Cardboard Liners

Abstract

To provide a cardboard liner which has excellent adhesive strength between a core and an exterior or interior liner and also provides good strength. [Solution] The cardboard liner of the present invention has a 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, the back layer and 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 pulp to 2.0 kg / t pulp in solids content, the content of the polyacrylamide-based paper strength agent in the back lower layer is 2.0 kg / t pulp to 12.0 kg / t pulp in solids content, and 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 has a signal intensity of 20% to 70% 0.5 seconds after the start of penetration.

Description

[Technical field]

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

[0002] Cardboard liners are lighter than wooden or resin containers, and have cushioning properties that prevent damage to the contents, and are therefore used in various fields including precision instruments. Such cardboard liners are manufactured by gluing (bonding) paperboards such as exterior liners, corrugators, and interior liners using a laminating machine (corrugator). Corrugators are manufactured by processing core raw paper into a flute (wave) shape using corrugated rolls provided on the laminating machine. An aqueous solution (laminating glue) containing adhesive components such as starch glue and PVA is applied to the flute tops (corrugation tops) of the corrugators, and the corrugators and the liner are bonded together. The corrugated cardboard liners after this bonding are subsequently subjected to processing such as creasing and cutting. Therefore, if the adhesive strength between the corrugators and the exterior or interior liner is weak, there is a risk that the corrugators and the exterior or interior liner will peel off from each other during the creasing, cutting, etc.

[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 of borax dissolved in a polyhydric alcohol aqueous solution to the surface of the core or 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 from each other, 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 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 a core of cardboard, and comprises at least a surface layer, a back lower layer and a back layer, the back 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 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 of pulp to 2.0 kg / t of pulp in solids content, the content of the polyacrylamide-based paper strength agent in the back lower layer is 2.0 kg / t of pulp to 12.0 kg / t of pulp in solids content, 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 being held at a temperature of 130°C for 60 seconds is 20% to 70%. Effect of the Invention

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

[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 a core of cardboard, and comprises at least a surface layer, a back lower layer and a back layer, the back 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 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 of pulp to 2.0 kg / t of pulp in solids content, the content of the polyacrylamide-based paper strength agent in the back lower layer is 2.0 kg / t of pulp to 12.0 kg / t of pulp in solids content, 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 being held at a temperature of 130°C for 60 seconds is 20% to 70%.

[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 in the total pulp component 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, thereby ensuring the adhesive strength of each layer of the cardboard liner and further improving the strength of the cardboard liner. The content of the polyacrylamide-based paper strength agent in the back layer is 0.1 kg / t pulp to 2.0 kg / t pulp in terms of solid content, and the content of the polyacrylamide-based paper strength agent in the back lower layer is 2.0 kg / t pulp to 12.0 kg / t pulp in terms of solid content, so that the (water-based) laminating glue required for high-speed lamination has excellent permeability, and the strength of the cardboard liner is improved, and good lamination between the liner and the core in the cardboard sheet obtained from the cardboard liner can be obtained. In addition, since the back layer and back lower layer do not contain a sizing agent, it is possible to increase the initial water absorption of the cardboard liner of the present invention. As a result, the corrugated board liner has an appropriate range of laminating adhesive permeability, with the signal strength 0.5 seconds after the start of permeation in a dynamic permeability test of the surface of the back layer after being held at a temperature of 130°C for 60 seconds being 20% ​​to 70%, and good lamination can be obtained between the liner and the core in the corrugated board sheet obtained from the corrugated board liner. Specifically, by having the signal strength 0.5 seconds after the start of permeation in a dynamic permeability test of the surface of the back layer being 20% ​​to 70%, the (water-based) laminating adhesive required for high-speed lamination remains appropriately on the back surface of the corrugated board liner, enabling strong lamination. The reason for holding the temperature at 130°C for 60 seconds when measuring the signal intensity is that this is the time required for the polyacrylamide-based paper strength agent to solidify and form a film and to 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 manufacturing process of cardboard sheets can be grasped more accurately. Therefore, the corrugated cardboard liner has excellent adhesive strength between the core and the exterior or interior liner, and also provides good strength, even when laminated at high speed.

