METHOD FOR MAKING THE SAME Field of the Invention

The present invention concerns a ply paper product having high absorption features. Specifically, the Invention concerns a paper product made of one or more plies of a material comprising wood-pulp, such as tissue paper, for making household and/or industrial rolls, paper napkins or serviettes In which, especially for kitchen rolls, the water absorption performances are very Important

Description of the Prior Art Household or industrial paper products are Usually made of at least two coupled paper plies, which are smooth or provided with specific patterns made by embossing, and coupled each other at the tips of the embossed protuberances by gluing, pressing or other operations,

The absorption and the absorptive time of a certain amount of a liquid, that Is the absorption rate, are fundamental parameters characterizing household and/or Industrial papers and they are mainly Influenced by chemical-physical features of the paper product, and in particular by the amount, kind and arrangement of fibers.

The chemical«physlca| features being the same, the presence of embossing on the surface of the paper product also modifies and Is capable of improving the paper absorption. In fact, water absorptive tests prove that with regard to a smooth paper, by deepening the embossing of the paper ply a greater water absorption is obtained, even if it goes together with a proportional increasing of the absorptive time, that Is a reduction of the absorption rate.

Further absorption tests prove that absorption Increases when embossing Is made by causing tears or perforations In the paper ply.

In GB 816,284 Is disclosed and claimed an absorbent paper whose absorption Is improved by machining it for creating crasts and depressions on the surface in which, during said machining, the paper ply is sheared at specific zones thanks to a specific arrangement of the embossing rollers, so as to elongate the paper ply beyond the elastic limit and making tears or perforations on the surface. The elongation is made in the sloping portions connecting a crest and the adjacent depression of the paper ply and it Is obtained by taking two embossing surfaces, In which protrusions of one surface mate recesses of the other surface, close one to another in a way that the distance between the embossing surfaces is lower than the thickness of the paper ply to be embossed only at the sloping portions connecting a crest to the adjacent depression. The presence of fractures on the surface of the paper breaks and reveals some fibers, so that water absorption Is Improved. However, such fractures lead to a worsening of the mechanical properties of the paper, in particular Its tensile strength both In a dry and In a wet state. A different arrangement, shape and size of the fractures may allow a greater improvement of the absorption With a fewer reduction of the above mechanical properties,

In GB 1,395,447 ia disclosed and claimed a paper product for hygienic or sanitary applications having great softness, and a method for making the same, which, at the same time, has good stretch properties in all directions without compromising its mechanical properties. Such features are obtained by making fractures or perforations on the paper surface, being elongated in specific directions, In particular in a paper web feeding direction, However, the above solution does not deal with the matter of improving the absorption of the paper product,

In US 4,307,141 Is disclosed a two plies paper product having good absorption In Which two paper piles are mirroring coupled and each ply comprises elongated crests which substantially form square portions and the paper piles are coupled together at sals crests. In the recess inside each square portion are made inward directed little perforated crests so that due to coupling the two plies the recesses form pocket portions provided with inward directed perforated crests on both sides. The elongated crests and the perforated crests are made in a single embossing operation by properly shaped embossing rollers. The product of this solution has very good softness and good absorption as the perforated crests are directed towards pocket portions, but said perforated crests, that most contribute to increase the absorption are only made at the recesses. In addiction, as the perforated crests are note, and cannot be, realized at the elongated crests, means that a compromise has to be found between the need of having big elongated crests on order to assure a safe coupling of the two plies and the need of limiting their size in order to increase the area where the perforated crests can be provided.

Obviously, many other paper products and method for making such products have been developed and patented for Increasing the water absorption features of paper products by providing fractures or perforations in the surface of at least one paper ply forming the paper product, but It Is still felt the need of developing paper products having increased absorption, such increased absorption being obtained by multiple plies, embossed and coupled without adding specific chemical substances.

Summary of the invention An object of the present invention is to provide a paper product made of two or more paper piles having innovative peculiar features, In particular concerning water absorption and water absorptive time.

