Classifications

• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes
  • D21H27/30—Multi-ply
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H11/00—Pulp or paper, comprising cellulose or lignocellulose fibres of natural origin only
  • D21H11/02—Chemical or chemomechanical or chemothermomechanical pulp
  • D21H11/04—Kraft or sulfate pulp
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H21/00—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties
  • D21H21/14—Non-fibrous material added to the pulp, characterised by its function, form or properties; Paper-impregnating or coating material, characterised by its function, form or properties characterised by function or properties in or on the paper
  • D21H21/18—Reinforcing agents
• • D—TEXTILES; PAPER
  • D21—PAPER-MAKING; PRODUCTION OF CELLULOSE
  • D21H—PULP COMPOSITIONS; PREPARATION THEREOF NOT COVERED BY SUBCLASSES D21C OR D21D; IMPREGNATING OR COATING OF PAPER; TREATMENT OF FINISHED PAPER NOT COVERED BY CLASS B31 OR SUBCLASS D21G; PAPER NOT OTHERWISE PROVIDED FOR
  • D21H27/00—Special paper not otherwise provided for, e.g. made by multi-step processes

Definitions

• the present invention relates to paperboard, particularly paperboard suitable for use as a cardboard liner, box making, laminated paper, etc., and to a method for manufacturing the same.
• Corrugated cardboard is manufactured by attaching a liner to one or both sides of a corrugated core using a corrugator.
• Corrugated cardboard is used for packaging various items because it is lightweight and inexpensive. During transportation, packaged items may collide with the cardboard from the inside, or the cardboard may be subjected to external impact during storage. For this reason, cardboard liners are required to have high bursting strength so that they will not break even when subjected to impact. Paperboard that requires bursting strength is generally blended with softwood kraft pulp as the raw pulp. This is because softwood kraft pulp has longer fibers than hardwood kraft pulp, and thus paper with excellent strength can be obtained.
• Patent Document 1 proposes a cardboard liner with excellent impact resistance that includes at least a surface layer, a subsurface layer, and a back layer, the surface layer containing softwood kraft pulp, the surface layer containing 80% or more by mass of softwood kraft pulp, the subsurface layer containing softwood kraft pulp and recycled corrugated cardboard pulp, the surface layer containing 25% to 35% by mass of softwood kraft pulp, the back layer containing recycled corrugated cardboard pulp and recycled magazine paper pulp, the back layer containing 30% to 70% by mass of recycled corrugated cardboard pulp, and the back layer containing 30% to 70% by mass of recycled magazine paper pulp.
• the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a paperboard that has excellent strength and print quality.
• the means for solving the above problems are as follows. 1. It has a surface layer, one or more middle layers, and a back layer; The hardwood kraft pulp content is 20% by mass or more based on the total pulp mass, The surface layer contains 50 to 100% by mass of softwood kraft pulp, A paperboard having a compression energy of 2.0 to 25.0 gf ⁇ cm/cm 2 and a compression recovery rate of 40 to 95%. 2. The paperboard according to 1., wherein the back layer contains 40 to 100% by weight of hardwood kraft pulp. 3. The paperboard according to 1. or 2., wherein the back layer contains an internal paper strength agent in an amount of 0.3 to 0.8% by mass based on the mass of the pulp. 4.
• the hardwood kraft pulp content is 20 to 95 mass%
• the softwood kraft pulp content is 5 to 50 mass%
• the recycled paper pulp content is 0 to 75 mass%, based on the total pulp mass; 4.
• the paperboard according to any one of 1. to 4. characterized in that the proportion of the basis weight of the back layer to the total basis weight is 30% by weight or more and 50% by weight or less.
• the paperboard of the present invention has excellent print quality and is suitable for applications in which patterns and color printing are applied.
• the paperboard of the present invention is less likely to develop line cracks (break lines arising from lined lines (shallow grooves) imparted to the base paper) when folded, and can maintain high strength even when used as packaging material for boxes and the like.
• the paperboard of the present invention can be suitably used, for example, as cardboard liners, medium base paper, paperboard for folding cartons, paperboard for box making, laminated paper, and the like.
