WO2024004859A1

WO2024004859A1 - Laminate sheet and liquid container

Info

Publication number: WO2024004859A1
Application number: PCT/JP2023/023328
Authority: WO
Inventors: 智宏秋田; 晴香井出; 由典小林
Original assignee: 王子ホールディングス株式会社
Priority date: 2022-06-27
Filing date: 2023-06-23
Publication date: 2024-01-04

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

The present invention relates to laminated paper and a liquid container using the laminated paper.

As liquid paper containers (liquid containers) used for milk cartons and the like, containers are used in which water resistance is imparted to the paper base material that constitutes the paper container using various methods. Typical methods for imparting water resistance to a paper base include a method of adding a sizing agent to the paper base and a method of laminating a thermoplastic resin on the surface of the paper base.

For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2009-242999) discloses an object of providing a three-layer base paper for liquid containers that is less prone to folding and has excellent printability even at a low blending ratio of softwood pulp. A base paper for liquid containers consisting of three paper layers: an inner layer and an outer layer provided on both sides of the inner layer, the weight ratio of the outer layer:inner layer:outer layer being 1:2:1 to 1:3:1. Yes, J. TAPPI No. 18-2:2000, the outer layer has an internal bonding strength of 0.20 to 0.36 N.m, and the inner layer has an internal bond strength of 0.05 to 0.28 N.m. Disclosed.

There was a problem in that liquid containers made from laminated paper would leak if they were dropped or subjected to vibration during transportation. However, such problems have not been considered in the base paper for liquid containers described in Patent Document 1.

The present invention has been made in view of the above situation. That is, an object of the present invention is to provide a liquid container with excellent impact resistance and a laminated paper used for the liquid container.

The present inventors have proposed a laminated paper having a paper base material and a thermoplastic resin layer laminated on at least one surface of the paper base material, in which the number of layers of the paper base material is 4 or more, and It has been found that by setting the formation index of the laminated paper to a specific value or more, a liquid container made of the laminated paper has excellent impact resistance.

The present invention was completed based on such knowledge. That is, the present invention has the following configuration.
[1] A laminated paper comprising 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 has four or more layers. A laminated paper that is a base material and has a formation index of 25 or more.
[2] The laminated paper according to [1], wherein the basis weight of each layer of the paper base material is 150 g/m ² or less.
[3] The laminated paper according to [1] or [2], wherein the content of the polyacrylamide compound in the paper base is 0.05% by mass or more and 0.50% by mass or less.
[4] 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 or more and 10 g/m ² or less, [1] to [ The laminated paper according to any one of [3].
[5] The laminated paper according to [4], wherein the adhesive component contains starch.
[6] The method according to [1] to [5], wherein at least one surface of the paper base material is provided with one or more selected from the group consisting of a surface sizing agent and a surface strength agent and an adhesion aid. Laminated paper as described in any one of the above.
[7] The laminated paper according to [6], wherein the adhesion auxiliary agent contains a polyethyleneimine resin.
[8] The laminated paper according to [6] or [7], wherein the amount of the adhesion aid applied is 0.01 g/m ² or more and 1.0 g/m ² or less.
[9] The paper base material has thermoplastic resin layers on both sides, 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, The laminated paper according to any one of [1] to [8].
[10] The laminated paper according to any one of [1] to [9], which is used for liquid containers.
[11] A liquid container made of the laminated paper according to any one of [1] to [10].

FIG. 1 is an example of a schematic cross-sectional view showing the layer structure of the laminated paper of the present embodiment.

Hereinafter, embodiments of the present invention will be specifically described. Although the constituent elements described below may be explained based on typical embodiments and specific examples, the present invention is not limited to such embodiments. In this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after the "~" as lower and upper limits. When numerical ranges are described in stages, the upper and lower limits of each numerical range can be combined arbitrarily. In addition, in this specification, unless otherwise specified, operations and measurements of physical properties, etc. are performed at room temperature (20 to 25° C.)/relative humidity of 40 to 50%.

[Laminated paper]
The laminated paper of this embodiment is a laminated paper having a paper base material and a thermoplastic resin layer laminated on at least one surface of the paper base material, the paper base material having four or more layers. The laminated paper is a paper base material having a number of layers, and the formation index of the laminated paper is 25 or more.
According to the laminated paper of this embodiment, a liquid container with excellent impact resistance is provided. Although the mechanism that produces this effect is not certain, it is presumed as follows.
By using a paper base material with four or more layers, it becomes easy to peel between the layers, and when formed into a liquid container, it is easy to bend appropriately at ruled lines, and has excellent structural impact resistance. It is thought that it will become a liquid container. Additionally, if there are weak areas in the laminated paper when subjected to impact, those areas may tear and the impact resistance will decrease, but by setting the formation index to 25 or higher, a uniform laminate can be achieved. By using paper, containers such as liquid containers made from the laminated paper are considered to have excellent impact resistance.
Note that the effects of the present invention are not limited to the above mechanism.
Furthermore, in the following description, a laminated paper with excellent impact resistance means that a container made from the laminated paper has excellent impact resistance (particularly drop resistance and vibration resistance).

FIG. 1 is a cross-sectional view illustrating the structure of the laminated paper of this embodiment. As shown in FIG. 1, the laminated paper 100 has a paper base material 10 and a thermoplastic resin layer 20. Although FIG. 1 illustrates a laminated paper 100 having thermoplastic resin layers 20 on both sides of the paper base material 10, the thermoplastic resin layer 20 is provided only on either side of the paper base material 10. Good too. Moreover, when the thermoplastic resin layers 20 are provided on both sides of the paper base material 10, the thermoplastic resin layers 20 on both sides may have the same composition or may have different compositions.
Among these, from the viewpoint of processability into a liquid container, it is preferable to have thermoplastic resin layers 20 on both sides of the paper base material 10.

The laminated paper of this embodiment has the above-mentioned structure, thereby imparting water resistance and heat sealability. Heat sealing is possible by stacking laminated papers and applying heat and pressure. In addition, if the heat-sealability is good, the heat-sealed part is formed by overlapping two sheets of laminated paper and applying heat and pressure, and the exposed area of the paper base tends to be large after one of the laminated papers is peeled off. . This is because the thermoplastic resin layer melts due to heat sealing and does not peel off at the interface between the thermoplastic resin layers, but instead separates within or between the layers of the paper base material, exposing the paper base material. This is considered to be an indicator that favorable heat sealability is exhibited. Therefore, with laminated paper having good heat-sealability, the paper base material is exposed when a liquid container produced by heat-sealing is opened.
Moreover, it is preferable that the laminated paper of this embodiment has excellent adhesiveness between the paper base material and the thermoplastic resin layer. As a result, the laminated paper of this embodiment has excellent water resistance.

