Paperboard and manufacturing method thereof

Abstract

The present invention addresses the problem of providing a paperboard having excellent strength and printing quality. As a solution, provided is a paperboard characterized by having a surface layer, one or more middle layers, and an inner layer, containing 20 mass% or more of broad-leaved kraft pulp with respect to the total pulp mass, the surface layer containing 50-100 mass% of coniferous kraft pulp, the compression energy being 2.0-25.0 gf.cm / cm2, and the compression recovery rate being 40-95%.

Description

Technical Field

[0001] The present invention relates to a paperboard, in particular to a paperboard suitable for use as surface paper for corrugated paperboard or for making boxes, composite paper and the like, and a manufacturing method thereof. Background Art

[0002] Corrugated cardboard is manufactured by using a corrugating machine to attach surface paper to one or both sides of a corrugated core paper.

[0003] Corrugated cardboard is used for packaging a variety of items due to its light weight and low price. However, corrugated cardboard can be subject to impact from the packaging within during transportation, or to external shock during storage. Therefore, the face paper used for corrugated cardboard must possess high burst strength to withstand impact. Generally, coniferous kraft pulp is used as the raw material for cardboard requiring this burst strength. This is because coniferous kraft pulp has longer fibers than broadleaf kraft pulp, resulting in superior strength.

[0004] For example, Patent Document 1 proposes a face paper for corrugated cardboard having excellent impact resistance, comprising at least a surface layer, a subsurface layer, and a back layer, wherein the surface layer contains coniferous kraft pulp, the content of coniferous kraft pulp in the surface layer being 80% by mass or more, the subsurface layer contains coniferous kraft pulp and corrugated cardboard waste pulp, the content of coniferous kraft pulp in the subsurface layer being 25% by mass or more and 35% by mass, and the back layer contains corrugated cardboard waste pulp and magazine waste pulp, the content of corrugated cardboard waste pulp in the back layer being 30% by mass or more and 70% by mass, and the content of magazine waste pulp in the back layer being 30% by mass or more and 70% by mass.

[0005] Patent Literature Patent Document 1: Japanese Patent Application Laid-Open No. 2020-193396 Summary of the Invention In recent years, mail order sales have dramatically increased, leading some mail order businesses to use uniquely printed corrugated packaging, with a focus on more refined print designs. Furthermore, it has been discovered that paperboard containing a high proportion of coniferous kraft pulp has low cushioning properties and therefore poor adhesion to printing plates. Consequently, the quality of printed designs and other content on the corrugated surface is poor.

[0006] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a paperboard having excellent strength and printing quality.

[0007] The method for solving the above-mentioned problems is as follows.

[0008] 1. A paperboard, characterized by comprising a surface layer, one or more middle layers and an inner layer, Contains 20% by mass or more of broadleaf kraft pulp relative to the total pulp mass, The surface layer contains 50-100% by mass of coniferous kraft pulp. Compression energy is 2.0~25.0gf·cm / cm 2 , the compression recovery rate is 40~95%.

[0009] 2. The paperboard according to 1., wherein the inner layer contains 40-100% by mass of hardwood kraft pulp.

[0010] 3. The paperboard according to 1. or 2., characterized in that the inner layer contains 0.3-0.8 mass % of an internal paper strength enhancer relative to the mass of the pulp.

[0011] 4. The paperboard according to any one of 1. to 3., characterized in that, relative to the total pulp mass, the content of hardwood kraft pulp is 20-95% by mass, the content of coniferous kraft pulp is 5-50% by mass, and the content of waste paper pulp is 0-75% by mass. The surface layer does not contain waste paper pulp.

[0012] 5. The paperboard according to any one of 1. to 4., wherein the ratio of the basis weight of the inner layer to the total basis weight is 30% by mass or more and 50% by mass or less.

[0013] 6. A face paper for corrugated cardboard, characterized in that it is composed of the cardboard described in any one of 1. to 5.

[0014] The paperboard of the present invention exhibits excellent printing quality and is suitable for pattern or color printing. It is also less susceptible to creasing cracks (fracture lines arising from the creasing lines (shallow grooves) of the base paper) during bending, and maintains high strength even when used as packaging materials such as boxes. The paperboard of the present invention is suitable for applications such as face paper for corrugated board, core base paper, paperboard for paper products, paperboard for boxmaking, and composite paper. DETAILED DESCRIPTION

[0015] The paperboard of the present invention comprises a surface layer, one or more middle layers and an inner layer. Contains 20% by mass or more of broadleaf kraft pulp relative to the total pulp mass, The surface layer contains 50-100% by mass of coniferous kraft pulp. Compression energy is 2.0~25.0gf·cm / cm 2 , the compression recovery rate is 40~95%.

