Laminate sheet and liquid container

Abstract

Provided are a liquid container having excellent shock resistance and a laminate sheet used in the liquid container. This laminate sheet comprises a sheet base material and a thermoplastic resin layer laminated on at least one surface of the sheet base material. The sheet base material has four or more layers, and the laminate sheet has a formation index of 25 or more.

Description

Laminated paper and liquid containers

[0001] The present invention relates to a laminated paper and a liquid container made using the laminated paper.

[0002] Paper containers for liquids (liquid containers) used for milk cartons and the like are containers in which water resistance has been imparted to the paper base material that constitutes the paper container by various methods. Typical methods for imparting water resistance to a paper base material include adding a sizing agent to the paper base material and laminating a thermoplastic resin onto the surface of the paper base material.

[0003] For example, Patent Document 1 (JP 2009-242999 A) discloses a three-layer liquid container base paper that is resistant to fold cracks and has excellent printability even with a low softwood pulp content, and that is made of three paper layers: an inner layer and outer layers provided on both sides of the inner layer, the weight ratio of outer layer:inner layer:outer layer being 1:2:1 to 1:3:1, and the internal bond strength, as specified in J. TAPPI No. 18-2:2000, being 0.20 to 0.36 N m for the outer layer and 0.05 to 0.28 N m for the inner layer, with the aim of providing a three-layer liquid container base paper that is resistant to fold cracks and has excellent printability even with a low softwood pulp content.

[0004] There has been a problem that liquid containers made from laminated paper may leak if dropped or subjected to vibrations during transportation, but such problems were not addressed in the liquid container base paper described in Patent Document 1.

[0005] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a liquid container having excellent impact resistance and a laminated paper to be used for the liquid container.

[0006] The inventors have discovered that in a laminated paper having a paper base material and a thermoplastic resin layer laminated on at least one side of the paper base material, by making the number of layers of the paper base material four or more and making the formation index of the laminated paper a specific value or more, a liquid container made using the laminated paper will have excellent impact resistance.

[0007] The present invention has been completed based on these findings. That is, the present invention has the following configurations: [1] A laminated paper having a paper base material and a thermoplastic resin layer laminated on at least one side of the paper base material, the paper base material having four or more layers, and the laminated paper having a formation index of 25 or more. [2] The basis weight of each layer of the paper base material is 150 g / m ２ [3] The laminated paper according to [1] or [2], wherein the content of the polyacrylamide compound in the paper base material is 0.05% by mass or more and 0.50% by mass or less. [4] The laminated paper according to [1] or [2], wherein an adhesive component is applied between each layer of the paper base material, and the amount of the adhesive component applied between each layer is 2.0 g / m ２ 10g / m or more ２ The laminated paper according to any one of [1] to [3], wherein the adhesive component comprises starch. [5] The laminated paper according to [4], wherein the adhesive component comprises starch. [6] The laminated paper according to any one of [1] to [5], wherein at least one selected from the group consisting of a surface sizing agent and a surface strength agent and an adhesive aid are applied to at least one surface of the paper base material. [7] The laminated paper according to [6], wherein the adhesive aid comprises a polyethyleneimine resin. [8] The laminated paper according to [6], wherein the amount of the adhesive aid applied is 0.01 g / m ２ 1.0g / m or more ２ [9] The laminated paper according to any one of [1] to [8], which has thermoplastic resin layers on both sides of a paper base material, and the ratio of the thickness of the thermoplastic resin layer on the back side to the thickness of the thermoplastic resin layer on the front side is 1.2 or more and 2.5 or less.

[10] The laminated paper according to any one of [1] to [9], which is used for a liquid container.

[11] A liquid container made using the laminated paper according to any one of [1] to

[10] .

[0008] 1 is a schematic cross-sectional view showing an example of the layer structure of laminated paper according to an embodiment of the present invention;

[0009] Hereinafter, embodiments of the present invention will be described in detail. The following description of the constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined arbitrarily. Furthermore, in this specification, unless otherwise specified, operations and measurements of physical properties, etc. are performed under conditions of room temperature (20 to 25°C) and relative humidity of 40 to 50%.

[0010] [Laminated Paper] The laminated paper of this embodiment comprises a paper substrate and a thermoplastic resin layer laminated on at least one side of the paper substrate, wherein the paper substrate has four or more layers and a formation index of 25 or higher. The laminated paper of this embodiment provides a liquid container with excellent impact resistance. While the mechanism behind this effect is unclear, it is presumed to be as follows: By using a paper substrate with four or more layers, delamination is facilitated, making it easier to properly bend along the creases when molded into a liquid container, resulting in a liquid container with excellent structural impact resistance. Furthermore, if the laminated paper has weaker areas upon impact, these areas will tear, reducing impact resistance. However, by achieving a formation index of 25 or higher, a uniform laminated paper can be obtained, and containers such as liquid containers made from this laminated paper are thought to have excellent impact resistance. The effects of the present invention are not limited to the above mechanism. In the following description, a laminated paper having excellent impact resistance means that a container made from the laminated paper has excellent impact resistance (particularly, drop resistance and vibration resistance).

[0011] FIG. 1 is a cross-sectional view illustrating the configuration of laminated paper according to this embodiment. As shown in FIG. 1, laminated paper 100 includes a paper substrate 10 and a thermoplastic resin layer 20. While FIG. 1 illustrates laminated paper 100 having thermoplastic resin layers 20 on both sides of the paper substrate 10, the thermoplastic resin layer 20 may be provided on only one side of the paper substrate 10. Furthermore, when thermoplastic resin layers 20 are provided on both sides of the paper substrate 10, the thermoplastic resin layers 20 on both sides may have the same composition or different compositions. Among these, from the viewpoint of processability into liquid containers, it is preferable to have thermoplastic resin layers 20 on both sides of the paper substrate 10.

[0012] The laminated paper of this embodiment has the above-described configuration, which provides water resistance and heat sealability. Heat sealing is possible by stacking laminated papers and applying heat and pressure. Furthermore, when two laminated papers are stacked and heated and pressurized to form a heat seal, a large area of ​​the paper substrate tends to be exposed after peeling one of the laminated papers. This is because the thermoplastic resin layer melts during heat sealing, and peels off within or between the layers of the paper substrate, rather than at the interface between the thermoplastic resin layers, exposing the paper substrate. This is considered to be an indicator of favorable heat sealability. Therefore, laminated paper with good heat sealability exposes the paper substrate when a liquid container made by heat sealing is opened. Furthermore, the laminated paper of this embodiment preferably has excellent adhesion between the paper substrate and the thermoplastic resin layer. This allows the laminated paper of this embodiment to have excellent water resistance.