[0011] It is preferable that the surface layer is mainly composed of recycled corrugated cardboard pulp, and the content of the recycled corrugated cardboard pulp in the total pulp components of the surface layer is 100% by mass. In this way, by making the surface layer mainly composed of recycled corrugated cardboard pulp and making the content of the recycled corrugated cardboard pulp in the total pulp components of the surface layer 100% by mass, the Cobb sizing degree of the surface layer located at the outermost surface as a packaging material for corrugated cardboard can be set low while maintaining good bonding properties and improving the strength required for 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 glue required for high-speed lamination is appropriately retained on the surface of the back surface of the corrugated board 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 lateral specific compressive strength is 130 N·m 2 The burst strength of the corrugated cardboard liner is preferably 2.60 kPa m 2 / g or more, and the lateral specific compressive strength is 130 N·m 2 / g or more, it is possible to improve the impact resistance required for the cardboard liner. The "transverse direction" mentioned above refers to the direction perpendicular to the flow direction of the fibers (papermaking direction) (CD 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 or specific examples, but the present invention is not limited to such embodiments.

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

[0016] The corrugated board liner may have a single layer or multiple intermediate layers between the surface layer and the bottom layer, each layer having a basis weight of 30.0 g / m 2 More than 100.0g / m 2 That is, the cardboard liner may be a multi-layer paper having at least three layers, and when it is a multi-layer paper having four layers or more, for example, a configuration having a middle layer between the lower back layer and the upper surface layer, or a configuration having a second middle layer between the lower back layer and the middle layer. In this way, by making the 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 is preferably composed mainly of recycled corrugated cardboard pulp.

[0018] For the surface layer, other pulps than recycled cardboard pulp can be used within the scope that does not impair the effects of the present invention, such as disintegrated recycled paper pulp, disintegrated and deinked recycled paper pulp, deinked and bleached recycled paper pulp, etc., produced from recycled magazine paper pulp, 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 certificate paper, etc. Furthermore, mechanical pulp such as groundwood pulp (GP), thermomechanical pulp (TMP), bleached chemi-thermomechanical pulp (BCTMP), etc. may be used as 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 containing 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 as a packaging material for corrugated cardboard, it is possible to improve the strength required for 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 waste cardboard pulp in the back layer is preferably 75% by mass, more preferably 80% by mass. The upper limit of the content of the waste cardboard pulp in the back layer is preferably 85% by mass, more preferably 83% by mass. The upper limit of the content of the waste magazine pulp in the back layer is 25% by mass, more preferably 20% by mass. The lower limit of the content of the waste magazine pulp is preferably 15% by mass, more preferably 17% by mass. In order to maintain the quality of the cardboard liner, it is necessary to suppress the increase in humidity in the cardboard liner and to improve the lamination property of the back layer, so it is preferable to set the Cobb sizing degree high. By using both the waste cardboard pulp and the waste magazine pulp as the main components of the raw material pulp of the back layer located on the backmost layer side as a packaging material for cardboard, the strength required for the cardboard liner can be improved while providing good lamination property.

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

[0023] For the surface layer, other pulps than recycled cardboard pulp can be used within the scope that does not impair the effects of the present invention, such as disintegrated recycled paper pulp, disintegrated and deinked recycled paper pulp, deinked and bleached recycled paper pulp, etc., produced from recycled magazine paper pulp, 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 certificate paper, etc. Furthermore, mechanical pulp such as groundwood pulp (GP), thermomechanical pulp (TMP), bleached chemi-thermomechanical pulp (BCTMP), etc. may be used as necessary.

