Embossing unit with multiple pressure rollers

Abstract

 The embossing unit to emboss a web material (N) comprises at least a first embossing roller (1; 3), associated with which are at least two pressure rollers (31A 31B; 11A, 11B), which are moved alternately to an operating position in contact with the first embossing roller.

Description

Technical field

[0001] The present invention relates to machines for paper converting and more specifically to embossing units, i.e. machines, units or devices that perform embossing operations on continuous paper webs, in particular made of tissue paper.

State of the art

[0002] In tissue paper converting to produce kitchen towels, toilet paper, paper handkerchiefs and other disposable articles, paper plies from reels produced in the paper mill are processed with embossing operations aimed at imparting particular physical properties to the paper, such as softness, apparent thickness and absorption capacity. Embossing also has the function of decorating the surface of the paper product and, at least in some cases, is the operation required to join the various plies forming the final web material.

[0003] Many embossing units are provided with at least one embossing roller provided with surface protuberances or protrusions, cooperating with a counter-roller or pressure roller, which frequently is coated on the cylindrical surface thereof with an elastically yielding material, such as rubber or the like. The coating has a smooth surface and, by pressing the two rollers against each other with sufficient force, the protuberances of the embossing roller compress the elastically yielding coating of the pressure roller. By feeding the web material between the embossing roller and the pressure roller, permanent deformation of the web material, and consequently embossing thereof, is obtained.

[0004] Embossing units of this type can be simple, i.e. with a single embossing roller-pressure roller pair, or complex, with several embossing roller-pressure roller pairs, also having the function of applying a glue to one of the embossed plies and laminating two or more plies therebetween to form a multi-ply product. In these cases, they are also called embossing-laminating units, as two or more plies are laminated to one another therein, after a glue is applied to the surface of at least some of the protuberances formed by embossing on one or other of the plies. Examples of embossers for tissue paper are described inter alia in US patents 6.245.414; 6.032.712; 6.053.232; 6.578.617; 6.470.945; 6.755.928; 6.681.826 and in the international publication WO-A-04/002727, as well as in the European patent EP-A-0370972.

Objects and summary of the invention

[0005] To obtain different products, embossing rollers with patterns that can vary even considerably are increasingly used today. It has been noticed that in many cases the use of a particular engraving pattern, i.e. of a particular arrangement of the protuberances of the embossing roller, should be associated with specific properties, such as and in particular a specific hardness value of the elastically yielding coating of the pressure roller.

[0006] The object of the present invention is therefore to provide an embossing unit that takes account of this need and makes the embossing unit more simple and versatile to use even, for example, with variable embossing patterns that require different pressure rollers.

[0007] In substance, according to the invention, there is provided an embossing unit, comprising at least a first embossing roller, associated to which are at least two pressure rollers which are moved alternately to the operating position in contact with said first embossing roller. The two pressure rollers can as a rule also be the same as each other, in which case they are utilized alternately, for example, to reduce wear, or to distribute wear on the two rollers and consequently reduce the number of interventions for pressure roller replacement.

[0008] Nonetheless, the invention is particularly advantageous when the two pressure rollers differ from each other, for example with regard to the properties of the yielding surface coating. The two rollers could also differ from each other in dimensions, if this were necessary to perform particular types of processing.

[0009] In general, the two or more pressure rollers associated with the embossing roller can be supported by separate assemblies or devices, movable towards and away from the embossing roller. For example, there can be provided rectilinear guides for translation of slides supporting the pressure rollers, and which are arranged so as to move one or other of the two pressure rollers towards the embossing roller. However, in a particularly simple and reliable embodiment, the embossing unit comprises a single supporting member for at least two pressure rollers, said supporting member being arranged to alternately move one or the other of said at least two pressure rollers to an operating position in contact with said first embossing roller. In a possible particularly advantageous embodiment, the supporting member comprises an angularly movable element on which said at least two pressure rollers are supported, said angularly movable element having at least two angular operating positions.

[0010] When the embossing unit comprises several embossing rollers, advantageously each of these rollers can be associated with two pressure rollers that can be used alternately.

[0011] Further advantageous features and embodiments of the invention are set forth in the appended dependent claims.

Brief description of the drawings

[0012] The invention will be more apparent by following the description and accompanying drawing which, in the single figure, shows a schematic side view of an embossing-laminating unit to which the invention is applied.

Detailed description of the preferred embodiment of the invention

[0013] The accompanying figure shows a diagram of an embossing unit, and more specifically an embossing-laminating unit, to which the invention is applied. It must be understood that the invention, as more generically defined above and as indicated in the claims, could also be incorporated in embossing units of other types.

