Liners for cardboard and corrugated cardboard

Abstract

To provide cardboard that exhibits excellent strength and scratch resistance even in high-humidity environments. [Solution] Having a surface layer, one or more middle layers, and a back layer, It contains 30% or more by mass of hardwood kraft pulp relative to the total pulp mass. A cardboard characterized by having a remaining SCT compressive strength of 60% or more after being stored for 1 hour in a high-humidity environment (23°C, 90%).

Description

[Technical Field]

[0001] The present invention relates to paperboard, particularly paperboard suitable for corrugated cardboard liners, box making, laminated paper, etc., and a method for manufacturing the same. [Background technology]

[0002] Corrugated cardboard is manufactured by laminating a liner to one or both sides of a corrugated core using a corrugator. Corrugated cardboard is lightweight and inexpensive, making it suitable for packaging a wide variety of goods. However, corrugated cardboard can be subjected to internal impacts during transport or external shocks during storage. Therefore, corrugated cardboard liners require high burst strength to prevent tearing under impact. Paperboard requiring high burst strength generally uses softwood kraft pulp as its raw material. This is because softwood kraft pulp has longer fibers compared to hardwood kraft pulp, resulting in paper with superior strength.

[0003] For example, Patent Document 1 proposes a corrugated cardboard liner with excellent impact resistance, comprising at least a surface layer, a subsurface layer, and a back layer, wherein the surface layer contains softwood kraft pulp with a softwood kraft pulp content of 80% by mass or more, the subsurface layer contains softwood kraft pulp and recycled corrugated cardboard pulp with a softwood kraft pulp content of 25% by mass or more and 35% by mass or less, and the back layer contains recycled corrugated cardboard pulp and recycled magazine pulp with a recycled corrugated cardboard pulp content of 30% by mass or more and 70% by mass or less, and a recycled magazine pulp content of 30% by mass or more and 70% by mass or less. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-193396 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] In the transportation of various goods using cardboard boxes, crushing or bulging sometimes occurred in the bottom layer of the box. Upon diligent investigation into the cause, it was confirmed that compressive strength and other properties decreased under high humidity conditions. Furthermore, while developing cardboard that suppresses the decrease in compressive strength under high humidity conditions, although the decrease in compressive strength was suppressed, a decrease in scratch resistance was observed. This invention has been made in view of these circumstances, and aims to provide cardboard that is excellent in strength and scratch resistance even in high humidity environments. [Means for solving the problem]

[0006] The means to solve the above problems are as follows: 1. It has a surface layer, one or more middle layers, and a back layer. It contains 30% or more by mass of hardwood kraft pulp relative to the total pulp mass. A cardboard characterized by having a remaining SCT compressive strength of 60% or more after being stored for 1 hour in a high-humidity environment (23°C, 90%). 2. The surface layer contains 50-100% by mass of coniferous kraft pulp, The cardboard according to claim 1, characterized in that the backing layer contains 40 to 100% by mass of hardwood kraft pulp. 3. All layers, including the surface layer, one or more middle layers, and the back layer, contain a sizing agent. The water absorption rate at the edge (2 minutes) is 30 g / m 2 The cardboard according to 1. or 2., characterized in that it is as follows: 4. All layers, including the surface layer, one or more middle layers, and the back layer, contain a paper strengthening agent. A cardboard according to any one of claims 1 to 3, characterized in that its abrasion resistance is 150 mg or less. 5. The total pulp mass consists of 30-95% hardwood kraft pulp, 5-50% softwood kraft pulp, and 0-65% recycled paper pulp. The paperboard according to any one of 1. to 4., wherein the surface layer does not contain wastepaper pulp. 6. The paperboard according to any one of 1. to 5., wherein 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. 7. A liner for corrugated cardboard comprising the paperboard according to any one of 1. to 6.

Advantages of the Invention

[0007] In the paperboard of the present invention, the decrease in strength such as compressive strength is suppressed in a high humidity environment. The paperboard of the present invention is excellent in abrasion resistance. Therefore, the paperboard of the present invention is particularly suitable for a liner for corrugated cardboard used in a high humidity environment.

