JP7320144B2 - Manufacturing method of liner for corrugated board - Google Patents

Description

The present invention relates to corrugated board liners.
This application claims priority based on Japanese Application No. 2020-191267 filed on November 17, 2020, and incorporates all the content described in the above Japanese Application.

Corrugated board liners of standard quality are used for corrugated board sheets used in packaging containers. Corrugated cardboard liners are lighter than those made of wood or resin, and have cushioning properties that prevent the contents from being damaged. Therefore, they are used in various fields including precision equipment.

As a multi-layered paper used for such packing packaging containers, for example, Patent Document 1 discloses a paper substrate having a first layer, a second layer, and a third layer in order, in which the second layer, which is the middle layer, A technique is disclosed in which a paper substrate having excellent double-sided printability and double-sided lamination suitability can be obtained by increasing the density of the first and third layers, which are the outer layers, higher than the density of the (See Patent Document 1). This document discloses that the suitability for printing and lamination can be improved by changing the density characteristics of each layer structure.

In the kraft paper disclosed in Patent Document 2, when it is processed and used as a bag, it is a kraft paper that rarely causes bag breakage. It is disclosed that the kraft paper has excellent elongation properties and strength properties by manufacturing the kraft paper so that the elongation at break and the like have a specific relationship. In Patent Document 3, kraft pulp is viscous beaten so that the pulp slurry concentration is 4.0 to 4.5% by weight and the weight average fiber length is 2.3 to 4.0 mm, and the defibration freeness is 600 ml to 680 ml. By making paper from the kraft pulp, it is possible to impart high air permeability to the paper support while maintaining the strength of the paper support within the JIS standard. Kraft paper for heavy-duty packaging has been disclosed (see Patent Documents 1, 2, and 3).

Thus, in the prior art, emphasis is placed on improving tear strength, tensile performance, workability, printability, and the like.

On the other hand, in recent years, from the standpoint of conservation of wood resources and economic efficiency, the use of waste paper as raw material pulp has been oriented. Used paper pulp used as a raw material for recycled paper is widely known as brown-colored used paper pulp. However, corrugated waste paper pulp, unlike magazine and newspaper waste paper pulp, has a problem that there are many sticky contaminants that cause quality deterioration of recycled paper, and the color is not stable. Kraft waste paper pulp is also used from the viewpoint of the quality of such waste paper pulp that can be secured.

JP 2017-002433 A JP 2014-053372 A JP 2006-089889 A

However, on poorly paved roads, packaging containers are likely to be damaged during transportation due to vibrations caused by the roughness of the road surface. In addition, since product information and the like are printed on the surface of such a liner for corrugated board and a laminate film is adhered to the surface, the liner for corrugated board is required to have sufficient strength under the above environment. Therefore, in order to use corrugated board liners for applications that support impact on roads with poor pavement conditions and use in hot and humid environments, it is necessary to ensure that the corrugated board liner has excellent impact resistance and that it can be used during transportation and in hot and humid environments. It is required to improve the impact resistance in

In general, as a method to increase the impact resistance of corrugated board liners, it is considered to use a lot of paper strength enhancers to improve paper strength. and soaring drug costs. In recent years, there has also been a demand for recycled paper and eco-friendly materials for corrugated board liners. In particular, in recent years, from the viewpoint of improving the strength of kraft packaging bags, heavy bags in which resin films are inner-layered in kraft paper bags have been used, and reuse of such heavy bags is also desired.

The present invention has been made based on the above circumstances. Intended to provide a liner.

A corrugated board liner according to an aspect of the present invention includes at least a surface layer, an intermediate layer, and a back layer, the surface layer contains soft tree kraft pulp, and the content of the soft tree kraft pulp in the surface layer is 80% by mass or more. wherein the middle layer contains corrugated waste paper pulp, and the content of the softwood kraft pulp in the middle layer is 30% by mass or less, and the back layer contains softwood kraft pulp, corrugated waste paper pulp, and kraft waste paper pulp. The kraft-based waste paper pulp is a kraft paper-derived waste paper pulp laminated with a plastic film on one side, and the content of the corrugated board waste paper 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.

According to the present invention, it is possible to provide a corrugated board liner that can improve impact resistance during transport on a poorly paved road surface or in a hot and humid environment while reusing waste paper pulp.

[Description of the embodiment of the present invention]
A corrugated board liner according to an aspect of the present invention includes at least a surface layer, an intermediate layer, and a back layer, the surface layer contains soft tree kraft pulp, and the content of the soft tree kraft pulp in the surface layer is 80% by mass or more. wherein the middle layer contains corrugated waste paper pulp, and the content of the softwood kraft pulp in the middle layer is 30% by mass or less, and the back layer contains softwood kraft pulp, corrugated waste paper pulp, and kraft waste paper pulp. The kraft-based waste paper pulp is a kraft paper-derived waste paper pulp laminated with a plastic film on one side, and the content of the corrugated board waste paper 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.

