WO2022107733A1

WO2022107733A1 - Cardboard liner

Info

Publication number: WO2022107733A1
Application number: PCT/JP2021/041976
Authority: WO
Inventors: 淳史川林
Original assignee: 大王製紙株式会社
Priority date: 2020-11-17
Filing date: 2021-11-15
Publication date: 2022-05-27
Also published as: CN116472231B; KR20230106630A; CN116472231A; JPWO2022107733A1; JP7320144B2

Abstract

This cardboard liner according to one aspect comprises at least a front surface layer, a middle layer, and a rear surface layer. The front surface layer contains softwood kraft pulp. The softwood kraft pulp content of the front surface layer is 80% by mass or greater. The middle layer contains cardboard waste paper pulp and the softwood kraft pulp content of the middle layer is 30% by mass or less. The rear surface layer contains the softwood kraft pulp, the cardboard waste paper pulp, and kraft-type waste paper pulp. The kraft-type waste paper pulp is waste paper pulp derived from kraft paper having a plastic film laminated on one surface thereof. The cardboard waste paper pulp content of the rear surface layer is 30% to 70% by mass (inclusive). The ratio of the basis weight of the front surface layer in relation to the total basis weight is 20% to 35% (inclusive). It is preferable that the burst index of the cardboard liner in an atmosphere that is 60°C and 80% RH be 3.4 kPa·m2/g or greater.

Description

Liner for cardboard

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

For corrugated cardboard sheets used for packaging packaging containers, general quality corrugated board liners are used. Corrugated cardboard liners are lighter than those made of wood or resin containers, and because they have cushioning properties, the contents are not easily damaged, so they are used in various fields including precision equipment.

As a multi-layer paperboard used for such a packaging container, for example, in Patent Document 1, a second layer, which is a middle layer in a paper base material having a first layer, a second layer, and a third layer in order, is described. Disclosed is a technique capable of obtaining a paper substrate having excellent double-sided printing suitability and double-sided laminating suitability by increasing the density of the first layer and the third layer, which are the outer layers, rather than the density of the above. (See Patent Document 1). Here, it is disclosed that the aptitude for printing and laminating can be improved by changing the characteristics of the density in each layer configuration.

The kraft paper disclosed in Patent Document 2 is a kraft paper that is less likely to cause bag breakage when processed into a bag and used, and is involved in breaking elongation in the vertical and horizontal directions, and further in vertical and horizontal directions. Kraft paper having excellent elongation characteristics and strength characteristics is disclosed by using kraft paper manufactured so that the breaking elongation and the like of the paper 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 disintegration freeness is 600 ml to 680 ml. By making the kraft pulp into paper, it is possible to impart high air permeability to the paper support while maintaining the strength of the paper support within the JIS standard, and the raw material cost can be reduced with a low rice tsubo and the manufacturing cost. The kraft paper for heavy wrapping that can reduce the amount of pulp is disclosed (see Patent Document 1, Patent Document 2 and Patent Document 3).

As described above, in the prior art, improvement of tear strength, tensile performance, workability, printability, etc. is emphasized.

On the other hand, in recent years, from the viewpoint of protection of wood resources and economic efficiency, the use of used paper as raw material pulp has been oriented. As used paper pulp used as a raw material for recycled paper, corrugated cardboard used paper is widely known as tea-based used paper pulp. However, unlike the used paper pulp of magazines and newspapers, the used paper pulp of corrugated cardboard has a problem that the color is not stable because there are many sticky foreign substances that cause deterioration of the quality of recycled paper. From the viewpoint of the quality of recycled paper pulp secured in this way, kraft recycled paper pulp is also used.

Japanese Unexamined Patent Publication No. 2017-002433 Japanese Unexamined Patent Publication No. 2014-053372 Japanese Unexamined Patent Publication No. 2006-089889

However, on roads with poor pavement environment, the packaging container is liable to be damaged due to vibration according to the roughness of the road surface during transportation, and a hot and humid environment called abnormal weather is also occurring in Japan. Further, since product information and the like are printed on the surface of such a corrugated cardboard liner and a laminated film is bonded to the surface of the corrugated cardboard liner, sufficient strength is required for the corrugated cardboard liner under the above environment. Therefore, the corrugated board liner has excellent impact resistance in order to be used for impacts on roads with poor pavement environment and use in hot and humid environments, and during transportation and in hot and humid environments. It is required to improve the impact resistance in.

Generally, as a method for improving the impact resistance of a corrugated board liner, it is conceivable to use a large amount of a paper strength enhancer to improve the paper strength. And soaring drug costs are a problem. In recent years, corrugated cardboard liners are also required to be recycled from used paper and made into environmentally friendly materials. In particular, in recent years, from the viewpoint of improving the strength of a kraft packaging bag, a heavy bag in which a resin film is inner-layered in a kraft paper bag has been used, and reuse of such a heavy bag is also required.

