Liner for corrugated cardboard

Abstract

To provide a liner for a corrugated cardboard having excellent adhesive strength of a middle core and an exterior or interior liner as well as capable of obtaining good strength.SOLUTION: In a liner for a corrugated cardboard, a back layer contains a magazine waste paper pulp and a corrugated cardboard waste paper pulp, a content of the magazine waste paper pulp to the total pulp component of the back layer is 25.0 mass% or less, the back layer and a back lower layer contain a polyacrylamide-based paper strength-enhancing agent and do not contain a size agent, a content of the polyacrylamide-based paper strength-enhancing agent in the back layer is 0.1 kg / pulp t or more and 2.0 kg / pulp t or less in terms of solid content, a content of the polyacrylamide-based paper strength-enhancing agent in the back lower layer is 2.0 kg / pulp t or more and 12.0 kg / pulp t or less in terms of solid content, and a signal strength after 0.5 second from the start of permeation in a dynamic permeation test of a laminated surface of a center core in the back layer after holding for 60 seconds under a temperature condition of 130°C is 20% or more and 70% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a liner for corrugated cardboard. [Background technology]

[0002] Corrugated cardboard liners are lightweight compared to wooden or plastic containers, and their cushioning properties help prevent damage to contents, making them suitable for a variety of applications, including precision machinery. These cardboard liners are manufactured by laminating (gluing) cardboard components, such as exterior liners, corrugating mediums, and interior liners, in a laminating machine (corrugator). Corrugating mediums are manufactured by processing medium raw paper into a flute shape using corrugating rolls installed in the laminating machine. An aqueous solution (laminating glue) containing an adhesive component, such as starch glue or PVA, is applied to the flute tops (corrugation tops) of the corrugating medium, thereby bonding the corrugating medium to the liner. After this bonding, the corrugated cardboard liner is subsequently subjected to processing steps such as creasing and cutting. Therefore, if the adhesive strength between the corrugating medium and the exterior or interior liner is weak, there is a risk of the corrugating medium and the exterior or interior liner peeling off during the creasing, cutting, or other processes.

[0003] Therefore, various proposals have been made to improve the adhesive strength of cardboard liners. For example, in the prior art, a cardboard liner with improved adhesive strength has been proposed by applying a lamination speed enhancer made by dissolving borax in a polyhydric alcohol aqueous solution to the surface of the corrugating medium or the liner (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 7-238263 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, the lamination speed in the manufacturing process of cardboard liners has sometimes been increased to approximately 300 m / min to 450 m / min. Even when laminating at high speeds, there is a demand for the core and the exterior or interior liner to be less likely to peel off, and for further improvements in the strength of the cardboard.

[0006] The present invention has been made based on the above circumstances, and aims to provide a cardboard liner that has excellent adhesive strength between the core and the exterior or interior liner, even when bonded at high speed, and that also provides good strength. [Means for solving the problem]

[0007] A cardboard liner according to one embodiment of the present invention is a cardboard liner laminated to the core of cardboard, and comprises at least a surface layer, a back lower layer, and a back layer, wherein the back layer contains recycled magazine paper pulp and recycled corrugated cardboard pulp, the content of the recycled magazine paper pulp relative to the total pulp components of the back layer being 25.0 mass% or less, the back layer and the back lower layer contain a polyacrylamide-based paper strength agent but do not contain a sizing agent, the content of the polyacrylamide-based paper strength agent in the back layer is 0.1 kg / t or more and 2.0 kg / t or less of pulp, calculated as solids, and the content of the polyacrylamide-based paper strength agent in the back lower layer is 2.0 kg / t or more and 12.0 kg / t or less of pulp, calculated as solids, and the signal intensity 0.5 seconds after the start of penetration in a dynamic penetration test of the surface of the back layer after holding at a temperature of 130°C for 60 seconds is 20% or more and 70% or less. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a cardboard liner that has excellent adhesive strength between the core and the exterior or interior liner even when laminating at high speed, and that also provides good strength. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the embodiment of the present invention] A cardboard liner according to one embodiment of the present invention is a cardboard liner laminated to the core of cardboard, and comprises at least a surface layer, a back lower layer, and a back layer, wherein the back layer contains recycled magazine paper pulp and recycled corrugated cardboard pulp, the content of the recycled magazine paper pulp relative to the total pulp components of the back layer being 25.0 mass% or less, the back layer and the back lower layer contain a polyacrylamide-based paper strength agent but do not contain a sizing agent, the content of the polyacrylamide-based paper strength agent in the back layer is 0.1 kg / t or more and 2.0 kg / t or less of pulp, calculated as solids, and the content of the polyacrylamide-based paper strength agent in the back lower layer is 2.0 kg / t or more and 12.0 kg / t or less of pulp, calculated as solids, and the signal intensity 0.5 seconds after the start of penetration in a dynamic penetration test of the surface of the back layer after holding at a temperature of 130°C for 60 seconds is 20% or more and 70% or less.

