Liner for corrugated cardboard

Abstract

A liner for corrugated cardboard according to one aspect of the present invention comprises at least a surface layer, a surface lower layer, and a back layer, wherein: the content of the softwood kraft pulp in the total pulp of the surface layer is 45-75 mass%; the freeness of corrugated cardboard recycled pulp in the surface layer is at most 300 mL; the content of the softwood kraft pulp in the total pulp of the surface lower layer is 30-70 mass%; the content of the corrugated cardboard recycled pulp in the total pulp of the back layer is 97-100 mass%; the freeness of the corrugated cardboard recycled pulp is at most 300 mL; and the basis weight is at least 290 g / m2. The compressive strength measured by a ring crush method is preferably at least 695 N. The folding endurance in the vertical direction is preferably 295-900 times.

Description

Cardboard liner

[0001] The present invention relates to a liner for corrugated cardboard. This application claims priority under Japanese application No. 2024-196265, filed on 8 November 2024, and incorporates all the provisions of the said Japanese application.

[0002] Corrugated cardboard liners, used in packaging containers, are lighter than those made of wood or plastic, and their cushioning properties prevent damage to the contents. For these reasons, they are used in a variety of fields, including precision equipment.

[0003] As a liner for corrugated cardboard, for example, Patent Document 1 discloses a heavy-duty kraft paper for packaging in which kraft pulp is viscously beaten at a pulp slurry concentration of 4.0 to 4.5% by weight to a weight-average fiber length of 2.3 to 4.0 mm, and the kraft pulp is made into paper so that the disintegration freeness is 600 ml to 680 ml. This method maintains the strength of the paper support within JIS standards while providing high air permeability to the paper support, and allows for lower raw material costs at a low basis weight, thereby reducing manufacturing costs.

[0004] Japanese Patent Publication No. 2006-089889

[0005] These corrugated cardboard liners are combined with core paper to form corrugated cardboard sheets, which are then used for various packaging boxes. In recent years, the function of corrugated cardboard boxes has expanded beyond simply protecting goods from physical forces during storage and transportation; multi-color printing is increasingly being used to add a visual appeal to the products, allowing them to be displayed or auctioned while still packed inside. Therefore, corrugated cardboard liners that can also be used for packaging purposes are required to possess not only high strength but also an excellent appearance.

[0006] Furthermore, corrugated cardboard liners are required to possess not only the strength and appearance characteristics mentioned above, but also processing suitability, such as suitability for box making and lamination, for forming corrugated cardboard.

[0007] This invention was made based on the circumstances described above, and aims to provide a corrugated cardboard liner that is excellent in strength and appearance while possessing suitability for box making and lamination.

[0008] A corrugated cardboard liner according to an embodiment of the present invention comprises at least a surface layer, a subsurface layer, and a back layer, wherein the surface layer and subsurface layer contain softwood kraft pulp and recycled corrugated cardboard pulp, the back layer contains recycled corrugated cardboard pulp, the content of softwood kraft pulp in the total pulp of the surface layer is 45% by mass or more and 75% by mass or less, the freeness of recycled corrugated cardboard pulp in the surface layer is 300 mL or less, the content of softwood kraft pulp in the total pulp of the subsurface layer is 30% by mass or more and 70% by mass or less, the content of recycled corrugated cardboard pulp in the total pulp of the back layer is 97% by mass or more and 100% by mass or less, the freeness of recycled corrugated cardboard pulp is 300 mL or less, and the basis weight is 290 g / m² ２ That's all.

[0009] According to the present invention, it is possible to provide a corrugated cardboard liner that has excellent strength and appearance while possessing suitability for box making and lamination.

