Printable multilayer paper for packaging and a method for its production.

Abstract

Printable multilayer paper for packaging and a method for its production. The invention relates to a method for producing a printable multilayer paper, or paper intended for printing, for packaging, as well as a printable multilayer paper, or paper intended for printing, for packaging. The method comprises supplying or producing a first bleached pulp comprising cellulose fiber, as well as supplying or producing a second pulp comprising cellulose fibers. As the second pulp comprising cellulose fibers, a mixture is supplied or produced herein consisting of, relating to 100% by weight of the total dry matter of the second pulp, 40% by weight to 80% by weight of unbleached cellulose material and 20% by weight to 60% by weight of bleached cellulose material.

Description

1 / 28 DESCRIPTIVE REPORT “PRINTABLE MULTILAYER PAPER FOR PACKAGING AND METHOD FOR ITS PRODUCTION”

[001] The invention relates to a method for producing a printable or printable multilayer paper for packaging, as well as a printable or printable multilayer paper for packaging.

[002] Manufacturers and / or distributors of products generally require printed packaging for their products, for example, to display graphic representations of the products contained and / or product information to consumers. Currently, such product packaging is practically commonplace in all sectors, whether in food or household appliance production or in commerce, for example. Increasingly, high print quality, especially high color density, brightness, and contrast of printed images applied to packaging paper, is necessary to present the product contained in the most attractive way possible in order to stimulate purchases.

[003] Printable packaging papers can, on the one hand, be designed as stand-alone packaging papers, as in the case of outer packaging papers, for example. Alternatively, a generic packaging paper can also form a component, particularly an outer printable paper layer of packaging, as is often the case with cardboard packaging. Generic multilayer or paper-layered paper papers are also called liner, paper liner, or kraft liner. In this sense, the objective, printable, multilayer packaging paper can also be called liner, paper liner, or kraft liner.

[004] To enable the best possible print quality, particularly high color density and brightness, as well as contrast, a surface with a high degree of whiteness is desirable for printing on the packaging papers in question. For this purpose, bleached pulp is frequently used to produce printable papers for packaging. On the one hand, they are Petition 870230091874, dated 10 / 17 / 2023, pp. 188 / 221 2 / 28 known printable packaging papers are produced entirely from bleached cellulose or consist exclusively of bleached cellulose fiber material. The disadvantages of these fully bleached papers include deterioration, primarily of the mechanical properties of the resulting packaging, due to the chemical treatment of the cellulose, as well as the increased load of chemicals required by the process and, naturally, the associated increased production costs.

[005] In addition, there are known multi-layered packaging papers or paper liners which have an outer top layer or cover layer of bleached fiber material intended for printing and an underlying backing layer of unbleached cellulose fiber material, including unbleached recycled fiber material. However, the surface of the top layer of these multi-layered packaging papers intended for printing generally has a greyish or brown appearance, depending on the type of unbleached cellulose material used to make the backing layer. This is because the unbleached fiber material of this lower backing layer practically shines through the top or cover layer of bleached fiber material. Naturally, this results in disadvantages with regard to print quality, particularly, the printed images may appear distorted in terms of color.To achieve a high degree of whiteness in these multilayer packaging papers, the use of a top layer with a very high basis weight was previously necessary or known. However, this, in turn, has a negative impact in terms of resource efficiency and manufacturing costs.

[006] A multilayer packaging paper or a corresponding (paper) liner is known, for example, from EP 1 392 923 B1.

[007] The objective of the present invention is to overcome the existing disadvantages of the prior art and to provide, on the one hand, an improved method, from an ecological and economic point of view, for the production of printable paper. Petition 870230091874, dated 10 / 17 / 2023, pp. 189 / 221 3 / 28 for packaging, by means of a method that makes it possible to produce paper with good mechanical properties and, at the same time, good printability, especially high whiteness. Furthermore, the invention aims to provide packaging paper with good mechanical properties and, at the same time, good printability, which is produced in an improved way, from an economic and environmental point of view.

[008] This objective is solved by a method in accordance with the claims.

[009] The method, according to the invention, for producing a printable or printable multilayer paper for packaging or wrapping paper comprises the steps

[010] To supply or produce a first bleached pulp comprising cellulose fibers and production of a first sheet of paper comprising the first pulp by forming a first pulp comprising the first pulp and dewatering / drying that first pulp,

[011] To supply or produce a second cellulose comprising cellulose fibers and to produce a second sheet of paper comprising the second cellulose by forming a second pulp comprising the second cellulose and dehydrating / drying that second pulp,

[012] Joining both sheets of paper into a multilayer sheet of paper, in such a way that, through the first sheet of paper, an upper or outer covering layer is formed and, through the second sheet of paper, a supporting layer of the multilayer sheet of paper is formed directly joined to this upper covering layer,

[013] optionally, produce one or more other layers of paper and join at least one of these other layers of paper to the support layer,

[014] optionally, another drying of the multilayer paper sheet,

[015] and make the multilayer paper sheet.

[016] As second cellulose comprising cellulose fibers, it is supplied or Petition 870230091874, dated 10 / 17 / 2023, pp. 190 / 221 4 / 28 produced a mixture consisting of, corresponding to 100% by weight of the total dry matter of the second pulp, 40% by weight to 80% by weight of unbleached pulp material and 20% by weight to 60% by weight of bleached pulp material.

[017] Here and hereafter, the term pulp is understood to mean an aqueous suspension of the respective cellulose. As usual, other terms such as fiber pulp, fiber-water suspension, fiber suspension, pulp suspension, etc. may also be used synonymously. An initial consistency of the first and second pulp may be, for example, 0.5% to 2%. Optionally, common auxiliary materials may also be added to the first and / or second pulp, in addition to the respective cellulose materials. Examples include bulk starch, PAC (polyaluminum chloride), ASA (alkyl succinic anhydride) or other sizing agents, moisture-resistant agents, bentonite, etc. As is known, the proportion by weight of these auxiliary chemicals in the pulps may be small.

[018] By unbleached cellulose material, it should be understood, in a very general way, a cellulose material that is not bleached in the course of the production process of printable multilayer paper.