[0024] The lower limit of the content of the 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 the recycled corrugated cardboard pulp is 95% by mass, preferably 90% by mass. By setting the content of the recycled corrugated cardboard pulp in the lower back layer within the above range, the bursting strength ratio can be improved while recycling the recycled cardboard pulp.

[0025] In addition to recycled corrugated paper pulp and recycled magazine paper 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 tea paper, recycled kraft envelope paper, recycled newspapers, recycled flyers, recycled office paper, white recycled paper, Kent recycled paper, structural recycled paper, and recycled land certificate paper can be used for each layer of the cardboard liner, provided that the effects of the present invention are not impaired. Mechanical pulp such as groundwood pulp (GP), thermomechanical pulp (TMP), and bleached chemi-thermomechanical 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 board liner, the durability against humidity in the corrugated board liner can be increased, 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 anhydride (ASA), neutral rosin sizing agents, rosin sizing agents, etc. 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 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. In the present invention, the rosin-based sizing agent also includes emulsions of these alone or a mixture thereof, and emulsions of these alone and then mixed. Furthermore, emulsions of the above emulsions to which various polymers have been added to further improve sizing properties 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 solid content, 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 solid content, 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 cardboard liner can be given sufficient water resistance and the durability against humidity in the cardboard liner can be increased. Furthermore, by further adding cationic starch, the paper strength of the surface layer can be increased, and a cardboard liner with high strength can be obtained. Note that "kg / t of pulp" represents the amount (kg) of addition on an absolute dry basis per ton of pulp raw material for the cardboard liner.

[0029] On the other hand, the back layer and the back underlayer do not contain a sizing agent. The back layer and the back underlayer do not contain a sizing agent, which makes it possible to increase the initial water absorption of the cardboard liner. As a result, the cardboard liner has a suitable range of laminating adhesive permeability, with the signal intensity 0.5 seconds after the start of permeation being 20% ​​to 70% in a dynamic permeability test on the surface of the back layer after holding for 60 seconds at a temperature of 130°C, and can obtain good lamination between the liner and the core in the cardboard sheet obtained from the cardboard liner.

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

[0031] As polyacrylamide-based paper strength enhancers, amphoteric polyacrylamide resin-based paper strength enhancers are preferred. Amphoteric polyacrylamide is a polymer of cationic monomers and anionic monomers with acrylamide, and is directly fixed to pulp fibers via its own cationic group. In addition, amphoteric polyacrylamide resin-based paper strength enhancers are characterized by the ability to control the molecular structure and molecular weight.

[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 solid content. 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 solid content. 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 solid content. 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 solid content. By having the content of polyacrylamide-based paper strength enhancer in the back layer be between 0.1 kg / t pulp and 2.0 kg / t pulp, calculated as solids, and the content of polyacrylamide-based paper strength enhancer in the back lower layer be between 2.0 kg / t pulp and 12.0 kg / t pulp, calculated as solids, the (water-based) laminating glue 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 properties between the liner and the core in the cardboard sheet obtained from the cardboard liner.

[0033] In addition, it is preferable that the surface layer also contains a polyacrylamide-based paper strength enhancer. By containing a polyacrylamide-based paper strength enhancer in the surface layer, the strength of the cardboard liner can be further improved. The lower limit of the amount of the paper strength enhancer added to the surface layer is preferably 0.50 kg / t of pulp in solid content, and more preferably 1.0 kg / t of pulp. In addition, the upper limit of the amount of the paper strength enhancer added to the surface layer is preferably 4.0 kg / t of pulp in solid content, and more preferably 3.5 kg / t of pulp. If the addition ratio of the paper strength enhancer in the surface layer is less than 0.80 kg / t of pulp, the strength improvement effect of the cardboard liner may be difficult to obtain. If the addition ratio of the paper strength enhancer in the surface layer exceeds the above upper limit, the drainage deteriorates, and the pulp raw material is easily discharged in the squeezing and dewatering process of the press part of the papermaking machine. In addition, in the above press part, the pulp raw material residue may adhere to the doctor blade used to peel off the wet paper stuck to the roll, and the quality of the surface layer may be deteriorated.

