FIELD OF THE INVENTION

The invention relates to the technical sector concerning the production of articles made of embossed paper, generally of a single-use disposable type, such as for example table-cloths, napkins, towels, toilet paper.

More in detail, the invention relates to a particular multi-layered embossed paper and a corresponding method for obtaining the embossed paper.

DESCRIPTION OF THE PRIOR ART It is known that these disposable articles are generally made using two or more layers of paper glued to one another and usually subjected to an embossing process.

In known ways the embossing process first comprises a permanent deformation impressed on a sheet of initially-smooth paper by corresponding embossing rollers, such as to obtain reliefs distributed according to a predetermined pattern or design and ruffle the sheet.

This process then comprises glue spotting application, on the tops of the embossing reliefs of at least one sheet by means of an applicator roller that operates tangentially with respect to the embossing roller, and counter-rotates with respect thereto.

The sheets destined to constitute the layers of the article are then coupled following a predetermined design according to which the glue spots of the first sheet can encounter, by way of example, the tops of the reliefs of the second sheet, or the depressions thereof.

The glue used for this operation is of the type in a watery solution, quick-drying, and can be mixed if required with colorant substances. In the last above case colour spots are obtained corresponding to the glue spots, which go to decorate the surface of the article.

Further decorations can be obtained on one or both sheets of the external layers by means of a printing process, usually performed preliminarily to the embossing operation and the layer-coupling operation. SUMMARY OF THE INVENTION

An aim of the present invention is to disclose a multi-layer embossed paper able to provide an optimum ability to absorb liquids and high mechanical resistance, while at the same time guaranteeing a pleasant softness and a particularly delicate tactile sensation.

A further aim of the present invention is to provide a multi-layer embossed paper that requires an extremely limited use of glue, to the advantage of the production costs and especially the environmental impact.

A further aim of the present invention is to disclose a method for obtaining the multi- layer embossed paper which is distinguished by rapid and simple operating steps.

The above aims are attained by a multi-layer embossed paper characterised in that it comprises: at least a first sheet provided with a toothed profile comprising a first crenellated distribution of teeth having a surface density D1 and a height H1 , and a second crenellated distribution of teeth having a surface density D2<D1 and a height H2>H1 , identifying a toothed stepped profile; at least a second sheet provided with a toothed profile comprising at least a first crenellated distribution of teeth having a surface density D3 and a height H3; and in that it comprises glue on at least reliefs of the first sheet having a height H2, such as to enable mutual coupling of the reliefs with the corresponding reliefs or depressions of the second sheet. In particular embodiments of the invention the multi-layer embossed paper of the invention comprises one or more of the following characteristics, considered singly or in combination:

• the first distribution of teeth of the toothed profile of the second sheet has a surface density of D3=D1 and a height 1-13=1-11 of the teeth; · the toothed profile of the second sheet further comprises a second crenellated distribution of teeth having surface density D4<D3 and height H4>H3, defining a toothed profile having a step, preferably similar to the step of the first sheet;

• the toothed profile of the second sheet has a surface density D4=D2 and a height H4=H2 of the teeth; · the first crenellated distribution of teeth of the toothed profile of the first sheet has a surface density D1 comprised between 10 and 60 teeth/cm ² , preferably between 20 and 50 teeth/cm ² ; the second crenellated distribution of teeth of the toothed profile of the first sheet has a surface density D2 comprised between 5 and 30 teeth/cm ² , preferably between 7 and 20 teeth/cm ² ; the first crenellated distribution of teeth of the toothed profile of the second sheet has a surface density D3 comprised between 10 and 60 teeth/cm ² , preferably between 20 and 50 teeth/cm ² ; the second crenellated distribution of teeth of the toothed profile of the second sheet has a surface density D4 comprised between 5 and 30 teeth/cm ² , preferably between 7 and 20 teeth/cm ² .