[0014] In particular, the accompanying figure shows a nested type embosser-laminator, but it must be understood that the invention could also be used in embossers (or more precisely embosser-laminators) of the tip-to-tip type, in simple embossers and in other embossing machines or units in general, wherein with at least one embossing roller a pair of pressure rollers are associated, usable alternately to satisfy the need to provide elastic pressure surfaces with different properties according to the type of material to be processed, the type of embossing pattern or the like.

[0015] With reference now to the diagrammatic drawing shown in the accompanying figure, the embossing-laminating unit illustrated therein has a first embossing roller 1 provided on the surface thereof with projections or protuberances 1P and rotating about a first axis of rotation A1. The embossing unit also has a second embossing roller 3 provided with embossing protuberances 3P and rotating about an axis A3 substantially parallel to the axis A1 of the embossing roller 1. As this particular example refers to a nested type embossing unit, the rollers 1 and 3 are arranged so that in the nip defined therebetween there is no reciprocal contact between the protuberances 1P and 3P, but the protuberances 1P correspond with the empty areas between the protuberances 3P. It would also be possible for the arrangement of the two rollers 1, 3 to be adjustable to switch from a nested configuration to a tip-to-tip configuration.

[0016] Preferably, associated with the first embossing roller 1 is a first supporting member 5, which in a possible embodiment comprises an oscillating arm 7 pivoting about an axis of oscillation 7A substantially parallel to the axes A1, A3 of the rollers 1 and 3. In a possible embodiment, the oscillating arm 7 is double, i.e. has oscillating elements constrained to each other, for example through a torsion bar, on the two side panels of the machine. Alternatively, the two oscillating arms 7 are not constrained to each other and end their movement against respective adjustable stops.

[0017] On the oscillating arm 7, about an axis 9A parallel to the axis 7A, there is pivoted a supporting element 9 angularly movable, i.e. oscillating or rotating, about the axis 9A. In the example shown, the element 9 has an approximately butterfly-shaped configuration and supports a first pair of pressure rollers 11A and 11B which can cooperate alternately with the embossing roller 1. In the layout shown in Figure 1, the pressure roller 11A cooperates with the embossing roller 1, while the pressure roller 11B is in the idle position. In practice, as the oscillating arm 7 is double, the supporting element 9 is also double, and two small butterfly-shaped side panels will be provided supported respectively by the two oscillating arms arranged on the two side panels of the machine. The positions shown in the figure are not the only ones that can be taken by the rollers 11A and 11B. For example, the position of the two ends of the operating roller could be slightly staggered with respect to each other, so that the axis of the roller 11A is slightly angled with respect to the axis A1 of the embossing roller 1 against which it is pushed. In other words, the axes of the rollers 11A, 1 are slightly skewed. This reciprocal inclination of the axes of the rollers allows the pressure exerted by the pressure roller 11A against the embossing roller 1 to be varied at will. In fact, flexure caused by different thrusts, which leads to uneven embossing, can be compensated, according to known techniques, by slightly inclining the pressure roller 11A with respect to the embossing roller 1.

[0018] For narrow embossing units, for example to produce napkins, it would also be possible to use single arms which support the rollers in a cantilevered fashion.

[0019] Each of the pressure rollers 11A, 11B is provided with a coating 12A, 12B made of an elastically yielding material, such as synthetic rubber. Typically and preferably the coatings 12A, 12B differ from each other by at least one feature which can, for example, be the hardness of the material, the specific weight thereof, the thickness thereof or the like. In this way it is possible to alternately move one or other of the pressure rollers 11A, 11B to the operating position according to manufacturing needs.

[0020] The double oscillating arm 7 is controlled in its oscillation movement according to the double arrow f7 about the axis 7A by at least one actuator 13, which can be a piston-cylinder actuator as in the example illustrated, or of another type. An actuator 13 can be provided on each side panel of the machine or also a single actuator in a central or side position, according to the dimensions of the machine and to other needs, for example depending upon the pressure with which the rollers 11A, 11B must be pressed against the embossing rollers 1.

[0021] To move the roller 11B to the operating position, once the machine has been stopped the arm 7 can be oscillated by means of the actuator 13, so as to move the currently operating pressure roller away from the embossing roller and then rotate the supporting element 9 of the rollers 11A, 11B through about 180° to exchange the position thereof. An intermediate position taken by the rollers 11A, 11B during the exchange movement is shown with a dashed line in the figure. However, for cleaning or easy maintenance of the embossing rollers, it is advantageous also to provide an intermediate stopping position along the arc of rotation of the arm 9, for example of about 90° with respect to the position shown in the figure, thereby creating a space between the pressure rollers and the embossing roller 1.