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, still more preferably 50 or more, even more preferably 60 or more, and the upper limit is not particularly limited, but from the viewpoint of ease of manufacture, it is preferably 200 or more. Below, it is more preferably 150 or less, still more preferably 100 or less, even more preferably 80 or less. From the above viewpoint, the formation index of the laminated paper is preferably 30 to 200, more preferably 45 to 150, still more preferably 50 to 100, even more preferably 60 to 100, even more preferably 60 to 80.
In order to set the formation index within a desired range, the paper base material may have four or more layers. By increasing the number of layers of the paper base material, uneven distribution of pulp fibers can be suppressed and the formation index can be increased. Further, by setting the basis weight per layer to 150 g/m ² or less as described later, uneven distribution of pulp fibers can be suppressed and the formation index can be increased.
The formation index is calculated by calculating the degree of variation in the amount of transmitted light by converting the amount of transmitted light through the laminated paper into a histogram. This means that the laminated paper has a uniform distribution with little unevenness. The formation index of the laminated paper is measured by the method described in the Examples. Note that the formation index may be measured from any side of the laminated paper.

The basis weight of the laminated paper is preferably 100 g/m ² or more, more preferably 200 g/m ² or more, even more preferably 250 g/m ² or more, even more preferably 300 g/m ² or more, and preferably 600 g/m 2 or more. /m ² or less, more preferably 500 g/m ² or less, still more preferably 420 g/m ² or less. 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 , even more preferably 250 to 420 g/m ² , 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, still more preferably 200 μm or more, even more preferably 300 μm or more, particularly preferably 400 μm or more, and preferably 1000 μm or less, more preferably 800 μm or less. , 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, even more preferably 300 to 550 μm, even more preferably 400 to 550 μm.
The density of the laminated paper is preferably 0.40 g/cm ³ or more, more preferably 0.50 g/cm ³ or more, even more preferably 0.60 g/cm ³ or more, particularly preferably 0.70 g/cm ³ or more. , and preferably 1.10 g/cm ³ or less, more preferably 1.00 g/cm ³ or less, even more preferably 0.90 g/cm ³ or less, particularly preferably 0.85 g/cm ³ or less. 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 , and even more preferably 0.60 to 0.90 g/cm ³ . More preferably, it is 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 controlling the basis weight, thickness, density, etc. of the laminated paper within the above ranges, the laminated paper can exhibit better moldability.

In addition to the paper base material and the thermoplastic resin layer, the laminated paper may have other layers other than the paper base material and the thermoplastic resin layer depending on the application. At this time, at least one side of the paper base material may be in a laminated form such as paper base material/other layer/thermoplastic resin layer, or may be in a laminated form such as paper base material/thermoplastic resin layer/other layer. A laminated form such as this may also be used. In these laminated forms, the layers may be directly laminated or indirectly laminated. Other layers include a water-soluble polymer (polyvinyl alcohol (PVA), etc.) layer, a pigment coating layer containing pigment and a binder as main components, aluminum foil (Al foil), a metal vapor deposition layer, and an inorganic oxide (silica, Examples include a vapor deposited layer (such as alumina), a nylon layer, a barrier layer such as an EVOH (ethylene-vinyl alcohol copolymer) layer, a printed layer, and an adhesive layer.

Each layer constituting the laminated paper of this embodiment will be explained below.
[Paper base material]
In this embodiment, the paper base material is mainly paper, and the paper base material is not particularly limited as long as it is a commonly used paper containing plant-derived wood pulp as a main component.
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 having a multilayer structure (multilayer paper) having four or more pulp layers.
The paper base material has a number of layers of 4 or more, preferably 5 or more, and preferably has a number of 7 or less, and 6 or less. is more preferable, and it is particularly preferable that the number of layers is five. That is, the number of layers of the paper base material is preferably 5 to 7, more preferably 5 to 6.
Because the paper base material has a multilayer structure, the paper thickness and basis weight per layer are reduced, and variations in the paper base material as a whole (uneven distribution of pulp fibers in the paper base material) are suppressed, resulting in excellent impact resistance. Therefore, it is preferable. Further, by setting the number of layers within the above range, it is possible to easily adjust the interlayer strength to a desired range, and the ease of manufacture is excellent, which is preferable.

In this specification, the surface of the paper base material or laminated paper is the side opposite to the liquid-contacted surface, and is the side on which printing is normally applied. Further, the back side of the paper base material or laminated paper is the liquid contact side.
Furthermore, among the multiple paper layers, the surface layer is the pulp layer closest to the surface among the pulp layers, and the back layer is the pulp layer closest to the back surface among the pulp layers, and the inner layer is the pulp layer closest to the surface among the pulp layers. refers to the pulp layer sandwiched between the surface layer and the back layer.

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 or less, and preferably 20 g/m ² or more, more preferably 30 g/m ² or more, and even more preferably 40 g /m ² or more, more preferably 45 g/m ² or more. 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 , even more preferably 40 to 130 g/m ² , and 45 to 130 g/m ² . Good too.
By setting the basis weight of each pulp layer within the above range, it is possible to obtain a laminated paper with a high formation index, which is preferable.

The basis weight of the paper base material (all layers) is preferably 200 g/m ² or more, more preferably 250 g/m ² or more, even more preferably 300 g/m ² or more, and preferably 800 g/m ² or less, It is more preferably 600 g/m ² or less, still more preferably 500 g/m ² or less, even more preferably 400 g/m ² or less. That is, the basis weight of the paper base is preferably 200 to 800 g/m ² , more preferably 250 to 600 g/m ² , even more preferably 300 to 500 g/m ² , even more preferably 300 to 400 g/m ² be.
By setting the basis weight of the paper base material (all layers) within the above range, it is possible to exhibit excellent strength and moldability when used as a liquid container.