[0010] [Description of Embodiments of the Present Invention] The corrugated cardboard liner according to the embodiment of the present invention comprises at least a surface layer, a subsurface layer, and a back layer, wherein the surface layer and subsurface layer contain softwood kraft pulp and recycled corrugated cardboard pulp, the back layer contains recycled corrugated cardboard pulp, the content of softwood kraft pulp in the total pulp of the surface layer is 45% by mass or more and 75% by mass or less, the freeness of recycled corrugated cardboard pulp in the surface layer is 300 mL or less, the content of softwood kraft pulp in the total pulp of the subsurface layer is 30% by mass or more and 70% by mass or less, the content of recycled corrugated cardboard pulp in the total pulp of the back layer is 97% by mass or more and 100% by mass or less, and the basis weight is 290 g / m² ２ That's all.

[0011] Thus, by having the surface and subsurface layers contain softwood kraft pulp and recycled corrugated cardboard pulp, and by having the softwood kraft pulp content of the total pulp in the surface layer, which is the outermost layer for corrugated cardboard packaging, be between 45% and 75% by mass, the folding strength and compressive strength can be improved, and the appearance can be enhanced. Furthermore, by having the softwood kraft pulp content of the total pulp in the subsurface layer be between 30% and 70% by mass, the folding strength and compressive strength of the corrugated cardboard liner can be improved. Moreover, by having the back layer, which is the innermost layer for corrugated cardboard packaging, contain recycled corrugated cardboard pulp, and by having the recycled corrugated cardboard pulp content of the total pulp in the back layer be between 97% and 100% by mass, the folding strength can be enhanced while maintaining good lamination suitability, and the box-making suitability can be improved. Since the freeness of the recycled corrugated cardboard pulp in the surface layer is 300 mL or less, foreign matter in the surface layer is reduced, thereby improving the compressive strength of the corrugated cardboard liner. Furthermore, the basis weight is 290 g / m². ２ As a result of the above, the compressive strength of the corrugated cardboard liner can be improved. Therefore, the corrugated cardboard liner has excellent strength and appearance while possessing suitability for box making and lamination.

[0012] It is preferable that the lateral compressive strength of the corrugated cardboard liner measured by the ring crush method is 695 N or higher. A lateral compressive strength of 695 N or higher makes the molded corrugated cardboard case less prone to crushing, resulting in good shape retention and protection of the contents. "Compressive strength by the ring crush method" refers to the lateral compressive strength measured in accordance with "Paper and corrugated cardboard liners - Compressive strength test method - Ring crush method" described in JIS-P8126 (2005). "Lateral direction" refers to the direction perpendicular to the papermaking direction.

[0013] It is preferable that the longitudinal folding strength of the corrugated cardboard liner is between 295 and 900 folds. Having the longitudinal folding strength within this range suppresses creasing and ensures good suitability for box making. The "longitudinal folding strength" is a value measured in accordance with the MIT testing machine method of JIS-P8115 (2001). The "longitudinal direction" refers to the papermaking direction.

[0014] It is preferable that the content of softwood kraft pulp in the surface layer relative to the total content of softwood kraft pulp in the corrugated cardboard liner is 50% by mass or more and 60% by mass or less. By having a softwood kraft pulp content of 50% by mass or more and 60% by mass or less in the surface layer relative to the total content of softwood kraft pulp, the strength can be improved without impairing the appearance.

[0015] [Details of Embodiments of the Invention] The present invention will be described in detail below. The following descriptions of constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments.

[0016] <Liner for corrugated cardboard> The corrugated cardboard liner according to the embodiment of the present invention comprises at least a surface layer, a surface sub-layer, and a back layer in this order. The corrugated cardboard liner may also have a back sub-layer between the surface sub-layer and the back layer. In other words, the corrugated cardboard liner may be made of at least three or more layers of multilayer paper. By having the corrugated cardboard liner in this structure, the flexibility of the paper layers can be increased, and the suitability for box making can be improved.

[0017] [Surface layer] The surface layer contains coniferous kraft pulp (NUKP) and recycled corrugated cardboard pulp.