The present invention has been made based on the above circumstances, and is for corrugated cardboard that can improve impact resistance during transportation on a road surface with a poor pavement environment or in a hot and humid environment while reusing used paper pulp. The purpose is to provide a liner.

The corrugated liner according to one aspect of the present invention includes at least a surface layer, a middle layer and a back surface layer, 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 middle layer contains waste cardboard pulp, the content of the coniferous kraft pulp in the middle layer is 30% by mass or less, and the back surface layer contains coniferous kraft pulp, waste cardboard pulp and kraft waste paper pulp. The kraft-based waste paper pulp is a waste paper pulp derived from kraft paper having a plastic film laminated on one side thereof, and the content of the cardboard waste paper 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.

According to the present invention, it is possible to provide a corrugated board liner capable of improving impact resistance during transportation on a road surface with a poor pavement environment or in a high temperature and high humidity environment while reusing used paper pulp.

[Explanation of Embodiment of the present invention]
The corrugated liner according to one aspect of the present invention includes at least a surface layer, a middle layer and a back surface layer, 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 middle layer contains waste cardboard pulp, the content of the coniferous kraft pulp in the middle layer is 30% by mass or less, and the back surface layer contains coniferous kraft pulp, waste cardboard pulp and kraft waste paper pulp. The kraft-based waste paper pulp is a waste paper pulp derived from kraft paper having a plastic film laminated on one side thereof, and the content of the cardboard waste paper 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.

As described above, the surface layer contains softwood kraft pulp, and the content of softwood kraft pulp in the surface layer located on the outermost surface side as a packaging material for corrugated cardboard is set to 80% by mass or more, and the content ratio is increased. Since it is possible to improve the impact resistance in a high temperature and high humidity environment and obtain high folding resistance, it is excellent in the effect of suppressing line cracking. In addition, by using coniferous kraft pulp, waste corrugated paper pulp, and kraft-based waste paper pulp as raw material pulp for the back surface layer located on the backmost side as a packaging material for corrugated cardboard, good bonding properties can be achieved. , The relative burst strength in a hot and humid environment can be improved. Further, by setting the content of the corrugated cardboard waste paper pulp in the back surface layer to 30% by mass or more and 70% by mass or less, it is possible to improve the relative burst strength in a high temperature and high humidity environment while reusing the used paper pulp. Further, the middle layer contains the used corrugated paper pulp, and the content of the coniferous kraft pulp in the middle layer is set to 30% by mass or less to increase the content of the used corrugated paper pulp, so that the used paper pulp can be reused and pasted. It is possible to improve the specific burst strength in a compatible and hot and humid environment. Further, since the ratio of the basis weight of the surface layer to the total basis weight is 20% or more and 35% or less, the flexibility and cushioning property of the corrugated board liner are maintained while maintaining the impact resistance in a high temperature and high humidity environment. Can be guaranteed. Therefore, according to the corrugated cardboard liner, it is possible to provide a corrugated board liner that can withstand the impact during transportation on a road surface having a bad pavement environment and can exhibit excellent impact resistance even in a hot and humid environment. can. Further, according to the present invention, it is possible to obtain a corrugated board liner having excellent box-making properties. Here, "craft waste paper with a resin film laminated on at least one side" is for heavy bags (rice bag, powder bag, feed bag, chemical bag, cement bag, etc.) that are processed into bags for heavy objects. Two-layer or three-layer kraft in which a plastic film (thin film of resin (so-called vinyl) such as polyethylene, polypropylene, polyester, nylon, polyvinyl chloride) is laminated on one side (inner side in the form of a bag) of kraft paper. Refers to used 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 specific burst strength is within the above range, the corrugated board liner can improve the impact resistance during transportation on a road surface having a bad pavement environment or in a high temperature and high humidity environment.

A coating layer is formed on the surfaces of the front 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 is starch or starch and anionic. When the content ratio of starch to the total content of the anionic sizing agent and the starch in the coating layer of the back surface layer containing the sizing agent 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, and the surface is The dynamic contact angle of the layer after 1 second is preferably 80 degrees or more and 110 degrees or less. The corrugated board liner has a smooth surface because the coating layer is formed on the surfaces of the front surface layer and the back surface layer, so that the pulp fibers in the surface layer in contact with the coating layer can be sealed. Can be secured. 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, so that the corrugated cardboard can be used. The burst strength of the liner can be improved. Further, when 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, the printability on the surface layer side of the corrugated board liner is improved. Smoothing of the printed surface can be ensured. Further, since the dynamic contact angle of the surface layer after 1 second is 80 degrees or more and 110 degrees or less, the ink inking property at the time of flexographic printing for corrugated cardboard is good, and the ink penetrates into the paper appropriately. The surface quality can be suitable for printing fine characters, barcodes, QR codes (registered trademarks), 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 softwood kraft pulp of the corrugated cardboard liner is within the above range, the burst strength, which is an important paper quality of the corrugated cardboard case, can be ensured, and the corrugated cardboard case is also excellent in box making and processing suitability.