[0013] In this embodiment, the formation index of the laminated paper is 25 or more from the viewpoint of impact resistance. The formation index is preferably 30 or more, more preferably 45 or more, even more preferably 50 or more, and even more preferably 60 or more. The upper limit is not particularly limited, but from the viewpoint of ease of production, it is preferably 200 or less, more preferably 150 or less, even more preferably 100 or less, and even more preferably 80 or less. From the above viewpoints, the formation index of the laminated paper is preferably 30 to 200, more preferably 45 to 150, even more preferably 50 to 100, even more preferably 60 to 100, and even more preferably 60 to 80. To achieve the desired formation index range, the paper substrate may be made of four or more layers. Increasing the number of layers of the paper substrate can suppress uneven distribution of pulp fibers and increase the formation index. Furthermore, the basis weight per layer is 150 g / m2, as described below. ２ By satisfying the following conditions, uneven distribution of pulp fibers can be suppressed and the formation index can be increased. The formation index is calculated by plotting the amount of light transmitted through the laminated paper as a histogram and calculating the degree of variation in the amount of light transmitted. A larger value indicates less variation in the amount of light transmitted, less uneven distribution of pulp fibers in the paper base, and a more uniform laminated paper. The formation index of laminated paper is measured using the method described in the Examples. The formation index may be measured from either side of the laminated paper.

[0014] The basis weight of the laminated paper is preferably 100 g / m ２ More preferably, 200 g / m ２ More preferably, 250 g / m ２ More preferably, 300 g / m ２ and preferably 600 g / m ２ or less, more preferably 500 g / m ２ More preferably 420 g / m or less ２ That is, the basis weight of the laminated paper is preferably 100 to 600 g / m ２ , more preferably 200 to 500 g / m ２ , more preferably 250 to 420 g / m ２, and even more preferably 300 to 420 g / m ２ The thickness of the laminated paper is preferably 100 μm or more, more preferably 150 μm or more, even more preferably 200 μm or more, still more preferably 300 μm or more, particularly preferably 400 μm or more, and is preferably 1000 μm or less, more preferably 800 μm or less, even more preferably 600 μm or less, particularly preferably 550 μm or less. That is, the thickness of the laminated paper is preferably 100 to 1000 μm, more preferably 150 to 800 μm, even more preferably 200 to 600 μm, still more preferably 300 to 550 μm, and even more preferably 400 to 550 μm. The density of the laminated paper is preferably 0.40 g / cm ３ More preferably, 0.50 g / cm ３ More preferably, 0.60 g / cm ３ More preferably, 0.70 g / cm ３ and preferably 1.10 g / cm ３ or less, more preferably 1.00 g / cm ３ More preferably, 0.90 g / cm ３ Particularly preferably 0.85 g / cm ３ That is, the density of the laminated paper is preferably 0.40 to 1.10 g / cm ３ , more preferably 0.50 to 1.00 g / cm ３ , more preferably 0.60 to 0.90 g / cm ３ , and even more preferably 0.70 to 0.85 g / cm ３ By setting the basis weight, thickness, and density of the laminated paper within the above ranges, the paper strength when molded into a liquid container can be set within an appropriate range. Furthermore, by setting the basis weight, thickness, density, etc. of the laminated paper within the above ranges, the laminated paper can exhibit better moldability.

[0015] In addition to the paper substrate and thermoplastic resin layer, laminated paper may also have other layers besides the paper substrate and thermoplastic resin layer depending on the application. In this case, at least one side of the paper substrate may have a laminated structure such as paper substrate / other layer / thermoplastic resin layer, or a laminated structure such as paper substrate / thermoplastic resin layer / other layer. In these laminated structures, the layers may be directly or indirectly laminated to each other. Examples of such other layers include a water-soluble polymer (such as polyvinyl alcohol (PVA)) layer, a pigment coating layer primarily composed of a pigment and a binder, an aluminum foil (Al foil), a metal vapor deposition layer, an inorganic oxide (such as silica or alumina) vapor deposition layer, a nylon layer, a barrier layer such as an EVOH (ethylene-vinyl alcohol copolymer) layer, a printed layer, an adhesive layer, and the like.

[0016] Each layer constituting the laminated paper of this embodiment will be described below. [Paper Base Material] In this embodiment, the paper base material is primarily paper, and there are no particular limitations on the paper base material, so long as it is a commonly used paper whose main component is plant-derived wood pulp. The paper base material has four or more layers. That is, it has a multilayer structure having four or more pulp layers, and the paper base material is composed of paper (multilayer paper) having a multilayer structure having four or more pulp layers. The paper base material has four or more layers, preferably five or more layers, and preferably seven or fewer layers, more preferably six or fewer layers, and particularly preferably five layers. That is, the number of layers of the paper base material is preferably five to seven, more preferably five to six. Having a multilayer structure for the paper base material reduces the paper thickness and basis weight per layer, suppressing variation throughout the paper base material (uneven distribution of pulp fibers in the paper base material), and providing excellent impact resistance, which is preferable. Furthermore, by setting the number of layers within the above range, it becomes easy to adjust the interlaminar strength within a desired range, and manufacturing is easy, which is preferable.

[0017] In this specification, the surface of a paper substrate or laminated paper is the side opposite the liquid-contacting surface, which is usually the side on which printing is performed. The back surface of a paper substrate or laminated paper is the liquid-contacting surface side. Among the multiple paper layers, the surface layer is the pulp layer closest to the surface, the back layer is the pulp layer closest to the back, and the inner layer is the pulp layer sandwiched between the surface layer and the back layer.

[0018] In this embodiment, the basis weight of each of the four or more pulp layers may be the same or different. The basis weight of each pulp layer is preferably 150 g / m ２ or less, more preferably 130 g / m ２ and preferably 20 g / m ２ More preferably, 30 g / m ２ More preferably, 40 g / m ２ More preferably, 45 g / m ２ That is, the basis weight of each pulp layer is preferably 20 to 150 g / m ２ , more preferably 30 to 150 g / m ２ , more preferably 40 to 130 g / m ２ and 45 to 130 g / m ２ By setting the basis weight of each pulp layer within the above range, a laminated paper with a high formation index can be obtained, which is preferable.

[0019] The basis weight of the paper base (all layers) is preferably 200 g / m ２ More preferably, 250 g / m ２ More preferably, 300 g / m ２ and preferably 800 g / m ２ or less, more preferably 600 g / m ２ More preferably 500 g / m or less ２ More preferably, 400 g / m or less ２ That is, the basis weight of the paper substrate is preferably 200 to 800 g / m ２ , more preferably 250 to 600 g / m ２ , more preferably 300 to 500 g / m ２, and even more preferably 300 to 400 g / m ２ By setting the basis weight of the paper base material (all layers) within the above range, the strength of the liquid container when made into one can be excellent, and moreover, excellent formability can be exhibited.