[0010] In this way, the cardboard liner has at least a surface layer, a back lower layer, and a back layer, the back layer containing recycled magazine paper pulp and recycled cardboard paper pulp, the content of the recycled magazine paper pulp relative to the total pulp components of the back layer being 25.0 mass% or less, and the back layer and back lower layer containing a polyacrylamide-based paper strength enhancer, which ensures the adhesive strength of each layer of the cardboard liner and further improves the strength of the cardboard liner. The polyacrylamide-based paper strength agent content in the back layer is 0.1 kg / t pulp to 2.0 kg / t pulp inclusive, calculated as solids, and the polyacrylamide-based paper strength agent content in the back lower layer is 2.0 kg / t pulp to 12.0 kg / t pulp inclusive, calculated as solids, which provides excellent permeability for the (aqueous) laminating glue required for high-speed lamination, thereby improving the strength of the corrugated cardboard liner and achieving good lamination between the liner and the corrugated cardboard sheet obtained from the corrugated cardboard liner. Furthermore, the absence of a sizing agent in the back layer and back lower layer allows for increased initial water absorption of the corrugated cardboard liner of the present invention. As a result, the corrugated cardboard liner has an appropriate range of laminating adhesive permeability, with the signal strength 0.5 seconds after the start of penetration in a dynamic penetration test of the surface of the back layer after holding it at a temperature of 130°C for 60 seconds being 20% ​​to 70%, and good lamination can be achieved between the liner and the corrugated cardboard sheet obtained from the corrugated cardboard liner. Specifically, by having the signal strength 0.5 seconds after the start of penetration in a dynamic penetration test of the surface of the back layer be 20% to 70%, the (water-based) laminating adhesive required for high-speed lamination can be appropriately retained on the back surface of the corrugated cardboard liner, enabling strong lamination. The reason for holding the temperature at 130°C for 60 seconds during the signal intensity measurement is that this is the time required for the polyacrylamide-based paper strength agent to solidify and form a film, thereby exerting its function as a paper strength agent. The inventors discovered that by reproducing this condition, the effects of the polyacrylamide-based paper strength agent during the cardboard sheet manufacturing process can be more accurately understood. Therefore, the corrugated cardboard liner has excellent adhesive strength between the core and the exterior or interior liner, and good strength can be obtained even when the corrugated cardboard liner is bonded at high speed.

[0011] It is preferable that the surface layer is mainly composed of recycled corrugated cardboard pulp, and that the content of the recycled corrugated cardboard pulp relative to all pulp components of the surface layer is 100% by mass. In this way, by having the surface layer mainly composed of recycled corrugated cardboard pulp and having the content of the recycled corrugated cardboard pulp relative to all pulp components of the surface layer being 100% by mass, it is possible to set the Cobb sizing degree of the surface layer located at the outermost surface as a packaging material for corrugated cardboard low, while maintaining good lamination properties and improving the strength required of a corrugated cardboard liner.

[0012] The ash content of the back layer is preferably 16.0% by mass or more and 20.0% by mass or less. When the ash content of the back layer is 14.0% by mass or more, the (water-based) laminating adhesive required for high-speed lamination can be adequately retained on the surface of the back surface of the corrugated cardboard liner, enabling stronger lamination.

[0013] The specific burst strength of the corrugated cardboard liner is 2.60 kPa·m 2 / g or more, and the specific compressive strength in the lateral direction is 130 N·m 2 It is preferable that the burst strength of the corrugated cardboard liner is 2.60 kPa m 2 / g or more, and the specific compressive strength in the lateral direction is 130 N·m 2 / g or more, the impact resistance required for a corrugated cardboard liner can be improved. The "cross direction" mentioned above refers to the direction perpendicular to the flow direction of the fibers (papermaking direction).

[0014] [Details of the embodiment of the present invention] The present invention will be described in detail below. The following description of the components may be based on representative embodiments and specific examples, but the present invention is not limited to such embodiments.

[0015] <Corrugated cardboard liner> The corrugated cardboard liner according to an embodiment of the present invention is a corrugated cardboard liner laminated on a corrugated cardboard core, and comprises at least a surface layer, a back lower layer, and a back layer, in this order. The corrugated cardboard core is not particularly limited, and any known corrugated cardboard core can be used. The corrugated cardboard liner is cut to a predetermined size as needed to form a single-sided liner or a double-sided liner. The corrugated cardboard liner is formed into a corrugated shape (corrugation processing) and bonded to a corrugated cardboard core with adhesive applied to the corrugated crests on one side or both sides to produce a corrugated cardboard. The back surface of the back layer of the corrugated cardboard liner becomes the lamination surface of the back layer with the corrugated cardboard core.

[0016] The corrugated cardboard liner may have a single layer or multiple intermediate layers between the surface layer and the back lower layer, each layer having a basis weight of 30.0 g / m 2 More than 100.0g / m 2 The above can be applied. That is, the corrugated cardboard liner only needs to be a multi-layer paper having at least three layers, and in the case of a multi-layer paper having four or more layers, examples include a configuration in which a middle layer is provided between the lower back layer and the upper surface layer, or a configuration in which a second middle layer is provided between the lower back layer and the middle layer. In this way, by making the corrugated cardboard liner into a multi-layer structure, the flexibility of the paper layers can be increased, and the suitability for box making and strength can be improved. The waste paper pulp used in the present invention conforms to the classification of waste paper pulp defined by the Waste Paper Recycling Promotion Center, a public interest incorporated association.

