Corrugated paperboard

Abstract

The corrugated paperboard of one embodiment of the present invention comprises at least a surface layer, an intermediate layer and a back layer, wherein the surface layer contains coniferous kraft pulp, and the content of the coniferous kraft pulp in the surface layer is 80% by mass or more, the intermediate layer contains corrugated paper waste pulp, and the content of the coniferous kraft pulp in the intermediate layer is 30% by mass or less, the back layer contains coniferous kraft pulp, corrugated paper waste pulp and kraft paper waste pulp, and the kraft paper waste pulp is waste pulp from kraft paper with a plastic film laminated on one side, the content of the corrugated paper waste pulp in the back layer is 30% by mass or more and 70% by mass or less, and the ratio of the basis weight of the surface layer to the total basis weight is 20% or more and 35% or less. The bursting index of the corrugated paperboard in an atmosphere of 60°C and 80%RH is preferably 3.4 kPa·m 2 / g or above.

Description

Technical Field

[0001] The invention relates to a boxboard for corrugated paper.

[0002] This application claims the priority based on Japanese application No. 2020-191267 filed on November 17, 2020, and cites all the contents described in the above Japanese application. Background Art

[0003] Corrugated cardboard used in packaging containers for packaging is a normal quality corrugated liner. Compared with wooden or resin containers, corrugated liner is lightweight and has cushioning properties, so the contents are less likely to break, so it is used in various fields, including precision equipment.

[0004] As a multi-layer paper used in such a packaging container for packaging, for example, Patent Document 1 discloses the following technology: in a paper base material having a first layer, a second layer, and a third layer in sequence, by making the density of the first layer and the third layer as the outer layer higher than the density of the second layer as the middle layer, a paper base material having excellent double-sided printing suitability and double-sided lamination suitability can be obtained (see Patent Document 1). Here, it is disclosed that the printing and lamination suitability can be improved by changing the density characteristics of each layer structure.

[0005] Among the kraft papers disclosed in Patent Document 2, the following kraft paper is disclosed: when processed into bags for use, the kraft paper rarely causes bag breakage, and the kraft paper is manufactured in a manner that the longitudinal and transverse elongations at break are adjusted to have a specific relationship, thereby having excellent elongation characteristics and strength characteristics. Patent Document 3 discloses a heavy-duty packaging kraft paper, which is viscous-beaten to a kraft pulp concentration of 4.0 wt% to 4.5 wt% and a weight-average fiber length of 2.3 mm to 4.0 mm, and is paper-made from the kraft pulp to a dissociation freeness of 600 ml to 680 ml, thereby maintaining the strength of the paper support within the JIS standard, and providing the paper support with high air permeability, and reducing the raw material cost with a low basis weight, thereby reducing the manufacturing cost (see Patent Documents 1, 2, and 3).

[0006] Thus, in the prior art, emphasis has been placed on improving tear strength (tearing strength), tensile properties, processing suitability, printing suitability, and the like.

[0007] On the other hand, in recent years, efforts have been made to use waste paper as raw material pulp from the perspective of protecting wood resources and economic efficiency. As the waste paper pulp that becomes the raw material of recycled paper, corrugated waste paper is widely known as brown (tea-based) waste paper pulp. However, unlike magazine and newspaper waste paper pulp, corrugated waste paper pulp has many sticky foreign matter and unstable color (color and taste), which are the causes of low quality of recycled paper. From the perspective of ensuring the quality of waste paper pulp, kraft waste paper pulp is also used.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Publication No. 2017-002433

[0011] Patent Document 2: Japanese Patent Publication No. 2014-053372

[0012] Patent Document 3: Japanese Patent Publication No. 2006-089889 Summary of the invention

[0013] Technical problem to be solved by the invention

[0014] However, for roads with poor paving environments, packaging containers are easily damaged due to vibrations caused by the roughness of the road surface during transportation, and further, a high temperature and high humidity environment, which is also called abnormal weather in China, occurs. In addition, product information or a laminated film is printed on the surface of such corrugated paperboard, so the corrugated paperboard needs to have sufficient strength in the above environment. Therefore, in order to be used for applications corresponding to impacts on roads with poor paving environments and use in high temperature and high humidity environments, the corrugated paperboard is required to have excellent impact resistance and improve the impact resistance during transportation and in high temperature and high humidity environments.

[0015] As a common method to improve the impact resistance of corrugated paperboard, it is possible to consider using more paper strength enhancers for improving paper strength. However, in this case, the corrugated paperboard becomes hard as a whole, and the problem of cracking of the indentation line and the high cost of reagents become problems. In addition, in recent years, there is a demand for recycling waste paper and achieving environmentally friendly materials for corrugated paperboard. In particular, in recent years, from the perspective of improving the strength of kraft packaging bags, heavy bags (heavy bags) with resin films on the inner layer of kraft paper bags have been used, and there is also a demand for recycling such heavy bags.

[0016] The present invention is made based on the above situation, and an object of the present invention is to provide a corrugated cardboard boxboard that can realize the recycling of waste paper pulp and improve the impact resistance when transported on roads with poor paving environment or in a high temperature and high humidity environment.

[0017] Technical means to solve technical problems

[0018] A corrugated paperboard boxboard according to one embodiment of the present invention comprises at least a surface layer, an intermediate layer and a back layer, wherein the surface layer contains coniferous kraft pulp, the content of the coniferous kraft pulp in the surface layer is 80% by mass or more, the intermediate layer contains corrugated paper waste pulp, and the content of the coniferous kraft pulp in the intermediate layer is 30% by mass or less, the back layer contains coniferous kraft pulp, corrugated paper waste pulp and kraft-based waste paper pulp, the kraft-based waste paper pulp is waste paper pulp from kraft paper with a plastic film laminated on one side, the content of the corrugated paper waste paper pulp in the back layer is 30% by mass or more and 70% by mass or less, and the basis weight of the surface layer is 20% or more and 35% or less relative to the total basis weight.