Modes for Carrying Out the Invention

[0008] The paperboard of the present invention is less likely to have a decrease in compressive strength even in a high humidity environment. The paperboard of the present invention is excellent in printing quality and is suitable for applications where patterns and color printing are performed. When the paperboard of the present invention is subjected to bending, ruling cracks (broken lines generated from ruled lines (shallow grooves) provided on the base paper) are less likely to occur, and the strength can be kept high even when used as a packaging material for boxes and the like. The paperboard of the present invention is suitable for use in the rainy season to summer in Japan, or in warm and high humidity regions such as around 30 degrees north latitude to 30 degrees south latitude, such as Okinawa, Taiwan, Southeast Asian countries, and Central and South American countries. During these times and regions, for example, it can be suitably used as a liner for corrugated cardboard, a middle core base paper, a paperboard for paper containers, a paperboard for making boxes, a laminated paper, and the like.

[0009] <( The paperboard of the present invention has a surface layer, one or more middle layers, and a back layer, contains 30% by mass or more of hardwood kraft pulp based on the total pulp mass, The residual rate of the SCT compressive strength after storage at 1 hour in a high humidity environment (23°C·90%) is 60% or more. [[ID= (30]]In this specification, the description of "A to B" (A and B are numerical values) means a numerical range including both ends thereof, that is, A or more and B or less.

[0010] 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 the back layer being the outermost layers. The number of layers of the paperboard of the present invention is three or more, and the number of middle layers can be appropriately set according to the required basis weight and the like. Here, the back layer refers to the lower surface during papermaking and the layer formed by first supplying raw materials to the wire part in a multi-layer papermaking machine, and the surface layer refers to the opposite side of the back layer, that is, the upper surface during papermaking and the layer formed by finally supplying raw materials to the wire part in a multi-layer papermaking machine.

[0011] The paperboard of the present invention contains 30% by mass or more of hardwood kraft pulp based on the total pulp mass. Although the mechanism is unclear, hardwood kraft pulp is excellent in the retention rate of SCT compressive strength in a high-humidity environment. In addition to hardwood kraft pulp, the paperboard of the present invention can include various wood fiber-derived pulps such as softwood kraft pulp, wastepaper pulp, groundwood pulp (GP), refiner ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), chemithermomechanical pulp (CTMP), etc., and non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, etc. As the hardwood kraft pulp and the softwood kraft pulp, either unbleached kraft pulp (LUKP / NUKP) or bleached kraft pulp (LBKP / NBKP) can be used. However, when used for applications where whiteness is not required, unbleached kraft pulp is preferable in that it has excellent strength and can be produced with low energy because a bleaching process is not required.

[0012] From the perspective of cost reduction, it is preferable to use inexpensive wastepaper pulp as other pulps. However, from the perspectives of strength and abrasion resistance in a high-humidity environment, it is preferable that at least one of the surface layer and the back layer of the paperboard of the present invention does not contain wastepaper pulp, more preferably the surface layer does not contain wastepaper pulp, even more preferably both the surface layer and the back layer do not contain wastepaper pulp, and even more preferably all layers do not contain wastepaper pulp. The Canadian standard filtration efficiency of the pulp used in each layer of the present invention is not particularly limited, but it is preferably 300 ml CSF or more and 600 ml CSF or less.

[0013] In the paperboard of the present invention, it is preferable that the amount of hardwood kraft pulp relative to the total pulp mass is 30 to 95% by mass, the amount of softwood kraft pulp is 5 to 50% by mass, and the amount of recycled paper pulp is 0 to 65% by mass. The amount of hardwood kraft pulp relative to the total pulp mass is more preferably 40% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 65% ​​by mass or more, and even more preferably 70% by mass or more, from the viewpoint of SCT compressive strength and abrasion resistance in a high humidity environment. Furthermore, 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, and even more preferably 85% by mass or less. In the paperboard of the present invention, the amount of softwood kraft pulp relative to the total pulp mass is more preferably 10% by mass or more, and even more preferably 15% by mass or more. Furthermore, the amount of softwood kraft pulp relative to the total pulp mass is preferably 45% by mass or less, and more preferably 40% by mass or less.

