BR112014013473B1 - embossing roller, embossing unit, cellulosic tissue material made of tissue paper, and method for equalizing the mechanical strength of an embossed cellulosic tissue material - Google Patents

Abstract

Embossing Roller, Embossing Unit and Embossing Cellulosic Plein Method and Embossed Cellulosic Fabric Material. The present invention relates to an embossing roller having a plurality of embossing protrusions (P3), each containing a base (41), a side surface (45) and a top surface (43) . The side surface (45) of at least some of the protrusions of the embossing (P3) having variable slope along the extent of the perimeter of the protrusion.

Description

TECHNICAL FIELD

[001] The present invention relates to the field of production of the so-called tissue paper or crepe paper, in particular, toilet paper, kitchen towels, paper napkins or handkerchiefs and the like. More particularly, the present invention relates to improvements in embossing units and methods for mechanical processing of tissue paper.

TECHNICAL STATUS

[002] The tissue paper or crepe paper is used for the production of various items for home, professional items, as well as for industrial use. In particular, tissue paper is used to produce toilet paper, kitchen towels and other sheet or roll products. In various applications, tissue paper undergoes a mechanical embossing process. Substantially, the embossing process consists of passing one or multiple plies of tissue paper through a defined nip between an embossing roller and a pressure roller. The embossing roller is provided with protrusions which coat the surface of the pressure roller. In some embodiments, both the embossing roller and pressure roller are made of a rigid material, eg steel, and the protrusions on one roller fit with the cavities of the other.

[003] In other, more widely used embodiments, the embossing roller has protuberances that penetrate an elastic production coating layer of the pressure roller and deform it from the substantially cylindrical shape that this layer has when the pressure roller not working and not in contact with the embossing roller. The two rollers are pressed together so that the protuberances penetrate the lateral surface of the pressure roller due to compression deformation of the pressure roller's production liner. The cellulosic material forming the fabric material and passing through the nip between the two rollers is permanently deformed and the embossing projections are thereby formed having a pattern corresponding to the pattern of the protrusions on the embossing roller.

[004] The embossing process entails a great mechanical stress on the paper fold and localized rupture of its cellulosic fibers.

[005] Embossing is used for aesthetic reasons to decorate the paper fold, as well as and above all, for technical and functional reasons, for example, to create glue areas to glue more folds together, thereby forming a fabric material with multi-ply. Glue is applied to the outer surfaces of the embossing projections and therefore is applied in limited areas. Embossing is also used to modify, change or improve tissue specific characteristics such as thickness, softness and absorbency.

[006] Folded cellulosic fibers are subjected to a great tension in the areas where the fold is deformed through embossing; therefore, shapes, dimensions and the arrangement of the embossing protrusions cannot be chosen arbitrarily, as specific criteria must be taken into account, which limits the choice of the embossing pattern. During the creation of a new embossing pattern, one must therefore be committed to meeting the technical and functional requirements and the need for the paper not to be subjected to excessive stress, otherwise localized breaks or a Excessive weakening of the cellulosic material could occur.

[007] To generate the embossing protrusions, the cylindrical surface of the embossing rollers is engraved. Prior engraving techniques provided for mechanical processing through fiber removal. Recent engraving techniques are based on laser and chemical etching. The use of embossing rollers engraved by ancient techniques (forming, for example, pyramid-shaped truncated bumps), the deformation of the cellulosic fold material is evenly distributed. On the other hand, fold weakening is not homogeneous due to the non-isotropic arrangement of cellulosic fibers, as explained below.

[008] When using current engravings (obtained through chemical etching and various formats), the appearance of the embossing pattern is significantly better, however, the fold is not uniformly deformed; this results not only in heterogeneous weakening, but also in heterogeneous elongations and consequently in creasing, loosening and localized displacement of the fold during processing.

[009] As is well known to those skilled in the art, tissue paper is generally produced through wet or water processes. In a refinery, a pulp of water and cellulosic fibers is produced with a dry matter percentage below 5%, typically in the order of 2-4%. If necessary, additives such as moisture resistant resins, dyes or the like are added; and the pulp is distributed over the machine heads ("machine heads") in a fabric or forming felt. The water is then gradually drained from the pulp layer formed on the forming fabric or felt, so as to increase the percentage of dry matter within the pulp layer. When the percentage of dry matter is such that the cellulosic material layer acquires an adequate mechanical strength, the fiber layer is transferred to drying means, for example, a Yankee cylinder, drying rollers or the like.

[0010] Even if the pulp fibers have a completely random orientation, as soon as the pulp is distributed over the forming fabric, most of the fibers are arranged in the machine direction, that is, parallel to the supply direction of the fabric. formation, thanks to the way in which they were distributed on the forming fabric, through a continuous flow of pulp supplied by the linear nozzles of the machine head, according to the direction of supply of the forming fabric. As a result, the finished cellulosic material does not have the isotropic characteristics of mechanical strength and more precisely, it has lower strength in the cross-machine direction and higher strength in the longitudinal direction, that is, in the machine direction. The material has substantially lower tensile strength in the cross machine direction than in the machine direction. This also limits the shape and orientation of the embossing protrusions and projections that will be generated onto the cellulosic material and therefore must be taken into account when creating a new engraving pattern. In fact, embossing causes tensile stress and elongation on the cellulosic material.

[0011] In addition, the embossing obtained through the protrusions with simple geometry (typically, the protrusions in the form of a truncated pyramid or truncated cone) on the one hand reduces the mechanical force and, on the other hand, increases the difference between the mechanical force in the longitudinal direction (machine direction) and the mechanical force in the transverse machine direction, raising the anisotropic behavior of the embossed cellulosic material.

[0012] This typically occurs in embossing units where the embossing roller cooperates with a roller coated with the layer of elastic production material with a substantially cylindrical surface, that is, without cavities in which the protuberances of the embossing relief are inserted. In this case, a pressure is actually exerted between the two rollers, causing the embossing protrusions to partially penetrate the coating made of elastic production material, with a consequent localized elongation of the fabric or material with fold in correspondence with the sides of each protrusion, where the fabric or folded material is pressed between the protrusion and the production surface of the pressure roller.

[0013] US-A-2005/0173085 describes an embossing unit and an embossing method for processing a cellulosic material so as to degrade it in the machine direction rather than the transverse machine direction. . This popular embossing unit uses embossing rollers engraved with protrusions and cavities, ie male and female embossing rollers. The embossing rollers cooperate so that the protrusions of a male embossing roller penetrate into the cavities of a female embossing roller. The use of three distinct embossing rollers of this type, defining two sequentially arranged embossing grips, is intended to obtain a cellulosic bend processing that degrades the mechanical characteristics of the bend in the machine direction while preserving its strength in the cross machine direction.

[0014] EP-A-2353858 describes a unit for embossing wrapping or packaging sheets, in particular, for cigarette filter. The processing of plastic films is described in particular. The embossing unit described here comprises a pair of embossing rollers which cooperate through their meshing. In some embodiments described in this prior art document, to transmit motion between the embossing rollers, the protrusions of the two rollers are generated by embossing with different depths so that the sides of the protrusions in the machine direction are longer than sides in cross machine direction. The protuberances of the embossing therefore have a variable height, as their bases rest not on a cylindrical surface, but on a step surface, which is deeper in correspondence with the side oriented in the direction. of machine and shallower in correspondence with the side in the cross machine direction. The consequent greater extension of the machine direction oriented sides increases the torque transmitted from a motorized embossing roller to a rotation driven embossing roller. Neither the problem of the anisotropic mechanical characteristics of the cellulosic material nor the way to modify the mechanical strength of the embossed fold are mentioned here.