It is preferable that the freeness of the dissociated pulp of the surface layer dissociated in accordance with JIS-P8220 (1998) is 450 ml or more and 500 ml or less. When the freeness of the dissociated 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 the box-making suitability in a high temperature and high humidity environment.

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

The method for producing a liner for cardboard according to an embodiment according to another aspect of the present invention is a method for producing a liner for cardboard having at least a front surface layer, a middle layer and a back surface layer, and a raw material pulp is produced using a Nagami papermaking machine. It comprises a step of making paper, a step of dehydrating the paper after the step of making paper using a dehydrator having a shoe press, a step of drying the paper, and a step of smoothing the surface of the paper. 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 middle layer contains corrugated waste paper pulp, and the content of the coniferous kraft pulp in the middle layer. Is 30% by mass or less, the back surface layer contains coniferous kraft pulp, corrugated waste paper pulp and kraft waste paper pulp, and the kraft waste paper pulp is waste paper derived from kraft paper on which a plastic film is laminated on one side. It is a pulp, and the content of the used corrugated paper pulp in the back surface layer is 30% by mass or more and 70% by mass or less.

The method for manufacturing the corrugated board liner comprises the above steps, and in the corrugated board liner manufactured by the method for manufacturing the corrugated board liner, the front surface layer, the middle layer and the back surface layer are coniferous kraft pulp, corrugated cardboard waste paper pulp, and kraft system. When the content of the coniferous kraft pulp in the front surface layer and the middle layer and the content of the corrugated cardboard waste paper pulp in the back surface layer are within the above range, the waste paper pulp is regenerated. It is possible to manufacture corrugated board liners that can improve impact resistance during transportation on roads with poor paving environments and in hot and humid environments while making use of them.

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

<Liner for cardboard>
The corrugated board liner according to the embodiment of the present invention includes at least a front surface layer, a middle layer, and a back surface layer in this order. Further, the corrugated board liner may have a single layer or a plurality of layers between the middle layer and the back surface layer. That is, the corrugated board liner may be at least three or more layers of multi-layer paper, and in the case of four or more layers of multi-layer paper, a second middle layer is provided between the middle layer and the back surface layer. It is preferable that the structure is such that a second back surface layer is provided between the middle layer and the back surface layer. As described above, it is preferable that the middle layer, the back surface layer, or a combination thereof has a multi-layer structure, and by having such a structure, the corrugated board liner enhances the flexibility of the paper layer and is manufactured not only in impact resistance but also in impact resistance. It is possible to improve the suitability of cardboard.

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

The lower limit of the content of the softwood kraft pulp in the surface layer is 80% by mass, preferably 90% by mass. By increasing the content of softwood kraft pulp in the surface layer located on the outermost surface side as a packaging material for corrugated board to 80% by mass or more and increasing the content ratio, it is possible to improve impact resistance in a hot and humid environment. In addition to being able to obtain high folding resistance, it is excellent in the effect of suppressing line cracking. If the content of softwood kraft pulp in the surface layer is less than 80%, it may be difficult to ensure the desired impact resistance. Further, when the content of softwood kraft pulp in the surface layer is less than 80%, the content of long fibers is reduced, so that the folding resistance of the surface layer is lowered and there is a possibility that line cracking is likely to occur. From the viewpoint of recyclability, it is preferable to use the surface layer within a range in which the content of used paper pulp is less than 20% and the impact resistance is not deteriorated.

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

The lower limit of the content of the corrugated cardboard waste paper pulp on the back surface is 30% by mass, preferably 31% by mass. The upper limit of the content of the corrugated cardboard used paper pulp is 70% by mass, preferably 60% by mass. In order to maintain the quality of the 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 the adhesiveness of the back surface layer. The corrugated board liner is required for a corrugated board liner while having good adhesiveness by setting the content of the corrugated cardboard waste paper pulp as the raw material pulp of the back surface layer located on the backmost side as a packing material within the above range. The suitability for box making can be improved.

The lower limit of the content of the kraft-based recycled paper pulp in the back surface layer is preferably 5% by mass. The upper limit of the content of the kraft-based recycled paper pulp is preferably 45% by mass. By setting the content of the kraft-based recycled paper pulp in the back surface layer to the above range, the use of the kraft-based recycled paper pulp whose reuse is limited because the plastic film is laminated on one side is promoted. Can be done.

[Medium-rise]
The middle layer contains corrugated cardboard 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 content of the softwood kraft pulp in the middle layer is 30% by mass. The lower limit of the content of the softwood kraft pulp 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 to the above range, the content of corrugated cardboard waste paper pulp is increased, the waste paper pulp is reused, and the adhesiveness and the relative burst strength in a hot and humid environment are improved. can.

