Corrugated medium or liner containing nssc pulp

Abstract

The invention relates to a fluting or liner for corrugated board comprising a neutral sulphite semi-chemical (NSSC) pulp, wherein the NSSC pulp has an ash content of less than 1.8 wt.%, as determined according to standard ISO 1762:2019. The invention also relates to a corrugated board comprising the fluting and / or liner.

Description

Technical Field

[0001] This invention relates to a corrugated core paper or facing paper containing neutral sulfite semi-chemical (NSSC) pulp. Background Technology

[0002] Corrugated cardboard (sometimes also called corrugated hardboard or corrugated fiberboard) is a packaging material that can be transformed into different types of packaging solutions. Corrugated cardboard is a fiber-based material made from cellulose fibers, which may be virgin or recycled from used corrugated hardboard or other materials.

[0003] Corrugated board comprises a corrugated medium (fluting) and at least one non-corrugated medium (coating or linerboard) glued to the surface of the corrugated medium. For example, corrugated board may consist of a single corrugated medium glued between two layers of linerboard to form a sandwich structure. The sandwich structure can be formed in various ways, such as with single, double, and triple walls, as described in Kirwan M., J., Paper and Paperboard. Packaging Technology, Blackwell Publishing 2005.

[0004] One challenge in corrugated board production is the adhesion between the linerboard and the core paper. Insufficient adhesion leads to delamination, while adding too much adhesive to ensure sufficient adhesion can cause washboarding and curling of the corrugated board. It is crucial that the added adhesive is absorbed into the linerboard and / or the base paper. Delamination occurs if the adhesive is not absorbed by the core / linerboard, and the same happens if it is absorbed excessively into the core / linerboard.

[0005] Examples of different types of linerboard are kraft linerboard and testlinerboard. Kraft linerboard is typically produced from kraft pulp, which can be bleached or unbleached, and may comprise one or more layers, with the top layer often optimized for a good printable surface and good moisture resistance. Testlinerboard is primarily produced from recycled corrugated cardboard and is typically manufactured in two layers. Due to the presence of recycled fibers, testlinerboard generally has lower mechanical strength than kraft linerboard, particularly lower burst strength. Kraft linerboard is frequently used for packaging boxes where higher strength properties are required.

[0006] Corrugated core paper is formed from paper or paperboard that is corrugated using a corrugating machine by heating, humidifying and pressing.

[0007] Corrugated core paper is often made from neutral sulfite semi-chemical (NSSC) pulp. NSSC pulp (which is typically made from hardwood species) is known for its exceptional stiffness and high rigidity, making it suitable for corrugated core paper. Neutral sulfite semi-chemical (NSSC) pulping is a well-known, older process in the paper pulping industry. One reason for using NSSC pulping is its typically high yield, often exceeding 60%. In NSSC pulping, the cooking liquor contains sulfites such as Na₂SO₃ or (NH₄)₂SO₃, and alkalis such as NaOH or Na₂CO₃. "Neutral" refers to the pH value of the NSSC cooking liquor, which is typically between 6 and 10. The pulp can be cooked in batch or continuous digesters. Typically, cooking times are between 5 minutes and 3 hours, and cooking temperatures are 160-200°C. NSSC pulp contains a relatively high amount of residual lignin, such as 15-20%, which makes it stiff. The kappa value of NSSC pulp is typically above 70. NSSC pulping is "semi-chemical" because it also includes the mechanical refining of the pulp. Refining can be carried out, for example, at decomposer pressure or at atmospheric pressure using a disc refiner.

[0008] Currently, the strength and mechanical properties of corrugated core paper and base paper are improved by adding a small amount of chemical pulp to mechanical pulp. Typically, 5-15% chemical pulp is added. This, of course, not only increases costs but also leads to a decrease in dewatering speed. One potential approach is to blend semi-chemical pulps such as NSSC with unbleached kraft pulp, although this may result in undesirable optical spots and shading variations, as well as changes in sensory properties.

