JP7601010B2 - Base paper for processing, sheets for paper containers and paper containers - Google Patents

Description

The present invention relates to base paper for processing, a sheet for paper containers, and paper containers.

Conventionally, various paper products, such as cylinders, vessels, and lids for containers, are manufactured by bending base paper or a sheet laminated on the base paper. The stress induced in the base paper or sheet by such bending can cause cracks in the base paper or sheet. For this reason, various technologies have been developed to prevent cracks caused by such stress.

For example, the invention of Patent Document 1 is an example of a technology for preventing destruction of the laminate layer on the base paper due to folding cracks in the base paper. Patent Document 1 discloses a base paper for liquid containers in which the weight ratio of outer layer:inner layer:outer layer is 1:2:1 to 1:3:1, the inner bond strength of the outer layer is 0.20 to 0.36 N.m, and the inner bond strength of the inner layer is 0.05 to 0.28 N.m.

Furthermore, as an example of a technology for imparting to base paper a paper strength capable of suppressing cracking due to tensile forces during bending, there is the invention described in Patent Document 2. Patent Document 2 discloses a processing base paper in which a pigment coating layer containing a pigment and a binder is provided on at least one side of a base paper whose main component is pulp.

JP 2009-242999 A JP 2007-100222 A

In curling, the base paper or sheet needs to be bent to a certain angle, but if strong buckling equivalent to that in folding occurs in the paper layer, the buckling may cause product defects. This problem is particularly noticeable in curling (top curling) performed on the mouth of a paper cup or the like. Top curling is a curling process in which the edge of the base paper or the like is tightly curled outward to a small diameter of about 2 to 3 mm. Therefore, top curling requires adjusting the buckling of the paper layer caused by the large stress induced by the high curvature processing to an appropriate range, and furthermore, causing the adjusted buckling to occur continuously. In order to perform bending processes that are prone to causing product defects, such as top curling, in large quantities while maintaining a certain quality, the base paper for processing needs to have excellent bending suitability, but there was room for improvement in bending suitability in the base paper for processing in the conventional technology.

The object of the present invention is to provide a base paper and a sheet for paper containers that are excellent in bending suitability and can suppress the occurrence of product defects. Another object of the present invention is to provide a paper container using the base paper and a paper container using the sheet for paper containers.

Specifically, the present invention has the following configuration.

[1] A converting base paper whose main component is cellulose pulp and whose maximum bending stress in at least one direction within a bending angle range of 0 to 90 degrees is 215 N/m or less.
[2] The converting base paper according to [1], wherein the inflection point of the bending stress curve is in the bending angle range of 0 to 40 degrees.
[3] The converting base paper according to [1] or [2], in which the tensile strength in the MD direction is 35 kN/m or less, the tensile strength in the CD direction is 22 kN/m or less, and the average value of the tensile strengths in the MD direction and the CD direction is 28 kN/m or less.
[4] The converting base paper according to any one of [1] to [3], in which the tensile strength in the MD direction is T1 and the tensile strength in the CD direction is T2, the value of T1/T2 is 1.1 or more and less than 3.0.
[5] The converting base paper according to any one of [1] to [4], having an ash content of 0.5 to 40.0 mass% as measured by the ash content test method specified in JIS P 8251:2003.
[6] The converting base paper according to any one of [1] to [5], which is composed of two or more paper layers and has an interlaminar strength of 100 J/m2 or ^more as measured by the internal bond tester method specified in JAPAN TAPPI 18-2.
[7] The converting base paper according to [6], having an interlaminar strength of 1000 J/ ^m2 or less as measured by the internal bond tester method specified in JAPAN TAPPI 18-2.
[8] The converting base paper according to any one of [1] to [7], which is composed of three or more paper layers.
[9] The converting base paper according to [8], in which the value of W1/W2 is 1.05 to 2.10, where W1 is the average basis weight of the outermost paper layer and W2 is the average basis weight of the first inner layer located immediately inside the outermost paper layer.
[10] The converting base paper according to [8] or [9], wherein the ash content of the outermost paper layer, as measured by the ash content test method specified in JIS P 8251:2003, is at least 1.0% by mass lower than the ash content of the inner paper layer.
[11] The converting base paper according to any one of [8] to [10], wherein the ash content of the outermost paper layer is less than 0.5% by mass as measured by the ash content test method specified in JIS P 8251:2003.
[12] The converting base paper according to any one of [6] to [11], further comprising an adhesive layer between the paper layers, the adhesive layer containing starch or polyacrylamide.
[13] The paper layer contains a polyacrylamide-based paper strength agent,
The converting base paper according to any one of [1] to [12], wherein the content of the polyacrylamide-based paper strength agent per 100 parts by mass of the cellulose pulp is 0.02 parts by mass or more and less than 1 part by mass.
[14] The converting base paper according to any one of [1] to [13], having a basis weight of 200 to 400 g/ ^m2 and a density of 0.80 to 1.00 g/ ^cm3 .
[15] A sheet for paper containers having a thermoplastic resin layer on at least one side of the converting base paper according to any one of [1] to [14].
[16] The sheet for paper containers according to [15], wherein the maximum bending stress in at least one direction within a bending angle range of 0 to 90 degrees is 230 N/m or less.
[17] The converting base paper has the thermoplastic resin layer on both sides thereof,
The sheet for paper containers according to [15] or [16], wherein the melting point of one thermoplastic resin layer is at least 3° C. lower than the melting point of the other thermoplastic resin layer.
[18] A paper container made from the converting base paper according to any one of [1] to [14] or the paper container sheet according to any one of [15] to [17].

According to the present invention, it is possible to provide a base paper for processing and a sheet for paper containers that are excellent in bending processability and can suppress the occurrence of product defects. In addition, it is possible to provide paper containers with fewer product defects using the base paper for processing, and paper containers with fewer product defects using the sheet for paper containers.

This is an example where the bending stress curve graph has an inflection point. This is an example where the bending stress curve graph does not have an inflection point.

The following is a detailed description of an embodiment of the present invention. The following description of the constituent elements may be based on representative embodiments or specific examples, but the present invention is not limited to such embodiments. In this specification, the numerical range represented by "X to Y" means greater than or equal to X and less than or equal to Y.

[Base paper for processing]
The processing base paper of this embodiment is a base paper mainly composed of cellulose pulp, and the maximum bending stress in at least one direction in the range of bending angles of 0 to 90 degrees is 215 N/m or less. Since the processing base paper of this embodiment has the above-mentioned configuration, it has excellent bending suitability, and can suppress the occurrence of product defects during processing. For example, when the processing base paper of this embodiment is subjected to top curl processing (bending processing), the occurrence of wrinkles, cracks, peeling, etc. in the top curl portion is suppressed. Furthermore, such an effect is exerted not only when the processing base paper of this embodiment is subjected to top curl processing, but also when a folding process such as square processing is performed. Thus, since the processing base paper of this embodiment has excellent bending suitability, when a paper container (container) or the like is formed using the processing base paper of this embodiment, a paper container (container) with excellent appearance can be obtained.

In this embodiment, the processing base paper may be a single-ply material, but is preferably a multi-ply material composed of three or more paper layers. When the processing base paper is a multi-ply material, the paper layers constituting the processing base paper are preferably three or more layers, more preferably four or more layers, and even more preferably five or more layers.

(pulp)
The base paper for processing is mainly composed of cellulose pulp (hereinafter, also simply referred to as pulp). Here, the main component refers to a component that occupies 50% by mass or more of the components that constitute the base paper for processing. There is no particular limit to the type of cellulose pulp, but it is preferable to contain chemical pulp from the viewpoint of strength. There is no particular limit to the chemical pulp, but it is preferable to contain hardwood kraft pulp (LKP) or softwood kraft pulp (NKP). The pulp may be bleached pulp or unbleached pulp. Hereinafter, unless otherwise specified, LKP and NKP include bleached pulp or unbleached pulp, respectively, but hardwood bleached kraft pulp may be referred to as LBKP and softwood bleached kraft pulp may be referred to as NBKP. Acacia wood, eucalyptus wood, etc. can be used as LKP, and radiata pine wood, etc. can be used as NKP.

LKP has shorter fibers and is weaker than NKP, but the paper made from it has excellent texture and smoothness. In order to obtain good printability, good texture and smoothness are necessary for the processing base paper, so the content of LKP in the processing base paper is preferably 50% by mass or more, more preferably 60% by mass, and even more preferably 70% by mass or more, based on the total mass of the pulp components of the processing base paper. In addition, the content of NKP is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the pulp components. When the processing base paper is a multilayer material, the content of LKP in the outer layer (front layer and back layer) is preferably 50% by mass or more, more preferably 60% by mass, and even more preferably 70% by mass or more, based on the total mass of the pulp components of the outer layer. In addition, the content of NKP in the outer layer is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the pulp components of the outer layer. When the processing base paper is a multi-layer material, the content of LKP in the middle layer is preferably 50% by mass or more, more preferably 60% by mass, and even more preferably 70% by mass or more, based on the total mass of the pulp components of the middle layer. In addition, the content of NKP in the middle layer is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, based on the total mass of the pulp components of the outer layer.

The base paper for processing may contain pulps other than the above-mentioned NKP and LKP (hereinafter referred to as other pulps). Examples of other pulps include mechanical pulps such as stone ground pulp (SGP), pressurized stone ground pulp (PGW), refiner ground pulp (RGP), thermo ground pulp (TGP), chemi-ground pulp (CGP), groundwood pulp (GP), and thermomechanical pulp (TMP), disintegrated waste paper pulp (DIP) produced from brown waste paper, kraft envelope waste paper, magazine waste paper, newspaper waste paper, flyer waste paper, office waste paper, cardboard waste paper, white waste paper, Kent waste paper, imitation waste paper, and land certificate waste paper, and pulps produced chemically or mechanically from non-wood fibers such as kenaf, hemp, and reed. The content of other pulps is preferably less than 3% by mass, more preferably less than 2% by mass, and even more preferably less than 1% by mass, based on the total mass of the pulp components.

In general, the lower the freeness of pulp, the greater the tensile strength of the paper product. Freeness is also called freeness. Hereinafter, freeness in this specification refers to Canadian Standard Freeness (csf).

