JP2024003759A - Laminate paper and liquid container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide laminate paper that has superior printability and prevents the occurrence of paper powder, and a liquid container made from the laminate paper.

SOLUTION: Laminate paper includes a paper substrate, and a thermoplastic resin layer laminated on at least one side of the paper substrate. In pulp fibers constituting the paper substrate, fine fibers with an average fiber length of 0.2 mm or less constitute 20% or less of the total pulp fibers. The level of whiteness is 70% or more.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

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

BACKGROUND ART As paper containers for liquids used in milk cartons and the like, containers are used in which water resistance is imparted to the paper base material constituting the paper container by 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 discloses a laminated paper in which a resin film is laminated on the surface of a base paper, and the resin film is a nylon resin film with a metal vapor deposited layer formed on the surface. There is. Patent Document 1 aims to provide a laminated paper that does not easily bend even when placed in a humid usage environment.

JP 2018-1754 Publication

When a liquid container made from laminated paper is opened, if a large amount of paper dust is generated from the exposed paper base material of the laminated paper, there is a problem in that the paper dust mixes into the contents of the liquid container.
However, in the laminated paper described in Patent Document 1, such problems were not considered.

The present invention has been made in view of the above situation. That is, an object of the present invention is to provide a laminated paper that has excellent printability and suppresses the generation of paper dust, and a liquid container using the laminated paper.

The present inventors have determined the number ratio of fine fibers of pulp fibers constituting the paper base material in a laminated paper having a paper base material and a thermoplastic resin layer laminated on at least one surface of the paper base material. It has been found that by setting the whiteness within a specific range and making the whiteness of the laminated paper above a specific value, a laminated paper with excellent printability and suppressed generation of paper dust can be provided.

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 pulp fibers constituting the paper base material have an average fiber length of A laminated paper in which the number ratio of fine fibers of 0.2 mm or less is 20% or less and the whiteness is 70% or more.
[2] The laminated paper according to [1], which has an interlayer strength of 200 kPa or more and 450 kPa or less.
[3] The laminated paper according to [1] or [2], wherein the geometric mean of the tear strength in the longitudinal direction and the tear strength in the transverse direction is 2000 mN or more and 6500 mN or less.
[4] The laminated paper according to any one of [1] to [3], wherein the paper base material has four or more layers.
[5] 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 [ 4]. The laminated paper according to any one of [4].
[6] The laminated paper according to [5], wherein the adhesive component contains starch.
[7] The method according to [1] to [6], 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.
[8] The laminated paper according to [7], wherein the adhesive aid contains a polyethyleneimine resin.
[9] The laminated paper according to [7] or [8], wherein the amount of the adhesive aid applied is 0.01 g/m ² or more and 1.0 g/m ² or less.
[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].

According to the present invention, there are provided a laminated paper with excellent printability and suppressed generation of paper dust, and a liquid container using the laminated paper.

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

Embodiments of the present invention will be specifically described below. 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 addition, in this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as the lower limit value and upper limit value. When numerical ranges are described in stages, the upper and lower limits of each numerical range can be combined arbitrarily.

[Laminated paper]
The laminated paper of the present 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, in which pulp fibers constituting the paper base material are The number ratio of fine fibers having an average fiber length of 0.2 mm or less is 20% or less, and the whiteness is 70% or more.
According to this embodiment, a laminated paper with excellent printability and suppressed generation of paper dust is provided. Furthermore, the present invention has the additional effects of excellent adhesion to the heat-sealing layer and excellent heat-sealability. Although the mechanism that produces this effect is not certain, it is presumed as follows.
Fibers with a short fiber length, such as fine fibers, have less entanglement (bonding) between fibers and are easier to separate than fibers with a long fiber length. By setting the number ratio of fine fibers in the pulp fibers that make up the paper base material to 20% or less, paper dust is prevented from being generated from the paper base material due to the detachment of fine fibers when exposed when the liquid container is opened. It is thought that it has been suppressed. Further, it is considered that by setting the whiteness to 70% or more, the contrast between the printed portion and the non-printed portion was improved, and a laminated paper with excellent printability was obtained.
Note that the effects of the present invention are not limited to the above mechanism.