US-A-2005/0138981 describes embossing patterns for tissue embossing rollers. In some embodiments described herein, the embossing protrusions have a slope that varies along their length. No specific relationship is described between the change in the slope of the protuberance and the machine direction or transverse machine direction of the embossing roll, and the problem of the difference in the mechanical strength of the cellulosic fold between the machine direction and the transverse direction of machine is not mentioned.

[0016] DE-A-20 2007 011 885 describes an embossing roller with embossing protrusions, the sides of which have discontinuities in the form of projections or cavities. The shape of the embossed protrusion is intended to increase the compressive strength of the embossed fold. The problem of the difference in mechanical strength between the machine direction and the transverse machine direction of cellulosic folding before embossing is not addressed. No measures will be given here to solve this problem.

SUMMARY OF THE INVENTION

[0017] According to one aspect, to completely or at least partially solve at least one of the problems of the prior art, an embossing roller is provided with a geometric axis of rotation and a substantially cylindrical outer surface provided with a plurality of embossing protrusions, each of which has a base, a side surface and a top surface, in which the bases and top surfaces of the embossing protrusions are delimited by closed lines and in which, in flat view, the top surface is smaller than the base surface and lies inside the last one. In some embodiments, each protrusion has a longer dimension and a shorter dimension, the proportion of which is not greater than 20. The longer dimension and shorter dimension may alternatively be referred to as the base surface or as the top surface both. In fact, as will become clearly apparent below with reference to some embodiments, the protrusions may have a round base and an elongated top surface or vice versa. Alternatively, both the base and the top can be stretched, albeit in a different way. For example, if the base is round in shape, the top surface will be elongated and will therefore have a longer dimension and a shorter dimension. The top surface can be, for example, a rectangle and in this case it will have a longer side (longer dimension) and a shorter side (shorter dimension). In other embodiments, the top surface may be elliptical and in this case, the longest dimension will be that with the longest geometric axis of the ellipse and the shortest dimension will be that with the smallest geometric axis of the ellipse. The same can happen when the base has an elongated shape. In general, when the base and/or top surface have an elongated shape, the longest dimension and the shortest dimension can be identified.

[0018] To obtain a more uniform tension on the cellulosic sensing material embossed by the embossing roller and, therefore, a more uniform strength of the embossed product, the side surface of at least some of the embossing protrusions it has a variable slope along the length of the perimeter of the bulge.

[0019] The slope of the lateral surface can be defined at each point of the closed line that delimits, that is, it surrounds the base of the embossing protrusion, later also referred to as the baseline. The slope of the lateral surface of the protrusion can be set at any point on the baseline as follows. Considering the tangent to the baseline at the point in question, the geometric plane orthogonal to the tangent and passing through the considered point of the baseline. This plane intersects the lateral surface of the protrusion along a line that passes through the considered point. If the line intersects for a straight segment, the angle formed by it together with the base of the protrusion will define the slope of the lateral surface of the protrusion at the point considered. If in the area considered, the lateral surface for concave or convex, the intersecting line will then be a curved line with a concavity facing outwards or inwards. In this case, the mean slope can be identified, calculated, for example, by the average of the angles formed by the base of the protrusion and by the tangent lines of this curved line. Alternatively, considering the point on the baseline and the intersection point of the considered plane with the edge line of the top surface of the protrusion; the inclination of the lateral surface at the considered point can be defined as the angle formed between the base of the protrusion and the line that passes through said two points. The base of the protrusion is on a cylindrical surface of the embossing roller. However, the dimension of the base is significantly smaller than the cross-sectional diameter of the embossing roller and therefore the base of the protuberance can be assimilated or approximated to a flat surface, against which the slope of the mentioned line above can be set.

[0020] In advantageous embodiments, the inclination of the lateral surface of at least some protuberances changes in a continuous or substantially continuous manner, that is, gradually. Gradual, continuous or substantially continuous means that the change takes place without discontinuity and therefore the lateral surface of the bulge on it does not have any sharp corners. Thus, a more delicate processing of the embossed fold is obtained, without stress concentration and with a smoother surface and a more pleasant touch.

[0021] In some embodiments, the lateral surfaces with variable inclination have a substantially conical shape and not flat.

[0022] In advantageous embodiments, at least one of the closed lines, which delimits the base and the top surface of the protuberances, which has the lateral surface with variable inclination, is round. In some embodiments, one of the two closed lines delimiting the base and top of the bulge has an elliptical or ovoid shape. In general, the top surface is preferably delimited by a curved line, with no sharp corner, so as to obtain a softer and smoother embossed product, thereby also avoiding stress concentration and tearing risks. or drilling.

[0023] In some embodiments, the closed line that delimits the base is round and the closed line that surrounds the top surface is elliptical or ovoid, with the major geometric axis smaller than the diameter of the round base line. In other modalities, the closed line delimiting the base is elliptical or ovoid and the closed line surrounding the top surface is round and the smallest geometric axis of the line delimiting the base is longer than the diameter of the round line surrounding it. the top surface.

[0024] The closed line surrounding the top surface of the protrusion can be defined by a border formed between a substantially flat top surface (or more precisely, a cylindrical top surface with a radius corresponding to the radius of the embossing roller at relief) and the lateral surface of the bulge. In other embodiments, these two surfaces (top and side) can be joined by a rounded surface portion, that is, by a rounded edge.

[0025] Using such a roller designed for embossing, the embossed projections generated on the fabric material are defined by the same characteristics. The structural and morphological characteristics described above with reference to the roll protrusions are here planned, therefore, also with reference to the embossed projections of the embossed material.

[0026] In general, not all embossing protrusions of the embossing roller should have a side surface with a variable slope. Rather, it is possible that only some of these embossing protrusions have a variable angle, the others having a fixed angle. For example, some embossing protrusions may be truncated cone-like with a round cross-section or pyramid-like shape with a square base, and in this case, the slope of the lateral surface is constant along the entire perimeter of the protrusions. embossing. In general, at least a part, preferably more than 50%, more preferably more than 70% of the embossing protrusions of the embossing roller has a lateral surface with variable slope.

[0027] The change in the slope of the side surface of the embossing protrusion determines the way in which the embossed fabric material is deformed. The greater the slope relative to the base surface of the embossing protrusion, the greater the tension of the embossing. In fact, embossing causes a permanent localized deformation in the cellulosic material that forms the fabric material. This deformation results in an elongation due to penetration of the embossing protuberances into an elastic producing coating of a pressure roller defining together with the embossing roller an embossing grip, through which the fabric material to be embossed. Therefore, in correspondence with the embossing protrusion, the cellulosic material is elongated by an element which depends on the embossing protrusion penetration element within the elastic producing coating of the pressure roller. The greater the slope of the side of the embossing protrusion, i.e. the side surface of the embossing protrusion, the more concentrated is the elongation deformation and therefore the tensile stress on the fabric material. On the other hand, the smaller the slope, that is, the smaller the angle formed at a given point by the side surface and base of the embossing protrusion, the greater the length of the fabric material over which the permanent deformation is distributed and in this way, the lower the tensile stress.

[0028] It should be noted that due to the effect of the production technique, cellulosic fibers from cellulosic folding or a fabric material have a preferred orientation in the machine direction, that is, in the direction in which the material is produced, which it also corresponds to machine direction in subsequent embossing processing.

[0029] Cellulosic material therefore has a higher strength in the machine direction and a lower strength in the cross-machine direction. Consequently, by imposing, during embossing, a greater deformation in the machine direction and a lesser deformation in the cross-machine direction, it is possible to obtain a more uniform mechanical tensile strength for the final product. In reality, the greatest deformation of the embossing is imposed in a direction parallel to the machine direction, that is, in the direction in which the product is strongest. The least stress and the least strain are imposed in the transverse machine direction.