The thickness of the paper base material (all layers) is preferably 50 μm or more, more preferably 100 μm or more, even more preferably 200 μm or more, even 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, still more preferably 500 μm or less. That is, the thickness of the paper base material is preferably 50 to 600 μm, more preferably 100 to 550 μm, even more preferably 200 to 500 μm, even more preferably 300 to 500 μm.
The density of the paper base material (all layers) is preferably 0.4 g/cm ³ or more, more preferably 0.5 g/cm ³ or more, even more preferably 0.6 g/cm ³ or more, particularly preferably 0.7 g/cm 3 or more. cm ³ or more, and preferably 1.2 g/cm ³ or less, more preferably 1.1 g/cm ³ or less, even more preferably 1.0 g/cm ³ or less, even more preferably 0.9 g/cm ³ It is particularly preferably 0.8 g/cm ³ or less. That is, the density of the paper base material is preferably 0.4 to 1.2 g/cm ³ , more preferably 0.5 to 1.1 g/cm ³ , even more preferably 0.6 to 1.0 g/cm ³ , Even more preferably 0.7 to 0.9 g/cm ³ , even more preferably 0.7 to 0.8 g/cm ³ .
By setting the thickness and density of the paper base material (all layers) within the above range, it is possible to have excellent strength when used as a liquid container and to exhibit better moldability.

An adhesive component may be provided between each layer of the paper base material. Furthermore, an adhesive layer containing an adhesive component may be provided between each layer of the paper base material. 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 selected from the group consisting of starch, polyacrylamide, and polyamide-polyamine-epichlorohydrin resin, more preferably contains starch or polyacrylamide, and preferably contains starch. is even more preferable. By applying (coating) an adhesive component between each layer of the paper base material, the interlayer strength of the paper base material can be improved, and as a result, the laminated paper can have excellent formability and favorable interlayer peel strength. can.
The amount of adhesive component applied per each layer of the paper base material is adjusted to improve the interlayer strength of the paper base material, adjust the interlayer strength of the laminated paper having the paper base material to a desired range, and use the laminated paper. Preferably 2.0 g from the viewpoint of obtaining a liquid container that is easy to peel between layers when unsealing a liquid container made of paper, suppresses fuzzing of fibers on the surface of the peeled paper base material, and has a better texture when opened. /m ² or more, more preferably 2.5 g/m ² or more, even more preferably 3.0 g/m ² or more, and moderately low interlaminar strength and bending processability (ease of bending at ruled line areas). ) is preferably 10.0 g/m ² or less, more preferably 9.0 g/m ² or less, even more preferably 8.0 g/m ² or less. From the above viewpoint, the amount of the 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 , even more preferably It is 3.0 to 8.0 g/m ² .

(pulp)
It is preferable that the paper base material has pulp (preferably cellulose pulp) as a main component. Here, the main component refers to a component that accounts for 50% by mass or more based on 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, even more preferably 80% by mass or more, based on the total mass of the paper base material.

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

From the viewpoint of quality and cost, LBKP and NBKP are suitable as the pulp constituting the paper base material.
In this embodiment, the mass ratio of hardwood bleached kraft pulp and softwood bleached kraft pulp (LBKP:NBKP) of the paper base is preferably 10:90 to 100:0, more preferably 20:80 to 85:15, More preferably 25:75 to 75:25, even more preferably 25:75 to 70:30.
By setting the mass ratio of the bleached hardwood kraft pulp to the bleached softwood kraft pulp within the above range, excellent paper strength can be obtained when used as a liquid container, and the paper has excellent impact resistance, which is preferable. From the viewpoint of further improving drop resistance, LBKP:NBKP 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, and It is preferably 90% by mass or more, and particularly preferably 100% by mass. In addition, from the viewpoint of printability, the content of waste paper pulp and unbleached pulp is preferably 30% by mass or less, more preferably 20% by mass or less, still more preferably 10% by mass or less, even more preferably 5% by mass or less. , even more preferably less than 1% by mass, and particularly preferably not contained.

Known internal chemicals can be appropriately added to the paper base material. Examples of internal chemicals include sizing agents, fillers such as titanium dioxide, kaolin, talc, and calcium carbonate, paper strength enhancers, retention improvers, pH adjusters, freeness improvers, water resistance agents, softeners, and electrostatic charges. Antifoaming agents, antifoaming agents, slime control agents, dyes, pigments, etc. can be mentioned.

(Sizing agent)
Preferably, the paper base material contains a sizing agent. When the paper base material contains a sizing agent, 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 the sizing agent 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 sizing agents. Among these, alkyl ketene dimer sizing agents are preferred.

When the paper base material contains a sizing agent, the content of the sizing agent is preferably 0.001 parts by mass or more, more preferably 0.001 parts by mass or more, based on 100 parts by mass (dry mass) of the pulp contained in the paper base material. 01 parts by mass or more, 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, still more preferably 1.0 parts by mass or less, and even more preferably The amount is preferably 0.5 parts by mass or less, and even more preferably 0.3 parts by mass or less. That is, when the paper base material contains a sizing agent, the content of the sizing agent is preferably 0.001 to 5.0 parts by mass, based on 100 parts by mass (dry mass) of the pulp contained in the paper base material. More preferably 0.01 to 2.0 parts by weight, still more preferably 0.1 to 1.0 parts by weight, even more preferably 0.1 to 0.5 parts by weight, even more preferably 0.1 to 0.0 parts by weight. 3 parts by mass.
By setting the content of the sizing agent within the above range, the water resistance of the paper base material can be improved more effectively. Note that the content of the sizing agent in each layer of the paper base material is preferably the same from the viewpoint of production efficiency.

(Various internal additives)
In addition to the above-mentioned sizing agent, various internal additives may be added to the paper base material. Internal additives include, for example, paper strength enhancers, wet paper strength enhancers, retention improvers, freeness improvers, bulking agents, colored dyes, colored pigments, optical brighteners, pH adjusters, and pitch control agents. , preservatives, slime control agents, etc. Among these, it is preferable that at least one kind selected from a paper strength enhancer and a wet paper strength enhancer is added to the paper base material as an internal additive.