In addition to the above-mentioned coniferous tree kraft pulp, the above-mentioned cardboard waste paper pulp and the above-mentioned kraft waste paper pulp, each layer of the corrugated liner is used as other pulp such as magazine waste paper pulp, tea waste paper, kraft envelope waste paper, newspaper waste paper, leaflet waste paper, and office. Decomposed waste paper pulp, deinking / deinking waste paper pulp, deinking / bleaching waste paper pulp, etc. manufactured from used paper, upper white waste paper, Kent waste paper, structural waste paper, ground ticket waste paper, etc. can be used. Further, if necessary, mechanical pulp such as crushed wood pulp (GP), thermomechanical pulp (TMP), and bleached chemithermomechanical pulp (BCTMP) may be used.

[Additive]
(Size agent)
It is preferable to add a sizing agent to each layer of the corrugated board liner. Since each layer of the corrugated board liner contains a sizing agent, the durability of the corrugated board liner against humidity can be enhanced in a high temperature and high humidity environment, and the quality of the corrugated board liner can be maintained. Examples of the sizing agent include styrene-based sizing agents, alkyl ketene dimers (AKD), alkenyl succinic acid anhydride (ASA), neutral rosin sizing agents, rosin sizing agents and the like. Among these, a neutral rosin sizing agent is preferable.

The rosin sizing agent is not particularly limited, and those known in the papermaking field can be used. Examples of the rosin-based substance include fortified 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. Examples of rosin esters obtained by reacting rosins with polyhydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol and diglycerin can be mentioned. Further, in the present invention, the rosin-based sizing agent includes those obtained by emulsifying these alone or a mixture thereof, and those obtained by emulsifying alone and then mixing them. Further, the emulsified product to which various polymers are added in order to further improve the size expression is also included.

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

(Paper power enhancer)
It is preferable to add a paper strength enhancer to each layer of the corrugated board liner. By adding a paper strength enhancer, it is exhausted by the recycling process of used paper, and the bond between the fibers of corrugated cardboard waste paper pulp and magazine waste paper pulp made of relatively flat pulp fibers is strengthened. The relative burst strength in the atmosphere can be further improved.

Examples of the paper strength enhancer include a starch-based paper strength enhancer, an acrylamide-based paper strength enhancer, a vinyl alcohol-based paper strength enhancer, an amide epoxy-based paper strength enhancer, and among these, an acrylamide-based paper strength enhancer. Is preferable. More preferably, an amphoteric polyacrylamide resin-based paper strength enhancer is preferable. Amphoteric polyacrylamide is a polymer of a cationic monomer and an anionic monomer with acrylamide, and is directly fixed to pulp fibers via its own cationic group. Another characteristic of the amphoteric polyacrylamide resin-based paper strength enhancer is that the molecular structure and molecular weight can be controlled. Further, by further adding the amphoteric starch, the paper quality strength of each layer is enhanced, and a liner for corrugated board having high impact resistance can be obtained.

As the lower limit of the amount of the paper strength enhancer added to the entire corrugated board liner, 13.5 kg / pulp t is preferable in terms of solid content, and 16.0 kg / pulp t is more preferable. The upper limit of the amount of the paper strength enhancer added to the entire corrugated board liner is preferably 21.0 kg / pulp t, more preferably 18.5 kg / pulp t 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, it is possible to improve the relative burst strength in an atmosphere of 60 ° C. and 80% RH while ensuring the flexibility of the corrugated board liner.

As the lower limit of the amount of the paper strength enhancer added to the surface layer, 1.5 kg / pulp t is preferable, and 2.0 kg / pulp t is more preferable in terms of solid content. Further, as the upper limit of the amount of the paper strength enhancer added to the surface layer, 3.0 kg / pulp t is preferable, and 2.5 kg / pulp t is more preferable in terms of solid content. Impact resistance can be improved by containing a paper strength enhancer, but the inclusion of a paper strength enhancer may impair the flexibility of the paper layer. The corrugated board liner has a large amount of softwood kraft pulp added to the surface layer, which contributes to improving impact resistance. For this reason, by setting the amount of the paper strength enhancer added to the surface layer within the above range, it is possible to suppress breakage of the surface layer such as cracks in the ruled lines while ensuring flexibility, and when transporting on a road surface with a poor pavement environment. Impact resistance in a hot and humid environment can be further improved. Further, if the addition ratio of the paper strength enhancer in the surface layer exceeds the above upper limit, the drainage may be lowered, and the raw material pulp may be easily discharged in the pressing and dehydration steps of the press part of the paper machine. Further, in the above press part, the lees of the raw material pulp may adhere to the doctor blade used when peeling off the wet paper attached to the roll, and the quality of the surface layer may deteriorate.