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 whiteness of the laminated paper is 70% or more. Note that the whiteness should be at least 70% on one side of the laminated paper, and from the viewpoint of printing suitability, the whiteness on the printing side (the side opposite to the surface in contact with liquid) should be 70% or more. % or more, and more preferably the whiteness of both the printed surface and the liquid contact surface is 70% or more.
The whiteness of the laminated paper is 70% or more, preferably 75% or more, more preferably 78% or more, and the upper limit is not particularly limited, but from the viewpoint of ease of manufacture, it is preferably 95% or less, More preferably, it is 90% or less.
In order to bring the whiteness within the desired range, an example of a method is to use bleached pulp such as bleached hardwood kraft pulp or bleached softwood kraft pulp as the raw material pulp for the paper base material described below. On the other hand, when deinked pulp, old cardboard, etc. are used, the whiteness tends to decrease.
The whiteness of the laminated paper is measured by the method described in Examples.

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.
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 300 g/m ² or more, and preferably 600 g/m ² or less, more preferably It is 500 g/m ² or less, more preferably 450 g/m ² or less.
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.
By setting the thickness, basis weight, etc. of the laminated paper within the above range, the rigidity when molded into a liquid container can be set within an appropriate range. Further, by controlling the thickness, basis weight, etc. of the laminated paper within the above range, the laminated paper can exhibit better moldability.

The interlaminar strength of the laminated paper is preferably 200 kPa or more, more preferably 225 kPa or more, even more preferably 250 kPa or more, and preferably 450 kPa or less, more preferably 400 kPa or less, still more preferably 375 kPa or less, even more preferably 350 kPa. It is as follows.
By setting the interlaminar strength of the laminated paper within the above range, the paper strength required for liquid containers can be obtained, and it is also easy to peel between the layers when opening the liquid container, and the fibers become fluffy on the surface of the peeled paper base material. This is preferable because it suppresses the generation of paper dust.
In order to keep the interlaminar strength within the above range, it is necessary to adjust the adhesion component between the layers during multilayer papermaking, such as adjusting the amount and concentration of starch when producing the paper base material, and the paper base material. Examples include a method of adjusting the press pressure during dehydration during papermaking, and a method of adjusting the degree of beating of the pulp constituting the paper base material. By increasing the amount or concentration of the interlayer adhesive component, the interlayer strength tends to become stronger. Furthermore, by increasing the press pressure during dewatering during paper making, interlaminar strength tends to become stronger. Furthermore, by increasing the degree of beating of the pulp constituting the paper base material, interlaminar strength tends to become stronger.
Note that the interlayer strength of the laminated paper is the interlayer strength in the Z-axis direction (Z-axis strength) in accordance with JAPAN TAPPI 18-1:2007, and is specifically measured by the method described in Examples.