The preset aims of the invention are all obtained by means of a method for realising the multi-layer embossed paper, characterised in that it comprises following operating steps: transit of at least a first sheet, supplied from a first direction, across a first embossing roller provided on a lateral surface thereof with a first crenellated toothing having a surface density D1 and a uniform height H1 of the teeth, for performing a first embossing operation in cooperation with a counter-rotating first presser roller; a further transit of the first sheet across a second embossing roller, located downstream of the first embossing roller, provided on a lateral surface of a second crenellated toothing having a surface density D2<D1 and a uniform height H2>H1 of the teeth, such as to perform on the first sheet a further second embossing operation in cooperation with a second counter-rotating presser roller, such as to obtain a first sheet provided with reliefs having heights H1 , H2 distributed according to a predetermined step; transit of at least a second sheet, supplied from a second direction, across a third embossing roller provided on the lateral surface thereof with a third crenellated toothing having a surface density D3 and a uniform height H3 of the teeth, such as to perform a third embossing operation in cooperation with a counter-rotating third presser roller; application on at least the reliefs of the first sheet 1 having a height H2 of a layer of glue by means of an applicator group, preferably cooperating with the second embossing roller; mutual coupling of the reliefs of the first sheet having a height H2 on ^" which the glue is applied, with the reliefs or the depressions of the second sheet, by means of coupling means arranged downstream of the second and third embossing rollers.

The aims of the invention are obtained in the same way with a further method for realising the embossed multi-layer paper, characterised in that it comprises following operating steps: transit of a first sheet supplied from a first direction across a fourth embossing roller provided on the lateral surface thereof with a fourth toothing provided with a first crenellated distribution of teeth having a surface density D1 and a height H1 and a second crenellated distribution or teeth having a surface density D2<D1 and a height H2>H1 , such as to perform a first embossing operation in cooperation with a counter- rotating fourth presser roller, such as to obtain a first sheet provided with reliefs having heights H1 , H2 distributed in a predetermined step; transit of a second sheet supplied from a second direction across a fifth embossing roller provided on the lateral surface thereof with a fifth toothing provided with at least a first crenellated distribution of teeth having surface density D3 and height H3, in order to perform a second embossing operation in cooperation with a counter-rotating fifth presser roller; application on at least the reliefs of the first sheet having a height H2 of a layer of glue by means of an applicator group; mutual coupling of the reliefs of the first sheet having a height H2, on which the glue is applied, with the reliefs or the depressions of the second sheet by means of coupling means arranged downstream of the fourth and fifth embossing rollers.

According to particular embodiments, the method for realising multi-layer embossed paper of the invention comprises one or more of the following characteristics, considered singly or in combination:

• the second sheet transits across the fifth embossing roller provided with a fifth toothing further provided with a second crenellated distribution of teeth having a surface density D4<D3 and a height H4>H3, such as to obtain a second sheet provided with reliefs having heights H3, H4 distributed in a predetermined step, preferably similar to the step of the first sheet 1 ;

• the second sheet transits across the fifth ^' embossing roller provided with a fifth toothing, the second crenellated distribution of teeth of which has a surface density of D4=D2 and a height H4=H2 of the teeth;

• the second sheet transits across the third or fifth embossing roller, provided with a third or fifth toothing having a surface density D3=D1 and a height H3=H1 of the teeth. BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics of the invention will emerge in the following, in which some preferred but not exclusive embodiments are described by way of example, with reference to the accompanying tables of drawings, in which:

- figures from 1 to 4 illustrate profiles of four embodiments of a preferred structure of multi-layer embossed paper;

- figures from 1a to 4a illustrate corresponding profiles of the structure of embossed paper illustrated in figures from 1 to 4 with the sheets assembled differently;

- figures from 5 to 8 illustrate profiles of four embodiments of a further structure of multilayer embossed paper; - figures from 5a to 8a illustrate corresponding profiles of the structure of embossed paper illustrated in figures from 5 to 8 with the sheets assembled differently;

- figure 9 is a schematic view of a first type of machine, known as a three-roller machine, able to actuate the disclosed method;

