "it has now been discovered that the bulk of creped tissue webs can be increased simply by steaming the creped web while under tension. Steaming can be utilized to increase bulk with or without embossing."

[0011] US 5294475 discloses "generally as caliper increases due to greater embossing, the tensile strength of the cellulosic fibrous structure 20 decreases. This phenomenon can be mitigated, however, by heating the pattern rolls 28, as is well known in the art."

[0012] US 6913673 discloses "the heat and pressure applied to the sheet at the heated embossing nip 60 are sufficient to cause the fibers within the web to begin to plasticize. Particularly at those areas under the highest pressure, where the pattern elements are located on the pattern roller 62, also referred to as fiber bonding areas, the web fibers can become softer and begin to deform around one another. As the base sheet cools after it exits the heated embossing nip 60, the fibers in the fiber bonding areas can bond and become fused together resulting in a well-defined embossment at the fiber bonding areas of the sheet. Additionally, not only is the embossment well defined at production, retention of the embossing pattern is also increased due to the inter-fiber bonding and fusion. Though unknown, it is believed by the inventors that the lignins within the pulp are particularly affected by the heat and pressure within the heated embossing nip 60. It is believed that the pulp lignins begin to melt or glassinate and take on a more amorphous, glassy condition during the process. The heated embossing process can therefore provide an improved, glassine appearance to the final paper product."

[0013] US 8158047 discloses "it has been found that the combination of the application of water in the form of steam and the use of a heated engraved roller provides an advantageous impressed pattern upon the multi-ply sheet 100 shown in FIG. 50."

[0014] US 8858213 discloses "it is believed that the application of steam to a cellulose web material causes an increase in both the moisture content and effective temperature of the treated web material. This causes the cellulose web material to move from the region indicated on the graph as elastic (i.e., where the fiber tends to exhibit behavior typical elastic-like behavior) to the region where the cellulose substrate is capable of plastic deformation."

[0015] US 11090900 discloses "it is believe[d] that the moisture added to the fibrous structure ply 82 prior to embossing results in the modulus of the fibrous structure ply 82 and / or the filaments of the fibrous structure ply 82 to be decreased. The decreased modulus of the fibrous structure ply 82 and / or filaments thereof, increase the flexibility of the fibrous structure ply 82 and / or filaments thereof thus making the fibrous structure ply 82 and / or filaments thereof more easily deformable during the embossing operation" and "the heated emboss roll 98 may function to drive off the moisture present in the multi-ply fibrous structure 86 when it enters the embossing nip and results in the modulus of the multi-ply fibrous structure 86 and / or filaments thereof increasing."

[0016] US 11628645 discloses "in particular, the wet paper ply that has just been embossed remains in contact with the heating element, such as the micro-embossing cylinder itself, for a sufficiently long time to allow the drying of the ply itself, but without reducing the processing speed of the paper. In fact, the time during which the wet paper ply remains in contact with the heating element depends on the size of the wrapping of paper around the micro-embossing cylinder that is heated. The greater the extension of such wrapping, the greater the processing speed that can be ensured while maintaining the efficiency of the drying process of the wet paper ply just embossed."

[0017] US 20240116286A1 discloses applying known methods of internally heating steel embossing rollers to heat the pressure rollers internally.

[0018] A common thread in the aforementioned prior art is that, when a roller is heated, it is heated internally, and the roller that is heated is typically the steel engraved embossing roller. Steel embossing rollers have been heated with hot oil, hot water, electrical resistance, radiant heat, internal electromagnetic induction, and external electromagnetic induction. A drawback of the prior art heated steel embossing rollers is operator safety, given the high temperatures of heated embossing rollers. Another drawback of the prior art heated steel embossing rollers can include production time if operators need to wait for embossing rollers to cool down before accessing the machine, and / or wait for the embossing rollers to heat up before starting production, and / or wait for embossing rollers to cool down before exchanging an embossing roller for an embossing roller with a different embossing pattern engraved in it. A further drawback of the prior art heated steel embossing rollers relates to applications where glue is applied to the web that is heated, as the heated steel embossing rollers may adversely heat the adhesive and / or create thermal dimensional variances that change the gap between the applicator roller and the embossing roller. Another drawback of the prior art heated steel embossing rollers is high energy consumption to heat the embossing roller and cool the space or room in which the heated embossing roller resides. Still a further drawback of the prior art heated steel embossing rollers can include cost, especially in cases where the embossing rollers are internally heated. Yet another drawback of the prior art heated steel embossing rollers is the difficulty and the safety hazards involved with changing the heated steel embossing rollers for a different embossing pattern. For internally heated embossing rollers, the heating system needs to be disconnected and reconnected in order to change embossing rollers. For externally heated embossing rollers, the heating system may need to be moved out of the way in order to change the embossing rollers. Still yet another drawback of the prior art heated steel embossing rollers can include adverse effects to pattern phasing, when two embossing rollers are provided with patterns in registration with one another, and one or both of the rollers are heated. Additionally, a drawback of the prior art heated steel embossing rollers is the need to mitigate adverse effects of the heat on the pressure roller covers when the machine is stopped, and the web and convection are no longer removing heat from the pressure rollers. And yet another drawback of the prior art heated steel embossing rollers is the need to provide actively cooled bearings for the heated embossing rollers.