Further object of the present invention is to propose a paper product made of two or more paper plies in which high water absorption is obtained without increasing costs of raw materials since no special material is added such as, for Instance, SAP powders or the like.

Another object of the present invention Is to propose a method for making a paper product made of two or more paper plies having high water absorption which can be realised also by conventional machines. Another object of the present invention Is to propose a method for making a paper product by overlapping two or more paper plies as above described and having a high water absorption, such a method being able to consistently improve up to double the productivity of some of the machines involved in the paper product production process.

The above objects are obtained through a paper product with high water absorbency made of at least two paper plies having specific surface weight of from 10 to 100 g/m ² and providing on at least one surface salient patterns comprising a first set of discrete protrusions arranged in said pattern, and at least a second set of discrete protrusions having height and base area greater than the height and base area of the protrusions of said first set of. protrusions, in which at least some of the protrusions of said first set of protrusions have fractures located on top of the protrusion, characterized In that the protrusions of the first set of protrusions are located at the areas separating the protrusions of said second set of protrusions and also at the surface of the protrusions of said second set of protrusions even if, obviously, the fractures at the tap of the protrusions of the first set of protrusions located at the surface of the protrusions of the second set of protrusions are partially hidden when said second set of protrusions is realized.

Advantageously the first set of protrusions and the second set of protrusions are arranged on one side of each of said two paper plies and directed towards the Interior of said paper product.

Advantageously said at least two paper piles are coupled together according to one of the following arrangements: tip-tσ-tlp at the protrusions of said second set of protrusions; or necked, so that the protrusions of one paper ply are housed Jn the recesses of the other paper ply in a predefined or random configuration.

Advantageously the paper product of the invention comprises at least a further paper ply interposed between said at least two paper plies, said further paper ply providing at least a first set of protrusions having fractures on top. Advantageously the first set of protrusions has a density higher than 5 protrusions per cm ² and at least 40% of said protrusions have fractures on top.

Advantageously the protrusions have a base area greater than the area of the top surface. Advantageously said fractures located on top of the protrusions are at least partially composed of apertures having area Which Is smaller than the base area of said protrusions.

The above objects are also obtained through a paper product with high water absorbency made of at least four paper plies having specific surface weight of from 10 to 100 g/m ^z each of said paper plies providing at least one set of discrete protrusions, said at [east four paper piles being joined In couples at the top of the said protrusions so that they form two at least two plies paper products, characterized In that said two at least two plies paper products are joined together so that the adhesive force connecting them is less than 90% of the adhesive force connecting said at least two paper piles of each of said at least two piles paper products. Advantageously said at least two plies paper products are Joined together at connection portions arranged and sized substantially as the connection portions connecting said paper plies.

Advantageously the connection portions connecting said at least two plies paper products correspond to the connection portions connecting said paper piles of each at least two piles paper products or to part of them.

Alternatively paper product made of at least four paper plies comprises a set of mating recesses on each side, or a set of recesses on one side, said at least two piles paper products being joined together at the bottom of said recesses.

Advantageously the two at least two piles paper products are provided with Identical salient patterns made by said set of protrusions, said salient patterns being not aligned each other.

Preferably said paper piles of said at least two piles paper products are coupled nested so that the protrusions of one paper ply are housed In the recesses of the other paper ply.

Alternatively said paper plies of said at least two piles paper products are coupled tlp- to-tip at the protrusions of said set of protrusions.

Advantageously said paper product made of at least four paper plies is made of two at least two plies paper products providing at least two sets of protrusions, the protrusions of the first set of protrusions having a smaller size and being provided with fractures on top. The above objects are also obtained through a method for making a paper product apt to raaltre a paper product with high water absorbertcy as above disclosed providing at least one step of machining said paper product wherein at least one paper ply of said paper product is engraved by sharp tools for realizing In said paper ply said protrusions with fractures/apertures on top.

Advantageously the step of engraving said paper products Is αarriβd out by feeding said at least one paper ply between two cylinders wherein at least one of said cylinders provides sharp protuberances.

In particular both cylinders provide sharp protuberances if it is desired to obtain a paper ply having protrusions with apertures on top at both sides.

