JP2024150170A - Paper base material for humid forming, paper processed products and paper containers - Google Patents

Abstract

[Problem] A paper base material for humid forming that achieves a high level of formability and drop impact resistance through humid forming, and furthermore maintains the beauty of its surface even when it is moistened in a high-temperature, high-humidity environment and subjected to vibration. [Solution] A paper base material for humid forming, the paper base material having two or more paper layers, the thickness of the paper base material being 0.8 to 1.5 mm, one surface of the paper base material being side A and the other surface being side B, the Cobb water absorbency measured from side A of the paper base material being equal to or lower than the Cobb water absorbency measured from side B, the Cobb water absorbency measured from side A being 10 to 700 g/m2·60 seconds, the Cobb water absorbency measured from side B being 10 to 1000 g/m2·60 seconds, and both the average fiber width of the pulp contained in the paper layer constituting one surface of the paper base material and the average fiber width of the pulp contained in the paper layer constituting the other surface are 28.0 μm or less. [Selected Figure] None

Description

This disclosure relates to a paper substrate for moist forming, and a paper product and a paper container made using the paper substrate.

In recent years, efforts to reduce the use of plastic have been accelerating worldwide due to environmental concerns. Traditionally, plastic materials such as synthetic resins have been widely used for containers such as trays and bottles, as well as tableware, stationery, and medical equipment, but the replacement of plastic products with paper products is progressing.
Paper containers and the like require ease of folding for molding, i.e., moldability (flexibility), while strength after molding, such as drop impact resistance, is also required. However, there is a trade-off between the two as paper properties; for example, increasing the thickness of the base material improves drop impact resistance, but reduces moldability. Therefore, there is a demand for good paper that can achieve both moldability and drop impact resistance.
On the other hand, as a method for forming a thick paper base material, for example, Patent Document 1 discloses a forming method that includes a step of humidifying the liner before applying pressure when bending cardboard, thereby preventing the occurrence of wrinkles and tears during processing.

International Publication No. 2004/022327

However, according to the study by the present inventors, the technology of the above-mentioned documents is not sufficient in terms of both formability and drop impact resistance when more complicated processing is performed by humidification molding, such as for containers such as trays and bottles. Furthermore, containers such as trays and bottles are exposed to environments that make the surface easily moist, such as high temperature and humidity environments, during transportation and storage after molding, and may also be subjected to vibrations during transportation. A paper base material that can maintain the beauty of the surface even when exposed to such harsh environments has not yet been obtained.
The present disclosure provides a paper substrate for humid forming that achieves high levels of formability and drop impact resistance through humid forming, and further that can maintain the beauty of its surface even when moistened in a high-temperature, high-humidity environment and subjected to vibration.

The present disclosure relates to the following <1> to <8>.
<1> A paper substrate for moist forming,
The paper base material has two or more paper layers,
The thickness of the paper base material is 0.8 to 1.5 mm;
When one surface of the paper base material is designated as side A and the other surface is designated as side B,
The Cobb water absorbency measured from the A side of the paper base material is equal to or lower than the Cobb water absorbency measured from the B side,
The Cobb water absorbency measured from the A side is 10 to 700 g/ ^m2 ·60 seconds,
The Cobb water absorbency measured from the side B is 10 to 1000 g/ ^m2 ·60 seconds,
Both of the average fiber width of the pulp contained in the paper layer constituting one surface of the paper base material and the average fiber width of the pulp contained in the paper layer constituting the other surface of the paper base material are 28.0 μm or less.
A paper substrate for moist forming, comprising:
<2> The paper base material for moist forming according to <1>, wherein the average value of the longitudinal tensile strength of the paper base material per basis weight and the transverse tensile strength of the paper base material per basis weight, measured after adjusting the moisture content of the paper base material to 10% by mass, is 12.0 to 43.0 Nm/g.
<3> The paper base material is a multi-layer paper having two or more paper layers, or an interleaving paper having two or more base papers attached thereto,
The paper base material for moist forming according to <1> or <2>, wherein each of the two or more base papers includes the paper layer.
<4> The paper base material for moist forming according to any one of <1> to <3>, wherein the pulp contained in the paper layer contains hardwood kraft pulp and recycled paper pulp.
<5> The paper base material for moist forming according to any one of <1> to <4>, wherein the difference between the Cobb water absorbency measured from the side B and the Cobb water absorbency measured from the side A (side B-side A) is 20 to 900 g/ ^m2 ·60 seconds.
<6> A paper product obtained by using the paper base material for moist forming according to any one of <1> to <5>.
<7> A paper container using the paper base material for moist forming according to any one of <1> to <5>. <8> The paper container has a bottle shape,
The paper container according to <7>, wherein the A side constitutes at least a part of the outer surface of the paper container.

This disclosure makes it possible to provide a humidified paper substrate that achieves higher levels of formability and drop impact resistance, and that can maintain the beauty of its surface even when moistened in a high-temperature, high-humidity environment.

In this specification, the expressions "X or more and Y or less" or "X to Y" that express a numerical range mean a numerical range including the upper and lower limits that are the endpoints, unless otherwise specified. When a numerical range is described in stages, the upper and lower limits of each numerical range can be combined in any way.

The machine direction is the machine direction (MD) of the paper base material, which is the same as the direction in which the fibers are oriented. The cross direction is the direction perpendicular to the machine direction (CD).

The inventors have discovered that by making the paper base material a paper base material containing two or more paper layers, and controlling the thickness of the paper base material, the Cobb water absorbency of both surfaces of the paper base material, and the average fiber width of the pulp constituting both surfaces of the paper base material all within specific ranges, it is possible to obtain a paper base material for humid forming that can achieve a high level of formability through humid forming (hereinafter also simply referred to as "formability during humid forming") and drop impact resistance, and that can maintain the beauty of its surface even when it is moistened in a high-temperature, high-humidity environment and subjected to vibration (hereinafter also simply referred to as "beauty after wetting").

By setting the thickness of the paper base material within a specific range, the strength of the paper base material is improved, thereby controlling the drop impact resistance and the moldability during moistening. Furthermore, when one surface of the paper base material is side A and the other surface is side B, the Cobb water absorbency measured from side A is equal to or lower than the Cobb water absorbency measured from side B. The Cobb water absorbency measured from side A and the Cobb water absorbency measured from side B are set within a specific range. The relationship between these Cobb water absorbencies makes it possible to achieve moldability during moistening and beauty after wetting. Furthermore, the average fiber width of each of the pulps constituting both surfaces of the paper base material is set within a specific range. This makes it possible to control the swelling of the fibers during moistening and achieve beauty after wetting and moldability during moistening.

Therefore, the inventors believe that by controlling the thickness of the paper base material, the Cobb water absorbency of both surfaces of the paper base material, and the average fiber width of the pulp that constitutes both surfaces of the paper base material within specific ranges, it is possible to obtain a paper base material for humid molding that is excellent in all respects: formability during humid molding, drop impact resistance, and aesthetics after wetting.