[0009] The corrugated core paper and the liner paper are attached to each other by applying an adhesive between the corrugated base paper and the liner paper. The liner paper is attached to at least one surface of the corrugated base paper by the adhesive. The adhesive is preferably applied to at least one surface of the grooved corrugated base paper, and then the liner paper is attached to said surface. Any conventional adhesive in the art can be used. The adhesive can be, for example, a glue based on starch that can be extracted from a variety of plants. Some of the most common plants are corn, wheat, barley, rice, potato, cassava, and peas. The starch is preferably natural, i.e., unmodified. The adhesive may also contain water, sodium hydroxide, and boric acid. Other additives may also be added, such as additives to improve wet strength or adhesive bond strength. Additionally, other functional chemicals may be added to improve, for example, moisture resistance or gelling behavior, such as borax, glyoxal, or mixtures thereof.

[0010] A significant challenge in the production of corrugated base paper and corrugated board is moisture resistance. When corrugated board is exposed to moisture, water and water vapor can diffuse through the linerboard and soften the base paper. A common solution to this problem is to increase the basis weight of the corrugated core paper and / or linerboard, but this conflicts with the environmental requirement for lower basis weight materials that consume less raw materials.

[0011] Another solution is to provide a barrier layer on the linerboard to reduce the penetration of water and water vapor. However, this is only a partial solution, as moisture diffusion can still occur on opposite sides or via the edges, thus affecting the mechanical stability of the corrugated board. The barrier layer also increases costs and generally reduces the material's recyclability.

[0012] Corrugated core paper or base paper can also be treated or coated with hydrophobic chemicals, but this typically increases costs and can negatively impact the mechanical properties of the corrugated core paper. High levels of hydrophobic chemicals can also impair the adhesion between the corrugated core paper and the linerboard. In particular, NSSC pulp requires high levels of hydrophobic chemicals to achieve the desired level of water resistance in the finished corrugated core paper.

[0013] New machine concepts and increased machine speeds, coupled with the growing demand for source reduction, have further increased the demand for pulps with improved properties.

[0014] There is still a need for new and improved corrugated core paper and linerboard materials that combine strength, low basis weight, water / moisture resistance, low chemical consumption, low cost, and / or high recycling capacity. Detailed Implementation

[0015] The purpose of this invention is to provide a corrugated core paper or facing paper that solves or improves at least some of the above-mentioned problems.

[0016] Another object of the present invention is to provide a corrugated core paper or linerboard with improved water-repellent properties, which can reduce the amount of hydrophobic internal sizing agent required to achieve the desired level of water repellency in the finished corrugated core paper or linerboard.

[0017] Another object of the present invention is to provide a corrugated board comprising an improved corrugated core paper and / or a facing paper.

[0018] The above objectives, as well as other objectives that a person skilled in the art would recognize from this disclosure, are achieved through various aspects of this disclosure.

[0019] This invention is based on the inventive understanding that if the ash content of the NSSC pulp used in corrugated core paper or linerboard is reduced, the amount of hydrophobic internal sizing agent required to achieve the desired level of water resistance in the finished corrugated core paper or linerboard can be significantly reduced. It has also been found that reducing the ash content of the pulp reduces the amount of other wet-end chemicals (e.g., drainage / retention chemicals in corrugated core paper or linerboard).

[0020] Ash content reduction can be achieved by washing the pulp. Ash content can also be reduced by more effectively removing bark before the pulping process.

[0021] According to a first aspect shown herein, a corrugated core or facing paper for corrugated board is provided comprising neutral sulfite semi-chemical (NSSC) pulp, wherein the NSSC pulp has an ash content of less than 1.8% by weight as determined according to standard ISO 1762:2019.