[0019] Beneficial Effects

[0020] According to the present invention, it is possible to provide a corrugated cardboard boxboard which can realize the recycling of waste paper pulp and can improve the impact resistance when transported on a road surface with a poor paving environment or in a high temperature and high humidity environment. DETAILED DESCRIPTION

[0021] A corrugated paperboard boxboard according to one embodiment of the present invention comprises at least a surface layer, an intermediate layer and a back layer, wherein the surface layer contains coniferous kraft pulp, the content of the coniferous kraft pulp in the surface layer is 80% by mass or more, the intermediate layer contains corrugated paper waste pulp, and the content of the coniferous kraft pulp in the intermediate layer is 30% by mass or less, the back layer contains coniferous kraft pulp, corrugated paper waste pulp and kraft-based waste paper pulp, the kraft-based waste paper pulp is waste paper pulp from kraft paper with a plastic film laminated on one side, the content of the corrugated paper waste paper pulp in the back layer is 30% by mass or more and 70% by mass or less, and the basis weight of the surface layer is 20% or more and 35% or less relative to the total basis weight.

[0022] Thus, the surface layer contains softwood kraft pulp, and the content of softwood kraft pulp in the surface layer located on the outermost side as a packaging material for corrugated paper is made 80% by mass or more. By increasing the content ratio, it is possible to achieve an improvement in impact resistance in a high-temperature and high-humidity environment, and at the same time, a high folding strength can be obtained, so that the indentation line fracture suppression effect is excellent. In addition, as the raw material pulp of the back layer (the back layer is located on the outermost side as a packaging material for corrugated paper), softwood kraft pulp, corrugated paper waste paper pulp and kraft paper waste paper pulp are used in combination, so that it is possible to have good adhesion and improve the burst resistance index in a high-temperature and high-humidity environment. Furthermore, by making the content of the corrugated paper waste paper pulp in the back layer 30% by mass or more and 70% by mass or less, it is possible to achieve the recycling of waste paper pulp and improve the burst resistance index in a high-temperature and high-humidity environment. In addition, by making the middle layer contain corrugated paper waste pulp, and making the content of the softwood kraft pulp in the middle layer 30% by mass or less to increase the content of corrugated paper waste pulp, it is possible to achieve the recycling of waste paper pulp, and to improve the lamination property and the bursting index in a high temperature and high humidity environment. Furthermore, by making the basis weight of the surface layer greater than 20% and less than 35% relative to the total basis weight, it is possible to maintain the impact resistance in a high temperature and high humidity environment, and to ensure the softness and cushioning properties of the corrugated paper boxboard. Therefore, according to the corrugated paper boxboard, it is possible to provide a corrugated paper boxboard that can withstand the impact during transportation on a road surface with a poor paving environment and can exhibit excellent impact resistance even in a high temperature and high humidity environment. In addition, according to the present invention, a corrugated paper boxboard with excellent carton formability can be obtained. Here, "kraft waste paper having a resin film laminated on at least one side" means a kraft waste paper having a plastic film (a film of a resin (so-called vinyl) such as polyethylene, polypropylene, polyester, nylon, polyvinyl chloride, etc.) laminated on one side (inner side in the form of a bag) of kraft paper used for heavy-duty bags (the heavy-duty bags are bags processed to hold heavy objects) (rice and wheat bags, powder bags, feed bags, reagent bags (drug bags), cement bags, etc.) Two or three layers of kraft waste paper are laminated on one side (inner side in the form of a bag) of the kraft paper.

[0023] Preferably, the bursting index of the corrugated paperboard in an atmosphere of 60°C and 80% RH is 3.4 kPa·m 2 By setting the bursting index to be within the above range, the impact resistance of the corrugated cardboard can be improved when transported on a road surface with a poor laying environment or in a high temperature and high humidity environment.

[0024] Preferably, a coating layer is formed on the surface of the surface layer and the back layer, the coating layer of the back layer contains starch and an anionic sizing agent, the coating layer of the surface layer contains starch, or starch and anionic sizing agent, in the coating layer of the back layer, the content ratio of starch relative to the total content of the anionic sizing agent and the starch is 91.0 mass % or more and 96.0 mass % or less in terms of solid content, in the coating layer of the surface layer, the content ratio of starch relative to the total content of the anionic sizing agent and the starch is 91.0 mass % or more and 100.0 mass % or less in terms of solid content, and the dynamic contact angle of the surface layer after 1 second is 80 degrees or more and 110 degrees or less. The corrugated paperboard has coating layers formed on the surfaces of the surface layer and the back layer, and since the pulp fibers of the surface layer in contact with the coating layer can be filled, the surface smoothness can be ensured. By containing the anionic sizing agent in the coating layer of the back layer so that the content ratio of the anionic sizing agent and the starch is within the range, the rigidity of the coating layer can be improved, and thus the bursting strength of the corrugated paperboard can be improved. In addition, by making the content ratio of starch in the coating layer of the surface layer relative to the total content of the anionic sizing agent and the starch within the range, the printing adaptability of the surface layer side of the corrugated paperboard can be improved, and the smoothness of the printed surface can be ensured. In addition, by making the dynamic contact angle of the surface layer after 1 second to be more than 80 degrees and less than 110 degrees, the ink inking property of the corrugated paperboard during flexographic printing (flexo printing for dunball) is good, and the ink penetrates into the paper appropriately, so that the surface properties suitable for printing fine characters (fine characters), barcodes, two-dimensional codes (registered trademarks), etc. can be achieved.

[0025] In the corrugated paperboard, the content of the softwood kraft pulp is preferably 25% by mass or more and 60% by mass or less. By setting the content of the softwood kraft pulp of the corrugated paperboard to be within the above range, the bursting strength of the important paper quality (paper quality) of the corrugated paperboard can be ensured, and the corrugated paperboard has excellent box molding and processing adaptability.

[0026] The freeness of the dissociated pulp of the surface layer dissociated according to JIS-P8220 (1998) is preferably 450 ml or more and 500 ml or less. By making the freeness of the dissociated pulp of the corrugated paperboard to be 450 ml or more and 500 ml or less, the bursting index and the carton forming adaptability (box making adaptability) of the corrugated paperboard in a high temperature and high humidity environment can be improved.