[0019] Temperature control of the surface of the pressure roller and direct heating of the outside surface of the pressure roller is not shown in the aforementioned patent references. The aforementioned US 6913673 teaches away from heating the backing roll (i.e. the pressure roller) when it is a rubber coated backing roll: "in an alternative embodiment wherein the backing roll is not a rubber coated backing roll, backing roll 64 can be heated rather than the pattern roll 62. In another possible embodiment wherein the backing roll is not a rubber coated backing roll, both pattern roll 62 and backing roll 64 could be heated to the same or different temperatures simultaneously or alternatively." WO2023280722A1 defines functional rollers as pressure rollers, marrying rollers, cliche rollers or other rollers that apply a product to the web, but are not directly heated by their own heating device.

[0020] Applicant's standard design for many models of embossers and embosserlaminators dating back more than twenty-five years is to provide pressure rollers with means for cooling (possibly to compensate for heated embossing rollers) by drilling and tapping the pressure roller's journals. On a few occasions over that more than twenty- five year time period, applicant has also provided temperature control units comprising chillers to cool the pressure rollers of such embossers by circulating cooling water through the interior of the pressure rollers. However, heretofore, applicant has not directly heated a non-metallic pressure roller and controlled its temperature to enhance the embossing process. Rather, applicant has used conventional techniques of heating a steel embossing roller to control the embossing process and experienced one or more of the drawbacks discussed above. These drawbacks of the prior art are addressed in the description that follows below.

[0021] DESCRIPTION OF THE DRAWINGS

[0022] Fig. 1 shows an exemplary processing line with a two-station non-metallic roller to steel roller embosser.

[0023] Fig. 2 shows an exemplary processing line with a one-station non-metallic roller to steel roller embosser.

[0024] Fig. 3 is a side view of an example embosser-laminator.

[0025] Figures 4A-4D are schematics of example configurations and web paths for embosser-laminators for various paper grades and product types.

[0026] Fig. 5 is an isometric view of temperature sensors to detect the surface temperature of a pressure roller.

[0027] Fig. 6 is a side view of an example embosser-laminator (for instance, the embosser-laminator of Fig. 3) with heaters to heat the surfaces of the pressure rollers.

[0028] Fig. 7A and 7B are isometric views of a temperature control unit and system to cool the interior of a pressure roller.

[0029] Fig. 8 is an isometric view of a pressure roller loading system for an embosser or an embosser laminator.

[0030] Fig. 9 is a detail view of an actuator system for the pressure roller loading system of Fig. 8.

[0031] Fig. 10 is a cross sectional view of an actuator for the pressure roller loading system of Fig. 8.

[0032] Fig. 11 is a side view of the pressure roller loading system of Fig. 8. DETAILED DESCRIPTION

