JP7639640B2 - Base paper for paper containers and paper containers - Google Patents

Description

This disclosure relates to base paper for paper containers and paper containers.

Currently, due to environmental concerns, efforts to reduce or eliminate the use of plastic are accelerating worldwide. Plastic materials have been used primarily for packaging containers such as food trays, but paper packaging materials are being considered instead of plastic materials. For example, Patent Document 1 discloses a paper tray container that can be easily disassembled by hand.

Japanese Patent Application Publication No. 10-053235

Packaging containers made of paper need to be easy to fold into containers, i.e., formable (flexible), but they also need strength after forming, such as resistance to drop impact. However, there is a trade-off between the two as paper properties, and there is a demand for good paper that can achieve both formability and drop impact resistance.
The present disclosure relates to a base paper for paper containers and a paper container that can achieve both formability and drop impact resistance.

That is, the present disclosure relates to the following <1> to <8>.
<1> A base paper for paper containers having a paper base material containing pulp,
The base paper for paper containers was disintegrated into fibers to obtain the pulp. The fiber length of the pulp was measured in accordance with ISO 16065-2:2007.
The pulp has a length-weighted average fiber length of 0.7 mm to 1.5 mm;
The content of fibers having a fiber length of less than 0.6 mm among the fibers contained in the pulp is 28% by number to 57% by number,
The base paper for paper containers is characterized in that the content of fibers having a fiber length of 0.6 mm or more among the fibers contained in the pulp is 43% to 72% by number.
<2> The content ratio of fibers having a fiber length of less than 0.6 mm among the fibers contained in the pulp is 33% by number to 55% by number,
The paper container base paper according to <1>, wherein the content of fibers having a fiber length of 0.6 mm or more among the fibers contained in the pulp is 45% by number to 67% by number.
<3> The base paper for paper containers according to <1> or <2>, wherein the length-weighted average fiber length of the pulp is 0.8 mm to 1.0 mm.
<4> The base paper for paper containers according to any one of <1> to <3>, wherein the paper base material has a basis weight of 200 g/m ² to 450 g/m ² .
<5> The base paper for paper containers according to any one of <1> to <4>, wherein the density of the paper base material is 0.50 g/ cm ³ to 1.10 g/ cm ³ .
<6> The paper container base paper according to any one of <1> to <5>, wherein the paper container base paper has a thermoplastic resin layer on at least one surface of the paper base material.
<7> The base paper for paper containers according to any one of <1> to <6>, wherein the pulp has a softwood kraft pulp content of 10% by mass or more and 60% by mass or less.
<8> A paper container which is a molded product of the base paper for paper containers according to any one of <1> to <7>.

This disclosure makes it possible to provide base paper for paper containers that is both moldable and drop impact resistant.

Example of a blank sheet for use in a tray Example of a molded tray

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

The inventors of the present invention have conducted research into how to achieve both moldability and drop impact resistance, which are in a trade-off relationship as paper properties. First, the inventors of the present invention have investigated the length-weighted average fiber length of pulp. The smaller the value of the length-weighted average fiber length, the more flexible the paper is, and the lower the resilience when the paper is folded. In other words, the moldability is improved. However, if the length-weighted average fiber length is reduced, the strength decreases and the drop impact resistance also decreases.

Therefore, in order to achieve both moldability and drop impact resistance, the inventors further focused on the content ratio of fibers of a specific length, specifically the ratio of short fibers (fibers less than 0.6 mm) and long fibers (fibers 0.6 mm or longer) among the fibers contained in the pulp. They then discovered a relationship between the length-weighted average fiber length and the content ratio of fibers of a specific length that can achieve both moldability and drop impact resistance.

When pulp obtained by disintegrating base paper for paper containers into fibers is used and the fiber length of the pulp is measured in accordance with ISO 16065-2:2007, the length-weighted average fiber length of the pulp must be 0.7 mm to 1.5 mm. If the length-weighted average fiber length is less than the lower limit, the strength decreases and drop impact resistance decreases. On the other hand, if the length-weighted average fiber length exceeds the upper limit, moldability decreases.
The length-weighted average fiber length of the pulp is preferably 0.8 mm to 1.0 mm, and can be controlled by the type of pulp used, the amount of fine fibers, and the like.