The above objects are also obtained through a method for making a paper product made of at least four paper piles characterized In that it comprises steps of: feeding an at least two plies paper product to a longitudinal cut blade for longitudinally cutting said at least two plies paper products into two Identical portions; passing said portions of said at least two plies paper product through a flip- over mechanism In which one of said portions of said at least two plies paper product Is turned upside down and overlapped to the other; applying an adhesive to one side of one of said portions of said at least two piles paper product; coupling together said portions by passing them between a pair of coupling/embossing cylinders providing mating protuberances, or between an embossing cylinder providing protuberances and a smooth cylinder.

The above objects are also obtained through a method fro making a paper product mads of at least four paper plies in which each of said paper plies comprises at least one set of discrete protrusions located on one side of said paper ply and In which at least two of said paper piles are coupled together so that the protrusions of one paper ply are housed in the recesses of the other paper ply, and in which at least two more plies are coupled together so that the protrusions of one paper ply are housed in the recesses of the other paper ply, characterized in that It comprises steps of: feeding the external plies of said paper product made of at least four plies to coupliπg/ambossiπg cylinders thereof; - embossing said external piles by passing said external piles through said coupling/embossing cylinders and a counter-cylinder thereof, so that said first set of protrusions is made in said external piles; applying adhesive on top of said protrusions of said external piles by adhesive applying means thereof; coupling together said external plies at the top of at least some of said protrusions by passing said at least four paper plies between said coupling/embossing cylinders.

Advantageously between said step of applying adhesive and said stap of coupling together said external piles is comprised a step of coupling each of sais external plies with internal plies thereof, at least one of said Internal plies for each external ply providing a corresponding set of protrusions, said coupling step being obtained by passing said paper plies between said coupling/embossing cylinders thereof and further counter-cylinders thereof. Advantageously the coupling/embossing cylinders provide saiiaπt patterns of protuberances which are identical but not aligned.

Alternatively the coupiing/embossing cylinders provide protuberances which ara the same In shape and size but they are differently spaced.

If the external plies of the paper product made of at least four paper plies provide a further set of smaller protrusions perforated on top, before said step of feeding the external plies of said paper product made of at least four plies to coupling/embossing cylinders thereof, a step of embossing is provided In which each of said external plies is engraved by sharp protuberances for realizing in said external ply said protrusions with fractures and/or perforations on top. From tests performed on the above paper product has resulted that It has significant advantages in water absorbency. In particular, the water absorption rate is much greater than the one of conventional products when a same type of paper is used, In addiction, also the amount of absorbed water is much greater.

Another advantage of the present invention concerns the possibility of making the paper product by conventional machines, by simply replacing few components and by adding a simple and peculiar step.

Brief description of the drawings

The above and more advantages of the paper product with high water absorbency of the present Invention and of the method form making the same will be better understood by way of preferred embodiments examples, described in the following with reference to the accompanying drawings, in which: figure 1 shows a top view of a paper ply of a paper product according to the invention; - figure 2 shows a section view taken along line H-Il of fig. 1 ; figure 3 shows a top view, similar to the view of fig. 1, of a different embodiment of a paper ply of a paper product according to the invention; figure 4 shows a section view, similar to the view of fig. 2, of a conventional paper product; - figure 5 shows a section view, similar to the view of fig. 2, of another conventional paper product; figure θ shows a top view, similar to the view of fig. 1, of an embodiment of a paper product according to the invention; figure 7 shows a section view taken along line VII-VII of fig. 6; - figures 8 to 12 show section views, similar to the view of fig. 2, of further embodiments of a multi-ply paper product according to the invention; figure 13 shows a schematic section view of a device for performing operations apt to obtain a paper product according to the invention by a method according to the Invention; • figure 14 shows a detailed view of the work area of two cylinders for making a paper product according to the invention by a different embodiment of a method according to the invention; figure 15 shows a schematic view, similar to the view of fig. 13, of a device for making a paper product according to the invention by another embodiment of the method of the invention; figures 16 to 23 show embodiments of a paper product made of at least four paper plies according to the present Invention; figures 24 and 25 show two sets of cylinders through which Is performed a method according to the invention for making a paper product madg of at least four paper plies; figure 26 shows a perspective view of a further set of cylinders through which is performed a method according to the Invention for making a paper product made Of at least four paper plies. Detailed Description of Preferred Embodiments