Reducing the freeness increases the tensile strength, but at the same time, the paper tends to become harder and its moldability decreases. To achieve a base paper for processing that has a relatively high tensile strength and also has excellent moldability, it is preferable that the disintegrated freeness (csf) of the pulp is 410 to 600 ml. It is more preferable that the disintegrated freeness (csf) is 420 to 590 ml, and even more preferable that it is 430 to 580 ml.

Disintegrated freeness (csf) refers to the freeness value measured using a pulp slurry obtained by disintegrating the base paper for processing. Disintegrated freeness (csf) can be adjusted by increasing or decreasing the freeness of the cellulose pulp before papermaking. The freeness (csf) of the cellulose pulp before papermaking is preferably 360 to 550 ml, more preferably 370 to 540 ml, and even more preferably 380 to 530 ml.

(Filling)
As the filler to be mixed when making the base paper for processing, inorganic fillers and organic fillers generally used in the papermaking field can be used. Examples of inorganic fillers include clay, calcined kaolin, delaminated kaolin, heavy calcium carbonate, light calcium carbonate, light calcium carbonate-silica composite, magnesium carbonate, barium carbonate, titanium dioxide, zinc oxide, silicon oxide, amorphous silica, aluminum hydroxide, calcium hydroxide, magnesium hydroxide, zinc hydroxide, etc. Examples of organic fillers include urea-formalin resin, polystyrene resin, phenolic resin, micro hollow particles, etc. These fillers can be used appropriately depending on the purpose, but for the purpose of moderately lowering the tensile strength and moderately lowering the bending strength, the use of light calcium carbonate is preferred because of its ease of use.

The above-mentioned fillers can be used alone or in combination of two or more types depending on the application of the processing base paper, but in order to realize a processing base paper that can suppress the occurrence of product defects even when bending processing, which is likely to cause product defects, is performed, it is preferable to contain at least one inorganic filler. The inorganic filler may be added so that the ash content of the processing base paper is less than 0.5 mass%, but may also be added so that it is 0.5 mass% or more. The inorganic filler may be added so that the ash content of the processing base paper is 40.0 mass% or less, or 30.0 mass% or less, more preferably 25.0 mass% or less, 20.0 mass% or less, or 15.0 mass% or less. The above ash content is the ratio of ash content to the total mass of the processing base paper. More specifically, the ash content is a value calculated by the following formula.
Ash content (mass%) = (mass of ash contained in the base paper) / (bone dry mass of the base paper)
The mass of ash in the processing base paper is measured by the ash content test method (525°C combustion method) specified in JIS P 8251:2003. By setting the ash content of the processing base paper within the above range, it becomes easy to reduce the tensile strength while maintaining the interlaminar strength of the processing base paper. The interlaminar strength and tensile strength will be described later.

In the case where the processing base paper of this embodiment is a multi-layer material composed of three or more paper layers, the amount of filler may be increased or decreased for each paper layer. For example, the surface of the processing base paper, in other words the surface of the outermost paper layer, may be subjected to surface treatment such as lamination after papermaking. Since the filler may have a negative effect on these surface treatments, it is preferable to reduce the amount of filler in the outermost paper layer or to not use any filler. Specifically, in a processing base paper having three or more paper layers, it is preferable that the ash content of the outermost paper layer on the front and back sides is 1.0% or more less than the ash content of the inner paper layer. In addition, it is preferable that the ash content of the outermost paper layer is less than 0.5% by mass. The above ash content is the ratio of ash to the total mass of the outermost paper layer. In this way, by reducing the filler content in the outermost paper layer to be surface-treated and blending more filler in the inner layer than the outermost paper layer, it is easy to improve bending suitability without adversely affecting the surface treatment.

(Paper strength agent)
A paper strength enhancer may be blended when the base paper for processing is made. The paper strength enhancer is not particularly limited as long as it can appropriately increase the strength of the base paper for processing. For example, examples of dry strength enhancers include polyacrylamide-based paper strength enhancers (PAM-based paper strength enhancers) and starch. Examples of wet strength enhancers include melamine resin, urea resin, polyamide-polyamine-epichlorohydrin resin (polyamide-epichlorohydrin resin). Among them, it is preferable to use a polyacrylamide-based paper strength enhancer (PAM-based paper strength enhancer) as the paper strength enhancer.

For example, when the processing base paper contains a polyacrylamide-based paper strength enhancer (PAM-based paper strength enhancer), the content of the polyacrylamide-based paper strength enhancer (PAM-based paper strength enhancer) is preferably 0.02 parts by mass or more and less than 1.2 parts by mass, and more preferably 0.02 parts by mass or more and less than 1 part by mass, per 100 parts by mass of pulp. By keeping the content of the polyacrylamide-based paper strength enhancer within the above range, the paper is not made excessively hard, and the processing base paper can be controlled to be more suitable for bending processing.

(Other internal additives)
When preparing the base paper for processing, various other internal additives may be appropriately selected and used as necessary. Examples of the other internal additives include sizing agents, retention improvers, freeness improvers, bulk improvers, thickeners, aluminum sulfate, polyvalent metal compounds, silica sol, defoamers, coloring dyes, coloring pigments, fluorescent whitening agents, pH adjusters, pitch control agents, slime control agents, etc.

When the processing base paper is used for paper containers for the purpose of containing highly acidic contents, it is preferable that the processing base paper does not deteriorate even with the highly acidic contents. Highly acidic contents generally placed in paper containers include, for example, foods such as yogurt, and sour drinks. In order to realize processing base paper that does not deteriorate even with highly acidic contents, it is preferable to use an alkyl ketene dimer as a sizing agent. The alkyl ketene dimer does not reduce the sizing properties even when it comes into contact with highly acidic foods or drinks. The content of the alkyl ketene dimer is preferably 0.08 to 0.4 parts by mass, and more preferably 0.1 to 0.3 parts by mass, per 100 parts by mass of pulp.

(Papermaking)
The processing base paper is preferably a multi-layer material formed by combining three or more paper layers on the wire of a papermaking machine, and more preferably a multi-layer material formed by combining five or more paper layers. By increasing the number of paper layers, the basis weight of each paper layer can be reduced, making it easier to obtain a texture, improving the surface properties, and making it possible to obtain a processing base paper with good printability. In addition, the more paper layers there are, the easier it is to make a crease when processing is performed, and the easier it is to make a processing base paper that is easy to fold at the crease parts. Processing base paper composed of multiple paper layers is generally manufactured by combining multiple inlets to form a multi-layer paper.

When multiple paper layers are combined to form a multi-layer material, the paper layers may be bonded with an interlayer adhesive such as starch or polyacrylamide. That is, the base paper for processing may further have an adhesive layer between the paper layers, and in this case, the adhesive layer may contain starch or polyacrylamide. This can further increase the interlayer strength. Any amount of interlayer adhesive can be used depending on the required interlayer strength, but for example, when starch is used, about 0.1 to 3.0 g/ ^m2 can be used, and when polyacrylamide is used, about 0.01 to 0.3 g/ ^m2 can be used.

Here, in order to identify each paper layer that makes up the processing base paper, a name is given to each paper layer. Hereinafter, the paper layers located on the outermost sides of the front and back of the processing base paper will be referred to as the outermost paper layers. The paper layer immediately inside the two outermost paper layers will be referred to as the first inner layer. The paper layer immediately inside the first inner layer will be referred to as the second inner layer. Hereinafter, even if the number of paper layers increases, the paper layers will be named according to the same naming rules.

When the average basis weight of the outermost paper layers on the front and back sides is W1 and the average basis weight of the first inner layer is W2, the converting base paper is preferably made so that W1/W2 = 1.05 to 2.10, more preferably W1/W2 = 1.20 to 2.00, and even more preferably W1/W2 = 1.50 to 1.80. The average basis weight W1 of the outermost paper layers on the front and back sides is preferably 30 to 200 g/m ² , more preferably 50 to 100 g/m ² , and even more preferably 60 to 100 g/m ² , and the average basis weight W2 of the first inner layer is preferably 10 to 150 g/m ² , more preferably 20 to 100 g/m ² , and even more preferably 30 to 60 g/m ² .

The papermaking method and type of papermaking machine for the converted base paper are not particularly limited, and known papermaking methods and papermaking machines such as Fourdrinier papermaking machines, twin-wire papermaking machines, cylinder papermaking machines, gap formers, hybrid formers, on-top formers, and success formers can be selected. The lamination process of the paper layers is preferably a process in which the wet paper dewatered by at least one wire is transferred onto a lamination wire or felt plane separate from the wire, and the paper layers are laminated one by one in order on the plane of the lamination wire or felt.

After papermaking, the base paper for conversion is smoothed as necessary. Smoothing is carried out on-machine or off-machine using standard smoothing equipment such as a super calendar, gloss calendar, or soft calendar.

The ratio of the raw material discharge speed from the inlet to the wire speed is called the jet wire ratio, and by controlling this value, the fiber orientation can be controlled, and as a result, the aspect ratio of the tensile strength and bending strength can be adjusted. The jet wire ratio can be adjusted appropriately, for example between 0.80 and 1.20, while observing the balance between the vertical and horizontal directions of various strengths.

(Maximum bending stress)
The maximum bending stress refers to the maximum stress measured for each bending angle while bending a sample piece of paper from 0 to 90 degrees for 2 seconds. Examples of graphs of bending stress curves showing the correlation between bending angle and bending stress for the bending angle are shown in Figures 1 and 2. The horizontal axis of Figures 1 and 2 indicates bending angle, and the vertical axis indicates bending stress. That is, the maximum bending stress of the converting base paper in Figure 1 is 107.14 N/m for a bending angle of 81 degrees. The maximum bending stress of the converting base paper in Figure 2 is 138.11 N/m for a bending angle of 64 degrees.

A bending stiffness measuring machine (BST-150M, manufactured by Katayama Nukigata Seisakusho) is used to measure the maximum bending stress. The width of the sample paper piece to be measured is 38 mm, and the distance from the position where the sample paper piece is fixed (clamp part) to the bending position (stress measurement position) is 13 mm.

Hereinafter, the relationship between bending and maximum bending stress will be explained using top curl processing as an example. Note that, although top curl processing is given here as an example of a curl processing with a large curvature that is particularly prone to causing defects in the product, the processing base paper of this embodiment is suitable for various bending processes such as drawing and folding.