[0018] The lower limit of the content of softwood kraft pulp in the total pulp of the surface layer is 45% by mass, with 50% by mass being preferred. When the surface layer contains softwood kraft pulp and recycled corrugated cardboard pulp, and the softwood kraft pulp content of the surface layer, which is located on the outermost surface as packaging material for corrugated cardboard, is 45% by mass or more, the folding strength and compressive strength can be improved. If the softwood kraft pulp content in the surface layer is less than 45%, it may be difficult to secure the desired compressive strength. Also, if the softwood kraft pulp content in the surface layer is less than 45% by mass, the long fiber content decreases, which may reduce the folding strength of the surface layer and make it more prone to creasing. On the other hand, the upper limit of the content of softwood kraft pulp in the total pulp of the surface layer is 75% by mass, with 70% by mass being preferred. When the softwood kraft pulp content of the surface layer is 75% by mass or less, the appearance is excellent.

[0019] The content of softwood kraft pulp in the surface layer relative to the total content of softwood kraft pulp in the corrugated cardboard liner is preferably 50% by mass or more and 60% by mass or less, and more preferably 50% by mass or more and 59% by mass or less. By having a softwood kraft pulp content in the surface layer of 50% by mass or more and 60% by mass or less relative to the total content of softwood kraft pulp, the strength can be improved without impairing the appearance.

[0020] [Sub-layer] The sub-layer mentioned above contains coniferous kraft pulp and recycled corrugated paper pulp.

[0021] The lower limit of the content of softwood kraft pulp in the total pulp of the lower layer of the table above is 30% by mass, with 35% by mass being more preferable. By having a softwood kraft pulp content of 30% by mass or more in the total pulp of the lower layer of the table above, the folding strength and compressive strength can be improved. On the other hand, the upper limit of the softwood kraft pulp content is 70% by mass, with 65% by mass being preferable. By having a softwood kraft pulp content of 70% by mass or less in the total pulp of the lower layer of the table above, the folding strength can be improved. The lower layer of the table above contains softwood kraft pulp and recycled corrugated cardboard pulp, and by increasing the content of recycled corrugated cardboard pulp while keeping the softwood kraft pulp content within the above range, the folding strength and compressive strength of the corrugated cardboard liner can be improved while promoting the reuse of recycled paper pulp.

[0022] [Underlayer] From the viewpoint of increasing the basis weight, the corrugated cardboard liner may have an additional underlayer between the underlayer and the underlayer. The underlayer preferably contains recycled corrugated cardboard pulp. The underlayer may also contain softwood kraft pulp. The lower limit of the recycled corrugated cardboard pulp content in the total pulp of the underlayer may be 90% by mass or 95% by mass. The upper limit of the recycled corrugated cardboard pulp content may be 100% by mass. By having the underlayer contain recycled corrugated cardboard pulp and increasing the recycled corrugated cardboard pulp content, the folding strength and compressive strength of the corrugated cardboard liner can be improved while promoting the reuse of recycled pulp.

[0023] [Backing] The backing contains recycled corrugated cardboard pulp.

[0024] The lower limit of the content of recycled corrugated cardboard pulp in the total pulp of the backing layer is 97% by mass, but it may also be 100% by mass. The backing layer may also contain softwood kraft pulp. When the content of recycled corrugated cardboard pulp in the total pulp of the backing layer, which is the innermost layer in corrugated cardboard packaging material, is 97% by mass or more and 100% by mass or less, the ash content derived from recycled corrugated cardboard is increased, improving the lamination suitability, improving the folding strength, and improving the suitability for box making.

[0025] In addition to the coniferous kraft pulp and recycled corrugated cardboard pulp mentioned above, other pulps such as disintegrated recycled paper pulp, disintegrated and deinked recycled paper pulp, and deinked and bleached recycled paper pulp can be used for each layer of the corrugated cardboard liner. These pulps may also be disintegrated and deinked recycled paper pulp, deinked and bleached recycled paper pulp, etc., which are produced from recycled magazine paper pulp, recycled brown paper, recycled kraft envelope paper, recycled newspaper paper, recycled flyer paper, recycled office paper, recycled white paper, recycled Kent paper, recycled structural paper, recycled land certificate paper, etc. Furthermore, if necessary, mechanical pulps such as crushed wood pulp (GP), thermomechanical pulp (TMP), and bleached chemothermetic pulp (BCTMP) may also be used.

