WO2024190422A1 - Paperboard and method for manufacturing same - Google Patents

Paperboard and method for manufacturing same Download PDF

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Publication number
WO2024190422A1
WO2024190422A1 PCT/JP2024/007367 JP2024007367W WO2024190422A1 WO 2024190422 A1 WO2024190422 A1 WO 2024190422A1 JP 2024007367 W JP2024007367 W JP 2024007367W WO 2024190422 A1 WO2024190422 A1 WO 2024190422A1
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WO
WIPO (PCT)
Prior art keywords
mass
pulp
paperboard
layer
kraft pulp
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Application number
PCT/JP2024/007367
Other languages
French (fr)
Japanese (ja)
Inventor
勇介 秋山
祐也 松野
洸太 藤本
賢太郎 川▲崎▼
Original Assignee
日本製紙株式会社
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Application filed by 日本製紙株式会社 filed Critical 日本製紙株式会社
Publication of WO2024190422A1 publication Critical patent/WO2024190422A1/en

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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
    • 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
    • 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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Abstract

The present invention addresses the problem of providing paperboard having excellent strength and printing quality.　Provided as a solution is paperboard having a top layer, at least one middle layer, and a bottom layer and including at least 20 mass% of broad-leaved tree kraft pulp relative to the total pulp mass thereof, wherein: the top layer includes 50-100 mass% of needle-leaved tree kraft pulp; the compression energy is 2.0-25.0 gf·cm/cm2; and the compression recovery rate is 40-95%.

Description

板紙およびその製造方法Paperboard and its manufacturing method
　本発明は、板紙、特に、段ボール用ライナや製函、積層合紙等に好適な板紙と、その製造方法に関する。 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.
　段ボールは、波形に成形した中芯の片面あるいは両面にライナをコルゲーターで貼り合わせて製造される。
　段ボールは、軽量で安価であるため、種々の物品の梱包に使用されている。段ボールは、運搬時等に梱包物が内側から衝突する、あるいは、保管時等に外部から衝撃を受ける場合がある。そのため、段ボール用ライナには、衝撃を受けても破れないように高い破裂強さが要求される。破裂強さが要求される板紙は、一般的に、原料パルプとして、針葉樹クラフトパルプが配合される。これは、針葉樹クラフトパルプは広葉樹クラフトパルプと比較して繊維が長いことから、強度に優れた紙が得られるためである。 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.
　例えば、特許文献１には、少なくとも表面層、表下層及び裏面層を備え、表面層が針葉樹クラフトパルプを含有し、表面層における針葉樹クラフトパルプの含有量が８０質量％以上であり、表下層が針葉樹クラフトパルプ及び段ボール古紙パルプを含有し、表下層における針葉樹クラフトパルプの含有量が２５質量％以上３５質量％以下であり、裏面層が段ボール古紙パルプ及び雑誌古紙パルプを含有し、裏面層における段ボール古紙パルプの含有量が３０質量％以上７０質量％以下であり、裏面層における雑誌古紙パルプの含有量が３０質量％以上７０質量％以下である、耐衝撃性に優れた段ボール用ライナが提案されている。 For example, 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.
特開２０２０－１９３３９６号公報JP 2020-193396 A
　近年、通信販売の取り扱い量が急激に増加しており、通販業者によっては独自の印刷を施した段ボール包装が用いられているが、その印刷デザインも洗練されたものが求められている。そして、針葉樹クラフトパルプを高配合した板紙は、クッション性が低いため印刷版との密着性が悪く、段ボール表面に図柄等を印刷したときの印刷品質に劣ることが判明した。
　本発明は、このような事情に鑑みてなされたものであり、強度と印刷品質とに優れた板紙を提供することを課題とする。 In recent years, the volume of mail order sales has increased dramatically, and some mail order companies use cardboard packaging with original printing, but the printing designs are also required to be sophisticated. However, it was found that paperboard with a high content of softwood kraft pulp has poor cushioning properties and therefore poor adhesion to the printing plate, resulting in poor print quality when patterns are printed on the surface of the cardboard.
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.