Top curl processing is a curling process in which the edge of the base paper or a sheet made from the base paper is tightly curled outward to a small diameter of about 2 to 3 mm. There are several methods for top curl processing, but here we will explain an example that uses two curved dies. First, the upper molding die is placed on the top opening side of the paper container, and the periphery of the top opening of the paper container is curled outward to form the upper side of the top curl part. The curled part at this time is hereinafter also referred to as the top curl forming part. Next, the top curl part is formed by sandwiching the top curl forming part between the upper molding die and the lower molding die while rolling the periphery of the top opening into the curl along the curved surface of the lower molding die.

If the maximum bending stress of the converting base paper in the axial direction of the paper container is too high, in other words, if the converting base paper is difficult to bend and curl, the curvature of the curl formed when the upper side of the top curl is formed will be low and the curl will be large. Therefore, if the maximum bending stress of the converting base paper in the axial direction of the paper container is too high, the top curl formation area tends to be large. If the top curl formation area is too large, the shape of the top curl will be constant when the top curl formation area is sandwiched between the upper molding die and the lower molding die, so there is a risk that the excess part of the top curl formation area will be crushed when the top curl is fitted into the specified shape.

The crushed excess part at the top curl formation area may become wrinkles (hereinafter also referred to as horizontal wrinkles) that extend circumferentially around the paper container at the top curl section, which may impair the appearance and function of the paper container. Converting base paper that is difficult to bend due to excessively high maximum bending stress tends to easily cause defects in products during bending processes, not limited to the top curl process given as an example here. Such defects may mar the aesthetic appearance of products formed using the converting base paper and reduce product yields.

In this embodiment, the maximum bending stress in at least one direction is 215 N/m or less, preferably 155 N/m or less, more preferably 135 N/m or less, even more preferably 130 N/m or less, and even more preferably 125 N/m or less. The lower limit of the maximum bending stress in at least one direction is not particularly limited, but is preferably 50 N/m or more, more preferably 80 N/m or more. In this embodiment, it is preferable that the maximum bending stress in the MD direction (length direction of the papermaking machine) is within the above range. The bending stress can be adjusted to a desired range by adjusting the amount of paper strength agent or adjusting the beating of the pulp.

If the maximum bending stress in one direction of the processing base paper is 215 N/m or less, bending in that one direction can be easily performed. Even when bending processes that are likely to cause product defects, such as folding and top curling, are performed, defects such as wrinkles are less likely to occur, improving the yield of products made using the processing base paper. Furthermore, easier bending also improves the aesthetics of products made using the processing base paper.

When applying top curl processing to paper containers, paper tubes, etc. formed using processing base paper, it is preferable to create a top curl portion by rolling the processing base paper in one direction where the maximum bending stress is 215 N/m or less. In other words, it is preferable to form the paper container, paper tube, etc. so that the axial direction of the paper container, paper tube, etc. is the said direction.

The slope of the bending stress curve tends to become gentler once a certain bending angle is reached. The reason for this is thought to be as follows. In the bending process, a tensile force is applied to the outside of the fold, and a compressive force is applied to the inside of the fold. When the bending angle is shallow, the paper layer of the processing base paper elastically deforms due to the compressive force. When the folding continues and the bending angle exceeds a certain angle, the increased compressive force plastically deforms (buckles) part of the paper layer of the processing base paper, reducing the force required to fold beyond that angle, and the slope of the bending stress curve becomes gentler. The point at which a material begins to undergo plastic deformation in this way is generally referred to as the yield point of the material.

It is believed that converting base paper in which the slope of the bending stress curve turns negative at the yield point buckles more strongly due to compression force than converting base paper in which the maximum bending stress continues to rise even after the yield point. This buckling is important in bending. Buckling of the paper layer on the inside of the fold allows bending to be performed with less force, and product defects caused by excessive buckling of the paper layer and damage around the fold can be suppressed. Therefore, hereafter, when the slope of the bending stress curve turns negative at the yield point, the yield point is specifically referred to as an inflection point, and the inflection point is used as an index of bending suitability. Here, the inflection point is defined as the point where the slope of the tangent to the bending stress curve is less than 0 within the range from a certain point to an increase of 1 degree in the bending angle.

For example, in the bending stress curve of Figure 1, the slope of the bending stress curve decreases from a bending angle of 33 degrees. That is, in Figure 1, the point at which the bending angle is 33 degrees is the inflection point. On the other hand, in the bending stress curve of Figure 2, although the yield point where the slope becomes gentle exists between bending angles of 20 and 30 degrees, the slope of the tangent does not turn negative at this yield point. In the bending stress curve of Figure 2, the point at which the slope of the tangent turns negative is the bending angle of 64 degrees. Therefore, in Figure 2, the point at which the bending angle is 64 degrees is the inflection point.

Converting base paper with an inflection point at a shallow bending angle is beneficial for curling processes that require continuous buckling to occur on the inside of the bend in the area to be bent, and is particularly beneficial in top curl processes, which are curl processes with a high curvature.

For the above reasons, it is preferable that the bending stress curve has an inflection point in the bending angle range of 0 degrees or more and less than 40 degrees. Converting base paper with an inflection point in the bending angle range of 0 degrees or more and less than 40 degrees can be bent with a small force because buckling can be caused on the inside of the part to be bent even at a shallow bending angle. If bending can be performed with a small force, excessive stress is not induced in the converting base paper, so defects in products using the converting base paper can be suppressed and the yield of the product can be improved. The aesthetic appearance of products using the converting base paper can also be improved.

(Interlaminar strength)
The interlayer strength is the strength against a force acting in the direction of peeling the paper layers apart. When the converting base paper is constructed by multi-layer papermaking of two or more layers, the interlayer strength between the paper layers is preferably 95 J/m ² or more, more preferably 100 J/m ² or more, and even more preferably 250 J/m ² or more. The interlayer strength between the paper layers is preferably 1000 J/m ² or less, more preferably 700 J/m ² or less, and even more preferably 620 J/m ² or less. The interlayer strength is the geometric mean value of the interlayer strength in the longitudinal direction and the interlayer strength in the lateral direction of the converting base paper. The interlayer strength is measured by the internal bond tester method specified in JAPAN TAPPI 18-2. The interlayer strength can be adjusted within a desired range by adjusting the paper strength enhancer, adjusting the beating, and adjusting the amount of interlayer adhesive.

If the interlayer strength of the converting base paper is 100 J/m2 or ^more , the bond between the paper layers can be strengthened and peeling between the paper layers can be suppressed. On the other hand, if the interlayer strength is 1000 J/m2 ^{or less} , the paper layer on the inside of the bend in the target bending area can be buckled to follow the paper layer on the outside, which can contribute to suppressing peeling between the paper layers and reducing the bending stress during bending.

(Tensile strength)
Tensile strength is the breaking strength against a tensile force, and is also an index of the stiffness of the base paper. Generally, the tensile strength is large in the length direction (MD) of the papermaking machine, and small in the direction perpendicular to the MD (CD). Such a difference in tensile strength in a single piece of processing base paper occurs because the pulp fibers tend to be oriented in the length direction of the papermaking machine during papermaking. Paper products that require curling tend to have product defects due to the difficulty of bending the processing base paper, and an example of a paper product in which the stiffness of the processing base paper is particularly likely to cause product defects is a paper cup with a top curl processing at the mouth.

If the converting base paper has a large axial tensile force and is difficult to curl in the axial direction, the curvature of the curl formed when the upper side of the top curl is formed will be small, resulting in a large curl. Therefore, if the tensile strength of the converting base paper in the axial direction of the paper container is too high, the top curl formation area tends to be large. If the top curl formation area is too large, there is a risk that when the top curl formation area is sandwiched between the mold for upper molding and the mold for lower molding, the excess part of the top curl formation area that does not fit into the mold will be crushed.

The crushed excess part of the top curl formation area may cause wrinkles (hereinafter also referred to as horizontal wrinkles) in the top curl area that extend in the circumferential direction of the paper container, which may impair the appearance and functionality of the paper container. For these reasons, base paper to be processed into paper containers is required to be easy to bend in the direction that it is curled in the top curl process, i.e., in the axial direction of the paper container.

In addition, the sides of paper containers such as paper cups are formed into a cylindrical shape by joining both opposing ends, and are therefore subjected to a strong elastic recovery force (tensile force) in the circumferential direction. This tensile force can cause the adhesive layer to peel off. In particular, in the top curl section, the paper layer is prone to peeling due to the top curl processing, which has a large curvature, so when an elastic recovery force is applied to this area in the circumferential direction, the adhesive layer becomes even more likely to peel off. Therefore, base paper for processing that is processed into paper containers is required to be easy to bend in the circumferential direction of the paper container.

Thus, in the top curl portion of paper containers such as paper cups, the paper container must be easy to bend in the axial direction to form an aesthetically pleasing top curl portion, and at the same time, the paper container must be easy to bend in the circumferential direction to prevent the adhesive layer from peeling off due to the elastic recovery force acting in the circumferential direction of the paper container.

In this embodiment, it has been found that by specifying the tensile strength of the processing base paper not only in the MD direction but also in the CD direction, and further specifying the average value of the tensile strength in the CD direction and the MD direction, a processing base paper suitable for paper products that are bent in multiple directions can be obtained. For example, by setting the tensile strength of the processing base paper to 35 kN/m or less in the MD direction, the tensile strength in the CD direction, and the average value of the tensile strength in the MD direction and the CD direction to 22 kN/m or less, and setting the average value of the tensile strength in the MD direction and the CD direction to 28 kN/m or less, a processing base paper that is easier to bend in any direction of the base paper can be obtained. More preferably, the tensile strength of the processing base paper in the MD direction is 35 kN/m or less, the tensile strength in the CD direction is 22 kN/m or less, and the average value of the tensile strength in the MD direction and the CD direction is 26 kN/m or less. The tensile strength in the MD direction is preferably 33 kN/m or less, and is also preferably 15 kN/m or more, more preferably 20 kN/m or more, and even more preferably 25 kN/m or more. The tensile strength in the CD direction is preferably 20 kN/m or less, and is also preferably 10 kN/m or more, more preferably 13 kN/m or more, and even more preferably 15 kN/m or more. The average value of the tensile strength in the MD direction and the CD direction is preferably 25 kN/m or less, and is also preferably 15 kN/m or more, more preferably 18 kN/m or more, and even more preferably 21 kN/m or more. Furthermore, it is also preferable that the tensile strength in the MD direction of the converting base paper is 20 to 30 kN/m, the tensile strength in the CD direction is 10 to 20 kN/m, and the average value of the tensile strength in the MD direction and the CD direction is 15 to 24 kN/m. By setting the tensile strength in the MD and CD directions of the converting base paper within the above ranges, it is also possible to suppress an excessive increase in bending stress during bending processing. The tensile strength is a value measured on the converting base paper after humidity conditioning in a humidity-conditioned environment specified in JIS P 8111:1998 in accordance with the method specified in JIS P 8113:2006. As a measuring machine, a horizontal tensile tester (CODE SE-064 manufactured by L&W) can be used. The tensile strength can be adjusted to within a desired range by adjusting the amount of paper strength agent, adjusting the beating of the pulp, or adjusting the amount of filler added.