[0026] [Additives] In the present invention, various papermaking additives may be included in the corrugated cardboard liner, which consists of each layer, to the extent that they do not impair the effects intended for the present invention. For example, known additives such as sizing agents, paper strength enhancers, yield enhancers, pigment dispersants, pH adjusters, thickeners, flow improvers, defoamers, antifoaming agents, release agents, penetrating agents, ultraviolet absorbers, antioxidants, preservatives, anti-biodegrading agents, fluorescent decolorizing agents, pitch control agents, slime control agents, chemical fixatives such as aluminum sulfate, water-resistant agents such as polyamides, polyamines, and epichlorohydrin, fillers such as clay, talc, and calcium carbonate, basic dyes, acid dyes, anionic direct dyes, and cationic direct dyes may be added individually or in combination of two or more.

[0027] (Sizing agent) It is preferable to add a sizing agent to each layer of the corrugated cardboard liner. By having each layer of the corrugated cardboard liner contain a sizing agent, the durability of the corrugated cardboard liner can be increased and the quality of the corrugated cardboard liner can be maintained. Examples of the above sizing agent include styrene-based sizing agents, alkyl ketene dimers (AKD), alkenyl succinic anhydride (ASA), neutral rosin sizing agents, and rosin sizing agents. Among these, rosin sizing agents are preferred.

[0028] The rosin sizing agent is not particularly limited, and any known in the papermaking field can be used. Examples of rosin-based substances include reinforced rosins obtained by modifying rosins such as gum rosin, wood rosin, and tall oil rosin with α,β-unsaturated carboxylic acids such as fumaric acid, maleic acid, and acrylic acid, or their anhydrides, and rosin esters obtained by reacting the above rosins with polyhydric alcohols such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and diglycerin. Furthermore, in the present invention, rosin-based sizing agents also include emulsions of these alone or mixtures thereof, and emulsions of these alone followed by a mixture. In addition, the present invention also includes emulsions to which various polymers have been added to further improve sizing properties.

[0029] The lower limit of the amount of sizing agent added to each layer is preferably 0.3 kg / t of pulp in terms of solid content, and more preferably 0.5 kg / t of pulp. The upper limit of the sizing agent content in each layer is preferably 4.0 kg / t of pulp in terms of solid content, and more preferably 3.0 kg / t of pulp. By setting the amount of sizing agent added within the above range, sufficient water resistance can be imparted to the paperboard, thereby increasing its durability. Note that "kg / t of pulp" represents the amount added (kg) per ton of pulp.

[0030] (Paper Strength Enhancer) It is preferable to add a paper strength enhancer to each layer of the corrugated cardboard liner. By adding a paper strength enhancer, the bond between the corrugated cardboard recycled paper pulp, which is exhausted by the recycling process and consists of relatively flattened pulp fibers, and the fibers of other pulps is strengthened, thereby further improving the compressive strength.

[0031] Examples of paper strength enhancers include starch-based paper strength enhancers, acrylamide-based paper strength enhancers, vinyl alcohol-based paper strength enhancers, and amide epoxy-based paper strength enhancers, with acrylamide-based paper strength enhancers being preferred among these. More preferably, amphoteric polyacrylamide resin-based paper strength enhancers are preferred. Amphoteric polyacrylamide is produced by polymerizing cationic monomers and anionic monomers with acrylamide, and it directly fixes to pulp fibers via its own cationic groups. Another characteristic of amphoteric polyacrylamide resin-based paper strength enhancers is that their molecular structure and molecular weight can be controlled.