[0033] Figs. 1 and 2 show processing lines 10,12 with embossing machines 14,16 for embossing a cellulosic web material. The embossing machines 14,16 may comprise one or more embossing stations comprising an embossing roller and a pressure roller. Fig. 1 shows an example of an embossing machine 14 with two stations 18 each comprising a non-metallic pressure roller 20 and a steel embossing roller 22, and Fig. 2 shows an example of an embossing machine 16 with one station 24 comprising a non-metallic pressure roller 26 and a steel embossing roller 28. Fig. 3 shows a further embodiment of a embossing machine 30 with two stations 32 each comprising a non-metallic pressure roller 34 and a steel embossing roller 36. In Fig. 3, the embossing machine 30 comprises an embossing-laminating machine. In addition to the two embossing stations 32 comprising a steel embossing roller 36 and a non-metallic pressure roller 34, the machine has other components such as a marrying roller 38, and web handling elements such as a spreading roller 40, driven roller 42, and a load cell roller 44. One or more webs (plies) 46 of cellulosic product may be embossed in each embossing station 32, resulting in embossments in the web. A binding agent, for instance, water or an adhesive, may be applied to the tops of the embossments of the web(s) 46 directed through one of the embossing stations 32 prior to combining the webs. An applicator 48 may apply the binding agent to the web(s) directed through the top embossing station as shown in Fig. 3; alternatively, the applicator may apply the binding agent to the web(s) directed through the bottom embossing station. The adhesive may include a heat-activated component. Pressure may be applied to the combined web, for example, with the marrying roller 38.

[0034] Figs. 4A-4D show example configurations and paths for a web 46 for embosserlaminators for various paper grades and product types. Accordingly, the configurations and web paths in Figs. 4A-4D may be combined with one another to arrive at other configurations and web paths. Fig. 4A is an embosser-laminator 50 with two stations 52 having a non-metallic pressure roller 54 and steel embossing roller 56. Fig. 4B is similar to Fig. 4A, with the addition of the web handling elements 40,42,44 that are configured to provide no web wrap angle on the embossing roller 56 or on the pressure roller 54 - in other words, the web handling elements are configured to enable the tangential passage of each ply 46 between its respective embossing roller 56 and the pressure roller 54, with the web contacting the rollers 54,56 only at the embossing nip. Fig. 4C provides for two independent plies 46 directed to the upper embossing station. Fig. 4D shows a machine where an unembossed lower ply is laminated to an upper ply. Fig. 4B also provides for the web process of Fig. 4D via opening of the lower embossing nip (i.e., unloading the pressure roller) and operating the lower embossing roller as a driven guide roller.

[0035] When only one embossing station is provided, the outside surface of the pressure roller in that embossing station may be heated. When two embossing stations are provided, the outside surface of the pressure roller in only the upper station may be heated, the outside surface of the pressure roller in only the lower station may be heated, or outside surface of the pressure roller in both the upper station and the lower station may be heated. When an embossing station and heating means are provided, both embossing and embossing with heating may be utilized or not depending on the needs of the process. Also, in some implementations, it may be beneficial to cool the surface of one of the rollers and heat the interior of the roller, for example, the marrying roller.

[0036] In the examples of the machines in Figs. 1-3, the pressure roller 20,26,34 may comprise a cylindrical roll body with a journal at each end. The pressure roller 20,26,34 may be of conventional roller construction. The pressure roller 20,26,34 may be constructed for linear deflection, for example as described in European patent EP 2974857. The pressure roller 20,26,34 may also be provided with a cover comprising one or more non-metallic materials such as rubbers, thermoplastics, thermosets, thermoplastic elastomers, and silicones. The cover of the pressure roller 20,26,34 may be specified by material and hardness. Example pressure roller cover materials include nitrile, urethane, silicone, and Hypalon. The cover of the pressure roller 20,26,34 may be specified by a trade name for the cover from the cover supplier. Example cover suppliers include Rotadyne, Trelleborg, Clarke Roller, Valley Roller, and Hannecard. The material hardness of the pressure roller cover may have a Shore hardness of about 45 and 90 on the Shore A durometer scale (as set forth herein Shore A hardness tests conducted in accordance with ASTM D2240). The pressure roller cover material hardness may have a Shore hardness of 55 Shore A, 60 Shore A, or 65 Shore A. The pressure roller cover may comprise one material. The pressure roller cover may comprise more than one material for a dual-hardness cover, for example, a base material (inner material) with a Shore hardness of 90 Shore A and an outer material with a Shore hardness of 50 Shore A, 55 Shore A, 60 Shore A, 65 Shore A, or other hardness.