[0020] The thickness of the paper substrate (all layers) is preferably 50 μm or more, more preferably 100 μm or more, even more preferably 200 μm or more, still more preferably 300 μm or more, even more preferably 350 μm or more, and preferably 600 μm or less, more preferably 550 μm or less, and even more preferably 500 μm or less. That is, the thickness of the paper substrate is preferably 50 to 600 μm, more preferably 100 to 550 μm, even more preferably 200 to 500 μm, and even more preferably 300 to 500 μm. The density of the paper substrate (all layers) is preferably 0.4 g / cm ３ More preferably, 0.5 g / cm ３ More preferably, 0.6 g / cm ３ More preferably, 0.7 g / cm ３ and preferably 1.2 g / cm ３ or less, more preferably 1.1 g / cm ３ More preferably, 1.0 g / cm or less ３ More preferably, 0.9 g / cm or less ３ Particularly preferably 0.8 g / cm ３ That is, the density of the paper substrate is preferably 0.4 to 1.2 g / cm ３ , more preferably 0.5 to 1.1 g / cm ３ , more preferably 0.6 to 1.0 g / cm ３ , and even more preferably 0.7 to 0.9 g / cm ３ , and even more preferably 0.7 to 0.8 g / cm ３ By setting the thickness and density of the paper substrate (all layers) within the above ranges, the strength of the liquid container when made into one can be excellent, and moreover, excellent formability can be exhibited.

[0021] An adhesive component may be applied between each layer of the paper substrate. Furthermore, an adhesive layer containing the adhesive component may be provided between each layer of the paper substrate. Examples of adhesive components include starch, polyacrylamide, polyamide-polyamine-epichlorohydrin resin, and the like. These may be used alone or in combination of two or more. The adhesive component preferably contains one or more components selected from the group consisting of starch, polyacrylamide, and polyamide-polyamine-epichlorohydrin resin, more preferably starch or polyacrylamide, and even more preferably starch. Applying (coating) an adhesive component between each layer of the paper substrate can improve the interlayer strength of the paper substrate, resulting in laminated paper with excellent formability and favorable interlayer peel strength. The amount of adhesive component applied between each layer of the paper base material is preferably 2.0 g / m from the viewpoints of improving the interlayer strength of the paper base material, adjusting the interlayer strength of the laminated paper having the paper base material within a desired range, facilitating interlayer peeling when opening a liquid container made of the laminated paper, suppressing fiber fluffing on the surface of the peeled paper base material, and providing a liquid container with a good mouthfeel at the opened portion. ２ More preferably, 2.5 g / m ２ More preferably, 3.0 g / m ２ In order to appropriately reduce the interlaminar strength and improve the folding processability (ease of folding at the crease line), the thickness is preferably 10.0 g / m ２ or less, more preferably 9.0 g / m ２ More preferably, 8.0 g / m or less ２ From the above viewpoint, the amount of adhesive component applied between each layer of the paper base material is preferably 2.0 to 10.0 g / m ２ , more preferably 2.5 to 9.0 g / m ２ , more preferably 3.0 to 8.0 g / m ２ is.

[0022] (Pulp) The paper base material preferably contains pulp (preferably cellulose pulp) as its main component. Here, the term "main component" refers to a component that accounts for 50% by mass or more of the total mass of the paper base material. The pulp content is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more of the total mass of the paper base material.

[0023] Examples of pulp include softwood kraft pulps (NKP) such as bleached softwood kraft pulp (NBKP) and unbleached softwood kraft pulp (NUKP), hardwood kraft pulps (LKP) such as bleached hardwood kraft pulp (LBKP) and unbleached hardwood kraft pulp (LUKP), and other wood-based pulps, and non-wood based pulps such as hemp pulp. These pulps can be used alone or in combination of two or more.

[0024] From the standpoint of quality and cost, LBKP and NBKP are suitable as pulps constituting the paper base material. In this embodiment, the mass ratio of hardwood bleached kraft pulp to softwood bleached kraft pulp (LBKP:NBKP) in the paper base material is preferably 10:90 to 100:0, more preferably 20:80 to 85:15, even more preferably 25:75 to 75:25, and even more preferably 25:75 to 70:30. By keeping the mass ratio of hardwood bleached kraft pulp to softwood bleached kraft pulp within the above range, excellent paper strength is obtained when used as a liquid container, and excellent impact resistance is therefore preferable. From the standpoint of further improving drop resistance, the LBKP:NBKP ratio is preferably 62:38 to 100:0, more preferably 65:35 to 100:0. The content of bleached softwood kraft pulp and bleached hardwood kraft pulp in the pulp constituting the paper base material is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 100% by mass, from the viewpoint of achieving a desired range of whiteness. Furthermore, from the viewpoint of printability, the content of recycled paper pulp or unbleached pulp is preferably 30% by mass or less, more preferably 20% by mass or less, even more preferably 10% by mass or less, still more preferably 5% by mass or less, even more preferably less than 1% by mass, and particularly preferably zero.

[0025] Known internal additives can be added to the paper base material as appropriate, such as sizing agents, fillers such as titanium dioxide, kaolin, talc, and calcium carbonate, paper strength agents, retention aids, pH adjusters, drainage improvers, water-resistant agents, softeners, antistatic agents, antifoaming agents, slime control agents, dyes, and pigments.

[0026] (Sizing Agent) The paper base material preferably contains a sizing agent. By containing a sizing agent in the paper base material, the paper base material can exhibit better water resistance, and as a result, the water resistance of the laminated paper is also improved. Examples of sizing agents include various known paper sizing agents such as rosin-based, alkyl ketene dimer-based, alkenyl succinic anhydride-based, maleic anhydride-based, styrene-acrylic acid-based, and styrene-acrylic-based. Among these, alkyl ketene dimer-based sizing agents are preferred.

[0027] When the paper substrate contains a sizing agent, the content of the sizing agent is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, even more preferably 0.1 parts by mass or more, and preferably 4.0 parts by mass or less, more preferably 2.0 parts by mass or less, even more preferably 1.0 parts by mass or less, even more preferably 0.5 parts by mass or less, and even more preferably 0.3 parts by mass or less, relative to 100 parts by mass (dry mass) of pulp contained in the paper substrate. That is, when the paper substrate contains a sizing agent, the content of the sizing agent is preferably 0.001 to 5.0 parts by mass, more preferably 0.01 to 2.0 parts by mass, even more preferably 0.1 to 1.0 parts by mass, even more preferably 0.1 to 0.5 parts by mass, and even more preferably 0.1 to 0.3 parts by mass, relative to 100 parts by mass (dry mass) of pulp contained in the paper substrate. By keeping the content of the sizing agent within the above range, the water resistance of the paper substrate can be more effectively improved. Note that, from the viewpoint of manufacturing efficiency, it is preferable that the content of the sizing agent in each layer of the paper substrate is the same.

[0028] (Various internal additives) In addition to the sizing agent described above, various internal additives may be added to the paper base material. Examples of internal additives include paper strength agents, wet strength agents, retention aids, freeness improvers, bulking agents, coloring dyes, coloring pigments, fluorescent whitening agents, pH adjusters, pitch control agents, preservatives, slime control agents, etc. Among these, it is preferable that at least one selected from paper strength agents and wet strength agents be added to the paper base material as the internal additive.