[019] By means of the method mentioned above, a packaging paper can be produced with high whiteness and, at the same time, good mechanical properties. This occurs despite the use of a high proportion of unbleached cellulose material. Surprisingly, the basis weight or thickness of the cover layer can also be kept low without significantly compromising the whiteness of the surface of the cover layer intended for printing, as explained in more detail below, based on the corresponding values ​​of the packaging paper. In general, by means of the method specified above, a packaging paper or a packaging paper with good printability can be produced, particularly, high-quality printing images can be applied with color fidelity, which, moreover, meets the requirements for packaging papers in terms of robustness and mechanical resistance. Petition 870230091874, dated 10 / 17 / 2023, pp. 191 / 221 5 / 28

[020] At the same time, compared with the production of fully bleached packaging paper, the chemical load of the process can be reduced depending on the method. Due to the reduced use of bleached cellulose material and the low permissible basis weight of the cover layer, moreover, the amount of cellulose used can generally be kept small. This and the reduction in the use of chemicals also have a positive effect on the production costs of packaging paper.

[021] Preferably, as second pulp comprising cellulose fibers, a mixture may be supplied or produced consisting of, for 100% by weight of the total dry matter of the second pulp, 45% by weight to 75% by weight of unbleached cellulose material and 25% by weight to 55% by weight of bleached cellulose material.

[022] The unbleached cellulose material of the second cellulose may preferably be selected from a group consisting of fresh, unbleached short-fiber cellulose material, unbleached recycled fiber cellulose material or a mixture of unbleached cellulose materials from this group.

[023] Recycled fiber cellulose material should be understood, in particular, as cellulose material obtained by reprocessing used paper waste. Recycled fiber cellulose material is conceptually defined in ISO 4046-4:2016. The term recycled fiber cellulose material does not include cellulose material discarded or lost during the paper packaging production process, as defined in ISO 4046-3, also commonly called scrap.

[024] As bleached cellulose material for the second cellulose, a mixture of 30% by weight to 80% by weight of bleached short-fiber cellulose material and 20% by weight to 70% by weight of bleached long-fiber cellulose material may preferably be used.

[025] For the formation of bleached cellulose material from first cellulose, Petition 870230091874, dated 10 / 17 / 2023, pp. 192 / 221 6 / 28 can be used, particularly 70% by weight - 100% by weight of bleached short-fiber cellulose material. Depending on the requirements, however, up to 30% by weight of long-fiber cellulose material can also be used for the formation of bleached cellulose material from the first celluloses.

[026] The cellulose materials mentioned proved to be particularly suitable for the production of a packaging paper with desired or sufficiently good properties, particularly for obtaining good mechanical properties or sufficiently good strength and, at the same time, good printability.

[027] In an improvement of the method, it can be provided that, immediately before joining the first sheet of paper and the second sheet of paper, a dry content of the first sheet of paper is adjusted from 3% to 50% and a dry content of the second sheet of paper, from 3% to 50%.

[028] As a result, the joining of the two sheets of paper within the two indicated dry contents was particularly successful. Subsequently, the cover layer and the backing layer can also offer excellent adhesion to each other, for packaging paper. In particular, delamination of the two layers can be effectively avoided.

[029] Also, 100 kg to 150 kg of white pigment charge per ton of total dry matter of the first bleached pulp may be added to the first pulp or the first sheet of paper.

[030] Through this measure, it is possible to further enhance the printability of the surface of the packaging paper's cover layer. The white pigment load provides the cover layer with additional opacity or a covering effect compared to the underlying support layer. Surprisingly, the addition of such a large amount of filler, as indicated above, proved to be possible without, in particular, excessive losses in the mechanical properties of the packaging paper, particularly its mechanical strength, having to be accepted. Furthermore, the production costs of the paper for Petition 870230091874, dated 10 / 17 / 2023, pp. 193 / 221 7 / 28 of the packaging can be reduced even further this way.

[031] Preferably, calcium carbonate or lime may be added to the first pulp or the first sheet of paper as a white pigment filler.

[032] In a preferred embodiment of the method, it can be provided that the multilayer paper sheet, after complete drying, is produced to a final dry content with basis weight of 75 g / m2 to 120 g / m2, wherein the cover layer is produced with a basis weight of 50 g / m2 to 70 g / m2, and wherein the basis weight ratio of the cover layer to the basis weight of the support layer is 1.2:1 to 2:1.

[033] Basis weights or basis weights can be adjusted, as is already known, by controlling various method parameters, such as consistencies in a paper machine approach flow system, the amounts of pulp and consistency of the regulator applied to the regulator of a paper machine, passage speeds in different sections of a paper machine, and so on. A paper with the specified basis weights and basis weight ratios has proven to be particularly suitable for combining good mechanical properties and good printability. Furthermore, the specified measurements can provide a packaging paper with low material consumption, yet still with good properties.

[034] In another embodiment of the method, the second cellulose may be supplied or produced with a Schopper-Riegler value according to ISO 5267-1:2000 of 20 °SR to 35 °SR.

[035] A corresponding cellulose material proved to be particularly suitable for the formation of the second cellulose and subsequently proved to form the paper support layer for packaging. As with the initial cellulose materials, cellulose within the aforementioned range for the SchopperRiegler value can be obtained by means of mechanical milling and / or defibration, particularly in so-called refiners.

[036] Specifically, in a preferred application of the method, the second Petition 870230091874, dated 10 / 17 / 2023, pp. 194 / 221 8 / 28 cellulose can be supplied or produced with a kappa number according to ISO 302:2015 of 20 to 65.

[037] By using a second pulp with the corresponding kappa number from the indicated range, it is possible to define an appropriate degree of coloration of the paper support layer or packaging papers, without having to absorb long-term losses in the mechanical strength of the packaging paper. A kappa number within the indicated range can be adjusted, as is known, mainly by the selection and / or preparation of the corresponding cellulose materials, especially during chemical pulping, as well as by the composition of the cellulose materials to form the second pulp.

[038] In addition, the first bleached pulp may be supplied or produced with a kappa number according to ISO 302:2015 of 12 or lower, preferably 10 or lower.

[039] Suitable for the purpose, the method can also provide a leveling of the surface of the covering layer of the multilayer paper sheet intended for printing. In particular, this leveling can be achieved by calendering this surface using a calender, such as a hard-nozzle calender, a soft-nozzle calender, a long-nozzle calender, a shoe calender, or a metal belt calender.

[040] In the broadest sense, this can improve the quality of the surface intended for printing, further enhancing the quality of the printed images applied to that surface. Several control parameters, for example, pressure, temperature, and dwell time, for calendering in order to obtain the desired surface properties, for example, surface roughness, are generally familiar to those skilled in the art.