[0014] As recycled paper pulp, one or more types can be used, such as recycled corrugated cardboard, recycled paper pulp obtained by disintegrating unprinted recycled paper such as fine white, extra white, medium white, and damaged white paper, recycled paper printed on fine paper, fine coated paper, medium coated paper, newsprint, etc., recycled paper with writing on it, paper such as discarded confidential documents, recycled magazine paper, and recycled newspaper pulp (DIP) obtained by disintegrating and deinking recycled newspaper. Among these, recycled paper pulp derived from recycled corrugated cardboard (hereinafter referred to as recycled corrugated cardboard pulp) and recycled magazine paper are preferred in terms of cost and strength development.

[0015] 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, abrasion resistance, etc. can be maintained. For this reason, from the viewpoint of specific bursting strength and abrasion resistance, 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, since recycled paper pulp is inexpensive, the cost decreases as the amount of recycled paper pulp added increases. For this reason, from the viewpoint 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.

[0016] The paperboard of the present invention preferably has a surface layer containing 50 to 100% by mass of softwood kraft pulp. This gives the paperboard of the present invention excellent burst strength and abrasion resistance, as well as excellent printability. The surface layer may contain hardwood kraft pulp, recycled paper pulp, etc., but it is preferable that the proportion of softwood kraft pulp is the highest. Furthermore, it is preferable that the surface layer does not contain recycled paper pulp, and it is more preferable that the papermaking fibers of the surface layer consist only of softwood kraft pulp and hardwood kraft pulp. The amount of softwood kraft pulp in the surface layer is more preferably 60% by mass or more, even 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.

[0017] In the paperboard of the present invention, from the viewpoint of scratch resistance, the backing layer preferably contains 40 to 100% by mass of hardwood kraft pulp. The backing layer may contain softwood kraft pulp, recycled paper pulp, etc., but it is preferable that it does not contain recycled paper pulp, and it is more preferable that the papermaking fibers of the backing layer consist only of hardwood kraft pulp and softwood kraft pulp. The amount of hardwood kraft pulp in the backing 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.

[0018] The paperboard of the present invention only needs to contain 30% by mass or more of hardwood kraft pulp relative to the total pulp mass contained in the paperboard, and as long as this condition is satisfied, the pulp constituting the middle layer is not particularly limited. The middle layer may contain one or more types of pulps derived from wood fibers, such as softwood kraft pulp, hardwood kraft pulp, recycled paper pulp, crushed wood pulp (GP), refiner ground pulp (RGP), chemical pulp (CP), thermomechanical pulp (TMP), chemothermetic pulp (CTMP), and non-wood pulps obtained from kenaf, bagasse, bamboo, hemp, straw, etc. If there are two or more middle layers, the pulp composition constituting each middle layer may be the same or different.

[0019] In the present invention, it is preferable that the surface layer, one or more intermediate layers, and back layer of the paperboard contain a sizing agent, in order to maintain strength in a high-humidity environment. Examples of sizing agents include rosin-based sizing agents, rosin emulsion-based sizing agents, α-carboxylmethyl saturated fatty acids, neutral rosin-based sizing agents, alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), cationic polymer-based sizing agents, and one or more of these can be used. The amount of sizing agent in each paper layer is preferably 0.2% by mass or more, more preferably 0.25% by mass or more, and even more preferably 0.3% by mass or more, relative to the pulp mass, in order to maintain strength in a high-humidity environment. There is no particular upper limit to the amount of sizing agent, but it is about 1.0% by mass per 100g of pulp mass. Even if the amount of sizing agent exceeds 1.0% by mass relative to the pulp mass, the effect of maintaining strength in a high-humidity environment is almost saturated and hardly improves, and it becomes costly. In the paperboard of the present invention, the type and proportion of sizing agent in each paper layer may be the same or different.