[0022] "NSSC pulp" is obtained from "NSSC pulping," which is further defined in the background section. NSSC pulp can be hardwood pulp or softwood pulp, or a mixture thereof. NSSC pulp is preferably hardwood pulp or a hardwood / softwood pulp mixture having less than 15% by weight of softwood, preferably less than 10% by weight, and more preferably less than 5% by weight of softwood. Hardwood can be, for example, aspen, alder, poplar, eucalyptus, birch, acacia, or beech. NSSC pulp is preferably prepared by cooking in a cooking liquor containing sulfite (preferably Na₂SO₃ or (NH₄)₂SO₃) and alkali (preferably NaOH or Na₂CO₃). In some embodiments, the yield of NSSC pulp is 60% or more, preferably 65% ​​or more, preferably 70% or more, and more preferably 75% or more. The term "neutral" means that the pH of the NSSC cooking liquor is in the range of 6-10. The cooking time is preferably in the range of 5 minutes to 3 hours. The cooking temperature is preferably in the range of 160-200°C. NSSC pulp may contain a relatively high amount of residual lignin, such as 15-20%. According to ISO 3260, the kappa number of NSSC pulp is generally above 70, preferably above 80, more preferably above 95, and even more preferably above 100. NSSC pulping is "semi-chemical" because it also includes mechanical refining of the pulp. Refining can be carried out, for example, under degassing pressure or at atmospheric pressure using a disc refiner. Refining can be carried out in one or more steps at the same or different pulp consistencyes. The first refining step can preferably be carried out at a higher consistency, such as 5-35%, and the second refining step can be carried out at a lower consistency, such as <5%.

[0023] In some embodiments, the NSSC pulp in the corrugated core paper or linerboard has been washed to reduce ash content. The purpose of washing is to separate the pulp from the black liquor, to remove residual substances such as alkali lignin generated during cooking, and to purify the pulp. Washing can be performed using one or more conventional pulp washing methods and equipment, including but not limited to rotary vacuum washers, rotary pressure washers, pressure and atmospheric diffusion washers, horizontal belt washers, and / or dilution / extraction equipment. Washing involves diluting the NSSC pulp with water, followed by removing the water along with diluted colloidal substances, salts, impurities, and fines through a screen.

[0024] In some embodiments, NSSC pulp is prepared from wood containing less than 3% by weight, less than 2.5% by weight, less than 2% by weight, or preferably less than 1% by weight or less than 0.8% by weight of bark.

[0025] The reduction in ash content can be measured by measuring the ash content according to standard ISO 1762:2019. In some embodiments, the NSSC pulp has an ash content of less than 1.6 wt%, preferably less than 1.4 wt%, and more preferably less than 1.2 wt%, less than 1.0 wt%, or less than 0.9 wt%, as determined according to standard ISO 1762:2019. In some embodiments, the corrugated core paper or facing paper has an ash content of less than 1.6 wt%, preferably less than 1.4 wt%, and more preferably less than 1.2 wt%, less than 1.0 wt%, or less than 0.9 wt%, as determined according to standard ISO 1762:2019.

[0026] The reduction in ash content can also be measured by measuring the hot water extract conductivity of the NSSC pulp according to ISO 6587. In some embodiments, the NSSC pulp has a hot water extract conductivity of less than 15 mS / cm, preferably less than 10 mS / cm, and more preferably less than 8 mS / cm, as determined according to ISO 6587. In some embodiments, the corrugated core paper or facing paper has a hot water extract conductivity of less than 15 mS / cm, preferably less than 10 mS / cm, and more preferably less than 8 mS / cm, as determined according to ISO 6587.

[0027] In some embodiments, when decomposed in distilled water at 3.5% by weight, the conductivity of the NSSC pulp used in corrugated core paper or linerboard is less than 1200, less than 1000, less than 800 or less than 600, and more preferably less than 500, less than 450, less than 400, less than 350 or less than 300 mS / m.

[0028] In some embodiments, the NSSC pulp contains less than 2%, preferably less than 1.8%, more preferably less than 1.6% of Pulmac shives (sieve size 0.1 mm). It has been found advantageous to use pulp with a lower amount of shives.

[0029] In addition to reducing ash content, washing can also lead to a reduction in the cellulose fines content in NSSC pulp. As used herein, cellulose fines generally refer to cellulose particles that are significantly smaller than cellulose fibers. In some embodiments, fines, as used herein, refer to fine cellulose particles that can pass through a 200-mesh sieve (equivalent pore diameter 76 μm) of a conventional laboratory grading apparatus (SCAN-CM 66:05). The reduction in fines in NSSC pulp can, for example, range from 0.1 to 10% by weight, or from 0.5 to 7% by weight.

[0030] The inventors have discovered that by reducing the ash content of NSSC pulp, the amount of hydrophobic internal sizing agent required to achieve the desired level of water resistance in finished corrugated core paper or linerboard can be significantly reduced.