[0034] (Other additives) In the present invention, various papermaking additives may be added to the cardboard liner consisting of each layer such as the surface layer, the back lower layer, and the back layer, within the range that does not impair the intended effect of the present invention. For example, known additives such as retention improvers, pigment dispersants, pH adjusters, thickeners, flow improvers, defoamers, foam inhibitors, release agents, penetrating agents, ultraviolet absorbers, antioxidants, preservatives, mold inhibitors, fluorescent erasers, pitch control agents, slime control agents, chemical fixatives such as aluminum sulfate, water resistance 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 kinds.

[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 invention, the overall basis weight of the corrugated board liner is 120 g / m 2 from 250 g / m 2 and preferably 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 suppress damage to the packaging container when the contents are filled after forming.

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

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

[0038] (Post-defibration freeness of disintegrated pulp) The post-disintegration freeness of the disintegrated pulp is obtained by disintegrating the cardboard liner in accordance with the pulp disintegration method of JIS-P8220-1 (2012) to produce disintegrated pulp, and the disintegrated pulp is measured in accordance with the Canadian Standard Freeness Test Method of JIS-P8121-2 (2012). The post-disintegration freeness (Canadian Standard Post-Disintegration Freeness: CSF) of the cardboard liner is preferably 300 ml or more and 400 ml or less, more preferably 310 ml or more and 390 ml or less. If the lower limit of the post-disintegration freeness of the disintegrated pulp of the cardboard liner is less than 300 ml, there is a risk of a decrease in strength. In addition, if the upper limit of the post-disintegration freeness of the disintegrated pulp exceeds 400 ml, there is a risk of a decrease in productivity and a decrease in suitability for box making due to a decrease in papermaking properties.

[0039] (Ash content of the undercoat) 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 mass%, more preferably 16.5 mass%. On the other hand, the upper limit of the ash content is preferably 20.0 mass%, more preferably 19.0 mass%. When the ash content of the back layer is 16.0 mass% or more and 20.0 mass% or less, the (water-based) laminating glue required for high-speed laminating tends to remain on the surface of the back surface of the corrugated board liner in an appropriate manner. On the other hand, if the ash content exceeds 20.0 mass%, the laminating glue may be absorbed too much by the surface of the liner, which may weaken the effect of remaining on the surface of the core.

[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 back layer is less than the above lower limit, the humidity in the corrugated board liner may not be sufficiently suppressed, and bonding defects may occur. On the other hand, the upper limit of the Cobb sizing degree of the back 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 equal to or higher than the upper limit, the corrugated board liner may absorb moisture and cause rippling or wrinkles. By setting the Cobb sizing degree of the back layer in the 2-minute measurement range within the above range, the humidity in the corrugated board liner can be suppressed, and the quality of the corrugated board liner can be maintained. In order to maintain the quality of the corrugated board liner, it is necessary to suppress an increase in humidity in the corrugated board liner and improve the lamination property of the back layer. However, by using both recycled corrugated board pulp and recycled magazine paper pulp as the main components of the raw pulp of the back layer, the Cobb sizing degree can be set within the above range, and the strength can be improved while maintaining good lamination property.

[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, it is possible to prevent the laminating adhesive from excessively penetrating into the cardboard liner.

[0042] (Signal intensity 0.5 seconds after the start of permeation in dynamic permeability testing of the backing surface) The signal strength 0.5 seconds after the start of penetration in the dynamic penetration test of the backing layer surface is measured by contacting the back side of the cardboard liner with the test liquid, holding it at a temperature of 130°C for 60 seconds, and then measuring the signal strength 0.5 seconds after the test liquid starts to penetrate the backing layer surface. The dynamic penetration test uses ultrasound to grasp the penetration behavior of liquid 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 medium interface, and the lower the signal strength, the greater the loss, i.e., the greater the penetration, with 100% as the reference value. Therefore, the permeability of the adhesive can be evaluated by the signal strength from the dynamic penetration test.