[0020] In the paperboard of the present invention, it is preferable from the viewpoint of bursting strength that the surface layer, one or more intermediate layers, and back layer all contain 0.1 to 2.0% by mass of an internally added paper strength enhancer (hereinafter also referred to as an internally added paper strength enhancer) relative to the pulp mass. As the internally added paper strength enhancer, any material used in the papermaking field, such as polyacrylamide (PAM) or modified starch, can be used without particular limitation, but it is preferable to use a polyacrylamide-based material because it has a high paper strength enhancing effect. Any anionic, cationic, or amphoteric polyacrylamide-based material can be used. The amount of internally added paper strength enhancer relative to the pulp mass in each paper layer is more preferably 0.15% by mass or more, even more preferably 0.2% by mass or more, and even more preferably 0.25% by mass or more, from the viewpoint of bursting strength. Although it is possible to add more than 2.0% by mass of internally added paper strength enhancer relative to the pulp mass, adding more than 2.0% by mass will result in the paper strength enhancing effect being almost saturated and hardly improving, and will be costly. In the paperboard of the present invention, the type and blending ratio of the internally added paper strength enhancer in each paper layer may be the same or different.

[0021] The paperboard of the present invention may contain internal additives such as aluminum sulfate, aluminum chloride, sodium aluminate, basic aluminum compounds, water-soluble aluminum compounds, polyvalent metal compounds, and silica sol, to the extent that it does not affect the quality. The type and proportion of internally added strength agents and other internally added chemicals 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 internally added strength agents relative to the pulp in each layer is highest in the back layer.

[0022] Furthermore, known fillers may be added to each paper layer of the paperboard of the present invention as needed. 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 dioxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, and zinc hydroxide, as well as organic fillers such as urea-formaldehyde resin, polystyrene resin, and phenolic resin. One or more of these can be used. The proportion of fillers in each paper layer of the paperboard of the present invention may be the same or different.

[0023] The paperboard of the present invention may have a coating layer on its surface for purposes such as improving the strength of the paperboard or providing printability. Depending on the purpose, the coating layer may contain one or more known surface treatment chemicals such as external paper strength enhancers (hereinafter also referred to as surface paper strength enhancers), surface sizing agents, water repellents, pigments, binder resins, anti-slip agents, preservatives, defoaming agents, viscosity modifiers, and creasing prevention agents. The paperboard of the present invention preferably has a coating layer containing a surface strength agent for improved strength. The surface strength agent can be a starch-based agent such as polyacrylamide, polyvinyl alcohol, oxidized starch, cationized starch, or amphoteric starch, or a cellulose-based agent such as carboxymethylcellulose, but polyacrylamide is preferred. The coating amount of the surface strength agent is 0.05 g / m². 2 Preferably, it is 0.1 g / m2 It is more preferable that it is as above. Further, for the purpose of improving weather resistance, the coating layer preferably contains a surface sizing agent and a water repellent. Examples of the surface sizing agent include the same ones as those for internal addition described above, and examples of the water repellent include fluororesins, polyamide resins, wax emulsions, and the like.

[0024] The paperboard of the present invention has a residual rate of SCT compressive strength (short span compressive strength) after being stored in a high humidity environment (23°C·90%) for 1 hour of 60% or more. Note that this residual rate is the value obtained by dividing the value of the SCT compressive strength after being stored in a high humidity environment (23°C·90%) for 1 hour by the value of the SCT compressive strength after being stored at 23°C·50% for 24 hours. This residual rate of compressive strength is preferably 62% or more, more preferably 64% or more, further preferably 66% or more, still more preferably 68% or more, still more preferably 70% or more, still more preferably 72% or more, and still more preferably 74% or more.

[0025] The paperboard of the present invention has an end water absorption degree (2 minutes) of 30 g / m 2 It is preferably as follows. The paperboard of the present invention is suitable for use in a high humidity environment, but in a high humidity environment, it is likely to get wet due to condensation, rain, etc. When the side end of the paperboard or when ruled line cracking occurs, by having an end water absorption degree (2 minutes) of 30 g / m 2 or less, water infiltration from the ruled line cracking part can be prevented. The value of the end water absorption degree (2 minutes) is more preferably 25 g / m 2 or less, further preferably 20 g / m 2 or less, still more preferably 15 g / m 2 or less, still more preferably 10 g / m 2 or less, still more preferably 5 g / m 2 or less is still more preferably.

[0026] The cardboard of the present invention preferably has an abrasion resistance of 150 mg or less. This abrasion resistance value is determined in accordance with JIS K7204:1999, using an H-18 abrasion wheel, and is the abrasion mass when rotated 100 times on the surface. The abrasion resistance value is more preferably 140 mg or less, even more preferably 130 mg or less, even more preferably 120 mg or less, even more preferably 110 mg or less, and even more preferably 100 mg or less.

