Machine glazed paper

Abstract

The present disclosure relates to a machine-glazed (MG) paper having a Cobb value of 23 g / m2 / 60s or below as measured according to the standard method ISO 535:2023, wherein the paper comprises AKD and rosin size and the ratio of AKD to rosin size is within of from 1:4 to 3:4. The present disclosure furthermore relates to a method of producing the MG paper.

Description

TECHNICAL FIELD

[0001] The present disclosure pertains to the field of Machine Glazed (MG) papers, and in particular to MG papers having a Cobb value of 23 g / m 2< / 60s or below and a specified ratio of AKD and rosin size.BACKGROUND

[0002] Machine glazing is a paper finishing process that gives one side of the paper a smooth, glossy surface while leaving the other side with a rougher texture. The papermaking process generally starts with a standard papermaking, where pulp is formed into a continuous sheet of paper, the paper is then partially dried on drying cylinders and the partially dried paper is passed over a large, heated polished cylinder known as a Yankee dryer. The high temperature and pressure applied by the Yankee dryer smooth out the fibers on one side of the paper creating a glossy finish.

[0003] In papermaking sizing agents are added to the pulp stock to impart resistance to water and other liquids, improve printability, and enhance overall quality and performance of paper. Internal sizing agents such as Alkyl Ketene Dimer (AKD) and rosin size are added to provide hydrophobicity and water resistance to the paper.

[0004] However, the use of AKD and rosin size may also affect the machine glazing process and the adherence to the Yankee cylinder.

[0005] One problem is thus to balance between the desired properties for the paper and adhesion and efficient production and high-quality paper products.SUMMARY

[0006] One objective is to make available a high-quality MG paper with a relatively low Cobb value and with an improved and efficient method.

[0007] According to a first aspect, the present disclosure relates to a machine-glazed (MG) paper having a Cobb value of 23 g / m 2< / 60s or below as measured according to the standard method ISO 535:2023, wherein the paper comprises AKD and rosin size and the ratio of AKD to rosin size is within the range of from 1:4 to 3:4.

[0008] The Cobb60 value is measured according to the method ISO 535:2023.

[0009] Rosin size is a sizing agent added to the pulp stock to impart hydrophobicity and reduce its Cobb value. Rosin size may however increase the adherence of the MG paper to the Yankee cylinder. Excessive adherence can lead to uneven glazing and surface defects, such as fibers or small sections of the paper being pulled away. This high level of adherence may also reduce process efficiency due to frequent stoppages needed to resolve the adherence issues.

[0010] AKD (alkyl ketene dimer) may be used to further increase the paper's hydrophobicity, making it more water resistant if needed. AKD additionally reduces the adherence of the MG paper to the Yankee cylinder and may be added to reduce the adherence caused by the addition of rosin size. However, a too high amount of AKD may cause an insufficient adherence, resulting in poor glazing and an uneven surface. This may give the MG paper a duller finish instead of the desired high-gloss finish and an uneven surface texture, leading to a less uniform paper. Low adherence can also cause production inefficiencies, as the paper may detach prematurely or unpredictably from the Yankee cylinder, requiring more frequent adjustments and interruptions in the production line, thereby reducing overall productivity.

[0011] Hence, rosin size and AKD can be added to achieve papers with low Cobb values optionally within the range of from 2.1 kg / tonne to 4 kg / tonne based on dry weight of the paper and prevent excessive adherence. However, if the ratio of rosin size to AKD is too high, it can cause excessive foaming, which may negatively affect process and equipment efficiency, resulting in inferior or rejected paper. Conversely, if the ratio of rosin size to AKD is too low, the paper may be rejected from the Yankee cylinder resulting in poor glazing and an uneven surface.

[0012] It was found by the present inventors that for MG papers with a Cobb60 value as disclosed herein, the relative amounts of AKD and rosin size as disclosed herein provides a balanced solution which improves the production efficiency and provides a high-quality MG paper product.

[0013] The ratio of AKD to rosin size may be within the range of from 1:3 to 2:3. This has been found to further improve the surface quality of the MG paper and the production efficiency.

[0014] The amount of AKD in the MG paper may be within the range of from 0.7 kg / tonne to 2.5 kg / tonne based on dry weight of the paper. The specified range optimizes the hydrophobicity, surface quality, adherence properties and production efficiency of MG paper. This balance ensures that the MG paper meets the high standards required for both aesthetic and functional performance in packaging and other high-barrier applications.