The geometric mean of the tear strength in the longitudinal direction and the tear strength in the transverse direction of the laminated paper of this embodiment is preferably 2000 mN or more, more preferably 2500 mN or more, still more preferably 3000 mN or more, even more preferably 4000 mN or more. , and preferably 6500 mN or less, more preferably 6300 mN or less, and even more preferably 6000 mN or less. In this specification, the "longitudinal direction" of laminated paper means a direction corresponding to the papermaking direction (MD direction) of the paper base material. Moreover, the "lateral direction" of laminated paper means the direction corresponding to the width direction (CD direction) of the paper base material.
By setting the geometric mean of the tear strength in the longitudinal direction and the tear strength in the transverse direction of the laminated paper within the above range, the paper strength required for the liquid container can be obtained. In addition, tear strength measures the resistance to tearing, which means the ease with which each pulp fiber can be pulled out. If the pulp is difficult to pull out, the resistance increases and the tear strength increases. When opening a package, it is thought that if the pulp is easy to pull out to some extent and the resistance is low, the package can be opened without applying force. This is preferable because the liquid container can be easily opened when the liquid container is opened, the fluffing of the fibers on the surface of the peeled paper base material is suppressed, and the generation of paper dust is suppressed.
Further, the tear strength in the longitudinal direction is preferably 1800 mN or more, more preferably 2000 mN or more, even more preferably 2500 mN or more, even more preferably 3500 mN or more, and preferably 6500 mN or less, more preferably 6000 mN or less, and even more preferably is 5700 mN or less.
The tear strength in the transverse direction is preferably 2000 mN or more, more preferably 2500 mN or more, even more preferably 3000 mN or more, even more preferably 4000 mN or more, and preferably 6500 mN or less, more preferably 6400 mN or less, even more preferably 6300 mN. It is as follows.
Note that the tear strength in the longitudinal direction and the tear strength in the transverse direction of the laminated paper are measured in accordance with JIS P 8116:2000.
The tear strength of laminated paper can be adjusted by adjusting the amount of paper strength enhancer added, by adjusting the softness of the pulp that makes up the paper base, and by adjusting the type and blending ratio of the pulp that makes up the paper base. Examples include methods for adjusting. It is preferable to add the paper strength agent in an appropriate amount, but if the amount added is too large, the tear strength may decrease. The lower the beating degree of the pulp constituting the paper base material, the stronger the tear strength tends to be. Furthermore, when the blending amount of bleached softwood kraft pulp (NBKP) as the pulp constituting the paper base material is increased, the tear strength tends to become stronger.

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. Among these, from the viewpoint of ease of manufacture, it is preferable that no other layer is included.

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 preferably has a multilayer structure having two or more pulp layers, and preferably has a multilayer structure having three or more pulp layers. That is, the paper base material is preferably composed of paper with a multilayer structure (multilayer paper) having two or more pulp layers, and preferably composed of paper with a multilayer structure (multilayer paper) having three or more pulp layers. is preferred. The basis weight of each pulp layer may be the same or different. In this specification, the outer layer of the paper base material refers to the two outermost pulp layers of the multilayer structure, and the inner layer refers to the pulp layer sandwiched between them.
The paper base material preferably has a number of layers of 3 or more, more preferably 4 or more, and preferably 7 or less, and 5 or less. It is more preferable to have 5 layers, and it is particularly preferable to have 5 layers.
Because the paper base material has a multilayer structure, the paper thickness per layer becomes thinner, and when the paper base material is made into paper, fine fibers are easily pulled out of the wire, and the amount of fine fibers contained in the paper base material is reduced. Therefore, it is preferable. Further, by setting the number of layers within the above range, it is easy to adjust the interlaminar strength and tear strength to a desired range, and it is preferable because it is easy to manufacture.

The thickness of the paper base material is preferably 50 μm or more, more preferably 100 μm or more, even more preferably 200 μm or more, particularly preferably 300 μm or more, most preferably 350 μm or more, and preferably 600 μm or less, more preferably 500 μm or less. , more preferably 470 μm or less, even more preferably 450 μm or less.
Further, the basis weight of the paper base material is preferably 50 g/m ² or more, more preferably 100 g/m ² or more, even more preferably 200 g/m ² or more, particularly preferably 250 g/m ² or more, and preferably is 600 g/m ² or less, more preferably 500 g/m ² or less, even more preferably 400 g/m ² or less.
Furthermore, the density of the paper base material 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 and 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 or less, particularly preferably is 0.8 g/cm ³ or less.
By setting the thickness, basis weight, etc. of the paper base material within the above range, it is possible to have excellent strength when used as a liquid container, and to exhibit better moldability.