As the lower limit of the amount of the paper strength enhancer added in the middle layer, 6.0 kg / pulp t is preferable, and 7.0 kg / pulp t is more preferable in terms of solid content. Further, as the upper limit of the amount of the paper strength enhancer added in the middle layer, 9.0 kg / pulp t is preferable, and 8.0 kg / pulp t is more preferable in terms of solid content. By setting the amount of the paper strength enhancer added to each layer within the above range, it is possible to suppress the decrease in flexibility of the corrugated board liner due to the paper strength enhancer, and to suppress the breakage of the surface layer such as line cracking, resulting in a poor pavement environment. Impact resistance can be further improved during transportation on the road surface or in a hot and humid environment.

As the lower limit of the amount of the paper strength enhancer added to the back surface layer, 6.0 kg / pulp t is preferable, and 7.0 kg / pulp t is more preferable in terms of solid content. Further, as the upper limit of the amount of the paper strength enhancer added to the back surface layer, 9.0 kg / pulp t is preferable, and 8.0 kg / pulp t is more preferable in terms of solid content. By setting the amount of the paper strength enhancer added to the back surface layer within the above range, it is possible to further improve the impact resistance in a high temperature and high humidity environment while ensuring the flexibility of the corrugated board liner.

(Other additives)
In the present invention, the corrugated board liner composed of each layer such as the front surface layer, the middle layer, and the back surface layer may contain various papermaking additives as long as the effects intended for the present invention are not impaired. For example, yield improvers, pigment dispersants, pH adjusters, thickeners, fluidity improvers, defoamers, foam suppressants, mold release agents, penetrants, UV absorbers, antioxidants, preservatives, antiseptic. Baking agents, fluorescent defoamers, pitch control agents, slime control agents, chemical fixing agents such as sulfuric acid bands, water resistant agents such as polyamides, polyamines and epichlorohydrins, fillers such as clay, talc and calcium carbonate, basic dyes and acidic dyes. , Known additives such as anionic direct dyes and cationic direct dyes can be added alone or in combination of two or more.

[Coating layer]
The corrugated board liner has a smooth surface because the coating layer is formed on the surfaces of the front surface layer and the back surface layer, so that the pulp fibers in the surface layer in contact with the coating layer can be sealed. Can be secured.

The content ratio of starch to the total content of the anionic sizing agent and the starch in the coating layer of the back surface layer is preferably 91.0% by mass or more and 97.0% by mass or less in terms of solid content, preferably 93.0% by mass. 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, so that the corrugated cardboard can be used. 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 preferably 91.0% by mass or more and 100.0% by mass or less in terms of solid content, preferably 93.0. More preferably, it is by mass or more and 100.0% by mass or less. When 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, the printability on the surface layer side of the corrugated board liner is improved, and the printability of the printed surface is improved. Smoothing can be ensured. When the coating layer of the surface layer contains only starch, the permeability of the high-viscosity ink can be prevented and the printability can be improved. Further, since the coating 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 the starch include, but are limited to, corn starch, horse belly starch, tapioca starch, wheat starch, rice starch, oxidized starch made from these, and various modified starches of phosphoric acid esterified starch. is not. In addition, these starches can be used alone or in combination of two or more.

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

The coating layer includes the starch and anionic sizing agent, as well as various antislip agents, preservatives, rust inhibitors, antifoaming agents, viscosity modifiers, dispersants, flow modifiers, dyes, water resistant agents, water retaining agents and the like. Auxiliary agents may be included.

As the lower limit of the coating amount of the coating layer, 1.00 g / m ² is preferable and 1.70 g / m ² is more preferable in terms of solid content. On the other hand, as the upper limit of the coating amount, 2.25 g / m ² is preferable, and 2.17 g / m ² is more preferable. 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 in contact with the coating layer on the surface layer side of the corrugated board liner, thereby improving the printability. be able to. The coating amount refers to the total amount of the front surface layer and the back surface layer.

[Characteristics of liner for corrugated cardboard]
(Coniferous kraft pulp content)
The lower limit of the content of the softwood kraft pulp of the corrugated board liner is preferably 25% by mass, more preferably 27% by mass. The upper limit of the content of the softwood kraft pulp is preferably 60% by mass, more preferably 40% by mass. When the content of the softwood kraft pulp of the corrugated cardboard liner is within the above range, the burst strength, which is an important paper quality of the corrugated cardboard case, can be ensured, and the corrugated cardboard case is also excellent in box making and processing suitability.

(Basis weight)
Basis weight is measured according to JIS-P8124 (2011). In a further preferred embodiment of the present invention, the total basis weight of the corrugated board liner is preferably 160.0 g / m ² to 280.0 g / m ² , and 200.0 g / m ² to 230.0 g / m 2. It is more preferably m ² . 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 , and preferably 35.0 g / m ² to 45.0 g / m ² . Is more preferable. The basis weight of the middle layer is preferably 50.0 g / m ² to 90.0 g / m ² , and more preferably 60.0 g / m ² to 80.0 g / m ² . The basis weight of the back surface layer is preferably 60.0 g / m ² to 120.0 g / m ² , and more preferably 80.0 g / m ² to 100.0 g / m ² . In the corrugated board liner of the present invention, by setting the total basis weight within the above range, the moldability at the time of box making can be improved, and the contents are filled after molding even in a high temperature and high humidity environment. It is possible to prevent damage to the packaging container when the product is used.