In addition, in the above-mentioned fiber length measurement, it is necessary that the content of fibers having a fiber length of less than 0.6 mm among the fibers contained in the pulp is 28% by number to 57% by number, and the content of fibers having a fiber length of 0.6 mm or more is 43% by number to 72% by number.
Even if the length-weighted average fiber length is the same, it is presumed that the paper with more short fibers is easier to move than the paper with less short fibers. Therefore, flexibility is improved and moldability is good. However, if there are too many short fibers, strength is likely to decrease. If the content ratio of fibers with a fiber length of less than 0.6 mm exceeds the upper limit (the content ratio of fibers with a fiber length of 0.6 mm or more is less than the lower limit), strength decreases and drop impact resistance decreases.

On the other hand, even if the length-weighted average fiber length is the same, if the proportion of short fibers is small, the strength is improved, but it is presumed that the fibers are less likely to move due to the large proportion of long fibers. Therefore, flexibility and moldability are reduced. Therefore, if the content of fibers with a fiber length of less than 0.6 mm is below the lower limit (the content of fibers with a fiber length of 0.6 mm or more exceeds the upper limit), moldability is reduced.
As described above, by setting the length-weighted average fiber length, the content ratio of fibers having a fiber length of less than 0.6 mm, and the content ratio of fibers having a fiber length of 0.6 mm or more within the above specific ranges, it is possible to achieve both moldability and drop impact resistance.

The percentage of fibers with a fiber length of less than 0.6 mm in the fibers contained in the pulp is preferably 30% by number or more, more preferably 33% by number or more, even more preferably 35% by number or more, and even more preferably 38% by number or more. On the other hand, the upper limit is preferably 55% by number or less, more preferably 50% by number or less, even more preferably 45% by number or less, and even more preferably 42% by number or less.

The percentage of fibers with a fiber length of 0.6 mm or more among the fibers contained in the pulp is preferably 45% by number or more, more preferably 50% by number or more, even more preferably 55% by number or more, and even more preferably 58% by number or more. On the other hand, the upper limit is preferably 70% by number or less, more preferably 67% by number or less, even more preferably 65% by number or less, and even more preferably 62% by number or less.

The proportion of fibers with a fiber length of less than 0.6 mm (the proportion of fibers with a fiber length of 0.6 mm or more) in the fibers contained in the pulp can be controlled by the type of pulp used and by using a fiber classifier. In particular, by blending pulp with a short fiber length obtained by crushing pulp (for example, hardwood kraft pulp such as bleached hardwood kraft pulp) with a cutter mill or the like, it is easy to control the fiber content within the above specific range.

The basis weight of the paper base material is preferably 200 g/m ² to 450 g/m ² , more preferably 250 g/m ² to 400 g/m ² , and even more preferably 300 g/m ² to 380 g/m ^2. When the basis weight is equal to or greater than the lower limit, the strength is increased and drop impact resistance is further improved. On the other hand, when the basis weight is equal to or less than the upper limit, formability is more likely to be improved. Therefore, within the above numerical range, it is easier to achieve both formability and drop impact resistance.

The thickness of the paper base material is preferably 300 μm to 600 μm, more preferably 350 μm to 5500 μm, and even more preferably 400 μm to 500 μm.

The density of the paper base material is preferably 0.50 g/ cm3 ^to 1.10 g/ cm3 , more preferably 0.60 ^g / cm3 to 1.00 g/ cm3 , even more preferably 0.65 ^g / cm3 to 0.90 g/ ^cm3 , and even more preferably 0.70 g / cm3 ^to 0.80 g / cm3 . When the density is equal to or higher than ^the lower limit, the strength is increased and the drop impact resistance is further improved. On ^the other hand, when the density is equal to ^or lower than the upper limit, the moldability is more likely to be improved. Therefore, when the density is within the above numerical range, it is easier to achieve both moldability and drop impact resistance.