[0016] In the present specification, the expression “A to B” (A and B are numerical values) refers to a numerical range including the endpoints, that is, A or more and B or less.

[0017] The paperboard of the present invention comprises a surface layer, one or more middle layers, and a back layer, with the surface layer and the back layer being the outermost layers. The paperboard of the present invention may have three or more layers, and the number of middle layers may be appropriately adjusted based on factors such as the desired basis weight. The back layer refers to the lower surface during papermaking and is the first layer formed when the raw material is supplied to the wire section of a multi-layer papermaking machine. The surface layer is the opposite side of the back layer, i.e., the upper surface during papermaking, and is the last layer formed when the raw material is supplied to the wire section of a multi-layer papermaking machine.

[0018] The paperboard of the present invention contains 20% or more by mass of hardwood kraft pulp relative to the total pulp mass. Furthermore, the paperboard of the present invention contains 50% to 100% by mass of coniferous kraft pulp in at least its surface layer. Both hardwood kraft pulp and coniferous kraft pulp can be either unbleached kraft pulp (LUKP / NUKP) or bleached kraft pulp (LBKP / NBKP). For applications where whiteness is not a requirement, unbleached kraft pulp is preferred due to its excellent strength and the fact that it can be produced with low energy consumption, as it does not require a bleaching step.

[0019] In addition to hardwood kraft pulp and conifer kraft pulp, the paperboard of the present invention may contain various pulps derived from wood fibers, such as waste paper pulp, groundwood pulp (GP), groundwood chips pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), and chemithermomechanical pulp (CTMP), as well as non-wood pulps derived from materials such as kenaf, bagasse, bamboo, hemp, and straw. Inexpensive waste paper pulp is preferably used as the other pulp. However, the paperboard of the present invention preferably contains no waste paper pulp in at least one of the surface layer and the back layer, more preferably no waste paper pulp in the surface layer, and even more preferably no waste paper pulp in both the surface layer and the back layer.

[0020] 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.

[0021] In the paperboard of the present invention, the blending amount of hardwood kraft pulp is preferably 20-95% by mass, the blending amount of coniferous kraft pulp is preferably 5-50% by mass, and the blending amount of waste paper pulp is preferably 0-75% by mass, relative to the total pulp mass.

[0022] The amount of hardwood kraft pulp blended relative to the total pulp mass is more preferably 30% by mass or greater, further preferably 40% by mass or greater, even more preferably 60% by mass or greater, even more preferably 65% ​​by mass or greater, and even more preferably 70% by mass or greater. Furthermore, the amount of hardwood kraft pulp blended relative to the total pulp mass is preferably 95% by mass or less, more preferably 90% by mass or less, and even more preferably 85% by mass or less.

[0023] In the paperboard of the present invention, the blending amount of coniferous kraft pulp is preferably 10% by mass or greater, and even more preferably 15% by mass or greater, relative to the total pulp mass. Furthermore, the blending amount of coniferous kraft pulp is preferably 45% by mass or less, and even more preferably 40% by mass or less, relative to the total pulp mass.

[0024] Wastepaper pulp can be a mixture of one or more of the following: wastepaper pulp obtained by disintegrating corrugated cardboard wastepaper, unprinted wastepaper such as top white, extra white, medium white, and white waste; deinked pulp (DIP) obtained by disintegrating wastepaper printed on high-quality paper, high-quality coated paper, medium-quality paper, medium-quality coated paper, and rough paper; written wastepaper, discarded confidential documents, magazine wastepaper, and newspaper wastepaper. Of these, wastepaper pulp derived from corrugated cardboard wastepaper (hereinafter referred to as corrugated cardboard wastepaper) and magazine wastepaper are preferred from the perspectives of cost and strength.

[0025] In the paperboard of the present invention, the amount of waste pulp blended relative to the total pulp mass is not particularly limited. The lower the amount of waste pulp blended, the higher the burst strength maintained. Therefore, from the perspective of burst index, the amount of waste pulp blended 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, since waste pulp is inexpensive, increasing its blending amount can reduce costs. Therefore, from a cost perspective, the amount of waste pulp blended 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.