The paper substrate for moist forming according to the present disclosure will be described below.
The paper base material has two or more paper layers. Specifically, the paper base material is preferably a multilayer paper having two or more paper layers or a slip sheet in which two or more base papers are pasted. When the paper base material is a slip sheet, each of the two or more base papers includes a paper layer. Each of the base papers constituting the slip sheet may be a single-layer paper or a multilayer paper. When the paper base material has two or more paper layers, it becomes easier to arbitrarily adjust the raw material composition, basis weight, and papermaking conditions of each layer and each base paper.
The number of paper layers in the paper base material is preferably 2 to 9 layers, more preferably 2 to 4 layers, even more preferably 2 to 3 layers, and even more preferably 2 layers.

When the paper base material is a multi-layer paper having two or more paper layers, the paper base material is a base paper having a multi-layer structure obtained by multi-layer papermaking, which will be described later. There is no particular limit to the upper limit of the number of base paper layers that make up the multi-layer paper, but it is usually 9 layers or less. The paper base material is preferably a multi-layer paper having two layers.

When the paper substrate is an interleaving paper in which two or more base papers are pasted together, the interleaving paper further includes an adhesive layer between the two or more base papers. For example, the interleaving paper may be made of only base paper A, an adhesive layer, and base paper B, or may be made by laminating another base paper C via an adhesive layer. The upper limit of the number of base papers constituting the interleaving paper is not particularly limited, but is usually three or less. The paper substrate is preferably an interleaving paper in which two base papers are pasted together.
When the paper base material is an interleaving paper, the base paper contained in the interleaving paper may be a single-layer paper obtained by the single-layer papermaking process described later, or a multi-layer paper obtained by the multi-layer papermaking process described later, within the scope of not impairing the effects of the present disclosure. For two or more base papers, a single-layer paper and a multi-layer paper may be used in combination.

The thickness of the paper substrate for humid forming is 0.8 to 1.5 mm. If the thickness is 0.8 mm or more, the drop impact resistance is good. On the other hand, if the thickness is 1.5 mm or less, the moldability during humid forming is good. The thickness in the above range is a relatively thick range for a paper substrate for forming, and in the present disclosure, a paper substrate of such a thickness achieves high levels of moldability and drop impact resistance, and further has a beautiful surface. The thickness of the paper substrate for humid forming is preferably 0.9 to 1.5 mm, more preferably 1.0 to 1.4 mm.
In addition, when the paper base material is a laminated paper in which two or more base papers are adhered to each other, the thickness of the paper base material refers to the total thickness of the paper base material including the thickness of the adhesive layer between the two or more base papers.

In addition, when one surface of the paper substrate is designated as side A and the other surface is designated as side B, it is necessary that the Cobb water absorbency measured from side A of the paper substrate is equal to or lower than the Cobb water absorbency measured from side B. It is preferable that the Cobb water absorbency measured from side A of the paper substrate is lower than the Cobb water absorbency measured from side B. The Cobb water absorbency measured from side A is 10 to 700 g/ ^m2 ·60 seconds, and the Cobb water absorbency measured from side B is 10 to 1000 g/ ^m2 ·60 seconds. When the Cobb water absorbency measured from side A of the paper substrate and the Cobb water absorbency measured from side B are the same, either side may be designated as side A.

Side B can be the surface to which water vapor is applied during humidification molding of the paper base material. When the Cobb water absorbency measured from side B is within the above range, the moisture absorbency is good, making it easier to improve moldability during humidification molding. Side A can also be the surface that can form at least a part of the outer surface of a paper product made using the paper base material. When the Cobb water absorbency measured from side A is within the above range, the water resistance of the outer surface of a paper product made using the paper base material is improved, making it easier to improve the beauty after wetting. In addition, when a label or the like is printed on side A and used as the outer surface, the beauty can be maintained even during humidification molding, which can also contribute to improving the design.

If the Cobb water absorbency measured from side A is 10 g/ ^m2 ·60 seconds or more, the moldability during wet molding is likely to be improved. If the Cobb water absorbency measured from side A is 700 g/ ^m2 ·60 seconds or less, the aesthetics after wetting are likely to be improved. The Cobb water absorbency measured from side A is preferably 10 to 500 g/ ^m2 ·60 seconds, more preferably 10 to 200 g/ ^m2 ·60 seconds, and even more preferably 12 to 50 g/ ^m2 ·60 seconds.

On the other hand, if the Cobb water absorbency measured from side B is 10 g/ ^m2 ·60 seconds or more, the moldability during humidification molding is easily improved. If the Cobb water absorbency measured from side B is 1000 g/ ^m2 ·60 seconds or less, excessive swelling during humidification molding can be suppressed, and the moldability during humidification molding is easily improved. The Cobb water absorbency measured from side B is preferably 11 to 1000 g/ ^m2 ·60 seconds, more preferably 90 to 900 g/ ^m2 ·60 seconds, even more preferably 300 to 900 g/ ^m2 ·60 seconds, and even more preferably 600 to 800 g/ ^m2 ·60 seconds.

The difference between the Cobb water absorbency measured from side B and the Cobb water absorbency measured from side A (side B-side A) is preferably 20 to 900 g/ ^m2 ·60 seconds, more preferably 300 to 800 g/ ^m2 ·60 seconds, and even more preferably 500 to 750 g/ ^m2 ·60 seconds. Within the above ranges, it is easy to further improve the moldability during humid molding and the aesthetics after wetting.

The Cobb absorbency can be controlled by the amount of sizing agent added, etc. In order to reduce the Cobb absorbency, the amount of sizing agent added can be increased. In addition, in order to make the Cobb absorbency measured from side A of the paper substrate smaller than the Cobb absorbency measured from side B, the amount of sizing agent added can be increased in the paper layer constituting the A side compared to the paper layer constituting the B side, or an overprint varnish (OP varnish) can be applied to the A side of the paper substrate.

The average fiber width of the pulp contained in the paper layer constituting one surface of the paper base material and the average fiber width of the pulp contained in the paper layer constituting the other surface are both 28.0 μm or less. If the average fiber width of the pulp contained in the paper layer constituting at least one surface of the paper base material exceeds the above upper limit, the fibers tend to swell during moistening and molding, and the beauty after moistening and the moldability during moistening and molding are reduced. In particular, the beauty after moistening is likely to decrease on the A-side, and the moldability during moistening and molding is likely to decrease on the B-side.
In measuring the average fiber width of the pulp, the paper layer constituting one surface and the paper layer constituting the other surface are separated and measured. The specific method will be described later.

The average fiber width of the pulp on both the one surface and the other surface is preferably 27.0 μm or less, more preferably 26.0 μm or less, and even more preferably 21.0 μm or less. There is no particular lower limit, but it is preferably 12.0 μm or more, and more preferably 15.0 μm or more.
For example, the average fiber width of the pulp on both the one surface and the other surface is preferably 12.0 μm to 27.0 μm, more preferably 12.0 μm to 26.0 μm on both, and even more preferably 15.0 μm to 21.0 μm on both.
It is also a preferred embodiment that the average fiber width of the pulp constituting the paper base material is within the above range.
The average fiber width of the pulp can be controlled by the mass ratio of softwood kraft pulp among the pulps constituting the paper base material. In order to reduce the average fiber width of the pulp, a method such as reducing the mass ratio of softwood kraft pulp constituting the paper base material can be used.

The length-weighted average fiber length of the pulp contained in the paper layer constituting one surface of the paper base material and the length-weighted average fiber length of the pulp contained in the paper layer constituting the other surface are both preferably 0.5 to 2.5 mm, more preferably 0.6 to 2.4 mm, and even more preferably 0.6 to 1.2 mm.
It is also a preferred embodiment that the length-weighted average fiber length of the pulp constituting the paper base material is within the above range.