• the paperboard of the present invention has a surface layer, one or more middle layers, and a back layer,
• the hardwood kraft pulp content is 20% by mass or more based on the total pulp mass
• the surface layer contains 50 to 100% by mass of softwood kraft pulp
• the compression energy is 2.0 to 25.0 gf ⁇ cm/cm 2
• the compression recovery rate is 40 to 95%.
• a to B (A and B are numerical values) means a numerical range including both ends, that is, A or more and B or less.
• the paperboard of the present invention is composed of a surface layer, one or more middle layers, and a back layer, with the surface layer and back layer being the outermost layers.
• the paperboard of the present invention has three or more layers, and the number of middle layers can be set appropriately depending on the required basis weight, etc.
• the back layer refers to the bottom surface during papermaking, and is the layer formed when the raw materials are first supplied to the wire part in a multi-layer papermaking machine, while the surface layer refers to the side opposite the back layer, i.e., the top surface during papermaking, and is the layer formed when the raw materials are last supplied to the wire part in a multi-layer papermaking machine.
• the paperboard of the present invention contains at least 20% by mass of hardwood kraft pulp relative to the total pulp mass.
• at least the surface layer of the paperboard of the present invention contains 50 to 100% by mass of softwood kraft pulp.
• hardwood kraft pulp and softwood kraft pulp either unbleached kraft pulp (LUKP/NUKP) or bleached kraft pulp (LBKP/NBKP) can be used, but when used in applications where whiteness is not required, unbleached kraft pulp is preferred because it has excellent strength and can be produced with low energy as it does not require a bleaching process.
• the paperboard of the present invention may contain various pulps derived from wood fibers, such as hardwood kraft pulp and softwood kraft pulp, waste paper pulp, groundwood pulp (GP), refiner ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), and non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, and the like.
• wood fibers such as hardwood kraft pulp and softwood kraft pulp, waste paper pulp, groundwood pulp (GP), refiner ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), and non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, and the like.
• the other pulp it is preferable to use inexpensive waste paper pulp.
• it is preferable that at least one of the front layer and the back layer of the paperboard of the present invention does not contain waste paper pulp, it is more preferable that the front layer does not contain waste paper pulp, and it is
• the blending amount of hardwood kraft pulp is preferably 20 to 95 mass %
• the blending amount of softwood kraft pulp is preferably 5 to 50 mass %
• the blending amount of recycled paper pulp is preferably 0 to 75 mass % based on the total pulp mass.
• the amount of hardwood kraft pulp relative to the total pulp mass is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 60% by mass or more, even more preferably 65% by mass or more, even more preferably 70% by mass or more.
• the amount of hardwood kraft pulp relative to the total pulp mass is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less.
• the content of softwood kraft pulp relative to the total pulp mass is preferably 10% by mass or more, more preferably 15% by mass or more, and is preferably 45% by mass or less, more preferably 40% by mass or less.
• waste paper pulp one or a mixture of two or more types of waste paper can be used, including waste paper pulp made by disintegrating unprinted waste paper such as cardboard, white, extra white, medium white, and white damage; waste paper printed on fine paper, fine coated paper, medium quality paper, medium quality coated paper, and recycled paper; written waste paper, papers such as discarded confidential documents, waste magazines, and pulp made by disintegrating and deinking waste newspapers (DIP).
• waste paper pulp derived from waste cardboard (hereinafter referred to as waste cardboard pulp) and waste magazines are preferred in terms of cost and strength.
• the amount of recycled paper pulp relative to the total pulp mass is not particularly limited, but the lower the amount of recycled paper pulp, the higher the bursting strength can be maintained. Therefore, from the perspective of bursting strength ratio, the amount of recycled paper pulp relative to the total pulp mass is preferably 75% by mass or less, more preferably 70% by mass or less, even more preferably 50% by mass or less, even more preferably 30% by mass or less, even more preferably 10% by mass or less, even more preferably 5% by mass or less, and most preferably 0% by mass (not included).