[0031] Therefore, NSSC pulp is used in pulp compositions for corrugated core paper or linerboard used in corrugated board, wherein the pulp composition further comprises at least one internal sizing agent. The term "pulp composition" refers to an aqueous dispersion of cellulose fibers and non-cellulose additives used as ingredients in the manufacture of paper or paperboard in a paper machine.

[0032] The pulp composition of corrugated core paper or linerboard preferably comprises mainly NSSC pulp. Preferably, at least 50% by weight of the pulp composition is NSSC pulp based on dry weight. In other examples, at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 98% by weight of the pulp is NSSC pulp based on dry weight.

[0033] The non-NSSC pulp portion of the pulp composition may contain any type of fiber, such as hardwood and / or softwood fibers, and may include, for example, chemical pulp, mechanical pulp, thermomechanical pulp, or chemi-thermomechanical pulp (CTMP). The non-NSSC pulp portion of the pulp composition may also, for example, contain recycled fibers. For example, the pulp of this disclosure may consist essentially of NSSC pulp or a mixture of NSSC pulp and recycled fibers. "Recycled fibers" refers to fibrous materials that have previously been incorporated into certain paper or paperboard products. Alternatively, or additionally, the non-NSSC pulp portion of the pulp may, for example, contain reject pulp. For example, the pulp of this disclosure may consist essentially of NSSC pulp and reject pulp. "Reject pulp" refers to pulp prepared by refining screen residue from the pulping process.

[0034] In some embodiments, the pulp composition contains less than 10% by weight, preferably less than 5% by weight, and more preferably less than 2% by weight of recycled fibers. A small amount of recycled fibers is preferred because a significant amount of inorganic material is typically added via recycled fibers. In some embodiments, the corrugated core paper contains less than 10% by weight, preferably less than 5% by weight, and more preferably less than 2% by weight of recycled fibers.

[0035] The corrugated core paper and / or linerboard may further comprise an internal sizing agent. The internal sizing agent is preferably a hydrophobic sizing agent. In some embodiments, the internal sizing agent is selected from alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), rosin, and mixtures thereof. In a preferred embodiment, the internal sizing agent is an alkyl ketene dimer (AKD).

[0036] In some embodiments, based on dry weight, the amount of internal sizing agent in the corrugated core paper or linerboard is in the range of 0.5-6 kg / tn, preferably in the range of 0.5-4 kg / tn, more preferably in the range of 0.5-3 kg / tn, and even more preferably in the range of 1-2 kg / tn. Therefore, the amount of sizing agent in the corrugated core paper or linerboard is quite low.

[0037] At least one side of the corrugated core paper or linerboard preferably has a Cobb 30s value of 30 or less, preferably 25 or less, and more preferably 22 or less, as determined according to standard ISO 535. It is likely preferred that both sides of the corrugated core paper or linerboard have Cobb 30s values ​​of 30 or less, preferably 25 or less, and more preferably 22 or less, as determined according to standard ISO 535. Surprisingly, it has been found that adding clean NSSC pulp to the bottom or top layer of the linerboard or corrugated core paper does not negatively affect the Cobb value. Therefore, one or both sides of the linerboard or corrugated core paper containing clean NSSC pulp preferably have a Cobb 30s value of 30 or less, preferably 25 or less, and more preferably 22 or less, as determined according to standard ISO 535. NSSC pulp is typically used for the back sheet layer of corrugated core paper or linerboard, and it is then preferred that the back side of the corrugated core paper or linerboard has a Cobb 30s value of less than 30, preferably less than 25, and more preferably less than 22, as determined according to standard ISO 535.

[0038] To produce high-quality paper such as corrugated core paper or linerboard from large quantities of NSSC pulp at high machine speeds, it is crucial to effectively retain mineral fillers and fiber fines while achieving high dewatering rates. Particulate retention aids, typically utilizing anionic colloidal silica and / or clay-based particles combined with cationic polymers, have been developed to help address these challenges. Generally, particulate retention aids exhibit better retention and dewatering performance compared to classic monopolymer or dipolymer retention aids. In some embodiments, the corrugated core paper or linerboard further incorporates a particulate retention aid, preferably a multi-component particulate retention aid.