[0043] The lower limit of the signal strength 0.5 seconds after the start of penetration in the dynamic penetration test of the surface of the back layer is 20%, preferably 21%, more preferably 23%. The upper limit of the signal strength is 70%, preferably 50%, more preferably 35%. When the signal strength 0.5 seconds after the start of penetration in the dynamic penetration test of the surface of the back layer is 20% to 70%, the (water-based) laminating glue required for high-speed lamination is appropriately retained on the surface of the back side of the corrugated board 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) The burst strength index is specified in JIS-P8131 (2009). The burst strength index is the value obtained by dividing the burst strength of paper measured in accordance with JIS-P8131 (2009) expressed in kilopascals (kPa) by the basis weight. The lower limit of the burst 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 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 transverse specific compressive strength of the corrugated cardboard liner is 130N·m 2 / g or more, it is possible to maintain a strength suitable for use as a cardboard liner.

[0046] <Manufacturing method for cardboard liners> The method for manufacturing a cardboard liner is a method for manufacturing a cardboard liner to be laminated on a core of cardboard, the method comprising at least a surface layer, a back underlayer, and a back layer. The method for manufacturing a cardboard liner includes a step of making a raw pulp using a papermaking machine. The method for manufacturing a cardboard liner preferably 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 a desired freeness after disintegration. The raw pulp contains softwood kraft pulp, recycled corrugated paper pulp, recycled magazine paper pulp, or a combination thereof. First, pulp fibers are dispersed in water to obtain a slurry, and additives corresponding to each paper layer are added as necessary and mixed to prepare the paper material 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 underlayer, a back layer, etc., in a papermaking machine in a neutral range so that the pH of the corrugated board liner is 6 to 8. In the above papermaking process, the raw material pulp is made using a papermaking machine that makes paper from the pulp raw material sprayed onto a traveling wire. The papermaking machine is not particularly limited, and any known papermaking machine such as a Fourdrinier papermaking machine, a cylinder papermaking machine, a hybrid former, or a gap former can be used, and the paper is made into 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 moisture.

[0051] [Drying process] It is then dried in a dryer cylinder. After drying, the surface strength can be improved by performing a smoothing treatment. The smoothing treatment is preferably performed, for example, by pressing the cardboard liner between pressurizable reels. There are no particular limitations on the various finishing devices used for the smoothing treatment, but product finishing is performed, for example, by passing the paper through a machine calendar before the winder section, and / or a super calendar, gloss calendar, soft nip calendar, etc.

[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 embodied in various other forms in addition to the above-described forms 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 back layer.

[0055] The back lower layer may be made of virgin pulp such as bleached coniferous kraft pulp, unbleached coniferous kraft pulp, sulfite coniferous pulp, pulp made mainly from non-wood fibers such as kenaf, hemp, and reed, which are other fiber raw materials, chemically treated pulp, ground pulp made by mechanically pulping chips, chemi-ground pulp made by mechanically pulping wood or chips while adding chemicals, and semi-chemical pulp made by pulping chips in a refiner or the like after cooking until they become soft, as well as recycled magazine paper, including various papers having bleaching resistance such as recycled cardboard, recycled newspapers, coated paper, uncoated paper, plain paper, color-printed paper, and black-and-white-printed paper. It is also possible to mix synthetic pulp, etc. made from polyethylene, polypropylene, etc. with the above-mentioned plant fibers, or to blend various fibers such as organic fibers such as rayon fibers, acrylic fibers, and polyamide fibers, glass fibers, and carbon fibers in addition to synthetic pulp. EXAMPLES

[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": amphoteric 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. Moreover, Examples 6 to 8 were four-ply cardboard liners including a middle layer. Note that "-" in the following Tables 1 to 3 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 )] The measurement was performed 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 - Test methods for thickness and density" described in JIS-P8118 (2014).