In this way, the surface layer contains soft tree kraft pulp, and the content of soft tree kraft pulp in the surface layer located on the outermost surface side as a packing material for corrugated cardboard is set to 80% by mass or more, and by increasing the content ratio, Since it is possible to improve the impact resistance in a hot and humid environment and obtain high folding endurance, it is excellent in the effect of suppressing creases. In addition, by using softwood kraft pulp, corrugated waste paper pulp, and kraft waste paper pulp as the raw material pulp for the back layer located on the most back side as a packaging material for corrugated cardboard, it is possible to achieve good laminating properties. , the specific burst strength can be improved in a hot and humid environment. Furthermore, by setting the content of the waste paper pulp in the back layer to 30% by mass or more and 70% by mass or less, it is possible to improve the specific bursting strength in a hot and humid environment while reusing the waste paper pulp. In addition, the middle layer contains recycled corrugated paper pulp, and the content of the soft tree kraft pulp in the middle layer is increased to 30% by mass or less to increase the content of the recycled corrugated paper pulp, thereby reusing the recycled paper pulp. It can improve compatibility and specific burst strength in a hot and humid environment. Furthermore, the ratio of the basis weight of the surface layer to the total basis weight is 20% or more and 35% or less, so that the corrugated liner has flexibility and cushioning properties while maintaining impact resistance in a hot and humid environment. can be guaranteed. Therefore, according to the liner for corrugated board, it is possible to provide a liner for corrugated board that can withstand impact during transport on a road surface with poor pavement environment and exhibit excellent impact resistance even in a hot and humid environment. can. Further, according to the present invention, it is possible to obtain a liner for corrugated board excellent in box-making properties. Here, "recycled kraft paper with a resin film laminated on at least one side" is used for heavy bags (rice and wheat bags, powder bags, feed bags, chemical bags, cement bags, etc.) that are processed into bags for containing heavy items. Two-layer or three-layer kraft with plastic film (thin film of resin (so-called vinyl) such as polyethylene, polypropylene, polyester, nylon, polyvinyl chloride, etc.) on one side of kraft paper (inner side in bag form) It means old paper.

The corrugated board liner preferably has a specific burst strength of 3.4 kPa·m ² /g or more in an atmosphere of 60°C and 80% RH. When the relative bursting strength is within the above range, the corrugated board liner can have improved impact resistance during transport on a poorly paved road surface or in a hot and humid environment.

A coating layer is formed on the surface of the surface layer and the back surface layer, the coating layer of the back surface layer contains starch and an anionic sizing agent, and the coating layer of the surface layer contains starch or starch and an anionic It contains a sizing agent, and the content ratio of starch to the total content of the anionic sizing agent and the starch in the coating layer of the back layer is 91.0% by mass or more and 96.0% by mass or less in terms of solid content. The content of starch relative to the total content of the anionic sizing agent and the starch in the coating layer of the surface layer is 91.0% by mass or more and 100.0% by mass or less in terms of solid content, and the surface The dynamic contact angle of the layer after 1 second is preferably 80 degrees or more and 110 degrees or less. In the corrugated board liner, since the coating layer is formed on the surface of the surface layer and the back layer, it is possible to seal the pulp fibers of the surface layer in contact with the coating layer, so that the surface is smooth. can ensure By containing the anionic sizing agent so that the content ratio of the anionic sizing agent and the starch in the coating layer of the back surface layer is within the above range, the rigidity of the coating layer can be improved. The burst strength of the liner can be improved. Further, the content ratio of starch to the total content of the anionic sizing agent and the starch in the coating layer of the surface layer is within the above range, thereby improving the printability of the surface layer side of the corrugated board liner, Smoothness of the printing surface can be ensured. Furthermore, when the dynamic contact angle of the surface layer after 1 second is 80 degrees or more and 110 degrees or less, ink receptivity is good during flexographic printing for corrugated board, and the ink penetrates into the paper moderately. The surface properties can be made suitable for printing fine characters, bar codes, QR codes (registered trademark), and the like.

In the corrugated board liner, the content of the softwood kraft pulp is preferably 25% by mass or more and 60% by mass or less. When the content of the soft tree kraft pulp in the corrugated board liner is within the above range, the bursting strength, which is an important paper quality of the corrugated board case, can be ensured, and the corrugated board case can be made and processed easily.

It is preferable that the freeness of the disaggregated pulp of the surface layer that has been disaggregated according to JIS-P8220 (1998) is 450 ml or more and 500 ml or less. When the freeness of the disaggregated pulp of the corrugated board liner is 450 ml or more and 500 ml or less, the corrugated board liner can improve the specific burst strength and box-making suitability in a hot and humid environment.

It is preferable that the longitudinal folding endurance measured in accordance with JIS-P8115 (2001) is 150 times or more and 800 times or less, and the width direction folding endurance is 200 times or more and 1000 times or less. When the folding endurance in the vertical direction and the folding endurance in the width direction are within the above ranges, creases can be suppressed.

A method for manufacturing a corrugated board liner according to an embodiment of another aspect of the present invention is a method for manufacturing a corrugated board liner comprising at least a surface layer, an intermediate layer and a back layer, and comprises using a Fourdrinier paper machine to make raw pulp. a step of making paper, a step of dewatering the paper after the paper making step using a dewatering device having a shoe press, a step of drying the paper, and a step of smoothing the surface of the paper, The surface layer contains soft tree kraft pulp, the soft tree kraft pulp content in the surface layer is 80% by mass or more, the middle layer contains corrugated waste paper pulp, and the soft wood kraft pulp content in the middle layer is 30% by mass or less, the back layer contains softwood kraft pulp, corrugated waste paper pulp, and kraft waste paper pulp, and the kraft waste paper pulp is used paper derived from kraft paper laminated with a plastic film on one side It is pulp, and the content of the used corrugated paper pulp in the back layer is 30% by mass or more and 70% by mass or less.