[0015] The amount of AKD in the MG paper may be within the range of from 1 kg / tonne to 2 kg / tonne based on dry weight of the paper. This defined range even further optimizes the hydrophobicity, surface quality, adherence properties and production efficiency of the MG paper.

[0016] The amount of rosin size in the MG paper may be within the range of from 2 kg / tonne to 4.5 kg / tonne based on dry weight of the paper. The specified range of rosin size MG paper improves surface smoothness by filling in pores and creating a uniform coating. This enhancement increases the paper's hydrophobicity, reducing the likelihood of the paper sticking to the Yankee cylinder, thus ensuring smoother passage and uniform high-gloss finish. Additionally, this controlled amount of rosin size balances adherence to prevent surface defects from excessive sticking and to avoid insufficient glazing due to low adherence, thereby maintaining consistent paper quality and production efficiency.

[0017] The amount of rosin size in the MG paper may be within the range of from 2.1 kg / tonne to 4 kg / tonne based on dry weight of the paper. This specified range further improves and balances adherence to prevent surface defects from excessive sticking and to avoid insufficient glazing due to low adherence, thereby maintaining consistent paper quality and production efficiency.

[0018] The grammage of the MG paper may be at least 30 g / m 2< , optionally at least 40 g / m 2< , or optionally at least 50 g / m 2< .

[0019] The grammage of the MG paper may be within the range of from 30 and 110 g / m 2< .

[0020] The grammage of the MG paper may be within the range of from 40 and 95 g / m 2< . Optionally, the grammage of the MG paper may be within the range of from 40 and 95 g / m 2< . This covers both light and medium weight packaging. A relevant application for this MG paper is medical packaging, which must adhere to specific standards, including particular Cobb values.

[0021] The Cobb value of the MG paper may be 22 g / m 2< / 60s or below. Preferably the Cobb value of the MG paper is 21 g / m 2< / 60s or below, such as 20 g / m 2< / 60s or below. The Cobb value of the MG paper may within the range of from 15 to 21 g / m 2< / 60s.

[0022] The fibers in the MG paper may be kraft fibers. Optionally the kraft pulp fibers are bleached kraft pulp fibers. The use of kraft pulp fibers in the present context is advantageous due to their inherent strength, water resistance, superior bonding characteristics, and compatibility with hydrophobic sizing agents. These properties make kraft pulp an ideal choice for producing high-quality, water-resistant paper suitable for demanding applications such as packaging and medical uses.

[0023] The kraft fibers may comprise softwood fibers. Optionally 60 % by weight or more of the kraft fibers are softwood fibers.

[0024] The kraft fibers may comprise 60 to 95 % by dry weight of softwood fibers and 5 to 40 % by dry weight of hardwood fibers.

[0025] According to a second aspect, the present disclosure relates to a method of producing a machine-glazed (MG) paper having a Cobb value of 23 g / m 2< / 60s or below as measured according to the standard method ISO 535:2023, wherein the method comprises the following steps: a) providing a pulp, b) diluting the pulp into a pulp stock, c) adding AKD and rosin size to the pulp stock, wherein the ratio AKD to rosin size is within the range of from 1:4 to 3:4 and the combined amount of AKD and rosin size results in a paper having a Cobb value of 23 g / m 2< / 60s or below, d) diluting the pulp stock in a headbox, e) adding the diluted pulp stock from the headbox to a forming wire to obtain a paper web, f) pressing the paper web, and g) glazing the paper web in a glazing unit, thereby forming the MG paper.

[0026] Effects and features of the second aspect are largely analogous to those described above in connection with the first aspect. Embodiments mentioned in relation to the first aspect are largely compatible with the second aspect, and vice versa, of which some are exemplified below.

[0027] The pulp in step a) may be kraft pulp.

[0028] Optionally, the pulp in step a) may be bleached kraft pulp.

[0029] The pulp in step a) may comprise at least 60% by dry weight of softwood kraft pulp.

[0030] The pulp in step a) may comprise from 60 to 95 % by dry weight of softwood kraft pulp and 5 to 40 % by dry weight of hardwood kraft pulp.