[0017] [surface] The surface layer preferably contains recycled corrugated cardboard pulp as a main component.

[0018] In addition to recycled corrugated cardboard pulp, other pulps such as disintegrated recycled paper pulp, disintegrated and deinked recycled paper pulp, and deinked and bleached recycled paper pulp produced from recycled magazine paper, softwood kraft pulp, recycled tea paper, recycled kraft envelope paper, recycled newspaper paper, recycled flyer paper, recycled office paper, white recycled paper, Kent recycled paper, structural recycled paper, recycled land tax paper, etc. may also be used for the surface layer, as long as the effects of the present invention are not impaired. Furthermore, mechanical pulp such as groundwood pulp (GP), thermomechanical pulp (TMP), and bleached chemi-thermomechanical pulp (BCTMP) may also be used, if necessary.

[0019] The lower limit of the content of the recycled corrugated cardboard pulp in the surface layer is preferably 85% by mass, more preferably 90% by mass, and even more preferably 100% by mass. By including recycled corrugated cardboard pulp in the above content range as the main component of the raw material pulp of the surface layer located at the outermost surface of the corrugated cardboard packaging material, it is possible to improve the strength required of the corrugated cardboard liner while maintaining good lamination properties.

[0020] [Back layer] The backing layer contains recycled corrugated cardboard pulp and recycled magazine pulp.

[0021] The lower limit of the content of the recycled corrugated cardboard pulp in the back layer is preferably 75% by mass, more preferably 80% by mass. The upper limit of the content of the recycled corrugated cardboard pulp is preferably 85% by mass, more preferably 83% by mass. The upper limit of the content of the recycled magazine cardboard pulp in the back layer is 25% by mass, more preferably 20% by mass. The lower limit of the content of the recycled magazine cardboard pulp is preferably 15% by mass, more preferably 17% by mass. In order to maintain the quality of the corrugated cardboard liner, it is necessary to suppress an increase in humidity in the corrugated cardboard liner and improve the lamination property of the back layer, so it is preferable to set the Cobb sizing degree high. By using recycled corrugated cardboard pulp and recycled magazine cardboard pulp in combination as the main components of the raw material pulp of the back layer located on the innermost layer side of a corrugated cardboard packaging material, it is possible to improve the strength required of the corrugated cardboard liner while maintaining good lamination property.

[0022] [Back lower layer] The lower back layer is a layer to be laminated to the back layer, and is preferably composed mainly of recycled corrugated cardboard pulp.

[0023] In addition to recycled corrugated cardboard pulp, other pulps such as disintegrated recycled paper pulp, disintegrated and deinked recycled paper pulp, and deinked and bleached recycled paper pulp produced from recycled magazine paper, softwood kraft pulp, recycled tea paper, recycled kraft envelope paper, recycled newspaper paper, recycled flyer paper, recycled office paper, white recycled paper, Kent recycled paper, structural recycled paper, recycled land tax paper, etc. may also be used for the surface layer, as long as the effects of the present invention are not impaired. Furthermore, mechanical pulp such as groundwood pulp (GP), thermomechanical pulp (TMP), and bleached chemi-thermomechanical pulp (BCTMP) may also be used, if necessary.

[0024] The lower limit of the content of recycled corrugated cardboard pulp in the lower back layer is preferably 75% by mass, more preferably 80% by mass. The upper limit of the content of recycled corrugated cardboard pulp is 95% by mass, preferably 90% by mass. By setting the content of recycled corrugated cardboard pulp in the lower back layer within the above range, it is possible to improve the burst strength ratio while recycling the recycled paper pulp.

[0025] In addition to recycled corrugated cardboard pulp and recycled magazine pulp, other pulps such as softwood kraft pulp, disintegrated recycled paper pulp, disintegrated and deinked recycled paper pulp, and deinked and bleached recycled paper pulp produced from recycled brown paper, recycled kraft envelope paper, recycled newspapers, recycled flyers, recycled office paper, white recycled paper, Kent recycled paper, structural recycled paper, and recycled land tax paper can be used for each layer of the corrugated cardboard liner, provided that the effects of the present invention are not impaired. Furthermore, mechanical pulp such as groundwood pulp (GP), thermomechanical pulp (TMP), and bleached chemithermomechanical pulp (BCTMP) may also be used, if necessary.

[0026] [Additives] (sizing agent) The surface layer preferably contains a sizing agent. By containing a sizing agent in the surface layer of the corrugated cardboard liner, the durability of the corrugated cardboard liner against humidity in the liner can be increased, and the quality of the corrugated cardboard liner can be maintained. Examples of the sizing agent include styrene-based sizing agents, alkyl ketene dimers (AKD), alkenyl succinic anhydrides (ASA), neutral rosin sizing agents, and rosin sizing agents. Among these, rosin sizing agents are preferred from the viewpoint of ease of adjusting the sizing degree.