[0030] This results in a so-called "square" material, ie, in which the mechanical strength characteristics in the two directions (machine direction and cross machine direction) are substantially comparable to each other or in any way less different than in a traditional product. Substantially, to achieve this, at least some protrusions of the embossing must have a side surface with greater slope in the machine direction and less slope in the cross-machine direction. It is not necessary for all bulges to be formatted this way. It is sufficient that at least some of them are designed like this, while others have a constant slope or even a variable slope in the opposite mode (higher in the cross-machine direction and smaller in the machine direction). In the latter case, it is necessary that most embossing protrusions have a smaller lateral surface slope in the cross-machine direction and greater in the machine direction, while the other embossing protrusions have a greater slope in the cross-machine direction. and less tilt in machine direction.

[0031] With reference to the single embossing roller, the transverse machine direction is the direction parallel to the geometric axis of the roller, while the machine direction is orthogonal to it, that is, it is the tangent direction on the circumference of the section cross section of the embossing roller.

[0032] In some embodiments, an embossing roller is provided, in which the slope of the lateral surfaces of the embossing protrusions changes, so that all the tension in the embossing fold of the cellulosic material, embossed by the embossing roller, is smaller in a direction parallel to the geometric axis of rotation of the embossing roller, that is, in the cross-machine direction and larger in a direction orthogonal to the geometric axis of rotation of the embossing roller, that is, in the machine direction.

[0033] In some embodiments, at least some protuberances of the embossing have greater inclination in a direction parallel to the geometric axis of the rotation roll and less inclination in a direction orthogonal to the geometric axis of the rotation roll.

[0034] The density of the bulges can be, for example, between 10 and 200 bulges/cm2 and preferably between 15 and 180 bulges/cm2. The density can be in particular between 20 and 100 and more particularly 20 between 30 and 90 bulges/cm2 . In general, the density is preferably greater than 30 bulges/cm2 ; above this value, reference is made to embossed microengraving.

[0035] In some embodiments, the bases of the embossing protuberances have a longer dimension and a shorter dimension and the ratio between the longest dimension and the shortest dimension is greater than 1 and equal to or less than 10 and is preferably comprised between 1.1 and 7 and more preferably between 1.5 and 5. It is to be understood that the present description also includes any intermediate value between those indicated above and any subrange falling within the broader range defined above.

[0036] In some embodiments, the top surfaces of the embossing protrusions may have a substantially round extent. Base surfaces can be nearly elliptical in length.

[0037] Most embossing protrusions are preferably oriented with the longest dimension of their elliptical base in a direction parallel to the geometric axis of the embossing roller and with the shortest dimension in a direction orthogonal to the geometric axis of the roller.

[0038] In some embodiments, the protrusions may be designed differently and a different series of protrusions may be provided. For example, a first series of embossing protrusions may comprise directed protrusions with their longest dimension in a direction parallel to the geometric axis of the embossing roller and a second series of embossing protrusions may comprise directed protrusions with their shorter dimension in a direction parallel to the geometric axis of the embossing roller. In this case, the number of protrusions of the first series embossing may be greater than the number of protrusions of the second series embossing. The ratio between the number of protrusions of the first series embossing and the embossing number 10 protrusions of the second series may be, for example, greater than 1 and equal to or less than 10, it may be, for example, comprised between 1.2 and 5, preferably between 1.5 and 4 and more preferably between 1.8 and 2.5, it being understood that the present description also includes any intermediate value and any sub-range within the range broader defined above.

[0039] In some embodiments, the arrangement of the protrusions of the two series mentioned above can be defined so that each embossing protrusion of the second series is surrounded by a plurality of embossing protrusions of the first series, thereby forming a set of lumps. The protrusion set generally means a series of protrusions arranged in a repeated geometric pattern. The protrusions are therefore arranged on a surface of the embossing roller in accordance with a pattern provided by the repetition of a base pattern, which is in turn defined by a series or set of protrusions arranged in accordance with the geometric arrangement mentioned above. In some embodiments, each set of protrusions comprises six protrusions from the first series embossing that surrounds a corresponding protrusion from the second series. Some bulges from the first series can be shared with adjacent sets.

[0040] In some embodiments, to reduce vibrations, stresses and/or wear, the sets of protrusions are aligned according to the helical lines that extend over the cylindrical surface of the embossing roller. The helical lines may have an inclination of, for example, between 1° and 10°, preferably between 2° and 8° and more preferably between 3° and 7°, for example about 5°, relative to the geometric axis of the embossing roller. It is to be understood that the present description also includes any intermediate value and any sub-range falling within the broader range defined above.

[0041] In some embodiments, the bases of the embossing protrusions, or at least some of them, may be substantially elliptical in length. The elliptical bases can be combined with the round top surfaces or with the elliptical front surfaces provided so that the dimension and shape of the front and base surfaces make the slope of the lateral surface of the bulge variable along the length. of the bulge.

[0042] In some embodiments, the front surfaces of the embossing protrusions have a longer dimension and a shorter dimension and the ratio between the longest dimension and the shortest dimension is greater than 1 and equal to or less than 10, preferably comprised between 1.1 and 7 and more preferably comprised between 1.5 and 5, it being understood that the present description also includes any intermediate value and any sub-range falling within the broader range defined above. Front surfaces can be, for example, elliptical. At least some protrusions of the embossing may have an approximately round base.

[0043] In this case, at least most of the embossing protrusions are directed with their shortest dimension substantially parallel to the geometric axis of the embossing roller. In some embodiments, all embossing protrusions are directed with the longest dimension of the front surface in a direction substantially parallel to the geometric axis of the embossing roller.

[0044] In some embodiments, the embossing roller comprises a first series of embossing protrusions, arranged with the longest dimension of the front surface oriented in a direction parallel to the geometric axis of the embossing roller and a second series of said embossing protrusions oriented with the shortest dimension of the front surface parallel to the geometric axis of the embossing roller. The number of protrusions of the first series embossing is preferably greater than the number of protrusions of the second series embossing. The ratio between the number of protrusions of the first series embossing and the number of protrusions of the second series embossing may be, for example, greater than 1 and equal to or less than 10, e.g. .2 and 5, preferably between 1.5 and 4 and more preferably between 1.8 and 2.5. It is to be understood that the present description also includes any intermediate value and any sub-range falling within the broader range defined above.

[0045] In some embodiments, each second series embossing protrusion is surrounded by a plurality of first series embossing protrusions, thereby forming a set of protrusions. Each set of protrusions comprises, for example, six protrusions from the first series embossing that surrounds a protrusion from the second series. Adjacent sets may share some bulges from the first series. The assemblies can be aligned according to helical lines that extend across the cylindrical surface of the embossing roller. The inclination of this helical line or of the lines of the alignment of the set can be comprised between 1° and 10°, preferably between 2° and 8° and 5, more preferably between 3° and 7° in relation to the geometric axis of the roller of embossing. The slope can be, for example, almost 5°. It is to be understood that the present description also includes any intermediate value and any sub-range falling within the broader range defined above.

[0046] The embossing roller may also have additional embossing protrusions, shaped differently from said embossing protrusions. For example, the additional protuberances of the embossing can be provided with a decorative shape or a simple truncated cone or pyramid shape with a constant or substantially constant inclination of the lateral surface with respect to the radial direction.

[0047] According to another aspect, the present invention also relates to an embossing unit comprising at least a first embossing roller and a first pressure, the roller defining in place a first embossing grip and at least one first path for a first fabric material extending along a said embossing grip, characterized in that the first embossing roller is an embossing roller as described above.