• recycled paper pulp is inexpensive, so the more the amount is increased, the lower the cost. Therefore, from the perspective of cost, the amount of recycled paper pulp relative to the total pulp mass is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more.
• the surface layer of the paperboard of the present invention contains 50 to 100% by mass of softwood kraft pulp. This gives the paperboard of the present invention excellent bursting strength and printability.
• the surface layer can contain hardwood kraft pulp, recycled paper pulp, etc., but it is preferable that the proportion of softwood kraft pulp is the highest. It is also preferable that the surface layer does not contain recycled paper pulp, and it is more preferable that the papermaking fibers of the surface layer are only softwood kraft pulp and hardwood kraft pulp.
• the amount of softwood kraft pulp in the surface layer is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and most preferably 100% by mass.
• the back layer of the paperboard of the present invention preferably contains 40 to 100% by mass of hardwood kraft pulp.
• the back layer may contain softwood kraft pulp, recycled paper pulp, etc., but preferably does not contain recycled paper pulp, and it is more preferable that the papermaking fibers in the back layer are only hardwood kraft pulp and softwood kraft pulp.
• the amount of hardwood kraft pulp in the back layer is more preferably 60% by mass or more, even more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and most preferably 100% by mass.
• the paperboard of the present invention needs to contain at least 20% by mass of hardwood kraft pulp relative to the total mass of pulp contained in the paperboard, and the surface layer needs to contain 50-100% by mass of softwood kraft pulp, and there are no particular restrictions on the pulp that constitutes the middle layer as long as this is satisfied.
• the middle layer may contain one or more of various pulps derived from wood fibers, such as softwood kraft pulp, hardwood kraft pulp, recycled paper pulp, groundwood pulp (GP), refiner ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), and chemi-thermomechanical pulp (CTMP), and non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, etc.
• the pulp compositions that constitute each middle layer may be the same or different.
• the back layer preferably contains 0.3 to 0.8% by mass of an internal strength enhancer (hereinafter also referred to as internal strength agent) relative to the pulp mass from the viewpoint of burst strength.
• an internal strength enhancer hereinafter also referred to as internal strength agent
• PAM polyacrylamide
• modified starch-based agents used in the papermaking field can be used without any particular restrictions, but it is preferable to use polyacrylamide-based agents because of their high paper strength enhancing effect.
• any of anionic, cationic, and amphoteric agents can be used.
• the blending amount of the internal strength agent relative to the pulp mass in the back layer is more preferably 0.35% by mass or more, even more preferably 0.4% by mass or more, and even more preferably 0.45% by mass or more.
• the internal strength agent can be blended in an amount of more than 0.8% by mass relative to the pulp mass, but even if it is blended in an amount of more than 0.8% by mass, the paper strength enhancing effect is almost saturated and hardly improved, and the cost becomes high.
• the paperboard of the present invention may contain the above-mentioned internal strength agent in layers other than the back layer.
• the amount of the internal strength agent contained in the layers other than the back layer is not particularly limited, but is about 0.01% by mass or more and 0.5% by mass or less.
• the type and amount of the internal strength agent in each paper layer of the paperboard of the present invention may be the same or different. However, it is preferable that the amount of the internal strength agent relative to the pulp in each layer is the highest in the back layer.
• the paperboard of the present invention may contain a sizing agent to improve the weather resistance of the paperboard.
• sizing agents include rosin-based sizing agents, rosin emulsion-based sizing agents, ⁇ -carboxymethyl saturated fatty acids, neutral rosin-based sizing agents, alkyl ketene dimers (AKD), alkenyl succinic anhydrides (ASA), cationic polymer-based sizing agents, etc., and one or more of these may be used.
• internal additives such as aluminum sulfate, aluminum chloride, sodium aluminate, basic aluminum compounds, water-soluble aluminum compounds, polyvalent metal compounds, and silica sol may be added to the extent that they do not affect the quality.
• the blending ratio of the sizing agent and other internal additives in each paper layer of the paperboard of the present invention may be the same or different.
• fillers can be added to each layer of the paperboard of the present invention as necessary.