[0032] The lower limit for the amount of paper strength enhancer added to each layer is preferably 0.4 kg / t of pulp, and more preferably 0.8 kg / t of pulp, in terms of solid content. The upper limit for the amount of paper strength enhancer added to each layer is preferably 8.0 kg / t of pulp, and more preferably 6.0 kg / t of pulp, in terms of solid content. The lower limit for the total amount of paper strength enhancer added to the corrugated cardboard liner (synthetic mean of basis weight and amount added to each layer) is preferably 2.5 kg / t of pulp, and more preferably 3.0 kg / t of pulp, in terms of solid content. The upper limit for the total amount of paper strength enhancer added to the paperboard (synthetic mean of basis weight and amount added to each layer) is preferably 6.0 kg / t of pulp, and more preferably 5.5 kg / t of pulp, in terms of solid content. By setting the amount of paper strength enhancer added to each layer and to the entire corrugated cardboard liner within the above ranges, the compressive strength can be improved while ensuring the flexibility of the corrugated cardboard liner.

[0033] (Other Additives) In the present invention, various papermaking additives may be included in the corrugated cardboard liner, which consists of layers such as the surface layer, subsurface layer, and back layer, to the extent that they do not impair the effects intended for the present invention. For example, known additives such as yield improvers, pigment dispersants, pH adjusters, thickeners, fluidity improvers, defoamers, foam inhibitors, release agents, penetrating agents, ultraviolet absorbers, antioxidants, preservatives, anti-bacterial agents, fluorescent deactivators, pitch control agents, slime control agents, chemical fixatives such as aluminum sulfate, water-resistant agents such as polyamides, polyamines, and epichlorohydrin, fillers such as clay, talc, and calcium carbonate, basic dyes, acid dyes, anionic direct dyes, and cationic direct dyes may be added individually or in combination of two or more.

[0034] [Physical Properties of the Corrugated Board Liner] (Grammage) The grammage is measured in accordance with JIS-P8124 (2011). As the lower limit of the overall grammage of the corrugated board liner, it is 290 g / m ２ and 320 g / m ２ is preferable, and 340 g / m ２ is more preferable. When the grammage of the corrugated board liner is 290 g / m ２ or more, the compressive strength of the corrugated board liner can be improved. As the upper limit of the overall grammage of the corrugated board liner, from the perspective of reducing the weight of the corrugated board case, for example, it can be 500 g / m ２ . Also, the grammage of the surface layer constituting the corrugated board liner is preferably 60 g / m ２ to 80 g / m ２ . The grammage of the surface-bottom layer is preferably 60 g / m ２ to 70 g / m ２ . The grammage of the back-bottom layer is preferably 50 g / m ２ to 70 g / m ２ . The grammage of the back layer is preferably 120 g / m ２ to 200 g / m ２ .

[0035] (Flexural Strength) As the lower limit of the flexural strength in the longitudinal direction of the corrugated board liner, 295 times is preferable, 320 times is more preferable, and 325 times is even more preferable. When the flexural strength in the longitudinal direction is 295 times or more, cracking can be suppressed and the case-making suitability is good. On the other hand, as the upper limit of the flexural strength in the longitudinal direction, 900 times is preferable, 630 times is more preferable, and 600 times is even more preferable. When the flexural strength in the longitudinal direction is 900 times or less, the ease of processing during case-making and the flexibility of the flaps of the corrugated board case are improved, and the case-making suitability is improved.

[0036] (Freeness of the pulped linerboard) The linerboard for corrugated cardboard SHALL be pulped according to *JIS P8220-1 (2012)* Pulping Method for Pulp, and the freeness of the pulped linerboard SHALL be measured according to *JIS P8121-2 (2012)* Canadian Standard Freeness Test Method for Pulp. The Canadian Standard Freeness (CSF) of the pulped linerboard SHALL be preferably 390 mL or more and 490 mL or less. By setting the freeness of the pulped linerboard for corrugated cardboard within this range, the folding strength and compressive strength can be improved.