[0027] The paperboard of the present invention has a Cobb water absorption rate of 60 g / m² for both the surface and back layers, measured in accordance with JIS-P8140 (1998) with a measurement time of 120 seconds. 2 The following is preferable: The paperboard of the present invention is easily wettable, but the Cobb water absorption of the surface and back layers is 60 g / m². 2 The following conditions prevent water from seeping in from the surface: The water absorption rate of this Cobb layer in the surface and back is 55 g / m², independently of each other. 2 The following is more preferable: 50 g / m 2 The following is even more preferable: 45 g / m 2 The following is even more preferable: 40 g / m 2 The following is even more preferable: 35 g / m 2 The following are preferable.

[0028] The paperboard of the present invention is less prone to cracking along the crease lines. Preferably, the paperboard of the present invention has a crease cracking rate of 50% or less, evaluated under controlled conditions of 23°C and 50% humidity. A lower crease cracking rate is preferable, more preferably 46% or less, even more preferably 42% or less, and even more preferably 38% or less.

[0029] The basis weight of the paperboard of the present invention is not particularly limited, but for example, 50 g / m² 2 More than 800g / m 2 The following is possible. The paperboard of the present invention can be suitably used, for example, as corrugated cardboard, especially corrugated cardboard liners for packaging, core paper, paperboard for paper containers, paperboard for box making, paperboard for laminated paper, etc. In the case of multilayer papermaking with two or more paper layers, the total weight of all layers is 50 g / m². 2 More than 800g / m 2The following range can be set as appropriate; for example, when used as a liner for corrugated cardboard, it can be set to 70g / m². 2 More than 550g / m 2 The following is possible:

[0030] From the viewpoint of bursting strength, the ratio of the basis weight of the backing 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, the ratio of surface layer basis weight to total basis weight is preferably 10% to 30% by mass, and more preferably 12% to 25% by mass. The ratio of the basis weight of the entire intermediate layer to the total basis weight is preferably 30% to 50% by mass, and more preferably 35% to 45% by mass, from the viewpoint of bursting strength. If there are two or more intermediate layers, the basis weight ratio of each intermediate layer may be the same or different.

[0031] The paperboard according to the present invention has three or more paper layers, and known manufacturing (papermaking) methods and papermaking machines, such as those using a combination papermaking machine that combines a long wire papermaking machine, a twin wire papermaking machine, a cylinder papermaking machine, a gap former, a hybrid former (on-top former), etc., can be selected. Furthermore, the pH during papermaking can be in the acidic range (acidic papermaking), the pseudo-neutral range (pseudo-neutral papermaking), the neutral range (neutral papermaking), or the alkaline range (alkaline papermaking), and an alkaline agent may be applied to the surface of the paper layers after papermaking in the acidic range.

[0032] In the paperboard of the present invention, since the composition of raw materials such as pulp differs for each layer, a paper stock is prepared according to each layer and then the paper is made. When making the paperboard of the present invention, it is preferable to use a shaking device in the wire section. A shaking device is a device that slides the breast roll of the wire section in a direction perpendicular to the flow direction of the paper stock (also called the machine width direction). By using a shaking device, the basis weight is made uniform (the form is improved), so the number of thin areas compared to other parts that become the starting point of breakage is reduced, and the bursting strength is improved.

[0033] 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 × 100), which is the ratio of the velocity (J) of the jet liquid (pulp) injected from the headbox to the velocity (W) of the wire, to less than 100%, the jet liquid is pulled by the wire, allowing the pulp to 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 specific burst strength. The J / W ratio is preferably 81% to 99%, and more preferably 84% to 98%. In addition, strength can be improved by changing the basis weight distribution of each layer to increase the basis weight of the surface and / or back layer, or by adjusting the paper strength enhancer blending rate of each layer to make the paper strength enhancer blending rate higher in the surface and / or back layer than in the middle layer.