When the paper base material has two or more pulp layers, an adhesive component may be provided between each layer of the paper base material. Furthermore, an adhesive layer containing an adhesive component may be present between each layer of the paper base material. Examples of adhesive components include starch, polyacrylamide, polyamide-polyamine-epichlorohydrin resin, and the like. The adhesive component is preferably 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. More preferred.
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 interlayer strength of the laminated paper having the paper base material can be adjusted to a desired range. When a liquid container made of the laminated paper is adjusted, the layers easily peel off, and the fluffing of fibers on the surface of the peeled paper base material is suppressed, thereby further suppressing the generation of paper dust.
The amount of the 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/m2 or ^more , from the viewpoint of easy separation between layers when opening a liquid container made of paper, suppressing fluffing of fibers on the surface of the separated paper base material, and further suppressing the generation of paper dust. , more preferably 2.5 g/m ² or more, still more preferably 3.0 g/m ² or more, and from the viewpoint of appropriately lowering interlaminar strength and increasing bending suitability (ease of bending at ruled line portions). Then, it is preferably 10 g/m ² or less, more preferably 9.0 g/m ² or less, even more preferably 8.0 g/m ² or less.

(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 to softwood bleached kraft pulp (LBKP:NBKP) of the paper base is preferably 50:50 or more, more preferably 60:40 or more, and still more preferably 65:35. That's all. By setting the mass ratio of hardwood kraft pulp and softwood kraft pulp within the above range, the number ratio of fine fibers in the pulp fibers constituting the paper base material can be set within the desired range, and the generation of paper dust can be suppressed. This is preferable because it can be suppressed. Further, the mass ratio (LBKP:NBKP) of the bleached hardwood kraft pulp and the bleached softwood kraft pulp of the paper base material is preferably 100:0 or less, more preferably 90:10 or less, and still more preferably 85:15 or less. By setting the mass ratio of the hardwood kraft pulp to the softwood kraft pulp within the above range, the number of long fibers increases and the entanglement of the fibers becomes stronger, thereby improving the tear strength of the paper base material. By using such a paper base material, a laminated paper with excellent drop resistance can be obtained.
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. That is, from the viewpoint of keeping the whiteness within the desired range, 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, and even more preferably is 5% by mass or less, even more preferably less than 1% by mass, and is particularly preferably not contained.

Among the pulp fibers constituting the paper base material, the number ratio of fine fibers having an average fiber length of 0.2 mm or less is 20% or less. It is preferable to set the number ratio of the fine fibers to 20% or less because generation of paper dust can be suppressed.
From the above point of view, the number ratio of the fine fibers is preferably 19% or less, more preferably 17% or less, and still more preferably 15% or less, and the lower limit is not particularly limited, but from the viewpoint of ease of manufacture. , preferably 3% or more, more preferably 5% or more, even more preferably 7% or more.
In order to keep the number ratio of fine fibers within the above range, there is a method of making the fine fibers easier to remove from the wire bar by using multi-layer papermaking (thus reducing the thickness of each layer), and a method of making it easier to remove the fine fibers from the wire bar. An example of a method is to reduce the fine fibers by reducing the content of bleached softwood kraft pulp (NBKP). Another example is a method of reducing fine fibers by selecting the hole size of the mesh during paper making.
The number ratio of fine fibers in the pulp fibers constituting the paper base material is measured by the method described in Examples, and is the number ratio obtained by dividing the number of fibers with a length of 0.2 mm or less by the total number of fibers.

Known internal chemicals can be appropriately added to the paper base material. Internally added chemicals include, for example, sizing agents, fillers such as titanium dioxide, kaolin, talc, and calcium carbonate, paper strength enhancers, retention improvers, pH adjusters, drainage 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.