When both the length-weighted average fiber length of the pulp contained in the paper layer constituting one surface of the paper base material and the length-weighted average fiber length of the pulp contained in the paper layer constituting the other surface are below the above-mentioned upper limit, the fibers are less likely to swell during moist molding, which makes it possible to further improve the aesthetics after moistening on the aforementioned side A, and makes it easier to further improve the formability during moist molding on the aforementioned side B.
The length-weighted average fiber length of the pulp can be controlled by the mass ratio of softwood kraft pulp among the pulps constituting the paper base material. In order to reduce the length-weighted average fiber length of the pulp, a method such as reducing the mass ratio of softwood kraft pulp constituting the paper base material can be used.

The tensile strength of the paper base material per basis weight is hereinafter also referred to as the specific tensile strength. The average value of the longitudinal tensile strength of the paper base material per basis weight and the transverse tensile strength of the paper base material per basis weight (hereinafter also simply referred to as the "specific tensile strength when humidified") measured under a humidity controlled environment specified in JIS P 8111:1998 with the paper base material adjusted to a moisture content of 10% by mass is preferably 12.0 to 43.0 Nm/g. The specific tensile strength of the paper base material when humidified is more preferably 14.0 to 38.0 Nm/g, even more preferably 16.0 to 35.0 Nm/g, and even more preferably 20.0 to 30.0 Nm/g. By setting the specific tensile strength when humidified within the above range, the moldability during humidification molding can be further improved.

The longitudinal tensile specific strength is preferably 15.0 to 50.0 Nm/g, more preferably 17.0 to 40.0 Nm/g, and even more preferably 27.0 to 35.0 Nm/g. The transverse tensile specific strength is preferably 9.5 to 32.0 Nm/g, more preferably 13.0 to 27.0 Nm/g, and even more preferably 16.0 to 24.0 Nm/g. It is also preferable that both the longitudinal tensile specific strength and the transverse tensile specific strength of the paper base material when moistened satisfy the above range. By setting the longitudinal tensile specific strength and the transverse tensile specific strength when moistened within the above range, the moldability during moistening molding can be further improved.
The tensile strength index when humidified can be controlled by the amount of paper strength enhancer added, etc. To increase the tensile strength index when humidified, a method such as increasing the amount of paper strength enhancer added can be used.

The fiber orientation ratio of the paper base material is preferably 1.40 to 2.50. The fiber orientation ratio indicates the tendency of the fibers to align in the flow direction (longitudinal direction) during the process in which the pulp slurry is discharged onto the wire of a papermaking machine, dehydrated, and the paper layer is formed. In other words, the fiber orientation ratio indicates the degree of fiber orientation, and is a value of 1 or more. A low fiber orientation ratio indicates that the fibers are randomly oriented, and a high fiber orientation ratio indicates that the fibers are oriented in the longitudinal direction.
By having a fiber orientation ratio equal to or greater than the lower limit, the stiffness in the lateral direction of the paper base material can be appropriately controlled, and the paper base material is more likely to curl in the lateral direction during molding, and cracks and deformations can be suppressed, which makes it easier to improve the moldability during humid molding. By having a fiber orientation ratio equal to or less than the upper limit, the stiffness in the longitudinal direction of the paper base material can be appropriately controlled, and wrinkles in the longitudinal direction can be suppressed, which improves the aesthetics after wetting.

The fiber orientation ratio of the paper base material is more preferably 1.45 to 2.30, and even more preferably 1.50 to 2.10.
The fiber orientation ratio can be controlled by adjusting the ratio between the discharge speed of the pulp-containing paper material and the wire speed of the papermaking machine in the paper layer or base paper making process. This ratio is also called the J/W ratio (jet/wire ratio). To increase the fiber orientation ratio, a method such as increasing the J/W ratio can be used.

The basis weight of the paper base material is preferably 500 to 1400 g/m ² , more preferably 600 to 1300 g/m ² , and even more preferably 700 to 1220 g/m ^2. When the paper base material is an interleaving paper in which two or more base papers are attached, the basis weight of the paper base material refers to the total basis weight of the paper base material, including the weight of the adhesive layer between the two or more base papers.
By having the entire basis weight of the paper base material within the above range, it becomes easier to adjust the thickness of the paper base material, and it becomes easier to further improve drop impact resistance and moldability during humid molding.

The basis weight of the paper layer constituting the A side (basis weight of the A side) is preferably 250 to 700 g/m ² , more preferably 300 to 650 g/m ² , and even more preferably 350 to 600 g/m ^2. By being in the above range, it is easy to satisfy the desired Cobb water absorbency, and the aesthetics after wetting can be further improved.

The basis weight of the paper layer constituting the B side (basis weight of the B side) is preferably 250 to 700 g/m ² , more preferably 300 to 650 g/m ² , and even more preferably 350 to 600 g/m ^2. By being in the above range, the paper base material is easily swollen and the formability during moist forming can be further improved.

The ratio of the basis weight of the paper layer on the side constituting side A to the basis weight of the paper layer on the side constituting side B (side A/side B) is preferably 0.5 to 2.0, more preferably 0.8 to 1.2, and even more preferably 0.9 to 1.1. By being in the above range, it is easier to achieve moldability during humid molding, drop impact resistance, and aesthetics after wetting.

The paper layer is not particularly limited as long as it is a commonly used paper, and is preferably a paper containing plant-derived pulp as a main component, and more preferably a paper containing wood pulp as a main component. The raw pulp contained in the paper layer is preferably wood pulp, and more preferably kraft pulp. Kraft pulp, which differs in raw material, includes hardwood kraft pulp (LKP) and softwood kraft pulp (NKP). In addition, which differs in processing state, includes bleached kraft pulp (BKP), unbleached kraft pulp (UKP), and oxygen bleached kraft pulp (OKP), and from the viewpoint of printability, bleached kraft pulp (BKP) is preferred. Waste paper pulp may also be used.

Among these, the raw material pulp is preferably at least one selected from the group consisting of hardwood kraft pulp (LKP), softwood kraft pulp (NKP), and recycled paper pulp. It is more preferable to use hardwood kraft pulp (LKP) and recycled paper pulp in combination, or to use softwood kraft pulp (NKP) and hardwood kraft pulp (LKP) in combination. It is even more preferable that the pulp contained in the paper layer contains hardwood kraft pulp (LKP) and recycled paper pulp.

When hardwood kraft pulp (LKP) and recycled paper pulp are used in combination, the mass ratio (LKP/recycled paper pulp) is not particularly limited as long as it is a ratio used in general paper, but is preferably 10/90 to 90/10, more preferably 20/80 to 80/20, even more preferably 30/70 to 70/30, and even more preferably 40/60 to 60/40.
The mass ratio (NKP/LKP) of softwood kraft pulp (NKP) and hardwood kraft pulp (LKP) used in combination is not particularly limited as long as it is a ratio used in general paper, but is preferably 20/80 to 80/20, more preferably 40/60 to 80/20, and more preferably 50/60 to 80/20.
/50 to 70/30 is even more preferable.