[0037] With the goal of identifying optimal conditions for maximizing bulk, the inventors undertook research to investigate the effects of varying temperatures and moisture levels on the creation and retention of bulk during the embossing process. Dry crepe bathroom tissue grades, both recycled and virgin fiber, were studied. A screening experiment showed that heat and moisture both showed significant effect on bulk generation and tensile strength. Results were consistent with moisture having a plasticizing effect on the sheet, which was expected, while heat addition showed the opposite result, which was surprising. Further study undertaken to remove the drying effects of the heat, which had a masking effect on both moisture and heat, showed that caliper, tensile force at break, and elongation at break are all positively correlated with increasing moisture content of the sheet during embossing, which aligns well with the expected effects of moisture on the paper properties; and that caliper, tensile force at break, and elongation at break are all negatively correlated with increasing temperature of the sheet during embossing, which was again surprising given the known positive impact of heated embossing rollers as stated in the prior art.

[0038] Without wishing to be bound by any theory, it is believed that by heating the surface of the pressure roller 20,26,34, the properties of the cover of the pressure roller may be advantageously altered. Without wishing to be bound by any theory, it is believed that, by heating the surface of the pressure roller 20,26,34 from outside (or exterior of) the pressure roller, the cover of the pressure roller may have a very thin heated layer with a softer durometer than the remainder of the cover material. It is believed that it may be desirable for the cover of the pressure roller to have an inner layer providing a firm backing, and a softer outer layer to form around the embossing elements without excessive strain in the cover and the ability for the strain in the cover to recover by the time a given section of the cover enters the embossing nip again upon the next full rotation of the roller. While it may be possible to achieve the aforementioned effects with a dual hardness cover of the pressure roller, there are several reasons why it may be advantageous to heat the pressure roller 20,26,34 rather than simply use a pressure roller with a dual-hardness cover. To the extent that it is beneficial for the pressure roller to have a soft outer layer that is very thin, for example, on the order of 1 mm to 2 mm, it may be difficult to manufacture a dual-hardness cover for a pressure roller with an outer layer with such a desired thickness. Heating the surface of the cover of the pressure roller has the advantage of bringing the pressure roller up to operating temperature quickly during initial startup. Further, to the extent that it is beneficial to form a gradient across a cross-section of the cover (a gradient in properties such as temperature, hardness, etc.), a pressure roller with a dual-hardness cover may have a step change in properties instead of the gradient in cover properties that may otherwise result from heating the surface of the pressure roller (and optionally, as discussed in more detail later, cooling the interior of the pressure roller).

[0039] In discussing the advantages of a pressure roller 20,26,34 with control of the interior and exterior temperature, a closed loop control of the interior temperature, the exterior temperature, or both, may be employed. A pressure roller 20,26,34 with temperature control may achieve more consistent performance, and allow for the more effective development of the temperature gradient in the non-metallic cover during operation. With control of the gradient in the non-metallic cover of the pressure roller 20,26,34, the effective embossing properties of the cover may be intentionally manipulated within the constraints of the material to achieve desired performance for varied operating conditions and product properties.

[0040] To achieve a closed loop control to form a gradient of cover properties, the internal temperature of the body of the pressure roller 20,26,34 may be controlled. One method of control may include a circulating liquid temperature control system where operating parameters of the system including but not limited to fluid specific heat capacity, fluid flow rate, and supply fluid temperature and return fluid temperature, may be used to approximate the internal temperature of the body of the pressure roller 20,26,34. It is likely advantageous to indirectly measure the internal temperature of the body of the pressure roller 20,26,34 with such a system to maintain a simple system design and eliminate the need for internal sensors and means to gather signals and supply power to those sensors. In addition or the alternative, the exterior temperature of the surface of the cover of the pressure roller 20,26,34 may be monitored. One such method of monitoring may comprise a noncontact temperature sensing device, such as the Flir AX8 Ethernet / IP thermal imaging camera, to control the output of an external heating device. An empirical or analytical model of energy balance for the system may then be used to relate the temperature differential and running parameters to the desired gradient characteristics of the cover of the pressure roller.

[0041] Fig. 5 shows an example implementation of temperature sensors 60 to detect the surface temperature of the pressure roller 34 of the embossing-laminator of Fig. 3. Similar implementations may be used for the marrying roller and other process rollers. Flir AX8 Ethernet / IP thermal imaging cameras are one example of a temperature sensor with satisfactory accuracy and granularity. In an alternative embodiment, the surface temperature (and nip forces) of the pressure roller 20,26,34 may be measured with technology embedded in the roller cover, as is common in paper machine calendars.