[0031] The ratio of AKD to rosin size added in step c) may be within the range of from 1:3 to 2:3.

[0032] The amount of AKD added in step c) may be within the range of from 0.7 kg / tonne to 2.5 kg / tonne based on dry weight of the paper.

[0033] The amount of AKD added in step c) may be within the range of from 1 kg / tonne to 2 kg / tonne based on dry weight of the paper.

[0034] The amount of rosin size added in step c) may be within the range of from 2 kg / tonne to 4.5 kg / tonne based on dry weight of the paper.

[0035] The amount of rosin size added in step c) may be within the range of from 2.1 kg / tonne to 4 kg / tonne based on dry weight of the paper.

[0036] The method may produce an MG paper having a grammage of at least 30 g / m 2< , optionally at least 40 g / m 2< , such as at least 50 g / m 2< .

[0037] The method may produce an MG paper having a grammage within the range of from 30 and 110 g / m 2< .

[0038] The method may produce an MG paper having a grammage within the range of from 40 and 95 g / m 2< .

[0039] The method may produce an MG paper having a grammage within the range of from 50 and 95 g / m 2< .

[0040] Optionally, the combined amount of AKD and rosin size results in a paper having a Cobb value of the MG paper of 22 g / m 2< / 60s or below. Preferably, the combined amount of AKD and rosin size results in a paper having a Cobb value of the MG paper of 21 g / m 2< / 60s or below, such as 20 g / m 2< / 60s or below. The combined amount of AKD and rosin size may result in a paper having a Cobb value of the MG paper of y within the range of from 15 to 21 or below.

[0041] According to a third aspect the present disclosure relates to a method of producing a machine-glazed (MG) paper having a Cobb value of 23 g / m 2< / 60s or below as measured according to the standard method ISO 535:2023, wherein the method comprises the following steps: providing a pulp, a) diluting the pulp into a pulp stock, b) adding rosin size to the pulp stock, such that the amount of rosin size is within the range of from 2 kg / tonne to 4.5 kg / tonne based on dry weight of the final MG paper, c) diluting the pulp stock in a headbox, d) adding the diluted pulp stock from the headbox to a forming wire to obtain a paper web, e) pressing the paper web, f) adding a release agent to a Yankee cylinder in a glazing unit, and g) glazing the paper web on the Yankee cylinder in the glazing unit, thereby forming the MG paper having a Cobb value of 23 g / m 2< / 60s or below.

[0042] Rosin size is a sizing agent introduced to the pulp stock to impart hydrophobicity and reduce the Cobb value of the paper. As mentioned earlier, Rosin size can enhance the adherence of MG paper to the Yankee cylinder. Excessive adherence can lead to uneven glazing and surface defects, such as fibers or small sections of the paper being pulled away. This high level of adherence may also decrease process efficiency due to the frequent stoppages required to address the adherence issues.

[0043] In the method described in this disclosure, an adhesion-reducing agent is added to the Yankee cylinder of the glazing unit. This addition mitigates the issue of excessive adherence, resulting in a uniform glaze and higher-quality MG paper. Additionally, this approach has been observed to enhance process efficiency.

[0044] Effects and features of the third aspect are largely analogous to those described above in connection with the first and second aspect. Embodiments mentioned in relation to the first aspect and second aspects are largely compatible with the third aspect, and vice versa, of which some are exemplified below.

[0045] The pulp in step a) may be kraft pulp.

[0046] Optionally, the pulp in step a) may be bleached kraft pulp.

[0047] The pulp in step a) may comprise at least 60% by dry weight of softwood kraft pulp.

[0048] The pulp in step a) may comprise from 60 to 95 % by dry weight of softwood kraft pulp and 5 to 40 % by dry weight of hardwood kraft pulp.

[0049] The amount of rosin size added in step c) may be within the range of from 2.1 kg / tonne to 4 kg / tonne based on dry weight of the paper.

[0050] The release agent may be added to the Yankee cylinder by spraying.

[0051] The method may produce an MG paper having a grammage of at least 30 g / m 2< , optionally at least 40 g / m 2< , such as at least 50 g / m 2< .

[0052] The method may produce an MG paper having a grammage within the range of from 30 and 110 g / m 2< .

[0053] The method may produce an MG paper having a grammage within the range of from 40 and 95 g / m 2< .