Next, materials that can be used for the base paper for paper containers will be described.
Examples of the pulp constituting the paper base material include hardwood kraft pulps such as hardwood unbleached kraft pulp (LUKP) and hardwood bleached kraft pulp (LBKP); softwood kraft pulps such as softwood unbleached kraft pulp (NUKP) and softwood bleached kraft pulp (NBKP); mechanical pulps such as groundwood pulp (GP), pressurized groundwood pulp (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), chemi-mechanical pulp (CMP), and chemi-ground pulp (CGP); waste paper pulp; non-wood fiber pulps such as kenaf, bagasse, bamboo, and cotton; synthetic pulp, etc. These pulps may be used alone or in combination of two or more.

The pulp preferably contains pulp having a short fiber length (hereinafter also referred to as "fine fibers") obtained by crushing the above-mentioned pulp (for example, hardwood kraft pulp such as hardwood bleached kraft pulp) with a known crushing device such as a cutter mill. By using the fine fibers, it becomes easier to control the content ratio of fibers having a fiber length of less than 0.6 mm.
The fine fibers may have a length-weighted average fiber length of, for example, 0.2 mm or more and less than 0.6 mm.

The pulp preferably contains hardwood kraft pulp, softwood kraft pulp, and fine fibers, and more preferably contains bleached hardwood kraft pulp, bleached softwood kraft pulp, and fine fibers obtained by crushing bleached hardwood kraft pulp. Such a combination makes it easier to satisfy the length-weighted average fiber length and the content ratio of fibers of a specific length.

The hardwood kraft pulp content in the pulp is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, even more preferably 45% by mass or more, and particularly preferably 50% by mass or more. On the other hand, the upper limit is preferably 80% by mass or less, more preferably 75% by mass or less, even more preferably 70% by mass or less, and even more preferably 65% by mass or less.

The content of softwood kraft pulp in the pulp is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 13% by mass or more, and even more preferably 15% by mass or more. On the other hand, the upper limit is preferably 60% by mass or less, more preferably 50% by mass or less, even more preferably 40% by mass or less, and even more preferably 35% by mass or less.

The fine fiber content in the pulp is preferably 8% by mass or more, more preferably 12% by mass or more, even more preferably 15% by mass or more, and even more preferably 18% by mass or more. On the other hand, the upper limit is preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, and even more preferably 22% by mass or less.

The degree of beating of the pulp is not particularly limited, but is preferably 200 to 800 mL, more preferably 400 to 650 mL, in terms of Canadian standard freeness (CSF). CSF is measured according to JIS P 8121-2:2012 "Pulp - Freeness test method - Part 2: Canadian standard freeness method". The means of beating are not particularly limited, and known methods can be adopted. The hardwood kraft pulp and softwood kraft pulp may be beaten in advance, and the hardwood kraft pulp, softwood kraft pulp and fine fibers may be mixed and beaten to the desired degree of beating.

Additives may be used in the paper base material as necessary. Examples of additives include pH adjusters (sodium bicarbonate, sodium hydroxide, etc.), dry strength agents (polyacrylamide, starch, etc.), wet strength agents (polyamide polyamine epichlorohydrin resin, melamine-formaldehyde resin, urea-formaldehyde resin), internal sizing agents (rosin, alkyl ketene dimer, aluminum sulfate, etc.), drainage retention aids (polyacrylamide resin), defoamers, fillers (calcium carbonate, talc, etc.), dyes, etc. These additives may be used alone or in combination of two or more. There are no particular limitations on the amount of additives contained, and they may be within the range that is normally used.

[Method of manufacturing paper base material]
The method for producing the paper base material is not particularly limited, and a paper stock containing pulp may be made by a known method. The paper stock may further contain additives as necessary. Examples of additives include the additives described above. The paper stock can be prepared by adding additives to a pulp slurry as necessary. The pulp slurry is obtained by beating pulp in the presence of water. The pulp beating method and beating device are not particularly limited, and known beating methods and beating devices can be used.

The paper base material may be a single-layer paper, or may be a multi-layer paper (multilayer paper) consisting of two or more layers. In the case of multilayer paper, the number of layers is preferably 2 to 7, and more preferably 4 to 6. In multilayer paper, the raw material composition, basis weight, and papermaking conditions of each layer can be adjusted as desired, and starch or paper strength enhancers that strengthen interlayer adhesion may be contained between the layers.