[0042] The surface temperatures of the pressure rollers, marrying roller, and other process rollers may be correlated with the operating processing specification windows of the materials of the rollers to prevent roller damage, for example, by reducing machine speed or by stopping the machine. It should be appreciated that the threshold temperatures indicative of overheating may vary for different roller cover specifications. It may be beneficial to apply a classification methodology to images captured by the thermal imaging camera to identify anomalous regions in the temperature gradient on the surface of the roller. Anomalous regions could indicate conditions of uneven loading, incorrect pressure, roller crown, imminent failure (such as delamination of the cover from the roll body), or areas that could result in failure or defects in the process caused by contamination of the pressure roller or embossing roller.

[0043] Data indicative of the temperature of the surface of the cover of the pressure roller 20,26,34 may be combined with other operating parameters of the embossing station to predict the general operation of the pressure roller and any onset of an overhearing condition. For instance, pressure roller cover surface temperature may be combined with a normalized value generated by motor input power multiplied by the number of roller revolutions. Data on pressure roller cover surface temperature and nip force may be collected to determine general embossing station operation and whether nip force is contributing to pressure roller cover surface temperature. Data on pressure roller cover surface temperature, nip force, and web speed may be collected to determine whether nip force and / or web speed is contributing to pressure roller cover surface temperature.

[0044] Web caliper may also be measured and combined with pressure roller cover surface temperature to determine general embossing station operation. For example, web caliper may be measured with a camera or sensor oriented parallel to the axis of a guide roller and aligned with the cylindrical face of the roller. Or, web caliper may be measured with a camera or sensor oriented perpendicular to the axis of a guide roller and aligned with a radius of the guide roller. In implementations where the signals are insufficient to generate absolute caliper data reliably, or to produce consistent results with various different types of webs, the signals may still be satisfactory for determining relative caliper transformation of a given web pre- and post-embossing. Caliper transformation may be measured by measuring the combined caliper(s) of the web(s) entering the embosser or embosser-laminator, measuring the caliper of the combined web exiting the embosser or embosser-laminator, and comparing the two values. Pressure roller temperature data may be combined with caliper transformation data and used as limiter for increases in embossing nip force, to maximize the caliper transformation versus sheet strength degradation taking in account that there are diminishing returns on increased embossing nip force. Pressure roller temperature data may be combined with caliper transformation data to compensate for the start-up of pressure roller and the time needed for the pressure roller to warm up and reach a stable and desired operating temperature.

[0045] Regression analysis may be used to predict any pressure roller temperature rise so processing speed and / or embossing nip force may be adjusted before critical levels are reached. Pressure roller cover surface temperature may also be used to detect abnormal running conditions. Data indicative of temperature and load may be tracked to develop an useful operating life for the pressure roller. Load data may be determined by monitoring operating power levels or energy input into a roller. The factor of useful operating life for the pressure roller may be developed by multiplying the power level by the number of roller revolutions. The methods may allow development of a regression model for various pressure roller and their respective covers. The methods may also allow defining a "nominal" operating shape for the pressure roller. The methods may allow prediction of the operating shape of the pressure roller, and alerts may be generated when the predictions indicate that the pressure roller is not performing optimally.

[0046] In some implementations, it may be advantageous to modulate pressure roller surface temperature with web speed. Modulating temperature is one non-limiting way to accommodate the viscoelastic properties of the pressure roller cover. For example, as the web speed increases, the strain rate of the pressure roller cover may increase, resulting in a higher effective elastic modulus. If the resulting changes vary enough across the operable speed range to affect the embossing process, the surface temperature target may be changed to compensate for the variation. Changing the target surface temperature may serve to maintain uniform embossing performance with changing web speeds. In the most basic implementation, compensating for variations in elastic modulus by changing the target surface temperature may be determined by empirical data and incorporated into a regression function including strain magnitude, strain rate as related to web speed and geometry of the nip, and a target surface modulus. In one alternative embodiment, images from an embossing quality vision system may be analyzed (by an operator or via a machine learning system) over a range of web speeds and pressure roller temperatures to determine a satisfactory curve for pressure roller surface temperature versus web speed. In the case of a dynamic, machine learning model, such a system may be configured to automatically monitor the output embossed structure of the web for a defined characteristic or "quality metric" that would allow a control for the system to adjust the surface temperature of the pressure roller to yield the most optimum result for the current operating parameters of the embossing system.

