Patent Description:
In the tissue paper sector, plies of cellulose material are embossed and bonded together by means of various techniques, specifically by gluing, in order to obtain a multi-ply web material. Rolls of toilet paper, paper towels and other items made of tissue paper are produced in this way.

The multi-ply cellulose web material must meet often mutually contrasting requirements of a technical and aesthetic nature. In particular, the embossing pattern must be such as to impart the required characteristics of softness, liquid absorption capacity, thickness, crush resistance. Moreover, the embossing pattern shall be appropriately designed to provide appropriately distributed gluing spots, so that the plies that form the web material are bonded together effectively but with a limited amount of glue, both to reduce production costs and to avoid excessively stiffening the cellulose material. In particular, the glue should hold the plies of the web material bonded along the edges of the web material and along the perforation lines, when provided, for example in products in roll form.

Great efforts are expended in the design of the embossing rollers to obtain embossing patterns that satisfactorily meet these contrasting requirements. Examples of embossing methods of the current art are disclosed in<CIT>and <CIT>. This latter discloses a method according to the preamble of claim <NUM>.

In some cases, to obtain a cellulose product with better appearance and hence able to attract consumers' attention, printed patterns are combined with the embossed designs. These usually require the use of printing machines placed in line with the embossing unit. Printing machines are complex, expensive, difficult to operate and maintain and can have limited production rates, causing a reduction of the overall productivity of the line.

Therefore, there is a need to devise methods and cellulose products capable of overcoming or alleviating the limits of existing methods and products.

According to the invention, a method for producing a multi-ply web material is provided, including the features of claim <NUM>. Further embodiments and features are set forth in the dependent claims.

According to another aspect, a multi-ply cellulose web material is provided, formed by a plurality of sheets joined along transverse perforation lines and having a first longitudinal edge and a second longitudinal edge. The material comprises at least a first ply and a second ply of embossed cellulose material. In embodiments disclosed herein, the first ply comprises a first colored decorative pattern and a second decorative pattern defined by embossed protrusions oriented toward the second ply and on which glue is applied. The embossed protrusions to which the glue is applied are arranged, with respect to the longitudinal edges and to the transverse perforation lines, so that each sheet is provided with: at least one gluing spot in a rectangular area adjacent to each transverse perforation line, having a width of <NUM> and preferably of <NUM>; and at least one gluing spot in a rectangular area adjacent to each edge having a width of <NUM> and preferably of <NUM>.

Embodiments of the invention disclosed herein allow obtaining combined printed and embossed decorative patterns, using solely embossing rollers, with no need to use actual printing units, which are a critical point of the converting line, also because of their low production rates.

Using embossing units in sequence, not necessarily in phase with each other, with particular configurations of the embossing protuberances, exemplifying embodiments whereof will be described below, a multi-ply cellulose product is obtained with an optimal distribution of the embossing protuberances, on which a glue is applied to join the plies, and a distribution of preferably colored decorations, which can appear, to the naked eye, as printed decorations, but which instead are obtained by embossing rollers, combined with distributors of ink or more in general of a colored liquid.

To obtain particular effects, the glue can also be colored, preferably with a color different from the colored liquid used for decoration.

The invention will be better understood following the description and the accompanying drawings, which illustrate and exemplifying and non-limiting embodiment of the invention. More in particular, the drawings show:.

<FIG> schematically shows a first embodiment of a machine <NUM> for the production of an embossed web material made of tissue paper. The machine <NUM> can comprise a first embossing unit <NUM> and a second embossing unit <NUM>. In some embodiments, the machine <NUM> comprises a third embossing unit <NUM>.

In the embodiment of <FIG>, the first embossing unit <NUM> comprises a first embossing roller <NUM>, which can be provided with embossing protuberances <NUM>. The first embossing roller <NUM> is adapted to rotate around a respective rotation axis 11A in the direction indicated by the arrow f11. The first embossing roller <NUM> can be driven into rotation by a respective motor, not shown.

To the first embossing roller <NUM> can be associated a distributor <NUM> to distribute a liquid substance. The distributor can be adapted to distribute a water-base liquid. For example, the distributor <NUM> can be adapted to distribute an ink. As used herein, the term "ink" indicates any liquid substance, preferably water-based, containing a pigment. Preferably, the distributor <NUM> distributes a liquid not containing glue.

With the first embossing roller <NUM> cooperates a first pressure roller <NUM>, adapted to rotate according to the arrow f17 around a respective rotation axis 17A. The first pressure roller <NUM> can be provided with a lateral surface coated with a coating 17R, preferably made of elastically yielding material. The coating 17R can be made for example of rubber, synthetic rubber, or other suitable elastomeric material. The first embossing roller <NUM> and the first pressure roller <NUM> define a first embossing nip <NUM>, through which passes a first path for a ply V1 of web material, for example a ply of tissue paper. The ply V1 can consist of a single layer or of a plurality of layers of cellulose material. For example, the first ply V1 can have a grammage between <NUM>/m<NUM> and <NUM>/m<NUM>, preferably between <NUM>/m<NUM> and <NUM>/m<NUM>.

The first pressure roller <NUM> and the first embossing roller <NUM> are pressed against each other so that the embossing protuberances <NUM> penetrate in the elastically yielding coating 17R of the pressure roller <NUM> imparting a permanent deformation to the ply V1 of tissue paper that passes through the first embossing nip <NUM>. The distributor <NUM> is able to apply the liquid substance on at least some embossed protrusions formed on the ply V1 by the embossing protuberances <NUM> of the embossing roller <NUM>.