[0029] Specific examples of paper strength agents (dry strength agents) include polyacrylamide polymers, starches such as cationized starch, urea resins, polyamide-polyamine resins, polyethyleneimine, polyamines, polyvinyl alcohol, and polyethylene oxide. These may be used alone or in combination of two or more. Among these, preferred are at least one selected from the group consisting of cationized starch and polyacrylamide polymer, and more preferred are polyacrylamide polymers. When the paper base material contains a paper strength agent, the amount is preferably at least 0.01 parts by mass, more preferably at least 0.1 parts by mass, even more preferably at least 0.2 parts by mass, and even more preferably at least 0.3 parts by mass, relative to 100 parts by mass (dry mass) of pulp fibers contained in the paper base material, and is preferably at most 5.0 parts by mass, more preferably at most 3.0 parts by mass, and even more preferably at most 1.5 parts by mass. That is, when the paper base material contains a paper strength agent, the amount is preferably 0.01 to 5.0 parts by mass, more preferably 0.1 to 3.0 parts by mass, even more preferably 0.2 to 1.5 parts by mass, and even more preferably 0.3 to 1.5 parts by mass, per 100 parts by mass (dry mass) of pulp fibers contained in the paper base material. By keeping the content of the paper strength agent within the above range, the strength of the paper base material can be more effectively increased.

[0030] Specific examples of wet strength agents include melamine resins, urea resins, and polyamide-polyamine-epichlorohydrin resins. These may be used alone or in combination of two or more. When the paper base contains a wet strength agent, the content of the wet strength agent is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and preferably 1.0 parts by mass or less, more preferably 0.5 parts by mass or less, and even more preferably 0.3 parts by mass or less, per 100 parts by mass (dry mass) of pulp contained in the paper base. That is, when the paper base contains a wet strength agent, the content of the wet strength agent is preferably 0.01 to 1.0 parts by mass, more preferably 0.05 to 0.5 parts by mass, and even more preferably 0.05 to 0.3 parts by mass, per 100 parts by mass (dry mass) of pulp contained in the paper base. By setting the content of the wet strength agent within the above range, the wet strength of the paper base can be more effectively increased.

[0031] In this embodiment, it is preferable to contain a polyacrylamide-based compound as an internal additive, and in particular, it is preferable to contain a polyacrylamide-based compound as a paper strength enhancer. The content of the polyacrylamide-based compound (preferably a polyacrylamide-based paper strength enhancer) in the paper base material is preferably 0.05% by mass or more, and may be 0.10% by mass or more, 0.15% by mass or more, or 0.20% by mass or more, and preferably 0.50% by mass or less, 0.40% by mass or less, 0.30% by mass or less, or 0.25% by mass or less. Although the addition of a polyacrylamide-based compound increases paper strength, it generally tends to cause fibers to aggregate, resulting in a decrease in the formation index. By setting the content of the polyacrylamide-based compound within the above range and using a paper base material with four or more layers, the decrease in the formation index can be suppressed, resulting in a laminated paper with higher paper strength and excellent impact resistance, which is preferable. From the viewpoint of achieving both drop resistance and vibration resistance, the content of the polyacrylamide compound (preferably a polyacrylamide-based paper strength agent) in the paper base material is preferably 0.25% by mass or less. From the above viewpoint, the content of the polyacrylamide compound (preferably a polyacrylamide-based paper strength agent) in the paper base material is preferably 0.05 to 0.50% by mass, more preferably 0.05 to 0.40% by mass, even more preferably 0.05 to 0.30% by mass, and even more preferably 0.05 to 0.25% by mass. The content of the polyacrylamide compound in the paper base material is measured by the method described in the Examples.

[0032] From the viewpoint of enhancing surface strength, the paper substrate preferably contains, in addition to the internal additive, one or more selected from the group consisting of a surface sizing agent and a surface strength agent. Improving the surface strength of the paper substrate can prevent the phenomenon in which, when the laminated paper is used as a liquid container, liquid containers rub against each other during transport, causing the thermoplastic resin layer (described below) and the paper substrate surface to peel off from the paper substrate. Examples of surface sizing agents include alkyl ketene dimer compounds. Examples of surface strength agents include modified starches such as oxidized starch, enzyme-treated starch, and acid-treated starch; aqueous resins such as polyvinyl alcohol (PVA); styrene-acrylic acid copolymers; and styrene-methacrylic acid copolymers. These may be used alone or in combination of two or more. Among these, the surface strength agent preferably includes modified starch or an aqueous resin such as polyvinyl alcohol, more preferably modified starch, and even more preferably oxidized starch. When one or more types selected from the group consisting of surface sizes and surface strength agents are used in the size press process, it is preferable to use an adhesive aid such as a vinyl resin, epoxy resin, urethane resin, polyester resin, or polyethyleneimine resin mixed with the size press liquid in order to more effectively enhance adhesion to the thermoplastic resin layer described below. That is, it is preferable to apply one or more types selected from the group consisting of surface sizes and surface strength agents and an adhesive aid to at least one surface of the paper substrate. The adhesive aids may be used alone or in combination of two or more types. Among the adhesive aids, the adhesive aid preferably includes one or more types selected from the group consisting of vinyl resins and polyethyleneimine resins, and more preferably polyethyleneimine resin. The amount of the surface size and surface strength agent applied is preferably 0.01 g / m in terms of solid content in order to enhance the surface strength of the paper substrate. ２ More preferably, 0.1 g / m ２ More preferably, 0.5 g / m ２ More preferably, 0.8 g / m ２ From the viewpoint of ensuring the surface strength of the paper substrate to be appropriate and ensuring folding processability (ease of folding at the crease line), it is preferable that the paper substrate has a density of 5.0 g / m ２or less, more preferably 3.0 g / m ２ More preferably, 1.5 g / m or less ２ From the above viewpoint, the amount of the surface sizing agent and the surface strength agent to be applied is preferably 0.01 to 5.0 g / m in terms of solid content. ２ , more preferably 0.1 to 3.0 g / m ２ , more preferably 0.5 to 1.5 g / m ２ When a surface sizing agent and a surface strength agent are used in combination, the amount of each agent applied is preferably within the above range. The amount of the adhesive aid applied is preferably 0.01 g / m in terms of solid content, from the viewpoint of improving adhesion to the thermoplastic resin layer described below. ２ More preferably, 0.05 g / m ２ More preferably, 0.08 g / m ２ From the viewpoint of recyclability of the laminated paper, it is preferable that the paper substrate and the thermoplastic resin layer are easily peeled off, so that the thickness is preferably 5.0 g / m ２ or less, more preferably 3.0 g / m ２ More preferably, 1.5 g / m or less ２ More preferably, 1.0 g / m or less ２ More preferably, 0.5 g / m or less ２ Below 0.3 g / m, particularly preferably ２ From the above viewpoint, the amount of the adhesion promoter applied is preferably 0.01 to 5.0 g / m in terms of solid content. ２ , more preferably 0.01 to 3.0 g / m ２ , more preferably 0.01 to 1.5 g / m ２ , and even more preferably 0.01 to 1.0 g / m ２ , and even more preferably 0.01 to 0.5 g / m ２ , particularly preferably 0.05 to 0.3 g / m ２ is.