[0027] The longitudinal folding strength measured according to JIS-P8115 (2001) is preferably 150 to 800 times, and the transverse folding strength is preferably 200 to 1000 times. By setting the longitudinal folding strength and the transverse folding strength to be within the above ranges, cracking of the indentation line can be suppressed.

[0028] Regarding a method for manufacturing corrugated paperboard according to another embodiment of the present invention, the method is a method for manufacturing corrugated paperboard having at least a surface layer, an intermediate layer, and a back layer, and comprises a step of using a fourdrinier papermaking machine to make paper from raw material pulp, a step of using a dehydrating device having a shoe press (シュープレス) to dehydrate the paper after the papermaking step, a step of drying the paper, and a step of smoothing the surface of the paper, wherein the surface layer contains the coniferous wood The invention relates to a method for preparing a paper-based composite material comprising: manufacturing a paper-based composite material comprising: a first paper-based composite material and a second paper-based composite material; a first paper-based composite material comprising: a first paper-based composite material and a second paper-based composite material; a second ...

[0029] The method for manufacturing corrugated paperboard includes the above-mentioned steps. In the corrugated paperboard manufactured according to the method for manufacturing corrugated paperboard, the surface layer, the middle layer and the back layer contain softwood kraft pulp, corrugated paper waste pulp and kraft paper waste pulp or a combination thereof. By making the content of the softwood kraft pulp in the surface layer and the middle layer and the content of the corrugated paper waste pulp in the back layer within the above-mentioned range, it is possible to manufacture a corrugated paperboard that realizes the recycling of waste paper pulp and can improve the impact resistance when transporting on a road surface with a poor paving environment or in a high temperature and high humidity environment.

[0030] [Details of Embodiments of the Invention]

[0031] The present invention will be described in detail below. The description of the constituent elements described below is based on representative embodiments and specific examples, but the present invention is not limited to such embodiments.

[0032] <Corrugated paperboard>

[0033] The corrugated paperboard according to the embodiment of the present invention at least has a surface layer, an intermediate layer and a back layer in sequence. In addition, the corrugated paperboard may also have a single layer or multiple layers between the intermediate layer and the back layer. That is, the corrugated paperboard can be a multi-layer paper with at least 3 layers. In the case of a multi-layer paper with more than 4 layers, it is preferred to have a second intermediate layer between the intermediate layer and the back layer, and a second back layer between the intermediate layer and the back layer. In this way, it is preferred to make the intermediate layer, the back layer or a combination thereof into a multi-layer structure. By adopting such a structure, the corrugated paperboard can improve the softness of the paper layer, which can not only improve the impact resistance, but also improve the adaptability of the carton molding.

[0034] [Surface layer]

[0035] The surface layer contains softwood kraft pulp (NUKP).

[0036] The lower limit of the content of the softwood kraft pulp in the surface layer is 80% by mass, preferably 90% by mass. By making the content of the softwood kraft pulp in the surface layer located on the outermost side as a packaging material for corrugated paper 80% by mass or more and increasing the content ratio, it is possible to achieve an improvement in impact resistance in a high temperature and high humidity environment, and at the same time, a high folding strength can be obtained, so the indentation line fracture suppression effect is excellent. In the case where the content of the softwood kraft pulp in the surface layer is less than 80% by mass, it may be difficult to ensure the desired impact resistance. In addition, in the case where the content of the softwood kraft pulp in the surface layer is less than 80% by mass, the folding strength of the surface layer is reduced due to the reduction in the content of long fibers, and it may become easy to cause indentation line fracture. In addition, from the viewpoint of recyclability, the surface layer is preferably used within a range where the content of waste paper pulp is less than 20% and the impact resistance is not reduced.

[0037] [Back layer]

[0038] Regarding the back layer, the back layer contains softwood kraft pulp, corrugated paper waste pulp and kraft paper waste pulp. By using softwood kraft pulp, corrugated paper waste pulp and kraft paper waste pulp together as the raw pulp for the back layer (the back layer is located on the back side as a packing material for corrugated paper), it is possible to improve the burst resistance index in a high temperature and high humidity environment while having good adhesion. Furthermore, by using corrugated paper waste pulp and kraft paper waste pulp as the raw pulp for the back layer, the recycling of waste paper pulp can be achieved. In particular, by using kraft paper waste pulp, which has few uses for recycling due to the accumulation of plastic film, the recycling of kraft paper waste pulp can be promoted.

[0039] The lower limit of the content of the waste corrugated paper pulp in the back layer is 30% by mass, preferably 31% by mass. The upper limit of the content of the waste corrugated paper pulp is 70% by mass, preferably 60% by mass. In order to maintain the quality of corrugated paperboard in a high temperature and high humidity environment, it is necessary to suppress the increase in humidity in the corrugated paperboard and improve the adhesion of the back layer. For the corrugated paperboard, by making the content of the waste corrugated paper pulp as the raw pulp of the back layer (the back layer is located on the back side as a packaging material) within the above range, it is possible to improve the carton molding adaptability required for the corrugated paperboard while having good adhesion.

[0040] The lower limit of the content of the kraft waste paper pulp in the back layer is preferably 5% by mass. The upper limit of the content of the kraft waste paper pulp is preferably 45% by mass. By setting the content of the kraft waste paper pulp in the back layer to the above range, it is possible to promote the utilization of the kraft waste paper pulp, which has limited uses for recycling due to the lamination of a plastic film on one side.

[0041] [Middle layer]

[0042] The middle layer contains corrugated paper waste pulp, and the content of the softwood kraft pulp in the middle layer is 30% by mass or less.

[0043] The upper limit of the content of the coniferous kraft pulp in the middle layer is 30% by mass. The lower limit of the content of the coniferous kraft pulp can be 0% by mass, preferably 1% by mass. The content of the coniferous kraft pulp in the middle layer is more preferably 10% by mass or more and 30% by mass or less. By making the content of the coniferous kraft pulp in the middle layer within the above range, the content of corrugated paper waste pulp is increased, thereby enabling the recycling of waste pulp, and improving the lamination property and the bursting resistance index in a high temperature and high humidity environment.