As hardwood kraft pulp (LKP), hardwood bleached kraft pulp (LBKP) is preferred, and as softwood kraft pulp (NKP), softwood bleached kraft pulp (NBKP) is preferred.

For hardwood kraft pulp (LKP), wood chips of well-known hardwoods such as eucalyptus, tanoak, and acacia can be used. For softwood kraft pulp (NKP), wood chips of well-known softwoods such as larch, spruce, cedar, slash pine, and lodgepole pine can be used.

The Canadian Standard Freeness (CSF) of the pulp is not particularly limited, but is preferably 350 to 700 ml, and more preferably 400 to 500 ml.
The CSF is a value of freeness measured by a Canadian standard freeness tester in accordance with JIS-P8121 after disintegrating a sample with a standard disintegrator in accordance with JIS-P8220.

Internal additives may be added when preparing the paper layer or base paper. Examples of internal additives include sizing agents, fillers, paper strength agents, retention improvers, pH adjusters, drainage improvers, water resistance agents, softeners, antistatic agents, defoamers, slime control agents, dyes and pigments, etc.

From the viewpoint of easily controlling the Cobb water absorbency of the paper base material, it is preferable that the paper base material contains a sizing agent. There is no particular limitation on the sizing agent, and any known sizing agent can be used. Examples of the sizing agent include rosin-based sizing agents, alkyl ketene dimers, alkenyl succinic anhydrides, and styrene-containing polymers such as styrene-(meth)acrylate copolymers. The sizing agent is preferably a rosin-based sizing agent.
The content of the rosin-based sizing agent may be such that the desired Cobb water absorbency can be obtained. For example, the content is preferably 0.05 to 2.00 parts by mass per 100 parts by mass of pulp. The content of the sizing agent in the paper layer can be measured by mass spectrometry using pyrolysis GC/MS.

From the viewpoint of making it easier to control the tensile strength index of the paper base material when moistened, it is preferable that the paper layer contains a paper strength agent.
Paper strength enhancers include dry strength enhancers and wet strength enhancers, and examples of the dry strength enhancers include cationic starch, polyacrylamide, carboxymethyl cellulose, etc., and examples of the wet strength enhancers include polyamide polyamine epichlorohydrin, urea formaldehyde resin, melamine formaldehyde resin, etc. The paper base material preferably contains a dry strength enhancer, and a polyacrylamide-based dry strength enhancer is more preferred.

The content of the paper strength agent in the paper layer constituting the aforementioned A-side is preferably 0.01 to 0.8 mass %. In the paper layer constituting the aforementioned B-side, the content is preferably 0.001 to 0.3 mass %. The content of the paper strength agent in the paper layer can be measured by mass spectrometry using pyrolysis GC/MS.

When preparing the paper layer or base paper, it is preferable to add 0.09 to 0.42 parts (solids equivalent) of paper strength agent to 100 parts (solids equivalent) of pulp slurry, more preferably 0.11 to 0.37 parts (solids equivalent), and even more preferably 0.13 to 0.33 parts (solids equivalent). The above ranges make it easier to control the specific tensile strength of the paper base material when moistened.

In making the paper layer or base paper, a known wet paper machine can be appropriately selected and used, such as a Fourdrinier paper machine, a gap former type paper machine, a cylinder type paper machine, and a short wire type paper machine.

In making paper layers or base paper, for example, the paper stock is cast onto a wire or the like, dehydrated to obtain a wet paper, and multiple wet papers are stacked as necessary, and this single-layer or multi-layer wet paper is pressed and dried. In this case, if multiple wet papers are not stacked, a single-layer base paper is obtained, and if multiple wet papers are stacked, a multi-layer base paper is obtained. When obtaining a multi-layer base paper, starch or polyacrylamide, which strengthens the interlayer adhesion, may be applied between the layers during the papermaking process, and the layers may be stacked together.

When starch is applied, the amount of starch (for example, the amount of starch applied after drying) is preferably 0.1 to 5.0 g/ ^m2 , and more preferably 0.5 to 2.0 g/ ^m2 .
The paper layer or base paper formed by the papermaking machine is preferably transported on a felt and dried in a dryer. A multi-stage cylinder dryer may be used as a pre-dryer before drying in the dryer.

The paper layer or base paper obtained as described above may be surface-treated with a calendar to make the thickness and profile uniform. A known calendaring machine can be appropriately selected and used for the calendaring.

The Oken smoothness (JIS P 8155:2010) of the paper layer or base paper is not particularly limited, but is preferably 5 seconds or more, and more preferably 10 to 1000 seconds. In addition, the 75° gloss of the paper layer or base paper is not particularly limited, but is preferably 5% or more, and more preferably 10 to 70%.

When the paper substrate is a laminate of two or more base papers, it further includes an adhesive layer between the two or more base papers. In other words, when the paper substrate is a laminate, the base papers are laminated via an adhesive layer. The adhesive layer may be any layer made of a material having adhesive properties. The adhesive layer is preferably a resin-based adhesive suitable for dry lamination and wet lamination. An adhesive suitable for wet lamination is more preferable.

The adhesive layer may be formed by laminating the base paper and the base paper using an adhesive. There are no particular limitations on the adhesive, but water-based, solvent-based, UV-based, and other types of adhesives can be used, and among these, water-based adhesives are preferred. In other words, the adhesive layer is preferably a water-based adhesive layer formed from a water-based adhesive. Furthermore, among the water-based adhesives, it is preferable to use at least one selected from the group consisting of acrylic adhesives, polyurethane adhesives, epoxy adhesives, and isocyanate adhesives, and acrylic adhesives are more preferred from the viewpoints of ease of control of adhesive strength and heat resistance.

When an adhesive is used, the amount of the adhesive layer per unit area (e.g., the amount of coating after drying) is preferably 1 to 50 g/m ² , and more preferably 3 to 10 g/m ^2. It is preferable to coat the base paper so that the solid content is within this amount.

For coating, it is preferable to use a coating liquid containing an adhesive, and it is more preferable to use a mixed coating liquid in which a curing agent is mixed with a coating liquid containing an adhesive. For example, the adhesive layer is preferably a cured product of a water-based adhesive.

The adhesive layer may be a layer containing a thermoplastic resin. By using a thermoplastic resin, it is possible to easily obtain an interleaving paper as a laminate by coating the base paper with the resin that has been heated and melted, and then laminating another base paper.
The thermoplastic resin used in the thermoplastic resin layer is not particularly limited, and may be appropriately selected from known thermoplastic resins.

The method for producing the interleaf paper is not particularly limited, and any known method can be used. An example of the production method is shown below.
First, base paper A including paper layer A capable of forming side A and base paper B including paper layer B capable of forming side B are prepared, and an adhesive that will become the adhesive layer is coated on one side of base paper A, and base paper B is wet laminated to this coated surface to obtain an interleaving paper.

As mentioned above, the interleaving paper contains two or more base papers (for example, base paper A and base paper B), but it may contain three or more base papers. When the interleaving paper contains three or more base papers, the adhesive layers that bond the base papers together may be different or the same.

The obtained paper base material may be cut to an appropriate size taking into consideration the size and shape of the stored items, and suitability for transportation and display. Cutting is preferably performed by punching in order to efficiently obtain interleaf sheets of the same shape.
The punching process is preferably carried out using a high-speed automatic punching machine, a flat-bed punching machine, or a rotary punching machine, and more preferably a high-speed automatic punching machine. The high-speed automatic punching machine and the flat-bed punching machine can easily and efficiently obtain paper base materials in shapes such as a rectangle, a rounded rectangle, an ellipse, etc.