The solids concentration of the pulp slurry during beating is not particularly limited, but is preferably about 1 to 20% by mass, and more preferably about 2 to 10% by mass. The pulp content in the paper stock or paper base material is also not particularly limited, and may be within a range that is normally used. For example, it is preferably 60% by mass or more and 100% by mass or less, more preferably 80% by mass or more and less than 100% by mass, and more preferably 90% by mass or more and 98% by mass or less, based on the total mass of the paper stock (solids) or paper base material.

In making the paper substrate, a known wet paper machine can be appropriately selected and used, such as a Fourdrinier paper machine, a gap former type paper machine, a cylinder paper machine, or a short wire paper machine.
When the paper base material has a multi-layer structure, starch such as potato starch may be added between the layers by spraying or the like during the papermaking process.

During papermaking, a coating layer such as a water-soluble polymer layer may be provided on at least one surface of the paper substrate. These layers may be used alone or in combination of two or more. The water-soluble polymer is not particularly limited, but examples thereof include polyvinyl alcohol (PVA), starches such as oxidized starch, polyacrylamides, and polyethyleneimines. Starches are preferably applied. There is no particular limit to the method of forming the coating layer, and known methods such as a size press, a blade coater, and a rod coater can be used. The amount of the coating layer is preferably about 0.2 g/m ² to 2.0 g/m ² in terms of solid content, and more preferably about 0.5 g/m ² to 1.5 g/m ² (in terms of solid content).

After papermaking, a calendering and drying process can be carried out as necessary by a known method to obtain a paper base material. The linear pressure applied during the calendering process is not particularly limited and may be appropriately controlled depending on the basis weight and pulp material. It is preferably 70 kN/m to 200 kN/m, and more preferably 100 kN/m to 150 kN/m.

The obtained paper base material can be used as it is as base paper for paper containers. From the viewpoint of improving waterproofness and stain resistance, a thermoplastic resin layer may be provided on at least one side of the paper base material, if necessary. In addition, other resin layers may be provided on the base paper for paper containers to an extent that does not impair the above-mentioned effects. The base paper for paper containers may have a thermoplastic resin layer on one side of the paper base material, or may have thermoplastic resin layers on both sides of the paper base material.

The thermoplastic resin used in the thermoplastic resin layer is not particularly limited, and may be appropriately selected from known thermoplastic resins.
Specific examples of the resin include polyester-based resins such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate; polyolefin-based resins such as polyvinyl chloride, polyvinylidene chloride, polybutene, polybutadiene, ethylene-vinyl acetate copolymer, polyethylene, polypropylene, ethylene-propylene copolymer, and polymethylpentene; polycarbonate; polyurethane; polyamide; polyacrylonitrile; and poly(meth)acrylate.

Among these, polyolefins such as polyethylene, polypropylene, and ethylene-propylene copolymers, and polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid, and polybutylene succinate are preferred, polyethylene, polypropylene, polyethylene terephthalate, polylactic acid, and polybutylene succinate are more preferred, polyethylene and polypropylene are even more preferred, and polyethylene is even more preferred.
In addition to the above materials, biomass resins and biodegradable resins may be used as the resin. These resins may be used alone or in combination of two or more.

The thermoplastic resin is preferably one that can be laminated to the sheet substrate as a lamination layer. Among thermoplastic resins, polyethylene is preferred because of its excellent extrusion lamination properties and barrier properties.
Polyethylene (PE) is roughly classified into linear low density polyethylene (LLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE). Among these, low density polyethylene (LDPE) is preferred because of its excellent extrusion lamination property and foaming property.

The thermoplastic resin layer may be produced by a known production method, such as a melt extrusion method, a melt casting method, or a calendar method. The thickness of the thermoplastic resin layer is not particularly limited, but is preferably 1 μm or more, more preferably 5 μm or more, and even more preferably 8 μm or more. On the other hand, the upper limit of the thickness is preferably 100 μm or less, more preferably 80 μm or less, and even more preferably 50 μm or less.

The use of the obtained paper container base paper is not particularly limited, and by forming it into an appropriate molded body, it can be used for various paper containers such as trays, cups, and packs. For example, it can be formed into paper containers such as paper plates, paper cups, paper packs, and paper trays. That is, the present disclosure provides a paper container that is a molded body of the paper container base paper. For example, the paper container base paper is preferably a base paper for food containers, and the paper container is preferably used as a paper container for food. The molding method is not particularly limited, and known methods can be adopted. For example, it can be molded into a desired shape by folding molding, press molding, etc. It is preferable that the paper container is folded and molded.