[0037] (Freeness of the corrugated cardboard waste pulp in the surface layer) The upper limit of the freeness of the corrugated cardboard waste pulp in the surface layer of the linerboard for corrugated cardboard SHALL be 300 mL, preferably 280 mL. By setting the freeness of the corrugated cardboard waste pulp in the surface layer within this range, foreign matter in the surface layer can be reduced, improving the compressive strength of the linerboard for corrugated cardboard. On the other hand, the lower limit of the freeness of the corrugated cardboard waste pulp in the surface layer SHALL be preferably 260 mL. By setting the freeness of the corrugated cardboard waste pulp in the surface layer within this range, the burst strength can be improved and the appearance can be enhanced by reducing the size of contaminants.

[0038] (Lateral compressive strength by the ring crush method) The lower limit of the lateral compressive strength by the ring crush method for the linerboard for corrugated cardboard SHALL be preferably 695 N or more, more preferably 730 N or more. By setting the lateral compressive strength within this range, the formed corrugated cardboard case is less likely to collapse, and the shape retention and protection performance of the contents are improved. On the other hand, from the perspective of recycling, the upper limit of the lateral compressive strength may be, for example, 900 N.

[0039] <Manufacturing method of the linerboard for corrugated cardboard> The manufacturing method of the linerboard for corrugated cardboard is a method for manufacturing a linerboard for corrugated cardboard having at least a surface layer, a subsurface layer, and a back layer. The manufacturing method of the linerboard for corrugated cardboard includes a step of forming raw pulp into paper using a paper machine. The manufacturing method of the linerboard for corrugated cardboard preferably includes a step of beating the raw pulp forming each layer to a desired freeness.

[0040] [Beaten Process] In the beaten process, the raw pulp constituting each layer is beaten to achieve the desired freeness. The raw pulp includes softwood kraft pulp, recycled corrugated cardboard pulp, recycled magazine pulp, or a combination thereof. First, the pulp fibers are dispersed in water to obtain a slurry, to which additives corresponding to each paper layer are added as needed and mixed to prepare the paper stock for each layer.

[0041] [Papermaking Process] Next, using these raw material slurries, papermaking is performed in a paper machine in a neutral range so that the pH of the corrugated cardboard liner is between 6 and 8, by forming layers such as a surface layer, subsurface layer, and back layer. In the above papermaking process, the raw pulp is made using a paper machine that forms paper from pulp raw materials sprayed onto a moving wire. The paper machine is not particularly limited, and known paper machines such as wire mesh paper machines, cylinder mesh paper machines, hybrid formers, and gap formers can be used, and paper is made in four or more layers. In addition, a coating layer may be provided on the surface to improve printability after the papermaking process.

[0042] [Pressing process] Next, the product is pressed with pressure rolls to remove moisture.

[0043] [Drying Process] Next, the material is dried in a dryer cylinder. After drying, surface strength can be improved by performing a smoothing treatment. The smoothing treatment is preferably carried out by applying pressure to the corrugated cardboard liner between pressurizable reels. There are no particular restrictions on the various finishing devices used for the smoothing treatment, but the product is finished by passing the paper through a machine calender in front of the winder section, and / or a super calender, gloss calender, soft nip calender, etc.

[0044] Finally, wind it onto a reel to obtain a cardboard liner.

[0045] <Other Embodiments> The present invention is not limited to the embodiments described above, and can be implemented in various modified and improved forms in addition to those described above.

[0046] For example, the corrugated cardboard liner may further include one or more intermediate layers between the lower surface layer and the lower back layer.

[0047] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0048] The methods for measuring the physical properties of the examples and comparative examples are as follows.

[0049] [Basic weight (g / m ２ The measurement was performed in accordance with the "Method for Measuring Basis Weight of Paper and Corrugated Cardboard Liners" described in JIS-P8142 (1998).

[0050] [Freeness (mL)] The obtained corrugated cardboard liner was disintegrated into disintegrated pulp in accordance with the pulp disintegration method of JIS-P8220-1 (2012), and this disintegrated pulp was measured in accordance with the Canadian standard filtration rate test method of JIS-P8121-2 (2012).