Referring first to figures 1 and 2 show β portion of a paper ply, "10, which can be part of a paper product of the present Invention as one of the paper piles composing the paper product. The paper ply 10, Initially a smooth ply, or a substantially smooth ply according to Its roughness or wriπkledness typical of the type of paper which is used, is embossed for forming conical protrusions, 11, on the top side, 12, and further conical protrusions, 13, an the bottom side, 14, such protrusions 11 and 13 being arranged to form salient and recessed patterns on both sides of the paper ply 10. On top of the protrusions 11 and 13 are formed apertures 15, 16, thereof having circular shape in the present embodiment.

An easy method for making a paper ply 10 provides, a shown In fig. 13, passing a paper web, N ₁ between a pair of cylinders, 40, for instance metallic cylinders, providing sharp conical protuberancss, 41, on the circumferential surface, said protuberances being arranged so that the sharp protuberances of one cylinder fall in the spaces between the sharp protuberances of the other cylinder.

A very similar paper product can be formed as shown In fig. 14 In which a paper web N Is passed between a cylinder 40 having sharp protuberances 41 and a cylinder, SO, having partially flattened protuberances, 51, coupled and arranged each other so that the sharp protuberances of the cylinder 40 fall in the spaces between the flattened protuberances of the cylinder 50. A paper ply 10d having perforatsd protrusions on one side and πon perforated protrusions on the other side is obtained.

The cylinders 40 could have sharp protuberances of any size and shape according to the protrusions to be obtained In the paper ply, In fig. 3 is shown a different embodiment of a paper ply which can be comprised In a paper product according to the present invention in which a paper ply, 10a, Is provided protrusions 11a, 13a arranged just like the protrusions of fig. 1 but they are square base pyramids. The protrusions 11a and 13a are perforated on top as well.

The paper plies of flga. 1-3 could be formed from any type of mixture for making hygienic-sanitary paper, the eo called tissue paper. In particular they can be formed from pure wood pulp as well as from wood pulp and recovered paper in any proportion,

In not limiting example shown in figures, embossing Is performed on a paper ply having specific surface weight of 20 g/m ^a and a thickness of 0,09 mm, and the protrusions 11 and 13 or 11a, 13a are about 110 protrusions per crn ^a . The conical protrusions 11 and 13 are spaced of 0,96 mm and they have a base diameter of 0,3Smm with a height of 0,3mm and a diameter of the apertures 14 of 0,08 mm.

A paper ply as above described, in particular provided with apertures 15 and 16 on top Of embossed protrusions has a higher water absorption and fewer absorption time with regard to a similar embossed paper ply In which the protrusions are not perforated on top, as at the boundary of the apertures the ends of portions of fibers are revealed and water Is captionβd by capillarity. The fact that the revealed ends of portions of fibers are on top of the protrusions makes still easier the absorption of water by capillarity,

M addiction, each protrusion provided an aperture or fracture on top form kind of a funnel which promotes the water flow In one direction but obstruct the water flow in the other direction. In particular, in multi ply paper products In which apertures are inward directed, the water easily flows Inwards and outward water floe is obstructed so that water is kind of trapped within the papar plies,

The apertures on top of the protrusions can be of any size and shape, for Instance they could be longitudinally or in a oross direction elongated, or they could be simple fractures on the surface of the paper ply, obviously on top of the protrusions.