In the embodiment of <FIG>, the second embossing unit <NUM> comprises a second embossing roller <NUM>, provided with embossing protuberances <NUM> and able to rotate around a rotation axis 23A according to arrow f23. The second embossing roller <NUM> can be driven into rotation by a motor, not shown. To the second embossing roller <NUM> is associated a distributor <NUM> of a liquid substance, for example adapted to apply a glue on embossed protrusions generated by the second embossing roller <NUM> on the first ply of tissue paper V1, as described farther on.

The second embossing roller <NUM> cooperates with a second pressure roller <NUM>, adapted to rotate around a respective rotation axis 27A according to the arrow f27. The second pressure roller <NUM> can be provided with a coating 27R made of elastically yielding material, analogous or similar to the coating 17R of the first pressure roller <NUM>. The second embossing roller <NUM> and the second pressure roller <NUM> form between them a second embossing nip <NUM> through which extends the path of the first ply V1. In the second embossing nip, the first ply V1 can be subjected to a second embossing, i.e. mechanical deformation operation by effect of the penetration of the embossing protuberances <NUM> of the second embossing roller <NUM> in the elastically yielding coating 27R of the second pressure roller <NUM>, which is pressed against the second embossing roller <NUM>.

In the embodiment illustrated in <FIG>, the second embossing unit <NUM> comprises a third embossing roller <NUM>, adapted to rotate according to the arrow f31 around a rotation axis 31A, by means of a motor, not shown. The third embossing roller <NUM> is provided with embossing protuberances <NUM>. The third embossing roller <NUM> cooperates with a third pressure roller <NUM>, adapted to rotate around a respective rotation axis 35A according to the arrow f35. The third pressure roller <NUM> can be provided with an elastically yielding coating 35R, analogous or similar to the coating 17R of the first pressure roller <NUM> and to the elastically yielding coating 27R of the second pressure roller <NUM>. Between the third embossing roller <NUM> and the third pressure roller <NUM> is defined an embossing nip <NUM>, whereat the embossing protuberances <NUM> of the third embossing roller <NUM> press against the elastically yielding coating 35R of the third pressure roller <NUM> and penetrate in said coating 35R, so as to emboss a second ply of tissue paper V2, which is fed along a respective feed path. The second ply of tissue paper V2 can have a grammage between <NUM>/m<NUM> and <NUM>/m<NUM>, preferably between <NUM>/m<NUM> and <NUM>/m<NUM>.

The path of the second ply of tissue paper V2 extends around the third pressure roller <NUM> and around the third embossing roller <NUM> and thence towards the second embossing roller <NUM>. After being embossed between the third embossing roller <NUM> and the third pressure roller <NUM>, the second ply V2 is detached from the third embossing roller <NUM> and follows the path towards the second embossing roller <NUM>. The path of the ply V1 and the path of the ply V2 join in a lamination nip <NUM>, defined between the second embossing roller <NUM> and a laminating roller <NUM>, adapted to rotate around a respective rotation axis 39A according to the arrow f39. The laminating roller <NUM> can be coated with an elastically yielding material, for example an elastomer, a natural or synthetic rubber, preferably having greater hardness than the hardness of the coating 17R of the first pressure roller <NUM> and of the coating 27R of the second pressure roller <NUM>. In other embodiments, the laminating roller <NUM> can have a rigid cylindrical surface. The term "rigid" means, in this context, a surface that does not undergo detectable compression deformations at the pressure that is generated between the embossing protuberances <NUM> of the second embossing roller <NUM> and the laminating roller <NUM>.

In some embodiments, the laminating roller <NUM> is mounted idle and driven in rotation by pressure with the embossing roller. In other embodiments, the laminating roller <NUM> can be motorized.

In the laminating nip <NUM>, the second ply V2 is pressed against the first ply V1 can cause the mutual gluing of the plies, as described in more detail below.

The third embossing unit <NUM>, if present, can comprises a fourth embossing roller <NUM> adapted to rotate according to the arrow f41 around its own rotation axis 41A and provided with embossing protuberances <NUM>. The fourth embossing roller can be made to rotate by a motor, not shown. The fourth embossing roller <NUM> cooperates with a fourth pressure roller <NUM> adapted to rotate according to the arrow f45 around a respective rotation axis 45A. The fourth pressure roller <NUM> can be provided with an elastically yielding coating 45R, similarly to the pressure rollers <NUM>, <NUM>, <NUM>. The fourth embossing roller <NUM> and the fourth pressure roller <NUM> are pressed against each other at a fourth embossing nip <NUM>. Through the fourth embossing nip <NUM> extends the path of a third ply of tissue paper V3, which is embossed by effect of the protuberances <NUM> of the fourth embossing roller <NUM> which penetrate in the elastically yielding coating 45R of the fourth pressure roller. The third ply of tissue paper V3 can have a grammage between <NUM>/m<NUM> and <NUM>/m<NUM>, preferably between <NUM>/m<NUM> and <NUM>/m<NUM>.

While in <FIG> the embossing roller <NUM> is positioned above the pressure roller <NUM>, a reverse configuration, where the embossing roller <NUM> is under the pressure roller <NUM>, is not excluded and in fact it may be preferred. If the embossing roller <NUM> is in a higher position, the protrusions generated thereby on the ply V3 are oriented opposite with respect to the ply V1. If the embossing roller <NUM> is positioned in a lower position, i.e. under the pressure roller <NUM>, the protrusions generated by the embossing unit <NUM> are oriented towards the ply V1.

The path of the third ply V3 can join the path of the first ply V1 to advance, together with it, towards the second pressure roller <NUM> of the second embossing unit <NUM>. The numeral <NUM> indicates a guide roller on which the paths of the plies V1 and V2 can converge.