[0039] In some implementations, the microparticles in the microparticle retention system are selected from silica microparticles, bentonite microparticles, and cellulose nanoparticles.

[0040] In some implementations, the particulate retention system comprises a water-soluble polymer, preferably a cationic polymer.

[0041] In some implementations, the amount of particulate retention aid system in corrugated core paper or linerboard is in the range of 50 g / tn to 5 kg / tn based on dry weight, and more preferably in the range of 100 g / tn to 2 kg / tn.

[0042] Corrugated core paper or linerboard may also contain additional components commonly used in the production of corrugated core paper or linerboard, such as natural starch or starch derivatives, microfibrillated cellulose (MFC), cellulose derivatives such as sodium carboxymethyl cellulose, fillers, retention and / or emission chemicals, flocculants, antiflocculation additives, dry strength additives, softeners, crosslinking aids, sizing agents, dyes and colorants, wet strength resins, fixatives, defoaming aids, microbial and slime control aids, or mixtures thereof.

[0043] Corrugated core paper or linerboard is typically a single-layer product, but it can also be a multi-layer product. Corrugated core paper or linerboard is usually formed in a gap former, but it can also be formed in a Fourdrinier type forming machine. The press section can be equipped with a shoe press to maximize production.

[0044] The basis weight of corrugated core paper or linerboard can preferably be in the range of 80-300 gsm.

[0045] In some embodiments, the corrugated core paper or linerboard has an equilibrium moisture content (EMC) of less than 10% by weight, preferably less than 8% by weight, at 50% RH, as determined according to standard ISO 287.

[0046] In some embodiments, the corrugated core paper or facing paper has a cd / md elongation value greater than 1.8, preferably greater than 1.9, and more preferably greater than 2.0, as determined according to standard ISO 1924-3.

[0047] In some embodiments, the corrugated core paper or facing paper has a dynamic friction of less than 0.5, preferably less than 0.45, and more preferably less than 0.4, as determined according to standard ASTM D 1894-63.

[0048] According to a second aspect shown herein, a corrugated board is provided, comprising a corrugated core paper and / or a facing paper according to a first aspect. The corrugated board comprises at least one layer of non-corrugated facing paper and at least one layer of corrugated core paper. In the normal production of the corrugated board, the corrugated core paper is corrugated and then glued to the facing paper. For example, the corrugated board may consist of a single layer of corrugated core paper sandwiched between two layers of facing paper.

[0049] While the invention has been described with reference to various exemplary embodiments, those skilled in the art will understand that various changes can be made and elements can be substituted with equivalents without departing from the scope of the invention. Furthermore, many modifications can be made to adapt particular situations or materials to the teachings of the invention without departing from the basic scope of the invention. Therefore, it is intended that the invention be limited to the specific embodiments disclosed as the best mode contemplated for carrying out the invention, but that the invention encompass all embodiments falling within the scope of the appended claims.

[0050] Example

[0051] Examples show that washed NSSC slurry can be used in sheet manufacturing and provides improved mechanical properties and different responses to liquid absorption.

[0052] Example 1 (Comparative)

[0053] NSSC beech pulp was obtained in dry form, then broken down into feedstock, and produced to 150 g / m³ on a Fourdrinier pilot paper machine. 2 The single-layer web material is produced at a speed of 45 m / min and a batching temperature of 45°C.

[0054] Example 2 (Comparative)

[0055] The NSSC beech pulp used in Example 1 was finely ground to a higher SR value, and the web was prepared as in Example 1. The increased SR due to fine grinding particularly increased the tensile index (Geom).

[0056] Example 3

[0057] Water used in Eimco belt washing units (40m³ per ton of slurry) 3 The NSSC beech pulp used in Example 1 was washed with fresh water. 2.7% of the fines were removed along with colloidal substances and impurities (including electrolytes) in the liquid phase. As a result of the washing, the pH of the pulp suspension increased, confirming the removal of electrolytes and the reduction in ash content. Webs were prepared as in Example 1. A slight increase in tensile strength and elongation was noted.