[0047] There are several aspects to consider when selecting, locating, and mounting a device to directly heat a pressure roller, particularly a device to directly heat the exterior surface of the pressure roller. Preferably, the housing of any heating device would remain touch-safe, primarily to reduce the safety hazards to which people working on the machine are exposed and to reduce the fire risk due to dust, and also to avoid any adverse effects to nearby equipment or raw materials such as paper and adhesives. Depending on the heat source, insulation may be required to keep the heating device touch-safe. While heating the surface of the pressure roller through the web is not precluded, especially since theories in the prior art suggests it is beneficial to heat some grades of web, it may be preferable to locate the heating device at a location where the heat would not have to pass through the web. It may be preferable to locate the heating device such that it moves with the pressure roller, to ensure that the pressure roller and the heating device do not interfere with one another. It may be preferable to locate the heating device such that it remains stationary, so that any cables or hoses do not need to move, and as such are less exposed to wear. It is preferable to locate the heating device such that it is not exposed to binding agent (which may drip from the applicator) or falling debris, and such that exposure to the dust that is liberated from the web in the embossing process is minimized. Space for the heating device is limited by spaces already occupied by other equipment such as dust control hoods or roller cleaning devices. If space is limited, it may be necessary to mount the heating device in the structure of another device such as a dust control hood. It is preferable to locate the heating device such that it does not interfere with the removal of any process rollers that are sometimes changed in an embosser or an embosser-laminator. If the heating device must interfere with the removal of any process rollers, it is preferable to avoid interfering with the removal of those rollers that are more frequently changed, which in some situations may include the embossing rollers.

[0048] Fig. 6 shows example locations for heat sources 62 in the embosser laminator 30 of Fig. 3. The heat source 62 may comprise an infrared heat emitter. Such an infrared heat emitter may provide a suitable heat source for directly increasing the temperature of the surface of the pressure roller 34. Infrared heat emitters are available from, for example, Baldwin Technologies, Heraeus, Weco International, and XDS. An advantage of an externally heated pressure roller versus prior art heated embossing rollers is that energy consumption may be less: for example, around 4-10 kW per roller for a heated pressure roller versus 75-150 kW per roller for a heated steel embossing roller. The surface of the pressure roller may be heated, for example, to a temperature in the range of around 25-260 degrees Celsius, depending in part on the maximum continuous operating temperature and peak operating temperature of the pressure roller cover material specified by the supplier of the cover material. In addition or the alternative, the heat source 62 may be a hot air generator with a knife jet that impinges the surface of the pressure roller. In addition or the alternative, the heat source 62 may be a thermoelectric heat pump concept (Peltier heat pump). In addition or the alternative, the heat source 62 may be a heat cartridge, for example, available from Omega Engineering. In addition or the alternative, the heat source 62 may be a flexible heater, for example, available from Omega Engineering. In addition or the alternative, the heat source 62 may be internal to the body of the pressure roller and heat the surface of the pressure roller from the interior. Such rollers are available from American Roller, Tokuden, and Converter Accessory Corporation.

[0049] It may be beneficial to cool the interior of the pressure roller to control the gradient properties of the cover during operation. In one aspect, it may be beneficial to initially control the temperature of the interior of the pressure roller by heating or cooling until the machine reaches operating temperature. It may be beneficial to cool the interior of the pressure roller, possibly to a greater extent than during operation, when the machine slows down (for example during a web splice event) or stops such that the web is removing less heat, to prevent excessive heat buildup in the pressure roller.

[0050] Figs. 7A and 7B are examples of a temperature control system 64 to cool the interior of a pressure roller 66 with a circulating fluid. The circulating fluid may be water. The circulating fluid may be maintained at a temperature in the range of around 30 to 50 degrees Celsius. The hoses / pipes connecting the temperature control system 64 to the journals of the pressure roller are not shown in Figs. 7A-7B. The temperature of the inner portion of the cover of the pressure roller 66 may be measured, or the temperature of the interior of the pressure roller 66 may be measured, or the temperature of the circulating fluid may be measured. Driving the pressure roller is another way to prevent heat buildup in the roller. An air knife may be provided to cool the pressure roller and / or the heat source.