　上記課題を解決するための手段は以下の通りである。
１．表層、１層以上の中層、裏層を有し、
　全パルプ質量に対して、広葉樹クラフトパルプを２０質量％以上含み、
　前記表層が、針葉樹クラフトパルプを５０～１００質量％含み、
　圧縮エネルギーが２．０～２５．０ｇｆ・ｃｍ／ｃｍ２、圧縮回復率が４０～９５％であることを特徴とする板紙。
２．前記裏層が、広葉樹クラフトパルプを４０～１００質量％含むことを特徴とする１．に記載の板紙。
３．前記裏層が、パルプ質量に対して、内添紙力増強剤を０．３～０．８質量％含むことを特徴とする１．または２．に記載の板紙。
４．全パルプ質量に対して、広葉樹クラフトパルプ含有量が２０～９５質量％、針葉樹クラフトパルプ含有量が５～５０質量％、古紙パルプ含有量が０～７５質量％であり、
　前記表層が、古紙パルプを含有しないことを特徴とする１．～３．のいずれかに記載の板紙。
５．全坪量に対する前記裏層の坪量の割合が、３０質量％以上５０質量％以下であることを特徴とする１．～４．のいずれかに記載の板紙。
６．１．～５．のいずれかに記載の板紙からなる段ボール用ライナ。 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%, and 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 3., wherein the surface layer does not contain recycled paper pulp.
5. 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.
6. A cardboard liner made of the paperboard according to any one of 1. to 5.
　本発明の板紙は、印刷品質に優れており、絵柄やカラー印刷を施す用途に適している。本発明の板紙は、折り曲げ加工をした際に罫線割れ（原紙に付与された罫線（浅い溝）から発生する破損線）が生じにくく、箱等の包材とした際にも強度を高く保つことができる。本発明の板紙は、例えば、段ボール用ライナ、中しん原紙、紙器用板紙、製函用の板紙、積層合紙等に好適に利用することができる。 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.
　本発明の板紙は、表層、１層以上の中層、裏層を有し、
　全パルプ質量に対して、広葉樹クラフトパルプを２０質量％以上含み、
　前記表層が、針葉樹クラフトパルプを５０～１００質量％含み、
　圧縮エネルギーが２．０～２５．０ｇｆ・ｃｍ／ｃｍ２、圧縮回復率が４０～９５％である。
　なお、本明細書において、「Ａ～Ｂ」（Ａ、Ｂは数値）との記載は、その両端を含む数値範囲、すなわち、Ａ以上Ｂ以下を意味する。 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 , and the compression recovery rate is 40 to 95%.
In this specification, the expression "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.
　本発明の板紙は、表層、１層以上の中層、裏層とで構成され、表層と裏層とが最外層である。本発明の板紙の層数は、３層以上であり、要求される坪量等に応じて中層の層数を適宜設定することができる。なお、裏層とは、抄紙時における下面であり、かつ多層抄き抄紙機において最初にワイヤーパートへ原料が供給されて形成される層を指し、表層とは裏層の反対側、つまり抄紙時における上面であり、かつ多層抄き抄紙機において最後にワイヤーパートへ原料が供給されて形成される層を意味する。 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.
　本発明の板紙は、全パルプ質量に対して、広葉樹クラフトパルプを２０質量％以上含む。また、本発明の板紙は、少なくとも表層が針葉樹クラフトパルプを５０～１００質量％含有する。広葉樹クラフトパルプと針葉樹クラフトパルプとしては、未晒クラフトパルプ（ＬＵＫＰ／ＮＵＫＰ）、晒クラフトパルプ（ＬＢＫＰ／ＮＢＫＰ）のどちらも使用することができるが、白さが求められない用途に用いる場合、未晒クラフトパルプが、強度に優れるうえ、漂白工程が不要なため低エネルギーで生産できる点で好ましい。 The paperboard of the present invention contains at least 20% by mass of hardwood kraft pulp relative to the total pulp mass. In addition, at least the surface layer of the paperboard of the present invention contains 50 to 100% by mass of softwood kraft pulp. As 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.
　本発明の板紙は、広葉樹クラフトパルプ、針葉樹クラフトパルプの他に、古紙パルプ、砕木パルプ（ＧＰ）、リファイナーグラウンドパルプ（ＲＧＰ）、ケミカルパルプ（ＣＰ）、サーモメカニカルパルプ（ＴＭＰ）、ケミサーモメカニカルパルプ（ＣＴＭＰ）等の木材繊維由来の各種パルプ、ケナフ、バガス、竹、麻、ワラなどから得られた非木材パルプ等を含むことができる。他のパルプとしては、安価な古紙パルプを用いることが好ましい。ただし、本発明の板紙は、表層と裏層の少なくとも一方が古紙パルプを含有しないことが好ましく、表層が古紙パルプを含有しないことがより好ましく、表層と裏層の両方が古紙パルプを含有しないことがさらに好ましい。
　本発明の各層で使用するパルプのカナダ標準濾水度は特に制限されないが、３００ｍｌＣＳＦ以上６００ｍｌＣＳＦ以下であることが好ましい。 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. As the other pulp, it is preferable to use inexpensive waste paper pulp. However, 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 even more preferable that both the front layer and the back layer do not contain waste paper pulp.