In addition, when the tensile strength of the processing base paper in the MD direction is T1 and the tensile strength in the CD direction is T2, the value of T1/T2 is preferably 0.9 or more, more preferably 1.0 or more, even more preferably 1.1 or more, even more preferably 1.3 or more, and even more preferably 1.4 or more. In addition, the value of T1/T2 is preferably less than 3.5, more preferably less than 3.0, even more preferably less than 2.5, and even more preferably less than 2.0. By setting the value of T1/T2 in such a range, a processing base paper with a good balance of strength against tensile force in both the CD direction and the MD direction can be obtained. The value of T1/T2 can be adjusted by adjusting the fiber orientation ratio by adjusting the jet wire ratio, etc.

(grammage)
The total basis weight of the processing base paper is preferably 200 to 550 g/ ^m2 , and more preferably 200 to 400 g/ ^m2 . When the total basis weight of the processing base paper is equal to or greater than the above lower limit, sufficient strength is obtained for processing into products. On the other hand, when the total basis weight of the processing base paper is equal to or less than the above upper limit, excessive stress is unlikely to occur during bending, and processing suitability is excellent. In addition, when the total basis weight of the processing base paper is equal to or less than the above upper limit, it is easy to buckle only a portion of the paper layer on the inside of the bend when the processing base paper is bent.

In the converting base paper, when the average basis weight of the outermost paper layers on the front and back sides is W1 and the average basis weight of the first inner layer is W2, it is preferable that W1/W2 = 1.05 to 2.10, and more preferably W1/W2 = 1.20 to 2.00. The average basis weight W1 of the outermost paper layers on the front and back sides is preferably 30 to 200 g/m ² , more preferably 50 to 100 g/m ² , and even more preferably 60 to 100 g/m ² , and the average basis weight W2 of the first inner layer is preferably 10 to 150 g/m ² , more preferably 20 to 100 g/m ² , and even more preferably 30 to 60 g/m ^2. By increasing the basis weight of the outermost paper layer, the moisture retention of the outermost layer is increased, and more hydrogen bonds can be formed between the outermost layer and the first inner layer when these paper layers are laminated, which has the effect of improving the interlayer strength. As a result, peeling between the outermost paper layer and the first inner layer can be suppressed. Also, by increasing the basis weight of the outermost paper layer, the strength of the outermost paper layer can be increased, and peeling between the outermost paper layer and the first inner layer can be suppressed. Furthermore, by increasing the basis weight of the outermost paper layer, when opposing sides of the converting base paper are bonded together with an adhesive layer to form a paper tube or paper container, the phenomenon in which the paper layer is taken up by the adhesive layer and peeled off from the converting base paper (adhesive layer peeling) can be suppressed.

(density)
The density of the processing base paper is preferably 0.80 to 1.00 g/ ^cm3 . When the density of the processing base paper is 0.80 g/ ^cm3 or more, sufficient strength is obtained for processing into products. On the other hand, when the density of the processing base paper is 1.00 g/ ^cm3 or less, excessive stress is unlikely to be generated when the processing base paper is folded, and the processing suitability is excellent. In addition, when the density of the processing base paper is 1.00 g/cm3 or ^less , it is easy to buckle only a part of the inside when the processing base paper is folded.

The base paper for processing of this embodiment is highly suitable for bending, and is therefore suitable for paper containers, paper lids, paper tubes, paper decorations, and various other paper products manufactured by various bending processes such as squeezing, folding, curling, etc., or by combining these bending processes. Paper containers include, for example, paper plates, paper bowls, paper boxes, paper cartons, paper cups, paper cups, and various other container-shaped paper products.

The processing base paper of this embodiment is easily bent in multiple directions, and is particularly suitable for paper containers formed by bending in multiple directions, such as paper cups with a top curl portion. Specifically, product defects can be suppressed even when processing that is likely to cause product defects, such as top curl processing, is performed. Therefore, the processing base paper of this embodiment is particularly suitable for paper products that have a top curl portion, such as paper containers such as paper cups and paper cups.

[Paper containers made from converted base paper]
The paper container formed from the above-mentioned converting base paper will be described. The method of forming the paper container using the converting base paper is not particularly limited, and the paper container can be manufactured by a known method. As described in the above description of the maximum bending stress of the converting base paper, when the paper container has a top curl portion, it is preferable to form the paper container so that the direction in which the maximum bending stress of the converting base paper is 215 N/m or less is the axial direction of the paper container. The maximum bending stress in the axial direction is more preferably 155 N/m or less, and even more preferably 135 N/m or less. In general, from the viewpoint of improving the compressive strength of the entire paper container, the converting base paper is processed so that the MD direction of the converting base paper is the axial direction of the paper container.

[Paper container sheets]
The paper container sheet is formed by laminating a thermoplastic resin layer on at least one side of the above-mentioned converting base paper. The thermoplastic resin layer imparts various functions to the paper container sheet, such as waterproofness and heat insulation.

(Maximum bending stress)
Since the paper container sheet has a thermoplastic resin layer, it has a higher maximum bending stress than the base paper for processing. For this reason, the maximum bending stress of the paper container sheet in at least one direction in the range of bending angles of 0 to 90 degrees is preferably 215 N/m or less. In a paper container sheet having a maximum bending stress of 230 N/m or less in at least one direction in the range of bending angles of 0 to 90 degrees, a paper container can be easily formed by bending. If the maximum bending stress of the paper container sheet in one direction is 230 N/m or less, wrinkles in the base paper constituting the paper container sheet due to bending in that one direction and cracks in the thermoplastic resin layer associated with the wrinkles can be suppressed for the same reasons as those described for the maximum bending stress of the base paper for processing. By suppressing wrinkles in the base paper and cracks in the thermoplastic resin, the yield and aesthetics of paper containers using the paper container sheet can be improved. For example, when forming a paper container to be top curled, for the same reason as described for the maximum bending stress of the base paper, it is preferable to form the top curl portion by rolling the paper container sheet in one direction where the maximum bending stress is 230 N/m or less. In other words, it is preferable to form the paper container so that the said direction is the axial direction.

(Thermoplastic resin layer)
Some examples of the role of the thermoplastic resin layer in the paper container sheet are given below. For example, a thermoplastic resin layer may be laminated on at least one side of the base paper to impart waterproofing to the paper container sheet, thereby forming a paper container sheet capable of forming paper containers for use with sols, gels, liquids, etc. The paper container sheet may be formed as a paper container sheet for heat-insulating paper containers by laminating a thermoplastic resin layer on at least one side of the base paper so as to foam when heated. When a paper container formed from a paper container sheet for heat-insulating paper containers is heated, the thermoplastic resin layer softened by heating contains water vapor evaporated from the paper layer, etc., and foams, forming a foam layer. In this way, by heating a paper container formed from a paper container sheet for heat-insulating paper containers, a heat insulating effect is obtained by the foam layer, and a heat-insulating paper container is obtained.

As the thermoplastic resin, both crystalline and non-crystalline resins can be used. Specifically, polyethylene (LDPE, MDPE, HDPE, LLDPE, etc.), polyolefin resins such as polypropylene and polymethylpentene, polyester resins such as PET and PBT, polyamide resins, biodegradable resins such as polylactic acid, PHB, PBS, PBAT, PCL, and PHBH, polystyrene, polyvinyl chloride, acrylonitrile butadiene styrene (ABS) resin, acrylic resin, modified polyphenylene ether (PPE), etc. can be mentioned. The thermoplastic resin layer may be formed as a single layer composed of a single resin, may be formed as a single layer composed of multiple resins, or may be formed as multiple layers composed of the same or different resins. Among the above thermoplastic resins, polyethylene is preferred because of its excellent extrusion lamination properties. In addition, polyethylene has excellent foaming properties, so it is suitable for paper container sheets for use in insulating paper containers.

In the case of a paper container sheet, a thermoplastic resin layer may be disposed on both sides of the base paper for conversion. In this case, the thermoplastic resins constituting the thermoplastic resin layers on both sides may be of the same type, but it is preferable that they are of different types. For example, it is preferable that the melting point of one thermoplastic resin layer is 3°C or more lower than the melting point of the other thermoplastic resin layer.

In addition, when a paper container sheet has thermoplastic resin layers on both sides of the base paper, and one of the thermoplastic resin layers is an insulating layer (a layer that is foamed) and the other is a layer for waterproofing or other purposes (a layer that is not foamed), it is preferable that the melting point of the thermoplastic resin in the insulating layer is at least 3°C lower than the melting point of the thermoplastic resin in the layer for waterproofing or other purposes.

By providing such a difference in melting point in the thermoplastic resin layer, even when the temperature at which the insulating layer softens and begins to foam is reached when the paper container sheet is heated, the layer used for waterproofing and other purposes does not soften and suppresses the evaporation of water vapor. By suppressing the evaporation of water vapor, the foaming ability of the insulating layer is improved, resulting in a paper container with high insulating properties. Note that the same effect as that of a thermoplastic resin layer can be obtained even when metal foil is laminated instead of a thermoplastic resin layer as a layer used for waterproofing and other purposes. In addition, various options are available for the layer structure of the paper container sheet according to the use of the paper container, as follows:

For example, if a water-soluble polymer layer (PVA layer) is provided between the base paper and the thermoplastic resin layer (thermal insulation layer) of a paper container sheet for thermal insulation paper container use, the thermoplastic resin layer can be foamed uniformly. If a water-soluble resin layer or metal foil is provided on the thermoplastic resin layer (thermal insulation layer), water vapor from the paper layer, etc. is prevented from penetrating the thermoplastic resin layer, and the water vapor is kept within the thermoplastic resin layer, improving the foaming property of the thermoplastic resin layer. In addition, it is possible to extend the life of the contents by using a gas barrier film, aluminum foil, aluminum-deposited resin layer, etc., which have water vapor barrier properties and oxygen barrier properties. In addition, a coating layer mainly composed of pigments and adhesives may be provided on the paper container sheet, or a printed layer, etc. may be laminated.