Specific examples of paper strength enhancers (dry paper strength enhancers) include polyacrylamide polymers, starches such as cationized starch, urea resins, polyamide-polyamine resins, polyethylene imine, polyamines, polyvinyl alcohol, polyethylene oxide, etc. Can be mentioned. These may be used alone or in combination of two or more. Among these, it preferably contains one or more selected from the group consisting of cationized starch and polyacrylamide-based polymers, and more preferably contains polyacrylamide-based polymers.
When the paper base material contains a paper strength enhancer, preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, based on 100 parts by mass (dry mass) of pulp fibers contained in the paper base material. , more preferably 0.2 parts by mass or more, even more preferably 0.3 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, still more preferably 1.0 parts by mass or less. It is 5 parts by mass or less. That is, when the paper base material contains a paper strength agent, preferably 0.01 to 5.0 parts by mass, more preferably 0 parts by mass, based on 100 parts by mass (dry mass) of pulp fibers contained in the paper base material. .1 to 3.0 parts by weight, more preferably 0.2 to 1.5 parts by weight, even more preferably 0.3 to 1.5 parts by weight. By setting the content of the paper strength enhancer within the above range, the strength of the paper base material can be increased more effectively.

Specific examples of wet paper strength agents include melamine resins, urea resins, polyamide-polyamine-epichlorohydrin resins, and the like. These may be used alone or in combination of two or more.
When the paper base material contains a wet paper strength agent, the content of the wet paper strength agent is preferably 0.01 parts by mass or more based on 100 parts by mass (dry mass) of the pulp contained in the paper base material. , 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, still more preferably 0.3 parts by mass or less. That is, when the paper base material contains a wet paper strength agent, the content of the wet paper strength agent is preferably from 0.01 to 100 parts by mass (dry mass) of the pulp contained in the paper base material. The amount is 1.0 parts by weight, more preferably 0.05 to 0.5 parts by weight, and even more preferably 0.05 to 0.3 parts by weight. By controlling the content of the wet paper strength enhancer within the above range, the wet strength of the paper base material can be increased more effectively.

In this embodiment, it is preferable to contain a polyacrylamide-based compound as an internal additive, and it is particularly preferable to contain a polyacrylamide-based compound as a paper strength enhancer.
The content of the polyacrylamide compound (preferably polyacrylamide paper strength enhancer) in the paper base material is preferably 0.05% by mass or more, may be 0.10% by mass or more, and may be 0.05% by mass or more, and may be 0.10% by mass or more. It may be 15% by mass or more, and may be 0.20% by mass or more, and preferably 0.50% by mass or less, and may be 0.40% by mass or less, and 0.30% by mass or less. It may be less than 0.25% by mass, or less than 0.25% by mass.
Addition of a polyacrylamide compound increases paper strength, but generally the formation index tends to decrease because the fibers aggregate. By setting the content of the polyacrylamide compound within the above range and using a paper base material having four or more layers, a decrease in the formation index is suppressed, and the paper has higher strength and impact resistance. This is preferable because it allows laminated paper with excellent properties to be obtained. From the viewpoint of achieving both drop resistance and vibration resistance, the content of the polyacrylamide compound (preferably polyacrylamide paper strength enhancer) in the paper base material is preferably 0.25% by mass or less. From the above viewpoint, the content of the polyacrylamide compound (preferably polyacrylamide paper strength enhancer) in the paper base material is preferably 0.05 to 0.50% by mass, more preferably 0.05 to 0.50% by mass. The amount is 40% by weight, more preferably 0.05 to 0.30% by weight, even more preferably 0.05 to 0.25% by weight.
The content of the polyacrylamide compound in the paper base material is measured by the method described in Examples.

From the viewpoint of increasing surface strength, the paper base material preferably has one or more selected from the group consisting of a surface sizing agent and a surface strength agent in addition to the internal additive. When the surface strength of the paper base material improves, when laminated paper is used as a liquid container, the liquid containers will rub against each other during transportation, and the thermoplastic resin layer and the surface of the paper base material, which will be described later, will peel off from the paper base material. The phenomenon can be suppressed.
Examples of the surface sizing agent include alkyl ketene dimer compounds.
Surface paper strength agents include oxidized starch, enzyme-treated starch, modified starch such as acid-treated starch, water-based resins such as polyvinyl alcohol (PVA), styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, etc. It will be done. These may be used alone or in combination of two or more. Among these, the surface paper strength agent preferably contains modified starch and a water-based resin such as polyvinyl alcohol, more preferably contains modified starch, and still more preferably contains oxidized starch.
When using one or more selected from the group consisting of surface size and surface paper strength agents in the size press process, from the viewpoint of more effectively increasing the adhesion with the thermoplastic resin layer described later, vinyl may be added to the size press liquid. It is preferable to use a mixture of adhesion aids such as resin, epoxy resin, urethane resin, polyester resin, and polyethyleneimine resin. That is, it is preferable that at least one surface of the paper base material is provided with one or more selected from the group consisting of a surface sizing agent and a surface strength agent and an adhesion aid. The above adhesion aids may be used alone or in combination of two or more. Among the above adhesion aids, the adhesion aid preferably contains one or more selected from the group consisting of vinyl resins and polyethyleneimine resins, and more preferably contains polyethyleneimine resins.
From the viewpoint of increasing the surface strength of the paper base material, the amount of surface sizing agent and surface strength agent applied is preferably 0.01 g/m ² or more, more preferably 0.1 g/m ² or more, in terms of solid content. More preferably, it is 0.5 g/m ² or more, even more preferably 0.8 g/m ² or more, and the surface strength of the paper base material is moderate, and the bending processability (ease of bending at ruled line parts) is achieved. ) is preferably 5.0 g/m ² or less, more preferably 3.0 g/m ² or less, even more preferably 1.5 g/m ² or less. From the above viewpoint, the amount of surface sizing agent and surface strength agent applied is preferably 0.01 to 5.0 g/m 2 , more preferably 0.1 to 3.0 g/m ² , and more preferably 0.01 to 5.0 g/m ² in terms of solid content. Preferably it is 0.5 to 1.5 g/m ² . When a surface sizing agent and a surface paper strength agent are used in combination, it is preferable that the amount of each applied is within the above range.
The amount of adhesion auxiliary agent applied is preferably 0.01 g/m ² or more, more preferably 0.05 g/m ² or more, in terms of solid content, from the viewpoint of improving adhesiveness with the thermoplastic resin layer described later. It is preferably 0.08 g/m ² or more, and from the viewpoint of recyclability of the laminated paper, it is preferable that the paper base material and the thermoplastic resin layer are easily separated, so it is preferably 5.0 g/m ² or less, More preferably 3.0 g/m ² or less, still more preferably 1.5 g/m ² or less, even more preferably 1.0 g/m ² or less, even more preferably 0.5 g/m ² or less, particularly preferably 0 .3g/ ^m2 or less. From the above viewpoint, the amount of adhesion aid applied is preferably 0.01 to 5.0 g/m ² , more preferably 0.01 to 3.0 g/m 2 , even more preferably 0.01 g/m ² in terms of solid content. ~1.5 g/m ² , even more preferably 0.01 to 1.0 g/m ² , even more preferably 0.01 to 0.5 g/m ² , particularly preferably 0.05 to 0.3 g/m 2 It is ² .