[0048] In some embodiments, the embossing unit may comprise a second embossing roller and a second pressure roller, defining in place a second embossing grip and at least a second path to a second material of fabric extending along the second embossing nip, said second embossing roller being an embossing roller as described above. The embossing unit can be an end-to-end embossing unit. In this case, the first embossing roller and the second embossing roller form a laminating nip, through which the paths of the fabric materials pass. The distance between the two embossing rollers is set to cause the lamination of the two or more fabric materials in the lamination grip. In other embodiments, the embossing rollers can be arranged so as to obtain a grouped embossing and in this case, a laminating roller can be provided downstream of the nip between the two embossing rollers, cooperating with one of the two embossing rollers for embossing the fabric materials. In both cases, at least one glue dispensing unit can be provided to apply glue onto the embossing projections generated by one of the embossing rollers prior to laminating the fabric materials.

[0049] In general, an unetched pressure roller, i.e. having a substantially surface, is associated with the embossing roller.

[0050] The pressure roller associated with the embossing roller advantageously has a coating of elastic producing material. When the embossing unit is in operation, the pressure roller and the embossing roller are arranged with such a center-to-center distance that the embossing protrusions of the embossing roller penetrate the elastic producing layer of the pressure roller, deforming it elastically. The cellulosic material fabric is deformed due to the penetration effect of the embossing protrusions into the elastic producing liner of the pressure roller.

[0051] Generally, a pressure roller for each embossing roller is provided. It is, however, possible to also use the same pressure roller to cooperate with two or more embossing rollers, arranged, for example, in sequence along the circumferential extension of the pressure roller.

[0052] It is also possible to use more pressure rollers cooperating with the same embossing roller.

[0053] The present invention also relates to a cellulosic detectable material comprising at least one ply of embossed cellulosic material with embossed projections, each embossed projection having a base, a side surface and a top surface , said base and said top surface being delimited by closed lines. In accordance with the invention, the side surface of at least some embossed projections has a variable slope along the extent of the perimeter of the projection. The fabric material may also comprise other embossed projections, shaped differently than those with variable slope, for example, those projections having side surfaces with constant slope.

[0054] In some embodiments, the fabric material is processed so that the slope of the side surface of the projections is variable, so that the embossing element of the fabric material in the machine direction is larger than the engraving element embossing of the fabric material in the cross machine direction. When referring to the product, the machine direction is the direction according to which the fabric material is disposed on the production or processing machines. In general, machine direction can be identified as the direction of most cellulosic fibers, as the latter are mainly or predominantly machine direction oriented. When the fabric material has an indefinite length, that is, for example, a product on a roll, the machine direction is also the extension of the longitudinal direction of the product, that is, the length direction. The transverse machine direction is oriented 90° to the machine direction.

[0055] The embossing element means the permanent deformation to which the product or fabric material is subjected due to embossing. The embossing element is therefore proportional to or is somehow connected with the percentage elongation of the material, ie the elongation per unit length.

[0056] The fabric material can also have more than one ply, eg two plies. The two or more plies can be glued together by means of end-to-end or grouped glueing or the like. In general, the fabric material may have embossed projections having shapes that correspond to the shapes of the embossing protrusions of the embossing roller that generated them. The characteristics of shape, density, arrangement, direction, etcetera, of the protuberances defined with reference to the embossing roller according to the invention can therefore also be defined as the characteristics of the embossed projections of the fabric material .

[0057] According to a further aspect, a method is provided to equalize the mechanical strength of an embossed cellulosic fabric material, for example, tissue paper, having a cellulosic fiber distribution preferably directed in the machine direction. The method comprises the following steps:

[0058] arranging at least a first embossing roller and a first pressure roller provided with a layer of elastic production coating, defining in place a first embossing grip and at least a first path for the bending of fabric material, said path extending along the first embossing nip;

[0059] provide, on a cylindrical side surface of the embossing roller, a plurality of embossing protrusions, where at least some of them have a variable slope along the length of the perimeter of the embossing protrusion, at least some of them of said embossing protrusions having greater inclination in a direction orthogonal to the geometric axis of rotation of the roller and less inclination in a direction parallel to the geometric axis of rotation of the roller;

[0060] embossing the fold of fabric material in the embossing grip through the embossing protrusions, the variable slope of the side surface of at least some of said embossing protrusions generating a total embossing bending stress embossing of embossed cellulosic material smaller in a direction parallel to the geometric axis of rotation of the embossing roller (cross machine direction) and larger in a direction orthogonal to the geometric axis of rotation of the embossing roller (direction of machine).

[0061] Substantially according to the method described here, the mechanical force of the cellulosic material ply, which is formed with the fibers preferably oriented in the machine direction, is uniformed by the imposition of a deformation of the embossing through the roller unit embossing roller provided with protrusions and the flat pressure roller (i.e., without protuberances) having an elastic production coating. The mechanical force is made more uniform by tensioning the cellulosic material more in the machine direction and less in the cross-machine direction. This is possible by causing the protrusions to penetrate the elastic producing coating of the pressure roller and the sides of at least some protrusions on the embossing roller to have variable slope. The change in slope is made so that at least some protrusions of the embossing have a steeper side surface in the machine direction than in the cross-machine direction. When the embossing protrusion penetrates the elastic production thickness of the pressure roller, the greater inclination in the machine direction causes, along the side surface of the embossing roller protrusion, deformation of the cellulosic fold, which is greater than the bend deformation along the cross machine direction on the less steep side.

[0062] When the protrusion with variable slope penetrates into the elastic production layer, the cellulosic material fold is subjected to deformation due to tension along the lateral surface of the protrusion. When it is pressed between the smooth elastic producing surface of the pressure roller and the top surfaces of the protrusions of the embossing roller, the fold of cellulosic fabric material is deformed locally with traction along the sides of the protrusions of the press roller. embossing. Where the lateral surface of the bulge is steeper, the deformation is more concentrated and therefore more stress is applied to the cellulosic fold. This occurs in machine direction. In the cross-machine direction, where the slope of the protrusion side is smaller, the strain is distributed over a greater length and therefore the strain percentage (and therefore the mechanical stress) is lower.

[0063] The end result that can be achieved in this way in a surprisingly simple way is a more uniform mechanical force of the embossed fold.

[0064] Regarding embossing systems that use groups of three male and female embossing rollers, a greater isotropy of the mechanical characteristics of the bend is obtained in a much simpler way. This is both due to the fewer rolls used and the need to have only one embossed roll for each individually embossed ply, rather than three embossed rolls that must all cooperate together to emboss a single ply.

[0065] By using an embossing roller cooperating with a smooth (unembossed) pressure roller with an elastic production coating, it is also possible to obtain a micro-embossing, i.e. an embossing, for example, with densities of 30 bulge/cm2 or greater. Micro-embossing, that is, such high densities of protuberances per surface unit, cannot be achieved in embossing units that use male and female embossing rollers. In addition, the devices and methods described herein enable embossing which makes the embossed fabric material more uniform also using standard embossing units, eg end-to-end, simply using an embossed roller with an embossing pattern as described above. This allows a tissue manufacturer who already has one or more traditional embossing units to improve their production by simply replacing the embossing rollers, while keeping the other characteristics unchanged. of the embossing unit. This does not occur in other known systems that try to achieve greater uniformity of mechanical strength through the degradation of the fabric material, especially along the machine direction and its preservation in the cross machine direction, which requires special engraving units in embossing, where the nature and structure of embossing and pressure rollers, as well as their number and arrangement are specifically studied to achieve this result. These embossing units are more expensive than a traditional embossing unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The present invention will be better understood by means of the description below and the attached drawings, which show a non-limiting embodiment of the invention. More particularly, in the drawings:

[0067] Figure 1 is a side view of a first embossing unit in which the invention can be incorporated;

[0068] Figure 1a is an enlargement of detail 1a of Figure 1;

[0069] Figure 2 is a side view if another embossing unit can be incorporated in the invention;

[0070] Figure 2a is an enlargement of detail 2a of Figure 2;

[0071] Figure 3 schematically shows a plan development of a portion of an embossing roller usable in one of the embossing units described above;

[0072] Figures 3a and 3b show sections according to IIIA and IIIB of figure 3; Figure 3c shows a schematic enlargement of the protrusion and its geometric elements, defining the slope of the lateral surface of the protrusion at a generic point of the base line of the protrusion;

[0073] Figure 4 shows a flat development of an embossing roller usable in the embossing units, illustrated above in a flat development;

[0074] Figures 4a, 4b, 4c and 4d show sections according to IVA-IVA, IVB-IVB, IVC-IVC and IVD-IVD of figure 4;

[0075] Figure 5 shows a plan development of a portion of an embossing roller in one more modality;

[0076] Figure 6 shows an enlarged schematic cross section of a fabric material with two pleats, obtained by means of an embossing unit, as in figure 1 and the series of protrusions as in figure 4;

[0077] Figure 7 is the section according to VII-VII of figure 6;

[0078] Figure 8 shows an enlarged schematic section of a fabric material embossed through an embossing unit as in figure 1 with an embossing roller having embossing protrusions as in figure 3; and

[0079] Figure 9 shows a local section according to IX-IX of figure 8.

DETAILED DESCRIPTION OF A MODE

[0080] Figure 1 schematically shows an embossing unit, in which the invention can be incorporated. In the illustrated example, the embossing unit is an end-to-end unit, that is, the embossing rollers are arranged so as to laminate the folds forming the fabric material in the grip between the same embossing rollers. embossing, in which at least some protrusions of one embossing roll are pressed against corresponding protrusions on the other embossing roll.

[0081] These embossing units are known inse; an example of such an embossing unit is described, for example, in US 6032712. Here, only the essential elements of the embossing unit will be mentioned. More particularly, the embossing unit of figure 1, indicated entirely with numeral 1, comprises a first embossing roller 3 which cooperates with a first pressure roller 7. The pressure roller 7 has a coating of Elastic production, for example, made of rubber and indicated with 7B.

[0082] A second embossing roller 5 cooperates with the first embossing roller 3. A laminating nip 6 is defined between the embossing rollers 3 and 5. The second embossing roller 5 cooperates with a second pressure roller 9, whose outer cylindrical surface is coated with an elastic production material, indicated with 9B, for example rubber. The two embossing rollers 3 and 5 have embossing protrusions, indicated schematically with P3 in the magnification of figure 1A. The shape of these bulges can vary; some examples will be described below with reference to figures 3 and below.

[0083] With the first embossing roller 3, a gluing unit 11 coatua, which applies glue on the embossed projections, formed by the protuberances of the embossing P3 on a first fold 10 V1 arranged in the embossing grip in relief formed between the embossing roller 3 and the pressing roller 7 and along the rolling nip 6. A second bend V2 is arranged around the pressing roller 9, in the embossing nip defined between the latter and the embossing roller 5, and then glued to the fold VI of the laminating grip 6.

[0084] At the output of the lamination clamp 6, a fabric material is obtained, which is schematically indicated with N.

[0085] Each fold VI and V2 can be, in turn, composed of more layers. In some embodiments not shown, between the two plies VI and V2 a third ply may also be disposed, which may be flat or pre-embossed in a separate embossing unit.

[0086] Figure 2 schematically shows a grouped embossing unit. Such embossing units 20 are known in se. An example of a grouped embossing unit is described in US Patent No. 3867225.

[0087] Schematically, the embossing unit 21 of figure 2 comprises a first embossing roller 23 cooperating with a first pressure roller provided with a side surface coated with an elastic production material 25B, for example rubber . A glue dispenser 27 cooperates with the first embossing roller 23. The embossing unit 21 comprises a second embossing roller 29 which cooperates with a second pressure roller 31 coated with an elastic producing material 3IB .

[0088] A first bend VI is arranged around the first pressure roller 25 and is embossed in the embossing grip formed between the pressure roller 25 and the first embossing roller 23. The glue dispenser 27 applies glue on the embossed projections generated on the first fold VI; thereby, the embossed ply VI is glued to ply V2 by lamination in a laminating nip 36 formed between the first embossing roller 23 and a laminating roller 33. The second ply V2 is disposed around the second roller pressure 31 and embossed in the embossing grip formed between the second pressure roller 31 and the second embossing roller 29.

[0089] Embossing rollers 23 and 29 are provided with protrusions indicated schematically with P9 in figure 2A which shows an enlargement of area IIA 5 of figure 2. The shape of the protrusion will be described in more detail below with reference to some modalities. The arrangement of the embossed projections formed on the folds VI and V2 is defined so that these projections formed on the fold VI are inserted, that is, grouped, in the spaces formed among the embossed projections of the fold V2 or vice versa , as known to those skilled in the art.

[0090] A possible embodiment of the embossing protrusions of one of the embossing rollers described above will be illustrated in greater detail below with reference to figures 3, 3A and 3B.

[0091] Figure 3 shows a plane development of a portion of the cylindrical surface of an embossing roller of the embossing unit 1, 5, 23 or 29. Figure 3 shows substantially part of the surface embossing roller , as it would be if the cylindrical surface of the roller rested on a flat surface; the embossed protrusions, generically indicated with P3 are therefore represented in a front view, that is, orthogonal to the top surface of the protrusions.

[0092] In this mode, each protrusion P3 of the embossing roller has a base 20 delimited by a substantially round base line 41. D indicates the base diameter of the protrusion P3.

[0093] Each protuberance P3 has a top surface indicated with 43. In this embodiment, the top surface 43 has a substantially elliptical shape with a longer dimension dl and a shorter dimension d2. The protrusions are directed so that the longer dimension dl of the top surface 43 is substantially parallel to the machine direction indicated with MD in figure 3, while the shorter dimension d2 is substantially parallel to the cross machine direction indicated by arrow CD in figure 3. As is known, the transverse machine direction CD is substantially parallel to the geometric axis of the roll, while the machine direction MD is orthogonal to the geometric axis of the roll and therefore parallel to the supply direction of the material ply processed by the embossing roller. The MD machine direction corresponds to the longitudinal extent of the fabric material and therefore of the fold VI or the fold V2. The MD machine direction therefore also corresponds to the preferred direction of the cellulosic fibers forming the folds VI and V2, due to the fact that this is also the direction in which the cellulosic fiber pulp is disposed on the machine. paper.

[0094] As mentioned in the introduction, cellulosic bending has a greater mechanical force in the MD machine direction and a lower mechanical force in the CD machine direction as a result of the preferred direction of the cellulosic fibers, according to the MD machine direction relative to the CD machine cross steering.

[0095] Due to the fact that the top surface 43 of each protrusion P3 has an elliptical shape with a longer dimension dl and a shorter dimension d2, while the base surface delimited by the baseline 41 has a round shape with a constant dimension (diameter D), each protrusion P3 has a lateral surface 45 whose inclination is variable along the lateral surface about the central geometric axis of the protrusion. This can be easily understood by looking at figures 3A and 3B, which show two cross sections, according to the orthogonal planes IIIA-IIIA and IIIB -IIIB in figure 3 respectively.

[0096] Practically, the plane of section IIIA-IIIA is orthogonal to the geometric axis of the embossing roller and, therefore, to the transverse direction of machine CD, while the plane of section IIIB-IIIB is a radial plane, i.e. , it contains the geometry axis of the roll.