[0034] The manufacturing (papermaking) method and papermaking machine after the wire section are not particularly limited, as long as they do not impair the required strength and production efficiency of the paperboard, and those commonly used in papermaking machines can be used. The type of press used in the press section of the paper machine is not particularly limited, but any known press device can be used, such as a straight-through press, reverse press, inbar press, twin-bar press, pickup press, UniPress, TriNip press, TriVent press, shoe press, or mini-shoe press. The press conditions are also not particularly limited and can be set appropriately within the normal operating range. However, since increasing the press time makes it easier for hydrogen bonds to form between fibers and improves the strength of the paperboard, it is preferable to manufacture at a low speed within a range that does not impair production efficiency.

[0035] The type of dryer (drying device) used in the dry part process of the paper machine is not particularly limited as long as it does not impair production efficiency or the strength of the paperboard. Known drying devices such as the hot air drying method and the multi-cylinder drying method commonly used in paper machines can be used, and the number of drying devices installed can be as few as one, or two or more, such as pre-dryers and after-dryers. Furthermore, there are no particular limitations on the drying conditions, and they can be set appropriately within the normal operating range.

[0036] Furthermore, when a coating layer is provided, a coating solution containing surface treatment chemicals such as surface strength agents, surface sizing agents, and water repellents is applied after papermaking. There are no particular limitations on the method of applying the coating solution, and known devices such as two-roll size presses, gate roll coaters, sim sizers, and sprayers can be used as appropriate. The calender may be bypassed or processed within the normal operating range. [Examples]

[0037] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples. The cardboard obtained in the following examples and comparative examples was measured using the following method. The results are shown in Tables 3 to 6. (Basic weight) Measurements were taken in reference to JIS P 8124:2011. (thickness) Measurements were taken in reference to JIS P 8118:2014. (density) The basis weight and thickness were determined based on JIS P 8118:2011 and JIS P 8124:2014.

[0038] (Cobb water absorption) Measurements were taken in accordance with JIS P 8140:1998. Specifically, 100 ml of distilled water was brought into contact with a piece of paper, and after 2 minutes, the weight of the absorbed water per unit area was measured. (Water absorption at the end) The cardboard samples were cut into 5cm squares, polyethylene tape was applied to both the front and back surfaces (to prevent water absorption only at the edges of the paper), and the samples were immersed in a 0.05% brilliant blue aqueous solution for 2 minutes. The weight difference before and after immersion was used to calculate the weight. (Split lines) A 5cm square sheet of cardboard sample was folded in half using a screw servo press (Muto Design Co., Ltd., MSV-10-200S) at a speed of 175mm / min, a pressure of 5.0kN, and a pressing time of 0.3s, with the surface facing outwards and the fold line oriented in the CD direction of the cardboard. The length of the cracked area on the surface of the sample was then measured and divided by the total sample length (5cm) to determine the creasing rate.

[0039] (Abrasion resistance) In accordance with JIS K7204:1999, an H-18 wear wheel was used, and the wear mass was measured after 100 rotations on the surface. (SCT compression strength) Measurements were taken in accordance with JIS P 8156:2012. (Remaining SCT compression strength) The SCT compressive strength of samples that were left to stand for 1 hour, 5 hours, and 24 hours in an environment of 23°C and 90% humidity was measured, and this value was divided by the SCT compressive strength of a sample that was conditioned at 23°C, 50% humidity for 24 hours to calculate the SCT compressive strength.

[0040] (Transportation test: 9-tier stack, bottom tier) Sample and core paper 170g / m² 2 A box measuring 500mm (length) x 350mm (width) x 250mm (height) was created using corrugated cardboard sheets laminated with [material name]. The surface layer of the sample (cardboard obtained in the example and comparative example) was positioned on the surface of the corrugated cardboard box. Nine boxes containing 10kg of contents were stacked on a pallet, and after 30 minutes in an environment of 23°C and 90% humidity, they were dropped from a height of 5cm to apply impact. After being left undisturbed for 5 days, the deformation of the bottom box was visually inspected and evaluated according to the following criteria. [Table 1]

[0041] (Transportation test: After unloading, in the lowest position) After checking the degree of crushing of the boxes as described above, the boxes were lowered while rubbing them, and the degree of peeling of the top surface (surface) of the bottom box was visually checked and evaluated according to the following criteria. [Table 2]