[0027] The rosin sizing agent is not particularly limited, and any known rosin sizing agent in the papermaking field can be used. Examples of rosin-based substances include fortified rosins obtained by modifying rosins such as gum rosin, wood rosin, and tall oil rosin with α,β-unsaturated carboxylic acids or their anhydrides, such as fumaric acid, maleic acid, and acrylic acid, and rosin esters obtained by reacting the above rosins with polyhydric alcohols, such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, and diglycerin. Furthermore, the rosin-based sizing agent of the present invention includes emulsions of these rosins alone or mixtures thereof, as well as emulsions of these rosins emulsified alone and then mixed together. Furthermore, emulsions containing various polymers to further improve sizing performance are also included.

[0028] The lower limit of the amount of sizing agent added to the surface layer is preferably 3.0 kg / t of pulp in terms of solids, more preferably 3.50 kg / t of pulp. The upper limit of the amount of sizing agent added to the surface layer is preferably 8.5 kg / t of pulp in terms of solids, more preferably 8.0 kg / t of pulp. By setting the amount of sizing agent added to the surface layer within the above range, the corrugated cardboard liner can be provided with sufficient water resistance and its durability against humidity within the corrugated cardboard liner can be improved. Furthermore, by further adding cationic starch, the paper strength of the surface layer can be increased, resulting in a corrugated cardboard liner with high strength. Note that "kg / t of pulp" refers to the amount (kg) added on an oven-dry basis per ton of pulp raw material for the corrugated cardboard liner.

[0029] On the other hand, the back layer and back underlayer do not contain a sizing agent. The absence of a sizing agent in the back layer and back underlayer allows for increased initial water absorption of the corrugated cardboard liner. This allows the corrugated cardboard liner to have an appropriate range of laminating adhesive permeability, with the signal intensity at 0.5 seconds from the start of penetration in a dynamic permeability test of the surface of the back layer after holding at a temperature of 130°C for 60 seconds being 20% ​​to 70%. This allows for good lamination between the liner and the corrugated cardboard core in the corrugated cardboard sheet obtained from the corrugated cardboard liner.

[0030] (Paper strength agent) The back layer and the lower back layer contain a polyacrylamide-based paper strength enhancer, which strengthens the bonds between the fibers of the recycled corrugated cardboard pulp and the recycled magazine paper pulp, which are exhausted during the recycling process of waste paper and consist of relatively flat pulp fibers, thereby ensuring the adhesive strength of each layer of the corrugated cardboard liner and further improving the strength of the corrugated cardboard liner.

[0031] Among polyacrylamide-based paper strength enhancers, amphoteric polyacrylamide resin-based paper strength enhancers are preferred. Amphoteric polyacrylamide is formed by polymerizing cationic and anionic monomers with acrylamide, and is directly attached to pulp fibers via its own cationic group. Another feature of amphoteric polyacrylamide resin-based paper strength enhancers is that the molecular structure and molecular weight can be controlled.

[0032] The upper limit of the content of the polyacrylamide-based paper strength agent in the back layer is 2.0 kg / t of pulp or less, preferably 1.5 kg / t of pulp, and more preferably 1.0 kg / t of pulp, calculated as solids. The lower limit of the content of the polyacrylamide-based paper strength agent in the back layer is 0.10 kg / t of pulp, and preferably 0.20 kg / t of pulp, calculated as solids. The upper limit of the content of the polyacrylamide-based paper strength agent in the lower back layer is 12.0 kg / t of pulp, preferably 10.0 kg / t of pulp, and more preferably 9.0 kg / t of pulp, calculated as solids. The lower limit of the content of the polyacrylamide-based paper strength agent in the lower back layer is 2.0 kg / t of pulp, and more preferably 3.0 kg / t of pulp, calculated as solids. By having the content of polyacrylamide-based paper strength enhancer in the back layer be 0.1 kg / t pulp or more and 2.0 kg / t pulp or less in solids content, and the content of polyacrylamide-based paper strength enhancer in the back lower layer be 2.0 kg / t pulp or more and 12.0 kg / t pulp or less in solids content, the (water-based) laminating adhesive required for high-speed lamination remains appropriately on the surface of the back surface of the cardboard liner, thereby improving the strength of the cardboard liner and achieving good lamination between the liner and the core in the cardboard sheet obtained from the cardboard liner.

[0033] The surface layer also preferably contains a polyacrylamide-based strength agent. By including a polyacrylamide-based strength agent in the surface layer, the strength of the corrugated cardboard liner can be further improved. The lower limit of the amount of strength agent added to the surface layer is preferably 0.50 kg / t of pulp, more preferably 1.0 kg / t of pulp, in terms of solids. The upper limit of the amount of strength agent added to the surface layer is preferably 4.0 kg / t of pulp, more preferably 3.5 kg / t of pulp, in terms of solids. If the addition rate of the strength agent in the surface layer is less than 0.80 kg / t of pulp, the strength improvement effect of the corrugated cardboard liner may be difficult to achieve. If the addition rate of the strength agent in the surface layer exceeds the upper limit, drainage may be impaired, and the pulp raw material may be easily discharged during the squeezing and dewatering processes in the press part of the papermaking machine. Furthermore, in the press part, residue from the pulp raw material may adhere to the doctor blade used to peel off the wet paper stuck to the roll, potentially degrading the quality of the surface layer.