[0097] α1 and α2 indicate the angles that represent the inclination of the lateral surface, that is, on the side of the protrusion P3 in the section respectively along a plane parallel to the MD machine direction (figure 3A) and along a direction parallel to the CD transverse machine direction (figure 3B). Practically, these angles are formed by the line obtained by the intersection between the section plane and the lateral surface of the protrusion in relation to the base surface of the protrusion, which can be assimilated to a flat surface due to the smaller dimensions of the protrusion in relative to the radius of the embossing roller.

[0098] The angle α1 is larger, that is, the slope of the side surface 45 of the protrusion P3 is larger in the machine direction, while the angle α2 is smaller in the cross machine direction CD.

[0099] Due to this different slope, the portion of embossed cellulosic material 30 by the single protrusion P3 is subjected to a greater percentage of deformation in the MD machine direction and a smaller one in the transverse CD machine direction. This is due to the fact that the side is steeper in machine direction than in cross machine direction. Consequently, as the elongation of the cellulosic fold forming the fabric material is, in absolute terms, equal in both directions and is practically defined by the degree of penetration of said bulge into the elastic producing material lining the pressure roller Correspondingly, this deformation is distributed over a longer length in the cross-machine direction and over a shorter length in the machine direction, so that practically, the elongation percentage will be higher in the machine direction and lesser in the cross-machine direction.

[00100] Substantially, the embossed cellulosic fabric material or the fold will consequently be subjected to a greater tension and % elongation in the machine direction, i.e., in the direction that is more resistant, than in the cross machine direction CD , that is, in the direction that is less resistant. As a result, a cellulosic material is obtained with all the most uniform strength characteristics in various directions. The different degree of embossing, that is, the different percentage of deformation, compensates for the different resistance of cellulosic folding in both CD and MD directions.

[00101] Figure 3 schematically shows an enlargement of a generic P3 protrusion 15 and some geometric elements, on which it is generally possible to define, in general terms, the lateral surface inclination 45 of the P3 protrusion at a generic point IP of a baseline 41 that surrounds the base of the P3 bulge. At the generic point IP along the baseline 41 that delimits the base of the protrusion P3, the line "t" is delineated, tangent to the baseline 41. Then the plane P is delineated passing through the point IP and orthogonal to the tangent t . This plane P intersects the lateral surface 45 of the protrusion P3 along an intersection line "L". In most cases, this L line is a straight line. The inclination of the lateral surface 45 of the protrusion P3 at the point IP is provided by the angle α formed between the line L and the base surface surrounded by the base line 41 which can be approximated to a plane. In the most generic case, in which the intersection line L of plane P with the side surface 45 is not a straight line or cannot be approximated to a straight line, it will be possible to define a point 2P on the edge line of this line. Front or top surface 43. A line or line segment that passes through points IP and 2P is now considered. This line forms with the base surface of the protrusion the angle α which defines the (average) slope of the lateral surface 45 at point IP.

[00102] In figures 3A and 3B, H indicates the height of the protrusion. Height H is the distance between the top surface of the protrusion and the base. As the radius dimension of the embossing roller is significantly larger (by some orders) than the dimension (height and width) of the protrusions, the top surface 43 and base surface are very small relative to the diameter of the roller. (both over the top and the base of the bulges); these surfaces can therefore be approximated to flat surfaces. The height H is then the distance between the two flat surfaces. Practically, the closed line delimiting the base of a single protrusion is on a cylindrical surface which can be approximated, for the reasons mentioned above, to a flat surface. What has been illustrated above applies both to the protrusions in figures 3A to 3C and to the protrusions with different shapes, eg those described below.

[00103] Figure 4 shows, similarly to Figure 3, a plane development of a portion of an embossing roller of a different modality.

[00104] In this case, the P3 protrusions that have a lateral surface with a variable slope are combined with a second series of P3X protrusions shaped as a truncated cone with a round base, which therefore have a constant slope of the lateral surface to the along the entire extension bulge. Preferably, as shown in Figure 4, the P3 bulges are significantly larger than the P3X bulges. In particular, each P3X bulge is surrounded by six P3 bulges. In other embodiments, the P3X protrusions can be omitted and, if necessary, replaced by the P3 protrusions.

[00105] A similar configuration with a P3X truncated cone shaped protrusion can also be provided in combination with the P3 protrusions designed as in figure 3.

[00106] The change of inclination of the sides of the protrusion P3 of figures 4, 4A and 4B is obtained with a different geometry from that represented in figures 3, 3A and 3B.

[00107] More particularly, the protrusions P3 of figure 4, 4A, 4B have a base surface delimited by an elliptical curve 51. The front surface of the protrusions P3 indicated with 53 has a rounded extension. D1 indicates the diameter of the frontal surfaces 53, while D2 and D3 respectively indicate the longest dimension and the shortest dimension of the elliptical bases of the protrusion P3, delimited by curve 51.

[00108] As shown in the two sections of figures 4A and 4B, in this way an inclination is also obtained in larger size according to the angle α1 and smaller according to the angle α2 of the lateral surface 55 of the protrusions P3 in this modality. The protrusions are directed so that the longer dimension D2 of the base of the protrusions P3 is substantially parallel to the cross machine direction CD, while the shorter dimension D3 is parallel to the machine direction MD, for the same reasons described in more detail with reference to figures 3, 3A and 3B.

[00109] Therefore, in this mode again, through the P3 protuberances with variable inclination, the percentage of deformation, i.e. a % of elongation, along the embossing of the cellulosic fold is obtained, greater in the machine direction and smaller in the cross machine steering.

[00110] As mentioned, the P3X protrusions have, vice versa, sides with constant inclination, as schematically represented in the two sections of figures 4C and 4D obtained according to orthogonal planes, parallel to the transverse machine direction and the machine direction respectively.

[00111] Figure 5 shows, in a plane representation similar to that of figures 3 and 4, one more embodiment of an embossing roller according to the invention. MD and CD again indicate machine direction and cross machine direction.

[00112] In this mode, the embossing roller has two series of protuberances 15 indicated by P3 and P3Y, with different format and orientation. The P3 protrusions are designed like the P3 protrusions in Figure 4 and Figures 4A and 4B. P3Y protrusions are similar to P3 protrusions, but oriented differently with the longer dimension of the elliptical base parallel to the machine direction and the shorter dimension parallel to the transverse machine direction. Furthermore, in the embodiment of Figure 5, insofar as the P3Y protrusions are of interest, the difference between the diameter of the top surface dimension and the two maximum and minimum dimensions of the base is smaller than the dimensions of the P3 protrusions . In other embodiments, the P3Y bulges may differ from the P3 bulge only in direction, having a geometric shape identical to the P3 bulges.

[00113] It is important to note that the number of protrusions P3Y is substantially less than the number of protrusions P3 so as to maintain the higher percentage of deformation in the machine direction than in the cross-machine direction. In the illustrated embodiment, each protrusion P3Y is surrounded by six protrusions P3 arranged with the centers of the round top surfaces according to the vertices of a hexagon which, in this example, is slightly irregular due to the effect of the elliptical shape of the bases of the protrusions P3. Those P3 bulges that surround the P3Y bulge form a set of bulges.

[00114] As shown in figure 5, the sets of protrusions are arranged according to alignments, which are slightly inclined in relation to the MD machine direction and the CD cross machine direction. More particularly, the alignment directions of the assemblies, indicated with L1 and L2 in Figure 5, form angles of about 5° with respect to the cross machine direction CD and the machine direction MD respectively. In this way, a more uniform use of the pressure rollers and less vibrations in the machine are obtained.