The measurement methods for each physical property are described below.
<Length-weighted average fiber length of pulp, content of fibers with a fiber length of less than 0.6 mm, and content of fibers with a fiber length of 0.6 mm or more>
The pulp fiber length in the base paper for paper containers is measured in accordance with ISO 16065-2:2007. Specifically, the measurement is as follows.
The base paper for paper containers is cut into 40 cm squares, soaked in ion-exchanged water, adjusted to a solids concentration of 2% by mass, and soaked for 24 hours. After soaking for 24 hours, a standard defibrator (manufactured by Kumagai Riki Kogyo Co., Ltd.) is used for 20 minutes to defibrate the pulp into fibers. If undefibrated pulp remains, the defibration process is carried out again for 20 minutes to defibrate the pulp into fibers. If the base paper for paper containers has a resin layer, the above defibration process is carried out in the form with the resin layer, and the slurry (dispersion liquid of pulp fibers) is separated. If the resin layer can be removed, it is preferable to carry out the defibration process in the form without the resin layer. The defibration is carried out in accordance with JIS P8220-2:2012.
Using the obtained pulp fiber sample, the "length-weighted average fiber length" is measured using a fiber length measuring device (model FS-5 with UHD base unit, manufactured by Valmet).
The device can also detect and measure each fiber using an attached camera. The device calculates the content ratio of different fiber lengths, and calculates the content ratio of fibers with a fiber length of less than 0.6 mm and the content ratio of fibers with a fiber length of 0.6 mm or more based on the total content ratio of fiber lengths.
In addition, for the measurement of "fiber length" here, fibers having a length of 0.2 mm or more and 7.6 mm or less are selected.

<Basance weight>
The basis weight of the paper base material is measured in accordance with JIS P 8124:2011.
In addition, when the base paper for paper containers has a resin layer in addition to a paper base material, the basis weight of the paper base material can be calculated after specifying the material, thickness, density, etc. of the resin layer using known methods and the following procedure.
Specifically, the weight of the paper substrate with the resin layer cut to a specified size is measured (total weight), then the paper substrate with the resin layer is immersed in an enzyme such as cellulase to confirm that the paper substrate has been completely dissolved, the weight of only the resin layer (resin layer weight) is then measured, and the weight of only the paper substrate is calculated by subtracting the weight of the resin layer from the total weight, and the basis weight of the paper substrate is measured.

<Thickness>
The thickness of the paper base material (paper thickness) is measured in accordance with JIS P 8118: 2014. When the paper container base paper has a resin layer in addition to the paper base material, the thicknesses of the paper base material layer and the thermoplastic resin layer are measured from an observation image of the cross section of the paper container base paper under an electron microscope (SEM).

<Density>
The density of the paper base material is calculated from the thickness and basis weight obtained by the above-mentioned measuring method.

The features of the present invention are explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. Furthermore, unless otherwise specified, "parts" refers to "parts by mass." Furthermore, the operations of the examples and comparative examples were carried out at room temperature (20-25°C) and normal humidity (40-50% RH) unless otherwise specified.