<FIG>, <FIG> show a front view and a local section according to III-III of <FIG> of a portion of the cylindrical surface of the first embossing roller <NUM> in one embodiment.

In the embodiment illustrated in <FIG> and <FIG> the embossing protuberances <NUM> comprise a first series of protuberances <NUM> and a second series of protuberances <NUM>. In some embodiments, the protuberances <NUM> can have a height H1 (<FIG>), for example between about <NUM> and about <NUM>, preferably between about <NUM> and about <NUM>. The protuberances <NUM> can for example have a frusto-conical shape, with a circular or elliptic cross section, or frusto-pyramidal shaped with polygonal, for example quadrangular, cross section. In general, the protuberances <NUM> can be dot-shaped and define a micro-embossing pattern.

In possible embodiments, the cross section, i.e. the section orthogonal to the height of the protuberances <NUM> can have a maximum dimension and a minimum dimension, or a constant dimension. For example, in the case of frusto-conical shaped protuberances with a circular cross section, the dimension of the cross section is constant (equal to the diameter), variable (decreasing) from the base (maximum diameter) to the head (minimum diameter) of the protuberance. If the cross section is elliptic, at each height of the protuberance the cross section will be characterized by a smaller transverse dimension and by a greater transverse section, corresponding respectively to the minor axis and to the major axis of the ellipse. In this case, too, the section reduces (the major and minor axes decrease) along the height development from the base to the head of the protuberance. In case of protuberances with square or rectangular section, the greater transverse dimension is equal to the diagonal and the smaller transverse dimension is equal to the side of the square, or to the smaller side of the rectangle. The aforesaid dimensions decrease from the base to the head of the protuberance.

The protuberances <NUM> can have such a cross section that the greater dimension and the smaller dimension of each cross section are substantially of the same order of magnitude. For example, the ratio between greater dimension and smaller dimension of each cross section can be equal to or smaller than about <NUM>, preferably equal to or smaller than about <NUM>, more preferably equal to or smaller than about <NUM>. Advantageously, the cross section can be circular, hence with a ratio of <NUM> between greater dimension and smaller dimension.

Preferably, the protuberances <NUM> are isolated from each other, i.e. each protuberance has a head surface and a lateral surface that extends from the head surface towards the base of the protuberance.

In this sense, the protuberances <NUM> are dot-shaped and can define a background embossing patter, for example a micro-embossing pattern. The background embossing or micro-embossing can impart technical characteristics to the product, for example and in particular characteristics of fluffiness, softness, absorption capacity.

Vice versa, in some embodiments each protuberance <NUM> can have a complex shape, characterized by a body <NUM> and by pluralities of tips or appendages <NUM> that project from an upper surface, or head surface, <NUM> of the body <NUM> and that have a head surface <NUM>. As shown in particular in <FIG>, the body <NUM> of each protuberance <NUM> has a very ample plan dimension, so that multiple tips <NUM> can be present on the upper surface <NUM> of each protuberance <NUM>.

In <FIG>, the protuberances <NUM> define a decorative motif.

The protuberances of the second series of embossing protuberances <NUM> can have a total height H2 greater than the height H1 of the protuberances <NUM>. In the embodiment of <FIG> the embossing protuberances <NUM> have a body <NUM> having a height H1, from which the appendages or tips <NUM> project. The total height H2 is the height measured between the base of the embossing protuberance <NUM> and the head surface <NUM> of the tips <NUM>. The difference H2-H1 can measure some tens of a millimeter, for example between about <NUM> and about <NUM>, preferably around about <NUM>. Even though the body <NUM> of the protuberances <NUM> has, in the illustrated example, a height H1 equal to the height of the protuberances <NUM>, this is not necessary. It is advantageous that the total height H2 of the protuberances <NUM> be greater than the height H1 of the protuberances <NUM>, for the purposes that will be clarified farther on.

In some embodiments, the area of the surface <NUM> of each protuberance <NUM> is equal to a multiple of the total surface area of the head surfaces <NUM> of the tips <NUM>. For example, on a surface <NUM> of a single protuberance <NUM> some tens or many tens of tips <NUM> distanced from each other can be arranged.

In the exemplary embodiment of <FIG> the protuberances <NUM> form decorative images, in the example hot air balloons and airplanes. Each decorative image can be formed by a protuberance <NUM> whose body <NUM> has a contour corresponding to the contour of the decorative image. Inside the contour, the protuberance <NUM> can have a continuous flat surface at a height H1, or it can have inner cavities, as shown for example in <NUM>, to reduce the total surface area of the upper surface <NUM>.

<FIG>, show local sections according to the lines IIIA-IIIA, IIIB-IIIB and IIIC-IIIC of <FIG>, respectively. The section of <FIG> is carried out in an area that comprises a protuberance <NUM>, a surface portion <NUM> of the embossing roller <NUM> lacking protuberances, a portion of a protuberance <NUM>, with tips <NUM> (only one of which is visible in <FIG> shows a section carried out along the line IIIB-IIIB of a solid decorative protuberance <NUM>, with an ample upper surface <NUM> that is at a height H1 from the base and that occupies the entire surface delimited by the perimeter of the figure (in this case, a hot air balloon). On the upper surface <NUM> are positioned rows of tips <NUM> suitably spaced from one another.

<FIG> shows a cross section according to IIIC-IIIC of <FIG>, along a line that cuts a portion of a decorative protuberance <NUM> that, similarly to the one partially visible in <FIG>, has zones with a height H1 and inner cavities <NUM>.