[0034] (Other additives) In the present invention, various papermaking additives may be added to the corrugated cardboard liner, which is composed of the surface layer, the under-back layer, the back layer, etc., to the extent that the intended effects of the present invention are not impaired. For example, known additives such as retention aids, pigment dispersants, pH adjusters, thickeners, flow improvers, antifoaming agents, foam suppressors, release agents, penetrating agents, ultraviolet absorbers, antioxidants, preservatives, mildew inhibitors, fluorescent eliminators, 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 alone or in combination of two or more.

[0035] [Physical properties of cardboard liners] (Basic weight) The basis weight is measured in accordance with JIS-P8124 (2011). In a further preferred embodiment of the present invention, the overall basis weight of the corrugated board liner is 120 g / m 2 from 250 g / m 2 It is preferable that the thickness is 130 g / m 2 from 240 g / m2 In the cardboard liner, by setting the overall basis weight within the above range, it is possible to improve formability during box making and to prevent damage to the packaging container when the contents are filled after forming.

[0036] (paper thickness) The thickness is measured in accordance with "Paper and paperboard - Testing methods for thickness and density" as described in JIS-P8118 (2014). The overall thickness of the corrugated cardboard liner of the present invention is preferably 180 μm to 350 μm, and more preferably 190 μm to 320 μm. By keeping the overall thickness of the corrugated cardboard liner within the above range, strength and box-making properties can be improved.

[0037] (density) The lower limit of the density of the corrugated cardboard liner is 0.65 g / cm 3 is preferred, and 0.70 g / cm 3 The upper limit of the density is more preferably 0.95 g / cm. 3 is preferred, and 0.90 g / cm 3 When the density of the corrugated cardboard liner is within the above range, cushioning properties are imparted, and high strength can be achieved without adding more paper strength agent than necessary.

[0038] (Post-defibration freeness of defibrated pulp) The post-defibration freeness of the disintegrated pulp is measured by disintegrating the corrugated cardboard liner in accordance with the pulp disintegration method of JIS-P8220-1 (2012) to produce disintegrated pulp, and then measuring the disintegrated pulp in accordance with the Canadian Standard Freeness Test of JIS-P8121-2 (2012). The post-defibration freeness (Canadian Standard Post-defibration Freeness: CSF) of the corrugated cardboard liner is preferably 300 ml to 400 ml, more preferably 310 ml to 390 ml. If the lower limit of the post-defibration freeness of the disintegrated pulp of the corrugated cardboard liner is less than 300 ml, strength may be reduced. Furthermore, if the upper limit of the post-defibration freeness of the disintegrated pulp exceeds 400 ml, papermaking properties may be impaired, resulting in reduced productivity and reduced suitability for box making.

[0039] (Ash content of the lining layer) The ash content of the back layer is a value measured in accordance with JIS-P-8251 (2003) "Paper, paperboard, and pulp - Ash content test method - 525°C combustion method." The lower limit of the ash content of the back layer is preferably 16.0% by mass, more preferably 16.5% by mass. On the other hand, the upper limit of the ash content is preferably 20.0% by mass, more preferably 19.0% by mass. When the ash content of the back layer is 16.0% by mass or more and 20.0% by mass or less, the (water-based) laminating adhesive required for high-speed laminating tends to remain adequately on the back surface of the corrugated cardboard liner. On the other hand, if the ash content exceeds 20.0% by mass, the laminating adhesive may absorb too much water into the surface of the liner, which may weaken its ability to remain on the surface of the corrugated cardboard.

[0040] (Lining lump size) The cob sizing degree is measured in accordance with JIS-P8140 (1998) with a measurement time of 2 minutes. The lower limit of the cob sizing degree of the backing layer is 130 g / m 2 is preferred, and 140 g / m 2 If the Cobb sizing degree of the backing layer is less than the above lower limit, the humidity in the corrugated board liner may not be sufficiently suppressed, and lamination defects may occur. On the other hand, the upper limit of the Cobb sizing degree of the backing layer is 250 g / m2 is preferred, and 240 g / m 2 is more preferable. If the Cobb sizing degree of the back layer is above the above upper limit, the corrugated cardboard liner may absorb moisture and cause rippling or wrinkles. By keeping the Cobb sizing degree of the back layer within the above range after a measurement time of 2 minutes, the humidity in the corrugated cardboard liner can be suppressed, and the quality of the corrugated cardboard liner can be maintained. In order to maintain the quality of the corrugated cardboard liner, it is necessary to suppress an increase in humidity in the corrugated cardboard liner and improve the lamination property of the back layer. However, by using a combination of recycled corrugated cardboard pulp and recycled magazine paper pulp as the main components of the raw material pulp for the back layer, the Cobb sizing degree can be set within the above range, and good lamination property and improved strength can be maintained.