The use of the paper substrate is not particularly limited as long as it is for humidification molding, and it may be used as a paper processed product by humidification molding and further processing as appropriate. Examples of the paper processed products include paper containers such as paper bottles, paper cups, and paper trays, clothing hanging tools such as paper hangers and paper hanger hooks, and paper tableware such as paper plates, paper spoons, paper forks, paper knives, paper stirrers, and paper straws.
The paper substrate is preferably used as a paper container, more preferably as a bottle-shaped paper container. Furthermore, it is preferable that the above-mentioned side A constitutes at least a part of the outer surface of the paper container.

Moisture forming includes known methods of humidifying and forming, for example, a paper substrate is moistened and then processed into a desired shape by press forming, folding forming, or the like.
The method for humidifying the paper base material is not particularly limited, but includes a method of blowing water vapor onto one surface of the paper base material, etc. From the viewpoint of processability, it is preferable to blow water vapor onto the B side of the paper base material.
The moisture content of the paper base material when the water vapor is sprayed is preferably 5 to 30% by mass, more preferably 5 to 25% by mass, and even more preferably 8 to 15% by mass.

The measurement methods for each physical property are described below.
<Thickness of paper base material>
The thickness of the paper base material (paper thickness) is measured in accordance with JIS P 8118:2014 after humidity control in a humidity control environment specified in JIS P 8111:1998. A paper thickness meter (company name: Toyo Seiki Seisakusho Co., Ltd., model number: No. 132 digital thickness meter) can be used as the measuring device. Ten samples are measured, and the arithmetic average value is used.

<Cobb Water Absorbency>
The Cobb water absorbency is measured in accordance with JIS P8140:1998 after conditioning under a humidity-conditioning environment specified in JIS P 8111:1998. The temperature of the water (distilled water is used) to be contacted is 23°C, and the contact time is 60 seconds. The Cobb water absorbency of one surface and the other surface of the paper substrate is measured. The measuring device used is a Cobb sizing degree tester manufactured by Japan T.M.C. Co., Ltd. Ten samples are measured, and the arithmetic average value is adopted.

<Length-weighted average fiber length and average fiber width of refractory pulp>
After soaking the paper substrate in 80°C water for one hour, the paper layer constituting side A is separated from the paper layer constituting side B. Specifically, the paper layers are carefully separated manually while checking each layer. If the paper layers are difficult to peel off, the process of soaking in 80°C water is repeated. If the paper substrate is an interleaf paper and adhesive is attached to the paper layer to be measured, use a knife or cutter to remove as much of the adhesive as possible.
The separated paper layer is cut into a 40 cm square, soaked in ion-exchanged water adjusted to a concentration of 2%, and soaked for 24 hours.
After soaking for 24 hours, the pulp is defibrated into fibers using a standard defibrator (manufactured by Kumagai Riki Kogyo Co., Ltd.) in accordance with JIS P8220-2:2012 until no undefibrated fibers remain.
The slurry after disintegration (dispersion of pulp fibers) is adjusted to a solids concentration of 0.1% by mass, and the pulp solids concentration is calculated in accordance with JIS P8225: 2003. The slurry after disintegration is adjusted to a solids concentration of 0.004% by mass and 500 g of slurry, and the amount taken is recorded. The solids concentration and the amount of slurry taken are used to calculate the dry weight of the sample.
The obtained slurry is used to measure the "length-weighted average fiber length" and "fiber width" using a fiber length measuring machine (Valmet FS-5 with UHD base unit, manufactured by Valmet) in accordance with ISO 16065-2:2007.
The instrument can also detect and measure each fiber using an attached camera, and images are taken in a measurement cell with a depth of field of 0.5 mm in accordance with the ISO 16505-2:2007 standard. The instrument captures fiber lengths of 0.01 mm to 10.00 mm. Fibers of 0.2 mm to 7.0 mm are selected for the measurement of "fiber length" and "fiber width." The average fiber width is the arithmetic mean value of the fiber widths of all the fibers obtained.

<Specific tensile strength when humidified>
The tensile strength of the paper substrate is measured using a load cell tensile tester (manufactured by A&D Co., Ltd., model number RTG-1310) with the distance between the two grippers set to 100 mm and the pulling speed set to 5 mm/min. The measurement environment is a humidity controlled environment specified in JIS P 8111:1998.
The test pieces were cut to a width of 15 mm and a length of 140 mm, and placed in a constant temperature and humidity chamber set to a temperature of 50° C. and a relative humidity of 65% so that the moisture content was adjusted to 10% by mass. The moisture content was calculated by the following formula.
Moisture content (mass%)={(mass of test piece (after hydration)−absolute dry mass of test piece)/mass of test piece (after hydration)}×100
If the moisture content is not 10% by mass, adjust the relative humidity setting of the thermo-hygroscopic chamber, place the specimen in the thermo-hygroscopic chamber again, and repeat the adjustment until the moisture content reaches 10% by mass. The bone dry mass is the mass of the specimen when it is cooled to room temperature after being placed in a dryer at 105°C for 1 hour, and is measured in advance. The specimen adjusted to a moisture content of 10% by mass is stored in an aluminum pouch until immediately before measurement.
The specific tensile strength is determined by dividing the obtained tensile strength by the basis weight measured in accordance with JIS P 8124: 2011. The specific tensile strength in the machine direction and the specific tensile strength in the cross direction are measured at 10 points each, and the arithmetic average value of these is used.

<Fiber orientation ratio>
The fiber orientation ratio of the paper substrate is measured by measuring the ultrasonic propagation velocity (Vmd) in the longitudinal direction of the paper substrate and the ultrasonic propagation velocity (Vcd) in the transverse direction of the paper substrate using a Sonic Sheet Tester (SST) manufactured by Nomura Shoji Co., Ltd. The ratio (Vmd/Vcd) is taken as the fiber orientation ratio. Ten samples are measured, and the arithmetic average value is used.

The invention will be explained in detail below using examples, but the scope of the invention is not limited to the description of the examples. Also, unless otherwise specified, "parts" refers to "parts by mass."

(Example 1-1)
(Paper base material)
A multi-layer paper base material having two paper layers (paper layer A and paper layer B) was manufactured by the following procedure.
As the pulp raw material for the paper layer A, LBKP (acacia pulp and eucalyptus pulp manufactured by Oji Paper Co., Ltd.) and waste paper pulp (waste magazine paper and waste newspaper paper) were mixed in a mass ratio of 50:50 and beaten using a double disc refiner to obtain a pulp slurry. The beating conditions were adjusted so that the freeness of the pulp slurry was 400 to 450 ml, including the pulp concentration, processing amount, and beating power.
To 100 parts (solids content) of the obtained pulp slurry, 1.20 parts (solids content) of aluminum sulfate (liquid aluminum sulfate manufactured by Asahi Chemical Industry Co., Ltd.) were added as an internal paper strength enhancer (PS373-20 manufactured by Arakawa Chemical Industry Co., Ltd.), 0.20 parts (solids content) of a polyacrylamide-based dry strength enhancer (PS373-20 manufactured by Arakawa Chemical Industry Co., Ltd.) as an internal sizing agent, and 1.00 parts (solids content) of a rosin-based sizing agent (Sizepine N811M manufactured by Arakawa Chemical Industry Co., Ltd.) as an internal sizing agent were added to prepare the paper material for paper layer A.