[0054] The method may produce an MG paper having a grammage within the range of from 50 and 95 g / m 2< .

[0055] The Cobb value of the MG paper may be 22 g / m 2< / 60s or below. Preferably the Cobb value of the MG paper is 21 g / m 2< / 60s or below, such as 20 g / m 2< / 60s or below. The Cobb value of the MG paper may within the range of from 15 to 21 or below.BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Aspects and embodiments are now described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a flowchart illustrating the steps of a method according to embodiments of the present disclosure. Fig. 2 is a flowchart illustrating the steps of a method according to embodiments of the present disclosure. Fig. 3 shows a graph illustrating approved machine glazed paper samples. DETAILED DESCRIPTION

[0057] The aspects of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown.

[0058] These aspects may, however, be embodied in many different forms and should not be construed as limiting; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and to fully convey the scope of all aspects of invention to those skilled in the art. Like numbers refer to like elements throughout the description.

[0059] In a first aspect, the present disclosure thus relates to an MG paper having a Cobb value of 23 g / m 2< / 60s or below, as measured according to the standard method ISO 535:2023, wherein the paper comprises AKD and rosin size and the ratio of AKD to rosin size is within of from 1:4 to 3:4.

[0060] The Cobb60 value is a measure of the water absorbency of a paper, in this disclosure an MG paper. Specifically, it quantifies the amount of water absorbed by a square meter of the paper in 60s. This measurement is relevant to describe the suitability for applications where moisture resistance is critical. The test involves placing a sample of the MG paper in contact with water for 60s and then measuring the increase in weight per unit area (grams per square meter, g / m 2< ). A higher Cobb60 value indicates greater water absorption, which might be undesirable for packaging or printing purposes where resistance to water is needed.

[0061] Machine glazing is a process used in paper manufacturing to produce a glossy finish on one side of the paper. This is achieved by passing the paper through a machine with a heated, smooth metal cylinder called a Yankee dryer or a glazing cylinder. The heat and pressure from the cylinder create a polished surface, enhancing the paper's smoothness. Machine-glazed paper is commonly used for products that require a high-gloss appearance, such as labels, wrapping papers, and certain types of packaging.

[0062] Papers with high hydrophobicity, and consequently lower Cobb60 values, may present greater challenges with reduced adherence to the glazing cylinder. This resistance to bonding can make it more difficult to achieve the desired level of gloss and smoothness and may also result in an uneven surface texture, resulting in a less uniform paper.

[0063] The present inventors have found that by balancing the levels of AKD and rosin size, an improvement the production efficiency and enhances the surface quality of the MG paper was obtained.

[0064] To achieve a reduced Cobb value, such as 23 g / m 2< / 60s or lower, such as 22 g / m 2< / 60s or lower, such as 21 g / m 2< / 60s or lower, such as 20 g / m 2< / 60s or lower, such as within the range of from 15 to 20 g / m 2< / 60s, internal sizing agents including AKA and rosin size have been added to the paper during papermaking.

[0065] The amount of AKD in the MG paper may be within the range of from 0.7 kg / tonne to 2.5 kg / tonne based on dry weight of the paper, optionally within the range of from 1 kg / tonne to 2 kg / tonne based on dry weight of the paper.

[0066] The amount of rosin size in the MG paper may be within the range of from 2 kg / tonne to 4.5 kg / tonne based on dry weight of the paper, optionally within the range of from 2.1 kg / tonne to 4 kg / tonne based on dry weight of the paper.

[0067] The fibers in the MG paper may be kraft pulp fibers. Optionally the kraft pulp fibers are bleached kraft pulp fibers.

[0068] The kraft pulp fibers may comprise softwood fibers. Optionally from 60 % by weight or more of the kraft pulp fibers are softwood fibers, such as from 60 to 95 % by dry weight of softwood fibers and from 5 to 40 % by dry weight of hardwood fibers.