[0041] (Air permeability) The air permeability of the cardboard liner is preferably 8 seconds or more, and more preferably 9 seconds or more. By having the air permeability of 8 seconds or more, excessive penetration of the laminating adhesive into the cardboard liner can be suppressed.

[0042] (Signal intensity 0.5 seconds after the start of penetration in dynamic penetration testing of the lining surface) In a dynamic penetration test of the backing layer surface, the signal strength 0.5 seconds after the start of penetration is measured by contacting the back of the corrugated cardboard liner with the test liquid, holding it at 130°C for 60 seconds, and then measuring the signal strength 0.5 seconds after the test liquid begins to penetrate the backing layer surface. The dynamic penetration test uses ultrasound to understand the penetration behavior of liquids into porous materials such as paper. This dynamic penetration test quantifies the energy loss due to reflection, refraction, transmission, and absorption of ultrasound at the interface between the media. With 100% as the reference value, lower signal strength indicates greater loss, i.e., greater penetration. Therefore, the permeability of a laminating adhesive can be evaluated based on the signal strength obtained in the dynamic penetration test.

[0043] The lower limit of the signal intensity 0.5 seconds after the start of penetration in a dynamic penetration test of the surface of the backing layer is 20%, preferably 21%, more preferably 23%. The upper limit of the signal intensity is 70%, preferably 50%, more preferably 35%. When the signal intensity 0.5 seconds after the start of penetration in a dynamic penetration test of the surface of the backing layer is 20% or more and 70% or less, the (water-based) laminating adhesive required for high-speed lamination can be adequately retained on the surface of the back of the corrugated cardboard liner, enabling strong lamination. The signal intensity can be adjusted by the sizing agent, paper strength agent and ash content of the back layer and the content of the sizing agent and paper strength agent of the lower back layer.

[0044] (specific burst strength) Bursting strength index is specified in JIS-P8131(2009). Bursting strength index is the value obtained by dividing the bursting strength of paper measured in kilopascals (kPa) according to JIS-P8131(2009) by the basis weight. The lower limit of the bursting strength index of the corrugated board liner is 2.60 kPa m 2 / g, 2.70 kPa m 2 When the bursting strength index is within the above range, the corrugated cardboard liner can have good strength.

[0045] (Lateral compressive strength and specific compressive strength) The transverse compressive strength of the corrugated cardboard liner is measured in accordance with JIS-P8126 (2005). The specific compressive strength is the value obtained by dividing the compressive strength by the basis weight. The specific compressive strength of the corrugated cardboard liner in the transverse direction is 130 N·m 2 / g or more, it is possible to maintain a strength suitable for use as a cardboard liner.

[0046] <Method for manufacturing cardboard liners> The method for manufacturing a corrugated cardboard liner is a method for manufacturing a corrugated cardboard liner to be laminated on a core of corrugated cardboard, the corrugated cardboard liner having at least a surface layer, a back lower layer, and a back layer. The method for manufacturing a corrugated cardboard liner includes a step of making raw pulp using a papermaking machine. The method for manufacturing a corrugated cardboard liner preferably also includes a step of beating the raw pulp constituting each layer to a desired freeness after defibration.

[0047] [Defining process] In the beating process, the raw pulp constituting each layer is beaten to the desired freeness after disintegration. The raw pulp contains softwood kraft pulp, recycled corrugated cardboard pulp, recycled magazine pulp, or a combination thereof. First, 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 paper layer.

[0048] [Paper making process] Next, these raw material slurries are used to make a paper by combining a surface layer, a back lower layer, a back layer, etc. in a papermaking machine in a neutral range so that the pH of the corrugated cardboard liner is between 6 and 8. In the papermaking process, the raw material pulp is made into paper using a papermaking machine that makes paper from pulp raw material sprayed onto a traveling wire. The papermaking machine is not particularly limited, and known papermaking machines such as a Fourdrinier papermaking machine, a cylinder papermaking machine, a hybrid former, a gap former, etc. can be used, and paper is made into a multi-layer paper with three or more layers.

[0049] In order to improve printability after the papermaking process, a coating layer may be provided on the surface.

[0050] [Pressing process] Next, the mixture is pressed with a pressure roll to remove water.

[0051] [Drying process] Next, it is dried in a dryer cylinder. After drying, the surface strength can be improved by smoothing the linerboard. The smoothing is preferably performed by, for example, pressing the linerboard between pressurizable reels. There are no particular limitations on the finishing devices used for smoothing the linerboard. For example, the linerboard may be passed through a machine calender before the winder, and / or a super calender, gloss calender, soft nip calender, or the like to finish the product.

[0052] Finally, the cardboard liner is obtained by winding it onto a reel.

[0053] <Other embodiments> The present invention is not limited to the above-described embodiment, and can be implemented in various other forms, including those described above, with various modifications and improvements.