[0026] The paperboard of the present invention contains 50-100% by mass of coniferous kraft pulp in the surface layer. As a result, the paperboard of the present invention exhibits excellent bursting strength and printability. The surface layer may contain broadleaf kraft pulp, waste paper pulp, etc., but preferably, coniferous kraft pulp accounts for the highest proportion. Furthermore, the surface layer preferably contains no waste paper pulp, and more preferably, the papermaking fibers in the surface layer consist solely of coniferous kraft pulp and broadleaf kraft pulp. The amount of coniferous kraft pulp in the surface layer is preferably 60% by mass or greater, more preferably 80% by mass or greater, further preferably 90% by mass or greater, even more preferably 95% by mass or greater, and most preferably 100% by mass.

[0027] The paperboard of the present invention preferably contains 40-100% by mass of hardwood kraft pulp in the inner layer. The inner layer may contain softwood kraft pulp, waste paper pulp, etc., but preferably contains no waste paper pulp. More preferably, the papermaking fibers in the inner layer consist solely of hardwood kraft pulp and softwood kraft pulp. The amount of hardwood kraft pulp in the inner layer is more preferably 60% by mass or greater, more preferably 70% by mass or greater, even more preferably 80% by mass or greater, even more preferably 90% by mass or greater, and most preferably 100% by mass.

[0028] The paperboard of the present invention contains 20% or more by mass of hardwood kraft pulp relative to the total pulp mass of the paperboard, and the surface layer contains 50-100% by mass of coniferous kraft pulp. As long as these conditions are met, the pulp constituting the middle layer is not particularly limited. The middle layer may contain one or more of various wood fiber pulps such as softwood kraft pulp, hardwood kraft pulp, waste paper pulp, groundwood pulp (GP), regrinded wood pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), and chemithermomechanical pulp (CTMP), as well as non-wood pulps derived from kenaf, bagasse, bamboo, hemp, straw, and the like. When there are two or more middle layers, the pulp compositions of each middle layer may be the same or different.

[0029] The paperboard of the present invention preferably contains an internal paper strengthening agent (hereinafter referred to as an internal paper strengthening agent) in the back layer at a level of 0.3-0.8% by mass relative to the mass of the pulp, which is preferred from the perspective of bursting strength. The internal paper strengthening agent added to the back layer can be any of polyacrylamides (PAMs) or modified starches commonly used in the papermaking industry, but polyacrylamides are preferred for enhanced paper strengthening. Anionic, cationic, and amphoteric polyacrylamides can be used. From the perspective of bursting strength, the amount of the internal paper strengthening agent added to the back layer is preferably 0.35% by mass or greater, more preferably 0.4% by mass or greater, and even more preferably 0.45% by mass or greater, relative to the mass of the pulp. While an amount exceeding 0.8% by mass relative to the mass of the pulp is acceptable, the paper strengthening effect is nearly saturated even at levels exceeding 0.8% by mass, resulting in increased costs.

[0030] The paperboard of the present invention may also contain the aforementioned internal paper strength agent in layers other than the inner layer. In this case, the amount of the internal paper strength agent contained in the layers other than the inner layer is not particularly limited and may be between approximately 0.01% and 0.5% by mass. The type and amount of the internal paper strength agent in each paper layer of the paperboard of the present invention may be the same or different. However, the amount of the internal paper strength agent in each layer relative to the pulp is preferably greatest in the inner layer.

[0031] The paperboard of the present invention may contain an internal sizing agent to improve its weather resistance and other properties. Examples of such sizing agents include rosin-based sizing agents, rosin emulsion-based sizing agents, and α-carboxymethyl saturated fatty acids. Other examples include neutral rosin-based sizing agents, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), and cationic polymer-based sizing agents. One or more of these sizing agents may be used. Furthermore, as long as these agents do not affect quality, internal chemicals such as barium sulfate, aluminum chloride, sodium aluminate, basic aluminum compounds, water-soluble aluminum compounds, polyvalent metal compounds, and silica sol may be added. The ratios of sizing agents and other internal chemicals in each paper layer of the paperboard of the present invention may be the same or different.

[0032] Furthermore, each layer of the paperboard of the present invention may contain known fillers as needed. Examples of fillers include inorganic fillers such as kaolin, calcined kaolin, exfoliated kaolin, clay, calcined clay, exfoliated clay, illite, heavy calcium carbonate, light calcium carbonate-silicon dioxide composites, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide, as well as organic fillers such as urea-formalin resin, polystyrene resin, and phenolic resin. One or more fillers may be used. The filler ratios in each paper layer of the paperboard of the present invention may be the same or different.