[Paper containers using paper container sheets]
A paper container formed with a paper container sheet will be described. The paper container is composed of the above-mentioned processing base paper or the above-mentioned paper container sheet. The method for forming the paper container using the paper container sheet is not particularly limited, and the paper container can be manufactured using a known method. As described in the above description of the maximum bending stress of the paper container sheet, it is preferable that the paper container having a top curl portion is formed so that the axial direction of the paper container is the direction in which the maximum bending stress of the paper container sheet is 215 N/m or less.

The effects of the present invention will be described in detail below with reference to examples. In the examples and comparative examples, "parts" and "%" refer to "parts by mass" and "% by mass", respectively, unless otherwise specified. Furthermore, unless otherwise specified, the operations in the examples and comparative examples were carried out at a temperature of 20-25°C and a relative humidity of 40-50%. In the following description of the examples, the "outermost paper layer" corresponds to the first and fifth layers in the table, respectively, the "first inner layer" corresponds to the second and fourth layers in the table, respectively, and the "second inner layer" corresponds to the third layer in the table.

[material]
The materials used in the examples and comparative examples are as follows.
(1) Pulp: LBKP: Acacia wood, Eucalyptus wood
NBKP: Douglas fir, radiata pine, cedar (2) Paper strength enhancer: Polyacrylamide-based paper strength enhancer (PAM)
(3) Wet strength agent: polyamide polyamine epichlorohydrin (PAE) resin (4) Cationic starch (5) Aluminum sulfate (6) Sizing agent: alkyl ketene dimer sizing agent (AKD)
(7) Internal filler: calcium carbonate (8) Water-soluble resin: intermediate saponification type polyvinyl alcohol (PVA), saponification degree 96.5 mol%
(9) Thermoplastic resin: low density polyethylene (LDPE), density 918 kg/m ³ , melting point 103° C.
(10) High melting point thermoplastic resin: medium density polyethylene (MDPE), density 940 kg/m ³ , melting point 133° C.

[Measurement method]
The methods for measuring the paper quality of base paper for converting and paper container sheets are as follows.
(1) Maximum bending stress: The bending stress was measured using a bending stiffness measuring instrument (BST-150M, manufactured by Katayama Nukigata Seisakusho) for the converting base paper after humidity conditioning in a humidity-conditioning environment specified in JIS P 8111: 1998. The width of the measurement sample was 38 mm, the distance from the clamp part to the folding position was 13 mm, and the bending stress was measured as the maximum value of the measured load in units of N/m while folding from 0 to 90 degrees over 2 seconds.
(2) Interlaminar strength: Measured in the longitudinal and transverse directions of the converting base paper in accordance with JAPAN TAPPI 18-2, and calculated as the geometric mean value. The double-sided tape used was 3M 400.
(3) Tensile strength: Measured in accordance with the method specified in JIS P 8113: 2006 for the converting base paper after humidity conditioning in a humidity-conditioning environment specified in JIS P 8111: 1998. A horizontal tensile tester (manufactured by L&W, CODE SE-064) was used as the measuring machine.
(4) Basis weight: The basis weight of the converting base paper was measured in accordance with JIS P 8124:2011.
(5) Density: The basis weight of the converting base paper was measured in accordance with JIS P 8118:2014.
(6) Ash content: The ash content of the converting base paper was measured according to the ash content test method (525°C combustion method) specified in JIS P 8251:2003.

[Base paper for processing]
Example 1
LBKP was used as the pulp, and 0.5 parts of aluminum sulfate, 0.4 parts of cationic starch, 0.45 parts of a paper strength enhancer (PAM-based paper strength enhancer), 0.23 parts of an alkyl ketene dimer-based sizing agent, and 0.07 parts of a PAE-based wet paper strength enhancer were added to 100 parts of the pulp raw material in terms of solid content, and calcium carbonate was added as a filler so that the ash content was 7.2% by mass relative to the total solid content mass to prepare a pulp slurry. Using the pulp slurry, five layers were made with a twin-wire papermaking machine so that the basis weight of the outermost paper layer was 85 g/m ² , the basis weight of the first inner layer was 50 g/m ² , and the basis weight of the second inner layer was 50 g/m ² . During papermaking, the jet wire ratio of each former was adjusted so that the MD/CD ratio of the tensile strength of the converting base paper was 1.65. In this manner, the converting base paper of Example 1 was obtained.

Example 2
The converting base paper of Example 2 was obtained in the same manner as in Example 1, except that LBKP was used as the pulp, and a pulp slurry was used in which, based on 100 parts of pulp raw material (solid content equivalent), 0.5 parts of aluminum sulfate, 0.55 parts of cationic starch, 0.50 parts of a PAM-based paper strength agent, 0.23 parts of an alkyl ketene dimer- ^based sizing agent, 0.07 parts of a PAE-based wet strength agent, and calcium carbonate was added as a filler so that the ash content was 8.0 mass% relative to the total solids mass. The paper was made so that the outermost paper layer had a basis weight of 80 g/ ^m2 , the first inner layer had a basis weight of 47 g/ ^m2 , the second inner layer had a basis weight of 46 g/m2, and the MD/CD ratio of tensile strength was 1.56.

Example 3
The converting base paper of Example 3 was obtained in the same manner as in Example 1, except that the same LBKP and chemicals as in Example 2 were added, and calcium carbonate was added as a filler to a pulp slurry so that the ash content was 16.0 mass% relative to the total solids mass, and the paper was made so that the outermost paper layer had a basis weight of 106 g/ ^m2 , the first inner layer had a basis weight of 63 g/ ^m2 , the second inner layer had a basis weight of 62 g/ ^m2 , and the MD/CD ratio of the tensile strength was 1.77.

Example 4
The converting base paper of Example 4 was obtained in the same manner as in Example 1, except that the same LBKP and chemicals as in Example 2 were added, and calcium carbonate was added as a filler to a pulp slurry so that the ash content was 25.0 mass% of the total solids mass, and the paper was made so that the outermost paper layer had a basis weight of 120 g/ ^m2 , the first inner layer had a basis weight of 90 g/ ^m2 , the second inner layer had a basis weight of 90 g/ ^m2 , and the MD/CD ratio of the tensile strength was 1.87.

Example 5
The converting base paper of Example 5 was obtained in the same manner as in Example 1, except that LBKP was used as the pulp, and a pulp slurry was prepared by adding, in terms of solid content, 0.5 parts of aluminum sulfate, 0.4 parts of cationic starch, 0.75 parts of a paper strength agent (PAM-based paper strength agent), 0.30 parts of an alkyl ketene dimer-based sizing agent, and 0.07 parts of a PAE-based wet strength agent to 100 parts of the pulp raw material, so that the MD/CD ratio of the tensile strength was 1.35.

Example 6
The converting base paper of Example 6 was obtained in the same manner as in Example 1, except that LBKP was used as the pulp, and a pulp slurry was used to add, in terms of solid content, 0.5 parts of aluminum sulfate, 0.4 parts of cationic starch, 1.10 parts of a paper strength agent (PAM-based paper strength agent), 0.23 parts of an alkyl ketene dimer-based sizing agent, and 0.14 parts of a PAE-based wet strength agent to 100 parts of the pulp raw material. The paper was made so that the basis weight of the outermost paper layer was 80 g/ ^m2 , the basis weight of the first inner layer was 47 g/ ^m2 , the basis weight of the second inner layer was 46 g/ ^m2 , and the MD/CD ratio of the tensile strength was 1.47.

(Example 7)
A single-layer converting base paper of Example 7 was obtained in the same manner as in Example 1, except that LBKP was used as the pulp, and a pulp slurry containing 0.5 parts of aluminum sulfate, 0.20 parts of cationic starch, 0.25 parts of a paper strength agent (PAM-based paper strength agent), 0.30 parts of an alkyl ketene dimer sizing agent, and 0.07 parts of a PAE-based wet strength agent was added to 100 parts of the pulp raw material in terms of solid content, and the paper was made into a single layer on a Fourdrinier papermaking machine to have a basis weight of 320 g/m2 ^and an MD/CD ratio of tensile strength of 1.66.

(Example 8)
The converting base paper of Example 8 was obtained in the same manner as in Example 1, except that LBKP was used as the pulp, and a pulp slurry was used to add, in terms of solid content, 0.5 parts of aluminum sulfate, 0.40 parts of cationic starch, 0.70 parts of a paper strength agent (PAM-based paper strength agent), 0.23 parts of an alkyl ketene dimer-based sizing agent, and 0.14 parts of a PAE-based wet strength agent per 100 parts of pulp raw material. The paper was made so that the basis weight of the outermost paper layer was 80 g/ ^m2 , the basis weight of the first inner layer was 47 g/ ^m2 , the basis weight of the second inner layer was 46 g/ ^m2 , and the MD/CD ratio of the tensile strength was 1.37.

(Example 9)
The converting base paper of Example 9 was obtained in the same manner as in Example 1, except that LBKP was used as the pulp, and a pulp slurry was prepared by adding, in terms of solid content, 0.5 parts of aluminum sulfate, 0.40 parts of cationic starch, 0.90 parts of a paper strength agent (PAM-based paper strength agent), 0.23 parts of an alkyl ketene dimer-based sizing agent, and 0.14 parts of a PAE-based wet strength agent to 100 parts of the pulp raw material, so that the MD/CD ratio of the tensile strength was 1.78.

(Example 10)
The converting base paper of Example 10 was obtained in the same manner as in Example 1, except that LBKP was used as the pulp, and a pulp slurry was prepared by adding, in terms of solid content, 0.5 parts of aluminum sulfate, 0.40 parts of cationic starch, 0.75 parts of a paper strength agent (PAM-based paper strength agent), 0.23 parts of an alkyl ketene dimer sizing agent, and 0.14 parts of a PAE-based wet strength agent to 100 parts of the pulp raw material, so that the MD/CD ratio of the tensile strength was 1.76.