When the paper base material contains a sizing agent, the content of the sizing agent (in terms of solid content) is preferably 0.001 parts by mass or more based on 100 parts by mass (dry mass) of pulp fibers contained in the paper base material. , more preferably 0.01 parts by mass or more, still 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. It is not more than 0.5 parts by mass, even more preferably not more than 0.3 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 manufacturing 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. Among these, preferably one or more selected from the group consisting of cationized starch and polyacrylamide-based polymers, and more preferably cationized starch.
When the paper base material contains a paper strength enhancer, the content of the paper strength enhancer (in terms of solid content) is preferably 0.00 parts by mass (dry mass) of pulp fibers contained in the paper base material. 01 parts by mass or more, more preferably 0.1 parts by mass or more, even more preferably 0.2 parts by mass or more, and preferably 5.0 parts by mass or less, more preferably 3.0 parts by mass or less, even more preferably is 1.5 parts by mass or less, more preferably 1.0 parts by mass or less. 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.
When the paper base material contains a wet paper strength agent, the content of the wet paper strength agent (in terms of solid content) is preferably 0 with respect to 100 parts by mass (dry mass) of the pulp contained in the paper base material. The amount is .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. . 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.

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 is improved, it is possible to suppress the phenomenon that the liquid containers rub against each other and the thermoplastic resin layer and the paper base material turn over from the surface of the paper base material when the liquid containers are transported.
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 is preferably a modified starch or a water-based resin such as polyvinyl alcohol, more preferably a modified starch, and still more preferably an 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, vinyl resin or epoxy resin is added to the size press liquid from the viewpoint of improving adhesion with the thermoplastic resin layer described later. It is preferable to use a mixture of adhesion aids such as 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. Among the above adhesion aids, the adhesion aid is preferably one or more selected from the group consisting of vinyl resins and polyethyleneimine resins, and more preferably includes 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. When a surface sizing agent and a surface paper strength agent are used together, the amount of each applied is preferably 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.

(Manufacturing method of paper base material)
The paper base material is preferably manufactured by a manufacturing method that includes a papermaking process in which three or more pulp layers, preferably four or more layers, more 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 to apply a mixture of one or more selected from the group consisting of a surface paper strength agent and a surface paper strength agent and an adhesion aid, from the viewpoint of increasing the adhesiveness with the thermoplastic resin layer described later. is more preferable.
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 it is preferable to use polyethylene and polypropylene. More preferred. 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 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 100 g/m ² Below, it is more preferably 50 g/m ² or less, even more preferably 40 g/m ² or less.
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.
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 each thermoplastic resin layer formed are as described above. Preferably, the range is within the range. 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.
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 papermaking process, it is preferable to make paper from the paper base material using a multilayer papermaking 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) Fiber form The laminated papers obtained in the Examples and Comparative Examples were cut into 40 cm square pieces, the thermoplastic resin layers (laminate layers) on the front and back sides were peeled off by hand, and then the paper was cut into pieces with a concentration of 2%. It was soaked in ion-exchanged water for 24 hours. After soaking for 24 hours, the pulp was disintegrated into fibers using a standard disintegrator (manufactured by Kumagai Riki Kogyo Co., Ltd.) until there were no undisintegrated fibers. The slurry (pulp fiber dispersion) after disintegration with the thermoplastic resin layer removed was collected.
The fiber morphology is determined by measuring the length-weighted average fibers of the above-mentioned defibrated slurry in accordance with JIS P 8226:2006, and dividing the number of length-weighted average fibers of 0.2 mm or less by the total number of fibers. Fine fibers (%). A fiber length measuring device (Valmet Fiber Image Analyzer ValmetFS5, manufactured by Valmet) was used for the measurement.

(2) Basis weight of paper base material and laminated paper The above basis weight was measured according to JIS P 8124:2011.
(3) Thickness of paper base material The thickness of the paper base material was measured according to JIS P 8118:2014 when a pressure of 100 kPa±10 kPa was applied to a circular area (200 mm ² ) of the test piece.
(4) Thickness of Thermoplastic Resin Layer A 100 mm x 100 mm piece of laminated paper was cut out, and after peeling off the thermoplastic resin layer from the cut test piece, it was 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 ).