The Canadian Standard Freeness of the pulp used in each layer of the present invention is not particularly limited, but is preferably 300 ml CSF or more and 600 ml CSF or less.
　本発明の板紙において、全パルプ質量に対する広葉樹クラフトパルプの配合量は２０～９５質量％、針葉樹クラフトパルプの配合量は５～５０質量％、古紙パルプの配合量は０～７５質量％であることが好ましい。
　全パルプ質量に対する広葉樹クラフトパルプの配合量は、３０質量％以上がより好ましく、４０質量％以上がさらに好ましく、６０質量％以上がよりさらに好ましく、６５質量％以上がよりさらに好ましく、７０質量％以上がよりさらに好ましい。また、全パルプ質量に対する広葉樹クラフトパルプの配合量は、９５質量％以下が好ましく、９０質量％以下がより好ましく、８５質量％以下がよりさらに好ましい。
　本発明の板紙において、全パルプ質量に対する針葉樹クラフトパルプの配合量は、１０質量％以上がより好ましく、１５質量％以上がさらに好ましい。また、全パルプ質量に対する針葉樹クラフトパルプの配合量は、４５質量％以下が好ましく、４０質量％以下がより好ましい。 In the paperboard of the present invention, 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 %, and 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.
In the paperboard of the present invention, 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.
　古紙パルプとしては、段ボール古紙、上白、特白、中白、白損等の未印刷古紙を離解した古紙パルプ、上質紙、上質コート紙、中質紙、中質コート紙、更紙等に印刷された古紙、および筆記された古紙、廃棄機密文書等の紙類、雑誌古紙、新聞古紙を離解後脱墨したパルプ（ＤＩＰ）等の１種、または２種以上を混合して使用することができる。これらの中で、コストと強度発現の点から、段ボール古紙由来の古紙パルプ（以下、段ボール古紙パルプという）、雑誌古紙が好ましい。 As 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). Of these, 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.
　本発明の板紙において、全パルプ質量に対する古紙パルプの配合量は特に制限されないが、古紙パルプの配合量が少ないほど破裂強さを高く保つことができる。そのため、比破裂強さの点からは、全パルプ質量に対する古紙パルプの配合量は７５質量％以下であることが好ましく、７０質量％以下がより好ましく、５０質量％以下がさらに好ましく、３０質量％以下がよりさらに好ましく、１０質量％以下がよりさらに好ましく、５質量％以下がよりさらに好ましく、０質量％（含まない）が最も好ましい。一方、古紙パルプは安価なため、配合量が増えるほど低コストとなる。そのため、コストの点からは、全パルプ質量に対する古紙パルプの配合量は５質量％以上であることが好ましく、１０質量％以上がより好ましく、１５質量％以上がさらに好ましい。 In the paperboard of the present invention, 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). On the other hand, 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.
　本発明の板紙は、表層が、針葉樹クラフトパルプを５０～１００質量％含む。これにより、本発明の板紙は破裂強さに優れ、また印刷適性にも優れている。表層は、広葉樹クラフトパルプ、古紙パルプ等を含むことができるが、針葉樹クラフトパルプの割合が最も高いことが好ましい。また、表層は、古紙パルプを含まないことが好ましく、表層の製紙用繊維が針葉樹クラフトパルプと広葉樹クラフトパルプのみであることがより好ましい。表層における針葉樹クラフトパルプの配合量は、６０質量％以上が好ましく、８０質量％以上がより好ましく、９０質量％以上がさらに好ましく、９５質量％以上がよりさらに好ましく、１００質量％であることが最も好ましい。 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.
　本発明の板紙は、裏層が、広葉樹クラフトパルプを４０～１００質量％含むことが好ましい。裏層は、針葉樹クラフトパルプ、古紙パルプ等を含むことができるが、古紙パルプを含まないことが好ましく、裏層の製紙用繊維が広葉樹クラフトパルプと針葉樹クラフトパルプのみであることがより好ましい。裏層における広葉樹クラフトパルプの配合量は、６０質量％以上がより好ましく、７０質量％以上がさらに好ましく、８０質量％以上がよりさらに好ましく、９０質量％以上がよりさらに好ましく、１００質量％であることが最も好ましい。 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.