The method for manufacturing a corrugated board liner includes the above steps, and in the corrugated board liner manufactured by the method for manufacturing a corrugated board liner, the surface layer, the intermediate layer, and the back layer are made of softwood kraft pulp, corrugated waste paper pulp, or kraft paper. It contains waste paper pulp or a combination thereof, and the content of the softwood kraft pulp in the surface layer and the middle layer and the content of the corrugated waste paper pulp in the back layer are within the above ranges, so that the waste paper pulp is recycled. It is possible to manufacture a corrugated board liner that can improve impact resistance during transportation on a road surface with poor pavement environment and in a hot and humid environment while promoting utilization.

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

<Liner for cardboard>
A corrugated board liner according to an embodiment of the present invention comprises at least a surface layer, an intermediate layer and a back layer in this order. Further, the corrugated board liner may have a single layer or multiple layers between the intermediate layer and the back layer. That is, the corrugated board liner may be a multi-layered paper having at least three layers, and in the case of a multi-layered paper having four or more layers, a second middle layer is provided between the middle layer and the back layer. It is preferable that the structure includes a second back layer between the intermediate layer and the back layer. In this way, it is preferable that the middle layer, the back layer, or a combination thereof have a multi-layered structure. The box aptitude can be improved.

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

The lower limit of the softwood kraft pulp content in the surface layer is 80% by mass, preferably 90% by mass. As a packing material for corrugated cardboard, the content of softwood kraft pulp in the surface layer located on the outermost side is set to 80% by mass or more, and by increasing the content ratio, it is possible to improve impact resistance in a hot and humid environment. In addition, since high folding endurance can be obtained, it is excellent in the effect of suppressing creases. If the softwood kraft pulp content in the surface layer is less than 80%, it may be difficult to ensure the desired impact resistance. In addition, when the content of soft tree kraft pulp in the surface layer is less than 80%, the content of long fibers is reduced, so the folding endurance of the surface layer is lowered, and creases are likely to occur. From the point of view of recyclability, the surface layer preferably contains less than 20% waste paper pulp and is used within a range that does not reduce the impact resistance.

[Back layer]
The back layer contains softwood kraft pulp, corrugated waste paper pulp, and kraft waste paper pulp. By using softwood kraft pulp, corrugated waste paper pulp, and kraft waste paper pulp as the raw material pulp for the back layer located on the backmost side of the packaging material for corrugated cardboard, it is possible to achieve high-temperature bonding while maintaining good bonding properties. It can improve the specific burst strength in a humid environment. Furthermore, by using corrugated board waste paper pulp and kraft waste paper pulp as raw material pulp for the back layer, waste paper pulp can be reused. In particular, by using kraft waste paper pulp, which has few uses for reuse due to the plastic film being laminated, promotion of reuse of kraft waste paper pulp can be enhanced.

The lower limit of the content of the used corrugated paper pulp in the back surface is 30% by mass, preferably 31% by mass. The upper limit of the content of the used corrugated paper pulp is 70% by mass, preferably 60% by mass. In order to maintain the quality of a corrugated board liner in a hot and humid environment, it is necessary to suppress an increase in humidity in the corrugated board liner and improve lamination properties of the back layer. The corrugated board liner has a content of the recycled corrugated board pulp as the raw material pulp of the back layer located on the backmost side of the packing material within the above range, thereby providing good laminating properties and meeting the requirements of the corrugated board liner. Aptitude for box making can be improved.

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, promotion of the use of the kraft waste paper pulp, which has limited reuse applications due to the plastic film laminated on one side thereof, is promoted. can be done.

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

The upper limit of the softwood kraft pulp content in the middle layer is 30% by mass. The lower limit of the softwood kraft pulp content may be 0% by mass, preferably 1% by mass. The content of the softwood kraft pulp in the middle layer is more preferably 10% by mass or more and 30% by mass or less. By setting the content of softwood kraft pulp in the middle layer within the above range, the content of recycled corrugated paper pulp is increased, and while the recycled pulp is reused, lamination properties and specific burst strength in a hot and humid environment are improved. can.

In addition to the softwood kraft pulp, the corrugated waste paper pulp, and the kraft waste paper pulp, each layer of the corrugated board liner is made of other pulp such as waste magazine pulp, waste tea paper, waste kraft envelope paper, waste newspaper paper, waste leaflet paper, and office pulp. De-inked waste paper pulp, de-inked/de-inked waste paper pulp, de-inked/bleached waste paper pulp, etc., which are produced from waste paper, white waste paper, Kent waste paper, structural waste paper, and landmark waste paper, can be used. Mechanical pulps such as ground wood pulp (GP), thermomechanical pulp (TMP), bleached chemithermomechanical pulp (BCTMP) and the like may also be used as necessary.

[Additive]
(Sizing agent)
The corrugated board liner preferably has a sizing agent added to each layer. Since each layer of the corrugated board liner contains a sizing agent, it is possible to increase the durability of the corrugated board liner against humidity in a hot and humid environment, and it is possible to maintain the quality of the corrugated board liner. Examples of the sizing agents include styrenic sizing agents, alkyl ketene dimers (AKD), alkenyl succinic anhydrides (ASA), neutral rosin sizing agents, and rosin sizing agents. Among these, a neutral rosin sizing agent is preferred.