Example 1
As the pulp raw material, hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP) were each beaten to a CSF (Canadian Standard Freeness) of 600 ml using a double disc refiner. On the other hand, the fine fibers were prepared by mechanically crushing a dry sheet of LBKP using a cutter mill (HORAI Corporation, HA8 2542 30E, screen 0.24 mm).
The obtained pulp slurry and fine fibers were mixed in the blending ratio shown in Table 1. That is, LBKP pulp slurry A (55% by mass), NBKP pulp slurry B (35% by mass), and fine fiber C (10% by mass) were mixed. The obtained mixture was beaten to a CSF (Canadian Standard Freeness) of 500 ml at a concentration of 3%.
The beaten pulp slurry was used to prepare a paper stock by adding, per 100 parts of pulp in terms of solid content, 0.55 parts (solid content equivalent) of cationic starch (P-3Y, manufactured by Pillar Starch Co., Ltd.) as an internal paper strength enhancer, 0.25 parts (solid content equivalent) of an alkyl ketene dimer sizing agent (AD1612, manufactured by Seiko PMC Co., Ltd.) as an internal sizing agent, 0.18 parts (solid content equivalent) of aluminum sulfate, and 0.12 parts (solid content equivalent) of a polyamide amine epichlorohydrin wet strength agent (WS4024, manufactured by Seiko PMC Co., Ltd.) as a wet strength agent.
This paper stock was used to make a 5-layer paper using a Fourdrinier paper machine. During the papermaking process, 2.50 parts (solid content equivalent) of potato starch was sprayed between each layer using an interlayer spray, and after the 5 layers were combined, 1.0±0.2 g/ ^m2 (solid content equivalent) of oxidized starch was applied to the surface of the paper base using a size press. Using a calendar, treatment was performed under a linear pressure of 120 kN/m to obtain a paper base with a basis weight of 340 g/ ^m2 used in Example 1.
The obtained paper base material was used as the base paper for paper containers of Example 1.

<Examples 2 to 7, 12, and 13>
The base papers for paper containers of Examples 2 to 7, 12 and 13 were obtained in the same manner as in Example 1, except that the amounts of the LBKP pulp slurry, the NBKP pulp slurry and the fine fibers were changed as shown in Table 1.

Example 8
The paper container base paper of Example 8 was obtained in the same manner as in Example 3, except that the basis weight was changed to 250 g/ ^m2 by adjusting the discharge rate of the pulp slurry.

<Example 9>
The paper container base paper of Example 9 was obtained in the same manner as in Example 3, except that the basis weight was changed to 400 g/ ^m2 by adjusting the discharge rate of the pulp slurry.

Example 10
A base paper for paper containers of Example 10 was obtained in the same manner as in Example 1, except that the linear pressure of the soft nip calendar was changed to 80 kN/m.

Example 11
A base paper for paper containers of Example 11 was obtained in the same manner as in Example 1, except that the linear pressure of the soft nip calendar was changed to 180 kN/m.

<Example 14>
The base paper for paper containers of Example 14 was obtained in the same manner as in Example 3, except that 10 μm of propylene resin (company name: SunAllomer Co., Ltd., product number: PHA03A) was laminated as a thermoplastic resin on one side of the obtained paper base material.

Example 15
The base paper for paper containers of Example 15 was obtained in the same manner as in Example 3, except that 40 μm of propylene resin (company name: SunAllomer Co., Ltd., product number: PHA03A) was laminated as a thermoplastic resin on one side of the obtained paper base material.

<Example 16>
The base paper for paper containers of Example 16 was obtained in the same manner as in Example 3, except that 20 μm of ethylene resin (company name: Japan Polyethylene Corporation, product number: LC522) was laminated as a thermoplastic resin on one side of the obtained paper base material.

<Example 17>
The base paper for paper containers of Example 17 was obtained in the same manner as in Example 3, except that 20 μm of propylene resin (company name: SunAllomer Co., Ltd., product number: PHA03A) was laminated as a thermoplastic resin on both sides of the obtained paper base material.

<Comparative Examples 1 to 7>
Base papers for paper containers of Comparative Examples 1 to 7 were obtained in the same manner as in Example 1, except that the amounts of LBKP pulp slurry, NBKP pulp slurry, and fine fibers were changed as shown in Table 1.

The obtained base paper for paper containers was used to carry out the following evaluations.
(Moldability)
A blank sheet as shown in FIG. 1 (which can be formed into a tray as shown in FIG. 2 as disclosed in JP-A-10-053235) was prepared using base paper for paper containers and left to stand for one day in an environment of 23±5° C. and 50±10% Rh.
Under the above environment, the shaded area (flange portion) in FIG. 1 was folded by hand, and a 1 kg tape pressing roller (manual) (manufactured by Yasuda Seiki Seisakusho, product number: No. 349) was used to roll the folded portion back and forth twice at a speed of about 10 mm/s to press it, and the product was left to stand for 30 minutes.
The sample was visually inspected, and the degree of opening (angle) of all four sides was measured with a protractor, and the average value of the four sides was calculated. Five trays were prepared for each of the examples and comparative examples, and tests were conducted on each of them, with the worst result (the tray angle that was the most widely opened) being adopted.
The measurement results were judged according to the following criteria.
5: Angle less than 30° 4: Angle 30° or more and less than 60° 3: Angle 60° or more and less than 90° 2: Angle 90° or more and less than 120° 1: Angle 120° or more 3 or more was judged as good. When the angle is less than 90°, a double flange is formed, which makes it easy to fix when bonding by heat sealing or hot melt.