(5) Whiteness The whiteness of the laminated paper was measured according to JIS P 8148:2000.
(6) Interlayer strength (Z-axis strength)
The interlayer strength of the laminated paper was measured according to JAPAN TAPPI 18-1:2007, specifically as follows. A special double-sided tape was attached to the Z-axis strength measurement jig, and a 25 mm x 25 mm test piece was attached. Double-sided tape was applied to the other measuring jig, and the measuring jigs were pressed together for 20 seconds at 0.5 MPa using a simple press machine. The measurement jig was pulled in the Z-axis direction at a speed of 20 mm/min using a vertical Tensilon (manufactured by A&D Co., Ltd., RTG-1310), and the peak strength was taken as the interlaminar strength (Z-axis strength).
(7) Tear strength The tear strength of laminated paper was measured according to JIS P 8116:2000.

[Example 1]
(Paper base material)
100 parts of LBKP as a pulp raw material was refined using a double disc refiner to obtain a pulp slurry. To 100 parts of pulp (dry mass) of the obtained pulp slurry, 0.60 parts of cationized starch (in terms of solid content) was added as an internal paper strength enhancer, and 0.60 parts of an alkyl ketene dimer-based sizing agent was added as an internal sizing agent. A paper stock was prepared by adding 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 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 calendered to obtain a paper base material having a basis weight of 299 g/m ² and a thickness of 413 μm. 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).

(Thermoplastic resin layer)
LDPE (low density polyethylene) was laminated as a thermoplastic resin onto the front surface (highly smooth surface) and back surface (low smooth surface) 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, and 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) 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 was melted using a frame seal, and the body was bonded together to obtain a cylindrical sleeve (folding carton). 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]
As pulp raw materials, 90 parts of LBKP and 10 parts of NBKP were refined using a double disc refiner to obtain a pulp slurry. To 100 parts of pulp (dry mass) of the obtained pulp slurry, 0.60 parts of cationized starch (in terms of solid content) was added as an internal paper strength enhancer, and 0.60 parts of an alkyl ketene dimer-based sizing agent was added as an internal sizing agent. A paper stock was prepared by adding 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 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 is sprayed between each layer using an interlayer spray, and after 5 layers are combined, 1.5 g/m 2 of oxidized starch is applied to the surface 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 calendered to obtain a paper base having a basis weight of 315 g/m ² and a thickness of 427 μm. 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 paper base material so that the thickness and basis weight met the conditions listed in Table 1.

[Example 3]
As pulp raw materials, 80 parts of LBKP and 20 parts of NBKP were refined using a double disc refiner to obtain a pulp slurry. For 100 parts of pulp (dry mass) of the obtained pulp slurry, 0.30 parts of polyacrylamide paper strength agent (solid content equivalent) was added as an internal paper strength enhancer, and alkyl ketene dimer size was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts of the agent (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 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 is sprayed between each layer using an interlayer spray, and after 5 layers are combined, 1.5 g/m 2 of oxidized starch is applied to the surface 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 and a thickness of 441 μm.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that the obtained paper base material was laminated with a thermoplastic resin layer so that the thickness and basis weight met the conditions listed in Table 1. .

[Example 4]
As pulp raw materials, 70 parts of LBKP and 30 parts of NBKP were refined using a double disc refiner to obtain a pulp slurry. For 100 parts of pulp (dry mass) of the obtained pulp slurry, 0.30 parts of polyacrylamide paper strength agent (solid content equivalent) was added as an internal paper strength enhancer, and alkyl ketene dimer size was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts of the agent (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 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 is sprayed between each layer using an interlayer spray, and after 5 layers are combined, 1.5 g/m 2 of oxidized starch is applied to the surface 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 calendered to obtain a paper base material having a basis weight of 325 g/m ² and a thickness of 444 μm.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that the obtained paper base material was laminated with a thermoplastic resin layer so that the thickness and basis weight met the conditions listed in Table 1. .