[041] The objective of the invention is also solved by a multilayer paper for or intended for packaging, printable or designed for printing, according to the claims.

[042] Packaging paper comprises

[043] - a topmost covering layer comprising, Petition 870230091874, dated 10 / 17 / 2023, pp. 195 / 221 9 / 28 predominantly, a first bleached cellulose fiber material or consisting predominantly of a first bleached cellulose fiber material,

[044] - as well as a support layer comprising predominantly a second cellulose fiber material or consisting predominantly of a bleached cellulose fiber material, bonded directly to the uppermost cover layer.

[045] The second cellulose fiber material is formed by a mixture consisting of, in relation to 100 % by weight of the total dry matter of the second cellulose fiber material, 40 % by weight to 80 % by weight of unbleached fiber material and 20 % by weight to 60 % by weight of bleached fiber material.

[046] Through these characteristics, it is possible to supply a very good printable packaging paper, which, in particular, exhibits a high degree of whiteness on the surface to be printed of the cover layer, and thus also ensures high gloss and color fidelity of the images printed on this substrate. At the same time, packaging paper with good mechanical properties can be supplied. Surprisingly, the basis weight or thickness of the cover layer can also be kept low without significantly compromising the whiteness of the surface of the cover layer intended for printing. This is explained in more detail below, based on the corresponding values ​​of the packaging paper.

[047] Furthermore, a corresponding packaging paper can be produced by a method as described above, which method stands out for its high efficiency, both ecologically and economically. Preferably, the second cellulose fiber material can be formed from a mixture consisting of, in relation to 100% by weight of the total dry matter of the second cellulose fiber material, 45% by weight to 75% by weight of unbleached fiber material and 25% by weight to 55% by weight of bleached fiber material. Unbleached fiber material means fiber material that, during the production process of the printable multilayer paper, has not been bleached or results from a material of Petition 870230091874, dated 10 / 17 / 2023, pp. 196 / 221 10 / 28 unbleached cellulose.

[048] The cover layer of packaging paper, or its outward-facing surface, is intended for printing, and this cover layer, in the application of the paper, forms the outer layer of packaging intended for printing. Packaging paper can be used primarily independently for packaging purposes as primary packaging and is also suitable as outer packaging paper for wrapping articles or objects. Another common use of packaging paper is to apply or glue it to another primary packaging, such as cardboard. In particular, it is possible to use packaging paper as printable liner paper for cardboard or similar packaging. Even so, the paper in question is suitable as a component of secondary packaging or alone, as secondary packaging, i.e., as packaging or a packaging component of packaging without direct contact with the packaged products.

[049] In a preferred embodiment of packaging paper, the unbleached fiber material of the second cellulose fiber material may be selected from a group consisting of fresh unbleached long fiber material, unbleached recycled fiber material or a mixture of unbleached fiber materials from that group.

[050] As discussed above in relation to the term recycled fiber cellulose material, the term recycled fiber material also refers to a fiber material processed by reprocessing used paper waste into new paper, in this case, multilayer packaging paper. As mentioned above, reference is also made to the conceptual definition according to ISO 40464:2016 with respect to the term recycled fiber material.

[051] In addition, the bleached fiber material of the second cellulose fiber material may be formed by a mixture of 30% by weight to 80% by weight of bleached short fiber material and 20% by weight to 70% by weight of bleached long fiber material. Petition 870230091874, dated 10 / 17 / 2023, pp. 197 / 221 11 / 28

[052] Furthermore, it can be provided that the bleached fiber material of the first cellulose fiber material comprises 70% by weight to 100% by weight of the bleached short fiber material. By this, the bleached fiber material of the first cellulose fiber material also comprises 30% by weight of bleached long fiber material.

[053] The bleached fiber material of the second cellulose fiber material may, in particular, have a Kappa number according to ISO 302:2015 of 12 or lower, preferably 10 or lower, and particularly 5 or lower.

[054] The cellulose fiber materials mentioned have proven to be particularly suitable for obtaining desired or sufficiently good properties, particularly for obtaining good mechanical properties or sufficiently good strength and, at the same time, good printability.

[055] In another embodiment of packaging paper, its cover layer may have a white pigment load, in which, an ash residue according to ISO 1762:2015 of the cover layer may be from 10% by weight to 14% by weight.

[056] By means of this, it is possible to further enhance the printability of the surface of the packaging paper's cover layer. The white pigment load provides the cover layer with additional opacity or a covering effect compared to the underlying support layer. Surprisingly, it has been shown that with such a high filler content, it is not necessary to absorb excessive losses in the mechanical properties of the packaging paper. The measurable ash residue in papers is mainly formed by mineral or inorganic additives, depending on the materials or additives used in the production process. Regarding the method for producing packaging paper, it should be noted, for the sake of completeness, that during the dewatering or drying process of the paper sheet pulp formed in a paper machine, there is always an inevitable loss of the inorganic aggregates used, for example, during dewatering in a wire section.This inevitable loss. Petition 870230091874, dated 10 / 17 / 2023, pp. 198 / 221 12 / 28 therefore leads to a reduction in measurable ash residue on the paper compared to the input quantities of inorganic aggregates added in the method.

[057] Preferably, the white pigment filler can be made up of calcium carbonate or lime.

[058] In an improvement of packaging paper, the paper may exhibit, when its cover layer is impacted by water, according to ISO 535:2014, a Cobb-60 value of 30 g / m2 to 40 g / m2.

[059] This feature can improve the printability of packaging paper. In particular, the absorption of common water-based inks and their drying on the paper can be improved and, in particular, it is possible to avoid unwanted bleeding of printing ink. The Cobb-60 value can be influenced mainly by the materials used, as is known, but also by the use of additives, such as sizing agents, for example, alkenyl succinic anhydride (ASA).

[060] Packaging paper may have a basis weight of 75 g / m2a 120 g / m2, where the cover layer can have a basis weight of 50 g / m2 to 70 g / m2, and the basis weight ratio of the cover layer to the substrate layer can be 1.2:1 to 2:1.

[061] A paper with the specified basis weights and basis weight ratios has proven to be particularly suitable for combining good mechanical properties and good printability. What is surprising here is the fact that the basis weight or basis weight of the cover layer can be kept so low that it is still possible to obtain good printability.

[062] In another form of packaging paper design, a paper burst pressure index, according to ISO 2758:2014, can be 3.5 kPa*m2 / ga 4.5 kPa*m2 / g.