[0022] Once the position of the rollers 11A, 11B has been exchanged with the actuator 13 the roller 11B is pressed against the cylindrical side surface of the embossing roller 1. Angular members (not shown) to lock the supporting element of the rollers 11A, 11B in one or in the other of the two alternative operating positions can be provided on the arm 7.

[0023] A similar supporting member 25 is associated with the embossing roller 3. The parts of this supporting member are indicated with the same reference numbers as the parts of the supporting member 25, increased by 20. Therefore, the number 27 indicates the arm oscillating about the axis 27A and pivoting on which, oscillating about the axis 29A, is the supporting element 29 of the two pressure rollers 31A and 31B, which can be taken alternately to the operating position. In the condition in Figure 1 the roller 31A is operating and the roller 31B is idle. The numbers 32A and 32B indicate the elastic coatings of the two pressure rollers 31A and 31B, while 33 indicates the actuator that controls the oscillating movements according to the double arrow f27 of the oscillating arm 27.

[0024] When the volumes and the dimensions of the rollers allow this, the supporting element 9 or 29 could be provided with more than two pressure rollers, for example it could support three pressure rollers or an even higher number of rollers.

[0025] In a way known per se, a glue applicator 41, not described in greater detail, is associated with the embossing roller 3, and is used to apply glue to the protuberances produced by embossing on a ply V3 of web material fed through the embossing nip between the embossing roller 3 and one or other of the pressure rollers 31A, 31B. V1 indicates the second ply fed through the embossing nip between the embossing roller 1 and one or other of the pressure rollers 11A, 11B.

[0026] Since in this example the embossing unit is of the nested type, in the nip between the embossing rollers 1 and 3 the embossed ply V1 is transferred from the embossing roller 1 to the embossing roller 3 and the two plies are laminated together by means of a laminating roller 43, so that the two plies V1, V3 are bonded together at the level of at least some of the protuberances 3P of the embossing roller 3. The reference N indicates the composite embossed web material delivered from the embossing-laminating unit.

[0027] In a way known per se, the embossing rollers 1 and 3 can be rollers with interchangeable sleeve to facilitate the replacement of the embossing patterns.

[0028] It is understood that the drawing only shows an example provided by way of a practical arrangement of the invention, and that the invention may vary in forms and arrangement without however departing from the scope of the concept underlying said invention.

Claims

1. An embossing unit to emboss a web material, comprising at least a first embossing roller, associated with which are at least two pressure rollers which are moved alternately to an operating position in contact with said first embossing roller.

2. Embossing unit according to claim 1, comprising a first supporting member for said at least two pressure rollers, said supporting member being arranged to alternately move one or other of said at least two pressure rollers to an operating position in contact with said first embossing roller.

3. Embossing unit according to claim 1 or 2, wherein said two pressure rollers differ from each other.

4. Embossing unit according to claim 3, wherein said two pressure rollers have respective elastically yielding cylindrical surfaces, which have different elastic properties for the two rollers.

5. Embossing unit according to claim 4, wherein said two pressure rollers have cylindrical surfaces with different hardnesses.

6. Embossing unit according to one or more of claims 2 to 5, wherein said supporting member comprises an angularly movable element on which said at least two pressure rollers are supported, said angularly movable element having at least two angular operating positions.

7. Embossing unit according to claim 6, wherein said angularly movable element is supported on an axis of oscillation or rotation integral with a movable support to move said angularly movable element towards or away from the embossing roller.

8. Embossing unit according to claim 7, wherein said movable support comprises an oscillating arm.

9. Embossing unit according to claim 7 or 8, wherein said movable support is controlled by an actuator, which controls the movement of the angularly movable element towards or away from the embossing roller and which provides the thrust with which the pressure roller in the operating position is thrust against the embossing roller.

10. Embossing unit according to one or more of the previous claims, comprising a second embossing roller, defining with the first embossing roller a nip through which the web material being processed is fed, and wherein at least two respective pressure rollers are associated with said second embossing roller.

11. Embossing unit according to claim 10, wherein said two pressure rollers associated with said second embossing roller are supported by means of a second supporting member substantially the same as the first supporting member.

12. Embossing unit as claimed in one or more of the previous claims, characterized in that in the operating position the pressure roller and the respective embossing roller have axes that are skewed in relation to each other.

Drawing