[0042] • Examples, comparative examples Tables 3-6 show the pulp used in each layer. The recycled paper pulp consists of recycled corrugated cardboard pulp and recycled magazine paper in a mass ratio of 80:20. For the mechanical processing of the pulp, a double conifer was used for the surface layer, and a double disc refiner was used for the middle and back layers. The filtration efficiency (CSF) at the outlets of the double conifer and double disc refiner is shown in the respective tables as the filtration efficiency (CSF) immediately after mechanical processing. In each layer, an internal sizing agent (rosin-based) was added relative to the pulp in the amounts shown in each table to create the paper stock. The pulp for each layer was assembled using a multi-layer papermaking machine in the following order: back layer (35% by mass), two middle layers (25% by mass in the back layer, 20% by mass in the front layer), and top layer (20% by mass), so that the mixing ratio and total basis weight of each layer would be as shown in each table. The J / W ratio of the top layer, two middle layers, and back layer was all set to 90%, and in the wire section, a shaking device was activated during the back layer formation to obtain the paperboard.

[0043] [Table 3]

[0044] [Table 4]

[0045] [Table 5]

[0046] [Table 6]

[0047] ·result The cardboard obtained in the embodiment of the present invention maintained its strength even when used in a high-humidity environment, preventing the box from collapsing, and also exhibiting minimal surface wear. From a comparison of the results of Examples 1-4 and Comparative Example 1, the results of Example 13 and Comparative Example 5, and the results of Example 14 and Comparative Example 7, it was confirmed that increasing the amount of internal sizing agent maintained the SCT compressive strength and improved abrasion resistance and edge water absorption. Furthermore, from a comparison of the results of Example 3 and Comparative Example 1, the results of Example 13 and Comparative Example 5, and the results of Example 14 and Comparative Example 7, it was confirmed that the internal sizing agent in the middle layer significantly improved the SCT compressive strength and edge water absorption. From the results of Examples 3, 5, and 6 and Comparative Examples 2 and 3, and from the comparison of the results of Example 10 and Comparative Example 4, Example 13 and Comparative Example 6, and Example 14 and Comparative Example 8, it was confirmed that the higher the ratio of LKP to total pulp mass, the better the SCT compressive strength is maintained and the better the abrasion resistance. A comparison of the results from Examples 3 and 7-9 confirmed that the lower the ratio of NKP in the surface layer, the more likely creasing is to occur, and that the ratio of NKP in the surface layer affects wear resistance. A comparison of the results from Examples 3 and 10-12 confirmed that while increasing the amount of paper strengthening agent improves SCT compressive strength, abrasion resistance, and edge water absorption, it also increases the likelihood of creasing.

Claims

1. It has a surface layer, one or more middle layers, and a back layer. It contains 30% or more by mass of hardwood kraft pulp relative to the total pulp mass. The surface layer, one or more middle layers, and back layer all contain 0.2% by mass or more and 1.0% by mass or less of a sizing agent, and 0.1% by mass or more and 2.0% by mass or less of an internally added paper strength agent. A corrugated cardboard liner characterized by being made of cardboard in which the remaining SCT compressive strength after storage for one hour in a high-humidity environment (23°C, 90%) is 60% or more.

2. The aforementioned surface layer contains 50 to 100% by mass of coniferous kraft pulp. The corrugated cardboard liner according to claim 1, characterized in that the backing layer contains 40 to 100% by mass of hardwood kraft pulp.

3. The water absorption rate at the end (2 min) is 30 g / m ２ The corrugated cardboard liner according to claim 1 or 2, characterized in that it is as follows:

4. The corrugated cardboard liner according to claim 1 or 2, characterized in that it has abrasion resistance of 150 mg or less.

5. The total pulp content is 30-95% by mass of hardwood kraft pulp, 5-50% by mass of softwood kraft pulp, and 0-65% by mass of recycled paper pulp. The corrugated cardboard liner according to claim 1 or 2, characterized in that the surface layer does not contain recycled paper pulp.

6. The corrugated cardboard liner according to claim 1 or 2, characterized in that the ratio of the basis weight of the backing layer to the total basis weight is 30% by mass or more and 50% by mass or less.

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