• examples of fillers include inorganic fillers such as kaolin, calcined kaolin, delaminated kaolin, clay, calcined clay, delaminated clay, illite, heavy calcium carbonate, light calcium carbonate, light calcium carbonate-silica composite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, and organic fillers such as urea-formaldehyde resin, polystyrene resin, and phenolic resin, and one or more types can be used.
• the filler content in each paper layer of the paperboard of the present invention may be the same or different.
• the paperboard of the present invention may have a coating layer on its surface for the purpose of improving the strength of the paperboard, imparting printability, etc.
• the coating layer may contain one or more of known surface treatment chemicals such as an external paper strength agent (hereinafter also referred to as a surface strength agent), a surface sizing agent, a water repellent, a pigment, a binder resin, an anti-slip agent, an antiseptic, an antifoaming agent, a viscosity modifier, and an anti-crease agent.
• an external paper strength agent hereinafter also referred to as a surface strength agent
• a surface sizing agent e.g., a water repellent, e.g., a water repellent, a pigment, a binder resin, an anti-slip agent, an antiseptic, an antifoaming agent, a viscosity modifier, and an anti-crease agent.
• the surface strength agent may be a polyacrylamide-based agent, a polyvinyl alcohol-based agent, a starch-based agent such as oxidized starch, cationic starch, amphoteric starch, or a cellulose-based agent such as carboxymethyl cellulose, but a polyacrylamide-based agent is preferred.
• the coating amount of the surface strength agent is preferably 0.05 g/ m2 or more, and more preferably 0.1 g/ m2 or more.
• the coating layer preferably contains a surface sizing agent and a water repellent agent.
• the surface sizing agent include those similar to those for internal addition described above, and examples of the water repellent agent include fluorine-based resins, polyamide-based resins, wax emulsions, etc.
• the paperboard of the present invention has a compression energy of 2.0 to 25.0 gf ⁇ cm/cm 2 and a compression recovery rate of 40 to 95%.
• the compression energy indicates the energy required for compression, and the larger this value is, the easier it is to compress.
• the compression recovery rate indicates the recovery rate when returning to the original state from a compressed state, and the closer to 100(%), the higher the recovery rate is.
• the paperboard of the present invention satisfies the above compression energy and compression recovery rate, and therefore has excellent cushioning properties and can adhere closely to a printing plate, and therefore has excellent printability. In addition, because the paperboard of the present invention has excellent cushioning properties, it is less likely to break at the crease when folded.
• the compression energy is preferably 2.2 gf ⁇ cm/cm 2 or more, more preferably 2.4 gf ⁇ cm/cm 2 or more, and even more preferably 2.6 gf ⁇ cm/cm 2 or more.
• the compression recovery rate is preferably 43% or more, more preferably 46% or more, and even more preferably 50% or more.
• the paperboard of the present invention is less susceptible to crease cracks. It is preferable that the paperboard of the present invention has a crease crack rate of 50% or less when evaluated under conditions of 23°C and 50% humidity. The lower this crease crack rate, the more preferable, 46% or less is more preferable, 42% or less is even more preferable, and 38% or less is even more preferable.
• the paperboard of the present invention preferably has a burst strength index (burst strength divided by basis weight) of 2.2 kPa ⁇ m2 /g or more as defined in JIS P 8131:2009.
• the burst strength index is more preferably 2.4 kPa ⁇ m2 /g or more, even more preferably 2.6 kPa ⁇ m2 /g or more, even more preferably 2.8 kPa ⁇ m2 /g or more, and most preferably 3.0 kPa ⁇ m2 /g or more.
• the upper limit of the burst strength index of the paperboard of the present invention is not particularly limited, but is, for example, 4.0 kPa ⁇ m2 /g or less.
• the basis weight of the paperboard of the present invention is not particularly limited, but can be, for example, 50 g/m 2 or more and 800 g/m 2 or less.
• the paperboard of the present invention can be suitably used, for example, as cardboard, particularly as a liner for cardboard for packaging, corrugating medium, paperboard for paper containers, paperboard for box making, paperboard for laminated paper, etc.