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 ratio of the basis weight of the surface layer is within the above range, the flexibility and cushioning property of the corrugated board liner can be ensured while maintaining the impact resistance in a high temperature and high humidity environment.

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

(Paper thickness)
Paper thickness is measured according to "Paper and Paperboard-Thickness and Density Test Method" described in JIS-P8118 (2014). The total paper thickness of the corrugated board liner of the present invention is preferably 200 μm to 350 μm, and more preferably 250 μm to 300 μm. Further, the paper thickness of the surface layer constituting the corrugated board liner is preferably 50 μm to 115 μm. The paper thickness of the middle layer is preferably 85 μm to 115 μm. The paper thickness of the back surface layer is preferably 85 μm to 125 μm. By setting the total paper thickness of the corrugated cardboard liner and the paper thickness of each layer within the above ranges, impact resistance and box making property can be improved.

(Degree of bump size)
The degree of bump size is measured with the measurement time as 1 minute in accordance with JIS-P8140 (1998). As the lower limit of the bump size of the corrugated board liner, 10 g / m ² is preferable, and 30 g / m ² is more preferable. If the hump size of the corrugated board liner is less than the above lower limit, the humidity in the corrugated board liner may not be sufficiently suppressed in a hot and humid environment, and poor bonding may occur during processing into a paper container or the like. There is a risk of inviting. On the other hand, as the upper limit of the bump size of the corrugated board liner, 50 g / m ² is preferable, and 40 g / m ² is more preferable. When the degree of bump size of the corrugated board liner is equal to or greater than the above upper limit, the corrugated board liner may cause wrinkles or wrinkles due to moisture absorption. When the degree of bump size of the front surface layer and the back surface layer in the measurement time of 1 minute is within the above range, the humidity in the corrugated board liner can be suppressed in a high temperature and high humidity environment, and the quality of the corrugated board liner can be maintained. Can be planned.

(Ratio burst strength)
The specific burst strength is specified in JIS-P8131 (2009). The specific burst strength is a value obtained by dividing the burst strength of paper expressed in kilopascals (kPa) units measured in accordance with the above JIS-P8131 (2009) by the above basis weight. As the lower limit of the specific burst strength of the corrugated board liner in an atmosphere of 60 ° C. and 80% RH, 3.4 kPa · m ² / g is preferable, and 3.5 kPa · m ² / g is more preferable. When the specific burst strength is within the above range, the corrugated board liner can improve the impact resistance during transportation on a road surface having a bad pavement environment or in a high temperature and high humidity environment. The above "60 ° C., 80% RH" is measured in accordance with 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 dropping one drop of 2.0 μl of distilled water on the surface of the sample, and the wettability of the surface of the liner for corrugated sheet. to decide. The contact angle indicates the angle that the free surface of the distilled water forms with the surface of the sample when the distilled water is in contact with the surface of the sample. The more it becomes, the better the wettability. The dynamic contact angle of the surface layer after 1 second is preferably 80 degrees or more and 110 degrees or less, and more preferably 85 degrees or more and 100 degrees or less. In addition, since the dynamic contact angle of the surface layer after 1 second is within the above range, the ink inking property at the time of flexographic printing for corrugated board is good, and the ink penetrates into the paper appropriately, so that fine print and barcode are used. , QR code (registered trademark) and the like can be made to have a surface property suitable for printing.

(Freeness of dissociated pulp)
The corrugated board liner is made into dissociated pulp by dissociating the corrugated liner in accordance with the method of dissociating the pulp of JIS-P8220-1 (2012), and the dissociated pulp is made into Canada of JIS-P8121-2 (2012). It is preferable that the post-dissolution freeness (Canadian standard freeness: CSF) measured according to the standard freeness test method is 450 ml or more and 500 ml or less. If the lower limit of the freeness of the dissociated pulp of the corrugated board liner is less than 450 ml, the specific burst strength in a hot and humid environment may decrease. Further, if the upper limit of the freeness of the disintegrated pulp exceeds 500 ml, the productivity may be lowered and the box-making suitability may be lowered due to the deterioration of the papermaking property.

(Fold resistance)
The vertical folding resistance of the corrugated board liner is measured according to "Paper and Paperboard-Folding Strength Test Method-MIT Testing Machine Method" described in JIS-P8115 (2001). The bending resistance in the vertical direction 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 folding resistance in the width direction of the corrugated board liner is the folding strength in the width direction in the papermaking direction. The folding resistance in the width direction is preferably 200 times or more and 1000 times or less, and more preferably 400 times or more and 820 times or less. When the folding resistance in the vertical direction and the folding strength in the width direction are within the above ranges, cracking of the ruled lines can be suppressed.