The rosin sizing agent is not particularly limited, and those known in the field of paper manufacturing can be used. Rosin-based substances include, for example, 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 the above-mentioned Rosin esters obtained by reacting rosins with polyhydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol and diglycerin can be mentioned. In the present invention, the rosin-based sizing agent also includes those obtained by emulsifying these alone or a mixture thereof, and those obtained by emulsifying them alone and then mixing them. Furthermore, the emulsified product to which various polymers are added in order to further improve the sizing property is also included.

The lower limit of the amount of the sizing agent added to each layer is preferably 1.25 kg/t of pulp, more preferably 1.5 kg/t of pulp in terms of solid content. The upper limit of the content of the sizing agent in each layer is preferably 1.8 kg/t of pulp, more preferably 1.5 kg/t of pulp in terms of solid content. By setting the amount of the sizing agent to be added within the above range, the corrugated board liner can be imparted with sufficient water resistance, and the durability against humidity in the corrugated board liner can be enhanced in a hot and humid environment. In addition, "kg/pulp t" represents the addition amount (kg) with respect to 1 ton of pulp.

(paper strength agent)
The corrugated board liner preferably has a paper strength agent added to each layer. By adding the paper strength enhancer, the fibers of corrugated board waste paper pulp and magazine waste paper pulp, which are exhausted by the recycling process of waste paper and consist of relatively flat pulp fibers, are strengthened. The specific burst strength in the atmosphere can be further improved.

Examples of paper strength agents include starch-based paper strength agents, acrylamide-based paper strength agents, vinyl alcohol-based paper strength agents, amide epoxy-based paper strength agents, etc. Among these, acrylamide-based paper strength agents is preferred. Amphoteric polyacrylamide resin-based paper strength agents are more preferred. Amphoteric polyacrylamide is obtained by polymerizing a cationic monomer or an anionic monomer with acrylamide, and is directly fixed to pulp fibers via its own cationic group. In addition, amphoteric polyacrylamide resin-based paper strength agents are characterized by their ability to control the molecular structure and molecular weight. Moreover, by further adding amphoteric starch, the paper strength of each layer is enhanced, and a corrugated board liner with high impact resistance can be obtained.

The lower limit of the amount of the paper strength enhancer added to the entire corrugated board liner is preferably 13.5 kg/t of pulp, more preferably 16.0 kg/t of pulp in terms of solid content. The upper limit of the amount of the paper strength enhancer added to the entire corrugated board liner 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 strength enhancer added to the entire corrugated board liner within the above range, the specific burst strength under an atmosphere of 60° C. and 80% RH can be improved while ensuring the flexibility of the corrugated board liner.

The lower limit of the amount of the paper strength enhancer added to the surface layer is preferably 1.5 kg/t of pulp, more preferably 2.0 kg/t of pulp in terms of solid content. The upper limit of the amount of the paper strength enhancer added to the surface layer is preferably 3.0 kg/t of pulp, more preferably 2.5 kg/t of pulp in terms of solid content. Although impact resistance can be improved by including a paper strength enhancer, the inclusion of a paper strength enhancer may impair the flexibility of the paper layer. The liner for corrugated board has a large amount of softwood kraft pulp added to the surface layer, which contributes to the improvement of impact resistance. For this reason, by setting the amount of the paper strength agent added to the surface layer within the above range, it is possible to suppress breakage of the surface layer such as creases while ensuring flexibility, and when transporting on a road surface with poor pavement environment, It can further improve the impact resistance in a hot and humid environment. Furthermore, when the addition ratio of the paper strength agent in the surface layer exceeds the above upper limit, the freeness is lowered, and the raw material pulp may be easily discharged during the pressing and dewatering steps of the press part of the paper machine. In addition, in the press part, scum of the raw material pulp may adhere to the doctor blade used when removing the wet paper stuck to the roll, and the quality of the surface layer may be deteriorated.

The lower limit of the amount of the paper strength agent added to the middle 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 enhancer added to the middle 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 each layer within the above range, it is possible to suppress the deterioration of the flexibility of the corrugated board liner due to the paper strength agent, while suppressing the breakage of the surface layer such as creases, resulting in a poor pavement environment. It can further improve impact resistance during transport on road surfaces and in hot and humid environments.

The lower limit of the amount of the paper strength enhancer 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 enhancer 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 enhancer to be added to the back layer within the above range, the impact resistance in a hot and humid environment can be further improved while ensuring the flexibility of the corrugated board liner.

(Other additives)
In the present invention, the corrugated board liner comprising each layer, such as the surface layer, middle layer, and back layer, may contain various papermaking additives within a range that does not impair the intended effects of the present invention. For example, yield improvers, pigment dispersants, pH adjusters, thickeners, fluidity improvers, antifoaming agents, foam inhibitors, release agents, penetrants, UV absorbers, antioxidants, preservatives, antiseptics, Viscosity agents, fluorescence erasing agents, pitch control agents, slime control agents, chemical fixing agents such as aluminum sulfate, waterproofing agents such as polyamide, polyamine, epichlorohydrin, etc., fillers such as clay, talc, calcium carbonate, basic dyes, acid dyes , anionic direct dyes, and cationic direct dyes can be added singly or in combination of two or more.