Also the protrusions 11 and 13 can be of any size and shape different from the conical or pyramidal shape shown in figures 1 and 3. Furthermore, not all the protrusions could be perforated on top and perforated protrusions could come In turns with non perforated protrusions even having a different shape or size. The density of the protrusions perforated on top could be reduced to a limit of some protrusions per cm ² , according for Instance to the chemical composition of the mixture, the specific surface welgnt of the paper, the desired absorbency,

The paper ply 10 provided with protrusions perforated on top Is further embossed and it is coupled by specific conventional operations to further paper plies, which could have or not perforated protrusions, for forming a multi ply paper product having a much better water absorption with regard of conventional paper product composed of a same number of paper plies,

In figures 4 and 5 are shown conventional paper products in which a paper product provided with protrusions having apertures on top is coupled with smooth paper plies.

In fig, 4 is shown a paper product In which a paper ply, 10b, is provided with protrusions, 11b, with apertures, 15b, on top, in which the protrusions are on one side, 12b, and It is coupled to a smooth paper ply, 20.

The paper ply 10b can be advantageously obtained as shown in fig. 15 where a pair of cylinders, 40, 60, for Instance In metallic material, In which the circumferential surface of the cylinder 40 is provided with conical sharp protuberances, 41 while the cylinder 60 is covered with a resilient material, 61, such ad rubber or the like. The resulting paper ply ,10b is provided with conical protrusions formed by the cylinder 40 which are perforated on top and they are on just one side of the paper ply. In figure 5 a paper ply 10, according to the first embodiment, Is Joined to two smooth paper piles 20, one on one side and the other on the opposite side thereof.

In figures 6 and 7 is shown a paper product, 10Of ₁ according to the present Invention composed of three paper piles. The middle paper ply 10 has on both sides protrusions perforated on top. The middle paper ply 10 Is comprised between two more paper plies, 10c. Each paper ply 10c comprises a first set of protrusions, 11σ, perforated on top and inwards directed, and a second set of nαπ perforated protrusions, 18, of a bigger size and inwards extending too.

The external paper piies 10c are joined each other tip-to-tip and the middle paper ply 10 rests comprised between. In figure 8 is shown a paper product, 100a, comprising two identical paper plies, 10c, provided with a first set of inwards directed perforated protrusions and a second set of embossed protrusions coupled tip-to-tip,

This kind of joining forms cavities, 19, within the paper product which can fill with water or other liquid to be absorbed. The funnel-like shape of the perforated protrusions 11c makes easier the water to enter and obstruct the water escaping, so It contributes to further improve the water absorption of the paper product. The protrusions of the first set are obtained by a first embossing operation and they are arranged so that they uniformly cover the surface of the paper ply 10c. The second set of protrusions, having a greater size, is obtained in a further embossing operation. During said further embossing operation the perforated protrusions of the first set which are in correspondence to the protrusions of ths second set are at least partially flattened but the fibers at the apertures thereof are torn and revealed, and such they remain even upon flattening, so that they relevantly contribute to increase the global water absorption of the paper product.

Certainly further embodiments of muttl ply paper products can be advantageously provided by joining by conventional operations paper plies according to the present Invention and conventional paper plies which can be smooth as well as embossed paper piles, and they can be joined in a nested arrangement In Which the tips of the protrusions of one paper ply are arranged In the spaces between the protrusions of another side, or they can be

Joined with a random arrangement, by gluing, by pressing them together or by other conventional techniques.

In fig. 0 the paper piles 10c are joined nested In order to form the paper product 100b, In fig, 10 is shown a paper product 10Oc comprising two paper plies 1Oc ₁ arranged nested and between them is comprised a paper ply 10 having on both sides perforated protrusions. Obviously the paper plies 10c could be also randomly arranged and they could comprise further paper piles 10, 10b or even smooth paper plies, In fig. 11 is shown a paper product 10Od comprising two pairs of paper plies 10c In which the paper plies of a pair are couples In a nested mode and the pairs are joined together In a tip-to-tip mode.

In fig. 12 Is shown a paper product 100e comprising a first pair composed of a paper ply 10c and a paper ply 10 and a further identical pair joined to the first pair, Specific advantageous embodiments of B paper product according to the present

Invention are shown in figures 16 to 23,

In the above figures are shown paper products made of four paper plies which are formed Joining together two paper products each composed of two paper plies.