(Manufacturing method of paper base material)
The paper base material is preferably manufactured by a manufacturing method that includes a papermaking process in which four or more pulp layers, preferably five or more pulp layers are laminated. Multilayer paper, which has a structure in which many pulp layers are laminated, is used as a manufacturing technology for paperboard, etc., and generally, multilayer paper machines such as circular mesh paper machines and Fourdrinier paper machines are used. It can be manufactured by Further, the pH during papermaking may be in any of the acidic region (acidic papermaking), pseudo-neutral region (pseudo-neutral papermaking), neutral region (neutral papermaking), and alkaline region (alkaline papermaking). In addition, it may be a paper base material with a multilayer structure in which the contents of various additives are different in the inner layer and the outer layer (surface layer (printed layer) and back layer). It can be manufactured using a paper machine.

When making paper based paper, a known wet paper machine (for example, a fourdrinier paper machine, a gap former paper machine, a cylinder paper machine, a short wire paper machine, etc.) should be selected and used as appropriate. Bye. The paper layer formed by the paper machine is conveyed with felt and dried with a dryer. A multi-stage cylinder dryer may be used as a pre-dryer before drying.

From the viewpoint of increasing the surface strength of the paper base material, one or more types selected from the group consisting of the above surface sizing agent and surface paper strength agent are applied to one or both sides of the paper base material obtained as above. It is preferable that at least one selected from the group consisting of a surface sizing agent and a surface strength agent and an adhesion aid be mixed and applied, from the viewpoint of improving the adhesion with the thermoplastic resin layer described later. More preferred.
As a coating device, a known size press machine or the like can be used. Further, the paper base material obtained as described above may be subjected to surface treatment using a calendar to make the thickness and profile uniform. For the calendering process, a known calendering machine can be appropriately selected and used. Furthermore, a size press agent may be applied before calendering.

[Thermoplastic resin layer]
A thermoplastic resin layer is laminated on at least one side of the paper base material. The thermoplastic resin layer may be a single layer or a multilayer. Note that the thermoplastic resin layer may be laminated on both sides of the paper base material. In this specification, the phrase "laminated on a surface" means that it may be directly laminated or indirectly laminated via another layer. .

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

The thermoplastic resin layer may be formed of a single layer of a single resin, a single layer of a mixture of multiple resins, or a multilayer of these (for example, a single resin layer/a single resin layer). It may be formed as a single resin layer, a single resin layer/mixed resin layer, or a mixed resin layer/mixed resin layer.

The amount of the thermoplastic resin layer formed (basis weight) is not particularly limited, but is preferably 5 g/m ² or more, more preferably 10 g/m ² or more, and preferably 150 g/m ² or less, more preferably It is 100 g/m ² or less, more preferably 50 g/m ² or less, even more preferably 40 g/m ² or less. 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 , even more preferably 10 to 50 g/m ² , even more preferably 10 to 40 g/m ² It is.
The 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, still more preferably 50 μm or less, and even more preferably It is 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, even more preferably 10 to 40 μm.
In addition, the amount and thickness of the thermoplastic resin layer formed above means the amount and thickness formed on one side, and when forming on both sides, the amount and thickness of the thermoplastic resin layer formed on each side are as described above. It is preferable that it is in the range of . For the front (printed side) and back side (liquid wetted side), the amount and thickness of thermoplastic resin formed on the back side (liquid wetted side) is smaller than the amount and thickness of thermoplastic resin formed on the front side (printed side). It is preferable to make it large. This prevents the contents from penetrating into the paper base material and suppresses leakage of the contents and bulging due to a decrease in the strength of the paper base material.
The thickness of the thermoplastic resin layer on the surface (printing surface) is preferably 5 μm or more, more preferably 10 μm or more, and preferably 40 μm or less, more preferably It is 30 μm or less, more preferably 25 μm or less. From the above viewpoint, the thickness of the thermoplastic resin layer on the surface (printed surface) is preferably 5 to 40 μm, more preferably 10 to 30 μm, and still more preferably 10 to 25 μm.
The thickness of the thermoplastic resin layer on the back surface (liquid contact 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 has excellent processability. From the viewpoint of ease of obtaining laminated paper, the thickness is preferably 50 μm or less, more preferably 40 μm or less. From the above viewpoint, the thickness of the thermoplastic resin layer on the back surface (liquid contact surface) is preferably 5 to 50 μm, more preferably 15 to 40 μm, and still more preferably 20 to 40 μm.
From the above viewpoint, the ratio (back surface/front surface) of the thickness of the thermoplastic resin layer on the back surface (liquid contact surface) to the thickness of the thermoplastic resin layer on the front surface (printed surface) is preferably 1.2 or more, more preferably is 1.4 or more, and preferably 2.5 or less, more preferably 2.0 or less. From the above viewpoint, the thickness ratio (back surface/front surface) of the thermoplastic resin layer is preferably 1.2 to 2.5, more preferably 1.4 to 2.0. The ratio of the amount of thermoplastic resin layer formed (back side/front side) is also preferably within the same range as above.
By setting the amount and thickness of the thermoplastic resin layer within the above range, it is possible to prevent the liquid filled in the container from penetrating the paper base material, and also improve the suitability for molding into liquid containers. You can also do that.

[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 method for producing laminated paper preferably includes a paper-making process of a paper base material and a laminating process of laminating a thermoplastic resin layer on at least one surface of the paper base material.

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

In the paper making process, it is preferable to make the paper base material using a multilayer paper machine. The paper making process is as described above.

[Liquid container]
The laminated paper of this embodiment is preferably for liquid containers. The present invention also provides a blank sheet or a liquid container using the above-mentioned laminated paper. As a method for producing the blank sheet and the liquid container, any known method can be appropriately selected and used.