[Example 5]
As pulp raw materials, 60 parts of LBKP and 40 parts of NBKP were refined using a double disc refiner to obtain a pulp slurry. To 100 parts of pulp (dry mass) of the obtained pulp slurry, 0.60 parts of cationized starch (in terms of solid content) was added as an internal paper strength enhancer, and 0.60 parts of an alkyl ketene dimer-based sizing agent was added as an internal sizing agent. A paper stock was prepared by adding 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 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 is sprayed between each layer using an interlayer spray, and after 5 layers are combined, 1.5 g/m 2 of oxidized starch is applied to the surface 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 calendered to obtain a paper base material having a basis weight of 338 g/m ² and a thickness of 436 μm.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that the obtained paper base material was laminated with a thermoplastic resin layer so that the thickness and basis weight met the conditions listed in Table 1. .

[Example 6]
As pulp raw materials, 50 parts of LBKP and 50 parts of NBKP were refined using a double disc refiner to obtain a pulp slurry. For 100 parts of pulp (dry mass) of the obtained pulp slurry, 0.30 parts of polyacrylamide paper strength agent (solid content equivalent) was added as an internal paper strength enhancer, and alkyl ketene dimer size was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts of the agent (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 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 is sprayed between each layer using an interlayer spray, and after 5 layers are combined, 1.5 g/m 2 of oxidized starch is applied to the surface 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 calendered to obtain a paper base material having a basis weight of 294 g/m ² and a thickness of 391 μm.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that the obtained paper base material was laminated with a thermoplastic resin layer so that the thickness and basis weight met the conditions listed in Table 1. .

[Example 7]
As pulp raw materials, 60 parts of LBKP and 40 parts of NBKP were refined using a double disc refiner to obtain a pulp slurry. For 100 parts of pulp (dry mass) of the obtained pulp slurry, 0.30 parts of polyacrylamide paper strength agent (solid content equivalent) was added as an internal paper strength enhancer, and alkyl ketene dimer size was added as an internal sizing agent. A paper stock was prepared by adding 0.25 parts of the agent (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 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 5 layers are combined, 1.5 g/m 2 of oxidized starch is applied to the surface 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 calendered to obtain a paper base material having a basis weight of 333 g/m ² and a thickness of 457 μm.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that the obtained paper base material was laminated with a thermoplastic resin layer so that the thickness and basis weight met the conditions listed in Table 1. .

[Comparative example 1]
As pulp raw materials, 60 parts of LBKP and 40 parts of NBKP were refined using a double disc refiner to obtain a pulp slurry. To 100 parts of pulp (dry mass) of the obtained pulp slurry, 0.60 parts of cationized starch (in terms of solid content) was added as an internal paper strength enhancer, and 0.60 parts of an alkyl ketene dimer-based sizing agent was added as an internal sizing agent. A paper stock was prepared by adding 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 the surface 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 calendered to obtain a paper base material having a basis weight of 319 g/m ² and a thickness of 457 μm.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that the obtained paper base material was laminated with a thermoplastic resin layer so that the thickness and basis weight met the conditions listed in Table 1. .

[Comparative example 2]
As pulp raw materials, 50 parts of LBKP and 50 parts of NBKP were refined using a double disc refiner to obtain a pulp slurry. To 100 parts of pulp (dry mass) of the obtained pulp slurry, 0.60 parts of cationized starch (in terms of solid content) was added as an internal paper strength enhancer, and 0.60 parts of an alkyl ketene dimer-based sizing agent was added as an internal sizing agent. A paper stock was prepared by adding 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 the surface 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 calendered to obtain a paper base material having a basis weight of 329 g/m ² and a thickness of 450 μm.
A laminated paper and a gable-top paper container were obtained in the same manner as in Example 1, except that the obtained paper base material was laminated with a thermoplastic resin layer so that the thickness and basis weight met the conditions listed in Table 1. .