[0033] The paperboard of the present invention may have a coating layer on its surface for purposes such as improving its strength or imparting printability. Depending on the intended purpose, the coating layer may contain one or more known surface treatment agents such as an external paper strength enhancer (hereinafter referred to as a surface strength agent), a surface sizing agent, a water repellent, a pigment, a binder resin, an anti-slip agent, a preservative, a defoaming agent, a viscosity modifier, and an anti-cracking agent.

[0034] From the viewpoint of improving strength, the paperboard of the present invention preferably has a coating layer containing a surface paper strength agent.

[0035] Surface paper strength agents can be polyacrylamide, polyvinyl alcohol, oxidized starch, cationic starch, amphoteric starch and other starches, carboxymethyl cellulose and other celluloses, etc., preferably polyacrylamide. The coating amount of the surface paper strength agent is preferably 0.05g / m 2 More than 0.1 g / m 2 above.

[0036] In addition, in order to improve weather resistance, the coating layer preferably contains a surface sizing agent and a water-repellent. As the surface sizing agent, the same substances as those used for the internal addition can be cited, and as the water-repellent, fluorine-based resins, polyamide resins, wax emulsions, etc. can be cited.

[0037] The compression energy of the paperboard of the present invention is 2.0~25.0gf·cm / cm2 , and the compression recovery rate ranges from 40% to 95%. Compression energy represents the energy required for compression, with higher values ​​indicating greater compressibility. The compression recovery rate refers to the ability to recover from a compressed state to its original state, with values ​​closer to 100% indicating greater recovery.

[0038] By meeting the aforementioned compression energy and compression recovery requirements, the paperboard of the present invention exhibits excellent cushioning properties and, since it can be laminated to printing plates, offers excellent printing suitability. Furthermore, due to its excellent cushioning properties, the paperboard of the present invention is less susceptible to cracking along the compression line when bent.

[0039] The compression energy is preferably 2.2 gf·cm / cm 2 More than 2.4 gf·cm / cm 2 More than 2.6 gf·cm / cm 2 above.

[0040] The compression recovery rate is preferably 43% or more, more preferably 46% or more, and further preferably 50% or more.

[0041] The paperboard of the present invention is less susceptible to cracking at the compression line. The compression line crack rate of the paperboard of the present invention, evaluated at 23°C and 50% humidity, is preferably 50% or less. The lower the compression line crack rate, the better, more preferably 46% or less, even more preferably 42% or less, and even more preferably 38% or less.

[0042] The paperboard of the present invention preferably has a bursting index (a value obtained by dividing the bursting strength by the basis weight) specified in Japanese Industrial Standard JIS P 8131:2009 of 2.2 kPa·m 2 / g or more. The burst resistance index is more preferably 2.4 kPa·m 2 / g or more, more preferably 2.6 kPa·m 2 / g or more, more preferably 2.8 kPa·m 2 / g or more, and most preferably 3.0 kPa·m 2 The upper limit of the bursting index of the paperboard of the present invention is not particularly limited, and is, for example, 4.0 kPa·m 2 / g or less.

[0043] The basis weight of the paperboard of the present invention is not particularly limited, and can be set to 50 g / m 2 Above 800g / m 2 The paperboard of the present invention can be suitably used for corrugated paperboard, especially for corrugated paperboard for packaging, core paper, paperboard for paper containers, paperboard for box making, paperboard for composite paper, etc. In the case of multi-layer papermaking with two or more paper layers, the total weight of all layers can be 50 g / m 2 Above 800g / m 2The following range is appropriately set. For example, when used as a surface paper for corrugated cardboard, it can be set to 70g / m 2 Above 550g / m 2 the following.

[0044] The ratio of the basis weight of the back layer to the total basis weight is preferably 30% by mass or more and 50% by mass or less, and more preferably 32% by mass or more and 45% by mass or less, from the viewpoint of bursting strength.

[0045] The ratio of the basis weight of the surface layer to the overall basis weight is preferably from the viewpoint of bursting strength to not less than 10% by mass and not more than 30% by mass, more preferably not less than 12% by mass and not more than 25% by mass.

[0046] The ratio of the basis weight of the total middle layer to the overall basis weight is preferably from the perspective of burst strength, not less than 30% by mass and not more than 50% by mass, and more preferably not less than 35% by mass and not more than 45% by mass. When there are two or more middle layers, the ratio of the basis weights of the middle layers may be the same or different.