In all the sections of <FIG>, the upper surface <NUM> of the decorative protuberances <NUM> is far greater, even greater by one or two orders of magnitude, than the head surface of the protuberances <NUM>.

If the upper surface <NUM> of each protuberance <NUM> is far greater, for example greater by one or two orders of magnitude, than the head surface of the protuberances <NUM>, the penetration of the protuberances <NUM> in the elastically yielding coating 17R of the pressure roller <NUM> is limited and can entail a modest permanent deformation of the cellulose material forming the ply V1, or nearly no permanent deformation at all. As will be clarified in greater detail hereafter, in this case the pattern formed by the protuberances <NUM> gives rise to a colored design on the ply V1, which can be perceived by the eye of the consumer as a print, rather than as an embossing. Hence, a print decoration effect is obtained using an embossing unit, instead of a printing machine, with the advantages that come from avoiding the use of this latter type of machine which can entail several drawbacks in the converting line, for example a lower production rate.

In some embodiments, the area of the head surface of each protuberance <NUM> can be equal to or greater than, for example about double or triple the area of the head surface <NUM> of the protuberances <NUM>. The protuberances <NUM> can have, for example, a circular head surfaces with a diameter between about <NUM> and about <NUM> and the tips <NUM> can have a circular head surface with a diameter between about <NUM> and about <NUM>.

With an arrangement of the type described, the ply V1 is embossed by penetration of the protuberances <NUM> and of the tips <NUM> in the elastically yielding coating 17R. As observed above, in some embodiments the penetration of the main body <NUM> of the protuberances <NUM> in the elastically yielding coating 17R is limited by effect of the extensive area of the head surface <NUM> of these protuberances. Consequently, the ply V1 can be embossed in a deeper manner at the protuberances <NUM> and only lightly at the tips <NUM>, remaining substantially smooth around the tips <NUM>. Since the height H2 is greater than the height H1, the distributor <NUM> of liquid substance applies the liquid substance only on the radially more projecting surfaces of the embossed ply V1, which correspond to the head surfaces <NUM> of the tips <NUM>, so that the ply V1 is colored in points at these tips <NUM>. Making the appendages or tips <NUM> with small transverse dimensions, hence with a small head surface, it is possible to obtain very fine patterns that on the ply V1 are visible as small points (pixels) of color, pigmented with the liquid substance applied by the distributor <NUM>.

In embodiment variants, the liquid applied by the distributor <NUM> can be colorless and/or can comprise an adhesive substance; hence it can have a gluing capability. In the case of an adhesive substance, the glue can be highly diluted, for example it can be <NUM> to <NUM> times more diluted than normal glue used for mutually gluing embossed cellulose plies made of tissue paper.

The application of a colorless liquid, or of a liquid contained a certain amount of adhesive substance, can facilitate the subsequent mutual gluing of the plies in the second embossing unit, as described in more detail hereafter.

The protuberances <NUM> of the first series of protuberances can form a background embossing or micro-embossing. For example, the protuberances <NUM> can be distributed with a density between about <NUM> and about <NUM> protuberances/cm<NUM>, preferably between about <NUM> and about <NUM> protuberances/cm<NUM>. Each protuberance <NUM> can have a head surface area for example between about <NUM> and about <NUM><NUM>. This embossing or micro-embossing formed by the protuberances <NUM> imparts technical characteristics of fluffiness, thickness and/or absorption to the cellulose material that forms the ply V1. As shown in <FIG>, the protuberances <NUM> are not distributed uniformly on the surface of the embossing roller <NUM>, because they are absent in the area in which the embossing protuberances <NUM>, of the second series, are positioned. The density indicated above is referred to areas in which there is a continuous distribution of protuberances <NUM>.

In some embodiments, the protuberances <NUM> are positioned in areas of the embossing roller <NUM> devoid of protuberances <NUM>, so that on the embossed ply V1 the cellulose material remains smooth around and inside the decorative motifs formed by the coloration of the ply V1 at the tips <NUM>. In <FIG>, the areas of the roller <NUM> devoid of protuberances <NUM> are indicated by the numeral <NUM>. On the ply V1 to this area corresponds a substantially smooth area of the ply V1, which gives more emphasis to the decorative motifs obtained from the application of the liquid substance on the areas of the ply V1 deformed by the tips <NUM>.

In <FIG> and <FIG>, the decorative motifs are generated by protuberances <NUM> that have tips <NUM> on their head surfaces, so as to reduce the surface of the cellulose ply on which the colored liquid substance L is applied. However, in other embodiments, each protuberance <NUM>, or at least some of them, may have a substantially flat head surface and a height H2 from the base of the protuberance <NUM>. In this way, a coarser decoration is obtained.

<FIG> is a front view of a possible embodiment of the second embossing roller <NUM>. <FIG> shows a section according to VA-VA of <FIG>, of one of the embossing protuberances <NUM>. <FIG> shows a local section according to the line VB-VB of <FIG>. The embossing protuberances <NUM> can have a body <NUM> with a head surface <NUM> from which tips <NUM> project. The reference H3 indicates the height of the body <NUM> the reference H4 indicates the total height of the tips <NUM> of each protuberance <NUM>, i.e. the distance of the head surfaces of the tips <NUM> from the base of the protuberances <NUM>. In other embodiments, the protuberances <NUM> (or some of them) can have a simple shape, similar to the protuberances <NUM> shown in <FIG>, and a height H4.

The heights H3 and H4 can be equal to the heights H1 and H2, respectively. In other embodiments, the height H3 can be different from the height H1 and/or the height H4 can be different from the height H2.