[0033] (Method for manufacturing paper substrate) The paper substrate is preferably manufactured by a manufacturing method including a papermaking step in which four or more, preferably five or more, pulp layers are laminated. Multilayer paper having a configuration in which many pulp layers are laminated is used as a manufacturing technique for paperboard, etc., and can generally be manufactured using a multilayer papermaking machine such as a cylinder-type papermaking machine or a Fourdrinier-type papermaking machine. The pH during papermaking may be in the acidic range (acidic papermaking), pseudo-neutral range (pseudo-neutral papermaking), neutral range (neutral papermaking), or alkaline range (alkaline papermaking). The paper substrate may also have a multilayer structure in which the contents of various additives differ between the inner layer and outer layer (surface layer (printing layer) and back layer), and such a multilayer structure substrate can be manufactured using a multilayer papermaking machine described below.

[0034] In the papermaking of paper substrates, a known wet papermaking machine (e.g., a Fourdrinier papermaking machine, a gap former papermaking machine, a cylinder papermaking machine, a short wire papermaking machine, etc.) may be appropriately selected and used. The paper layer formed by the papermaking machine is transported on a felt and dried in a dryer. A multi-stage cylinder dryer may be used as a pre-dryer before drying in the dryer.

[0035] From the viewpoint of increasing the surface strength of the paper substrate, it is preferable to coat one or both sides of the paper substrate obtained as described above with one or more selected from the group consisting of the surface sizing agent and surface strength agent. Furthermore, from the viewpoint of increasing adhesion to the thermoplastic resin layer described below, it is more preferable to coat a mixture of one or more selected from the group consisting of the surface sizing agent and surface strength agent and an adhesion aid. As the coating device, a known size press or the like can be used. Furthermore, the paper substrate obtained as described above may be subjected to a surface treatment using a calendar to achieve uniform thickness and profile. For the calendar treatment, a known calendaring machine can be appropriately selected and used. Furthermore, a size press agent may be applied before the calendar treatment.

[0036] [Thermoplastic resin layer] The thermoplastic resin layer is laminated on at least one surface of the paper substrate. The thermoplastic resin layer may be a single layer or multiple layers. The thermoplastic resin layer may be laminated on both surfaces of the paper substrate. In this specification, the term "laminated on a surface" means that the layer may be directly laminated or indirectly laminated via another layer.

[0037] The thermoplastic resin constituting the thermoplastic resin layer can be either a crystalline or amorphous thermoplastic resin, depending on the application. Examples of the thermoplastic resin include polyethylene (low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), etc.), polypropylene, polyolefin resins such as polymethylpentene, polyester resins such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), polyamide resins, biodegradable resins such as polylactic acid (PLA), polyhydroxybutyric acid (PHB), polybutylene succinate (PBS), poly(butylene adipate-co-butylene terephthalate) (PBAT), polycaprolactone (PCL), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene (ABS) resin, acrylic resin, and modified polyphenylene ether (PPE). Among these, it is preferable to use polyolefin resins such as polyethylene (LDPE, MDPE, HDPE, LLDPE, etc.), polypropylene, polymethylpentene, etc., or polylactic acid (PLA) as the thermoplastic resin, and it is more preferable to use at least one of polyethylene and polypropylene. These thermoplastic resins may be used alone or in combination of two or more.

[0038] The thermoplastic resin layer may be formed as a single layer of a single resin, or may be formed as a single layer by mixing a plurality of resins, or may be formed as a multi-layer structure of these (for example, single resin layer / single resin layer, single resin layer / mixed resin layer, mixed resin layer / mixed resin layer).

[0039] The amount (basis weight) of the thermoplastic resin layer is not particularly limited, but is preferably 5 g / m ２ More preferably, 10 g / m ２ and preferably 150 g / m ２ or less, more preferably 100 g / m ２ More preferably 50 g / m or less ２ More preferably, 40 g / m or less ２ That is, the amount of the thermoplastic resin layer formed is preferably 5 to 150 g / m ２ , more preferably 5 to 100 g / m ２ , more preferably 10 to 50 g / m ２ , and even more preferably 10 to 40 g / m ２The thickness of the thermoplastic resin layer is not particularly limited, but is preferably 5 μm or more, more preferably 10 μm or more, and preferably 150 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, and even more preferably 40 μm or less. That is, the thickness of the thermoplastic resin layer is preferably 5 to 150 μm, more preferably 5 to 100 μm, even more preferably 10 to 50 μm, and even more preferably 10 to 40 μm. Note that the amount and thickness of the thermoplastic resin layer referred to above refer to the amount and thickness formed on one surface. When formed on both surfaces, the amount and thickness of the thermoplastic resin layer on each surface are preferably within the above ranges. Note that, with respect to the front surface (printing surface) and the back surface (liquid-contacting surface), it is preferable that the amount and thickness of the thermoplastic resin formed on the back surface (liquid-contacting surface) be greater than the amount and thickness of the thermoplastic resin formed on the front surface (printing surface). This prevents the contents from penetrating the paper substrate and suppresses leakage of the contents and bulging due to a decrease in the strength of the paper substrate. The thickness of the thermoplastic resin layer on the front surface (printing surface) is preferably 5 μm or more, more preferably 10 μm or more, from the viewpoint of easily obtaining a laminated paper with excellent printability, and is preferably 40 μm or less, more preferably 30 μm or less, and even more preferably 25 μm or less. From the above viewpoints, the thickness of the thermoplastic resin layer on the front surface (printing surface) is preferably 5 to 40 μm, more preferably 10 to 30 μm, and even more preferably 10 to 25 μm. The thickness of the thermoplastic resin layer on the back surface (liquid-contacting surface) is preferably 5 μm or more, more preferably 15 μm or more, and even more preferably 20 μm or more, from the viewpoint of easily exhibiting water resistance, and is preferably 50 μm or less, more preferably 40 μm or less, from the viewpoint of easily obtaining a laminated paper with excellent processability. From the above viewpoints, the thickness of the thermoplastic resin layer on the back surface (liquid-contacting surface) is preferably 5 to 50 μm, more preferably 15 to 40 μm, and even more preferably 20 to 40 μm. From the above viewpoints, the ratio of the thickness of the thermoplastic resin layer on the back surface (liquid-contacting surface) to the thickness of the thermoplastic resin layer on the front surface (printing surface) (back surface / front surface) is preferably 1.2 or more, more preferably 1.4 or more, and is preferably 2.5 or less, more preferably 2.0 or less.From the above viewpoints, the thickness ratio of the thermoplastic resin layer (rear surface / front surface) is preferably 1.2 to 2.5, more preferably 1.4 to 2.0. The ratio of the amount of the thermoplastic resin layer formed (rear surface / front surface) is also preferably within the same range as above. By setting the amount and thickness of the thermoplastic resin layer within the above ranges, it is possible to prevent the liquid filled in the container from penetrating into the paper base material, and also to improve the suitability for molding into liquid containers.

[0040] [Method for manufacturing laminated paper] The laminated paper of this embodiment is manufactured by a manufacturing method including a laminating step of laminating a thermoplastic resin layer on at least one surface of a paper base material. Specifically, the manufacturing method for laminated paper preferably includes a papermaking step of the paper base material and a laminating step of laminating a thermoplastic resin layer on at least one surface of the paper base material.