[Coating layer]
In the corrugated board liner, since the coating layer is formed on the surface of the surface layer and the back layer, it is possible to seal the pulp fibers of the surface layer in contact with the coating layer, so that the surface is smooth. can ensure

The content ratio of starch to the total content of the anionic sizing agent and the starch in the coating layer of the back layer is preferably 91.0% by mass or more and 97.0% by mass or less, and 93.0% by mass in terms of solid content. More preferably, it is 96.0% by mass or less. By containing the anionic sizing agent so that the content ratio of the anionic sizing agent and the starch in the coating layer of the back surface layer is within the above range, the rigidity of the coating layer can be improved. The burst strength of the liner can be improved. In addition, the content ratio of starch to the total content of the anionic sizing agent and the starch in the coating layer of the surface layer is preferably 91.0% by mass or more and 100.0% by mass or less in terms of solid content, and 93.0%. % by mass or more and 100.0 mass % or less is more preferable. By setting the content ratio of starch to the total content of the anionic sizing agent and the starch in the coating layer of the surface layer within the above range, the printability of the surface layer side of the corrugated board liner is improved, and the printing surface is improved. Smoothing can be ensured. When the coating layer of the surface layer contains only starch, it is possible to prevent penetration of high-viscosity ink and improve printability. Furthermore, since the coated layer of the surface layer contains only starch, the adhesiveness of the hot-melt glue when closing the upper flap of the corrugated cardboard case is improved.

Examples of starch include corn starch, potato starch, tapioca starch, wheat starch, rice starch, and various modified starches such as oxidized starch and phosphate esterified starch made from these raw materials, but are limited to these. isn't it. These starches may be used alone or in combination of two or more.

Examples of anionic sizing agents include rosin soap sizing agents, rosin emulsion sizing agents, specially modified rosin sizing agents, alkenyl succinic acid, alkenyl succinic anhydride, anionic alkylketene dimers, olefin resins, styrene resins, styrene-acrylic resins, styrene-maleic acid-acrylic resins, wax-based sizing agents, and the like.

In addition to the starch and anionic sizing agent, the coating layer contains various additives such as anti-slip agents, preservatives, anti-rust agents, defoaming agents, viscosity modifiers, dispersants, flow modifiers, dyes, water resistance agents, and water retention agents. It may contain an auxiliary agent.

The lower limit of the coating amount of the coating layer is preferably 1.00 g/m ² and more preferably 1.70 g/m ² in terms of solid content. On the other hand, the upper limit of the coating amount is preferably 2.25 g/m ² , more preferably 2.17 g/m ² . When the coating amount of the coating layer is within the above range, it is possible to seal between the pulp fibers of the surface layer that is in contact with the coating layer on the surface layer side of the corrugated board liner, thereby improving the printability. be able to. The above coating amount refers to the total amount of the surface layer and the back layer.

[Characteristics of liner for cardboard]
(Content of softwood kraft pulp)
The lower limit of the softwood kraft pulp content in the corrugated board liner is preferably 25% by mass, more preferably 27% by mass. The upper limit of the softwood kraft pulp content is preferably 60% by mass, more preferably 40% by mass. When the content of the soft tree kraft pulp in the corrugated board liner is within the above range, the bursting strength, which is an important paper quality of the corrugated board case, can be ensured, and the corrugated board case can be made and processed easily.

(basis weight)
Basis weight is measured according to JIS-P8124 (2011). In a further preferred form of the invention, the total basis weight of the corrugated liner is preferably from 160.0 g/m ² to 280.0 g/m ² , preferably from 200.0 g/m ² to 230.0 g/m 2 . More preferably ^m2 . Further, the basis weight of the surface layer constituting ^the corrugated board liner is preferably 30.0 g/m ² to 80.0 g/m 2 , more preferably 35.0 g/m ² to 45.0 g/m ² . is more preferred. The basis weight of the middle layer is preferably 50.0 g/m ² to 90.0 g/m ² , more preferably 60.0 g/m ² to 80.0 g/m ² . The basis weight of the back layer is preferably 60.0 g/m ² to 120.0 g/m ² , more preferably 80.0 g/m ² to 100.0 g/m ² . In the corrugated board liner of the present invention, by keeping the overall basis weight within the above range, it is possible to improve the moldability during box making, and the contents can be filled after molding even in a hot and humid environment. It is possible to suppress the damage of the packaging container when it is pressed.

The lower limit of the ratio of the basis weight of the surface layer to the total basis weight of the corrugated board liner is 20%, preferably 21%. The upper limit of the ratio of the basis weight of the surface layer to the total basis weight is 35%, preferably 32%. When the basis weight ratio of the surface layer is within the above range, the flexibility and cushioning properties of the corrugated board liner can be ensured while maintaining impact resistance in a hot and humid environment.

(density)
The lower limit of the density of the corrugated board liner is preferably 0.65 g/cm ³ , more preferably 0.67 g/cm ³ . The upper limit of the paper thickness is preferably 0.85 g/cm ³ , more preferably 0.80 g/cm ³ . When the density of the corrugated board liner is within the above range, cushioning properties can be imparted, and high impact resistance can be exhibited without adding a paper strength enhancer more than necessary.