　本発明の板紙は、板紙が含有する全パルプ質量に対して広葉樹クラフトパルプを２０質量％以上含み、表層が針葉樹クラフトパルプを５０～１００質量％含めばよく、これを満足する限り中層を構成するパルプは特に制限されない。中層は、針葉樹クラフトパルプ、広葉樹クラフトパルプ、古紙パルプ、砕木パルプ（ＧＰ）、リファイナーグラウンドパルプ（ＲＧＰ）、ケミカルパルプ（ＣＰ）、サーモメカニカルパルプ（ＴＭＰ）、ケミサーモメカニカルパルプ（ＣＴＭＰ）等の木材繊維由来の各種パルプ、ケナフ、バガス、竹、麻、ワラなどから得られた非木材パルプ等の１種または２種以上を含むことができる。中層が２層以上である場合、各中層を構成するパルプ組成は同一であってもよく、異なっていてもよい。 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. When there are two or more middle layers, the pulp compositions that constitute each middle layer may be the same or different.
　本発明の板紙は、裏層が、パルプ質量に対して内添紙力増強剤（以下、内添紙力剤ともいう）を０．３～０．８質量％含むことが、破裂強さの点から好ましい。裏層に配合する内添紙力剤としては、ポリアクリルアミド（ＰＡＭ）系や変性でん粉等の製紙分野で用いられているものを特に制限することなく使用することができるが、紙力増強効果が高いため、ポリアクリルアミド系を用いることが好ましい。ポリアクリルアミド系としては、アニオン性、カチオン性、両性のいずれも使用することができる。裏層におけるパルプ質量に対する内添紙力増強剤の配合量は、破裂強さの点から、０．３５質量％以上であることがより好ましく、０．４質量％以上であることがさらに好ましく、０．４５質量％以上であることがよりさらに好ましい。内添紙力剤を、パルプ質量に対して０．８質量％を越えて配合することもできるが、０．８質量％を越えて配合しても紙力増強効果はほぼ飽和してほとんど向上せず、高コストとなる。
　本発明の板紙は、裏層以外の層も上記した内添紙力剤を含むことができる。この場合、裏層以外の層が含む内添紙力剤の量は、特に制限されないが、０．０１質量％以上０．５質量％以下程度である。本発明の板紙の各紙層における内添紙力剤の種類と配合量は、同一であってもよく、異なるものであってもよい。ただし、各層におけるパルプに対する内添紙力剤の配合量は、裏層が最も多いことが好ましい。 In the paperboard of the present invention, 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. As the internal strength agent to be blended in the back layer, polyacrylamide (PAM)-based agents and 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. As the polyacrylamide-based agents, any of anionic, cationic, and amphoteric agents can be used. From the viewpoint of burst strength, 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. In this case, 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.
　本発明の板紙は、板紙の耐候性等を向上するために、サイズ剤を内添することができる。サイズ剤としては、例えば、ロジン系サイズ剤、ロジンエマルジョン系サイズ剤、α－カルボキシルメチル飽和脂肪酸等、また、中性ロジン系サイズ剤、アルキルケテンダイマー（ＡＫＤ）、アルケニル無水コハク酸（ＡＳＡ）、カチオンポリマー系サイズ剤等が挙げられ、１種または２種以上を使用することができる。また、品質に影響のない範囲で、硫酸バンド、塩化アルミニウム、アルミン酸ソーダ、塩基性アルミニウム化合物、水溶性アルミニウム化合物、多価金属化合物、シリカゾル等の内添薬品を内添することができる。なお、本発明の板紙の各紙層におけるサイズ剤、さらにその他の内添薬品の配合率は、同一であってもよく、また、異なるものであってもよい。 The paperboard of the present invention may contain a sizing agent to improve the weather resistance of the paperboard. Examples of sizing agents include rosin-based sizing agents, rosin emulsion-based sizing agents, α-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. In addition, 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.
　さらに、本発明の板紙の各層には、必要に応じて、公知の填料を内添させることができる。填料としては、例えば、カオリン、焼成カオリン、デラミネーティッドカオリン、クレー、焼成クレー、デラミネーティッドクレー、イライト、重質炭酸カルシウム、軽質炭酸カルシウム、軽質炭酸カルシウム－シリカ複合物、炭酸マグネシウム、炭酸バリウム、二酸化チタン、酸化亜鉛、酸化珪素、非晶質シリカ、水酸化アルミニウム、水酸化カルシウム、水酸化マグネシウム、水酸化亜鉛等の無機填料、及び尿素－ホルマリン樹脂、ポリスチレン樹脂、フェノール樹脂等の有機填料等が挙げられ、１種または２種以上を使用することができる。なお、本発明の板紙の各紙層における填料の配合率は、同一であってもよく、また、異なるものであってもよい。 Furthermore, known 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.