The glue distributor <NUM> applies glue on the areas of the ply V1 that correspond to the tips <NUM> of the protuberances <NUM> of the second embossing roller <NUM>. These glued areas are pressed against the other plies V2 and V3 in the lamination nip <NUM> to cause mutual gluing of the plies V1, V2 and V3 and obtain the multi-ply web material N at the output of the machine <NUM>. Gluing takes place at head surfaces <NUM> of the tips <NUM>, hence in very limited areas with respect to the area of the head surfaces <NUM> of the bodies <NUM> of the protuberances <NUM>.

As shown in <FIG>, the body <NUM> of the protuberances <NUM> can have a linear development, i.e. in plan view the protuberances <NUM> can have a smaller dimension (width) and a greater dimension (length), where the greater dimension is a multiple of the smaller dimension, for example at least five times the smaller dimension. Preferably, the greater dimension can be at least one order of magnitude greater than the smaller dimension, i.e. at least ten times greater. The protuberances <NUM> can extend according to closed lines, which define the contour of a motif of large dimensions.

Preferably, the protuberances <NUM> define decorative motifs, as shown in <FIG>. The tips <NUM> with which the protuberances <NUM> are provided serve the function of limiting the surface area of the ply V1 on which glue is applied by the glue distributor <NUM>. In this way, a decorative effect is obtained, given by the distribution of the tip <NUM> along the protuberances with decorative effect <NUM>, in particular if colored glue is used. In addition, good gluing is obtained thanks to the distribution of the glue in spots, and a reduced consumption of glue, with consequent cost reduction and obtainment of a softer product, thanks to the fact that the glued surface, which typically stiffens the treated material, is only a fraction of the front surface of the protuberances <NUM>.

The third embossing roller <NUM> and the fourth embossing roller <NUM>, if present, can be provided with micro-embossing protuberances with uniform distribution, so as to obtain plies V2 and V3 provided with embossed micro-protrusions. In other embodiments, the ply V2 and/or the ply V3 can be smooth. The micro-embossing of the plies V3 and V2, as well as that of the ply V1, can have a density of embossed protrusions from <NUM> to <NUM> protrusions/cm<NUM>, preferably between <NUM> and <NUM> protrusions/cm<NUM>, most preferably between <NUM> and <NUM> protrusions/cm<NUM>. The height of the embossing protrusions formed on the plies V2 and V3 can be smaller than those of the protrusions formed on the ply V1. However, products with only two plies may be produced, hence omitting the ply V3. In other embodiments, the ply V3 may follow the same path as the ply V1 through the embossing unit <NUM>.

Moreover, each of the plies V1, V2, V3 can, independently of the others, consist of a single layer or of multiple layers.

<FIG> shows a schematic cross section of a multi-ply web material N obtained from coupling the plies V1, V2 and V3 embossed and decorated with the machine of <FIG>. The protrusions generated in the plies are indicated with the letter P followed by the number corresponding to the reference number used to indicate the embossing protuberance or the tips that generated them. Hence, for example the ply V1 has protrusions P13. <NUM> generated by the protuberances <NUM> and protrusions P13. <NUM> generated by the tips <NUM>. By way of example, <FIG> shows an embossing P13. <NUM> around the protrusions P13. <NUM>, which can be generated by the body <NUM> of the embossing protuberances <NUM>, if they succeed in at least partially penetrating in the elastically yielding coating 17R of the first pressure roller <NUM>. In general, the large transverse dimension of the bodies <NUM> of the protuberances <NUM> causes them to penetrate to a small extent in the elastically yielding coating 17R and hence they impart little or nearly no permanent deformation to the cellulose ply V1.

In advantageous embodiments, the embossed protrusions <NUM> have reduced dimensions, with a circular, elliptic or quadrangular shape, for example, with a maximum dimension preferably not greater than <NUM>, preferably not greater than <NUM>, for example of the order of <NUM>. In this way, a decoration made of dots is obtained, i.e. substantially a decoration consisting of colored pixels, the combination whereof forms complex and colored decorative motifs of large dimensions. In this way, there is an extended decoration on the web material N with a limited consumption of colored liquid.

The area of the cellulose ply V1 surrounding the protrusions P13. <NUM> is substantially free of embossing, because it corresponds to the areas <NUM> (<FIG>). At a distance from the non-embossed areas that surround the protrusions P13. <NUM> the ply V1 is provided with embossing protrusions P13. <NUM> formed by the protuberances <NUM>. Moreover, on the ply V1 are provided protrusions P25 with head protrusions P25. <NUM>, formed by the protuberances <NUM> and respective tips <NUM>. The surface of the cellulose ply V1 of the protrusions P25. <NUM> is provided with glue C, which glues the plies V2 and V3 to the ply V1. As noted above, gluing is obtained by laminating the plies V1, V2, V3 in the laminating nip between the second embossing roller <NUM> and the laminating roller <NUM>.

<FIG> schematically shows the micro-embossing P33 generated on the ply V2 by the embossing protuberances <NUM> of the embossing roller <NUM>. Moreover, <FIG> schematically shows the micro-embossing P43 formed on the ply V3 by the protuberances P43 of the embossing roller <NUM>.

While <FIG> shows an embossed product whose ply V1 has an embossing, i.e. deformation, both at the protuberances <NUM> of the embossing roller <NUM>, and at the protuberances <NUM> and <NUM> of the embossing roller <NUM>, as noted above in some embodiments the shape and the dimension of the protuberances <NUM> and of the related tips <NUM> can be such as not to impart a permanent deformation to the ply V1 at the working pressure used and with the hardness selected for the elastically yielding coating 17R of the pressure roller. Alternatively, the aforesaid parameters (dimensions and shapes of the protuberances, embossing pressure, hardness of the coating 17R) are such as to impart a very limited deformation, for example a deformation only at the tips <NUM>.