[0044] In addition, in addition to the softwood kraft pulp, the corrugated waste paper pulp and the kraft waste paper pulp, other pulps such as debonded waste paper pulp, debonded deinked waste paper pulp, deinked bleached waste paper pulp produced from magazine waste paper pulp, tea paper waste paper, kraft envelope waste paper, newspaper waste paper, leaflet waste paper, office waste paper, high-quality white paper waste paper, Kent paper waste paper, structural paper waste paper, land certificate waste paper, etc. can be used in each layer of the corrugated paperboard. In addition, mechanical pulps such as groundwood pulp (GP), thermomechanical pulp (TMP), and bleached chemical thermomechanical pulp (BCTMP) can also be used as needed.

[0045] [additive]

[0046] (Sizing agent)

[0047] Preferably, the corrugated paperboard has a sizing agent added to each layer. By making each layer of the corrugated paperboard contain a sizing agent, the durability against humidity in the corrugated paperboard in a high temperature and high humidity environment can be improved, and the quality of the corrugated paperboard can be maintained. The sizing agent can include styrene-based sizing agents, alkyl ketene dimer (AKD), alkenyl succinic anhydride (ASA), neutral rosin sizing agents, and rosin sizing agents. Among them, neutral rosin sizing agents are preferred.

[0048] The rosin sizing agent is not particularly limited, and substances known in the field of papermaking can be used. Examples of rosin-based substances include reinforced rosins obtained by modifying rosins such as gum rosin, wood rosin, and tall oil rosin with α,β-unsaturated carboxylic acids such as fumaric acid, maleic acid, and acrylic acid, or their anhydrides; and rosin esters obtained by reacting polyols such as glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, and diglycerol with the rosins. In addition, in the present invention, the rosin-based sizing agent includes substances obtained by emulsifying them alone or their mixtures, and substances obtained by mixing them after emulsifying them alone. In addition, in the rosin-based sizing agent obtained by the emulsification, in order to further improve the sizing visualization, sizing agents obtained by adding various polymers are also included.

[0049] The lower limit of the amount of the sizing agent added to each layer is preferably 1.25 kg / ton of pulp in terms of solid content, and more preferably 1.5 kg / ton of pulp. In addition, the upper limit of the amount of the sizing agent in each layer is preferably 1.8 kg / ton of pulp in terms of solid content, and more preferably 1.5 kg / ton of pulp. By making the amount of the sizing agent added within the above range, sufficient water resistance can be imparted to the corrugated paperboard, and the durability against humidity in the corrugated paperboard can be improved under a high temperature and high humidity environment. In addition, "kg / ton of pulp" represents the amount added (kg) relative to 1 ton of pulp.

[0050] (Paper Strengthener)

[0051] The corrugated paperboard preferably has a paper strength enhancer added to each layer. By adding the paper strength enhancer, the fiber bonding between the corrugated paper waste pulp and the magazine waste pulp, which are fatigued by the recycling of waste paper and are composed of relatively flat pulp fibers, is strengthened, thereby further improving the burst resistance index in an atmosphere of 60°C and 80%RH.

[0052] Paper strength enhancers include starch-based paper strength enhancers, acrylamide-based paper strength enhancers, vinyl alcohol-based paper strength enhancers, amide epoxy-based paper strength enhancers, etc., among which acrylamide-based paper strength enhancers are preferred. Amphoteric polyacrylamide resin-based paper strength enhancers are more preferred. Amphoteric polyacrylamide is a substance obtained by polymerizing cationic monomers, anionic monomers and acrylamide, and is directly fixed on pulp fibers through its own cationic groups. In addition, amphoteric polyacrylamide resin-based paper strength enhancers are characterized in that the molecular structure and molecular weight can be controlled. In addition, by further adding amphoteric starch, the paper strength of each layer is improved, and a corrugated paperboard with high impact resistance can be obtained.

[0053] The lower limit of the amount of the paper reinforcing agent added to the entire corrugated paperboard is preferably 13.5 kg / t of pulp, more preferably 16.0 kg / t of pulp, in terms of solid content. In addition, the upper limit of the amount of the paper reinforcing agent added to the entire corrugated paperboard is preferably 21.0 kg / t of pulp, more preferably 18.5 kg / t of pulp, in terms of solid content. By setting the amount of the paper reinforcing agent added to the entire corrugated paperboard to be within the above range, the softness of the corrugated paperboard can be ensured, and the bursting index in an atmosphere of 60°C and 80%RH can be improved.

[0054] The lower limit of the amount of the paper strength enhancer added as the surface layer is preferably 1.5 kg / t of pulp in terms of solid content, and more preferably 2.0 kg / t of pulp. In addition, the upper limit of the amount of the paper strength enhancer added as the surface layer is preferably 3.0 kg / t of pulp in terms of solid content, and more preferably 2.5 kg / t of pulp. Although the impact resistance can be improved by containing the paper strength enhancer, the softness of the paper layer may be damaged due to the inclusion of the paper strength enhancer. In the surface layer of the corrugated paperboard, the amount of softwood kraft pulp added to help improve the impact resistance is large. Therefore, by making the amount of the paper strength enhancer added to the surface layer within the above range, it is possible to ensure softness while suppressing the damage and breakage of the surface layer such as the fracture of the indentation line, and further improve the impact resistance during transportation on a road surface with a poor laying environment or in a high temperature and humid environment. Furthermore, if the addition ratio of the paper strength enhancer added to the surface layer exceeds the above upper limit, the water filterability may be reduced, and the raw material pulp may be easily discharged in the pressing and dehydration process of the pressing section of the paper machine. Furthermore, in the press section, dregs of the raw pulp adhere to a blade used to peel off the wet paper adhering to the roll, and the quality of the surface layer may be degraded.

[0055] The lower limit of the amount of the paper strength agent added to the middle layer is preferably 6.0 kg / t of pulp in terms of solid content, and more preferably 7.0 kg / t of pulp. In addition, the upper limit of the amount of the paper strength agent added to the middle layer is preferably 9.0 kg / t of pulp in terms of solid content, and more preferably 8.0 kg / t of pulp. By setting the amount of the paper strength agent added to each layer to be within the above range, the softness of the corrugated box board caused by the paper strength agent can be suppressed, and the damage and fracture of the surface layer such as the crease line fracture can be suppressed, and the impact resistance during transportation on a road surface with a poor paving environment or in a high temperature and high humidity environment can be further improved.