　本発明の板紙は、板紙の強度向上や印刷適性付与等を目的として、表面に塗工層を有することができる。塗工層は、その目的に応じて、外添紙力増強剤（以下、表面紙力剤ともいう）、表面サイズ剤、撥水剤、顔料、バインダー樹脂、防滑剤、防腐剤、消泡剤、粘度調整剤、罫割防止剤等の公知の表面処理薬品の１種、または２種以上を含むことができる。
　本発明の板紙は、強度向上の点から、表面紙力剤を含む塗工層を有することが好ましい。表面紙力剤は、ポリアクリルアミド系、ポリビニルアルコール系、酸化澱粉、カチオン化澱粉、両性澱粉等の澱粉系、カルボキシメチルセルロース等のセルロース系等を用いることができるが、ポリアクリルアミド系が好ましい。表面紙力剤の塗工量が、０．０５ｇ／ｍ２以上であることが好ましく、０．１ｇ／ｍ２以上であることがより好ましい。
　また、耐候性の向上を目的として、塗工層は、表面サイズ剤、撥水剤を含むことが好ましい。表面サイズ剤としては、上記した内添用と同様のものが挙げられ、撥水剤としては、フッ素系樹脂、ポリアミド系樹脂、ワックスエマルジョン等が挙げられる。 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. Depending on the purpose, 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.
From the viewpoint of improving strength, the paperboard of the present invention preferably has a coating layer containing a surface strength 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.
For the purpose of improving weather resistance, the coating layer preferably contains a surface sizing agent and a water repellent agent. Examples of 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.
　本発明の板紙は、圧縮エネルギーが２．０～２５．０ｇｆ・ｃｍ／ｃｍ２、かつ、圧縮回復率が４０～９５％である。圧縮エネルギーは、圧縮時に要したエネルギーを表し、その値が大きければ圧縮されやすいことを示す。圧縮回復率は、圧縮された状態から元に戻る際の回復性を示しており、１００（％）に近いほど回復性があることを示す。
　本発明の板紙は、上記圧縮エネルギーと圧縮回復率を満足することにより、クッション性に優れており、印刷版と密着することができるため、印刷適性に優れている。また、本発明の板紙は、クッション性に優れていることにより、折り曲げた際に罫線割れが起こりにくい。
　圧縮エネルギーは、２．２ｇｆ・ｃｍ／ｃｍ２以上が好ましく、２．４ｇｆ・ｃｍ／ｃｍ２以上がより好ましく、２．６ｇｆ・ｃｍ／ｃｍ２以上がさらに好ましい。
　圧縮回復率は、４３％以上が好ましく、４６％以上がより好ましく、５０％以上がさらに好ましい。 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.
　本発明の板紙は、罫線割れが起こりにくい。本発明の板紙は、２３℃・５０％の調湿下で評価した罫割れ率が５０％以下であることが好ましい。この罫割れ率は、低いほうが好ましく、４６％以下がより好ましく、４２％以下がさらに好ましく、３８％以下がよりさらに好ましい。 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.
　本発明の板紙は、ＪＩＳ　Ｐ　８１３１：２００９に規定する比破裂強さ（破裂強さを坪量で除した値）が、２．２ｋＰａ・ｍ２／ｇ以上であることが好ましい。比破裂強さは、２．４ｋＰａ・ｍ２／ｇ以上であることがより好ましく、２．６ｋＰａ・ｍ２／ｇ以上であることがさらに好ましく、２．８ｋＰａ・ｍ２／ｇ以上であることがよりさらに好ましく、３．０ｋＰａ・ｍ２／ｇ以上であることが最も好ましい。本発明の板紙の比破裂強さの上限は特に制限されないが、例えば、４．０ｋＰａ・ｍ２／ｇ以下である。 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.
　本発明の板紙の坪量は、特に制限されないが、例えば、５０ｇ／ｍ２以上８００ｇ／ｍ２以下とすることができる。本発明の板紙は、例えば、段ボール、特に梱包用の段ボール用ライナ、中しん原紙、紙器用板紙、製函用の板紙、積層合紙用の板紙等として好適に用いることができる。２層以上の紙層を有する多層抄き紙の場合、全層の合計を５０ｇ／ｍ２以上８００ｇ／ｍ２以下の範囲で適宜設定することができ、例えば、段ボール用ライナとして用いる場合は、７０ｇ／ｍ２以上５５０ｇ／ｍ２以下とすることができる。 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. In the case of a multi-layer paper having two or more paper layers, 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.