[Comparative example 3]
As pulp raw materials, 70 parts of LBKP, 10 parts of NBKP, and 20 parts of waste paper pulp were beaten using a double disc refiner to obtain a pulp slurry. To 100 parts of pulp (dry mass) of the obtained pulp slurry, 0.60 parts of cationized starch (in terms of solid content) was added as an internal paper strength enhancer, and 0.60 parts of an alkyl ketene dimer-based sizing agent was added as an internal sizing agent. A paper stock was prepared by adding 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 the surface 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 calendered to obtain a paper base having a basis weight of 276 g/m ² and a thickness of 369 μm. 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 paper base material so that the thickness and basis weight met the conditions listed in Table 1.

(Paper powder evaluation of laminated paper)
A4-sized laminated paper was manually torn 10 times in the horizontal direction (perpendicular to the flow of pulp fibers) on black paper, and the number of paper particles that fell on the black paper (in an area of 100 mm x 100 mm) was visually counted. did. The test was conducted five times each, and the degree of paper dust generation was evaluated based on the average number of paper dust. The evaluation criteria are as follows.
A: Average number of pieces 0 to 25 pieces B: Average number of pieces 26 to 50 pieces C: Average number of pieces 51 or more

(Printability of laminated paper)
Fifty sheets of the laminated paper obtained in Examples and Comparative Examples were subjected to offset printing, and the clarity and uniformity of the ink color development were visually confirmed and evaluated as follows.
A: The color development of the ink was clear and uniform. B: The color development of the ink was not very clear and some unevenness was observed here and there, but this was not a problem for practical use.
C: The ink color development was not clear and unevenness was observed.

(Drop test of liquid container)
The gable-top paper containers obtained in Examples and Comparative Examples were repeatedly dropped onto a concrete floor from a height of 30 cm with the bottom facing vertically downward, and the number of times required until liquid leakage occurred was counted. did. A test was conducted on 8 samples, and the drop resistance was evaluated based on the average number of times until liquid leakage occurred (rounded to the nearest whole number). The evaluation criteria are as follows.
A: Average number of falls 16 times or more B: Average number of falls 10 to 15 times C: Average number of falls 9 times or less

From Table 1, the laminated papers of Examples 1 to 7, in which the proportion of fine fibers is 20% or less and the whiteness is 70% or more, suppress the generation of paper dust and are also excellent in printability. Met. Furthermore, the liquid container made from the laminated paper had excellent drop resistance.
On the other hand, in Comparative Examples 1 to 3 in which the number ratio of fine fibers exceeded 20%, the generation of paper dust was remarkable. Furthermore, in Comparative Example 3, in which the whiteness was less than 70%, the printability was also poor.

10 Paper base material 20 Thermoplastic resin layer 100 Laminated paper

Claims (11)

A laminated paper comprising a paper base material and a thermoplastic resin layer laminated on at least one surface of the paper base material,
Among the pulp fibers constituting the paper base material, the number ratio of fine fibers with an average fiber length of 0.2 mm or less is 20% or less,
The whiteness is 70% or more,
laminated paper. The laminated paper according to claim 1, having an interlayer strength of 200 kPa or more and 450 kPa or less. The laminated paper according to claim 1, wherein the geometric mean of tear strength in the longitudinal direction and tear strength in the transverse direction is 2000 mN or more and 6500 mN or less. The laminated paper according to claim 1, wherein the paper base material has four or more layers. The laminated paper according to claim 1, wherein an adhesive component is applied between each layer of the paper base material, and an amount of the adhesive component applied between each layer is 2.0 g/m ² or more and 10 g/m ² or less. . A laminated paper according to claim 5, wherein the adhesive component comprises starch. The laminated paper according to claim 1, 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. The laminated paper of claim 7, wherein the adhesion aid comprises a polyethyleneimine resin. The laminated paper according to claim 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. The laminated paper according to claim 1, which is used for liquid containers. A liquid container made of the laminated paper according to any one of claims 1 to 10.