As the pulp raw material for paper layer B, LBKP (acacia pulp and eucalyptus pulp manufactured by Oji Paper Co., Ltd.) and waste paper pulp (waste magazine paper and waste newspaper paper) were mixed in a mass ratio of 50:50 and beaten using a double disc refiner to obtain a pulp slurry. The beating conditions were adjusted as follows: pulp concentration, processing amount, and beating power so that the freeness of the pulp slurry was 400 to 450 ml.
To 100 parts (solids content) of the obtained pulp slurry, 0.30 parts (solids content) of aluminum sulfate (liquid aluminum sulfate manufactured by Asahi Chemical Industry Co., Ltd.), 0.20 parts (solids content) of a polyacrylamide-based dry strength agent (PS373-20 manufactured by Arakawa Chemical Industry Co., Ltd.), and 0.10 parts (solids content) of a rosin-based sizing agent (Sizepine N811M manufactured by Arakawa Chemical Industry Co., Ltd.) were added to prepare the paper material for paper layer B.

The paper materials for paper layers A and B were each made using a Fourdrinier papermaking machine to have a basis weight of 560 g/ ^m2 , with the J/W ratio adjusted to give a fiber orientation ratio of 1.62. Starch was then applied between the layers A and B at 1.0 g/ ^m2 by interlayer spray, and the layers were combined to obtain a paper base material with a basis weight of 1,121 g/ ^m2 .

(Example 1-2)
The paper base material of the paper layer A and the paper layer B were each made using a Fourdrinier paper machine so that the basis weight was 400 g/ ^m2 , and a paper base material of 801 g/ ^m2 was obtained under the same conditions as in Example 1-1.

(Examples 1 to 3)
The paper base material of the paper layer A and the paper layer B were each made using a Fourdrinier paper machine so that the basis weight was 320 g/ ^m2 , and a paper base material of 641 g/ ^m2 was obtained under the same conditions as in Example 1-1.

(Examples 1 to 4)
A paper base material was obtained under the same conditions as in Example 1-2, except that 1.30 parts (solid content equivalent) of aluminum sulfate and 1.10 parts (solid content equivalent) of a rosin-based sizing agent were added to 100 parts (solid content equivalent) of the pulp slurry of paper layer A.

(Examples 1 to 5)
A paper base material was obtained under the same conditions as in Example 1-2, except that 0.70 parts (solids content equivalent) of aluminum sulfate and 0.50 parts (solids content equivalent) of a rosin-based sizing agent were added to 100 parts (solids content equivalent) of the pulp slurry of paper layer A.

(Examples 1 to 6)
A paper base material was obtained under the same conditions as in Example 1-2, except that 0.50 parts (solids) of aluminum sulfate and 0.25 parts (solids) of a rosin-based sizing agent were added to 100 parts (solids) of the pulp slurry of paper layer A.

(Examples 1 to 7)
A paper base material was obtained under the same conditions as in Example 1-2, except that 0.70 parts (solids equivalent) of aluminum sulfate and 0.50 parts (solids equivalent) of a rosin-based sizing agent were added to 100 parts (solids equivalent) of the pulp slurry of paper layer B.

(Examples 1 to 8)
A paper base material was obtained under the same conditions as in Example 1-2, except that 1.00 part (solid content equivalent) of aluminum sulfate and 0.90 parts (solid content equivalent) of a rosin-based sizing agent were added to 100 parts (solid content equivalent) of the pulp slurry of paper layer B.

(Examples 1 to 9)
A paper base material was obtained under the same conditions as in Example 1-2, except that NBKP (Douglas fir pulp, radiata pine pulp, and cedar pulp manufactured by Oji Paper Co., Ltd.) and LBKP were mixed in a mass ratio of 60:40 as the pulp raw material for paper layer A.

(Examples 1 to 10)
A paper base material was obtained under the same conditions as in Example 1-2, except that NBKP and LBKP were mixed in a mass ratio of 80:20 as the pulp raw material for paper layer A.

(Examples 1 to 11)
A paper base material was obtained under the same conditions as in Example 1-2, except that NBKP and LBKP were mixed in a mass ratio of 60:40 as the pulp raw material for paper layer B.

(Example 1-12)
A paper base material was obtained under the same conditions as in Example 1-2, except that NBKP and LBKP were mixed in a mass ratio of 80:20 as the pulp raw material for paper layer B.

(Example 1-13)
A paper base material was obtained under the same conditions as in Example 1-2, except that 0.05 parts (solids equivalent) of a polyacrylamide-based dry strength agent was added per 100 parts (solids equivalent) of the pulp slurry of paper layer A, and 0.05 parts (solids equivalent) of a polyacrylamide-based dry strength agent was added per 100 parts (solids equivalent) of the pulp slurry of paper layer B.

(Example 1-14)
A paper base material was obtained under the same conditions as in Example 1-2, except that 0.50 parts (solids equivalent) of a polyacrylamide-based dry strength agent was added per 100 parts (solids equivalent) of the pulp slurry of paper layer A, and 0.50 parts (solids equivalent) of a polyacrylamide-based dry strength agent was added per 100 parts (solids equivalent) of the pulp slurry of paper layer B.

(Example 1-15)
A paper base material was obtained under the same conditions as in Example 1-2, except that the J/W ratio was adjusted so that the fiber orientation ratio was 1.42.

(Example 1-16)
A paper base material was obtained under the same conditions as in Example 1-2, except that the J/W ratio was adjusted so that the fiber orientation ratio was 2.48.

(Comparative Example 1-1)
The paper base material of the paper layer A and the paper layer B were each made using a Fourdrinier paper machine so that the basis weight was 200 g/ ^m2 , and a paper base material of 401 g/ ^m2 was obtained under the same conditions as in Example 1-1.

(Comparative Example 1-2)
The paper base material of the paper layer A and the paper layer B were each made using a Fourdrinier paper machine so that the basis weight was 800 g/ ^m2 , and a paper base material of 1601 g/ ^m2 was obtained under the same conditions as in Example 1-1.

(Comparative Example 1-3)
A paper base material was obtained under the same conditions as in Example 1-2, except that 0.30 parts (solid content equivalent) of aluminum sulfate and 0.10 parts (solid content equivalent) of a rosin-based sizing agent were added per 100 parts (solid content equivalent) of the pulp slurry of paper layer A, and 0.30 parts (solid content equivalent) of aluminum sulfate and 0.08 parts (solid content equivalent) of a rosin-based sizing agent were added per 100 parts (solid content equivalent) of the pulp slurry of paper layer B.

(Comparative Examples 1 to 4)
A paper base material was obtained under the same conditions as in Example 1-2, except that 1.40 parts (solid content equivalent) of aluminum sulfate and 1.20 parts (solid content equivalent) of a rosin-based sizing agent were added per 100 parts (solid content equivalent) of the pulp slurry of paper layer A, and 1.30 parts (solid content equivalent) of aluminum sulfate and 1.10 parts (solid content equivalent) of a rosin-based sizing agent were added per 100 parts (solid content equivalent) of the pulp slurry of paper layer B.