[0056] The lower limit of the amount of the paper strength agent added to the back layer is preferably 6.0 kg / t of pulp, more preferably 7.0 kg / t of pulp, in terms of solid content. The upper limit of the amount of the paper strength agent added to the back layer is preferably 9.0 kg / t of pulp, more preferably 8.0 kg / t of pulp, in terms of solid content. By setting the amount of the paper strength agent added to the back layer to be within the above range, the softness of the corrugated paperboard can be ensured while further improving the impact resistance in a high temperature and high humidity environment.

[0057] (Other additives)

[0058] In the present invention, various papermaking additives can be contained in the corrugated paperboard composed of the surface layer, the middle layer, the back layer and other layers within the range that does not impair the target effect of the present invention. For example, retention aids, pigment dispersants, pH adjusters, tackifiers, flow modifiers, defoamers, foam suppressants, mold release agents, penetrants, ultraviolet absorbers, antioxidants, preservatives, mildew inhibitors, fluorescent removers, resin control agents, slime killers, reagent fixatives such as aluminum sulfate, waterproofing agents such as polyamides, polyamines, and epichlorohydrin, fillers such as clay, talc, and calcium carbonate, basic dyes, acid dyes, anionic direct dyes, cationic direct dyes and other known additives can be added alone or in combination of two or more.

[0059] [Coating layer]

[0060] The corrugated liner board has coating layers formed on the surfaces of the front layer and the back layer, so that the spaces between pulp fibers of the front layer in contact with the coating layers can be filled, thereby ensuring smoothness of the surface.

[0061] In the coating layer of the back layer, the content ratio of starch is preferably 91.0 mass % or more and 97.0 mass % or less, and more preferably 93.0 mass % or more and 96.0 mass % or less, relative to the total content of the anionic sizing agent and the starch, in terms of solid content conversion. By containing the anionic sizing agent in the coating layer of the back layer so that the content ratio of the anionic sizing agent and the starch is within the range, the rigidity of the coating layer can be improved, and thus the bursting strength of the corrugated paperboard can be improved. In addition, in the coating layer of the surface layer, the content ratio of starch is preferably 91.0 mass % or more and 100.0 mass % or less, and more preferably 93.0 mass % or more and 100.0 mass % or less, relative to the total content of the anionic sizing agent and the starch, in terms of solid content conversion. In the coating layer of the surface layer, by making the content ratio of starch in the above range relative to the total content of the anionic sizing agent and the starch, the printing adaptability of the surface layer side of the corrugated paperboard can be improved, and the smoothness of the printed surface can be ensured. In the case where the coating layer of the surface layer contains only starch, the permeability of high-viscosity ink can be prevented, and the printing adaptability can be improved. Furthermore, by making the coating layer of the surface layer contain only starch, the adhesion of the hot melt adhesive when closing the upper cover of the corrugated paper box is improved.

[0062] Examples of starch include corn starch, potato starch, tapioca starch, wheat starch, rice starch, and various modified starches such as oxidized starch and phosphated starch using these as raw materials, but are not limited thereto. In addition, these starches may be used alone or in combination of two or more.

[0063] Examples of the anionic sizing agent include rosin soap sizing agents, rosin emulsion sizing agents, special modified rosin sizing agents, alkenyl succinic acid, alkenyl succinic anhydride, anionic alkyl ketene dimer, olefin resins, styrene resins, styrene-acrylic resins, styrene-maleic acid-acrylic resins, wax sizing agents, and the like.

[0064] In addition to the starch and anionic sizing agent, the coating layer may also contain various additives such as anti-slip agents, preservatives, rust inhibitors, defoamers, viscosity regulators, dispersants, flow modifiers, dyes, water resistance agents, water retention agents, etc.

[0065] The lower limit of the coating amount of the coating layer is preferably 1.00 g / m 2 , more preferably 1.70 g / m 2 On the other hand, the upper limit of the coating amount is preferably 2.25 g / m 2 , more preferably 2.17 g / m 2By setting the coating amount of the coating layer to the above range, the pulp fibers of the surface layer in contact with the coating layer on the surface layer side of the corrugated paperboard can be filled, thereby improving the printing suitability. The coating amount refers to the total amount of the surface layer and the back layer.

[0066] [Characteristics of corrugated paperboard]

[0067] (Content of softwood kraft pulp)

[0068] The lower limit of the content of the softwood kraft pulp of the corrugated paperboard is preferably 25% by mass, and more preferably 27% by mass. The upper limit of the content of the softwood kraft pulp is preferably 60% by mass, and more preferably 40% by mass. By making the content of the softwood kraft pulp of the corrugated paperboard within the above range, the bursting strength, which is an important paper quality of the corrugated box, can be ensured, and the corrugated box has excellent box molding and processing adaptability.

[0069] (Basis Weight)

[0070] The basis weight is measured in accordance with JIS-P8124 (2011). In a further preferred embodiment of the present invention, the basis weight of the entire corrugated cardboard is preferably 160.0 g / m 2 -280.0g / m 2 , more preferably 200.0 g / m 2 -230.0g / m 2 In addition, the basis weight of the surface layer of the corrugated paperboard is preferably 30.0 g / m 2 -80.0g / m 2 , more preferably 35.0 g / m 2 -45.0g / m 2 The basis weight of the middle layer is preferably 50.0 g / m 2 -90.0g / m 2 , more preferably 60.0 g / m 2 -80.0g / m 2 The basis weight of the back layer is preferably 60.0 g / m 2 -120.0g / m 2 , more preferably 80.0 g / m 2 -100.0g / m 2 In the corrugated cardboard boxboard of the present invention, by making the overall basis weight within the above range, the moldability during box molding can be improved, and the damage of the packaging container when filling the content after molding can be suppressed even in a high temperature and high humidity environment.