- figures from 10 to 15 are larger-scale illustrations of details A, B, C, D, E, F shown in figure 9;

- figure 16 is a schematic view of a second type of machine, known as a three-roller machine, also able to actuate the disclosed method;

- figures from 17 to 20 are larger-scale illustrations of details G, L, M, N shown in figure 16. DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to the above-described tables, reference numeral 3 relates to the disclosed multi-use embossed paper comprising, in a novel way:

✓ at least a first sheet 1 provided with a toothed profile comprising a first crenellated distribution of teeth having a surface density D1 and a height H1 , and a second crenellated distribution of teeth having a surface density D2<D1 and a height H2>H1, identifying a toothed stepped profile (P1, P2, P3, P4);

✓ at least a second sheet 2 provided with a toothed profile comprising at least a first crenellated distribution of teeth having a surface density D3 and a height H3; glue 31 on at least reliefs of the first sheet 1 having a height H2, such as to enable mutual coupling of the reliefs with the corresponding reliefs 200 or depressions 201 of the second sheet 2.

The glue 31 is preferably only applied on the reliefs of the first sheet 1 having a height H2.

The first distribution of teeth of the toothed profile of the second sheet 2 advantageously has a surface density of D3=D1 and a height 1-13=1-11 of the teeth.

With this structural geometry figures from 1 to 4 illustrate four profiles of a preferred embodiment of multi-layer embossed paper 3 in which the reliefs of the first sheet 1 having a height H2 and provided with glue 31 couple with the corresponding reliefs 200 of the second sheet 2; while figures from 1a to 4a show the same profiles of multi-layer embossed paper 3 in which the reliefs of the first sheet 1 having a height H2 (provided with glue 31) couple with facing depressions 201 of the second sheet 2.

Figures (1 , 1a), (2, 2a), (3, 3a), (4, 4a) are differentiated from one another by having different steps (P1 , P2, P3, P4) of the toothed profile identified by the first sheet 1 , according to the respective ratio (1 :1), (1 :2), (1 :3), (1 :4) between teeth having height H2 and teeth having height H1.

In a further embodiment of the multi-layer embossed paper 3, the toothed profile of the second sheet 2 further comprises a second crenellated distribution of teeth having surface density D4<D3 and height H4>H3, defining a toothed profile having a step (P10, P20, P30, P40), preferably similar to the step (P1 , P2, P3, P4) of the first sheet 1.

The second distribution of teeth of the toothed profile of the second sheet (2) advantageously has a surface density D4=D2 and a height H4=H2 of the teeth. With this structural geometry figures from 5 to 8 illustrate four profiles of a further embodiment of multi-layer embossed paper 3 in which the reliefs of the first sheet 1 having a height H2=H4 and provided with glue 31 couple with the corresponding reliefs 200 of the second sheet having a height H3=H1 ; while figures from 5a to 8a show the same profiles of multi-layer embossed paper 3 in which the reliefs of the first sheet 1 having a height H2=H4 (provided with glue 31) couple with facing depressions 201 of the second sheet 2.

As in the preceding case, figures (5, 5a), (6, 6a), (7, 7a), (8, 8a) are differentiated from one another by having different steps (P1, P2, P3, P4) of the toothed profile identified by the first sheet 1 , according to the respective ratio (1 :1), (1 :2), (1:3), (1 :4) between teeth having height H2=H4 and teeth having height 1-11=1-13. Generally it has been established that the disclosed multi-use embossed paper 3 provides an optimal relation between liquid-absorbing capacity and mechanical resistance, thus guaranteeing a pleasant softness and a tactile sensation that is particularly delicate, in the following cases:

- the first crenellated distribution of teeth of the toothed profile of the first sheet 1 has a surface density D1 comprised between 10 and 60 teeth/cm ² , preferably between 20 and 50 teeth/cm ² ;

- the second crenellated distribution of teeth of the toothed profile of the first sheet 1 has a surface density D2 comprised between 5 and 30 teeth/cm ² , preferably between 7 and 20 teeth/cm ² ; - the first crenellated distribution of teeth of the toothed profile of the second sheet has a surface density D3 comprised between 10 and 60 teeth/cm ² , preferably between 20 and 50 teeth/cm ² ;

- the second crenellated distribution of teeth of the toothed profile of the second sheet 2 has a surface density D4 comprised between 5 and 30 teeth/cm ² , preferably between 7 and 20 teeth/cm ² .