[0051] For adjusting the embossing nip force based on pressure roller surface temperature, caliper transformation, or other variables downstream of the embosser, such as roll product diameter and roll product firmness, it may be beneficial to control the position of the pressure roller 66 with a pressure roller loading system 68 comprising a servo actuator 70. Fig. 8 is an isometric view of the pressure roller loading system 68, which may be used in connection with the embossing machines shown in Figs. 1 or 2, or an embosser laminator for instance, as shown in Figs. 3 and 6. Figs. 9 -10 provide additional views of the servo actuator 70 for the pressure roller loading system 68 of Fig. 8. The servo actuator 70 is mounted to the frame 72 of the machine with degrees of freedom in two rotational directions 74,76 to allow for misalignment of the actuator 70 and thereby extend the life of the pressure roller loading system 68.

[0052] Heating the surface of the pressure roller(s) is beneficial for some products. Heating of the pressure roller(s) in conjunction with moisture control of the web may have additional benefits for some products. For some web products, it may be beneficial to raise the moisture content of the web to have non-condensing humidity, which, especially in the case of webs that were not recently produced on a paper machine, may recondition the web to have properties closer to a more recently produced web. Moisture in the form of water, dry steam, or saturated steam may be applied to the web using known methods prior to or during embossing.

[0053] Further embodiments can be envisioned by one of ordinary skill in the art after reading this disclosure. In other embodiments, combinations or sub-combinations of the above-disclosed invention can be advantageously made. The example arrangements of components are shown for purposes of illustration and it should be understood that combinations, additions, re-arrangements, and the like are contemplated in alternative embodiments of the present invention. Thus, various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the claims and that the invention is intended to cover all modifications and equivalents within the scope of the following claims.

Claims

What is claimed is:

1. A method for producing an embossed cellulosic web comprising the steps of: a. directly heating the outside surface of a pressure roller, and b. embossing the cellulosic web between an embossing roller and the pressure roller.

2. The method of claim 1 wherein the step of directly heating the outside surface of the pressure roller comprises heating the outside surface of the pressure roller with an infrared heater.

3. The method of claim 1 wherein the step of directly heating the pressure roller comprises heating the outside surface of the pressure roller to a temperature between 25 and 260 degrees Celsius.

4. The method of claim 1, wherein a cover of the pressure roller comprises a non-metallic material having a Shore Hardness of between 45 and 90 on the Shore A durometer scale.

5. The method of claim 1 further comprising the step of cooling the interior of the pressure roller.

6. The method of claim 1, further comprising the step of combining the web with at least one further web.

7. The method of claim 6, further comprising the step of embossing the at least one further web between a further embossing roller and a further pressure roller.

8. The method of claim 7 , further comprising the step of directly heating the outside surface of the further pressure roller.

9. The method of claim 8 further comprising the step of cooling the interior of the further pressure roller.

10. The method of claim 6, further comprising the step of providing one of water and an adhesive between the web and the further web.

11. The method of claim 10 further comprising the step of applying pressure to the combined webs.

12. The method of claim 10 wherein the step of providing one of water and an adhesive between the web and the further web comprises providing an adhesive with a heat-activated component.

13. The method of claim 1 further comprising the step of applying moisture to the web, wherein the moisture comprises one of: dry steam, saturated steam, water.

14. A machine for embossing at least one cellulosic web, the machine comprising: an embossing roller and a pressure roller, the embossing roller and pressure being adapted and configured to emboss the at least one cellulosic web; at least one temperature sensor adapted and configured to detect the temperature of the surface of the pressure roller; and a heater adapted and configured to directly heat the outside surface of the first pressure roller.

15. The machine of claim 14 wherein the heater is an infrared heater.

16. The machine of claim 14 further comprising a temperature control unit adapted and configured to control the temperature of the interior of the pressure roller.

17. The machine of claim 14 further comprising means to combine the web with at least one further cellulosic web.

18. The machine of claim 17 further comprising a further embossing roller and a further pressure roller adapted and configured to emboss the at least one further cellulosic web.

19. The machine of claim 18 further comprising: at least one further temperature sensor adapted and configured to detect the temperature of the surface of the further pressure roller; and a further heater adapted and configured to heat the outside surface of the further pressure roller.

20. The machine of claim 19 further comprising a temperature control unit adapted and configured to control the temperature of at least one of the interior of the pressure roller and the interior of the further pressure roller.

21. The machine of claim 17 further comprising an applicator to apply at least one of adhesive and water to one of the web and the further web.

22. The machine of claim 21 further comprising a marrying roller adapted and configured to apply pressure to the combined webs.

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