[0047] The paperboard according to the present invention comprises three or more paper layers. Known production (papermaking) methods and papermaking machines can be selected, such as a multi-layer papermaking machine comprising a combination of a Fourdrinier papermaking machine, a twin-wire papermaking machine, a cylinder papermaking machine, a gap former, or a hybrid former (top former). Furthermore, the pH during papermaking can be in the acidic region (acidic papermaking), the pseudo-neutral region (pseudo-neutral papermaking), the neutral region (neutral papermaking), or the alkaline region (alkaline papermaking). After papermaking in the acidic region, an alkaline agent may be applied to the surface of the paper layer.

[0048] Since the paperboard of the present invention has different formulations of raw material pulp etc. for each layer, it is necessary to prepare paper stock corresponding to each layer for papermaking.

[0049] When making the paperboard of the present invention, a shaking device is preferably used on the wire section. A shaking device causes the breast roll of the wire section to slide perpendicular to the paper stock flow direction (also known as the machine width direction). Using a shaking device can make the basis weight more uniform (improve paper evenness), thereby reducing areas that are thinner than other areas, which serve as the starting point for failure, and thus improving burst strength.

[0050] Furthermore, paperboard strength can be improved by adjusting the papermaking conditions for each layer. For example, by setting the J / W ratio (= J / W x 100), the ratio of the velocity (J) of the jet (paper stock) ejected from the headbox to the velocity (W) of the papermaking wire, to less than 100%, the jet is drawn by the wire, aligning the pulp in the papermaking direction (flow direction). Furthermore, paperboard with pulp oriented in the longitudinal direction (lengthwise) tends to have a higher burst index. The J / W ratio is preferably between 81% and 99%, and more preferably between 84% and 98%. Furthermore, strength can be improved by adjusting the basis weight distribution of each layer to increase the basis weight of the surface and / or back layers, or by adjusting the ratio of paper strengthening agents in each layer so that the surface and / or back layers have a higher ratio than the middle layer.

[0051] The production (papermaking) method and papermaking machine after the wire section are not particularly limited as long as the required paperboard strength and production efficiency are not impaired, and any production (papermaking) method and papermaking machine used for ordinary papermaking machines can be used.

[0052] The press type used in the press section of a papermaking machine includes, for example, a straight-through press, a reverse press, an inverted press, a twin-screw press, a pick-up press, a single-nip press, a three-nip press, a three-nip groove press, a shoe press, and a mini-shoe press, but is not particularly limited thereto, and known press equipment may be used. Furthermore, the pressing conditions are not particularly limited and may be appropriately set within normal operating ranges. However, extending the pressing time facilitates hydrogen bonding among fibers, thereby improving the strength of the paperboard. Therefore, it is preferable to operate at a low speed within a range that does not compromise production efficiency.

[0053] The type of dryer (drying device) used in the drying section of a papermaking machine is not particularly limited, as long as production efficiency and paperboard strength are not compromised. Known drying devices such as hot air drying and multi-drum drying systems commonly used in papermaking machines can be used. The number of drying devices installed may be one, or two or more, such as pre-dryers and post-dryers, may be provided. Drying conditions are also not particularly limited and can be appropriately set within normal operating ranges.

[0054] If 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 can be applied after papermaking. The method for applying the coating liquid is not particularly limited; known devices such as a two-roll size press, gate roll coater, SYM size press, and sprayer can be used as appropriate. Calendering can be bypassed or performed within standard operating procedures.

[0055] Example The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0056] The paperboards obtained in the following examples and comparative examples were tested using the following method. The results are shown in Table 1.

[0057] (Basis Weight) The measurement was performed with reference to Japanese Industrial Standard JIS P 8124.

[0058] (thickness) The measurement was performed with reference to Japanese Industrial Standard JIS P 8118.

[0059] (density) The thickness was determined based on basis weight and thickness according to Japanese Industrial Standards JIS P 8118 and JIS P 8124.

[0060] (burst index) The bursting strength was measured according to Japanese Industrial Standard JIS P 8131, and the bursting index was calculated by dividing the value by the basis weight.

[0061] (Crumbling of the pressure line) A cardboard sample cut into 5 cm squares was folded in half using a screw servo press (MSV-10-200S, manufactured by Muto Design Co., Ltd.) at a speed of 175 mm / min, a pressure of 5.0 kN, and a pressing time of 0.3 s, with the surface layer facing outward and the fold line oriented in the CD (cross-machine direction) of the cardboard. The length of the crack in the surface layer of the sample was measured and divided by the total length of the sample (5 cm) to determine the crease line rupture rate.