(paper thickness)
The paper thickness is measured in accordance with “Paper and paperboard—Testing methods for thickness and density” described in JIS-P8118 (2014). The overall paper thickness of the corrugated board liner of the present invention is preferably from 200 μm to 350 μm, more preferably from 250 μm to 300 μm. Further, the paper thickness of the surface layer constituting the corrugated board liner is preferably from 50 μm to 115 μm. The paper thickness of the intermediate layer is preferably 85 μm to 115 μm. Moreover, the paper thickness of the back layer is preferably from 85 μm to 125 μm. By setting the overall paper thickness of the corrugated board liner and the paper thickness of each layer within the above ranges, impact resistance and box-making properties can be enhanced.

(Cobb size degree)
The Cobb size degree is measured in accordance with JIS-P8140 (1998) with a measurement time of 1 minute. The lower limit of the hump sizing degree of the corrugated board liner is preferably 10 g/m ² , more preferably 30 g/m ² . If the corrugated board liner has a hump sizing degree less than the above lower limit, it may not be possible to sufficiently suppress the humidity in the corrugated board liner in a hot and humid environment, and lamination failure may occur during processing into paper containers, etc. may invite. On the other hand, the upper limit of the hump sizing degree of the corrugated board liner is preferably 50 g/m ² , more preferably 40 g/m ² . If the corrugated board liner has a hump sizing degree greater than or equal to the upper limit, the corrugated board liner may absorb moisture and cause waviness or wrinkles. Since the bump sizing degree of the surface layer and the back surface layer at a measurement time of 1 minute is within the above range, the humidity in the corrugated board liner can be suppressed in a hot and humid environment, and the quality of the corrugated board liner can be maintained. can be achieved.

(Relative burst strength)
The specific burst strength is specified in JIS-P8131 (2009). The specific bursting strength is a value obtained by dividing the bursting strength of paper measured in kilopascals (kPa) by the basis weight. The lower limit of the specific burst strength of the corrugated board liner 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. When the relative bursting strength is within the above range, the corrugated board liner can have improved impact resistance during transport on a poorly paved road surface or in a hot and humid environment. The above "60° C., 80% RH" is measured according to JIS-P8111 (1998).

(dynamic contact angle)
The dynamic contact angle refers to the contact angle measured by a dynamic contact angle measuring device after a predetermined time (seconds) has elapsed after one drop of 2.0 μl of distilled water is dropped on the surface of the sample, and it indicates the wettability of the corrugated liner surface. to decide. The contact angle indicates the angle formed by the free surface of distilled water and the surface of the sample when distilled water is in contact with the surface of the sample. The wettability improves as the value increases. 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, when the dynamic contact angle of the surface layer after 1 second is within the above range, ink receptivity is good during flexographic printing for corrugated board, and the ink penetrates into the paper moderately. , QR code (registered trademark), etc., can have a surface property suitable for printing.

(Freeness of disaggregated pulp)
The corrugated board liner is made into disaggregated pulp by disaggregating the corrugated liner in accordance with the pulp disaggregation method of JIS-P8220-1 (2012), and the disaggregated pulp is JIS-P8121-2 (2012) Canada The post-maceration freeness (Canadian Standard Freeness: CSF) measured according to the standard freeness test method is preferably 450 ml or more and 500 ml or less. If the lower limit of the freeness of the disaggregated pulp of the corrugated board liner is less than 450 ml, the specific burst strength in a hot and humid environment may decrease. Moreover, when the upper limit of the freeness of the disaggregated pulp exceeds 500 ml, there is a possibility that productivity and box-making aptitude may be lowered due to a decrease in paper-making properties.

(Folding strength)
The longitudinal folding endurance of the corrugated board liner is measured according to "Paper and paperboard--Folding endurance test method--MIT tester method" described in JIS-P8115 (2001). The vertical folding endurance is preferably 150 times or more and 800 times or less, more preferably 320 times or more and 660 times or less. On the other hand, the folding endurance in the width direction of the corrugated board liner is the folding endurance in the width direction in the papermaking direction. The folding endurance in the width direction is preferably 200 times or more and 1000 times or less, more preferably 400 times or more and 820 times or less. When the folding endurance in the vertical direction and the folding endurance in the width direction are within the above ranges, creases can be suppressed.

[Manufacturing method of liner for corrugated board]
The method of manufacturing the corrugated board liner is not particularly limited, but includes, for example, a beating process, a papermaking process, a coating process, and a drying process.

(Beating process)
In the beating step, the raw material pulp constituting each layer is beaten to a desired freeness. The raw material pulp contains soft tree kraft pulp, corrugated waste paper pulp, kraft waste paper pulp, or a combination thereof. First, a slurry obtained by dispersing pulp fibers in water is mixed with an additive corresponding to each paper layer as necessary to prepare a stock for each paper layer.

(Papermaking process)
Next, using these raw material slurries, paper is made by a paper machine in a neutral range so that the pH of the corrugated board liner is 6 or more and 8 or less. In the papermaking process, the raw material pulp is made into paper using a papermaking machine that makes paper from the pulp raw material jetted onto the running wire. The paper machine is not particularly limited, and a known paper machine such as a Fourdrinier paper machine, a cylinder paper machine, a hybrid former, a gap former, or the like can be used. Paper is made at

(Coating process)
It is preferable to include a step of applying a coating liquid to the surface layer and the back layer. A known coating machine can be used in the coating step.