[063] Through this, it is possible to provide a paper with sufficiently good mechanical strength for packaging purposes. Petition 870230091874, dated 10 / 17 / 2023, pp. 199 / 221 13 / 28

[064] In addition, a Scott-Bond value, according to TAPPI / ANSI T 569 om-14 for packaging paper, can be from 250 J / m2 to 450 J / m2.

[065] Through this characteristic, a packaging paper can be made available with good adhesion of the cover layer and the support layer, one over the other, and delamination of these two layers can be avoided during the use of the paper for packaging applications.

[066] Preferably, the cover layer of the packaging paper may have an opacity, in accordance with ISO 2471:2008, greater than 75%.

[067] In addition, the surface of the packaging paper cover layer may preferably have a whiteness in accordance with ISO 2470-1:2016 greater than 70%.

[068] Furthermore, in packaging paper, the surface of the coating layer may exhibit an L* value in the CIELab color spectrum, according to ISO 5631-2:2015, greater than 65.

[069] These features can further enhance the print quality of printed images applied to the surface of the paper's coating layer and, in particular, improve the color fidelity of these printed images.

[070] In an improvement of packaging paper, it can also be foreseen that a compression strength index of the strip, according to ISO 9895:2008, as a geometric mean, will be 15 Nm / g 30 Nm / g. The compression strength index of the strip expressed as a geometric mean, according to ISO 9895:2008, represents, as is known, the square root of the product of the corresponding measurements of the machine direction (MD) and the transverse direction (CD).

[071] This mechanical value is particularly important in packaging papers, since the compression resistance of a paper strip is adequate to counteract the stresses that frequently occur in packaging. Therefore, the specified characteristic can further enhance the strength of the paper and, consequently, also of the packaging formed from paper or which includes paper as a component. Petition 870230091874, dated 10 / 17 / 2023, pp. 200 / 221 14 / 28

[072] The Bendtsen roughness according to ISO 8791-2:2013 of the surface of the coating layer of paper intended for printing may vary from 100 mL / min to 300 mL / min.

[073] This can also further enhance the printability of the paper. Adjusting a corresponding Bendtsen roughness can be done by calendering, for example, as explained above.

[074] Furthermore, it may be advantageous if the Dennison wax absorption resistance of the paper, according to TAPPI T459 OM-13, is at least 14 as the critical wax resistance number.

[075] Such a packaging paper design can be particularly advantageous in a particular printing process application, for example, packaging paper printing can be enhanced using offset printing processes.

[076] For a better understanding of the invention, it is explained in more detail, also with reference to the following Figures.

[077] They show in a highly simplified schematic representation: Figure 1 shows an example of an embodiment for a step in the method of joining two sheets of paper by wet pressing; Figure 2 shows an example of an embodiment for a printable multilayer paper for packaging.

[078] By way of introduction it should be established that, in the various modalities described, the same component references or designations are assigned to the same parts, wherein the same component references or designations are respectively transposed to the same parts in the disclosures contained throughout the description. Likewise, the position indications chosen in the description, such as, for example, above, beside, etc., refer directly to the figure described as well as the one illustrated and, in case of a change in orientation, these position indications must be duly transposed to the new position.

[079] The method for producing the paper in question can be carried out Petition 870230091874, dated 10 / 17 / 2023, pp. 201 / 221 15 / 28 basically with steps of the method already known, by means of a paper machine. The method refers to the production of a printable multilayer paper for packaging, therefore, a paper with at least two layers of paper, which has at least one surface intended for printing. Since the methods or particularly the dehydration and drying steps performed on a paper machine are sufficiently known to those skilled in the art, a detailed description of these steps of the method based on figurative representations can be dispensed with here and in the following cases, these basic steps of the method, performed on a paper machine, being only mentioned below. The packaging paper in question can be produced by means of paper machine parameters common in paper production.

[080] Since the product of this production process has at least two layers of paper, the method comprises, on the one hand, supplying or producing cellulose fibers comprising bleached first celluloses, as well as, on the other hand, supplying or producing cellulose fibers comprising second celluloses. Thus, as is common in paper production on a paper machine, the production of a first sheet of paper comprising bleached first cellulose is followed by the production of a second sheet of paper comprising second cellulose.

[081] For this purpose, initially, a first pulp comprising the first cellulose is produced, as well as a second pulp comprising the second cellulose. For this purpose, the two celluloses can be suspended in an aqueous liquid, as already known. An initial consistency of the first and second pulp can be, for example, 0.5% to 2%. As is also common in paper production, the first pulp, the second pulp, or both pulps may also contain other additives besides the respective celluloses. Examples of such excipients are starch in bulk, PAC (polyaluminum chloride) or alum, ASA (alkyl succinic anhydride) or other sizing agents, bentonite or talc, pH adjusting agents, retention agents, etc. the selection of Petition 870230091874, dated 10 / 17 / 2023, pages 202 / 221 16 / 28 The type and quantity of such additives may be determined by a professional skilled in the art, in the technical field in question, for example, based on the desired detailed properties of the multilayer paper for packaging and / or also adapted to a specific paper machine design or adapted to a specific process operation.

[082] The first pulp and the second pulp may be fed into a paper machine into a so-called regulator or by means of one or more regulators. For completeness, it should be defined at this point that the term pulp should be understood as an aqueous suspension of the respective cellulose. As usual, other terms such as fiber pulp, fiber-water suspension, fiber suspension, pulp suspension, etc. may also be used as synonyms.

[083] As is known to those skilled in the art, in a paper machine, a sheet of paper is generally formed by the successive dehydration and drying of a pulp introduced by means of a regulator. A sheet of paper may be formed and at least thickened, for example, in a first dehydration step by means of a so-called sieve section, wherein a further drying of a sheet of paper formed in a paper machine may occur in a further drying step.

[084] Thus, in the method in question, the production or supply of a first sheet of paper by dehydrating / drying the first is also foreseen, as well as the production or formation of a second sheet of paper by dehydrating / drying the second pulp.

[085] For the production of multilayer paper for packaging, a step in the method is also naturally foreseen for joining the first sheet of paper and the second sheet of paper. Such joining can occur, basically, at different drying levels or consistencies of both sheets of paper, therefore also, for example, at different positions in a paper machine or, for example, after or during the process of different dewatering or drying stages in a paper machine. Petition 870230091874, dated 10 / 17 / 2023, pp. 203 / 221 17 / 28

[086] In this way, it is also foreseen in the method in question to join both sheets of paper, therefore, a joining of the first and second sheets of paper into a multilayer sheet of paper to form a multilayer sheet of paper. An example of an embodiment for such a joining process is represented in a simplified and schematic way in Figure 1.