Example 11
The converting base paper of Example 11 was obtained in the same manner as in Example 1, except that a pulp slurry prepared in the same manner as in Example 3 was used, and three layers were made so that the outermost paper layer had a basis weight of 133 g/ ^m2 , the first inner layer had a basis weight of 134 g/ ^m2 , and the MD/CD ratio of tensile strength was 1.77.

Example 12
The converting base paper of Example 12 was obtained in the same manner as in Example 1, except that the pulp slurry prepared in the same manner as in Example 1 was used, and the paper was made on a twin-wire papermaking machine so that the basis weight of all paper layers was 64 g/ ^m2 and the MD/CD ratio of tensile strength was 1.64.

Example 13
The converting base paper of Example 13 was obtained in the same manner as in Example 1, except that a pulp slurry prepared in the same manner as in Example 1 was used, and the paper was made so that the basis weight of the outermost paper layer was 70 g/ ^m2 , the basis weight of the first inner layer was 60 g/ ^m2 , the basis weight of the second inner layer was 60 g/ ^m2 , and the MD/CD ratio of the tensile strength was 1.64.

(Example 14)
The converting base paper of Example 14 was obtained in the same manner as in Example 2, except that the pulp was changed to a mixture of 70% LBKP and 30% NBKP, the basis weight of the outermost paper layer was 80 g ^{/ m2} , the basis weight of the first inner layer was 47 g/ ^m2 , the basis weight of the second inner layer was 46 g/m2, and the tensile strength MD/CD ratio was 1.94.

(Example 15)
The pulp for the outermost paper layer was a mixture of 70% LBKP and 30% NBKP. The pulp for the first inner layer and the second inner layer was 100% LBKP. The converting base paper of Example 15 was obtained in the same manner as in Example ² , except that the paper was made so that the basis weight of the outermost paper layer was 80 g/ ^m2 , the basis weight of the first inner layer was 47 g/ ^m2 , the basis weight of the second inner layer was 46 g/m2, and the MD/CD ratio of the tensile strength was 1.80.

(Example 16)
The pulp for the outermost paper layer was 100% LBKP. The pulp for the first inner layer and the second inner layer was a mixture of 70% LBKP and 30% NBKP. The converting base paper of Example 16 was obtained in the same manner as in Example ² , except that the paper was made so that the basis weight of the outermost paper layer was 80 g/ ^m2 , the basis weight of the first inner layer was 47 g/ ^m2 , the basis weight of the second inner layer was 46 g/m2, and the MD/CD ratio of the tensile strength was 1.80.

(Example 17)
The converting base paper of Example 17 was obtained in the same manner as in Example 2, except that the pulp was changed to a mixture of 50% LBKP and 50% NBKP, the basis weight of the outermost paper layer was 80 g ^{/ m2} , the basis weight of the first inner layer was 47 g/ ^m2 , the basis weight of the second inner layer was 46 g/m2, and the tensile strength MD/CD ratio was 1.75.

(Example 18)
The first and second inner layers were made using a pulp slurry prepared in the same manner as in Example 2, and the outermost paper layer was made using the same pulp slurry as in Example 2 except that the amount of filler added was half.The converting base paper of Example 18 was obtained in the same manner as in Example 2, except that the paper was made so that the basis weight of the outermost paper layer was 80 g/ ^m2 , the basis weight of the first inner layer was 47 g/ ^m2 , the basis weight of the second inner layer was 46 g/ ^m2 , and the MD/CD ratio of the tensile strength was 1.50.

(Example 19)
The same pulp slurry as in Example 2 was used for the first and second inner layers, except that calcium carbonate was added as a filler so that the ash content was 12.8 mass% relative to the total solids mass, and the same pulp slurry as in Example 2 was used for the outermost paper layer, except that no filler was added.The converting base paper of Example 19 was obtained in the same manner as in Example 2, except that the paper was made so that the basis weight of the outermost paper layer was 80 g/ ^m2 , the basis weight of the first inner layer was 47 g/ ^m2 , the basis weight of the second inner layer was 46 g/ ^m2 , and the MD/CD ratio of the tensile strength was 1.51.

(Comparative Example 1)
The converting base paper of Comparative Example 1 was obtained in the same manner as in Example 1, except that a pulp slurry prepared in the same manner as in Example 9 was used, and the paper was made so that the basis weight of the outermost paper layer was 106 g/ ^m2 , the basis weight of the first inner layer was 63 g/ ^m2 , the basis weight of the second inner layer was 62 g/ ^m2 , and the MD/CD ratio of the tensile strength was 1.68.

[Paper container sheets]
(Example 20)
A high melting point thermoplastic resin (medium density polyethylene, density 940 kg/m ³ , melting point 133° C.) was extruded to a thickness of 40 μm on one side of the converting base paper of Example 1 at a melting temperature of 360° C. and a lamination speed of 50 m/min. Then, using a cooling roll and a nip roll (JIS-A hardness: 70), the extrusion was pressed and pressure-bonded at a linear pressure of 2 kgf/cm to form a high melting point thermoplastic resin layer.

Next, a low-melting thermoplastic resin (low-density polyethylene, density 918 kg/m ³ , melting point 103° C.) was extruded at a melting temperature of 360° C. and a lamination speed of 50 m/min to a thickness of 50 μm onto the other surface of the converting base paper of Example 1. Thereafter, the material was pressed and compressed at a linear pressure of 2 kgf/cm using a cooling roll and a nip roll (JIS-A hardness: 70) to form a thermoplastic resin layer, and the paper container sheet of Example 20 was obtained.

(Example 21)
A thermoplastic resin layer was laminated on both sides of the converting base paper of Example 2 in the same manner as in Example 20 to obtain a paper container sheet of Example 21.

(Example 22)
A thermoplastic resin layer was laminated on both sides of the converting base paper of Example 6 in the same manner as in Example 20 to obtain a paper container sheet of Example 22.

(Example 23)
A paper container sheet of Example 23 was obtained by laminating a thermoplastic resin layer on both sides of the converting base paper of Example 7 in the same manner as in Example 20.

(Example 24)
A paper container sheet of Example 24 was obtained by laminating a thermoplastic resin layer on both sides of the converting base paper of Example 8 in the same manner as in Example 20.

(Example 25)
A thermoplastic resin layer was laminated on both sides of the converting base paper of Example 4 in the same manner as in Example 20 to obtain a paper container sheet of Example 25.

[Production of paper containers (round containers)]
Using the converting base paper and the paper container sheet obtained as described above, a paper cup, which is one form of paper container, was manufactured as follows. First, a blank for the body of the paper cup was printed and punched out, and the punched blank was rolled so that the MD direction of the converting base paper was the axial direction, and the ends were heat-sealed to produce a truncated cone-shaped tube with an upper opening diameter of 90 mm and a lower opening diameter of 65 mm. A bottom paper was attached to the lower part of the tube by heat sealing, and a top curl part with a diameter of 3 mm was formed at the top, to obtain a paper cup with a height of 110 mm.

[Evaluation method]
The paper cups obtained as described above were subjected to the following evaluations.

(Wrinkles at top curl)
The top curled portion of the canned paper cup was visually observed to evaluate the presence or absence of horizontal wrinkles according to the following criteria.
◎: No horizontal wrinkles are observed. ○: A few thin and short horizontal wrinkles are observed. △: Thin horizontal wrinkles are observed. ×: Deep and clear horizontal wrinkles have occurred.

(Delamination of seam parts)
The cross section of the paper at the seam in the top curl of the canned paper cup was visually observed and evaluated according to the following criteria.
◎: No intralayer peeling at the edge is observed. ○: Some intralayer peeling is observed. △: A lot of intralayer peeling is noticeable. ×: Intralayer peeling is observed and the paper layers are separated.

(Peel between laminates at top curl)
The lamination (heat sealing) adhesion of the seam at the top curl of the canned paper cup was visually observed and evaluated according to the following criteria.
◎: No curling up of the heat-sealed adhesive surface is observed at the seam. ○: A small gap is observed between the heat-sealed adhesive surfaces at the seam, but the adhesive is well bonded. △: A small curling up of the heat-sealed adhesive surface is observed at the seam. ×: At the seam, the sheet peels off from the heat-sealed adhesive surface, and curling up is very noticeable.

(Overall appearance of the container)
The printing conditions on the surfaces of the produced paper cups were compared and a visual evaluation was made to determine their superiority or inferiority.
◯: No unevenness or white spots are observed △: Some unevenness or white spots are observed ×: Unevenness or white spots are very noticeable

(Easy to hold)
The paper cups were picked up by hand and the feel when lightly gripped was evaluated according to the following criteria.
○: Moderate resilience, not easily deformed, and feels secure. △: Slight bending felt when gripped. ×: Bending and deformation occurred when gripped, giving a weak feeling.

[Production of paper containers (rectangular containers)]
Using the thus obtained base paper and paper container sheet, printing and punching were performed on blanks for the body and bottom of a paper cup. The punched blank for the body was pressed against a mold so that the MD direction of the base paper was the axial direction, and the ends were heat-sealed to form a tube with four arc-shaped corners and a rectangular cross section. The bottom paper was attached to the bottom of the tube by heat sealing to obtain a square container with a rectangular cross section. The cup was processed so that the height was 115 mm, the long side of the cup inner diameter was 100 mm, the short side was 75 mm, the R part of the corner was 25 mm, and the diameter of the top curl processed on the top part was 4 mm.

[Evaluation method]
The paper containers (rectangular containers) obtained as described above were subjected to the following evaluations.

(Cracks in the corners)
The manufactured square containers were visually inspected and the cracks at the corners were evaluated according to the following criteria.
○: No cracks on any corners. △: A thin crack-like line is seen on any corner. ×: A crack occurs on any corner.

(Delamination of curled portion)
The top curled portion of the canned rectangular container was visually observed, and the cross section of the paper at the seam portion was evaluated according to the following criteria.
○: No intralayer peeling is observed on the cross section. △: A lot of intralayer peeling is noticeable on the cross section. ×: Intralayer peeling is observed and the paper layers are separated.