(Drying process)
The paper is then dried in a dryer cylinder.

Finally, it is wound on a reel to obtain a corrugated board liner.

The method for manufacturing a corrugated board liner includes the above steps, and in the corrugated board liner manufactured by the method for manufacturing a corrugated board liner, the surface layer, the intermediate layer, and the back layer are made of softwood kraft pulp, corrugated waste paper pulp, or kraft paper. It contains waste paper pulp or a combination thereof, and the content of the softwood kraft pulp in the surface layer and the middle layer and the content of the corrugated waste paper pulp in the back layer are within the above ranges, so that the waste paper pulp is recycled. It is possible to manufacture a corrugated board liner that can improve impact resistance during transportation on a road surface with poor pavement environment and in a hot and humid environment while promoting utilization.

<Other embodiments>
The present invention is not limited to the above-described embodiments, and can be implemented in various modified and improved modes in addition to the above-described modes.

For example, the corrugated board liner may comprise a single layer or multiple intermediate layers between the intermediate layer and the back layer.

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples.

[Example 1]
Raw materials listed in the table were added to the pulp slurry.
(Additive)
(1) Rosin-based sizing agent “NS-77P” from Harima Kasei Co., Ltd. Special rosin sizing agent (solid content: 50%)
(2) Acrylamide-based paper strength agent “Hermid RB-520” from Harima Kasei Co., Ltd.: amphoteric polyacrylamide (solid content 20%)

[Examples 2 to 19 and Comparative Examples 1 to 3]
For corrugated board of Examples 2 to 19 and Comparative Examples 1 to 3 in the same manner as in Example 1, except that the type of raw material, the amount added, and the physical property values were as shown in Tables 1 to 4. Got a liner.

[evaluation]
Each corrugated board liner thus obtained was evaluated by the following method. Table 5 shows the evaluation results.
(1) Basis weight (g/m ² )
It was measured in accordance with "Paper and paperboard- Basis weight measurement method" described in JIS-P8142 (1998).
(2) Paper thickness (μm)
It was measured in accordance with "Paper and paperboard-Testing methods for thickness and density" described in JIS-P8118 (2014).
(3) Density (g/cm ³ )
It was measured in accordance with "Paper and paperboard-Testing methods for thickness and density" described in JIS-P8118 (2014).
(4) Post-disaggregation freeness (mL)
The resulting corrugated board liner is defiberized according to the pulp defiberization method of JIS-P8220-1 (2012) to obtain defiberized pulp, and the defiberized pulp is JIS-P8121-2 (2012) Canadian standard freeness. Measured according to the test method.
(5) Folding strength (times)
The folding endurance in the longitudinal direction and the width direction was measured according to "Paper and paperboard-Folding endurance test method-MIT tester method" described in JIS-P8115 (2001).
(6) Dynamic contact angle The dynamic contact angle was determined by dropping 2.0 μL of distilled water on the surface layer and the back layer using a dynamic contact angle measuring device (manufactured by Kyowa Interface Science Co., Ltd. “DM-701”). The contact angle was measured after 0.2 seconds of time.
(7) Cobb size degree Measured according to JIS-P8140 (1998). The Cobb size degree referred to in the present invention is a value measured by contacting the surface of the surface layer or the back surface layer with water for 1 minute.
(8) Box-making suitability The box-making properties of the corrugated board liners obtained in Examples and Comparative Examples were evaluated in four stages. In addition, the box-making property in the following evaluation means ease of bending during box-making and no cracks at the bent portion.
A: Box-forming property is very good, and there is no practical problem at all.
B: Good box-forming properties, no problem in practical use.
C: Slightly inferior in box-forming properties, causing problems in practical use.
D: Remarkably poor box-making properties, which is a problem in practice.
(9) Bursting strength and specific bursting strength Leave in a hot and humid constant temperature and high humidity environment of 60 ° C. and humidity of 80% for 6 hours, take out immediately after a predetermined time, and measure the bursting strength according to JIS-P8131 (2009). After measuring according to the above, the burst strength was divided by the basis weight to obtain the specific burst strength.
(10) Impact resistance in a hot and humid environment A cardboard case was manufactured using the cardboard liner obtained in Examples and Comparative Examples, and the cardboard case was transported in the container under conditions of 60°C and 80% RH. A test was conducted to determine the condition of the corrugated cardboard case by visual inspection, and it was evaluated on a 4-point scale.
A: No distortion or holes were observed in the corrugated cardboard case after transportation, and there is no practical problem.
B: The corrugated cardboard case after transportation is distorted and only the front liner is perforated, but the contents are not damaged and the texture is spoiled, but there is no practical problem.
C: The corrugated cardboard case after transportation is distorted or has holes that do not reach the back liner, and there is a high possibility that the contents will be damaged, which is a problem in practice.
D: Distortion and complete holes are observed in the corrugated cardboard case after transport, and there is a very high possibility that the contents will be damaged, which is a problem in practice.
(11) Suppression of creases Suppression of creases was evaluated using the following method.
A paper sample having a size of 210×297 mm is dried in a dryer at 45° C. for 15 minutes and folded back 180 degrees so that the paper surface faces outward. When folding, a roller of 12 kg is passed through for one way, and a load is applied by the roller's own weight to fold it. Of the bent portions, the length of the cracked (teared) portion was measured, and the degree of cracking (%) was measured according to the following formula and evaluated on a four-grade scale.
Calculation formula: Degree of cracking (%) = measured value (mm) / 210 mm x 100)
Evaluation criteria are shown below.
A: The degree of cracking is less than 5%.
B: The degree of cracking is 5% or more and less than 10%.
C: The degree of cracking is 10% or more and less than 15%.
D: The degree of cracking is 15% or more.
(12) Printability Printability was evaluated using the following method.
Using a simple flexographic printing machine, Flexiproof 100 (manufactured by RK Printcoat Instrument Co., Ltd.), the surface was printed with black flexographic ink with an anilox roll of 140 lines. As the printing evaluation, the blurring state of the ink was visually evaluated on a 4-grade scale.
Evaluation criteria are shown below.
A: There is no blur due to ink on the surface.
B: There is partial fine blur due to ink deposition on the surface.
C: There is insufficient transfer of ink to the surface, and fine blurring is present on the entire surface.
D: Numerous blurring due to insufficient transfer of ink to the surface.