[0071] The lower limit of the ratio of the basis weight of the surface layer to the total basis weight of the corrugated paperboard is 20%, preferably 21%. In addition, the upper limit of the ratio of the basis weight of the surface layer to the total basis weight is 35%, preferably 32%. By making the basis weight ratio of the surface layer within the above range, the impact resistance in a high temperature and high humidity environment can be maintained, and the softness and cushioning properties of the corrugated paperboard can be ensured.

[0072] (density)

[0073] The lower limit of the density of the corrugated paperboard is preferably 0.65 g / cm 3 , more preferably 0.67 g / cm 3 The upper limit of the density is preferably 0.85 g / cm 3 , more preferably 0.80 g / cm 3 By setting the density of the corrugated cardboard to be within the above range, cushioning properties can be imparted, and high impact resistance can be exhibited without adding a paper reinforcing agent more than necessary.

[0074] (Paper thickness)

[0075] The paper thickness is measured according to the "Paper and Board-Test Method for Thickness and Density" described in JIS-P8118 (2014). The overall paper thickness of the corrugated paperboard of the present invention is preferably 200μm-350μm, and more preferably 250μm-300μm. In addition, the paper thickness of the surface layer constituting the corrugated paperboard is preferably 50μm-115μm. The paper thickness of the middle layer is preferably 85μm-115μm. In addition, the paper thickness of the back layer is preferably 85μm-125μm. By making the overall paper thickness of the corrugated paperboard and the paper thickness of each layer within the above range, the impact resistance and carton formability can be improved.

[0076] (Erectile value)

[0077] The Kebo value is measured according to JIS-P8140 (1998) with the measurement time set to 1 minute. The lower limit of the Kebo value of the corrugated paperboard is preferably 10 g / m 2 , more preferably 30g / m 2 When the linerboard has a KE of less than the lower limit, the moisture in the linerboard may not be sufficiently suppressed in a high temperature and high humidity environment, and poor lamination may occur when the linerboard is processed into a paper container or the like. On the other hand, the upper limit of the KE of the linerboard is preferably 50 g / m 2 , more preferably 40g / m 2When the corrugated paperboard has a KE value of more than the upper limit, the corrugated paperboard may be corrugated or wrinkled due to moisture absorption. By setting the KE values ​​of the surface layer and the back layer at a measurement time of 1 minute to the range, the humidity in the corrugated paperboard can be suppressed in a high temperature and high humidity environment, and the quality of the corrugated paperboard can be maintained.

[0078] (Burst index)

[0079] The bursting index is defined by JIS-P8131 (2009). The bursting index is a value obtained by dividing the bursting strength of the paper expressed in kilopascals (kPa) measured in accordance with JIS-P8131 (2009) by the basis weight. The lower limit of the bursting index of the corrugated paperboard in an atmosphere of 60°C and 80% RH is preferably 3.4 kPa·m 2 / g, more preferably 3.5 kPa·m 2 / g. By setting the bursting index within the above range, the impact resistance of the corrugated paperboard when transported on a road surface with a poor laying environment or in a high temperature and high humidity environment can be improved. The above "60°C, 80% RH" is measured in accordance with JIS-P8111 (1998).

[0080] (Dynamic contact angle)

[0081] The dynamic contact angle is the contact angle measured by the dynamic contact angle measuring device after a drop of 2.0 μl of distilled water is dropped on the sample surface for a specified time (seconds). It is used to judge the wettability of the surface of corrugated paperboard. The contact angle represents the angle formed by the free surface of distilled water and the sample surface when the distilled water contacts the sample surface. The more obtuse the angle is, the worse the wettability is. On the contrary, the more acute the angle is, the better the wettability is. The dynamic contact angle of the surface layer after 1 second is preferably 80 degrees or more and 110 degrees or less, more preferably 85 degrees or more and 100 degrees or less. In addition, by making the dynamic contact angle of the surface layer after 1 second be within the range, the ink inking property of the corrugated paperboard during flexographic printing is good, and the ink penetrates into the paper appropriately, so that the surface properties suitable for printing of fine characters, barcodes, two-dimensional codes (registered trademarks), etc. can be achieved.

[0082] (Freeness of dissociated pulp)

[0083] The corrugated paperboard is preferably a paperboard that is dissociated by a pulp dissociation method according to JIS-P8220-1 (2012), thereby forming a dissociated pulp, and the dissociated freeness (Canadian standard freeness: CSF) of the dissociated pulp measured according to the Canadian standard freeness test method of JIS-P8121-2 (2012) is 450 ml or more and 500 ml or less. In the case where the lower limit of the freeness of the dissociated pulp of the corrugated paperboard is less than 450 ml, the bursting index under a high temperature and high humidity environment may be reduced. In addition, if the upper limit of the freeness of the dissociated pulp exceeds 500 ml, there is a possibility that the productivity is reduced due to the reduction in papermaking properties and the adaptability to carton molding is reduced.

[0084] (Bending strength)

[0085] The longitudinal folding strength of the corrugated paperboard is measured according to the "Paper and paperboard-Folding resistance test method-MIT test machine method" described in JIS-P8115 (2001). The longitudinal folding strength is preferably 150 times or more and 800 times or less, and more preferably 320 times or more and 660 times or less. On the other hand, the transverse folding strength of the corrugated paperboard is the transverse folding strength in the papermaking direction. The transverse folding strength is preferably 200 times or more and 1000 times or less, and more preferably 400 times or more and 820 times or less. By making the longitudinal folding strength and the transverse folding strength within the range, the fracture of the indentation line can be suppressed.

[0086] [Method for producing corrugated paperboard]

[0087] The method for producing the corrugated linerboard is not particularly limited, and may include, for example, a beating step, a papermaking step, a coating step, and a drying step.

[0088] (Beating process)

[0089] In the beating process, the raw material pulp constituting each layer is beaten so as to have a desired freeness. The raw material pulp includes softwood kraft pulp, corrugated paper waste pulp, kraft paper waste pulp or a combination thereof. First, pulp fibers are dispersed in water to obtain a slurry, and additives corresponding to each paper layer are added to the slurry as needed and mixed to prepare paper materials for each paper layer.