[087] The embodiment shown in Figure 1 illustrates the joining of the first sheet of paper 1 formed with the second sheet of paper 2 formed during drying by means of a so-called pressing section 3 of a paper machine, as this is particularly carried out. The embodiment shown in Figure 1 shows, here, only a cutaway of the pressing section for the purpose of illustrating the joining of the sheets of paper 1, 2. A pressing section 3 may form, as is already known, a drying stage that follows the screening section of a paper machine.

[088] It should be mentioned again at this point that the joining of the two paper sheets 1 and 2 can also be carried out basically at other points or at other times in the method. Thus, it is possible to join both paper sheets 1, 2 from two different regulators, possibly also during the sieving section, normally prior to a pressing section. Similarly, a joining of the first and second paper sheets 1, 2 can also be carried out after previous drying, to a final dry content or at least close to a final dry content of the paper sheets by means of gluing, lamination, etc.

[089] In the embodiment shown in Figure 1, the joining of both sheets of paper 1, 2 can occur, as illustrated, by pressing both sheets of paper 1, 2 against each other by means of pressure rollers 4, 5. As illustrated based on the embodiment in Figure 1, the sheets of paper 1, 2 are joined into a multilayer sheet of paper 6 in such a way that, through the first sheet of paper 1, a top cover layer 7 is formed and through the second sheet of paper 2, a support layer 8 is formed, joined directly to this top cover layer 7, or support layer of the sheet of paper. Petition 870230091874, dated 10 / 17 / 2023, pp. 204 / 221 18 / 28 multilayer 6.

[090] Preferably, it can be provided that, immediately before the joining of the first sheet of paper 1 and the second sheet of paper 2, a dry content of the first sheet of paper 1 is adjusted from 3% to 50% and a dry content of the second sheet of paper 2 from 3% to 50%. A corresponding dry content is found here in the normal water content range of sheets of paper in a pressing section.

[091] In principle, it is also naturally possible to produce one or more additional paper layers and join them to form the multilayer paper sheet 6, wherein at least one of these paper layers is eventually joined with the support layer 8 to form a multilayer paper sheet 6. This option is not shown in Figure 1 for reasons of clarity, but is, however, self-explanatory to those skilled in the art in the field of paper production. Additional paper layers to form the multilayer packaging paper may be appropriate depending on the intended use or requirements; however, a packaging paper with only two layers, and thus the formation of a two-layer paper sheet 6 for its production, as schematically illustrated in Figure 1, may in most cases be completely sufficient and desirable for reasons of material economy and for the simplest possible execution of the method.

[092] Regardless of the number of paper layers joined in a multilayer paper sheet 6, after joining, another drying of this paper sheet 6 may occur, for example, in subsequent stages of the pressing section 3 represented only sectionally in Figure 1. After a pressing section 3, as already known, a final drying may still be carried out by means of a so-called drying section until the desired final moisture content is reached.

[093] Finally, the dry, ready multilayer sheet 6 is assembled. The usual finishing process can be carried out, for example, by rolling the already dried 6-ply multilayer paper sheet onto a conveyor roller. Alternatively, however, the manufacturing process can also involve cutting the 6-ply multilayer paper sheet into Petition 870230091874, dated 10 / 17 / 2023, pages 205 / 221 19 / 28 a respectively desired dimension of a multilayer packaging paper and the stacking of the respective cut packaging paper pieces.

[094] The method provides that, as second pulp comprising cellulose fibers, a mixture is supplied or formed consisting of, relating to 100% by weight of the total dry matter of the second pulp, 40% by weight to 80% by weight of unbleached cellulose material and 20% by weight to 60% by weight of bleached cellulose material. Unbleached cellulose material is understood here as cellulose material that is not bleached in the course of the printable multilayer paper production process.

[095] The expression “consisting of” should be understood, in the above context, in absolute terms, referring to 100% by weight of the total dry matter of the second pulp. The specified % by weight ranges do not therefore include, for example, added additives and / or unavoidable small amounts of introduced impurities. Preferably, as second pulp comprising cellulose fibers, a mixture consisting of, referring to 100% by weight of the total dry matter of the second pulp, 45% by weight to 75% by weight of unbleached cellulose material and 25% by weight to 55% by weight of bleached cellulose material may be supplied or produced.

[096] The unbleached cellulose material of the second cellulose may preferably be selected from a group consisting of fresh, unbleached short-fiber cellulose material, unbleached recycled fiber cellulose material or a mixture of unbleached cellulose materials from this group.

[097] As bleached cellulose material for the second cellulose, a mixture of 30% by weight to 80% by weight of bleached short-fiber cellulose material and 20% by weight to 70% by weight of bleached long-fiber cellulose material may preferably be used.

[098] For the formation of bleached cellulose material from the first cellulose, preferably at least 70% by weight and up to 100% by weight may be used. Petition 870230091874, dated 10 / 17 / 2023, pp. 206 / 221 20 / 28 of the bleached short-fiber cellulose material. In addition, up to 30% by weight of long-fiber cellulose material may also be used to form the bleached cellulose material from the first celluloses.

[099] The term short-fiber cellulose material may be understood to mean cellulose material obtained particularly from hardwoods, which are distinguished by short average fiber lengths of cellulose fibers. The term long-fiber cellulose material may be understood to mean cellulose material obtained particularly from softwoods, which are distinguished by comparatively longer average fiber lengths of cellulose fibers. The relevant relationships are familiar to those skilled in the art in the field of papermaking. As is already known, it is possible to produce such cellulose materials by grinding the corresponding woods and mechanical and / or chemical decomposition to remove lignin particles, hemicellulose particles and other wood components, as well as any additional processing methods, such as mechanical post-treatment, for example, wet grinding or wet defibration in so-called refiners.

[0100] In particular, it may be suitable, in conducting the method, if the second pulp is supplied or produced with a Schopper-Riegler value according to ISO 5267-1:2000 of 20 °SR to 35 °SR. This can be achieved by processing the pulp, for example, by means of mechanical grinding or defibration in refiners, as already mentioned above.

[0101] Preferably, the so-called kraft pulp materials can be supplied or produced as short and long fiber cellulose materials, therefore, cellulose materials produced by means of the kraft process or kraft pulping. Such kraft pulps are also commonly referred to as sulfate pulp materials. The term recycled cellulose material is self-explanatory.