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

(Beating process)
In the beating step, the raw material pulp constituting each layer is beaten so as to have a desired freeness. The raw material pulp contains softwood kraft pulp, corrugated cardboard waste paper pulp, kraft-based waste paper pulp, or a combination thereof. First, an additive corresponding to each paper layer is added to the slurry obtained by dispersing pulp fibers in water as necessary and mixed to prepare a paper material for each paper layer.

(Papermaking process)
Next, using these raw material slurries, paper is made with a paper machine in the 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 using a paper machine that makes the pulp raw material ejected onto the traveling wire. The paper machine is not particularly limited, and a known paper machine such as a long net paper machine, a circular net paper machine, a hybrid former, a gap former, or the like can be used, and a multi-layer of three or more layers can be used. Paper is made at.

(Coating process)
It is preferable that the front surface layer and the back surface layer include a step of applying a coating liquid. In the coating process, a known coating machine can be used.

(Drying process)
Next, the paper is dried in a dryer cylinder.

Finally, wind it on a reel to get a liner for cardboard.

<Other embodiments>
The present invention is not limited to the above embodiment, and can be implemented in various modifications and improvements in addition to the above embodiment.

For example, the corrugated board liner may have a single layer or a plurality of middle layers between the middle layer and the back surface layer.

Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples.

[Example 1]
The raw materials listed in the table were added to the pulp slurry.
(Additive)
(1) Rosin-based sizing agent Harima Chemicals' NS-77P special rosin sizing agent (solid content 50%)
(2) Acrylamide-based paper strength enhancer Harima Chemicals'"HarmideRB-520": Zwitterionic polyacrylamide (solid content 20%)

[Examples 2 to 19 and Comparative Examples 1 to 3]
For corrugated cardboard of Examples 2 to 19 and Comparative Examples 1 to 3 in the same manner as in Example 1 except that the types of raw materials, the amount added, and the physical property values are as shown in Tables 1 to 4. I got a liner.

[evaluation]
Each of the obtained corrugated cardboard liners was evaluated by the following method. The evaluation results are shown in Table 5.
(1) Basis weight (g / m ² )
The measurement was performed in accordance with "Paper and Paperboard-Basis Weight Measuring Method" described in JIS-P8142 (1998).
(2) Paper thickness (μm)
The measurement was performed in accordance with "Paper and Paperboard-Thickness and Density Test Method" described in JIS-P8118 (2014).
(3) Density (g / cm ³ )
The measurement was performed in accordance with "Paper and Paperboard-Thickness and Density Test Method" described in JIS-P8118 (2014).
(4) Freeness after dissociation (mL)
The obtained corrugated board liner was disintegrated according to the method of disintegrating the pulp of JIS-P8220-1 (2012) to obtain dissociated pulp, and this disassembled pulp was used as the Canadian standard free water content of JIS-P8121-2 (2012). Measured according to the test method.
(5) Fold resistance (times)
The folding resistance in the vertical and width directions was measured according to "Paper and Paperboard-Folding Strength Test Method-MIT Testing Machine Method" described in JIS-P8115 (2001).
(6) Dynamic contact angle For the dynamic contact angle, 2.0 μL of distilled water was dropped on the front surface layer and the back surface layer using a dynamic contact angle measuring device (“DM-701” manufactured by Kyowa Interface Science Co., Ltd.). The contact angle 0.2 seconds after the hour was measured.
(7) Cobb size degree Measured according to JIS-P8140 (1998). The degree of bump size referred to in the present invention is a value measured by contacting the surface of the front surface layer or the back surface layer with water for 1 minute.
(8) Appropriateness for box making The box making properties of the corrugated board liners obtained in Examples and Comparative Examples were evaluated in four stages. The box-making property in the following evaluation means that the box is easy to bend at the time of box-making and that the bent portion is not cracked.
A: The box-making property is very good, and there is no problem in practical use.
B: Good box-making property, and there is no problem in practical use.
C: The box-making property is slightly inferior, and there is a problem in practical use.
D: The box-making property is remarkably inferior, which is a practical problem.
(9) Bursting strength and specific bursting strength The product was left in a high-temperature, high-humidity, constant-temperature, high-humidity environment at 60 ° C. and 80% humidity, and was taken out immediately after the lapse of a predetermined time, and the bursting strength was adjusted to JIS-P8131 (2009). After the measurement according to the above, the burst strength was divided by the above-mentioned basis weight to obtain the specific burst strength.
(10) Impact resistance in a hot and humid environment A corrugated cardboard case is manufactured using the corrugated cardboard liners obtained in Examples and Comparative Examples, and the corrugated cardboard case is transported in a container at 60 ° C. and 80% RH. The condition of the corrugated cardboard case was visually judged and evaluated on a 4-point scale.
A: No distortion or holes are found in the corrugated cardboard case after transportation, and there is no problem in practical use.
B: Although the corrugated cardboard case after transportation has distortion and holes only in the front liner, the contents are not damaged and the texture is impaired, but there is no practical problem.
C: Distortion and holes that do not reach the back liner are seen in the corrugated cardboard case after transportation, and there is a high possibility that the contents will be damaged, which is a practical problem.
D: Distortion and complete perforation are seen in the corrugated cardboard case after transportation, and there is a high possibility that the contents will be damaged, which is a practical problem.
(11) Rule crack suppressing property The rule crack suppressing property was evaluated by 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 180 degrees so that the paper surface is on the outside. When folding back, a 12 kg roller is passed one way and a load is applied by the roller's own weight to bend it. Among the bent portions, the length of the portion where the crack (tear) was generated was measured, the degree of cracking (%) was measured by the following formula, and the evaluation was made in 4 stages.
Calculation formula: cracking degree (%) = measured value (mm) ÷ 210 mm × 100)
The 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 The printability was evaluated using the following method.
The surface was printed with black flexo ink using Anilox roll 140 lines using a flexographic simple printing machine Flexiproof 100 (manufactured by RK Print Coat Instruments). As a printing evaluation, the ink blurring state was visually evaluated on a four-point scale.
The evaluation criteria are shown below.
A: There is no blurring due to the ink on the surface.
B: There is a small amount of blurring due to the ink on the surface.
C: There is insufficient transfer of ink to the surface, and there is minute blurring on the entire surface.
D: There is a lot of blurring due to insufficient transfer of ink to the surface.