[0069] According to a second aspect, and as illustrated in Fig. 1, the present disclosure relates to a method of producing a machine-glazed paper having a Cobb value of 23 g / m 2< / 60s or below as measured according to the standard method ISO 535:2023, wherein the method comprises the following steps: S1 - providing a pulp, S2 - diluting the pulp into a pulp stock, S3 - adding AKD and rosin size to the pulp stock, wherein the ratio AKD to rosin size is within the range of from 1:4 to 3:4 and the combined amount of AKD and rosin size results in a paper having a Cobb value of 23 g / m 2< / 60s or below, S4 - diluting the pulp stock in a headbox, S5 - adding the diluted pulp stock from the headbox to a forming wire to obtain a paper web, S6 - pressing the paper web, and S7 - glazing the paper web in a glazing unit, thereby forming the machine glazed paper.

[0070] According to a third aspect, and as illustrated in Fig. 2, the present disclosure relates to a method of producing a machine-glazed paper having a Cobb value of 23 g / m 2< / 60s or below as measured according to the standard method ISO 535:2023, wherein the method comprises the following steps: S10 - providing a pulp, S20 - diluting the pulp into a pulp stock, S30 - adding rosin size to the pulp stock, such that the amount of rosin size is within of from 2 kg / tonne to 4.5 kg / tonne based on the dry weight of the final MG paper, S40 - diluting the pulp stock in a headbox, S50 - adding the diluted pulp stock from the headbox to a forming wire to obtain a paper web, S60 - pressing the paper web, S70 - adding a release agent to the Yankee cylinder in a glazing unit, and S80 - glazing the paper web on the Yankee cylinder in a glazing unit, thereby forming the machine glazed paper. The release agent may be sprayed on the Yankee cylinder. The release agent may for example be any release agent suitable for Yankee cylinders, such as release agents from Petrofer, optionally the release agent may be a release agents within the Cotac series from Petrofer.EXPERIMENTAL SECTION

[0071] In the following experiments, various paper samples with grammages ranging from 60 g / m 2< to 70 g / m 2< were prepared according to the method described in the second aspect and illustrated in Fig. 1. The fibers used were bleached kraft fibers, comprising 70 wt.% softwood fibers and 30 wt.% hardwood fibers.

[0072] Samples were tested with varying amounts and relative proportions of AKD and rosin size. Fig. 3 shows the samples that were approved based on their performance during the glazing process. Approved samples are those that neither exhibited rejection from the MG cylinder nor too adhered to it during glazing.

[0073] The amounts of AKD and rosin size used in the approved samples are illustrated in the graph in Fig. 2, with the amount of AKD on the X-axis and the amount of rosin size on the Y-axis.

[0074] Each of the samples was evaluated for their Cobb values, with all paper samples having a Cobb60 of 23 g / m 2< / 60s or below. The approved samples had Cobb ranging from 17 to 21 g / m 2< / 60s, as measured by the standard method ISO 535:2023.

[0075] This experimental setup and the resulting data provide insights into the optimal sizing agent ratios for achieving desirable properties in MG papers.

[0076] For samples containing AKD in the range of from 0.7 kg / tonne to 2.5 kg / tonne, and rosin size in the range of from 2 kg / tonne to 4.5 kg, based on dry weight of the paper of the samples, with an AKD to rosin size ratio from 1:4 to 3:4, a surprising reduction of the samples experienced paper web rejection during glazing was observed.

[0077] For samples with AKD in the range of from 1 kg / tonne to 2 kg / tonne, and rosin size in the range of from 2.1 kg / tonne to 4 kg, based on dry weight of the paper, with an AKD to rosin size ratio from 1:3 to 2:3, a further improved efficiency of the glazing process was observed.

[0078] The experimental results indicate that the interaction between the AKD and rosin sizing agents plays a critical role in the performance of MG paper during the glazing process. The approved samples, which neither adhered to nor were rejected by the MG cylinder, demonstrated an optimal balance of AKD and rosin sizing agents.

[0079] The aspects of the present disclosure have mainly been described above with reference to a few embodiments and examples thereof. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

[0080] Thus, while various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

1. A machine-glazed (MG) paper having a Cobb value of 23 g / m2 / 60s or below as measured according to the standard method ISO 535:2023, wherein the paper comprises AKD and rosin size and the ratio of AKD to rosin size is within of from 1:4 to 3:4.

2. The MG paper according to claim 1, wherein the ratio of AKD to rosin size is within the range of from 1:3 to 2:3.

3. The MG paper according to claim 1 and 2, wherein the amount of AKD in the MG paper is within the range of from 0.7 kg / tonne to 2.5 kg / tonne based on dry weight of the paper, optionally within the range of from 1 kg / tonne to 2 kg / tonne based on dry weight of the paper.