[0102] The bleaching process to produce bleached cellulose materials includes, as is generally known, additional chemical decomposition to remove residual lignin and other coloring substances in a Petition 870230091874, dated 10 / 17 / 2023, pages 207 / 221 21 / 28 minimum extension. Bleaching is suitable for removing residual lignin, but also for removing coloring substances, for example, from recycled cellulose material.

[0103] Furthermore, during the method, the second pulp can be supplied or produced with a kappa number according to ISO 302:2015 of 20 to 65. A kappa number within the indicated range can be adjusted primarily by the selection and / or preparation of the corresponding cellulose materials, especially during chemical pulping, as well as by the composition of the cellulose materials to form the second pulp, as known by those skilled in the art in the technical field of papermaking.

[0104] In a preferred embodiment of the method, to the first pulp or the first sheet of paper 1, 100 kg to 150 kg of a white pigment charge may be added per ton of the total dry matter of the first bleached pulp. A corresponding charge of white pigment may also be added to the first pulp before the start of dewatering and formation of the first sheet of paper 1 or also after at least a first dewatering stage or a first level of dewatering of the first sheet of paper 1 formed. Preferably, calcium carbonate may be added to the first pulp or the first sheet of paper 1 as a white pigment charge.

[0105] As mentioned above, depending on the need or purpose of the multilayer printable packaging paper, other additives commonly used in paper production may also be added or used during its production, such as modified or native starch, sizing agents, retaining agents, fixing agents, moisture-resistant agents, etc.

[0106] In the method, the multilayer paper sheet 6 can be produced, particularly after complete drying to a final dry content with a basis weight of 75 g / m2 to 120 g / m2. In this context, the cover layer 7 of the multilayer paper sheet 6 can be produced with a basis weight of 50 g / m2 to 70 g / m2 and a basis weight ratio of the cover layer 7 can be adjusted to a Petition 870230091874, dated 10 / 17 / 2023, pp. 208 / 221 22 / 28 basis weight of the support layer 8 in 1.2:1 to 2:1.

[0107] Corresponding basis weights or basis weights can be adjusted, as is already known, by controlling various method parameters, such as consistencies in fiber preparation and in a paper machine approach flow system, the amounts of pulp and its consistency applied to the regulator of a paper machine, passage speeds in different sections of a paper machine and so on.

[0108] Furthermore, the method can also provide a leveling of the surface of the cover layer 7 of the multilayer paper sheet 6 intended for printing. In particular, this leveling can be achieved by calendering this surface using a calender, such as a hard-nozzle calender, soft-nozzle calender, long-nozzle calender, shoe calender or metal belt calender. To achieve the desired surface properties, for example, a certain surface roughness, it is known that the person skilled in the art controls or varies several settings during calendering, such as pressure, temperature and residence time.

[0109] An example of an embodiment for the aforementioned printable multilayer paper 9 for packaging is shown in Figure 2.

[0110] As can be seen from Figure 2, the aforementioned multilayer printable packaging paper 9 comprises an upper cover layer 10, as well as a support layer 11 directly bonded to the upper cover layer 10. The upper cover layer 10 predominantly comprises a first bleached cellulose fiber material and the support layer 11 predominantly comprises a second cellulose fiber material. This second cellulose fiber material of the support layer 11 is formed here by a mixture consisting of, relative to 100% by weight of the total dry matter of the second cellulose fiber material, 40% by weight to 80% by weight of the unbleached fiber material and 20% by weight to 60% by weight of the bleached fiber material. Petition 870230091874, dated 10 / 17 / 2023, pp. 209 / 221 23 / 28

[0111] The packaging paper 9 shown in Figure 2 is ultimately formed or produced by joining the paper sheets 1,2 represented in Figure 1 into a multilayer paper sheet 6, possibly further drying of this multilayer paper sheet 6 and, finally, finishing of the multilayer paper sheet 6.

[0112] Preferably, the second cellulose fiber material may be formed from a mixture consisting of, in relation to 100% by weight of the total dry matter of the second cellulose fiber material, 45% by weight to 75% by weight of the unbleached fiber material and 25% by weight to 55% by weight of the bleached fiber material.

[0113] The terms cellulose fiber material or fiber material in relation to the aforementioned packaging paper were selected, therefore, since the designations cellulose or cellulose material are not common for finished papers, but the term cellulose is more commonly used as a designation for a raw material for paper production. However, the different material designations chosen are, in this sense, only formal in nature, and this fact should not be understood as a material transformation of any kind during the production process, particularly not as a chemical transformation into a chemically different material. On the contrary, during the production of paper on a paper machine with cellulose as the starting material, no significant transformation of the material is expected, at least in the chemical sense, as is known to those skilled in the art.It is known that the processes in a paper machine mainly include mechanical and physical processes, such as, at least, the partial alignment of cellulose fibers and dehydration processes, etc. These issues clarified above apply to this entire document. Furthermore, an unbleached fiber material should be understood to be a fiber material that, during the production process of printable multilayer paper, has not been bleached or results from an unbleached cellulose material.

[0114] The packaging paper 9 shown in Figure 2 can be used, for example, as a standalone outer packaging paper for products such as Petition 870230091874, dated 10 / 17 / 2023, pages 210 / 221 24 / 28 primary packaging, but also as secondary packaging. The aforementioned paper 9 for packaging, however, can also be just a component of a package, particularly a top layer or facing the outside of a package, as is common, for example, in cardboard packaging.

[0115] Regardless, the packaging paper in question 9 has at least one printable or printable surface, which, as illustrated in Figure 2, is formed by the surface 12 of the cover layer 10 that points outwards.

[0116] The unbleached fiber material of the second cellulose fiber material may be selected from a group consisting of fresh, unbleached long fiber material, unbleached recycled fiber material or a mixture of unbleached fiber materials from that group.

[0117] In this context, it may be advantageous, for certain application purposes, if only fresh fiber material is used as the fiber material in all layers 10, 11, 13 of the packaging paper. In this case, the packaging paper in question may also be suitable as packaging in direct contact with dry, moist and greasy foods, provided that all legal requirements are met, for example, with regard to any additives. The use of recycled fiber material may be associated with limited suitability and additional expenses, but outside the area of ​​primary food packaging, the use of recycled fiber material can be very useful and advantageous.