The sheets 1 , 2 can comprise teeth having any geometry, by way of example pyramidal, or conical or elliptical.

The multi-use embossed paper 3 of the invention can be realised by means of corresponding methods applicable to a first type of machine having 3 rollers (figure 9) or a second type of machine having 2 rollers (figure 16).

With reference to figure 9, in the case of the 3-roller machine, the method for realising the multi-layer embossed paper 3 comprises following operating steps: transit of at least a first sheet 1, supplied from a first direction, across a first embossing roller 10 provided on a lateral surface thereof with a first crenellated toothing 11 having a surface density D1 and a uniform height H1 of the teeth, for performing a first embossing operation in cooperation with a counter-rotating first presser roller 12; a further transit of the first sheet 1 across a second embossing roller 15, located downstream of the first embossing roller 10, provided on a lateral surface of a second crenellated toothing 16 having a surface density D2<D1 and a uniform height H2>H1 of the teeth, such as to perform on the first sheet 1 a further second embossing operation in cooperation with a second counter-rotating presser roller 17, such as to obtain a first sheet 1 provided with reliefs having heights H1 , H2 distributed according to a predetermined step (P1 , P2, P3, P4); transit of at least a second sheet 2, supplied from a second direction, across a third embossing roller 20 provided on the lateral surface thereof with a third crenellated toothing 21 having a surface density D3 and a uniform height H3 of the teeth, such as to perform a third embossing operation in cooperation with a counter-rotating third presser roller 22; application on at least the reliefs of the first sheet 1 having a height H2 of a layer of glue 31 by means of an applicator group 30, preferably cooperating with the second embossing roller 15; mutual coupling of the reliefs of the first sheet 1 having a height H2 on which the glue 31 is applied, with the reliefs 200 or the depressions 201 of the second sheet 2, by means of coupling means 90 arranged downstream of the second and third embossing rollers 15, 20.

The layer of glue 31 is preferably applied on only the reliefs of the first sheet 1 having a height H2.

Applying the method to the 3-roller machine, assuming for the third toothing 21 of the third embossing roller 20 a surface density of D3=D1 and a height H3=H1 of the teeth, the multi-layer embossed paper illustrated in figures from 1 to 4 and in figures from 1a to 4a is realised.

With reference to figure 9, figures from 10 to 15 represent, in enlarged scale, the following profile details, in order:

✓ the first sheet 1 subjected to the action of the first toothing 11 of the first embossing roller 10 (ref. A);

✓ the second toothing 16 of the second embossing roller 15 (ref B); ✓ the first sheet 1 subjected to the action of the second toothing 16 of the second embossing roller 15 (ref. C);

✓ the first sheet 1 after application of the glue 31 on the reliefs of height H2 (ref. D);

^• s the second sheet 2 subjected to the action of the third toothing 21 of the third embossing roller 20 (ref. E); ✓ the embossed paper 3 obtained downstream of the embossing rollers, the second 15 and the third 20 (ref. F).