The laminated paper of this embodiment can be used for various purposes such as liquid containers such as milk cartons, paper cups, coffee containers, aseptic containers, paper containers such as foam cups, ice cups, insulation cups, and packaging containers, as well as packaging materials and insulation materials. It can be used for. Among these, the laminated paper of this embodiment is suitable for use in liquid containers. The present invention also provides a liquid container using the above-mentioned laminated paper. As a method for manufacturing the liquid container, any known method can be selected and used as appropriate.
The shape of the liquid container is not particularly limited, and examples include a roof-shaped container (gable top), a rectangular parallelepiped container (brick, straight, flat top), a triangular pyramid-shaped container, a cup container, a slant-top container, a regular tetrahedral container, etc. It will be done. Another embodiment of the invention is therefore the use of the above 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 (printed surface) of laminated paper is printed, ruled and punched, and then folded, and then the container is made. Delivered in a folded carton with vertical frame sealing. The provided folding cartons go through the stages of bottom sealing, sterilization, filling, and top sealing, and are distributed as gable-top liquid-filled products.
The liquid contained in the liquid container may be either food or non-food.The liquid contained in the liquid container is not particularly limited, and may include alcoholic beverages such as sake, shochu, and wine; milk, etc. Milk drinks; Juice, coffee, tea, black tea, and other beverages; Favorite foods (yoghurt, jelly, pudding, etc.), foods with liquids such as prepared foods; Pharmaceuticals; Car wax, shampoo, conditioner, detergent, bath salts, hair dye and chemical products such as toothpaste.

The barrier laminate of the present invention will be described in more detail with reference to Examples below, but the present invention is not limited thereto. Note that "parts" and "%" in Examples and Comparative Examples indicate "parts by mass" and "% by mass", respectively, unless otherwise specified.

[Measuring method]
The measurement methods carried out for paper base materials and laminated paper are shown below. Note that unless otherwise specified, measurements were performed in an environment at a temperature of 23° C.±1° C. and a relative humidity of 50±2% as described in JIS P 8111:1998.
(1) Basis weight of paper base material and laminated paper The basis weight of the paper base material and laminated paper was measured according to JIS P 8124:2011.
(2) Thickness of Thermoplastic Resin Layer A 100 mm x 100 mm piece of laminated paper was cut out, and the thermoplastic resin layer was peeled off from the cut test piece, and then immersed in a cellulase solution. After sufficient immersion, the test piece was further immersed in a copper ethylene diamine solution, and only the thermoplastic resin (PE coat) was collected. After washing with water and drying, it was accurately weighed, and the thickness of the thermoplastic resin layer was calculated from the density of the thermoplastic resin used (density of polyethylene = 0.923 g/cm ³ ).

[Example 1]
(Paper base material)
A pulp slurry was obtained by beating 60 parts of LBKP and 40 parts of NBKP as pulp raw materials using a double disc refiner. For 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.30 parts of polyacrylamide-based paper strength agent (in terms of solid content) was added as an internal paper strength enhancer, and an alkyl ketene dimer-based paper strength agent was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts of a sizing agent (in terms of solid content) and 0.10 parts of a polyamide-polyamine-epichlorohydrin wet paper strength enhancer (in terms of solid content) as a wet paper strength enhancer. . Using this stock, paper was made using a multi-layer Fourdrinier paper machine in a five-layer process. During the papermaking process, 7.5 g/m ² (solid content equivalent) of potato starch was sprayed between each layer using an interlayer spray, and after the 5 layers were combined, 1.5 g/m 2 of oxidized starch was applied to both sides of the paper base using a size press. 0 g/m ² (in terms of solid content) and 0.10 g/m ² (in terms of solid content) of polyethyleneimine were applied, and calendering was performed to obtain a paper base material having a basis weight of 267 g/m ² . The paper base material obtained here has different smoothness on the front and back sides. The highly smooth surface was defined as the front surface (printed surface), and the low smooth surface was defined as the back surface (liquid contact surface). The basis weight of each layer of the paper base material in Table 1 includes the potato starch sprayed between each layer, the oxidized starch and polyethyleneimine coated on the surface layer and the back layer.
In addition, the Oken type smoothness of the paper base material is compared to the wire surface (the surface where the paper layer is in contact with the wire when making the paper base material) when paper is made from paper stock with the same recipe as above. The felt surface (anti-wire surface, the surface where the paper layer comes into contact with the felt when the paper base material is made) tends to be higher. This is because the felt surface has more fine fibers and there are fewer gaps between the fibers, and the felt surface is easier to dehydrate and has a more uniform surface.

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

(Paper container)
After performing offset printing on the surface (front surface, printing surface) of the obtained laminated paper, ruled lines were provided at necessary locations and punched into a predetermined shape to obtain a blank material. Next, a part of the resin material of the blank material was melted using a frame seal, and the body portion was bonded together to obtain a cylindrical sleeve. Next, this cylindrical sleeve was supplied to a liquid filling machine, and after forming a bottom part on the filling machine, 1000 mL of water was filled and the top part was sealed to obtain a gable-top paper container with an inner capacity of 1000 mL. Ta.

[Example 2]
A pulp slurry was obtained by beating 50 parts of LBKP and 50 parts of NBKP as pulp raw materials using a double disc refiner. For 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.30 parts of polyacrylamide-based paper strength agent (in terms of solid content) was added as an internal paper strength enhancer, and an alkyl ketene dimer-based paper strength agent was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts of a sizing agent (in terms of solid content) and 0.10 parts of a polyamide-polyamine-epichlorohydrin wet paper strength enhancer (in terms of solid content) as a wet paper strength enhancer. . Using this stock, paper was made using a multi-layer Fourdrinier paper machine in a five-layer process. During the papermaking process, 7.5 g/m ² (solid content equivalent) of potato starch was sprayed between each layer using an interlayer spray, and after the 5 layers were combined, 1.5 g/m 2 of oxidized starch was applied to both sides of the paper base using a size press. 0 g/m ² (in terms of solid content) and 0.10 g/m ² (in terms of solid content) of polyethyleneimine were applied, and calendering was performed to obtain a paper base material having a basis weight of 333 g/m ² . The basis weight of each layer of the paper base material in Table 1 includes the potato starch sprayed between each layer, the oxidized starch and polyethyleneimine coated on the surface layer and the back layer.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated on the obtained paper base material so that the basis weight met the conditions shown in Table 1.