<FIG> shows a cross section similar to that of <FIG>, where however the embossed protrusions P13. <NUM> are practically invisible and only light embossed protrusions P13. <NUM> are present. In some situations on the finished product the protrusions P13. <NUM> could be practically invisible to the naked eye, by effect of the weak penetration of the tips <NUM> in the coating 17R of the pressure roller <NUM> and of the elastic recovery of the cellulose material forming the ply V <NUM>.

In the embodiment of <FIG> and <FIG>, the first embossing roller <NUM> comprises embossing protuberances <NUM> and <NUM> having different heights H1 and H2, while the second embossing roller <NUM> comprises embossing protuberances <NUM> all of the same height H4. However, this is not the only possible embodiment.

With continuing reference to <FIG>, <FIG> show a front view and a section according to VIII-VIII of a grooved surface of the first embossing roller <NUM> in another embodiment. <FIG> show a front view and a sectional view according to the line X-X of the second embossing roller <NUM> in a different embodiment.

In the embodiment of <FIG>, the first embossing roller can be provided with embossing protuberances <NUM> with an elongated linear shape and a constant height H6. The shape of protuberances <NUM> is linear and elongated in the sense that in a plan view (<FIG>) the width of each protuberance is much smaller than the length thereof. In practice, the protuberances <NUM> generate on the ply V1 linear decorations, whereat the web material V1 can be slightly embossed, to apply the pigmented liquid substance L through the distributor <NUM> only at the head surfaces 13A of the protuberances <NUM>. The protuberances <NUM> can have a height H6 for example between about <NUM> and about <NUM>, preferably between about <NUM> and <NUM>, for example between about <NUM> and about <NUM>.

The area of the head surfaces 13A of the protuberances <NUM> of <FIG> and the pressure between the embossing roller <NUM> and the pressure roller <NUM> can be such that the deformation imparted in the embossing nip <NUM> to the ply V1 and that remains in the finished product can be barely perceptible or even imperceptible for consumers, for example thanks to the fact that the deformation imparted during processing in the embossing nip <NUM> is entirely or nearly entirely in the elastic deformation range of the cellulose material forming the ply V1. In this case, using a colored liquid distributed by the distributor <NUM> on the areas of the ply V1 corresponding to the head surfaces 13A of the protuberances <NUM>, a substantially printing effect, instead of an embossing effect, is obtained. The minimum deformation of the ply V1 in the nip <NUM> is sufficient to cause the colored liquid to be applied by the distributor <NUM> only along the head surfaces 13A of the protuberances <NUM>.

The second embossing roller <NUM> shown in <FIG> can have embossing protuberances <NUM> having two different heights. More specifically, in the illustrated example, the embossing protuberances <NUM> comprise a first series of protuberances <NUM> and a second series of protuberances <NUM>. In some embodiments, the protuberances <NUM> can be cone frustum shaped or pyramid frustum shaped, or otherwise with simple dot geometric shape, with a cross section, according to a plane orthogonal to the height of the protuberances, having a greater dimension and a smaller dimension, the ratio of the greater and smaller dimension being preferably equal to or smaller than <NUM>, more preferably equal to or smaller than <NUM>, still more preferably lower than <NUM> and in particular equal to about <NUM>. They are substantially dot-shaped, non linear, protuberances. They have a height H7 for example between about <NUM> and about <NUM>, preferably between about <NUM> and about <NUM>. The maximum transverse dimension (i.e., in the case of cone frustum shaped protuberances with elliptic section, the major axis) of the head surface of the protuberances <NUM> can for example be between about <NUM> and about <NUM>, preferably between about <NUM> and about <NUM>.

The protuberances <NUM> can have a body <NUM> with a head surface <NUM>, from which tips <NUM> project, having respective head or frontal surfaces <NUM>. The total height of the protuberances <NUM> is indicated as H8 and it is greater, for example by about <NUM>-<NUM>, preferably by about <NUM>-<NUM> to the height of the body <NUM>. In the illustrated example, the height of the body <NUM> is equal to H7, but this is not necessary. In other embodiments, the body <NUM> of the protuberances <NUM> can have a height greater than or smaller than H7.

As shown in <FIG>, the protuberances <NUM> can have a linear extension, i.e. they extend for a length (in the front view of <FIG>) along the cylindrical surface of the embossing roller <NUM>, which is many times greater, for example greater by at least one order of magnitude, or greater by two orders of magnitude, than the width of the protuberances <NUM>. In some embodiments, the protuberances <NUM> can intersect each other, as shown in <FIG>, forming closed areas. In some embodiments, a micro-embossing formed by the protuberances <NUM> can be located inside the closed areas delimited by the protuberances having linear development <NUM>.

In some embodiments, the total height H8 of the protuberances <NUM> is greater than the height H6 of the protuberances <NUM>.

Thanks to the height difference H8-H7, when the ply V1 is embossed in the embossing nip <NUM>, the portions of ply V1 corresponding to the head surfaces <NUM> of the tips <NUM> are displaced radially outwards more than the remaining surface of the ply V1 and hence only these portions receive the glue applied by the distributor <NUM>. In the laminating nip <NUM>, the ply V1 is bonded by lamination and gluing to the plies V2 and V3 by effect of the pressure between the tips <NUM> and the laminating roller <NUM>. The plies V2 and V3 can be embossed or micro-embossed, and for this purpose the embossing rollers <NUM> and <NUM> as described above can be used.