(Overall appearance of the container)
The shape of the canned rectangular containers was visually observed and evaluated according to the following criteria.
○: When the cup is viewed from above, no distortion is observed in the shape. △: When the cup is viewed from above, some distortion is observed. ×: The cup is distorted and the cross section is a parallelogram.

Tables 1 and 2 show the evaluation results for paper containers made using the processing base papers of Examples 1 to 19 and Comparison Example 1.

As is clear from Tables 1 and 2, the paper cups of Examples 1 to 14 did not develop wrinkles in the top curl portion or peeling between the paper layers even when subjected to top curl processing, which is a curl processing with a large curvature, and the overall appearance of the container was excellent and easy to hold. In addition, the basis weight, tensile strength, etc. of the processing base paper used in Example 5 and the processing base paper used in Example 8 were almost the same, but no horizontal wrinkles were observed in the top curl portion of Example 8, resulting in a paper cup with an even more aesthetically pleasing appearance than Example 5. This is thought to be because the maximum bending stress of the processing base paper used in Example 8 was 135 N/m or less, and was more suitable for processing than the processing base paper used in Example 5. Furthermore, the bending angle of the inflection point of the processing base paper used in Example 8 being 40 degrees or less is also thought to contribute to the suppression of horizontal wrinkles in Example 8. On the other hand, the paper cups manufactured using the processing base paper of Comparative Example 1 had both maximum bending stresses that were too high, and wrinkles were particularly noticeable in the top curl portion.

Table 3 shows the evaluation results for paper cups made using the paper container sheets of Examples 20 to 25.

As is clear from Table 2, the paper cups of Examples 20 to 25 did not develop wrinkles in the top curl area, did not peel between the paper layers, or did not peel between the laminate and the base paper, even when they were subjected to top curl processing, which is a curling process with a large curvature.The overall appearance of the container was also excellent, and it was easy to hold.

[Base paper for processing]
(Example 101)
Pulp was prepared by using LBKP as pulp, adding 0.5 parts of starch and 0.5 parts of polyacrylamide as dry strength enhancers to 100 parts of pulp raw material in terms of solid content, and further adding calcium carbonate as a filler so that the ash content was 7.2% by mass relative to the total solid content mass. Using the pulp slurry, paper was made with a twin-wire papermaking machine so that the basis weight of the outermost paper layer was 85 g/m ² , the basis weight of the first inner layer was 50 g/m ² , and the basis weight of the second inner layer was 50 g/m ² . At this time, the paper was made using starch as an interlayer adhesive. In this way, a 5-layered processing base paper of Example 101 was obtained. During papermaking, the fiber orientation was adjusted by the speed difference between the jet and wire (jet wire ratio) to adjust the MD/CD ratio of the tensile strength of the processing base paper to 1.65.

(Example 102)
The converting base paper of Example 102 was obtained ⁱⁿ the same manner as in Example 101, except that calcium carbonate was added as a filler so that the ash content was 8.0 mass% relative to the total solid mass, and the paper was made so that the basis weight of the outermost paper layer was 80 g/m ² , the basis weight of the first inner layer was 47 g/m ^{2, and the basis weight of the second inner layer was 46 g/m 2.} During the papermaking process, the MD/CD ratio of the tensile strength was adjusted to 1.56 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 103)
The converting base paper of Example 103 was obtained in the same manner as in Example ^{101, except that calcium carbonate was added as a filler so that the ash content was 16.0 mass% relative to the total solid mass, and the paper was made so that the basis weight of the outermost paper layer was 106 g/m 2 ,} the basis weight of the first inner layer was 63 g/m 2, and the basis weight of the second inner layer was 62 g/m ^2. During the papermaking process, the MD/CD ratio of the tensile strength was adjusted to 1.77 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 104)
The converting base paper of Example 104 was obtained in the same manner as in Example 101, except that LBKP was used as the pulp, and a pulp slurry containing 0.5 parts of starch and 0.9 parts of polyacrylamide as dry strength agents per 100 parts of pulp raw material in terms of solid content was used to make paper so that the basis weight of the outermost paper layer was 80 g/m ² , the basis weight of the first inner layer was 47 g/m ² , and the basis weight of the second inner layer was 46 g/m ² . During papermaking, the MD/CD ratio of the tensile strength was adjusted to 1.45 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 105)
The converting base paper of Example 105 was obtained in the same manner as in Example 101, except that LBKP was used as the pulp, and a pulp slurry containing 0.5 parts of starch and 0.1 parts of polyacrylamide as dry strength agents per 100 parts of pulp raw material in terms of solid content was used to make paper so that the basis weight of the outermost paper layer was 80 g/m ² , the basis weight of the first inner layer was 47 g/m ² , and the basis weight of the second inner layer was 46 g/m ² . During papermaking, the MD/CD ratio of the tensile strength was adjusted to 1.42 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 106)
The converting base paper of Example 106 was obtained in the same manner as in Example 101, except that LBKP was used as the pulp, and a pulp slurry containing 0.2 parts of starch and 0.1 parts of polyacrylamide as dry strength agents per 100 parts of pulp raw material in terms of solid content was used to make paper so that the basis weight of the outermost paper layer was 80 g/m ² , the basis weight of the first inner layer was 47 g/m ² , and the basis weight of the second inner layer was 46 g/m ² . During papermaking, the MD/CD ratio of the tensile strength was adjusted to 1.45 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 107)
The converting base paper of Example 107 was obtained in the same manner as in Example 101, except that LBKP was used as the pulp, and a pulp slurry containing no dry strength agent or filler was used to make the outermost paper layer with a basis weight of 80 g/m ² , the first inner layer with a basis weight of 47 g/m ² , and the second inner layer with a basis weight of 46 g/m ² . During the papermaking process, the MD/CD ratio of the tensile strength was adjusted to 1.52 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 109)
Pulp slurry was prepared for the outermost paper layer by adding LBKP as the pulp, 0.5 parts of starch and 0.5 parts of polyacrylamide as dry strength enhancers to 100 parts of pulp raw material in terms of solid content, and calcium carbonate as a filler so that the ash content was 4.0% by mass relative to the total solid content mass. Next, pulp slurry was prepared for the first and second inner layers by adding LBKP as the pulp, 0.5 parts of starch and 0.5 parts of polyacrylamide as dry strength enhancers, and calcium carbonate as a filler so that the ash content was 8.0% by mass relative to the total solid content mass. Using these pulp slurries, the processing base paper of Example 109 was obtained in the same manner as in Example 101, except that paper was made so that the basis weight of the outermost paper layer was 80 g/m ² , the basis weight of the first inner layer was 47 g/m ² , and the basis weight of the second inner layer was 46 g/m ² . During papermaking, the fiber orientation was adjusted by the speed difference between the jet and wire (jet wire ratio) to adjust the MD/CD ratio of tensile strength to 1.50.

(Example 110)
Pulp slurry was prepared for the outermost paper layer by adding 0.5 parts of starch and 0.5 parts of polyacrylamide as dry strength enhancers to 100 parts of pulp raw material in terms of solid content. Next, pulp slurry was prepared for the first and second inner layers by adding 0.5 parts of starch and 0.5 parts of polyacrylamide as dry strength enhancers to 12.8% by mass of ash relative to the total solid content mass using LBKP as pulp. The processing base paper of Example 110 was obtained in the same manner as in Example 101, except that the paper was made using these pulp slurries so that the basis weight of the outermost paper layer was 80 g/m ² , the basis weight of the first inner layer was 47 g/m ² , and the basis weight of the second inner layer was 46 g/m ² . During papermaking, the fiber orientation was adjusted by the speed difference between the jet and wire (jet wire ratio) to adjust the MD/CD ratio of tensile strength to 1.51.

(Example 111)
The converting base paper of Example 111 was obtained in the same manner as in Example 101, except that LBKP was used as the pulp, and a pulp slurry containing no dry strength agent or filler was used to make the outermost paper layer have a basis weight of 54.5 g/m ² , the first inner layer have a basis weight of 32 g/m ² , and the second inner layer have a basis weight of 32 g/m ² . During the papermaking process, the MD/CD ratio of the tensile strength was adjusted to 1.49 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 112)
The converting base paper of Example 112 was obtained in the same manner as in Example 102, except that during papermaking, the fiber orientation was adjusted by the speed difference between the jet and wire (jet wire ratio) to adjust the MD/CD ratio of tensile strength to 1.09.

(Example 113)
The converting base paper of Example 113 was obtained in the same manner as in Example 101, except that the amount of calcium carbonate added when preparing the pulp slurry was changed so that the ash content relative to the total solids mass was 8.0 mass%, and further, the paper was made into three layers so that the basis weight of the outermost paper layer was 120 g/ ^m 2 and the basis weight of the first inner layer was 80 g/m ^2. During the papermaking process, the MD/CD ratio of the tensile strength was adjusted to 1.58 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 114)
The converting base paper of Example 114 was obtained in the same manner as in Example 101, except that when preparing the pulp slurry, the amount of calcium carbonate added was changed so that the ash content relative to the total solids mass was 8.0 mass%, and further, the paper was made so that the basis weight of the outermost paper layer was 64.5 g/m ² , the basis weight of the first inner layer was 57 g/m ^{2 ,} and the basis weight of the second inner layer was 57 g/m 2 . During the papermaking process, the MD/CD ratio of the tensile strength was adjusted to 1.56 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 115)
The processing base paper of Example 115 was obtained in the same manner as in Example 101, except that the amount of calcium carbonate added was changed so that the ash content relative to the total solid content mass was 8.0 mass% when preparing the pulp slurry, and further, the paper was made so that the basis weight of all paper layers was 60 g/ ^m2 . During the papermaking process, the MD/CD ratio of the tensile strength was adjusted to 1.58 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 116)
The converting base paper of Example 116 was obtained in the same manner as in Example 101, except that the amount of calcium carbonate added when preparing the pulp slurry was changed so that the ash content relative to the total solids mass was 8.0 mass%, and further, starch and polyacrylamide were used as interlayer adhesives, and paper was made so that the basis weight of the outermost paper layer was 80 g/m ² , the basis weight of the first inner layer was 47 g/m ² , and the basis weight of the second inner layer was 46 g/m ^2. During papermaking, the MD/CD ratio of the tensile strength was adjusted to 1.60 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 117)
The converting base paper of Example 117 was obtained in the same manner as in Example 101, except that when preparing the pulp slurry, the amount of calcium carbonate added was changed so that the ash content relative to the total solids mass was 8.0 mass%, and further, no interlayer adhesive was used, and paper was made so that the basis weight of the outermost paper layer was 80 g/m ² , the basis weight of the first inner layer was 47 g/m ² , and the basis weight of the second inner layer was 46 g/m ² . During papermaking, the MD/CD ratio of the tensile strength was adjusted to 1.56 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 118)
The converting base paper of Example 118 was obtained in the same manner as in Example 101, except that LBKP was used as the pulp, a pulp slurry containing 0.5 parts of starch and 0.2 parts of polyacrylamide as dry strength agents per 100 parts of pulp raw material in terms of solid content was used, and the paper was made on a cylinder papermaking machine so that the basis weight of the outermost paper layer was 80 g/m ² , the basis weight of the first inner layer was 47 g/m ² , and the basis weight of the second inner layer was 46 g/m ² . During the papermaking process, the MD/CD ratio of the tensile strength was adjusted to 1.30 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