[0051] [Example 1] The raw materials listed in Tables 1 to 4 were added to the pulp slurry. (Additives) (1) Rosin-based sizing agent: Harima Chemicals' "NS-77P" Special rosin sizing agent (50% solids) (2) Acrylamide-based paper strength enhancer: Harima Chemicals' "Hermid RB-520": Amphoteric polyacrylamide (20% solids)

[0052] [Examples 2 to 10 and Comparative Examples 1 to 12] Corrugated cardboard liners for Examples 2 to 10 and Comparative Examples 1 to 12 were obtained in the same manner as in Example 1, except that the types of raw materials, amounts added, and physical properties were as shown in Tables 1 to 4. In Tables 3 and 4 below, "-" indicates that the corresponding physical property was not measured.

[0053]

[0054]

[0055]

[0056]

[0057] [Evaluation] Each corrugated cardboard liner obtained was evaluated using the following method. The evaluation results are shown in Table 5.

[0058] (Longitudinal folding strength) The longitudinal folding strength was measured in accordance with the MIT testing machine method of JIS-P8115 (2001).

[0059] (Lateral compressive strength by ring crush method) The lateral compressive strength by ring crush method was measured in accordance with "Liners for paper and corrugated cardboard - Compressive strength test method - Ring crush method" described in JIS-P-8126-2005.

[0060] (Suitability for box making) Using the corrugated cardboard liner obtained in the examples and comparative examples as the front and back sides, the core paper (basis weight 120 g / m²) ２ Double-flute corrugated cardboard sheets with AB sections were manufactured using a corrugator. The condition of the crease line cracks at the folded parts when the resulting corrugated cardboard sheets were made into boxes was visually evaluated. A: No crease line cracks were observed. B: There were slight crease line cracks, but they were at a level that did not cause any practical problems. C: There were crease line cracks.

[0061] (Suitability for lamination) The corrugated cardboard liner obtained in the examples and comparative examples was used as the front and back sides of the core paper (basis weight 120 g / m²). ２ Using a corrugator, AB-flute double-flute corrugated cardboard sheets were manufactured. The adhesion between the corrugated cardboard liner and the core paper was evaluated according to the following criteria: A: The adhesion was good throughout the entire corrugated cardboard sheet. B: Adhesion defects were observed in a portion of the corrugated cardboard sheet.

[0062] (Cardboard case crushing evaluation) The corrugated cardboard liners obtained in the examples and comparative examples were used as the front and back surfaces, and the core paper (basis weight 120 g / m²) was used. ２ Using a corrugator, AB-flute double-flute corrugated cardboard cases were manufactured. 50 kg of contents were packed into the resulting cardboard cases, and the cases were stacked in five layers on a pallet. Three of these stacks were then placed on a pallet and left undisturbed for 24 hours. The crushing of the bottom cardboard case was then visually evaluated. The evaluation criteria were as follows (three levels), and those rated A and B were judged to satisfy the effects of the present invention. A: No crushing of the cardboard case. B: Some crushing of the cardboard case is observed, but it is at a level that does not cause practical problems. C: Crushing of the cardboard case is observed, and there are practical problems.

[0063] (Visual Evaluation) The visual appearance of the surface layer of the corrugated cardboard liners obtained in the examples and comparative examples was evaluated visually. The evaluation criteria were as follows, with three levels, and those with evaluations of A and B were judged to satisfy the effects of the present invention. A: No flocking or wrinkles, and the appearance is good. B: Some flocking or wrinkles are visible, but it is at a level that does not cause practical problems. C: Flocking or wrinkles are visible, and there are practical problems.

[0064]

[0065] As shown in Table 5 above, the softwood kraft pulp content in the total pulp of the surface layer is 45% to 75% by mass, the freeness of recycled corrugated cardboard pulp in the surface layer is 300 mL or less, the softwood kraft pulp content in the total pulp of the subsurface layer is 30% to 70% by mass, the recycled corrugated cardboard pulp content in the total pulp of the back layer is % to 100% by mass, and the basis weight is 290 g / m² ２ Examples 1 to 10 described above were all satisfactory in terms of folding strength, suitability for box making, suitability for lamination, lateral compression strength by ring crush method, corrugated cardboard case crushing evaluation, and appearance.