As shown in Table 5, the content of the coniferous kraft pulp in the surface layer is 80% by mass or more, the content of the coniferous kraft pulp in the middle layer is 30% by mass or less, and the content in the back surface layer is 30% by mass or less. In Examples 1 to 19, 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 bursting strength, specific bursting strength and impact resistance, box-making suitability, rule cracking suppressing property, and printing suitability in a humid environment were all good.

On the other hand, Comparative Example 1 in which the content of softwood kraft pulp in the surface layer was 70% by mass was inferior in relative burst strength, rule cracking inhibitory property and printability in a high temperature and high humidity environment. In Comparative Example 2 in which the content of softwood kraft pulp in the surface layer is 50% by mass, the bending resistance in the vertical direction is very low, the specific burst strength and printability in a high temperature and high humidity environment are inferior, and the ruled lines are formed. The crack suppression property was significantly reduced. Comparative Example 3 in which the content of the softwood kraft pulp in the front surface layer is 20% by mass, the back surface layer does not contain the softwood kraft pulp, and the content of the corrugated cardboard used paper pulp is 100% by mass is the resistance in the vertical direction and the width direction. The folding strength became very low, the line crack suppressing property and the printability were inferior, and the specific burst strength and the impact resistance in a high temperature and high humidity environment were remarkably lowered. Further, although not shown in the table, in Example 19 in which the coating layer of the surface layer contains only starch, the joint bonding at the time of forming the corrugated cardboard case was more excellent than in the 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 a packaging container for packaging, or a liner for a container for solid storage. In addition, it can be used as industrial paper in various fields such as distribution fields in a hot and humid environment.

Claims

With 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, and the content is 80% by mass or more.
The middle layer contains corrugated cardboard waste paper pulp, and the content of the softwood kraft pulp in the middle layer is 30% by mass or less.
The back surface layer contains softwood kraft pulp, corrugated cardboard waste paper pulp and kraft waste paper pulp.
The above-mentioned kraft-based recycled paper pulp is a recycled paper pulp derived from kraft paper in which a plastic film is laminated on at least one side.
The content of the corrugated cardboard waste paper pulp in the back surface layer is 30% by mass or more and 70% by mass or less.
A corrugated board liner in which the ratio of the basis weight of the surface layer to the total basis weight is 20% or more and 35% or less.
The corrugated board liner according to claim 1, wherein the specific burst strength in an atmosphere of 60 ° C. and 80% RH is 3.4 kPa · m 2 / g or more.
A coating layer is formed on the surfaces of the front surface layer and the back surface layer, and the coating layer is formed.
The coating layer of the back surface 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 surface 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.
The corrugated board liner according to claim 1 or 2, wherein the dynamic contact angle of the surface layer after 1 second is 80 degrees or more and 110 degrees or less.
The corrugated board liner according to claim 1, claim 2 or claim 3, wherein the content of the softwood kraft pulp is 25% by mass or more and 60% by mass or less.
The corrugated board liner according to any one of claims 1 to 4, wherein the freeness of the dissociated pulp of the surface layer dissociated in accordance with JIS-P8220 (1998) is 450 ml or more and 500 ml or less.
Claims 1 to claim 1 to which the vertical folding resistance measured in accordance with JIS-P8115 (2001) is 150 times or more and 800 times or less, and the width direction folding strength is 200 times or more and 1000 times or less. 5. The corrugated cardboard liner according to any one of 5.