　全体の坪量に対する裏層の坪量の割合は、破裂強さの点から、３０質量％以上５０質量％以下が好ましく、３２質量％以上４５質量％以下がさらに好ましい。
　全体の坪量に対する表層の坪量の割合は、破裂強さの点から、１０質量％以上３０質量％以下が好ましく、１２質量％以上２５質量％以下がより好ましい。
　全体の坪量に対する全中層の坪量の割合は、破裂強さの点から、３０質量％以上５０質量％以下が好ましく、３５質量％以上４５質量％以下がさらに好ましい。中層が２層以上である場合、各中層の坪量の割合は同一であってもよく、異なっていてもよい。 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. When the intermediate layer has two or more layers, the basis weight ratio of each intermediate layer may be the same or different.
　本発明に係る板紙は、３層以上の紙層を有するが、長網抄紙機、ツインワイヤー抄紙機、円網抄紙機、ギャップフォーマー、ハイブリッドフォーマー（オントップフォーマー）等を組み合わせた抄き合わせの抄紙機等を用いた公知の製造（抄紙）方法、抄紙機が選択可能である。また、抄紙時のｐＨは酸性領域（酸性抄紙）、疑似中性領域（疑似中性抄紙）、中性領域（中性抄紙）、アルカリ性領域（アルカリ性抄紙）のいずれでもよく、酸性領域で抄紙した後、紙層の表面にアルカリ性薬剤を塗布してもよい。 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. Furthermore, 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.
　本発明の板紙は、各層毎に原料パルプ等の配合が異なるため、各層に応じた紙料を調製して、抄紙する。
　本発明の板紙を抄紙する場合、ワイヤーパートは、シェーキング装置を使用することが好ましい。シェーキング装置とは、ワイヤーパートのブレストロールを紙料の流れ方向と垂直な方向（マシン幅方向とも呼ぶ。）に摺動させる装置である。シェーキング装置を使用することにより、坪量が均一化する（地合が向上する）ため、破壊の起点となる他の部分と比較して薄い箇所が減少して破裂強さが向上する。 In the paperboard of the present invention, 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.
When making the paperboard of the present invention, it is preferable to use a shaking device in the wire part. The 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). By using the shaking device, 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.
　さらに、各層の抄造条件を調整することにより、板紙の強度を向上させることもできる。例えば、ヘッドボックスから射出されるジェット液（紙料）の速度（Ｊ）と、ワイヤーの速度（Ｗ）との比であるＪ／Ｗ比（＝Ｊ／Ｗ×１００）を１００％未満とすることにより、ジェット液がワイヤーに引っ張られるため、パルプを抄紙方向（流れ方向）に配向させることができる。そして、パルプが縦方向（長手方向）に配向した板紙は、比破裂強さが向上する傾向がある。Ｊ／Ｗ比は、８１％以上９９％以下であることが好ましく、８４％以上９８％以下であることがより好ましい。また、各層の坪量配分を変更して表層および／または裏層の坪量を増加させること、各層の紙力増強剤配合率を調整して表層および／または裏層への紙力増強剤配合率を中層より高くすること等により、強度を向上させることができる。 Furthermore, the strength of the paperboard can be improved by adjusting the papermaking conditions of each layer. For example, by setting the J/W ratio (= J/W x 100), 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%, the jet liquid is pulled by the wire, and the pulp can be oriented in the papermaking direction (flow direction). Paperboard in which the pulp is oriented in the longitudinal direction (longitudinal direction) tends to have improved burst strength. The 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.
　ワイヤーパート以降の製造（抄紙）方法、抄紙機についても、要求される板紙の強度および生産効率を損なわない範囲で特に限定されず、通常の抄紙機に使用されているものを用いることができる。
　抄紙機のプレスパート工程におけるプレスの形式は、例えばストレートスルー型プレス、リバース型プレス、インバープレス、ツインバープレス、ピックアッププレス、ユニプレス、トライニッププレス、トライベントプレス、シュープレス、ミニシュープレス等、特に限定されるものではないが、公知のプレス装置を用いることができる。また、プレス条件についても特に限定はなく、通常の操業範囲で適宜設定できるが、プレス時間を長くすることで繊維がより水素結合しやすくなり、板紙の強度が向上することから、生産効率を損なわない範囲で低速抄造することが好ましい。 There are no particular limitations on the manufacturing (papermaking) method and papermaking machine used after the wire part, so long as they do not impair the required strength of the paperboard and production efficiency, and machines used in ordinary papermaking machines can be used.
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. 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.