With reference to figure 16, in the case of 2-roller machines, the method for realising the disclosed multi-layer embossed paper 3 comprises following operating steps: transit of a first sheet 1 supplied from a first direction across a fourth embossing roller 40 provided on the lateral surface thereof with a fourth toothing 41 provided with a first crenellated distribution of teeth having a surface density D1 and a height H1 and a second crenellated distribution or teeth having a surface density D2<D1 and a height H2>H1 , such as to perform a first embossing operation in cooperation with a counter-rotating fourth presser roller 42, such as to obtain a first sheet 1 provided with reliefs having heights H1 , H2 distributed in a predetermined step (P1 , P2, P3, P4); transit of a second sheet 2 supplied from a second direction across a fifth embossing roller 50 provided on the lateral surface thereof with a fifth toothing 51 provided with at least a first crenellated distribution of teeth having surface density D3 and height H3, in order to perform a second embossing operation in cooperation with a counter-rotating fifth presser roller 52; application on at least the reliefs of the first sheet 1 having a height H2 of a layer of glue 31 by means of an applicator group 30; mutual coupling of the reliefs of the first sheet 1 having a height H2, on which the glue 31 is applied, with the reliefs 200 or the depressions 201 of the second sheet 2 by means of coupling means 90 arranged downstream of the fourth 40 and fifth 50 embossing rollers.

The layer of glue 31 is preferably applied only on the reliefs of the first sheet 1 having a height H2. Applying the method to the 2-roller machine, assuming for the fifth toothing 51 of the fifth embossing roller 50 a surface density of D3=D1 and a height H3=H1 of the teeth, the multi-layer embossed paper illustrated in figures from 1 to 4 and in figures from 1a to 4a can be realised in the same way.

In a further mode of realisation of the method, the second sheet 2 transits across the fifth embossing roller 50 provided with a fifth toothing 51 further provided with a second crenellated distribution of teeth having a surface density D4<D3 and a height H4>H3, such as to obtain a second sheet 2 provided with reliefs having heights H3, H4 distributed in a predetermined step (P10, P20, P30, P40), preferably similar to the step (P1 , P2, P3, P4) of the first sheet 1. In this case, assuming for the second crenellated distribution of teeth a surface density of D4=D2 and a height H4=H2 of the teeth, the multi-layer embossed paper illustrated in figures from 5 to 8 and in figures from 5a to 8a can also be realised.

With reference to figure 16, figures from 17 to 20 represent, in an enlarged scale, the following details of the profiles: ✓ the first sheet 1 subjected to the action of the fourth toothing 41 of the first embossing roller 40 (ref. G);

✓ the first sheet 1 after application of the glue 31 on the reliefs of height H2 (ref. L);

✓ the second sheet 2 subjected to the action of the fifth toothing 51 of the fifth embossing roller 50 (ref. M); ✓ the embossed paper 3 obtained downstream of the fourth and fifth embossing rollers 40, 50 (ref. N).

The above-mentioned toothings (11, 16, 21 , 41 , 51) can comprise teeth of any geometry, by way of example pyramidal or conical or elliptical.

Independently of the type of method and machine used, according to known ways the mutual coupling of the first and second sheets 1 and 2 is done at the second or fourth embossing roller 15 or 40, with the aid of a sixth counter-rotating presser roller 91.

In further known modalities, the glue 31 applied on the reliefs of height H2 of the first sheet 1 can also have added colorant substances that emphasise and/or add to the decoration of the deriving multi-layer embossed paper 3. From the above it is clear how the proposed multi-layer embossed paper is able to guarantee an excellent absorbing capacity of liquids and a high mechanical resistance, while at the same time enabling a pleasant softness and a particularly delicate tactile sensation.

Though conserving good mechanical resistance properties, the region identified by the interstices between the two sheets enables increasing the absorbing capacity with respect to the known structures, especially thanks to the high percentage of empty spaces.

The possibility of enabling the coupling only at the reliefs of height H2>H1 of the first sheet, with reliefs and/or depressions of the second sheet, enables good flexibility to be maintained, as well a sliding sensation of the sheets that significantly increases the pleasant tactile sensation of softness.

In this way the unpleasant sensation of roughness and stiffness to the touch common in known-type embossed paper is avoided.

To this can be added the fact that the application of glue, provided preferably only on reliefs of height H2>H1 of the first sheet (instead of on all the reliefs, as in known solutions) enables a considerable reduction to be made in the amount of glue used, to the advantage of production costs and especially environmental impact.

The toothing of the sheets or embossing rollers can comprise teeth of any geometry, by way of example pyramidal, conical or elliptical.