(Drop impact resistance)
A blank sheet as shown in Fig. 1 was prepared using base paper for paper containers, and assembled by hand into the shape of a tray as shown in Fig. 2. The flange portion 1, flange corner portion 2, and corner flap 3 in Fig. 2 were fixed in advance by adhering double-sided adhesive tape (company name: 3M, product number: Scotch super strong double-sided tape Premier Gold Super Multipurpose PPS-10).
The tray-formed sample was filled with 350 g of sand and the flange was attached to the four sides with double-sided adhesive tape (
A film (company name: Mitsubishi Chemical, model number: Diamiron F001, 40 μm thickness) was attached to the four sides of the flange.
Five of the above trays were prepared for each Example and Comparative Example. The obtained samples were left to stand for one day in an environment of -5°C, and the following evaluation was performed immediately after removal. The tray was dropped without acceleration from a height of 80 cm onto a floor covered with a SUS plate, with the bottom surface of the tray kept horizontal so that the bottom surface or one of the four corners of the bottom surface first came into contact with the floor. Tests were performed with five trays prepared for each Example and Comparative Example, and the state of the trays after the test was observed. The measurement results were judged according to the following criteria.
5: No change was observed in any of the five trays before and after the evaluation.
4: Before and after the evaluation, in 1 to 4 of the 5 trays, no dents were formed in the four corners of the bottom surface of the tray, but distortion was formed in the bottom surface of the tray.
3: Before and after the evaluation, no dents were formed in the four corners of the bottom surface of all five trays, but distortion was formed in the bottom surface of the tray.
2: Before and after the evaluation, dents were formed in the four corners of the bottom surface of one to four of the five trays.
1: Before and after the evaluation, dents were formed in the four corners of the bottom surface of all five trays.
A score of 3 or higher was considered to be a good result.

The physical properties and evaluation results of Examples 1 to 17 and Comparative Examples 1 to 7 are shown in Table 2.

1: Flange part, 2: Flange corner part, 3: Corner flap

Claims (6)

A paper container base paper having a paper base material containing pulp,
The paper base has a basis weight of 200 g/m ² to 450 g/m ² ;
The density of the paper base is 0.50 g/cm ³ to 1.10 g/cm ³ ;
The pulp obtained by disintegrating the base paper for paper containers into fibers is used to measure the fiber length of the pulp by selecting fibers having a length of 0.2 mm or more and 7.6 mm or less in accordance with ISO 16065-2:2007.
The pulp has a length-weighted average fiber length of 0.7 mm to 1.5 mm;
The content of fibers having a fiber length of 0.2 mm or more and less than 0.6 mm among the fibers contained in the pulp is 28% by number to 57% by number,
The base paper for paper containers is characterized in that the content of fibers having a fiber length of 0.6 mm or more and 7.6 mm or less among the fibers contained in the pulp is 43% to 72% by number. The content of fibers having a fiber length of 0.2 mm or more and less than 0.6 mm among the fibers contained in the pulp is 33% by number to 55% by number,
The paper container base paper according to claim 1, wherein the content of fibers having a fiber length of 0.6 mm or more and 7.6 mm or less among the fibers contained in the pulp is 45% by number to 67% by number. The base paper for paper containers according to claim 1 or 2, wherein the length-weighted average fiber length of the pulp is 0.8 mm to 1.0 mm. The paper container base paper according to any one of claims 1 to 3 , wherein the paper container base paper has a thermoplastic resin layer on at least one surface of the paper base material. The paper container base paper according to any one of claims 1 to 4 , wherein the pulp contains softwood kraft pulp in an amount of 10% by mass or more and 60% by mass or less. A paper container which is a molded product of the paper container base paper according to any one of claims 1 to 5 .

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