[0118] The bleached fiber material of the second cellulose fiber material can be formed from a mixture of 30% by weight to 80% by weight of bleached short fiber material and 20% by weight to 70% by weight of bleached long fiber material.

[0119] The bleached fiber material of the first cellulose fiber material may preferably comprise 70% by weight to 100% by weight of bleached short fiber material, however, it may comprise up to 30% by weight of bleached long fiber material. Petition 870230091874, dated 10 / 17 / 2023, pages 211 / 221 25 / 28

[0120] As described above, corresponding fiber materials can be formed by using or producing cellulose materials by the production process already described above.

[0121] A paper 9 for packaging, depending on the intended use or requirements, may also comprise other paper layers, wherein at least one of these optional additional paper layers would be connected to the support layer 11. One such optional additional paper layer 13 is shown in dashed lines in Figure 2.

[0122] The cover layer 10 of said packaging paper 9 may, in particular, contain a white pigment filler as an additive. In this context, the ash residue, according to ISO 1762:2015, of the cover layer may be from 10 to 10% by weight to 14% by weight. The white pigment filler may preferably be composed of calcium carbonate.

[0123] The measurable ash residue in paper is mainly composed of mineral or inorganic additives, depending on the materials or additives used in the production process. However, the cellulose itself may also contain a small amount of ash, which can vary depending on the type of cellulose. Regarding the method for producing packaging paper, it should be noted, for completeness, that during the dewatering / drying process of the paper pulp formed in a paper machine, there is always an unavoidable loss of the inorganic aggregates used, for example, during dewatering in a wire section. This unavoidable loss, therefore, can lead to a reduction in the measurable ash residue in the paper compared to the input quantities of inorganic aggregates added in the method.

[0124] In addition, packaging paper has a basis weight of 75 g / m2 to 120 g / m2, where the cover layer can have a basis weight of 50 g / m2 to 70 g / m2, and where the basis weight ratio of the cover layer to the backing layer can be 1.2:1 to 2:1. Petition 870230091874, dated 10 / 17 / 2023, pages 212 / 221 26 / 28

[0125] Next, some particularly preferred properties of said paper 9 for packaging are explained in more detail, mainly based on characteristic values.

[0126] Packaging paper 9 may exhibit, when its cover layer 10 comes into contact with water, according to ISO 535:2014, a Cobb-60 value of 30 g / m2 to 40 g / m2. A corresponding Cobb-60 value may be adjusted primarily by the materials used, as is known, but also by the use of additives, such as sizing agents.

[0127] Furthermore, the burst pressure index of said packaging paper 9, according to ISO 2758:2014, can vary from 3.5 kPa*m2 / ga to 4.5 kPa*m2 / g.

[0128] A Scott-Bond value, according to TAPPI / ANSI T 569 om-14 of paper 9 for packaging, can be from 250 J / m2 to 450 J / m2. The Scott-Bond value describes the tendency of papers to delaminate the paper layers, in this case, in relation to the cover layer 10 and the support layer 11.

[0129] The packaging paper 9 itself may exhibit a strip compression strength index, according to ISO 9895:2008, as a geometric mean, of 15 Nm / ga 30 Nm / g. As is known to those skilled in the art, the strip compression strength index expressed as a geometric mean, according to ISO 9895:2008, represents the square root of the product of the corresponding measurements of the machine direction (MD) and the transverse direction (CD).

[0130] With regard to the characteristics relating to the visual appearance and, in this context, the printability of said packaging paper 9, its coating layer 10 may have an opacity according to ISO 2471:2008 greater than 75%.

[0131] In addition, the surface 12 of the cover layer 10 of the packaging paper 9 intended for printing may have a whiteness according to ISO 2470-1:2016 greater than 70%.

[0132] Furthermore, surface 12 of the covering layer 10 of said paper 9 Petition 870230091874, dated 10 / 17 / 2023, pp. 213 / 221 27 / 28 may exhibit an L* value in the CIELab color spectrum, according to ISO 5631-2:2015, greater than 65.

[0133] A packaging paper with these optical characteristics stands out for its excellent printability and is particularly suitable for printing high-quality color images with colorfastness.

[0134] Furthermore, the Bendtsen roughness, according to ISO 8791-2:2013, of the surface of the coating layer of paper intended for printing may vary from 100 mL / min to 300 mL / min.

[0135] Also, a Dennison wax absorption resistance of the paper, according to TAPPI T459 OM-13, can be at least 14, as the critical wax resistance number.

[0136] The embodiment examples show possible embodiment variants, it being observed at this point that the invention is not limited to the embodiment variants specifically represented, but also that various combinations of embodiment variants among themselves are possible, and these possibilities of variation are due, due to the theory of technical dealing with realized inventions, to the ability of the person versed active in this technical area.

[0137] The scope of protection is determined by the claims. The description and figures, however, should be consulted for the interpretation of the claims. Individual features and combinations of features of the different embodiments illustrated and described may represent stand-alone inventive solutions. The basic task of stand-alone inventive solutions can be inferred from the description.

[0138] All information regarding value ranges in the specific description should be understood in such a way that they may encompass any or all subdivisions of those ranges, for example, the indication of 1 to 10 should be understood in such a way that all partial ranges are covered, from the lower limit of 1 to the upper limit of 10, that is, all partial ranges begin with a lower limit of 1 or greater and end with an upper limit of 10 or less, for example, Petition 870230091874, dated 10 / 17 / 2023, pp. 214 / 221 28 / 28 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

[0139] Finally, for the record, it should be noted that, for a better understanding of the construction, elements have been partially illustrated out of scale and / or enlarged and / or reduced. LIST OF REFERENCES paper sheet paper sheet pressing section pressure roller pressure roller paper balm cover layer backing layer paper cover layer backing layer surface paper layer Petition 870230091874, dated 10 / 17 / 2023, pages 215 / 221