The surface of the ply V1 not occupied by the embossing formed by the protuberances <NUM> is at least in part occupied by the micro-embossing formed by the protuberances <NUM>.

<FIG> schematically shows a section of the web material N obtained with the embossing rollers of <FIG>. The plies of the web material are indicated with V1, V2 and V3, as in <FIG>. On ply V1 embossed protrusions P13 are formed, generated by the embossing protuberances <NUM> of the first embossing roller <NUM>, and embossed protrusions P25. <NUM> with tips P25. <NUM> generated by the double-height embossing protuberances <NUM>, <NUM>. A colored liquid L is applied on the head surfaces of the embossed protrusions P13. A glue C is applied on the most deformed areas of the plies V1, corresponding to the tips <NUM> of the protuberances <NUM>. By means of the glue C the ply V1 is glued to the plies V2 and V3, thanks to the pressure generated in the laminating nip <NUM>, between the second embossing roller <NUM> and the laminating roller <NUM>. On the ply V2 embossed protrusions P33 are formed, generated by the third embossing roller <NUM> with the embossing protuberances <NUM>. On the third ply V3, positioned between the first ply V1 and the second ply V2, embossed protrusions P43 are formed, generated by the embossing protuberances <NUM> of the fourth embossing roller <NUM>.

As noted above, the penetration of the linear protuberances <NUM> in the elastically yielding coating 17R of the pressure roller <NUM> can be very limited, for example such as not to leave an impression (permanent deformation) visible or perceptible by the naked eye on the finished product. In this way, by means of the colored liquid applied by the distributor <NUM>, an effect similar to printing is obtained on the finished product. <FIG> shows a section similar to the section of <FIG>, in which the embossed protrusions P13 are practically invisible, in the sense that they almost entirely disappear once the compression effect exercised by the protuberances <NUM> on the elastically yielding coating 17R ceases. In <FIG>, the reference L indicates the dye applied by the distributor <NUM>.

<FIG> show a further embodiment of the embossing rollers and of the product obtainable therewith. The rollers used therein are different from the preceding one mainly because the protuberances of the roller <NUM> are dot-shaped instead of linear. <FIG> shows a front view of the embossing protuberances <NUM> of the first embossing roller <NUM>, which can be in the form of cone frustum or pyramid frustum shaped tips with height H9 (<FIG>). The protuberances <NUM> form areas delimited on the ply V1 in which the distributor <NUM> applies the colored liquid, to form a dotted decoration. In other embodiments, the decoration can be formed by continuous lines obtained by means of linear embossing protuberances.

The shape of the protuberances <NUM> and the pressure between the embossing roller <NUM> and the pressure roller <NUM> can be such that in the embossing nip <NUM> the ply V1 undergoes a very small deformation and one such that, as in the embodiments described above, allows to apply with the distributor <NUM> a colored liquid in limited areas, thanks to the deformation of the ply V1, but such that (once the ply V1 has been detached from the embossing roller <NUM>) the deformation is completely or partially reabsorbed by effect of the elastic recovery of the cellulose material forming the ply V1, giving rise to a ply apparently decorated by printing and not embossed at the areas on which the embossing protuberances <NUM> acted.

<FIG> shows a front view of a portion of the cylindrical surface of the second embossing roller <NUM>, which in this case is provided with two series of embossing protuberances, indicated with reference numbers <NUM> and <NUM> in the section of <FIG>. The references H12 and H13 indicate the heights of the protuberances <NUM> and <NUM>. Preferably, H12 is greater than H13. Preferably, the protuberances <NUM> with greater height have linear development, i.e. they have, in a plan view, a greater dimension that is a multiple of the smaller dimension, for example a greater longitudinal dimension (length), which is greater by one or more orders of magnitude than the smaller transverse dimension (width). In some embodiments, around the protuberances <NUM> there can be areas <NUM> lacking protuberances <NUM>. The latter can be micro-embossing protuberances and can for example have a pyramid frustum or cone frustum shape with very small dimensions, for example with a cross section having smaller transverse dimension with respect to the smaller transverse dimension of the protuberances <NUM>. The protuberances <NUM> can in practice be dot-shaped.

The protuberances <NUM> form on the ply V1 embossing protrusions of greater height, on which glue is applied by the distributor <NUM>. By means of this glue, in the laminating nip <NUM> the ply V1 is bonded by gluing with the plies V2 and V3 by effect of the pressure of the head surfaces of the protuberances <NUM> against the laminating roller <NUM>.

<FIG> shows a schematic section of the web material N obtained with the rollers having the protuberances described with reference to <FIG>. Adopting the same criterion of the preceding figures, in <FIG> the ply V1 has embossed protrusions P13 formed by the embossing protuberances <NUM> of the first embossing roller <NUM>. These embossed protrusions P13 can have very small height. On the ply V1 embossed protrusions P25. <NUM> are also present, formed by the embossing protuberances <NUM> of the second embossing roller <NUM>, glued with the glue C to the plies V2 and V3. The reference P25. <NUM> indicate embossed protrusions formed by the embossing protuberances <NUM>. The ply V2 is provided with embossed protrusions P33 formed by the embossing protuberances <NUM> of the third embossing roller <NUM>, while the third ply V3 is provided with embossed protrusions P43 formed by the embossing protuberances <NUM> of the fourth embossing roller <NUM>. In the areas of bonding by gluing (head surfaces of the embossed protrusions P25. <NUM>, glue C), the embossed protrusions P33 and P43 can be crushed. As in the embodiments described above, the density of the embossed protrusions P43 and P33, and hence the density of the respective embossing protuberances <NUM> and <NUM>, can typically be those of a background micro-embossment, with density for example between <NUM> protrusions/cm<NUM> and <NUM> protrusions/cm<NUM>, preferably between <NUM> protrusions/cm<NUM> and <NUM> protrusions/cm<NUM>, for example.