In figures 16 to 19 are Illustrated paper products farmed by coupling according to different arrangements four paper plias 10c, that is paper plies provided on one side with s set of perforated protrusions 11 c and a further set of noπ perforated protrusions 1 S having a greater size. Two paper plies 10c coupled In a nested mode form the two plies paper product 100b shown in fig, 9, By overlapping two two plies paper products 100b the paper product made of four paper plies 200b shown in fig. 16 is obtained. The two piles paper products 100b are joined together so that, for a same product surface area, the adhesive force connecting them Is less than the adhesive force connecting each other the paper plies 10c composing each two plies paper product 100b (less than 90% the adhesive force connecting each other the paper plies 10c),

By experimental tests has been found that the water absorption of 3 paper product 200 made of four plies according to the Invention Is much greater than sum of the water absorption of the two plias paper products 100 composing It.

In addiction, kitchen rolls made with the paper product 200 are also very comfortable to be used. In fact, firstly sheet portion of such paper product has a very high water absorption BO that It is almost never needed to pick several sheet and overlap them, as It Is usually needed with conventional kitchen rolls, in order to obtain the desired absorbency. Furthermore, thanks to the little adhesive force Joining each other the two plies paper products 100 compared with the adhesive force Joining the paper piles of a pair, when the water absorption of a single two piles paper product 100 is enough, it Is very simple to manually separate the overlapped two plies paper products and to separately use them. From the production point of view the paper products 200 allow production methods Which consistently improve, and in soma cases double, the productivity of soma machineries involved in the production process,