• the total weight of all layers can be appropriately set in the range of 50 g/m 2 or more and 800 g/m 2 or less, and for example, when used as a cardboard liner, it can be 70 g/m 2 or more and 550 g/m 2 or less.
• the ratio of the basis weight of the back layer to the entire basis weight is preferably 30% by weight or more and 50% by weight or less, and more preferably 32% by weight or more and 45% by weight or less, from the viewpoint of burst strength.
• the ratio of the surface layer basis weight to the entire basis weight is preferably 10% by mass or more and 30% by mass or less, and more preferably 12% by mass or more and 25% by mass or less, from the viewpoint of burst strength.
• the ratio of the basis weight of all the intermediate layers to the whole basis weight is preferably 30% by mass or more and 50% by mass or less, more preferably 35% by mass or more and 45% by mass or less, from the viewpoint of burst strength.
• the basis weight ratio of each intermediate layer may be the same or different.
• the paperboard according to the present invention has three or more paper layers, and any known manufacturing (papermaking) method or papermaking machine can be selected, such as a combination papermaking machine that combines a Fourdrinier papermaking machine, a twin-wire papermaking machine, a cylinder papermaking machine, a gap former, a hybrid former (on-top former), etc.
• the pH during papermaking may be in the acidic range (acidic papermaking), pseudo-neutral range (pseudo-neutral papermaking), neutral range (neutral papermaking), or alkaline range (alkaline papermaking), and after papermaking in the acidic range, an alkaline agent may be applied to the surface of the paper layer.
• the blending of raw pulp and other ingredients differs for each layer, so that the paper stock is prepared according to each layer before papermaking.
• a shaking device is a device that slides the breast roll of the wire part in a direction perpendicular to the flow direction of the paper stock (also called the machine width direction).
• the basis weight is made uniform (the formation is improved), so that the number of thin parts compared to other parts that are the starting point of breakage is reduced, and the bursting strength is improved.
• the strength of the paperboard can be improved by adjusting the papermaking conditions of each layer.
• J/W ratio which is the ratio of the speed (J) of the jet liquid (paper material) ejected from the headbox to the speed (W) of the wire, to less than 100%
• J/W x 100 the ratio of the speed (J) of the jet liquid (paper material) ejected from the headbox to the speed (W) of the wire
• J/W x 100 the ratio of the speed (J) of the jet liquid (paper material) ejected from the headbox to the speed (W) of the wire
• J/W ratio is preferably 81% or more and 99% or less, and more preferably 84% or more and 98% or less.
• the strength can also be improved by changing the basis weight distribution of each layer to increase the basis weight of the surface layer and/or back layer, adjusting the paper strength agent content of each layer to make the paper strength agent content of the surface layer and/or back layer higher than that of the middle layer, etc.
• the type of press in the press part of the papermaking machine is not particularly limited, and any known press device can be used, for example, a straight-through press, a reverse press, an inbar press, a twin bar press, a pickup press, a unipress, a tri-nip press, a tri-vent press, a shoe press, a mini shoe press, etc.
• press conditions there are also no particular limitations on the press conditions, and they can be set appropriately within the normal operating range, but since a longer press time makes it easier for the fibers to hydrogen bond and improves the strength of the paperboard, it is preferable to make the paper at a low speed within a range that does not impair production efficiency.
• drying device used in the dry part process of the papermaking machine, so long as it does not impair production efficiency or the strength of the paperboard.
• Any known drying device such as the hot air drying method or multi-cylinder drying method used in normal papermaking machines, can be used.
• the number of drying devices installed can be one, or two or more pre-dryers, after-dryers, etc.
• drying conditions There are also no particular limitations on the drying conditions, and they can be set appropriately within the normal operating range.
• a coating liquid containing surface treatment chemicals such as a surface strength agent, a surface sizing agent, and a water repellent is applied after papermaking.
• surface treatment chemicals such as a surface strength agent, a surface sizing agent, and a water repellent
• known devices such as a two-roll size press, a gate roll coater, a shim sizer, and a spray can be used as appropriate.