　抄紙機のドライパート工程におけるドライヤー（乾燥装置）の形式についても、生産効率および板紙の強度を損なわない範囲であれば特に限定されるものではなく、通常の抄紙機に使用されている熱風乾燥方式、多筒式シリンダー乾燥方式等、公知の乾燥装置が使用でき、乾燥装置の設置数についても１台でもよく、プレドライヤー、アフタードライヤー等を２台以上設置してもよい。また、乾燥条件についても特に限定はなく、通常の操業範囲で適宜設定できる。 There are no particular limitations on the type of dryer (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. There are also no particular limitations on the drying conditions, and they can be set appropriately within the normal operating range.
　また、塗工層を設ける場合、抄紙した後に、表面紙力剤、表面サイズ剤、撥水剤等の表面処理薬品を含む塗工液を塗工する。塗工液を塗布する方法は特に限定はなく、ツーロールサイズプレス、ゲートロールコーター、シムサイザー、スプレー等の公知の装置を適宜用いることができる。カレンダーは、バイパスしてもよく、通常の操業範囲内で処理してもよい。 When a coating layer is provided, 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. There are no particular limitations on the method for applying the coating liquid, and 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.
　以下、本発明を実施例により説明するが、本発明は下記実施例のみに限定されるものではない。
　以下の実施例及び比較例で得られた板紙は、以下の方法で測定した。結果を表１に示す。
（坪量）
　ＪＩＳ　Ｐ　８１２４を参考に測定した。
（厚さ）
　ＪＩＳ　Ｐ　８１１８を参考に測定した。
（密度）
　ＪＩＳ　Ｐ　８１１８及びＪＩＳ　Ｐ　８１２４を参考に坪量と厚さから求めた。 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.
（比破裂強さ）
　ＪＩＳ　Ｐ　８１３１を参考に破裂強さを測定し、これを坪量で除して比破裂強さを算出した。
（罫割れ）
　５ｃｍ角の正方形にカットした板紙サンプルをスクリューサーボプレス（有限会社武藤設計社、ＭＳＶ－１０－２００Ｓ）を用いて速度１７５ｍｍ／ｍｉｎ、圧力５．０ｋＮ、加圧時間０．３ｓで、表層側が外側、かつ、折れ線が板紙のＣＤ方向となるように２つ折りにした後、サンプルの表層について割れている箇所の長さを実測し、サンプル全長（５ｃｍ）で除して罫割れ率を求めた。 (Specific burst strength)
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.
（圧縮エネルギー、圧縮回復率）
　板紙サンプルを縦５０ｍｍ、横１００ｍｍ幅の長方形にカットし、同形状のものを厚さが１ｍｍ程度となるように４枚積層し、ＫＥＳ－Ｇ５圧縮試験機（カトーテック社製）にて、２ｃｍ２の円形平面を持つ鋼板間を用いて、スピード５０ｓｅｃ／ｍｍの速度で最大応力５ｋＰａまで圧縮し、圧縮エネルギーと圧縮回復率を測定した。 (Compression energy, compression recovery 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. Using 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.
（印字濃度）
　作製した板紙の表層に、フレキソ印刷機（アイジーティーテスティングシステム株式会社製、印刷適正試験機Ｆ１）を使用して、シアンのベタ印字（大きさ：縦２ｃｍ×横３ｃｍ）を行った。１日後にマクベス濃度計（Ｇｒｅｔａｇ　Ｍａｃｂｅｔｈ　ＲＤ－１９）を用いて印字後の印字濃度（マクベス濃度）を測定した。
　印字濃度の値は高いほど好ましく、本条件においては、１．２以上が好ましい印字後のマクベス濃度である。
（印字光沢度）
　ＪＩＳ　Ｚ８７４１に準じて、上記のフレキソ印刷後のシアンのベタ部板紙表層の光沢度（光入射角７５度）を光沢度計（村上色彩技術研究所製、Ｔｒｕｅ　ＧＬＯＳＳ　ＧＭ－２６ＰＲＯ）を用いて印字後の光沢度を測定した。
　印字光沢度の値は高いほど好ましく、本条件においては、１２．５％以上が好ましい印字後の光沢度である。
（印刷品質：目視）
　上記のフレキソ印刷後のサンプルの印刷品質（印刷ムラ）を、目視にて以下の基準で評価した。
　○：印刷面にムラがほとんどなく、均一な画像が得られている。
　△：印刷面にムラが若干あり、画像が不均一である。
　×：印刷面にムラがあり、画像が非常に不均一である。 (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.
Δ: 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.