(Comparative Example 1-5)
A paper base material was obtained under the same conditions as in Example 1-2, except that 0.20 parts (solids) of aluminum sulfate and 0.04 parts (solids) of a rosin-based sizing agent were added to 100 parts (solids) of the pulp slurry of paper layer B.

(Comparative Example 1-6)
A paper base material was obtained under the same conditions as in Example 1-2, except that NBKP and LBKP were mixed in a mass ratio of 85:15 as the pulp raw material for paper layer A.

(Comparative Example 1-7)
A paper base material was obtained under the same conditions as in Example 1-2, except that NBKP and LBKP were mixed in a mass ratio of 85:15 as the pulp raw material for paper layer B.

(Example 2-1)
(Paper base material)
A paper base material was produced in the form of an interleaving paper in which two sheets of base paper (paper layer A and paper layer B) were bonded together with an adhesive by the following procedure.
As the pulp raw material for the paper layer A, LBKP (acacia pulp and eucalyptus pulp manufactured by Oji Paper Co., Ltd.) and waste paper pulp (waste magazine paper and waste newspaper paper) were mixed in a mass ratio of 50:50 and beaten using a double disc refiner to obtain a pulp slurry. The beating conditions were adjusted so that the freeness of the pulp slurry was 400 to 450 ml, including the pulp concentration, processing amount, and beating power.
To 100 parts (solids equivalent) of the obtained pulp slurry, 1.20 parts (solids equivalent) of aluminum sulfate (liquid aluminum sulfate manufactured by Asahi Chemical Industry Co., Ltd.) were added as an internal paper strength enhancer, 0.20 parts (solids equivalent) of a polyacrylamide-based dry paper strength enhancer (PS373-20 manufactured by Arakawa Chemical Industry Co., Ltd.) as an internal paper strength enhancer, and 1.00 parts (solids equivalent) of a rosin-based sizing agent (Size Pine N811M manufactured by Arakawa Chemical Industry Co., Ltd.) as an internal sizing agent were added to prepare a paper stock. The obtained paper stock was made using a Fourdrinier paper machine, adjusting the J/W ratio so that the fiber orientation ratio was 1.62, to obtain a paper layer A having a basis weight of 560 g/ ^m2 .

As the pulp raw material for paper layer B, LBKP (acacia pulp and eucalyptus pulp manufactured by Oji Paper Co., Ltd.) and waste paper pulp (waste magazine paper and waste newspaper paper) were mixed in a mass ratio of 50:50 and beaten using a double disc refiner to obtain a pulp slurry. The beating conditions were adjusted as follows: pulp concentration, processing amount, and beating power so that the freeness of the pulp slurry was 400 to 450 ml.
To 100 parts (solids equivalent) of the obtained pulp slurry, 0.30 parts (solids equivalent) of aluminum sulfate (liquid aluminum sulfate manufactured by Asahi Chemical Industry Co., Ltd.), 0.20 parts (solids equivalent) of a polyacrylamide-based dry strength agent (PS373-20 manufactured by Arakawa Chemical Industry Co., Ltd.), and 0.10 parts (solids equivalent) of a rosin-based sizing agent (Sizepine N811M manufactured by Arakawa Chemical Industry Co., Ltd.) were added to prepare a paper stock. The obtained paper stock was made using a Fourdrinier papermaking machine, adjusting the J/W ratio so that the fiber orientation ratio was 1.62, to obtain a paper layer B with a basis weight of 560 g/ ^m2 .

An acrylic emulsion adhesive was applied to one side of the obtained paper layer A ^at 5 g/m2, and the paper layer B was laminated to obtain a paper base material for an interleaf paper having a basis weight of 1125 g/ ^m2 .

(Example 2-2)
The paper base material was obtained under the same conditions as in Example 2-1, except that the paper layers A and B were each made using a Fourdrinier paper machine so that the basis weight was 400 g/ ^m2 , and the paper base material had a basis weight of 805 g/ ^m2 .

(Example 2-3)
The paper base material was obtained under the same conditions as in Example 2-1, except that the paper layers A and B were each made using a Fourdrinier paper machine to have a basis weight of 320 g/ ^m2 , and the paper base material had a basis weight of 645 g/ ^m2 .

(Example 2-4)
A paper base material was obtained under the same conditions as in Example 2-2, except that 1.30 parts (solids equivalent) of aluminum sulfate and 1.10 parts (solids equivalent) of a rosin-based sizing agent were added to 100 parts (solids equivalent) of the pulp slurry of paper layer A.

(Example 2-5)
A paper base material was obtained under the same conditions as in Example 2-2, except that 0.70 parts (solids equivalent) of aluminum sulfate and 0.50 parts (solids equivalent) of a rosin-based sizing agent were added to 100 parts (solids equivalent) of the pulp slurry of paper layer A.

(Example 2-6)
A paper base material was obtained under the same conditions as in Example 2-2, except that 0.50 parts (solids content equivalent) of aluminum sulfate and 0.25 parts (solids content equivalent) of a rosin-based sizing agent were added to 100 parts (solids content equivalent) of the pulp slurry of paper layer A.

(Example 2-7)
A paper base material was obtained under the same conditions as in Example 2-2, except that 0.70 parts (solids content equivalent) of aluminum sulfate and 0.50 parts (solids content equivalent) of a rosin-based sizing agent were added to 100 parts (solids content equivalent) of the pulp slurry of paper layer B.

(Example 2-8)
A paper base material was obtained under the same conditions as in Example 2-2, except that 1.00 part (solid content equivalent) of aluminum sulfate and 0.90 parts (solid content equivalent) of a rosin-based sizing agent were added to 100 parts (solid content equivalent) of the pulp slurry of paper layer B.

(Example 2-9)
A paper base material was obtained under the same conditions as in Example 2-2, except that NBKP (Douglas fir pulp, radiata pine pulp, and cedar pulp manufactured by Oji Paper Co., Ltd.) and LBKP were mixed in a mass ratio of 60:40 as the pulp raw material for paper layer A.

(Example 2-10)
A paper base material was obtained under the same conditions as in Example 2-2, except that NBKP and LBKP were mixed in a mass ratio of 80:20 as the pulp raw material for paper layer A.

(Example 2-11)
A paper base material was obtained under the same conditions as in Example 2-2, except that NBKP and LBKP were mixed in a mass ratio of 60:40 as the pulp raw material for paper layer B.

(Example 2-12)
A paper base material was obtained under the same conditions as in Example 2-2, except that NBKP and LBKP were mixed in a mass ratio of 80:20 as the pulp raw material for paper layer B.

(Example 2-13)
A paper base material was obtained under the same conditions as in Example 2-2, except that 0.05 parts (solids equivalent) of a polyacrylamide-based dry strength agent was added per 100 parts (solids equivalent) of the pulp slurry of paper layer A, and 0.05 parts (solids equivalent) of a polyacrylamide-based dry strength agent was added per 100 parts (solids equivalent) of the pulp slurry of paper layer B.

(Example 2-14)
A paper base material was obtained under the same conditions as in Example 2-2, except that 0.50 parts (solids equivalent) of a polyacrylamide-based dry strength agent was added per 100 parts (solids equivalent) of the pulp slurry of paper layer A, and 0.50 parts (solids equivalent) of a polyacrylamide-based dry strength agent was added per 100 parts (solids equivalent) of the pulp slurry of paper layer B.