[0058] Example 4

[0059] The NSSC beech pulp used as in Example 1 was mixed with washed NSSC birch pulp (washed as described in Example 3). The pulps were mixed at a 50-50 ratio. Webs were prepared as in Example 1. Significant improvements in tensile strength and elongation were observed.

[0060] Example 5

[0061] In this embodiment, washed NSSC birch pulp, as used in Example 4, was used without any other fibers. The web was prepared as in Example 1. Tensile strength and elongation were further improved.

[0062] Table 1. Slurry Compositions

[0063]

[0064] Table 2. Physical properties of the formed sheet

[0065]

[0066] Example 6

[0067] In this embodiment, washed NSSC pulp is added to the liner paper. The washed pulp has an ash content of less than 1.8% by weight.

[0068] Unwashed NSSC pulp was added to another linerboard for comparison. The unwashed NSSC pulp had an ash content of more than 1.8% by weight.

[0069] All the linerboard produced includes unbleached kraft pulp (100%) in the top sheet layer and recycled fiber (RCF) pulp in the back sheet layer with or without the addition of NSSC pulp.

[0070] Table 3. Results

[0071]

[0072] These tests clearly demonstrate that, as shown in Sample 3 (S3) in Table 3, the use of clean NSSC pulp in the linerboard provides a very good Cobb value, even on the back side. The Cobb value is at the same level as the reference sample. It is evident, as can be seen in Samples 1 and 2 (S1 and S2), that the use of unwashed NSSC pulp will provide linerboard with a high Cobb value, meaning these samples have significantly lower water resistance. Therefore, with this invention, linerboard with good (high) water resistance can be produced even with a small amount of internal sizing additives.

[0073] Unless otherwise stated, the physical properties discussed in this disclosure are determined according to the following criteria:

[0074]

[0075]

[0076] Unless otherwise stated, the standard method can then be used to determine the physical and mechanical properties in the transverse (cd) and machine direction (md).

Claims

1. Corrugated core paper or linerboard for corrugated board comprising neutral sulfite semi-chemical (NSSC) pulp, wherein the NSSC pulp has an ash content of less than 1.6% by weight as determined according to standard ISO 1762:2019.

2. The corrugated core paper or facing paper according to claim 1, wherein the NSSC pulp has been washed to reduce ash content.

3. The corrugated core paper or facing paper according to claim 1 or 2, wherein the NSSC pulp has an ash content of less than 1.4% by weight as determined according to standard ISO 1762:2019.

4. The corrugated core paper or facing paper according to claim 3, wherein the NSSC pulp has an ash content of less than 1.2% by weight as determined according to standard ISO 1762:2019.

5. The corrugated core paper or facing paper according to claim 3, wherein the NSSC pulp has an ash content of less than 1.0% by weight as determined according to standard ISO 1762:2019.

6. The corrugated core paper or facing paper according to claim 3, wherein the NSSC pulp has an ash content of less than 0.9% by weight as determined according to standard ISO 1762:2019.

7. The corrugated core paper or facing paper according to claim 1 or 2, wherein the NSSC pulp has a hot water extract conductivity of less than 10 mS / cm as determined according to ISO 6587.

8. The corrugated core paper or facing paper according to claim 7, wherein the NSSC pulp has a hot water extract conductivity of less than 8 mS / cm as determined according to ISO 6587.

9. The corrugated core paper or facing paper according to claim 7, wherein the NSSC pulp has a hot water extract conductivity of less than 5 mS / cm as determined according to ISO 6587.

10. The corrugated core paper or facing paper according to claim 1 or 2, wherein the corrugated core paper or facing paper comprises at least one internal sizing agent.

11. The corrugated core paper or facing paper according to claim 10, wherein the internal sizing agent is selected from alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), rosin, and mixtures thereof.

12. The corrugated core paper or facing paper according to claim 11, wherein the internal sizing agent is an alkyl ketene dimer (AKD).

13. The corrugated core paper or facing paper according to claim 10, wherein the amount of the internal sizing agent in the corrugated core paper or facing paper is in the range of 0.5-6 kg / tn based on dry weight.