4. The MG paper according to any one of claims 1 to 3, wherein the amount of rosin size in the MG paper is within the range of from 2 kg / tonne to 4.5 kg / tonne based on dry weight of the paper, optionally within the range of from 2.1 kg / tonne to 4 kg / tonne based on dry weight of the paper.

5. The MG paper according to any one of the preceding claims, wherein the grammage of the MG paper is at least 30 g / m2, optionally the grammage of the MG paper is at least 50 g / m2, optionally the grammage of the MG paper is within the range of from 30 and 110 g / m2, optionally the grammage of the MG paper is within the range of from 50 and 95 g / m2.

6. The MG paper according to any one of the preceding claims, wherein the Cobb value is 22 g / m2 / 60s or below, optionally the Cobb value is 21 g / m2 / 60s or below, optionally the Cobb value is 20 g / m2 / 60s or below, optionally the Cobb value is within the range of from 15 to 21 g / m2 / 60s.

7. The MG paper according to any one of the preceding claims, wherein the fibers in the MG paper are kraft fibers.

8. The MG paper according to claim 7, wherein at least 60 % by dry weight of the kraft fibers are softwood fibers, optionally 60 to 95 % by dry weight of the kraft fibers are softwood fibers and 5 to 40 % by dry weight are hardwood fibers.

9. Method of producing a machine-glazed paper having a Cobb value of 23 g / m2 / 60s or below as measured according to the standard method ISO 535:2023, wherein the method comprises the following steps: a) providing (S1) a pulp; b) diluting (S2) the pulp into a pulp stock; c) adding (S3) AKD and rosin size to the pulp stock, wherein the ratio AKD to rosin size is within the range of from 1:4 to 3:4 and the combined amount of AKD and rosin size results in a paper having a Cobb value of 23 g / m2 / 60s or below; d) diluting (S4) the pulp stock in a headbox; e) adding (S5)the diluted pulp stock from the headbox to a forming wire to obtain a paper web; f) pressing (S6) the paper web; and g) glazing (S7) the paper web in a glazing unit, thereby forming the machine glazed paper.

10. The method according to claim 9, wherein the amount of AKD in the MG paper is within the range of from 0.7 kg / tonne to 2.5 kg / tonne based on dry weight of the paper, optionally within the range of from 1 kg / tonne to 2 kg / tonne based on dry weight of the paper.

11. The method according to claim 9 or 10, wherein the amount of rosin size in the MG paper is within the range of from 2 kg / tonne to 4.5 kg / tonne based on dry weight of the paper, optionally within the range of from 2.1 kg / tonne to 4 kg / tonne based on dry weight of the paper.

12. A method of producing a machine-glazed paper having a Cobb value of 23 g / m2 / 60s or below as measured according to the standard method ISO 535:2023, wherein the method comprises the following steps: a) providing (S10) a pulp, b) adding (S20) rosin size to the pulp stock, such that the amount of rosin size is within the range of from 2 kg / tonne to 4.5 kg / tonne based on dry weight of the final MG paper, optionally within the range of from 2.1 kg / tonne to 4 kg / tonne based on dry weight of the paper, c) diluting (S30) the pulp stock in a headbox, d) adding (S40) the diluted pulp stock from the headbox to a forming wire to obtain a paper web, e) pressing (S50) the paper web, f) adding (S60) a release agent to a Yankee cylinder in a glazing unit, and g) glazing (S70) the paper web on the Yankee cylinder in the glazing unit, thereby forming the machine glazed paper having a Cobb value of 23 g / m2 / 60s or below.

13. The method according to any one of claims 9 to 12, wherein the pulp in step a) is kraft pulp.

14. The method according to claim 13, wherein the kraft pulp comprises at 60 % by dry weight or more of softwood pulp, optionally the kraft pulp comprises 60 to 95 % by dry weight of softwood pulp and 5 to 40 % by dry weight of hardwood pulp.

15. The method according to any one of claims 9 to 14, wherein the Cobb value is 22 g / m2 / 60s or below, optionally the Cobb value is 21 g / m2 / 60s or below, optionally the Cobb value is within the range of from 20 g / m2 / 60s to 15 g / m2 / 60s.

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