[Example 3]
A pulp slurry was obtained by beating 30 parts of LBKP and 70 parts of NBKP as pulp raw materials using a double disc refiner. For 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.50 parts of polyacrylamide paper strength agent (in terms of solid content) was added as an internal paper strength enhancer, and an alkyl ketene dimer system was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts of a sizing agent (in terms of solid content) and 0.10 parts of a polyamide-polyamine-epichlorohydrin wet paper strength enhancer (in terms of solid content) as a wet paper strength enhancer. . Using this stock, paper was made using a multi-layer Fourdrinier paper machine in a five-layer process. During the papermaking process, 7.5 g/m ² (solid content equivalent) of potato starch was sprayed between each layer using an interlayer spray, and after the 5 layers were combined, 1.5 g/m 2 of oxidized starch was applied to both sides of the paper base using a size press. 0 g/m ² (in terms of solid content) and 0.10 g/m ² (in terms of solid content) of polyethyleneimine were applied, and calendering was performed to obtain a paper base material having a basis weight of 337 g/m ² . The basis weight of each layer of the paper base material in Table 1 includes the potato starch sprayed between each layer, the oxidized starch and polyethyleneimine coated on the surface layer and the back layer.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated on the obtained paper base material so that the basis weight met the conditions shown in Table 1.

[Example 4]
A pulp slurry was obtained by beating 65 parts of LBKP and 35 parts of NBKP as pulp raw materials using a double disc refiner. For 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.20 parts of polyacrylamide-based paper strength agent (in terms of solid content) was added as an internal paper strength enhancer, and an alkyl ketene dimer-based paper strength agent was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts of a sizing agent (in terms of solid content) and 0.10 parts of a polyamide-polyamine-epichlorohydrin wet paper strength enhancer (in terms of solid content) as a wet paper strength enhancer. . Using this stock, paper was made using a multi-layer Fourdrinier paper machine in a five-layer process. During the papermaking process, 7.5 g/m ² (solid content equivalent) of potato starch was sprayed between each layer using an interlayer spray, and after the 5 layers were combined, 1.5 g/m 2 of oxidized starch was applied to both sides of the paper base using a size press. 0 g/m ² (in terms of solid content) and 0.10 g/m ² (in terms of solid content) of polyethyleneimine were applied, and calendering was performed to obtain a paper base material having a basis weight of 338 g/m ² . The basis weight of each layer of the paper base material in Table 1 includes the potato starch sprayed between each layer, the oxidized starch and polyethyleneimine coated on the surface layer and the back layer.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated on the obtained paper base material so that the basis weight met the conditions shown in Table 1.

[Example 5]
A pulp slurry was obtained by beating 50 parts of LBKP and 50 parts of NBKP as pulp raw materials using a double disc refiner. For 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.10 parts of polyacrylamide-based paper strength agent (in terms of solid content) was added as an internal paper strength enhancer, and an alkyl ketene dimer-based paper strength agent was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts of a sizing agent (in terms of solid content) and 0.10 parts of a polyamide-polyamine-epichlorohydrin wet paper strength enhancer (in terms of solid content) as a wet paper strength enhancer. . Using this stock, paper was made using a multi-layer Fourdrinier paper machine in a five-layer process. During the papermaking process, 7.5 g/m ² (solid content equivalent) of potato starch was sprayed between each layer using an interlayer spray, and after the 5 layers were combined, 1.5 g/m 2 of oxidized starch was applied to both sides of the paper base using a size press. 0 g/m ² (in terms of solid content) and 0.10 g/m ² (in terms of solid content) of polyethyleneimine were applied, and calendering was performed to obtain a paper base material with a basis weight of 352 g/m ² . The basis weight of each layer of the paper base material in Table 1 includes the potato starch sprayed between each layer, the oxidized starch and polyethyleneimine coated on the surface layer and the back layer.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated on the obtained paper base material so that the basis weight met the conditions shown in Table 1.

[Example 6]
A pulp slurry was obtained by beating 60 parts of LBKP and 40 parts of NBKP as pulp raw materials using a double disc refiner. For 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.30 parts of polyacrylamide-based paper strength agent (in terms of solid content) was added as an internal paper strength enhancer, and an alkyl ketene dimer-based paper strength agent was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts of a sizing agent (in terms of solid content) and 0.10 parts of a polyamide-polyamine-epichlorohydrin wet paper strength enhancer (in terms of solid content) as a wet paper strength enhancer. . Using this stock, paper was made using a multi-layer Fourdrinier paper machine in a five-layer process. During the papermaking process, 3.5 g/m ² (solid content equivalent) of potato starch is sprayed between each layer using an interlayer spray, and after the 5 layers are combined, 1.5 g/m 2 of oxidized starch is applied to both sides of the paper base using a size press. 0 g/m ² (in terms of solid content) and 0.10 g/m ² (in terms of solid content) of polyethyleneimine were applied, and calendering was performed to obtain a paper base material having a basis weight of 333 g/m ² . The basis weight of each layer of the paper base material in Table 1 includes the potato starch sprayed between each layer, the oxidized starch and polyethyleneimine coated on the surface layer and the back layer.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated on the obtained paper base material so that the basis weight met the conditions shown in Table 1.

[Comparative example 1]
A pulp slurry was obtained by beating 50 parts of LBKP and 50 parts of NBKP as pulp raw materials using a double disc refiner. For 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.60 parts of cationized starch (in terms of solid content) was added as an internal paper strength enhancer, and 0 part of an alkyl ketene dimer-based sizing agent was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts (in terms of solid content) and 0.10 parts (in terms of solid content) of a polyamide-polyamine-epichlorohydrin wet paper strength enhancer as a wet paper strength enhancer. Using this paper stock, paper was made using a four-drinier paper machine with three layers. During the papermaking process, 7.5 g/m ² (solid content equivalent) of potato starch is sprayed between each layer using an interlayer spray, and after the three layers are combined, 1.5 g/m 2 of oxidized starch is applied to both sides of the paper base using a size press. 0 g/m ² (in terms of solid content) and 0.10 g/m ² (in terms of solid content) of polyethyleneimine were applied, and calendering was performed to obtain a paper base material having a basis weight of 323 g/m ² . The basis weight of each layer of the paper base material in Table 1 includes the potato starch sprayed between each layer, the oxidized starch and polyethyleneimine coated on the surface layer and the back layer.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated on the obtained paper base material so that the basis weight met the conditions shown in Table 1.