[00115] Figures 6 to 9 schematically show cross-sections of portions of fabric material that can be obtained with a projected embossing unit as in figure 1 and with protrusions of the projected embossing as described above. More particularly, Figure 6 shows the portion of a fabric material N formed by embossed plies VI and V2 with embossed projections S1 and S2 glued in correspondence with the inwardly facing front surfaces of the fabric material and indicated with SF. Figure 7 shows a cross-section according to VII-VII of Figure 6, waves of the embossed projections SI, S2 on the folds VI and V2 have a shape corresponding to that of the embossing protrusions of figures 4A and 4B. The transverse planes of figures 6 and 7 are directed according to the machine direction and the transverse machine direction respectively.

[00116] The dimension of the top surface is equal in the two orthogonal directions of the sections in figures 6 and 7, since in this case, they are round surfaces, while the base surfaces of the projections S1 and S2 have dimensions varying between a maximum value. (in the section in figure 7, according to cross machine direction) and a minimum value (in section in figure 6, according to machine direction).

[00117] Figures 8 and 9 show, vice versa, local sections according to the orthogonal planes of a fabric material N formed again by folds VI and V2 with projections engraved in relief S1 and S2, whose shape corresponds to the shape of the protrusions of the embossing of figures 3, 3A and 3B, with SF elliptically shaped front surfaces and round base surfaces. In both cases, the slope of the embossed projections S1, S2 changes to machine direction (figure 8 section) and cross machine direction respectively (figure 9 section).

[00118] In general, the shapes of the embossed projections of the fabric material, obtained with an embossing roller or an embossing unit according to the invention will correspond to the shapes of the protrusions of the embossing roller or to the rollers of the embossing unit. The height of the embossed projections is generally different from the height of the embossed protrusions and it depends on the stiffness of the elastic-produced coating material, the pressure rollers and the linear pressure with which the pressure rollers press the rollers of embossing.

[00119] The characteristics of the embossed protrusions are therefore the same as the embossed projections formed on the folds of the fabric material.

[00120] The cross machine direction and the machine direction can be defined in the final product, which will generally be wound in the form of a roll. When the product is wound onto a roll, the machine direction is that of the longitudinal development of the fabric material and the transverse machine direction is that parallel to the geometric axis of the roll winding. Furthermore, when the fabric material is cut into sheets to form, for example, folded products such as napkins, handkerchiefs or the like in the final product, the machine direction can be detected as the direction of preferential orientation of the cellulosic fibers forming the folds that make up the fabric material, while the transverse machine direction is that orthogonal to the machine direction.

[00121] The following table shows experimental comparison values, obtained by embossing the paper material through a traditional embossing roller and embossing rollers according to what has been described here. The data in the table refer to the processing of a product subsequently wound onto a roll and they are useful for comparing the mechanical force parameters in the MD machine direction and the CD cross machine direction in the various cases, as well as for checking the obtaining the apparent thickness supplied and the winding volumes. In the left column, some useful parameters of the products used are shown. In the following columns, parameter values are shown for the various types of materials. More precisely, the four materials tested are as follows: B/S: unembossed fold of virgin paper

[00122] 1(6386): traditional embossing pattern with conical bulges, density 44.86 bulges/cm, embossing pressure 2.8 bar. Embossing pressure is the air pressure of the cylinder-type piston activators used to press the pressure roller and the embossing roller together. This parameter is significant in comparing and evaluating the various examples.

[00123] 11(6984): embossing pattern, as in figure 5, with 45.32 protuberances/cm, embossing pressure and winding length as above;

[00124] 111(6984): embossing pattern, as in figure 5, with 45.32 protuberances/cm , embossing pressure 3.5 bar and winding length 40m;

[00125] From the table below, it becomes apparent that for virgin paper (B/S) the machine direction (MD) strength is almost double the cross machine direction (CD) strength. The % elongation at break in the machine direction (MD) is equal to 15.7% while in the cross machine direction (CD) it is equal to 4.5%. This confirms that virgin paper, even before embossing, has a significantly lower tensile strength in the cross machine direction than in the machine direction. The second column shows how strength and % elongation data are heavily degraded by embossing. In fact, the resistance in the machine direction decreases from 250 to 203 N/m and in the cross machine direction from 128 to 68 N/m. The proportion between strength values decreases from 51.2% to 33.5%.

[00126] This means that embossing decreases the entire tensile strength and increases the anisotropic behavior of the paper, that is, its characteristic of lower strength in the cross-machine direction than in the machine direction.

[00127] The third sample illustrates that in embossing with protuberances as described above, degradation is less. In particular, the resistance in the machine direction only decreases up to 220 N/m, while in the cross machine direction only by 80 N/m. The ratio of breaking strength values decreases from 51.2 (not embossed paper) to 36.4 (embossed paper); this value is higher than the 33.5 obtained with a traditional embossing.

[00128] The fourth sample was obtained with the same embossing pattern, but with a higher pressure in the embossing. This was necessary to obtain a volume of embossed material equivalent to the volume of material in the second sample (standard embossing). Volume is provided by the diameter of the wound roll. In the case of the second sample (standard embossing) with 40 m of cellulosic wound material, a roll of 100 m diameter was obtained, while with the third sample only an 85 m diameter was obtained. Consequently, in the fourth sample, a higher embossing pressure was used, generating higher embossed projections with a consequent stronger degradation of tensile strength. In reality, the resistance in the machine direction goes from 220 N/m to 206 N/m, while in the cross machine directions it is still 80 N/m. The ratio of breaking strength in the cross machine direction to the machine direction improves from 36.4 for the third sample to 38.8 for the fourth sample.

[00129] In conclusion, embossing through the protuberances that have sides with variable slope allows, therefore, to obtain a cellulosic fabric material with less heterogeneous elongation at break in both MD and CD directions compared to an embossed material with a traditional embossing pattern comparable to the dimensions of the protuberances and therefore the density and volume of the final product (diameter of roll with equal length of wrapped fabric material).

[00130] It is also important to note that the degradation of tensile strength in the cross machine direction is made by embossing in all cases. However, with an embossing pattern as described above with the protrusions having variable slope side surfaces, this degradation is significantly less and does not increase when the embossing pressure increases beyond a given threshold.

[00131] The above examples show different shapes of embossed protrusions and different and corresponding embossed projections. In general, it should be noted that the shape of the bulges can be chosen, according to the characteristics of virgin paper. In other words, protrusions with different shapes can be arbitrarily combined to increase strength in a first direction without, however, risking strength in the orthogonal direction or for aesthetic reasons.

[00132] In fact, the tests conducted proved that for each bulge shape (or series or set of bulges) corresponds to a different reaction from the processed paper, that is, different results are obtained for the tensile strengths according to the two main directions (CD and MD).

[00133] In the illustrated examples reference has always been made to protrusions with a round or elliptical base or top, however, it is understood that other shapes can be used, for example protrusions with a square section (diamonds, rectangles, squares) or polygonal section with more than four sides with sharp corners or differently joined, obtained by chemical pickling or mechanical chip removal, provided so that the sides of the protrusion are angled differently between adjacent sides of the same protrusion, that is, between areas consecutively along the lateral surface of the same protrusion, so as to deform the paper in the ways indicated above.

[00134] It is understood that the drawings show only one example provided by way of a practical demonstration of the present invention, which may vary in forms and arrangements without, however, departing from the scope of the concept that highlights the present invention. Any reference numbers in the claims are provided for the sole purpose of making them easier to read in light of the description and drawings and they in no way limit the scope of protection represented by the claims.