Claims

1 / 5 CLAIMS 1. Method for producing a printable multilayer paper (9) for packaging, comprising - supplying or producing a first bleached pulp comprising cellulose fibers and producing a first sheet of paper (1) comprising the first pulp by forming a first pulp comprising the first pulp and dehydrating / drying that first pulp, - supplying or producing a second pulp comprising cellulose fibers and producing a second sheet of paper (2) comprising the second pulp by forming a second pulp comprising the second pulp and dehydrating / drying that second pulp, - joining both sheets of paper (1, 2) into a multilayer sheet of paper (6), such that, through the first sheet of paper (1), a top cover layer (7) is formed and, through the second sheet of paper (2),a support layer (8) is formed from the multilayer paper sheet (6) directly bonded to this uppermost cover layer (7), - optionally, producing one or more other paper layers and bonding at least one of these other paper layers to the support layer (8), - optionally, further drying the multilayer paper sheet (6), - manufacturing the multilayer paper sheet (6), characterized in that the second cellulose comprising cellulose fibers is supplied or produced as a mixture consisting of, relating to 100% by weight of the total dry matter of the second cellulose, 40% by weight to 80% by weight of unbleached cellulose material and 20% by weight to 60% by weight of bleached cellulose material, wherein the printable multilayer paper (9) is produced with an uppermost cover layer (10) comprising predominantly bleached first cellulose and with a support layer (11) comprising predominantly second cellulose,attached directly to the top layer of the covering. Petition 870260026772, dated 03 / 23 / 2026, page 14 / 18 2 / 5 (10) 2. A method according to claim 1, characterized in that the unbleached cellulose material of the second cellulose is selected from a group consisting of fresh, unbleached long-fiber cellulose material, unbleached recycled fiber cellulose material, or a mixture of unbleached cellulose materials from that group.

3. Method according to claim 1 or 2, characterized in that, as bleached cellulose material of the second cellulose, a mixture of 30% to 80% by weight of bleached short-fiber cellulose material and 20% to 70% by weight of bleached long-fiber cellulose material is used.

4. Method, according to any one of claims 1 to 3, characterized in that, for the formation of the bleached cellulose material from the first cellulose, 70% by weight - 100% by weight of bleached short-fiber cellulose material is used.

5. Method, according to any one of claims 1 to 4, characterized in that a dry content of the first sheet of paper (1) is adjusted from 3% to 50% and a dry content of the second sheet of paper (2) is adjusted from 3% to 50% immediately before joining the first sheet of paper (1) and the second sheet of paper (2).

6. Method, according to any one of claims 1 to 5, characterized by 100 kg to 150 kg of a white pigment charge per tonne of total dry matter of the first bleached cellulose being added to the first pulp or to the first sheet of paper (1).

7. Method according to claim 6, characterized in that calcium carbonate is added as a white pigment filler.

8. Method, according to any one of claims 1 to 7, characterized in that the multilayer paper sheet (6), after complete drying, is produced to a final dry content with basis weight of 75 g / m2 to 120 g / m2, wherein the cover layer (7) is produced with a basis weight of 50 g / m2 to 70 g / m2, and in Petition 870260026772, dated 23 / 03 / 2026, page 15 / 18 3 / 5 that a basis weight ratio of the cover layer (7) to the basis weight of the support layer (8) is 1.2:1 to 2:

1.

9. Method, according to any one of claims 1 to 8, characterized in that the second pulp is supplied or produced with a Schopper-Riegler value, according to ISO 5267-1:2000, of 20 °SR to 35 °SR.

10. Method, according to any one of claims 1 to 9, characterized in that the second pulp is supplied or produced with a kappa number, according to ISO 302:2015, of 20 to 65.

11. Printable multilayer paper (9) for packaging, produced according to the method defined in any one of claims 1 to 10, comprising - an upper cover layer (10) comprising predominantly a bleached cellulose fiber material, - a backing layer (11), comprising predominantly a second cellulose fiber material, bonded directly to the upper cover layer (10), characterized in that the second cellulose fiber material is formed from a mixture consisting of, corresponding to 100% by weight of the total dry matter of the second cellulose fiber material, 40% by weight to 80% by weight of the unbleached fiber material and 20% by weight to 60% by weight of the bleached fiber material.

12. Paper (9), according to claim 11, characterized in that the unbleached fiber material of the second cellulose fiber material is selected from a group consisting of fresh unbleached long fiber material, unbleached recycled fiber material or a mixture of unbleached fiber materials from that group.

13. Paper (9), according to claim 11 or 12, characterized in that the bleached fiber material of the second cellulose fiber material is formed from a mixture of 30% by weight to 80% by weight of bleached short fiber material and 20% by weight to 70% by weight of bleached long fiber material.

14. Paper (9), according to any one of claims 11 to 13, characterized in that the bleached fiber material of the first cellulose fiber material comprises 70% by weight to 100% by weight of bleached short fiber material.

15. Paper (9), according to any one of claims 11 to 14, characterized in that the cover layer (10) has a white pigment charge, wherein an ash residue, according to ISO 1762:2015, of the cover layer (10) is 10% by weight to 14% by weight.

16. Paper (9), according to claim 15, characterized in that the white pigment filler is formed from calcium carbonate.

17. Paper (9), according to any one of claims 11 to 16, characterized in that the paper (9), when the cover layer (10) impacts water, in accordance with ISO 535:2014, exhibits a Cobb-60 value of 30 g / m2 to 40 g / m2.

18. Paper (9), according to any one of claims 11 to 17, characterized in that it has a basis weight of 75 g / m2 to 120 g / m2, wherein the cover layer (10) has a basis weight of 50 g / m2 to 70 g / m2 and wherein the ratio of the basis weight of the cover layer (10) to the basis weight of the support layer (11) is 1.2:1 to 2:

1.

19. Paper (9), according to any one of claims 11 to 18, characterized by a burst pressure index, according to ISO 2758:2014, being 3.5 kPa*m2 / ga 4.5 kPa*m2 / g.

20. Paper (9), according to any one of claims 11 to 19, characterized in that a Scott-Bond value, according to TAPPI / ANSI T 569 om-14, is 250 J / m2 to 450 J / m2.

21. Paper (9), according to any one of claims 11 to 20, characterized in that the coating layer (10) has an opacity, according to ISO 2471:2008, greater than 75%. Petition 870260026772, dated 23 / 03 / 2026, p. 17 / 18 5 / 5 22. Paper (9), according to any one of claims 11 to 21, characterized in that a surface (12) of the cover layer (10) has a whiteness, according to ISO 2470-1:2016, greater than 70%.

23. Paper (9), according to any one of claims 11 to 22, characterized by a surface (12) of the coating layer (10) having an L* value in the CIELab color spectrum, according to ISO 5631-2:2015, greater than 65.

24. Paper (9), according to any one of claims 11 to 23, characterized in having a strip compression strength index, according to ISO 9895:2008, as geometric mean, of 15 Nm / g 30 Nm / g. Petition 870260026772, dated 23 / 03 / 2026, p. 18 / 18

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