[0041] As a method for laminating a thermoplastic resin layer onto a paper substrate, various known methods such as melt extrusion lamination, dry lamination, wet lamination, and thermal lamination can be appropriately used. When the thermoplastic resin layer is a single layer, melt extrusion lamination is preferred. During lamination, if necessary, the thermoplastic resin layer or the paper substrate may be subjected to an oxidation treatment such as corona treatment or ozone treatment. By performing these treatments, polar groups are generated on the surface of the thermoplastic resin layer or the paper substrate, thereby improving adhesion. These treatments may be performed on either the thermoplastic resin layer or the paper substrate, or both, and may be performed once or multiple times.

[0042] In the papermaking process, it is preferable to make the paper base material using a multi-layer papermaking machine. The papermaking process is as described above.

[0043] [Liquid container] The laminated paper of this embodiment is preferably used for a liquid container. The present invention also provides a blank sheet or a liquid container made using the above-mentioned laminated paper. The blank sheet and the liquid container can be manufactured by appropriately selecting a known method.

[0044] The laminated paper of this embodiment can be used for various applications, including liquid containers such as milk cartons, paper cups, coffee containers, and aseptic containers; paper containers such as foam cups, ice cream cups, insulated cups, and packaging containers; and packaging materials and insulating materials. In particular, the laminated paper of this embodiment is suitable for use in liquid containers. The present invention also provides a liquid container made using the above-described laminated paper. A known method can be appropriately selected and used to manufacture the liquid container. The shape of the liquid container is not particularly limited, and examples include gable-top containers, rectangular parallelepiped containers (brick, straight, and flat top), triangular pyramidal containers, cup containers, slant-top containers, and regular tetrahedron containers. Therefore, another embodiment of the present invention is the use of the above-described laminated paper in the manufacture of paper containers (preferably liquid paper containers). The method for producing a gable-top liquid container is not particularly limited, but for example, the surface (printing surface) of laminated paper is printed, creasing and punching are performed, and the container is further folded and frame-sealed in the vertical direction, resulting in a folded carton. The resulting folded carton undergoes bottom sealing, sterilization, filling, and top sealing before being distributed as a gable-top liquid-filled product. The liquid contained in the liquid container may be either food or non-food. Examples of liquids that can be contained in the liquid container include, but are not limited to, alcoholic beverages such as sake, shochu, and wine; dairy beverages such as milk; beverages such as juice, coffee, tea, and black tea; liquid foods such as beverages (yogurt, jelly, pudding, etc.) and prepared dishes; pharmaceuticals; and chemical products such as car wax, shampoo, conditioner, detergent, bath additives, hair dye, and toothpaste.

[0045] The barrier laminate of the present invention will be described in more detail below with reference to examples, but the present invention is not limited to these. In the examples and comparative examples, "parts" and "%" mean "parts by mass" and "% by mass", respectively, unless otherwise specified.

[0046] [Measurement Method] The measurement method used for the paper substrate and laminated paper is described below. Unless otherwise specified, measurements were performed in an environment of 23°C ± 1°C and 50±2% relative humidity as specified in JIS P 8111:1998. (1) Basis Weight of Paper Substrate and Laminated Paper The basis weight of the paper substrate and laminated paper was measured in accordance with JIS P 8124:2011. (2) Thickness of Thermoplastic Resin Layer A 100mm x 100mm piece of laminated paper was cut out, the thermoplastic resin layer was peeled from the cut specimen, and then immersed in a cellulase solution. After sufficient immersion, the specimen was further immersed in a copper ethylenediamine solution to extract only the thermoplastic resin (PE coating). After washing with water and drying, the specimen was weighed accurately to determine the density of the thermoplastic resin used (density of polyethylene = 0.923 g / cm). ３ ) The thickness of the thermoplastic resin layer was calculated.

[0047] [Example 1] (Paper base material) 60 parts of LBKP and 40 parts of NBKP were beaten using a double-disc refiner as pulp raw materials to obtain a pulp slurry. To 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.30 parts (solids equivalent) of a polyacrylamide-based strength agent as an internal paper strength enhancer, 0.25 parts (solids equivalent) of an alkyl ketene dimer-based sizing agent as an internal sizing agent, and 0.10 parts (solids equivalent) of a polyamide-polyamine-epichlorohydrin-based wet strength agent as a wet strength enhancer were added to prepare a paper stock. A five-layer paper was made using this paper stock using a multi-layer Fourdrinier paper machine. During the papermaking process, potato starch was sprayed between each layer at 7.5 g / m. ２ After five layers were combined, oxidized starch was sprayed onto both sides of the paper substrate using a size press at 1.0 g / m ２ (solid content equivalent) and polyethyleneimine at 0.10 g / m ２ (solid content equivalent) coated and calendered to a basis weight of 267 g / m ２The paper substrate obtained here had different smoothness on its front and back sides. The high-smoothness side was the front (printing side), and the low-smoothness side was the back (liquid-contacting side). The basis weight of each layer of the paper substrate in Table 1 includes the potato starch sprayed between each layer, and the oxidized starch and polyethyleneimine applied to the front and back layers. When paper substrates are made from the same stock formulation as described above, the Oken smoothness of the felt side (the side opposite the wire, the side where the paper layer came into contact with the felt when making the paper substrate) tends to be higher than that of the wire side (the side where the paper layer came into contact with the wire when making the paper substrate). This is because the felt side contains more fine fibers, resulting in fewer gaps between the fibers, and is more easily dehydrated and has a more uniform surface.

[0048] (Thermoplastic resin layer) LDPE (low density polyethylene) was laminated on both sides of the obtained paper substrate as a thermoplastic resin. The thermoplastic resin layer was laminated by melt extrusion lamination at a melt temperature of 310°C, and the thickness and basis weight of the thermoplastic resin layer were as shown in Table 1, to obtain laminated paper.

[0049] (Paper container) After offset printing on the surface (front surface, printed surface) of the obtained laminated paper, lines were provided where necessary and the blank was punched into a predetermined shape to obtain a blank. Next, a portion of the resin material in the blank was melted using a frame seal, and the body was attached to obtain a cylindrical sleeve. Subsequently, this cylindrical sleeve was fed into a liquid filling machine, and after forming a bottom portion on the filling machine, 1000 mL of water was filled and the top portion was sealed to obtain a gable-top paper container with a capacity of 1000 mL.