Claims (23)

1. Embossing roller (3, 5, 23, 29) having a geometric axis of rotation and a substantially cylindrical outer surface provided with a plurality of embossing protrusions (P3), each embossing protrusion having a base, a side surface (45, 55) and a top surface (43; 53), said base and said top surface being delimited and surrounded by closed lines (41; 51), the distance between base and surface of top defining a height of the protrusion, wherein the lateral surface (45; 55) of at least some of said protrusions of the embossing (P3) has a variable inclination along the length of the perimeter of the protrusion, said inclination changing continuously along the perimeter of the embossing protrusion, so that the lateral surface of the protrusions are devoid of sharp corners, so the full embossing tension of a ply of cellulosic material (V1, V2), etched in embossed by said embossing roller (3, 5, 23, 25), is smaller in a direction (CD) parallel to the geometric axis of rotation of the embossing roller (3, 5, 23, 25) and larger in a direction (MD) orthogonal to the geometric axis of rotation of the embossing roller, for at least some of said protrusions of the embossing (P3), said inclination being greater in a direction (MD) orthogonal to the geometric axis of roll rotation and smaller in a direction (CD) parallel to the geometric axis of roll rotation. 2. Embossing roller according to claim 1, characterized in that the base of said protrusions of the embossing (P3), delimited and surrounded by said closed line (41, 51), is on a surface cylindrical embossing roller, each embossing protrusion having constant height along its perimeter. 3. Embossing roller according to claim 1 or 2, characterized in that said protrusions (P3) are distributed according to a density comprised between 10 and 200 protrusions/cm. 4. Embossing roller according to any one of the preceding claims, characterized in that the bases of said embossing protrusions (P3) have a longer dimension and a shorter dimension and that the proportion between the dimension longer and the shortest dimension is greater than 1 and equal to or less than 10, preferably it is comprised between 1.1 and 7 and most preferably between 1.5 and 5. 5. Embossing roller according to claim 4, characterized in that the top surfaces have a substantially round extension. 6. Embossing roller according to claim 4 or 5, characterized in that most of said embossing protrusions (P3) are directed with their longest dimension in a direction (CD) parallel to the axis geometric of the embossing roller. 7. Embossing roller according to claim 4 or 5, characterized in that a first series of said embossing protrusions (P3) is directed with its longest dimension in a direction (CD) parallel to the geometric axis of the embossing roller and a second series of said embossing protrusions (P3Y) are directed with their shortest dimension in a direction (CD) parallel to the geometric axis of the embossing roller; and that the number of protrusions of the embossing (P3) of the first series is greater than the number of protrusions of the embossing (P3Y) of the second series. 8. Embossing roller according to claim 6 or 7, characterized in that the ratio between the number of protrusions of the embossing (P3) of the first series and the number of protrusions of the embossing (P3Y) of the second series is between 1.2 and 5, preferably between 1.5 and 4 and more preferably between 1.8 and 2.5. 9. Embossing roller according to claim 7 or 8, characterized in that each embossing protrusion (P3Y) of said second series is surrounded by a plurality of embossing protrusions (P3) of the first series, thus forming a set or series of protuberances. 10. Embossing roller according to claim 9, characterized in that each set of protrusions comprises six embossing protrusions of said first series of embossing protrusions. 11. Embossing roller according to claim 9, characterized in that said sets of protuberances (P3) are aligned according to helical lines extending over the cylindrical surface embossing roller. 12. Embossing roller according to claim 11, characterized in that said helical lines have an inclination of between 1° and 10°, preferably between 2° and 8° and more preferably between 3 ° and 7° with respect to the geometric axis of the embossing roller. 13. Embossing roller according to any one of claims 4 to 12, characterized in that the bases of said protrusions of the embossing (P3) have a substantially elliptical shape. 14. Embossing roller according to any one of claims 1 to 3, characterized in that the top surfaces of the protrusions of the embossing have a longer dimension and a shorter dimension and that the proportion between the longer dimension and the shortest dimension is greater than 1 and equal to or less than 10, preferably comprised between 1.1 and 7 and more preferably comprised between 1.5 and 5. 15. Embossing roller according to claim 14, characterized in that at least some of said embossing protrusions (P3) have an approximately round base. 16. Embossing roller according to claim 14 or 15, characterized in that at least the majority of said embossing protrusions are directed with their shorter dimension substantially parallel to the geometric axis of the embossing roller. relief. 17. Embossing roller according to claim 16, characterized in that all said embossing protrusions are directed with their longest dimension substantially parallel to the geometric axis of the embossing roller. 18. Embossing roller according to any one of the preceding claims, characterized in that it comprises additional embossing protrusions (P3X), formatted differently from said embossing protrusions. 19. Embossing roller according to claim 18, characterized in that said additional protrusions of the embossing have a lateral surface with substantially constant inclination with respect to the radial direction. 20. Embossing unit comprising at least a first embossing roller (3; 5; 23; 29) and a first pressure roller (7; 9; 25); 31) provided with an elastically produced coating layer (7B; 9B; 25B; 31B), defining in place a first embossing grip and at least a first path for a first ply (V1) of fabric material and extending along a said embossing grip, characterized in that a said first embossing roller (3; 5; 23; 29) is an embossing roller as defined in one or more of the preceding claims . 21. Embossing unit according to claim 20, characterized in that it comprises a second embossing roller (3; 5; 23; 29) and a second pressure roller (7; 9; 25 31) provided with an elastically produced coating layer (7B; 9B; 25B,; 31B) defining in place a second embossing grip and at least one second path for a second ply (V1; V2) of material of fabric and extending along a said embossing grip, said second embossing roller being an embossing roller as defined in one or more of claims 1 to 15. 22. Cellulosic fabric material (N) made of tissue paper characterized in that it comprises at least one ply (V1; V2) of embossed cellulosic material with embossed projections (S1; S2) and preferably having cellulosic fibers oriented in the machine direction (MD), in which each embossed projection comprises a base, a side surface and a top surface, said base and said top surface being delimited and surrounded by closed lines, in which the surface The side of at least some of said embossed projections has a variable slope along the length of the perimeter of the protrusion, said slope continuously changing along the perimeter of the embossed projections, so that an embossing element and, thus, the percentage elongation of the fabric material in said machine direction is greater than the embossing element and thus the percentage elongation of the material of fabric in the cross machine direction. 23. Method for equalizing the mechanical strength of an embossed cellulosic tissue material (N) made of tissue paper and having a preferential distribution of cellulosic fiber in the machine direction (MD); said method characterized in that it comprises the steps to: arrange at least a first embossing roller (3; 5; 23; 29) and a first pressure roller (7; 9; 25; 31) provided with a elastic production coating layer (7B; 9B; 25B; 31B), defining in place a first embossing grip and at least a first path for a fold (V1; V2) of fabric material, said path extending along the first embossing nip; providing, on a cylindrical side surface of the embossing roller (3; 5; 23; 29), a plurality of embossing protrusions (P3; P3Y), where at least some of them have a lateral surface (45; 55) with a variable slope along the length of the perimeter of the embossing protrusion, at least some of said embossing protrusions (P3; P3Y) having greater slope in a direction orthogonal to the geometric axis of roll rotation and lowest slope in u in the direction parallel to the geometric axis of rotation of the roll; emboss the fold (V1; V2) of fabric material in embossing clamping through embossing protrusions (P3; P3Y) causing said embossing protrusions to penetrate the elastic production coating layer (7B; 9B; 25B; 31B ) of the pressure roller (7; 9; 25; 31), the variable inclination of the lateral surface (45; 55) of at least some of said protrusions of the embossing (P3; P3Y) generating a total bending stress of the engraving embossing of embossed cellulosic material smaller in a direction (CD) parallel to the geometric axis of rotation of the embossing roller (cross machine direction) and larger in a direction (MD) orthogonal to the geometric axis of rotation of the embossing roller. embossing (machine direction).

Images