The above described paper products 20Qb and 20Od, shown in figs. 16 and 17, can be obtained In various ways that Is, for instance, the preferred production processes shown In figs. 24 and 25. Referring to fig. 24 the paper product made of four paper pliss 200b is formed by a set of cylinders comprising two coupling/embossing cylinders, 70 and 70', In particular, In the present embodiment, a paper ply 10b, previously embossed by a set of cylinders as shown in fig. 15, Is fed between a coupling/embossing cylinder 70 and a counter cylinder, 80, for forming, thanks to the protuberances on the circumferential surface of the coupling/embossing cylinder 70, a paper ply 10c which, rotating about the coupling/embossing cylinder 70, passes through an adhesive applying cylinder, 90, for applying a film of adhesive at the top of the protrusions 18 of the paper ply 10c. The paper ply 10c keeps rotating about the coupling/embossing cylinder 70 and at a further counter cylinder 80 meets another paper ply 1Oc ₁ obtained by a first embossing operation In which Is formed a paper ply 10b then transformed by further embossing In the paper ply 10c. Thanks to the film of adhesive at the top of the protrusions 18 and to the pressing action of the coupling/embossing cylinder 70 together with the counter cylinder 80, the paper piles 10c are Joined to form the two plies paper product 100b. ThanKs to a mirror set of cylinders 70', SO ¹ and 90' B further two plies paper product 100'b Is formed rotating about the coupling/embossing cylinder 70' and it meets the two piles paper product 100b at the coupling/embossing cylinders 70 and 70' contact zone. The rotation of the coupling/embossing cylinders 70 and 70' is mutually arranged so that the protuberances of the coupling/embossing cylinder 70 mget the protuberances of the coupling/embossing cylinder 70', The two piles paper products 100b and 100'b, If they are identical, are pressed together at the top of all the protrusions 18 thereof where the adheslva film was applied. This way, the two plies paper products 100b and 100'b forming the paper product 200b are joined at the same points which join together the paper plies forming the two plies paper products 100b and 1Q0'b, that Is at the top of the protrusions 18 of the paper plies 10c and 10'c which are in direct contact With the coupling/embossing cylinders 70 and 70', thanks to an amount of adhesive seeping through the other paper piles 10c and 10'c. Since the amount of seeping adhesive is certainly lower than the amount of adhesive Joining the paper plies of each two plies paper product 100b and 100'b and by properly adjusting the distance of the coupling/embossing cylinders 70 and 70', it Is possible to obtain an adhesive force Joining each other the two piles paper products 100b and 100'b lower than the adhesive force Joining each other the paper plies composing each two plies paper product 100b and 100'b. The entity of adhesive force joining each other the two plies paper products 100b and 100'b can be adjusted in different ways, still using a set of cylinders as above described and shown in figs, 24 and 25. In fact, by providing two plies paper products 100b and 10Q'b Which are not Identical the result is that not a!! the protrusions 18 of the paper ply 10c In contact with the coupling/embossing cylinder 70 meet the protrusions 18 of the paper ply 10'c in contact with the coupling/embossing cylinder 70', so reducing the number of points joining the two plies paper products 100b and 100'b, For instance, a reduction of the adhesive force is obtained if the paper piles 10c and 10'c have sets of protrusions 18 Which are the same both in size and In spacing, but In which the salient patterns of protrusions are not aligned mutually aligned. A similar result is obtained providing paper piies 10c and 10'o which differ in the size or spacing of the protrusions thereof. For Instance, it is possible to provide coupling/embossing cylinders 70 and 70' shaped so that they form the above different sets of protrusions in the external plies of the paper product made of four paper piles. In the first oaaβ the coupling/embossing cylinders 70 and 70" have same patterns of protrusions which are mutually misaligned of a certain amount, in the second case the coupling/embossing cylinders 70 and 70' have same protuberances in shape and size but differently spaced as concerns the distance between two adjacent protuberances or the arrangement of the protuberances on the circumferential surfaces of the coupling/embossing cylinders 70 and 70'. These last configurations are useful In particular when the four paper plies are joined together by a set of cylinders as shown In figs, 24 and 25, through which the paper products 200b and 20Od shown in figs. 16 and 17 and composed by two plies paper products 10Qd In which two paper plies 10c are Joined each other in a random mode, that Is without a specific mutual arrangement of the protrusions 18 thereof of the paper plies, Referring to fig. 25 It can be noted that in this case they are provided two mirror sets of cylinders 70, 80 , 90 and 70', 80" and 90'. In this case the paper plies 10c forming the two plies paper product 10Od and the paper plies 10'c forming the two piies paper product 100'd of flg, 17 are not previously joined each other, but the four paper plies separately reach the coupling zone between the couplingfembαssing cylinders 70 and 70', The four paper plies are joined together Where the protrusions 18 of the paper ply 10c In contact with the coupling/embossing cylinder 70 meet the protrusions 18 of the paper ply 10'o In contact with the coupling/embossing cylinder 70'. By providing a certain misalignment of the patterns of protrusions 18 of the paper ply 10c with the pattern of protrusions 18 of the paper ply 10'c, as well as by providing a different spacing of the protrusions 1B ₁ as above described, the four paper plies are joined together only at a certain number of protrusions, However, since the adhesive has been applied to all the protrusions 18 of the paper ply 10c in contact with the coupling/embossing cylinder 70 and to all the protrusions 18 of the paper ply 10'c in contact with the coupling/embossing cylinder 70', there is a supplementary adhesive force Joining the paper plies 10c and a supplementary adhesive force Joining the paper plies 1D'c which are overlapped each other even If there Is no pressing action exerted by the coupling/embossing cylinders 70 and 70'. So, also In this case, the paper plies 10c (and the paper plies 10'c) are joined each other with an adhesive force which Is greater than the adhesive force Joining each other the two piles paper products 100d and 100'd.

Further paper products made of four paper plies according to the Invention can be realized by different processing methods.

For Instance, in figures 18 and 19 are shown two paper products, 20Qe and 20 ^Q a respectively, which can be realized by a method as schematically shown In flg, 26. he paper product 200e of fig. 18 is substantially the same of the paper product 20Od of flg. 17, but the two plies paper products 10Od composing It are joined each other at further protrusions, 25, created during the two piles paper products 100d Joining operation. ThB paper product 200a of flg. 19 is obtained by joining each other the two plies paper products 100a of fig. 8, in which the during the joining operation are created the protrusions 25 on at least on paper ply, protrusions at which the two plies paper products 100a are joined.