14. The corrugated core paper or facing paper according to claim 13, wherein the amount of the internal sizing agent in the corrugated core paper or facing paper is in the range of 0.8-4 kg / tn based on dry weight.

15. The corrugated core paper or facing paper according to claim 13, wherein the amount of the internal sizing agent in the corrugated core paper or facing paper is in the range of 1-3 kg / tn based on dry weight.

16. The corrugated core paper or facing paper according to claim 1 or 2, further comprising a particulate retention aid system.

17. The corrugated core paper or linerboard according to claim 16, wherein the particulate retention aid system is a multi-component particulate retention aid system.

18. The corrugated core paper or facing paper according to claim 16, wherein the microparticles in the microparticle retention aid system are selected from silica microparticles, bentonite microparticles, and cellulose nanoparticles.

19. The corrugated core paper or facing paper according to claim 16, wherein the particulate retention aid system comprises a water-soluble polymer.

20. The corrugated core paper or facing paper according to claim 19, wherein the water-soluble polymer is a cationic polymer.

21. The corrugated core paper or facing paper according to claim 1 or 2, wherein at least one side of the corrugated core paper or facing paper has a Cobb (60s) value of less than 40 gsm as determined according to standard ISO 535.

22. The corrugated core paper or facing paper according to claim 21, wherein at least one side of the corrugated core paper or facing paper has a Cobb (60s) value of less than 35 gsm as determined according to standard ISO 535.

23. The corrugated core paper or facing paper according to claim 21, wherein at least one side of the corrugated core paper or facing paper has a Cobb (60s) value of less than 30 gsm as determined according to standard ISO 535.

24. The corrugated core paper or facing paper according to claim 1 or 2, wherein the corrugated core paper or facing paper contains less than 10% by weight of recycled fibers.

25. The corrugated core paper or facing paper according to claim 24, wherein the corrugated core paper or facing paper contains less than 5% by weight of recycled fibers.

26. The corrugated core paper or facing paper according to claim 24, wherein the corrugated core paper or facing paper contains less than 2% by weight of recycled fibers.

27. The corrugated core paper or facing paper according to claim 1 or 2, wherein the corrugated core paper or facing paper has a hot water extract conductivity of less than 15 mS / cm as determined according to ISO 6587.

28. The corrugated core paper or facing paper according to claim 27, wherein the corrugated core paper or facing paper has a hot water extract conductivity of less than 10 mS / cm as determined according to ISO 6587.

29. The corrugated core paper or facing paper according to claim 27, wherein the corrugated core paper or facing paper has a hot water extract conductivity of less than 8 mS / cm as determined according to ISO 6587.

30. The corrugated core paper or facing paper according to claim 1 or 2, wherein the corrugated core paper has an equilibrium moisture content (EMC) of less than 10% by weight at 50% RH as determined according to standard ISO 287.

31. The corrugated core paper or facing paper according to claim 30, wherein the corrugated core paper has an equilibrium moisture content (EMC) of less than 8% by weight at 50% RH as determined according to standard ISO 287.

32. The corrugated core paper or facing paper according to claim 1 or 2, wherein the corrugated core paper or facing paper has an elongation value of greater than 1.8 cd / md as determined according to standard ISO 1924-3.

33. The corrugated core paper or facing paper according to claim 32, wherein the corrugated core paper or facing paper has an elongation value of greater than 1.9 as determined according to standard ISO 1924-3.

34. The corrugated core paper or facing paper according to claim 32, wherein the corrugated core paper or facing paper has an elongation value of greater than 2.0 cd / md as determined according to standard ISO 1924-3.

35. The corrugated core paper or facing paper according to claim 1 or 2, wherein the corrugated core paper has a dynamic friction of less than 0.5 as determined according to standard ASTM D 1894-63.

36. The corrugated core paper or facing paper according to claim 35, wherein the corrugated core paper has a dynamic friction of less than 0.45 as determined according to standard ASTM D1894-63.

37. The corrugated core paper or facing paper according to claim 35, wherein the corrugated core paper has a dynamic friction of less than 0.4 as determined according to standard ASTM D1894-63.

38. Corrugated cardboard, comprising corrugated core paper and / or facing paper according to any one of claims 1 to 37.

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