[0054] For example, the corrugated cardboard liner may include one or more backing layers between the face layer and the backing layer.

[0055] The backing lower layer can be made of virgin pulp, such as bleached softwood kraft pulp, unbleached softwood kraft pulp, sulfite softwood pulp, and other pulps made primarily from non-wood fibers such as kenaf, hemp, and reed, ground pulp made by mechanically pulping chips, chemi-ground pulp made by mechanically pulping wood or chips with the addition of chemicals, and semi-chemical pulp made by cooking chips until soft and then pulping them in a refiner. It can also be made of recycled cardboard, recycled newspapers, coated paper, uncoated paper, plain paper, color-printed paper, black-and-white-printed paper, and other types of recycled magazine paper, including various bleach-resistant papers. It is also possible to use a mixture of the above-mentioned plant fibers with synthetic pulp made from polyethylene, polypropylene, or other raw materials, or to blend various fibers other than synthetic pulp, such as organic fibers such as rayon, acrylic, and polyamide fibers, as well as glass and carbon fibers. [Example]

[0056] 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.

[0057] [Example 1] The raw materials listed in the table were added to the pulp slurry. (additives) (1) Rosin-based sizing agents Harima Chemical's "NS-77P": Special rosin sizing agent (50% solids) (2) Acrylamide-based paper strength agents Harima Chemical's "Hermid RB-520": Zwitterionic polyacrylamide (20% solids)

[0058] [Examples 2 to 8 and Comparative Examples 1 to 8] Cardboard liners of Examples 2 to 8 and Comparative Examples 1 to 8 were obtained in the same manner as Example 1, except that the types and amounts of raw materials added were as shown in Tables 1 to 3. Examples 6 to 8 were four-layer cardboard liners that also included a middle layer. Note that "-" in Tables 1 to 3 below indicates that the corresponding component was not used.

[0059] [Table 1]

[0060] [Table 2]

[0061] [Table 3]

[0062] [evaluation] The resulting cardboard liners were evaluated by the following methods. The evaluation results are shown in Table 4.

[0063] [Basic weight (g / m 2 )] Measurement was carried out in accordance with "Paper and paperboard - Basis weight measurement method" described in JIS-P8142 (1998).

[0064] [Paper thickness (μm)] Measurements were made in accordance with "Paper and paperboard - Testing methods for thickness and density" described in JIS-P8118 (2014).

[0065] [Density (g / cm 3 )] It was calculated from the basis weight and paper thickness in accordance with "Paper and paperboard - Testing methods for thickness and density" described in JIS-P8118 (2014).

[0066] [Freeness after maceration] The obtained cardboard liner was disintegrated in accordance with the pulp disintegration method of JIS-P8220-1 (2012) to produce disintegrated pulp, and the freeness (mL) of this disintegrated pulp was measured in accordance with the Canadian standard freeness test method of JIS-P8121-2 (2012).

[0067] [Ash content] The ash content was measured in accordance with JIS-P8251 (2003).

[0068] [Lining nodule size] The Cobb sizing degree of the backing layer was measured in accordance with JIS-P8140 (1998) by contacting the surface of the backing layer with water for 2 minutes.

[0069] [Air permeability] Measurements were made in accordance with JIS-P8117:2009 "Paper and paperboard - Air permeability and air resistance test method (intermediate range) - Gurley method."

[0070] [Signal intensity 0.5 seconds after the start of penetration in dynamic penetration testing of the lining surface] The signal intensity 0.5 seconds after the start of penetration in the dynamic penetration test of the surface of the back layer was measured using a "Surface & Sizing Tester Model EST 12.2" manufactured by emtec. First, the back surface of the cardboard liner of Examples 1 to 8 and Comparative Examples 1 to 8 was contacted with the test liquid and held at a temperature of 130°C for 60 seconds. Then, the signal intensity was measured 0.5 seconds after the test liquid started to penetrate the surface of the back layer. Distilled water at 23°C was used as the test liquid, and the ultrasonic frequency for measurement was 2 MHz.

[0071] [Specific burst strength] The burst strength of the front and back surfaces was measured in accordance with JIS-P8131 (2009), and then the burst strength was divided by the basis weight to calculate the specific burst strength of the front and back surfaces. The average value of the burst strengths of the front and back surfaces was then calculated.

[0072] [Compressive strength and specific compressive strength] The compressive strength in the lateral direction was measured in accordance with JIS-P8126 (2005). The specific compressive strength was calculated by dividing the compressive strength by the basis weight.