[0066] On the other hand, the basis weight is 290 g / m². ２Comparative Example 1, which had less than 75% by mass of softwood kraft pulp in the surface layer and no softwood kraft pulp in the subsurface layer, had poor box-making suitability and poor evaluation of corrugated cardboard case crushing. Comparative Example 2, which had more than 75% by mass of softwood kraft pulp in the surface layer and no softwood kraft pulp in the subsurface layer, had poor appearance evaluation. Comparative Example 3, which had less than 30% by mass of the above softwood kraft pulp in the total pulp of the subsurface layer, had low folding strength and poor compression strength in the lateral direction by the ring crush method, and poor box-making suitability and poor evaluation of corrugated cardboard case crushing. Comparative Example 4, which had more than 70% by mass of the above softwood kraft pulp in the total pulp of the subsurface layer, had low folding strength and poor box-making suitability. Comparative Example 5, which had less than 45% by mass of softwood kraft pulp in the total pulp of the surface layer and more than 70% by mass of the above softwood kraft pulp in the total pulp of the subsurface layer, had low folding strength and poor box-making suitability. Comparative Example 6, in which the surface layer contained less than 45% by mass of softwood kraft pulp and the subsurface layer did not contain softwood kraft pulp, had low folding strength and lateral compressive strength by the ring crush method, and poor suitability for box making and poor evaluation of corrugated cardboard case crushing. Comparative Example 7, in which the surface layer did not contain recycled corrugated cardboard pulp and the subsurface layer did not contain softwood kraft pulp, had poor appearance. Comparative Example 8, in which the freeness of recycled corrugated cardboard pulp in the surface layer exceeded 300 mL, had low lateral compressive strength by the ring crush method and poor evaluation of corrugated cardboard case crushing. Basis weight: 290 g / m² ２ Comparative Example 9, which had less than 75% by mass of softwood kraft pulp in the surface layer, had low folding strength and lateral compressive strength by the ring crush method, and poor suitability for box making and corrugated cardboard case crushing evaluation. Comparative Example 10, which had more than 75% by mass of softwood kraft pulp in the surface layer, had poor appearance evaluation. Comparative Example 11, which had less than 97% by mass of the above-mentioned recycled corrugated cardboard pulp in the total pulp of the back layer, had low folding strength, and poor suitability for box making and lamination. Comparative Example 12, which had less than 45% by mass of softwood kraft pulp in the surface layer, had low lateral compressive strength by the ring crush method and poor suitability for box making.

[0067] The results above demonstrate that the corrugated cardboard liner possesses excellent strength and appearance while also being suitable for box making and lamination.

Claims

1. The material comprises at least a surface layer, a subsurface layer, and a back layer, wherein the surface layer and subsurface layer contain coniferous kraft pulp and recycled corrugated cardboard pulp, the back layer contains recycled corrugated cardboard pulp, the content of coniferous kraft pulp in the total pulp of the surface layer is 45% by mass or more and 75% by mass or less, the freeness of recycled corrugated cardboard pulp in the surface layer is 300 mL or less, the content of coniferous kraft pulp in the total pulp of the subsurface layer is 30% by mass or more and 70% by mass or less, the content of recycled corrugated cardboard pulp in the total pulp of the back layer is 97% by mass or more and 100% by mass or less, and the basis weight is 290 g / m² ２ That's all for the cardboard liner.

2. The corrugated cardboard liner according to claim 1, wherein the lateral compressive strength by the ring crush method is 695 N or more.

3. A corrugated cardboard liner according to claim 1 or claim 2, wherein the vertical folding strength is 295 times or more and 900 times or less.

4. The corrugated cardboard liner according to claim 3, wherein the content of the softwood kraft pulp in the surface layer relative to the total content of the softwood kraft pulp is 50% by mass or more and 60% by mass or less.

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