(Example 2-15)
A paper base material was obtained under the same conditions as in Example 2-2, except that the J/W ratio was adjusted so that the fiber orientation ratio was 1.42.

(Example 2-16)
A paper base material was obtained under the same conditions as in Example 2-2, except that the J/W ratio was adjusted so that the fiber orientation ratio was 2.48.

(Comparative Example 2-1)
The paper base material was obtained under the same conditions as in Example 2-1, except that the paper layer A and the paper layer B were each made using a Fourdrinier paper machine so that the basis weight was 200 g/ ^m2 , and the paper base material had a basis weight of 405 g/ ^m2 .

(Comparative Example 2-2)
The paper base material was obtained under the same conditions as in Example 2-1, except that the paper layers A and B were each made using a Fourdrinier paper machine so that the basis weight was 800 g/ ^m2 , and the paper base material had a basis weight of 1605 g/ ^m2 .

(Comparative Example 2-3)
A paper base material was obtained under the same conditions as in Example 2-2, except that 0.30 parts (solid content equivalent) of aluminum sulfate and 0.10 parts (solid content equivalent) of a rosin-based sizing agent were added per 100 parts (solid content equivalent) of the pulp slurry of paper layer A, and 0.30 parts (solid content equivalent) of aluminum sulfate and 0.08 parts (solid content equivalent) of a rosin-based sizing agent were added per 100 parts (solid content equivalent) of the pulp slurry of paper layer B.

(Comparative Example 2-4)
A paper base material was obtained under the same conditions as in Example 2-2, except that 1.40 parts (solid content equivalent) of aluminum sulfate and 1.20 parts (solid content equivalent) of a rosin-based sizing agent were added per 100 parts (solid content equivalent) of the pulp slurry of paper layer A, and 1.30 parts (solid content equivalent) of aluminum sulfate and 1.10 parts (solid content equivalent) of a rosin-based sizing agent were added per 100 parts (solid content equivalent) of the pulp slurry of paper layer B.

(Comparative Example 2-5)
A paper base material was obtained under the same conditions as in Example 2-2, except that 0.20 parts (solids) of aluminum sulfate and 0.04 parts (solids) of a rosin-based sizing agent were added to 100 parts (solids) of the pulp slurry of paper layer B.

(Comparative Example 2-6)
A paper base material was obtained under the same conditions as in Example 2-2, except that NBKP and LBKP were mixed in a mass ratio of 85:15 as the pulp raw material for paper layer A.

(Comparative Example 2-7)
A paper base material was obtained under the same conditions as in Example 2-2, except that NBKP and LBKP were mixed in a mass ratio of 85:15 as the pulp raw material for paper layer B.

<Moisture molding>
The paper substrates obtained in the examples and comparative examples were punched out to a length of 122 mm and a width of 167 mm to prepare blanks for humid molding. In an environment with a temperature of 23°C and a humidity of 50% RH, water vapor was sprayed onto side B of the blank so that the moisture content of the blank was 10% by mass, and an acrylic emulsion adhesive was applied to one of the joints at a 1 cm portion of the edge of the blank. The blank was placed between the male and female dies of a specified mold, and then pressure molded under conditions of a pressure of 0.3 kg/ ^cm2 and a press time of 5 seconds to produce cylindrical paper containers with a diameter of 50 mm.

<Evaluation of moldability during humid molding>
The outer and inner surfaces of the three paper containers obtained were observed and evaluated according to the following criteria. The results are shown in Tables 1 and 2.
A: 0 containers with cracks (tears or avoided areas), dents, or folds in the paper base material. B: 0 containers with cracks (tears or avoided areas) or dents in the paper base material, and 1 container with a fold. C: 0 containers with cracks (tears or avoided areas) or dents in the paper base material, and 2 containers with a fold. D: 1 or more containers with cracks (tears or avoided areas) or dents in the paper base material, or 3 containers with a fold.

<Evaluation of durability when dropped>
The obtained paper container was dropped from a height of 80 cm without acceleration onto a floor with a stainless steel plate placed on it, with one opening of the cylinder horizontal. The appearance of the paper container after the drop was observed and evaluated according to the following criteria. The results are shown in Tables 1 and 2. Note that "deformation" refers to a state in which a dent was found on the side of the cylinder and the paper base material was folded in one or more places.
A: No deformation was observed even after being dropped three times.
B: Deformation is observed after being dropped three times.
C: Deformation is observed after two drops.
D: Deformation is observed after one drop.

<Beauty after wetting>
The obtained paper container was left to stand for 1 hour in a high temperature and high humidity environment at a temperature of 80° C. and a relative humidity of 65%. After the vibration test, the appearance of the paper container was observed and the touch was confirmed, and the paper container was evaluated according to the following criteria. The results are shown in Tables 1 and 2. The vibration test was performed in accordance with JIS Z0232:2020 under conditions of random vibration and vertical orientation for 90 minutes.
A: No wrinkles were observed on the surface of side A of the paper container, and it felt firm to the touch.
B: No wrinkles are visible on the surface of side A of the paper container, but it feels soft to the touch.
C: Wrinkles appear on the surface of side A of the paper container, but it does not tear when touched.
D: Wrinkles have appeared on the surface of side A of the paper container, and some tears can be seen when touched.

Claims (8)

A paper substrate for moist forming, comprising:
The paper base material has two or more paper layers,
The thickness of the paper base material is 0.8 to 1.5 mm;
When one surface of the paper base material is designated as side A and the other surface is designated as side B,
The Cobb water absorbency measured from the A side of the paper base material is equal to or lower than the Cobb water absorbency measured from the B side,
The Cobb water absorbency measured from the A side is 10 to 700 g/ ^m2 ·60 seconds,
The Cobb water absorbency measured from the side B is 10 to 1000 g/ ^m2 ·60 seconds,
Both of the average fiber width of the pulp contained in the paper layer constituting one surface of the paper base material and the average fiber width of the pulp contained in the paper layer constituting the other surface of the paper base material are 28.0 μm or less.
A paper substrate for moist forming, comprising: The paper base material for moist forming according to claim 1, wherein the average value of the longitudinal tensile strength of the paper base material per basis weight and the transverse tensile strength of the paper base material per basis weight, measured after adjusting the moisture content of the paper base material to 10% by mass, is 12.0 to 43.0 Nm/g. The paper base material is a multi-layer paper having two or more layers of the paper, or a laminated paper having two or more base papers attached thereto,
The paper substrate for moist forming according to claim 1 , wherein each of the two or more base papers comprises the paper layer. The paper base material for moisturizing molding according to claim 1, wherein the pulp contained in the paper layer contains hardwood kraft pulp and recycled paper pulp. The paper base material for moist forming according to claim 1, wherein the difference between the Cobb water absorbency measured from side B and the Cobb water absorbency measured from side A (side B-side A) is 20 to 900 g/ ^m2 ·60 seconds. A paper product made using the paper base material for moist forming according to any one of claims 1 to 5. A paper container made using the paper base material for moist forming described in any one of claims 1 to 5. The paper container has a bottle shape,
The paper container according to claim 7 , wherein the side A constitutes at least a portion of an outer surface of the paper container.