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

[0066] [Freeness after disintegration] 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 lump size] The Cobb sizing degree of the backing layer was measured in accordance with JIS-P8140 (1998). The Cobb sizing degree was measured by contacting the surface of the backing layer with water for 2 minutes.

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

[0070] [Signal intensity 0.5 seconds after the start of permeation in dynamic permeability testing of the lining surface] The signal intensity 0.5 seconds after the start of permeation in the dynamic permeability test of the surface of the back layer was measured using a dynamic permeability tester "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 permeate the surface of the back layer. Distilled water at 23°C was used as the test liquid, and the ultrasonic frequency for measurement was 2MHz.

[0071] [Specific burst strength] The burst strength of the front and back sides 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 sides. The average value of the burst strength of the front and back sides 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 by using the products manufactured at a laminating speed of 300 m / min. Cardboard sheets were produced using the cardboard liners obtained in the examples and comparative examples in the following manner, and the condition of the cardboard sheets was visually evaluated according to a five-level rating scale. A, B, and C were deemed to be acceptable. (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 a corrugator, and a general core was used for the corrugated cardboard sheet as follows. In the corrugator process, the corrugating medium is stepped and then laminated to the single facer liner with laminating glue, and then in the double facer process, it is placed on the back side of the double facer liner, passed through a preheater roll, and laminated with laminating glue to create a continuous corrugated board sheet. The laminating speed in this case was 300 m / min. The laminating speed is the speed when each corrugated board liner is used as a single facer or double facer liner and laminated to the corrugating medium by the laminating machine. The following cores, laminating machines, and laminating pastes were used: Core: Reinforced core made by Iwaki Daio Paper Co., Ltd. (180g / m 2 ) Laminating machine: The corrugator CWDX manufactured by ISOWA Corporation was used. Adhesive: Low Cons made by Nippon Starch Co., Ltd. was used. Coating amount (double facer side 3.2g / 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 side 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 base paper is strong and can withstand actual operation. C: The bonding strength between the double facer side liner and the core base paper is somewhat weak, but can withstand actual operation. D: The bonding strength between the double facer side liner and the core base 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 base 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 lamination process were good when the products were evaluated at a lamination speed of 300 m / min using 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 sizing agents in the back layer and back lower layer, had high signal strength in the back layer and the properties of the cardboard sheet after the lamination process were very poor. In the cardboard liner of Comparative Example 4, in which the amount of the paper strength agent in the back layer exceeded the upper limit, the signal strength of the back layer was high, and the properties of the cardboard sheet after the lamination process were very poor. The corrugated board 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 board sheet after the lamination process were poor. The cardboard liner of Comparative Example 6, in which the back layer had a high blending ratio of recycled magazine paper pulp, had a low signal strength in the back layer, and the cardboard sheet had poor properties after the lamination process. The corrugated board 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 board sheet after the lamination process were poor. The 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 cardboard sheet after the lamination process.

[0077] From the above results, 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 for packing, and liners for containers for storing solids, and can be used as industrial paper in a variety of fields.

Claims

1. A cardboard liner laminated to a core of cardboard, comprising: At least a surface layer, a back layer, and a back layer; The back layer contains magazine waste paper pulp and cardboard waste paper pulp, The content of the waste magazine paper pulp in the total pulp component of the back layer is 25.0 mass% or less, The back layer and the back underlayer contain a polyacrylamide-based paper strength agent and do not contain a sizing agent; The content of the 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 intensity 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 said recycled cardboard pulp in the total pulp components of said surface layer is 100% by mass.

3. 3. The cardboard liner according to claim 1, wherein the ash content in 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 130N・m ２ 4. The corrugated board liner according to claim 3, wherein the elastic modulus is 1 / g or more.

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