<FIG> shows an embodiment in which the protrusions P13 generated by the embossing roller <NUM> with the embossing protuberances <NUM> are practically imperceptible. The reference L indicates the dye applied on these protrusions by the applicator <NUM>.

In all cases shown hitherto, there is never any relationship between the mutual position of one embossing with respect to the others, i.e. the mutual positioning of an embossing on the materials in plies with respect to the other embossing is random. This holds true both for the decorative subjects, and for micro-embossments. The embossing units <NUM>, <NUM>, <NUM> may also be in phase with each other, in transverse direction with respect to the direction of advance of the plies, or in longitudinal direction, or in both directions, so that the multi-ply product N at the output of the last embossing unit has decorations and/or micro-embossments that are in phase with each other or free.

In the examples described above, the embossing unit <NUM> is a "nested" unit, in which the protuberances generated by the embossing roller <NUM> on the ply V2 tend primarily to be inserted between protuberances formed on the set of the plies V1, V3 by the embossing roller <NUM>. This configuration can in certain cases be preferred, because it does not require a precise correspondence between embossing protuberances of the rollers <NUM> and <NUM> and hence it does not require a mutual phasing. However, it is possible for the embossing protuberances <NUM> of the embossing roller <NUM> to be arranged in atip-to-tip arrangement with the embossing protuberances <NUM> of the embossing roller <NUM>.

The web material N is transformed in a known manner to obtain rolls of wound web material. <FIG> schematically shows a roll R of material N. In general, the roll R is obtained by winding the web material in "logs" that are subsequently cut, orthogonally to the axis of winding, to obtain rolls R of the desired axial length A. The web material N of the roll R is divided by transverse perforation lines LP into individual sheets F detachable from one another at the time of use by tearing along the perforation lines.

To obtain a high quality product, the distribution of the embossed protrusions must be such as to obtain a correct application of glue. The critical areas in this respect are the longitudinal edges B1, B2 of the web material N forming the roll R and the area adjacent to the perforation lines LP. In use, the individual plies V1, V2, V3 that form the web material N should not be detached from each other along the edge lines B1, B2 and along the lines obtained by tearing at the perforation lines LP.

<FIG> shows a portion of web material N comprising a sheet F and a portion of the two adjacent sheets. In <FIG> and <FIG>, the embossing patterns are omitted for the sake of drawing simplicity. In <FIG>, rectangularly shaped areas or bands AP adjacent to each perforation line LP are indicated. Each area AP is delimited by the perforation line LP, by the two longitudinal edges B1, B2 and by a line L1, parallel to the perforation line LP and positioned at a distance lAP therefrom.

On each sheet, the reference AB indicates lateral areas consisting of longitudinal bands or strips extending along the edges B1, B2 of the web material N forming the roll R. Each of the two longitudinal bands or strips has a width lAB.

Hence, on each sheet F are defined two transverse bands or strips AP with width lAP and two longitudinal bands or strips with width lAB.

According to advantageous embodiments, the protuberances of the second embossing roller <NUM>, which define the embossed protrusions on which the glue C is applied are arranged in such a way as to obtain an appropriate distribution of the glued zones in the areas AB and AP, as described below.

According to advantageous embodiments, the distribution of the embossed protrusions generated by the embossing protuberances <NUM> is such that in any band or strip AP is present at least one gluing spot, independently of the axial dimension A of the roll. In advantageous embodiments, the width lAP of the bands or strips AP is equal to <NUM> and preferably equal to <NUM>. This means, substantially, that the distribution of the glue is such that in any strip AP with dimension lAP = <NUM>, or preferably lAP =<NUM>, glue is present to keep the plies bonded adjacently to the perforation line LP. This allows obtaining a product whose plies V1, V2, V3 do not tend to delaminate along the perforation lines.

Claim 1:
A method for producing a multi-ply web material (N), comprising the following steps:
- feeding a first ply (V1) into a first embossing nip (<NUM>), between a first embossing roller (<NUM>) and a first pressure roller (<NUM>);
- deforming the first ply (V1) by means of embossing protuberances (<NUM>; <NUM>; <NUM>) of the first embossing roller (<NUM>);
- applying a colored liquid to the first ply (V1) at the embossing protuberances (<NUM>; <NUM>; <NUM>);
- feeding the first ply (V1) into a second embossing nip (<NUM>), between a second embossing roller (<NUM>) and a second pressure roller (<NUM>) arranged downstream of the first embossing nip (<NUM>) along a feed path of the first ply (V1);
- embossing the first ply (V1) by means of embossing protuberances (<NUM>) of the second embossing roller (<NUM>), forming embossed protrusions (P25) on the first ply (V1);
- applying a glue (C) to at least some of the embossed protrusions (P25);
- bonding the first ply (V1) to a second ply (V2) by gluing;
characterized in that the embossing protuberances (<NUM>; <NUM>; <NUM>) of the first embossing roller (<NUM>) comprise a first series of embossing protuberances (<NUM>) and a second series of embossing protuberances (<NUM>), having a height (H2) greater than the height (H1) of the protuberances of the first series of embossing protuberances (<NUM>), and the step of applying the colored liquid comprises the step of applying the colored liquid at the protuberances of the second series of embossing protuberances (<NUM>).