[0062] (Compression energy, compression recovery rate) The cardboard sample was cut into a rectangle of 50 mm in length and 100 mm in width. Four pieces of the same shape were stacked to make the thickness about 1 mm. A KES-G5 compression tester (manufactured by Kato Tech Co., Ltd.) was used with a 2 cm 2 The circular flat steel plate is compressed at a rate of 50 sec / mm until the maximum stress reaches 5 kPa, and then the compression energy and compression recovery rate are measured.

[0063] (Print density) A cyan solid print (size: 2 cm x 3 cm) was applied to the surface of the prepared paperboard using a flexographic printing press (IGT Testing Systems Co., Ltd., Printing Suitability Tester F1). One day later, the print density (Macbeth density) was measured using a Macbeth densitometer (Gretag Macbeth RD-19).

[0064] The higher the print density value, the better. Under the present conditions, the Macbeth density after printing is preferably 1.2 or higher.

[0065] (Print glossiness) The glossiness of the cyan solid paperboard surface layer after flexographic printing was measured using a gloss meter (TrueGLOSS GM-26PRO, manufactured by Murakami Color Research Laboratory) (light incident angle 75 degrees) in accordance with Japanese Industrial Standard JIS Z8741.

[0066] The higher the glossiness of the print, the better. Under the present conditions, the glossiness after printing is preferably 12.5% ​​or higher.

[0067] (Printing quality: visual) The printing quality (printing spots) of the above-mentioned flexographically printed samples was visually evaluated according to the following criteria.

[0068] ○: There is almost no unevenness on the printed surface, and a uniform image can be obtained.

[0069] △: There are some spots on the printed surface, and the image is uneven.

[0070] ×: The printed surface has spots and the image is extremely uneven.

[0071] Examples and Comparative Examples The pulp used for each layer is shown in Tables 1 to 3. The waste paper pulp contained corrugated cardboard waste paper pulp and magazine waste paper at a mass ratio of 80:20.

[0072] For mechanical pulp treatment, a double-cone refiner was used for the surface layer, and a double-disc refiner was used for the middle and back layers. The CSF values ​​at the outlets of the double-cone refiner and double-disc refiner are shown in the tables as the CSF values ​​immediately after mechanical treatment.

[0073] In each layer, an internal paper strength agent (PAM) and an internal sizing agent (rosin) were added in the amounts shown in each table relative to the pulp to prepare paper materials.

[0074] Using the blending ratios and basis weights of all layers shown in the tables, the paper stock for each layer was prepared in the order of a back layer (35% by mass), two middle layers (25% by mass for the back layer and 20% by mass for the table), and a top layer (20% by mass). This paper was then manufactured using a multi-layer paperboard machine. The J / W ratios of the top layer, middle layer (two layers), and back layer were all set to 90%. A shaking device was activated during the production of the back layer in the wire section to produce paperboard.

[0075] [Table 1]

[0076] [Table 2]

[0077] [Table 3]

[0078] The paperboard obtained by the embodiment of the present invention has excellent cushioning properties, excellent printing quality, and a creasing line cracking rate of less than 50%.

[0079] In contrast, the paperboards obtained from the comparative examples had poor cushioning properties and low printing quality, with some paperboards having a creasing rate exceeding 50%, and some even exceeding 60%.

Claims

1. A cardboard, characterized in that: It has a surface layer, one or more middle layers and an inner layer. Contains 20% by mass or more of broadleaf kraft pulp relative to the total pulp mass, The surface layer contains 50-100% by mass of coniferous kraft pulp. Compression energy is 2.0~25.0gf·cm / cm 2 , the compression recovery rate is 40~95%.

2. The paperboard according to claim 1, characterized in that The inner layer contains 40 to 100% by mass of hardwood kraft pulp.

3. The paperboard according to claim 1 or 2, characterized in that: The inner layer contains 0.3 to 0.8 mass % of an internally added paper strengthening agent relative to the mass of the pulp.

4. The paperboard according to claim 1 or 2, characterized in that: With respect to the total pulp mass, the content of hardwood kraft pulp is 20-95% by mass, the content of coniferous kraft pulp is 5-50% by mass, and the content of waste paper pulp is 0-75% by mass. The surface layer does not contain waste paper pulp.

5. The paperboard according to claim 1 or 2, characterized in that: The ratio of the basis weight of the inner layer to the total basis weight is 30% by mass or more and 50% by mass or less.

6. A facial tissue for corrugated cardboard, characterized in that: The paperboard is made of the paperboard according to claim 1 or 2.

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