[0073] [Properties of cardboard sheets after lamination process] The properties of the cardboard sheets after the lamination process were evaluated using the manufactured products at a laminating speed of 300 m / min. Cardboard sheets were produced using the cardboard liners obtained in the examples and comparative examples according to the following procedure, and the condition of the cardboard sheets was visually evaluated using a five-point scale. Grades A, B, and C were considered pass. (1) Preparation of cardboard sheets The liner of the present invention was used for the single facer side liner (back side liner) and double facer side liner (front side liner) to be bonded by the corrugator, and a general core was used for the core, and the cardboard sheet was processed as follows. In the corrugator process, the corrugating medium was stepped and then bonded to the single-facer liner with adhesive. Next, in the double-facer process, the corrugated medium was placed on the backside of the double-facer liner, passed through a preheater roll, and bonded to the corrugated medium with adhesive to create a continuous corrugated cardboard sheet. The laminating speed was 300 m / min. The laminating speed was the speed when each corrugated cardboard liner was used as a single-facer or double-facer liner and bonded to the corrugating medium using a laminating machine. The following cores, laminating machines, and laminating adhesives were used: Core: Reinforced core (180g / m) made by Iwaki Daio Paper Co., Ltd. 2 ) Laminating machine: Corrugator CWDX manufactured by ISOWA Corporation was used. Laminating glue: Low Cons manufactured by Nippon Starch Co., Ltd. Coating amount (double facer side 3.2 g / m 2 , single facer side 5.0g / m 2 ), concentration (3.2% on double facer side, 3.0% on single facer side). (2) Evaluation criteria A: The bonding strength between the double facer liner and the core base paper is very strong, so there are no problems in actual operation. B: The bonding strength between the double facer side liner and the core raw paper is strong and can withstand actual operation. C: The bonding strength between the double facer side liner and the core raw paper is somewhat weak, but it can withstand actual operation. D: The bonding strength between the double facer side liner and the core raw paper is weak, and it may not be able to withstand actual operation. E: The bonding strength between the double facer side liner and the core raw paper is very weak, making it difficult to withstand actual operation.

[0074] [Table 4]

[0075] As shown in Table 4 above, for the cardboard liners of Examples 1 to 8, the properties of the cardboard sheets after the laminating process were evaluated and good results were obtained when the manufactured products were evaluated at a laminating speed of 300 m / min on a laminating machine.

[0076] On the other hand, the cardboard liner of Comparative Example 1, which contained a sizing agent in the back layer, Comparative Example 2, which contained a sizing agent in the back lower layer, and Comparative Example 3, which contained a sizing agent in both the back layer and the back lower layer, had a high signal strength in the back layer, and the properties of the cardboard sheet after the lamination process were very poor. The corrugated cardboard liner of Comparative Example 4, in which the amount of paper strength agent in the back layer exceeded the upper limit, had a high signal strength in the back layer, and the properties of the corrugated cardboard sheet after the lamination process were very poor. The corrugated cardboard liner of Comparative Example 5, in which the paper strength agent in the lower back layer exceeded the upper limit, had a high signal strength in the back layer, and the properties of the corrugated cardboard sheet after the lamination process were poor. The corrugated cardboard liner of Comparative Example 6, which had a high blending ratio of recycled magazine paper pulp in the back layer, had a low signal strength in the back layer, and the properties of the corrugated cardboard sheet after the lamination process were poor. The corrugated cardboard liner of Comparative Example 7, in which the content of the paper strength agent in the back layer was below the lower limit, had a low signal strength in the back layer, and the properties of the corrugated cardboard sheet after the lamination process were poor. The corrugated cardboard liner of Comparative Example 8, in which the content of the paper strength agent in the lower back layer was below the lower limit, had poor properties of the corrugated cardboard sheet after the lamination process.

[0077] As a result of the above, it is clear that the corrugated cardboard liner has excellent adhesive strength between the core and the exterior or interior liner, and also provides good strength, even when bonded at high speed.

[0078] The cardboard liner of the present invention can be suitably used as cardboard sheets or packaging bags used in packaging containers, liners for containers for storing solids, and can be used as industrial paper in a variety of fields.

Claims

1. A cardboard liner laminated on a corrugated cardboard core, It comprises at least a surface layer, a backing layer, and a backing layer, The backing layer contains recycled magazine paper pulp and recycled cardboard paper pulp, The content of the recycled magazine paper pulp relative to the total pulp components of the back layer is 25.0% by mass or less, The back layer and the back underlayer contain a polyacrylamide-based paper strength agent but do not contain a sizing agent, the content of a polyacrylamide-based paper strength agent in the back layer is 0.1 kg / t of pulp or more and 2.0 kg / t of pulp or less in terms of solid content; the content of a polyacrylamide-based paper strength agent in the lower back layer is 2.0 kg / t of pulp or more and 12.0 kg / t of pulp or less in terms of solid content; A cardboard liner in which the signal strength 0.5 seconds after the start of penetration in a dynamic penetration test of the laminated surface of the back layer with the core after being held at a temperature of 130°C for 60 seconds is 20% or more and 70% or less.

2. The surface layer is mainly made of recycled cardboard pulp, 2. The cardboard liner according to claim 1, wherein the content of the recycled cardboard pulp in the surface layer is 100% by mass.

3. The cardboard liner according to claim 1 or 2, wherein the ash content of the back layer is 16.0% by mass or more and 20.0% by mass or less.

4. Specific burst strength is 2.60 kPa・m ２ / g or more, Specific compressive strength in the lateral direction is 130 Nm ２ 4. The corrugated board liner according to claim 3, wherein the modulus of elasticity is 1 / g or more.

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