• the calendar may be bypassed, or processing may be carried out within the normal operating range.
• the present invention will be described below with reference to examples, but the present invention is not limited to the following examples.
• the paperboards obtained in the following Examples and Comparative Examples were measured by the following methods. The results are shown in Table 1. (grammage) The measurement was carried out with reference to JIS P 8124. (Thickness) The measurement was carried out with reference to JIS P 8118. (density) The thickness was calculated from the basis weight with reference to JIS P 8118 and JIS P 8124.
• the bursting strength was measured with reference to JIS P 8131, and the bursting strength ratio was calculated by dividing the bursting strength by the basis weight.
• Cracked lines A paperboard sample cut into a 5 cm square was folded in half using a screw servo press (Muto Design Co., Ltd., MSV-10-200S) at a speed of 175 mm/min, a pressure of 5.0 kN, and a pressure time of 0.3 s, with the surface side facing outward and the fold line in the CD direction of the paperboard. The length of the cracked area on the surface of the sample was then measured and divided by the total length of the sample (5 cm) to obtain the crease crack rate.
• the paperboard sample was cut into a rectangle 50 mm long and 100 mm wide, and four sheets of the same shape were stacked to a thickness of approximately 1 mm.
• a KES-G5 compression tester manufactured by Kato Tech Co., Ltd.
• the sample was compressed between steel plates with a 2 cm2 circular flat surface at a speed of 50 sec/mm to a maximum stress of 5 kPa, and the compression energy and compression recovery rate were measured.
• Print Density A solid cyan print (size: 2 cm length x 3 cm width) was printed on the surface layer of the prepared paperboard using a flexographic printer (printability tester F1, manufactured by IGT Testing Systems Co., Ltd.). After one day, the print density (Macbeth density) after printing was measured using a Macbeth densitometer (Gretag Macbeth RD-19). The higher the print density, the more preferable it is. Under these conditions, the Macbeth density after printing is preferably 1.2 or more.
• Print gloss In accordance with JIS Z8741, the gloss (light incidence angle 75 degrees) of the solid cyan portion of the paperboard surface after the above flexographic printing was measured using a gloss meter (True GLOSS GM-26PRO, manufactured by Murakami Color Research Laboratory). The higher the print gloss value, the more preferable it is. Under these conditions, the preferred gloss value after printing is 12.5% or more.
• Print quality visual
• the print quality (print unevenness) of the sample after the above flexographic printing was visually evaluated according to the following criteria. ⁇ : There is almost no unevenness on the printed surface, and a uniform image is obtained. ⁇ : There is some unevenness on the printed surface, and the image is not uniform. x: The printed surface is uneven, and the image is very non-uniform.
• the pulp used in each layer is shown in Tables 1 to 3.
• the recycled paper pulp contained recycled cardboard pulp and recycled magazine paper in a mass ratio of 80:20.
• the mechanical treatment of the pulp was performed using a double conifer for the surface layer and a double disc refiner for the middle and back layers.
• the freeness (CSF) at the outlet of the double conifer and double disc refiner is shown in each table as the freeness (CSF) immediately after mechanical treatment.
• an internal paper strength agent (PAM) and an internal sizing agent (rosin-based) were added in the amounts shown in each table relative to the pulp to prepare a paper stock.
• the paper materials for each layer were combined using a multi-layer board machine in the following order to obtain the blending ratios and total layer basis weights shown in each table: back layer (35% by mass), two middle layers (25% by mass in the back, 20% by mass in the front), and front layer (20% by mass).
• back layer 35% by mass
• middle layers 25% by mass in the back
• front layer 20% by mass
• the J/W ratios of the front layer, middle layer (two layers), and back layer were all 90%, and a shaking device was operated in the wire part when the back layer was made, to obtain paperboard.
• the paperboard obtained in the examples of the present invention had excellent cushioning properties, excellent print quality, and a creasing rate of less than 50%.
• the paperboard obtained in the comparative example had poor cushioning properties, resulting in poor print quality and a creasing rate of over 50%, and in some cases over 60%.

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