[0090] (Papermaking process)

[0091] Next, using these raw material slurries, papermaking is performed using a papermaking machine in a neutral region so that the pH of the corrugated paperboard is 6 or more and 8 or less. In the papermaking step, the raw material slurry is papermade using a papermaking machine that makes paper from the pulp raw material ejected onto a traveling wire. The papermaking machine is not particularly limited, and a known papermaking machine can be used. For example, a fourdrinier papermaking machine, a cylinder papermaking machine, a hybrid former, a gap former, etc. can be used to make paper in multiple layers of three or more layers.

[0092] (Coating process)

[0093] The surface layer and the back layer preferably include a step of applying a coating liquid. A known coater can be used in the coating step.

[0094] (Drying process)

[0095] Next, the paper is dried using a drying cylinder.

[0096] Finally, it is wound onto a shaft to obtain corrugated paper boxboard.

[0097] The method for manufacturing corrugated paperboard includes the above-mentioned steps. In the corrugated paperboard manufactured according to the method for manufacturing corrugated paperboard, the surface layer, the middle layer and the back layer contain softwood kraft pulp, corrugated paper waste pulp and kraft paper waste pulp or a combination thereof. By making the content of the softwood kraft pulp in the surface layer and the middle layer and the content of the corrugated paper waste pulp in the back layer within the above-mentioned range, it is possible to manufacture a corrugated paperboard that realizes the recycling of waste paper pulp and can improve the impact resistance when transporting on a road surface with a poor paving environment or in a high temperature and high humidity environment.

[0098] <Other Implementation Methods>

[0099] The present invention is not limited to the above-described embodiment, and can be implemented in various modified and improved forms other than the above-described forms.

[0100] For example, the corrugated liner board may include a single layer or a plurality of intermediate layers between the intermediate layer and the back layer.

[0101] Example

[0102] Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to the following examples.

[0103] [Example 1]

[0104] The raw materials listed in the table were added to the liquid slurry.

[0105] (additive)

[0106] (1) Rosin-based sizing agent

[0107] Harima Chemicals' "NS-77P" special rosin sizing agent (solid content 50%)

[0108] (2) Acrylamide-based paper strength enhancer

[0109] Harima Chemicals' "Harmaid RB-520": amphoteric polyacrylamide (solid content 20%)

[0110] [Example 2 to Example 19 and Comparative Example 1 to Comparative Example 3]

[0111] Except that the types of raw materials, addition amounts and physical property values ​​are as shown in Tables 1 to 4, the same method as in Example 1 was carried out to obtain corrugated cardboard boxes of Examples 2 to 19 and Comparative Examples 1 to 3.

[0112] [Table 1]

[0113]

[0114] [Table 2]

[0115]

[0116] [Table 3]

[0117]

[0118] [Table 4]

[0119]

[0120] [evaluate]

[0121] The evaluation results are shown in Table 5 for each of the obtained corrugated cardboard sheets.

[0122] (1) Basis weight (g / m 2 )

[0123] The measurement was conducted in accordance with “Paper and paperboard-Basis weight measurement method” described in JIS-P8124 (2011).

[0124] (2) Paper thickness (μm)

[0125] The measurement was conducted in accordance with “Paper and paperboard—Thickness and density test methods” described in JIS-P8118 (2014).

[0126] (3) Density (g / cm 3 )

[0127] The measurement was conducted in accordance with “Paper and paperboard—Thickness and density test methods” described in JIS-P8118 (2014).

[0128] (4) Freeness after dissociation (mL)

[0129] The obtained corrugated linerboard was disintegrated according to the pulp disintegration method of JIS-P8220-1 (2012) to obtain disintegrated pulp, and the disintegrated pulp was measured according to the Canadian standard freeness test method of JIS-P8121-2 (2012).

[0130] (5) Folding strength (times)

[0131] The folding strength in the longitudinal direction and the transverse direction was measured in accordance with "Paper and paperboard-Folding endurance test method-MIT tester method" described in JIS-P8115 (2001).

[0132] (6) Dynamic contact angle

[0133] The dynamic contact angle was measured using a dynamic contact angle measuring apparatus ("DM-701" manufactured by Kyowa Interface Science Co., Ltd.) at 0.2 seconds after 2.0 μL of distilled water was dropped on the surface layer and the back layer.

[0134] (7) Erectile value

[0135] The measurement is carried out in accordance with JIS-P8140 (1998). The so-called "bake value" in the present invention is a value obtained by bringing water into contact with the surface of the surface layer or the back surface layer for 1 minute and measuring the value.

[0136] (8) Carton molding adaptability

[0137] The carton formability of the corrugated cardboard sheets obtained in Examples and Comparative Examples was evaluated in four stages. The carton formability in the following evaluation refers to the ease of bending during carton molding and the absence of breakage at the bent portion.

[0138] A: The carton has very good formability and there is no problem in practical use.

[0139] B: The carton has good formability and there are no practical problems.

[0140] C: The carton formability is slightly poor, which poses practical problems.

[0141] D: The carton has very poor formability and is very problematic in practical use.

[0142] (9) Burst strength and burst index

[0143] The samples were placed in a constant temperature and humidity environment of 60°C and 80% humidity for 6 hours, and taken out immediately after the prescribed time. The bursting strength was measured according to JIS-P8131 (2009), and the bursting strength was divided by the basis weight to obtain the bursting index.

[0144] (10) Impact resistance in high temperature and high humidity environments

[0145] Corrugated cardboard boxes were manufactured using the corrugated cardboard linerboards obtained in Examples and Comparative Examples, and the boxes were transported in containers at 60°C and 80% RH. The state of the boxes was visually determined and evaluated in four stages.

[0146] A: No deformation or holes were found in the corrugated boxes after transportation, so there are no practical problems at all.

[0147] B: Although the corrugated cardboard boxes were deformed and had holes only on the surface of the cardboard after transportation, the contents were not damaged. Although the texture was damaged, there was no problem in practical use.

[0148] C: The corrugated cardboard boxes were deformed after transportation, and holes that did not reach the backing cardboard were found, which had a high possibility of damaging the contents, posing a practical problem.

[0149] D: After transportation, the corrugated cartons were found to be deformed and had complete holes, which made it very likely that the contents would be damaged, posing a serious practical problem.