(Example 119)
The converting base paper of Example 119 was obtained in the same manner as in Example 101, except that LBKP was used as the pulp, and a pulp slurry was used in which 0.2 parts of starch and 0.2 parts of polyacrylamide were added as dry strength agents to 100 ^parts of the pulp raw material in terms of solid content, and the paper was made on a Fourdrinier papermaking machine to form a single layer with a basis weight of 320 g/m2. During the papermaking process, the MD/CD ratio of the tensile strength was adjusted to 1.66 by adjusting the fiber orientation by the speed difference between the jet and wire (jet wire ratio).

[Paper container sheets]
(Example 120)
A high melting point thermoplastic resin (medium density polyethylene, density 940 kg/m ³ , melting point 133° C.) was extruded to a thickness of 40 μm on one side of the converting base paper of Example 104 at a melting temperature of 360° C. and a lamination speed of 50 m/min. Then, using a cooling roll and a nip roll (JIS-A hardness: 70), the extrusion was pressed and pressure-bonded at a linear pressure of 2 kgf/cm to form a high melting point thermoplastic resin layer.

Next, a low-melting thermoplastic resin (low-density polyethylene, density 918 kg/m ³ , melting point 103° C.) was extruded at a melting temperature of 360° C. and a lamination speed of 50 m/min to a thickness of 50 μm onto the other surface of the converting base paper of Example 104. Thereafter, the material was pressed and compressed at a linear pressure of 2 kgf/cm using a cooling roll and a nip roll (JIS-A hardness: 70) to form a thermoplastic resin layer, and the paper container sheet of Example 120 was obtained.

(Example 121)
A thermoplastic resin layer was laminated on both sides of the converting base paper of Example 101 in the same manner as in Example 120 to obtain a paper container sheet of Example 121.

[Paper containers]
Using the converting base paper of the examples and the paper container sheet of the examples obtained as described above, paper cups, which are one aspect of paper containers, were manufactured as follows. The converting base paper of Examples 101 to 119 was first processed into a paper container sheet and then processed into a paper cup. The method of processing the converting base paper of Examples 101 to 119 into a paper container sheet was the same as that of Example 120. First, a blank that would become the body of the paper cup was printed and punched out, and the punched blank was rolled so that the MD direction of the converting base paper was the axial direction, and the ends were heat-sealed to produce a truncated cone-shaped tube with an upper opening diameter of 90 mm and a lower opening diameter of 65 mm. A bottom paper was attached to the bottom of the tube by heat sealing, and a top curl part with a diameter of 3 mm was formed at the top to obtain a paper cup with a height of 110 mm.

[Evaluation method]
The paper cups obtained as described above were subjected to the following evaluations.

(Crack in top curl)
The top curled portion of the canned paper cup was visually observed to evaluate the presence or absence of cracks around the top curled portion according to the following criteria.
○: No cracks are observed. △: Very few thin cracks are observed. ×: Deep cracks are observed.

(Peeling of top curl)
The cross section of the paper at the seam in the top curl portion of the canned paper cup was visually observed and evaluated according to the following criteria.
○: No intralayer peeling is observed. △: Slight intralayer peeling is observed. ×: Intralayer peeling is observed and the paper layers are separated.

(Peel between laminates)
The seam of the paper cup thus produced was visually observed and evaluated according to the following criteria.
○: No curling up of the seam is observed. △: Some gaps are observed in the seam, but it is adhered. ×: Peeling occurs at the adhesive surface, and curling up of the seam is noticeable.

(Wrinkles at top curl)
The top curled portion of the canned paper cup was visually observed to evaluate the presence or absence of horizontal wrinkles according to the following criteria.
○: No horizontal wrinkles are observed. △: Light horizontal wrinkles are observed. ×: Deep and clear horizontal wrinkles are observed.

(Overall appearance of the container)
The printing conditions on the surfaces of the produced paper cups were compared and a visual evaluation was made to determine their superiority or inferiority.
◯: No unevenness or white spots are observed △: Some unevenness or white spots are observed ×: Unevenness or white spots are very noticeable

(Easy to hold)
The paper cups were picked up by hand and the feel when lightly gripped was evaluated according to the following criteria.
○: Moderate resilience, not easily deformed, and feels secure. △: Slight bending felt when gripped. ×: Bending and deformation occurred when gripped, giving a weak feeling.

[Evaluation method]
Tables 4 and 5 show the evaluation results for the paper cups using the converting base papers of the examples.

As is clear from Tables 4 and 5, the paper cups manufactured using the converted base papers of Examples 101 to 119 did not suffer from cracks, peeling, wrinkles, etc. at the joints or top curl portions, even when they were bent in both the MD and CD directions to form the side walls and top curl portions, and the overall appearance of the container was excellent and it was easy to hold.

Table 6 shows the evaluation results for paper cups using the paper container sheets of Examples 120 and 121.

As is clear from Table 6, the tensile strength of the paper container sheet of Example 120 manufactured using the converting base paper of Example 104, and the paper container sheet of Example 121 manufactured using the converting base paper of Example 101, did not change substantially even after lamination. The paper containers manufactured using the paper container sheets of Examples 120 and 121 did not suffer from peeling of the adhesive layer at the joints, cracks, peeling, wrinkles, etc. at the top curl, and the laminated thermoplastic resin was also difficult to peel off. The overall appearance of the container was also excellent, making it easy to hold.

Claims (18)

The main component is cellulose pulp, and the maximum bending stress in the bending angle range of 0 to 90 degrees in at least one direction is 215 N/m or less;
A converting base paper having a tensile strength in the MD direction of 35 kN/m or less, a tensile strength in the CD direction of 22 kN/m or less, and an average value of the tensile strengths in the MD direction and the CD direction of 28 kN/m or less. The main component is cellulose pulp, and the maximum bending stress in the bending angle range of 0 to 90 degrees in at least one direction is 215 N/m or less;
A converting base paper having a T1/T2 value of 1.1 or more and less than 3.0, where T1 is the tensile strength in the MD direction and T2 is the tensile strength in the CD direction. The main component is cellulose pulp, and the maximum bending stress in the bending angle range of 0 to 90 degrees in at least one direction is 215 N/m or less;
A converting base paper having a basis weight of 200 to 400 g/ ^m2 and a density of 0.80 to 1.00 g/ ^cm3 . The main component is cellulose pulp, and the maximum bending stress in the bending angle range of 0 to 90 degrees in at least one direction is 215 N/m or less;
A converting base paper that satisfies at least two of the following (1) to (3):
(1) The tensile strength in the MD direction is 35 kN/m or less, the tensile strength in the CD direction is 22 kN/m or less, and the average value of the tensile strengths in the MD direction and the CD direction is 28 kN/m or less;
(2) When the tensile strength in the MD direction is T1 and the tensile strength in the CD direction is T2, the value of T1/T2 is 1.1 or more and less than 3.0;
(3) The basis weight is 200 to 400 g/ ^m2 and the density is 0.80 to 1.00 g/ ^cm3 . The converting base paper according to any one of claims 1 to 4, in which the inflection point of the bending stress curve is in the bending angle range of 0 to 40 degrees. The converting base paper according to any one of claims 1 to 5, wherein the ash content measured by the ash content test method specified in JIS P 8251:2003 is 0.5 to 40.0% by mass. The converting base paper according to any one of claims 1 to 6, which is composed of two or more paper layers and has an interlaminar strength of 100 J/m2 or ^more as measured by the internal bond tester method specified in JAPAN TAPPI 18-2. The converting base paper according to claim 7, which has an interlaminar strength of 1000 J/m2 or ^less as measured by the internal bond tester method specified in JAPAN TAPPI 18-2. The converting base paper according to any one of claims 1 to 8, which is composed of three or more paper layers. The converting base paper according to claim 9, in which the value of W1/W2 is 1.05 to 2.10, where W1 is the average basis weight of the outermost paper layer and W2 is the average basis weight of the first inner layer located immediately inside the outermost paper layer. The converting base paper according to claim 9 or 10, wherein the ash content of the outermost paper layer measured by the ash content test method specified in JIS P 8251:2003 is at least 1.0% by mass less than the ash content of the inner paper layer. The converting base paper according to any one of claims 9 to 11, in which the ash content of the outermost paper layer measured by the ash content test method specified in JIS P 8251:2003 is less than 0.5% by mass. The converting base paper according to any one of claims 7 to 12, further comprising an adhesive layer between the paper layers, the adhesive layer containing starch or polyacrylamide. The converting base paper contains a polyacrylamide-based paper strength agent,
The processing base paper according to any one of claims 1 to 13, wherein the content of the polyacrylamide-based paper strength agent per 100 parts by mass of the cellulose pulp is 0.02 parts by mass or more and less than 1 part by mass. A sheet for paper containers having a thermoplastic resin layer on at least one side of the converting base paper according to any one of claims 1 to 14. The sheet for paper containers according to claim 15, wherein the maximum bending stress in at least one direction at a bending angle of 0 to 90 degrees is 230 N/m or less. The processing base paper has the thermoplastic resin layer on both sides thereof,
17. The sheet for paper containers according to claim 15 or 16, wherein the melting point of one thermoplastic resin layer is at least 3° C. lower than the melting point of the other thermoplastic resin layer. A paper container made from the converting base paper according to any one of claims 1 to 14 or the paper container sheet according to any one of claims 15 to 17.