[Comparative example 2]
A pulp slurry was obtained by beating 65 parts of LBKP and 35 parts of NBKP as pulp raw materials using a double disc refiner. For 100 parts of pulp (dry mass) in the obtained pulp slurry, 0.60 parts of cationized starch (in terms of solid content) was added as an internal paper strength enhancer, and 0 part of an alkyl ketene dimer-based sizing agent was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts (in terms of solid content) and 0.10 parts (in terms of solid content) of a polyamide-polyamine-epichlorohydrin wet paper strength enhancer as a wet paper strength enhancer. Using this stock, paper was made using a four-drinier paper machine with three layers. During the papermaking process, 7.5 g/m ² (solid content equivalent) of potato starch is sprayed between each layer using an interlayer spray, and after the three layers are combined, 1.5 g/m 2 of oxidized starch is applied to both sides of the paper base using a size press. 0 g/m ² (in terms of solid content) and 0.10 g/m ² (in terms of solid content) of polyethyleneimine were applied, and calendering was performed to obtain a paper base material having a basis weight of 333 g/m ² . The basis weight of each layer of the paper base material in Table 1 includes the potato starch sprayed between each layer, the oxidized starch and polyethyleneimine coated on the surface layer and the back layer.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that a thermoplastic resin layer was laminated on the obtained paper base material so that the basis weight met the conditions shown in Table 1.

The following evaluations were performed on the laminated papers and liquid containers obtained in Examples and Comparative Examples.
(Conformation index)
Equipment: M/K Systems 3D Sheet Analyzer Model M/K 975
Measurement conditions: Sensitivity RANGE 1, aperture 2.0mm
A measurement sample (laminated paper) of A4 size was set in the device, and after measurement under the above conditions, the displayed value was taken as a FORMATION INDEX.
In addition, in the above measuring device, the amount of transmitted light is measured while the rotating drum rotates, the data of the amount of transmitted light is converted into a histogram, and the degree of dispersion of the amount of transmitted light is automatically calculated from the obtained histogram. A larger value means higher uniformity.

(Drop test)
The gable-top paper containers obtained in Examples and Comparative Examples were filled with 1,000 mL of water and repeatedly dropped from a height of 30 cm onto a concrete floor with the bottom facing vertically downward until liquid leakage occurred. The number of times required was counted. The test was conducted 8 times each, and the drop resistance was evaluated using the following evaluation criteria based on the average number of times until liquid leakage occurred.
A: Average number of falls is more than 20 times B: More than 15 times and less than 20 times C: More than 10 times and less than 15 times D: Less than 10 times

(Vibration test)
A vibration test was conducted according to JIS Z 0200:2013 and JIS Z 0232:2020 8.4.4.
After placing the samples in a crate containing 12 bottles and applying vibration only in the vertical direction (random vibration: 2 to 200 Hz) in 15 minute increments for up to 30 minutes, the number of samples that leaked was counted, and the vibration resistance was determined as follows. It was evaluated using the following evaluation criteria.
A: 1 or less cartons with liquid leakage B: 2 to 5 cartons C: 6 to 9 cartons D: 10 or more cartons

(Method for measuring polyacrylamide compound content)
The content (in terms of solid content) of polyacrylamide compounds contained in the paper base material was measured using a pyrolysis GC/MS analyzer.
[Measurement condition]
Equipment used: GC8890/MSD5977B manufactured by Agilent Technologies Co., Ltd.
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 held for 15 minutes Pyrolysis device: Frontier Lab Co., Ltd., PY-3030D, decomposition temperature 500°C
Analysis: Calculate the content of polyacrylamide compounds using selected ion m/z 125

From Table 1, in the laminated papers of Examples 1 to 6, in which the paper base material is a paper base material having a number of layers of 4 or more, ie, 5 layers, and the formation index of the laminated paper is 25 or more, the laminated paper The liquid container made from this material had excellent drop resistance, vibration resistance, and impact resistance.
On the other hand, in Comparative Example 1, in which the paper base material is a paper base material having three layers, even if the formation index is 25 or more, the liquid containers made from the laminated paper are similar to Examples 1 to 6. It was inferior in drop resistance and vibration resistance, and inferior in impact resistance. Furthermore, in the case of the laminated paper of Comparative Example 2 in which the paper base material is a paper base material having three layers and has a formation index of less than 25, the liquid container made from the laminated paper is similar to that of Example 1. -6 and Comparative Example 1, the drop resistance and vibration resistance were inferior, and the impact resistance was inferior.

The laminated paper according to this embodiment has water resistance, and liquid containers made from the laminated paper have excellent impact resistance (particularly drop resistance and vibration resistance), and can be used as milk cartons, paper cups, coffee containers, aseptic containers, etc. It can be suitably used as liquid containers such as containers, paper containers such as foam cups, ice cups, insulation cups, packaging containers, as well as packaging materials, insulation materials, etc.

10 Paper base material 20 Thermoplastic resin layer 100 Laminated paper

Claims

A laminated paper comprising a paper base material and a thermoplastic resin layer laminated on at least one surface of the paper base material,
The paper base material is a paper base material having a number of layers of 4 or more,
the laminated paper has a formation index of 25 or more;
laminated paper.
The laminated paper according to claim 1, wherein the basis weight of each layer of the paper base material is 150 g/ m2 or less.
The laminated paper according to claim 1 or 2, wherein the content of the polyacrylamide compound in the paper base is 0.05% by mass or more and 0.50% by mass or less.
Any one of claims 1 to 3, 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 or more and 10 g/m 2 or less. Laminated paper according to item 1.
The laminated paper according to claim 4, wherein the adhesive component includes starch.
According to any one of claims 1 to 5, wherein at least one surface of the paper base material is provided with one or more selected from the group consisting of a surface sizing agent and a surface strength agent and an adhesive aid. Laminated paper as described.
The laminated paper according to claim 6, wherein the adhesion aid comprises a polyethyleneimine resin.
The laminated paper according to claim 6 or 7, wherein the amount of the adhesion aid applied is 0.01 g/m 2 or more and 1.0 g/m 2 or less.
Claim 1: The paper base material has thermoplastic resin layers on both sides, 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. The laminated paper according to any one of items 1 to 8.
The laminated paper according to any one of claims 1 to 9, which is used for liquid containers.
A liquid container made of the laminated paper according to any one of claims 1 to 10.