[0150] (11) Indentation line fracture inhibition

[0151] The indentation line breakage inhibition was evaluated using the following method.

[0152] A paper sample of 210×297 mm in size was dried in a dryer at 45°C for 15 minutes, and then folded 180 degrees so that the paper surface was facing outward. During folding, a 12 kg roller was passed in one direction, and the paper was bent by applying a load by the roller's own weight. The length of the broken (cracked) part of the bent part was measured, and the degree of breakage (%) was measured according to the following formula, and evaluated in 4 stages.

[0153] Calculation formula: Fracture degree (%) = measured value (mm) ÷ 210mm × 100

[0154] The evaluation criteria are as follows.

[0155] A: The fracture degree is less than 5%.

[0156] B: The degree of breakage is 5% or more and less than 10%.

[0157] C: The degree of fracture is 10% or more and less than 15%.

[0158] D: The degree of fracture is 15% or more.

[0159] (12) Printing adaptability

[0160] The printability was evaluated using the following method.

[0161] The surface was printed with black flexographic ink using a 140-line anilox roller using a flexographic printing press, Fractal Printer 100 (manufactured by RK Print Code Instrument Co., Ltd.). As a printing evaluation, the ink splashing state was visually evaluated in four stages.

[0162] The evaluation criteria are as follows.

[0163] A: There is no white spots on the surface of the ink.

[0164] B: There are some tiny white spots in the ink landing on the surface.

[0165] C: The ink is not transferred to the surface sufficiently, and there are slight white spots on the surface as a whole.

[0166] D: Insufficient transfer of ink to the surface causes a lot of white spots.

[0167]

[0168]

[0169] As shown in Table 5 above, for Examples 1 to 19 in which the content of the softwood kraft pulp in the surface layer is 80% by mass or more, the content of the softwood kraft pulp in the middle layer is 30% by mass or less, the content of the corrugated paper waste pulp in the back layer is 30% by mass or more and 70% by mass or less, and the ratio of the basis weight of the surface layer to the total basis weight is 20% or more and 35% or less, the bursting resistance, bursting index and impact resistance, carton molding adaptability, indentation line rupture inhibition, and printing adaptability under high temperature and humidity environments are all good.

[0170] On the other hand, for Comparative Example 1 in which the content of coniferous kraft pulp in the surface layer was 70% by mass, the bursting index, indentation line fracture inhibition, and printing adaptability in a high temperature and high humidity environment were poor. For Comparative Example 2 in which the content of coniferous kraft pulp in the surface layer was 50% by mass, the longitudinal folding strength was very low, the bursting index and printing adaptability in a high temperature and high humidity environment were poor, and the indentation line fracture inhibition was significantly reduced. For Comparative Example 3 in which the content of coniferous kraft pulp in the surface layer was 20% by mass, the back layer did not contain coniferous kraft pulp, and the content of corrugated waste paper pulp was 100% by mass, the longitudinal and transverse folding strengths were very low, the indentation line fracture inhibition and printing adaptability were poor, and the bursting index and impact resistance in a high temperature and high humidity environment were significantly reduced. Although not shown in the table, Example 19 in which the coating layer of the surface layer contained only starch showed better joint bonding during the formation of the corrugated box than other Examples 1 to 18.

[0171] The corrugated paperboard of the present invention is suitable for use as corrugated paperboard and packaging bags for packaging containers for packaging, and as paperboard for containers for storing solids. In addition, it can be used as industrial paper in various fields such as the circulation field under high temperature and high humidity environment.

Claims

1. A corrugated paperboard, in, The corrugated paperboard comprises at least a surface layer, a middle layer and a back layer. The surface layer contains softwood kraft pulp, The content of the softwood kraft pulp in the surface layer is 80% by mass or more, The middle layer contains corrugated paper waste pulp, and the content of the softwood kraft pulp in the middle layer is 30% by mass or less, The raw material pulp of the back layer is composed only of softwood kraft pulp, corrugated paper waste pulp and kraft paper waste pulp. The kraft paper waste pulp is waste paper pulp derived from kraft paper with a plastic film laminated on at least one side. The content of the corrugated paper waste pulp in the back surface layer is 30% by mass or more and 70% by mass or less, The ratio of the basis weight of the surface layer to the total basis weight is 20% or more and 35% or less, The bursting index of the corrugated paperboard in an atmosphere of 60°C and 80% RH is 3.4 kPa·m 2 / g or above.

2. The corrugated paperboard according to claim 1, in, A coating layer is formed on the surfaces of the surface layer and the back layer, The coating layer of the back layer contains starch and anionic sizing agent, The coating layer of the surface layer contains starch, or starch and anionic sizing agent, In the coating layer of the back surface layer, the content ratio of starch relative to the total content of the anionic sizing agent and the starch is 91.0 mass % or more and 96.0 mass % or less in terms of solid content, In the coating layer of the surface layer, the content ratio of starch is 91.0 mass % or more and 100.0 mass % or less relative to the total content of the anionic sizing agent and the starch in terms of solid content, The surface layer has a dynamic contact angle of 80 degrees or more and 110 degrees or less after one second.

3. The corrugated paperboard according to claim 1 or 2, in, The content of the softwood kraft pulp is 25% by mass or more and 60% by mass or less.

4. The corrugated paperboard according to claim 1 or 2, in, The freeness of the disintegrated pulp of the surface layer disintegrated according to JIS-P8220 (1998) is 450 ml or more and 500 ml or less.

5. The corrugated paperboard according to claim 1 or 2, in, The folding strength in the longitudinal direction measured in accordance with JIS-P8115 (2001) is 150 to 800 times, and the folding strength in the transverse direction is 200 to 1000 times.

6. The corrugated paperboard according to claim 1 or 2, in, The amount of the paper strengthening agent added to the back layer is 6.0 kg / ton of pulp or more and 9.0 kg / ton of pulp or less in terms of solid content.

7. The corrugated paperboard according to claim 1 or 2, in, The content of the kraft waste paper pulp in the back surface layer is 5% by mass or more and 45% by mass or less.

Images