[0050] [Example 2] 50 parts of LBKP and 50 parts of NBKP were beaten using a double-disc refiner as pulp raw materials to obtain a pulp slurry. To 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.30 parts (solids equivalent) of a polyacrylamide-based strength agent as an internal strength enhancer, 0.25 parts (solids equivalent) of an alkyl ketene dimer-based sizing agent as an internal sizing agent, and 0.10 parts (solids equivalent) of a polyamide-polyamine-epichlorohydrin-based wet strength agent as a wet strength enhancer were added to prepare a paper stock. Using this paper stock, a five-layer paper was made using a multi-layer Fourdrinier paper machine. During the papermaking process, potato starch was sprayed between each layer at 7.5 g / m. ２ After five layers were combined, oxidized starch was sprayed onto both sides of the paper substrate using a size press at 1.0 g / m ２ (solid content equivalent) and polyethyleneimine at 0.10 g / m ２ (solid content equivalent) coated and calendered to a basis weight of 333 g / m ２ The paper substrate of Example 1 was obtained. The basis weight of each layer of the paper substrate in Table 1 includes the potato starch sprayed between each layer, and the oxidized starch and polyethyleneimine applied to the front and back layers. Laminated paper and gable-top paper containers were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated onto the obtained paper substrate so that the basis weight met the conditions shown in Table 1.

[0051] [Example 3] 30 parts of LBKP and 70 parts of NBKP were beaten using a double-disc refiner as pulp raw materials to obtain a pulp slurry. To 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.50 parts (solids equivalent) of a polyacrylamide-based strength agent as an internal strength enhancer, 0.25 parts (solids equivalent) of an alkyl ketene dimer-based sizing agent as an internal sizing agent, and 0.10 parts (solids equivalent) of a polyamide-polyamine-epichlorohydrin-based wet strength agent as a wet strength enhancer were added to prepare a paper stock. A five-layer paper was made using this paper stock using a multi-layer Fourdrinier paper machine. During the papermaking process, potato starch was sprayed between each layer at a rate of 7.5 g / m. ２After five layers were combined, oxidized starch was sprayed onto both sides of the paper substrate using a size press at 1.0 g / m ２ (solid content equivalent) and polyethyleneimine at 0.10 g / m ２ (solid content equivalent) coated and calendered to a basis weight of 337 g / m ２ The paper substrate of Example 1 was obtained. The basis weight of each layer of the paper substrate in Table 1 includes the potato starch sprayed between each layer, and the oxidized starch and polyethyleneimine applied to the front and back layers. Laminated paper and gable-top paper containers were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated onto the obtained paper substrate so that the basis weight met the conditions shown in Table 1.

[0052] [Example 4] 65 parts of LBKP and 35 parts of NBKP were beaten using a double-disc refiner as pulp raw materials to obtain a pulp slurry. To 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.20 parts (solids equivalent) of a polyacrylamide-based strength agent as an internal strength enhancer, 0.25 parts (solids equivalent) of an alkyl ketene dimer-based sizing agent as an internal sizing agent, and 0.10 parts (solids equivalent) of a polyamide-polyamine-epichlorohydrin-based wet strength agent as a wet strength enhancer were added to prepare a paper stock. A five-layer paper was made using this paper stock using a multi-layer Fourdrinier paper machine. During the papermaking process, potato starch was sprayed between each layer at 7.5 g / m. ２ After five layers were combined, oxidized starch was sprayed onto both sides of the paper substrate using a size press at 1.0 g / m ２ (solid content equivalent) and polyethyleneimine at 0.10 g / m ２ (solid content equivalent) coated and calendered to a basis weight of 338 g / m ２ The paper substrate of Example 1 was obtained. The basis weight of each layer of the paper substrate in Table 1 includes the potato starch sprayed between each layer, and the oxidized starch and polyethyleneimine applied to the front and back layers. Laminated paper and gable-top paper containers were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated onto the obtained paper substrate so that the basis weight met the conditions shown in Table 1.

[0053] [Example 5] 50 parts of LBKP and 50 parts of NBKP were beaten using a double-disc refiner as pulp raw materials to obtain a pulp slurry. To 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.10 parts (solids equivalent) of a polyacrylamide-based strength agent as an internal strength enhancer, 0.25 parts (solids equivalent) of an alkyl ketene dimer-based sizing agent as an internal sizing agent, and 0.10 parts (solids equivalent) of a polyamide-polyamine-epichlorohydrin-based wet strength agent as a wet strength enhancer were added to prepare a paper stock. A five-layer paper was made using this paper stock using a multi-layer Fourdrinier paper machine. During the papermaking process, potato starch was sprayed between each layer at 7.5 g / m. ２ After five layers were combined, oxidized starch was sprayed onto both sides of the paper substrate using a size press at 1.0 g / m ２ (solid content equivalent) and polyethyleneimine at 0.10 g / m ２ (solid content equivalent) coated and calendered to a basis weight of 352 g / m ２ The paper substrate of Example 1 was obtained. The basis weight of each layer of the paper substrate in Table 1 includes the potato starch sprayed between each layer, and the oxidized starch and polyethyleneimine applied to the front and back layers. Laminated paper and gable-top paper containers were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated onto the obtained paper substrate so that the basis weight met the conditions shown in Table 1.

[0054] [Example 6] 60 parts of LBKP and 40 parts of NBKP were beaten using a double-disc refiner as pulp raw materials to obtain a pulp slurry. To 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.30 parts (solids equivalent) of a polyacrylamide-based strength agent as an internal strength enhancer, 0.25 parts (solids equivalent) of an alkyl ketene dimer-based sizing agent as an internal sizing agent, and 0.10 parts (solids equivalent) of a polyamide-polyamine-epichlorohydrin-based wet strength agent as a wet strength enhancer were added to prepare a paper stock. A five-layer paper was made using this paper stock using a multi-layer Fourdrinier paper machine. During the papermaking process, potato starch was sprayed between each layer at 3.5 g / m. ２After five layers were combined, oxidized starch was sprayed onto both sides of the paper substrate using a size press at 1.0 g / m ２ (solid content equivalent) and polyethyleneimine at 0.10 g / m ２ (solid content equivalent) coated and calendered to a basis weight of 333 g / m ２ The paper substrate of Example 1 was obtained. The basis weight of each layer of the paper substrate in Table 1 includes the potato starch sprayed between each layer, and the oxidized starch and polyethyleneimine applied to the front and back layers. Laminated paper and gable-top paper containers were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated onto the obtained paper substrate so that the basis weight met the conditions shown in Table 1.

[0055] Comparative Example 1 50 parts of LBKP and 50 parts of NBKP were beaten using a double-disc refiner as pulp raw materials to obtain a pulp slurry. To 100 parts of the pulp (dry mass) in the obtained pulp slurry, 0.60 parts (solids equivalent) of cationized starch as an internal paper strength enhancer, 0.25 parts (solids equivalent) of an alkyl ketene dimer sizing agent as an internal sizing agent, and 0.10 parts (solids equivalent) of a polyamide-polyamine-epichlorohydrin wet strength agent as a wet strength enhancer were added to prepare a paper stock. Using this paper stock, a three-layer paper was made using a multi-layer Fourdrinier paper machine. During the papermaking process, potato starch was sprayed between each layer at a rate of 7.5 g / m. ２ After the three layers were combined, oxidized starch was sprayed onto both sides of the paper substrate using a size press at a rate of 1.0 g / m (solid content equivalent). ２ (solid content equivalent) and polyethyleneimine at 0.10 g / m ２ (solid content equivalent) coated and calendered to a basis weight of 323 g / m ２ The paper substrate of Example 1 was obtained. The basis weight of each layer of the paper substrate in Table 1 includes the potato starch sprayed between each layer, and the oxidized starch and polyethyleneimine applied to the front and back layers. Laminated paper and gable-top paper containers were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated onto the obtained paper substrate so that the basis weight met the conditions shown in Table 1.