Referring to fig. 26 a paper produot 100 made of at least two piles Joined In a conventional way, that Is by gluing at the top of the protrusions 18 of one paper ply, Is fed to a longitudinal cut blade, 45, for longitudinally cutting the two plies paper product 100 In two Identical portions. Then , the two plies paper product 100 reaches flip-over mechanism, 55, in which, thanks to a set of rollers, one of said portions of said at least two plies paper product is turned upside down and overlapped to the other and it is kept at a certain distance. The upper portion is then passed through a proper glue applying roller, 65, and finally the two portions are joined by passing them through a pair of coupling/embossing cylinders, 75, which have protuberances for creating on both sides of the paper product made of four paper plies corresponding recesses, 25, which are visible in figs. 18 and 19 and they are properly arranged according to glue application areas of the surface of the glus applying roller 65. Alternatively, just one of the coupling/embossing cylinders 75 could be provided with protuberances and the other one could be a smooth cylinder, for forming Joining protrusions Just on one side of the paper product, The bottom of the recesses 25 are the Joint points Joining each other the two plies paper products In order to form the paper product 200 which has recesses on both sides. The size and number of joint points Joining each other the two plies paper products 100 depends only on the shape of the coupling/embossing cylinders 75 so that it is very easy to define the adhesive force Joining each other the two plies paper products, properly lower than the adhesive force Joining the paper piles 10 of each two plies paper product 100.

In conventional paper products, the area of the top surface of the embossed protrusions 18 Is between 2 and 30% the total area of the product and, as a consequence the same is the amount of Joining area with respect to the area of the surface of a paper product where the top surfaces of the protrusions are glued. Such a gluing mode allow joining the paper plies in a firm and uniform way preventing a manual separation of the paper plies without specific means which are not usually known by the final user, In a paper product made of at least four paper plies 200 according to the present

Invention, realized by using one of the above embodiments of the method of the invention or even by applying different methods, the adhesive force joining each other the two pliss paper products 100 Is ₁ for a same surface, preferably lower than 80% the adhesive force joining the paper plies composing the two plies paper products 100, so that, If needed, It Is easy to separate the two piles paper products 100.

Many of the advantages of the paper products made of at least four paper plies above described and shown in figs, 16 to 19 are still Valid even if the four paper plies are conventional paper plies. For instance they could be obtained by joining two piles paper products provided with a single set of noπ perforated protrusions 18, such as the paper products shown in figs. 20 to 23. Exactly, the paper product 300b of fig. 20 corresponds to the paper product 200b of fig. 16, the paper product 30Od of fig, 21 corresponds to the paper product 200d of fig. 17, the paper product 30Oe of fig. 22 corresponds to the paper product 20Oe of fig, 18 and paper product 300a of fig. 23 corresponds to the paper product 200a of fig. 19, The paper products 30Oa ₁ 300b, 300d and 30Oe can be obtained, for instance, through the advantageous embodiments of the method of tha Invention above described with reference to the production of the paper products 200a, 200b, 20Od and 20Oe.

Further embodiments of paper product made of at least four paper plies according to the Invention could be the result of joining together two piles paper products in which the paper piles have two sets of protrusions, a set of protrusions 18 of greater size and a set of protrusions 11 of small size which are not perforated on top.

These last embodiments just like the previously descried embodiments 300a, 300b,

30Od and 30Oe obviously have a lower water absorption compared with the embodiments involving paper plieβ with perforated protrusion but, however, they have a greater water absorbency than conventional paper products and, in addiction, they keep safe the other advantages of use and production above described.

Certainly, further embodiments of paper products could be carried out by applying the Inventive core of the present Invention and many other embodiments of the method of the present Invention may be provided still keeping safe ths above disclosed advantages and remaining within the ambit of protection of the following claims. In faot, ihε above disclosure of specific embodiments is useful to understand the field and scope of the present Invention, so that people skilled In the art Is able to put it Into practice by modifying and adapting the above disclosed embodiments; such modifications will be then considered as equivalent of the dlsolosad embodiments. The numbers and terminology used are to be intended merely for disclosure and for comprehending tha scope of the Invention and then they do not limit the invention.