・実施例、比較例
　各層に使用したパルプを表１～３に示す。古紙パルプは、段ボール古紙パルプと雑誌古紙とを８０：２０の質量比で含む。
　なお、パルプの機械的処理は、表層はダブルコニファイナー、中層および裏層はダブルディスクリファイナーを使用した。ダブルコニファイナーおよびダブルディスクリファイナー出口における濾水度（ＣＳＦ）を、機械的処理直後の濾水度（ＣＳＦ）として各表に示す。
　各層において、内添紙力増強剤（ＰＡＭ）と内添サイズ剤（ロジン系）を、対パルプで各表に示す量で加えて紙料とした。
　各表に示す配合割合と全層坪量となるように、各層用の紙料を、裏層（３５質量％）、中層２層（裏中２５質量％、表中２０質量％）、表層（２０質量％）の順に、多層抄き板紙抄紙機を用いて抄き合わせ、表層、中層（２層）、裏層のＪ／Ｗ比をいずれも９０％とし、ワイヤーパートにおいては裏層抄造時にシェーキング装置を作動させて、板紙を得た。 Examples and Comparative Examples 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.
In each layer, 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).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.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
　本発明である実施例で得られた板紙は、クッション性に優れており、優れた印刷品質を備え、罫割れ率が５０％未満であった。
　それに対し、比較例で得られた板紙は、クッション性に劣るため、印刷品質が低く、罫割れ率が５０％を超えるものがあり、中には６０％を超えるものもあった。 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%.
In contrast, 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%.

Claims (6)

  1. 　表層、１層以上の中層、裏層を有し、
    　全パルプ質量に対して、広葉樹クラフトパルプを２０質量％以上含み、
    　前記表層が、針葉樹クラフトパルプを５０～１００質量％含み、
    　圧縮エネルギーが２．０～２５．０ｇｆ・ｃｍ／ｃｍ２、圧縮回復率が４０～９５％であることを特徴とする板紙。     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. 　前記裏層が、広葉樹クラフトパルプを４０～１００質量％含むことを特徴とする請求項１に記載の板紙。 The paperboard according to claim 1, characterized in that the back layer contains 40 to 100% by mass of hardwood kraft pulp.
  3. 　前記裏層が、パルプ質量に対して、内添紙力増強剤を０．３～０．８質量％含むことを特徴とする請求項１または２に記載の板紙。 The paperboard according to claim 1 or 2, characterized in that the back layer contains 0.3 to 0.8 mass % of an internal paper strength enhancer relative to the mass of pulp.
  4. 　全パルプ質量に対して、広葉樹クラフトパルプ含有量が２０～９５質量％、針葉樹クラフトパルプ含有量が５～５０質量％、古紙パルプ含有量が０～７５質量％であり、
    　前記表層が、古紙パルプを含有しないことを特徴とする請求項１または２に記載の板紙。     With respect to the total pulp mass, the hardwood kraft pulp content is 20 to 95 mass%, the softwood kraft pulp content is 5 to 50 mass%, and the recycled paper pulp content is 0 to 75 mass%,
    3. The paperboard according to claim 1 or 2, wherein the surface layer does not contain recycled paper pulp.
  5. 　全坪量に対する前記裏層の坪量の割合が、３０質量％以上５０質量％以下であることを特徴とする請求項１または２に記載の板紙。 The paperboard according to claim 1 or 2, characterized in that the ratio of the basis weight of the back layer to the total basis weight is 30% by mass or more and 50% by mass or less.
  6. 　請求項１または２に記載の板紙からなる段ボール用ライナ。 A cardboard liner made of the paperboard according to claim 1 or 2.
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2007100278A (en) * 2005-10-07 2007-04-19 Daio Paper Corp Liner for exterior of corrugated cardboard
JP2009091687A (en) * 2007-10-09 2009-04-30 Daio Paper Corp Multilayer cardboard
WO2010113849A1 (en) * 2009-03-31 2010-10-07 日本製紙株式会社 Base paper for paper container and laminate sheet for paper container using same
JP7323113B1 (en) * 2022-12-23 2023-08-08 日本製紙株式会社 Paperboard

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KR20230106630A (en) 2020-11-17 2023-07-13 다이오 페이퍼 코퍼레이션 Liner for corrugated board

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2007100278A (en) * 2005-10-07 2007-04-19 Daio Paper Corp Liner for exterior of corrugated cardboard
JP2009091687A (en) * 2007-10-09 2009-04-30 Daio Paper Corp Multilayer cardboard
WO2010113849A1 (en) * 2009-03-31 2010-10-07 日本製紙株式会社 Base paper for paper container and laminate sheet for paper container using same
JP7323113B1 (en) * 2022-12-23 2023-08-08 日本製紙株式会社 Paperboard

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