[0056] Comparative Example 2 65 parts of LBKP and 35 parts of NBKP were beaten using a double-disc refiner as pulp raw materials to obtain a pulp slurry. To 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.60 parts (solids equivalent) of cationized starch as an internal paper strength enhancer, 0.25 parts (solids equivalent) of an alkyl ketene dimer sizing agent as an internal sizing agent, and 0.10 parts (solids equivalent) of a polyamide-polyamine-epichlorohydrin wet strength agent as a wet strength enhancer were added to prepare a paper stock. Using this paper stock, a three-layer paper was made using a multi-layer Fourdrinier paper machine. During the papermaking process, potato starch was sprayed between each layer at a rate of 7.5 g / m. ２ After the three layers were combined, oxidized starch was sprayed onto both sides of the paper substrate using a size press at a rate of 1.0 g / m (solid content equivalent). ２ (solid content equivalent) and polyethyleneimine at 0.10 g / m ２ (solid content equivalent) coated and calendered to a basis weight of 333 g / m ２ The paper substrate of Example 1 was obtained. The basis weight of each layer of the paper substrate in Table 1 includes the potato starch sprayed between each layer, and the oxidized starch and polyethyleneimine applied to the front and back layers. Laminated paper and gable-top paper containers were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated onto the obtained paper substrate so that the basis weight met the conditions shown in Table 1.

[0057] The laminated paper and liquid containers obtained in the examples and comparative examples were evaluated as follows. (Formation Index) Apparatus: M / K Systems 3D Sheet Analyzer Model M / K 975 Measurement conditions: Sensitivity Range 1, Aperture 2.0 mm An A4-sized measurement sample (laminated paper) was set in the apparatus, and after measurement under the above conditions, the displayed value was taken as the formation index (FORMATION INDEX). Note that the above measurement apparatus measures the amount of transmitted light while the rotating drum is rotating, and the data on the amount of transmitted light is plotted as a histogram. The degree of variation in the amount of transmitted light is automatically calculated from the obtained histogram. A higher value of the formation index indicates higher uniformity.

[0058] (Drop test) The gable-top paper containers obtained in the examples and comparative examples were filled with 1000 mL of water, and with the bottom surface facing vertically downward, they were repeatedly dropped from a height of 30 cm onto a concrete floor, and the number of times it took for liquid leakage to occur was counted. The test was conducted eight times each, and the drop resistance was evaluated based on the average number of times until liquid leakage occurred, using the following evaluation criteria: A: Average number of drops exceeds 20 B: More than 15 times and 20 times or less C: More than 10 times and 15 times or less D: 10 times or less

[0059] (Vibration Test) A vibration test was conducted in accordance with JIS Z 0200:2013 and JIS Z 0232:2020 8.4.4. The samples were placed in a crate containing 12 bottles, and vibrations (random vibration: 2 to 200 Hz) were applied in vertical directions only in 15-minute increments for up to 30 minutes. The number of samples that leaked was counted, and the vibration resistance was evaluated according to the following criteria: A: Leaking cartons: 1 or less B: 2 to 5 bottles C: 6 to 9 bottles D: 10 or more

[0060] (Method for measuring polyacrylamide compound content) The content of polyacrylamide compounds contained in the paper substrate (converted to solid content) was measured using a pyrolysis GC / MS analyzer. [Measurement conditions] Apparatus used: GC8890 / MSD5977B manufactured by Agilent Technologies, Inc. GC: Column HP-INNOWAX (length 30 m, inner diameter 0.25 μm, outer diameter 0.25 mm) Carrier gas: He MS: EI(+) Conditions: 50°C → (10°C / min) → 260°C, 15 minute hold Pyrolysis apparatus: PY-3030D manufactured by Frontier Labs, Inc., decomposition temperature 500°C Analysis: The content of polyacrylamide compounds was calculated using selected ion m / z 125

[0061]

[0062] As can be seen from Table 1, for the laminated papers of Examples 1 to 6, in which the paper base had five layers (four or more layers) and the laminated paper had a formation index of 25 or more, the liquid containers made from the laminated papers had excellent drop resistance, vibration resistance, and impact resistance. On the other hand, for Comparative Example 1, in which the paper base had three layers, even though the formation index was 25 or more, the liquid container made from the laminated paper was inferior in drop resistance and vibration resistance and impact resistance compared to Examples 1 to 6. Furthermore, for the laminated paper of Comparative Example 2, in which the paper base had three layers and a formation index of less than 25, the liquid container made from the laminated paper was inferior in drop resistance and vibration resistance and impact resistance compared to Examples 1 to 6 and Comparative Example 1.

[0063] The laminated paper according to this embodiment is water-resistant, and liquid containers made from this laminated paper have excellent impact resistance (particularly resistance to drops and vibrations), and can be suitably used for liquid containers such as milk cartons, paper cups, coffee containers, aseptic containers, paper containers such as foam cups, ice cups, insulated cups, and packaging containers, as well as packaging materials, insulating materials, etc.

[0064] 10 Paper substrate 20 Thermoplastic resin layer 100 Laminated paper

Claims

1. A laminated paper having a paper base material and a thermoplastic resin layer laminated on at least one surface of the paper base material, wherein the paper base material is a paper base material having 4 or more layers, and the texture index of the laminated paper is 25 or more. Laminated paper.

2. The basis weight of each layer of the paper base material is 150 g / m ２ The laminated paper according to claim 1, wherein the basis weight is 150 g / m or less.

3. The laminated paper according to Claim 1 or 2, wherein the content of the polyacrylamide-based compound in the paper base material is 0.05% by mass or more and 0.50% by mass or less.

4. An adhesive component is provided between each layer of the paper base material, and the amount of the adhesive component provided per layer is 2.0 g / m ２ or more and 10 g / m ２ or less. The laminated paper according to claim 1 or 2.

5. The laminated paper according to Claim 4, wherein the adhesive component contains starch.

6. The laminated paper according to Claim 1 or 2, wherein one or more selected from the group consisting of a surface sizing agent and a surface paper strength agent and an adhesion aid are applied to at least one surface of the paper base material.

7. The laminated paper according to Claim 6, wherein the adhesion aid contains a polyethyleneimine resin.

8. The application amount of the adhesion aid is 0.01 g / m ２ or more and 1.0 g / m ２ or less. The laminated paper according to claim 6.

9. The laminated paper according to Claim 1 or 2, having thermoplastic resin layers on both surfaces of the paper base material, wherein the ratio of the thickness of the thermoplastic resin layer on the back surface to the thickness of the thermoplastic resin layer on the front surface is 1.2 or more and 2.5 or less.

10. The laminated paper according to Claim 1 or 2, which is for a liquid container.

11. A liquid container made using the laminated paper according to Claim 1 or 2.