As shown in Table 5, 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, and the back layer In Examples 1 to 19, in which the content of the corrugated waste paper pulp 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 high-temperature Bursting strength, relative bursting strength and impact resistance in a humid environment, suitability for box-making, suppression of creasing, and suitability for printing were all excellent.

On the other hand, Comparative Example 1, in which the content of the softwood kraft pulp in the surface layer was 70% by mass, was inferior in relative burst strength, creasing resistance and printability in a hot and humid environment. Comparative Example 2, in which the content of softwood kraft pulp in the surface layer is 50% by mass, has a very low folding endurance in the longitudinal direction, and is inferior in relative burst strength and printability in a hot and humid environment. Crack suppression was remarkably lowered. Comparative Example 3, in which the content of softwood kraft pulp in the surface layer is 20% by mass, the back layer does not contain softwood kraft pulp, and the content of waste corrugated paper pulp is 100% by mass, is excellent in durability in the machine direction and width direction. The folding strength became very low, the creasing prevention property and the printability were inferior, and the specific burst strength and impact resistance in a hot and humid environment were remarkably lowered. In addition, although not shown in the table, in Example 19, in which the coating layer of the surface layer contains only starch, the joint bonding during the formation of the corrugated cardboard case was superior compared to other Examples 1 to 18. .

The corrugated cardboard liner of the present invention can be suitably used as a corrugated cardboard sheet or packaging bag used for packaging containers, or as a liner for containers for solid storage. In addition, it can be used as industrial paper in various fields such as the field of distribution in a hot and humid environment.

Claims (6)

A method for manufacturing a corrugated board liner comprising at least a surface layer, a middle layer and a back layer, comprising:
A step of making paper with a paper machine using a slurry obtained by dispersing pulp fibers of raw material pulp constituting at least the surface layer, the middle layer and the back layer in water,
In the above corrugated board liner,
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 waste paper pulp, and the content of the softwood kraft pulp in the middle layer is 30% by mass or less,
The back layer contains softwood kraft pulp, corrugated waste paper pulp and kraft waste paper pulp,
The kraft waste paper pulp is a kraft paper-derived waste paper pulp laminated with a plastic film on at least one side,
The content of the corrugated board waste paper pulp in the back layer is 30% by mass or more and 70% by mass or less,
A method for manufacturing a corrugated board liner, wherein the ratio of the basis weight of the surface layer to the total basis weight is 20% or more and 35% or less. 2. The method for producing a corrugated board liner according to claim 1, wherein the corrugated board liner has a specific burst strength of 3.4 kPa·m ² /g or more in an atmosphere of 60° C. and 80% RH. Further comprising a step of applying a coating liquid to the surfaces of the surface layer and the back surface layer,
In the above corrugated board liner,
A coating layer is formed on the surface of the surface layer and the back surface 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 an anionic sizing agent,
The content ratio of starch to the total content of the anionic sizing agent and the starch in the coating layer of the back layer is 91.0% by mass or more and 96.0% by mass or less in terms of solid content,
The content ratio of starch to the total content of the anionic sizing agent and the starch in the coating layer of the surface layer is 91.0% by mass or more and 100.0% by mass or less in terms of solid content,
3. The method for producing a corrugated board liner according to claim 1, wherein the surface layer has a dynamic contact angle of 80 degrees or more and 110 degrees or less after one second. 4. The method for producing a corrugated board liner according to claim 1, wherein the content of the soft tree kraft pulp in the corrugated board liner is 25% by mass or more and 60% by mass or less. 5. The corrugated board liner according to any one of claims 1 to 4, wherein the freeness of the disaggregated pulp of the surface layer disaggregated according to JIS-P8220 (1998) in the corrugated board liner is 450 ml or more and 500 ml or less. manufacturing method . The cardboard liner has a longitudinal folding endurance of 150 times or more and 800 times or less, and a width direction folding endurance of 200 times or more and 1000 times or less, as measured in accordance with JIS-P8115 (2001). A method for manufacturing a corrugated board liner according to any one of claims 1 to 5.