JP7655159B2 - Clupak Paper and Paper Products - Google Patents

Description

This disclosure relates to Clupak paper and paper products.

Conventionally, Clupak paper has been used as packaging paper, which is given stretchability by minutely shrinking the paper during papermaking. For example, Patent Document 1 discloses Clupak paper that is less likely to break even in heavy packaging applications by controlling the specific tensile strength in the longitudinal and transverse directions.

On the other hand, plastic materials have been mainly used for packaging containers such as food trays and packaging bodies such as pillow packaging bags. However, due to environmental concerns, there is currently research into using paper packaging materials instead of plastic containers.

International Publication No. 2015/008703

For the manufacture of packaging materials using paper, materials having extensibility are preferable from the viewpoint of formability. The present inventors have attempted to form food trays using conventional Clupak paper as described in Patent Document 1, but have found that wrinkles tend to form in the formed portions. In particular, this is insufficient for forming complex three-dimensional shapes such as deep trays.
The present disclosure relates to Clupak paper, which has high extensibility, sufficient conformability even when molded into complex three-dimensional shapes, and is less likely to develop wrinkles in molded parts, and to paper products using the Clupak paper.

That is, the present disclosure relates to the following <1> to <8>.
<1> Clupak paper having a paper base material containing pulp,
the Clupak paper has a longitudinal tensile stiffness ratio of 2.0 kN.m/g to 3.9 kN.m/g and a transverse tensile stiffness ratio of 1.5 kN.m/g to 2.9 kN.m/g, as measured in accordance with ISO/DIS 1924-3;
The Clupak paper has a breaking elongation in a longitudinal direction of 5.0% to 10.0%, and a breaking elongation in a transverse direction of 5.0% to 10.0%, as measured in accordance with JIS P 8113:2006.
<2> The Clupak paper has a tensile stiffness index in the longitudinal direction of 3.0 kN·m/g to 3.9 kN·m/g,
The Clupak paper according to <1>, wherein the Clupak paper has a tensile stiffness index in the transverse direction of 2.0 kN·m/g to 2.9 kN·m/g.
<3> The Clupak paper according to <1> or <2>, wherein the pulp obtained by defibrating the Clupak paper has a length-weighted average fiber length of 1.1 mm to 2.0 mm, as measured in accordance with ISO 16065-2:2007.
<4> The Clupak paper according to any one of <1> to <3>, wherein the paper base material has a basis weight of 30 g/m ² to 120 g/m ² .
<5> The Clupak paper according to any one of <1> to <4>, wherein the Clupak paper has a thermoplastic resin layer on at least one surface of the paper base material.
<6> The breaking elongation in the longitudinal direction of the Clupak paper is 7.0% to 9.7%,
The Clupak paper according to any one of <1> to <5>, wherein the Clupak paper has a breaking elongation in the transverse direction of 6.5% to 9.5%.
<7> The pulp contains softwood kraft pulp,
The Clupak paper according to any one of <1> to <6>, wherein the content of softwood kraft pulp in the pulp is 25% by mass or more.
<8> A paper product which is a molded body of the Clupak paper according to any one of <1> to <7>.

This disclosure makes it possible to provide Clupak paper that is highly extensible, has sufficient conformability even when molded into complex three-dimensional shapes, and is less likely to wrinkle in the molded parts.

Schematic diagram of press processing Example of a tray made from Clupak paper

In the present disclosure, the description of a numerical range such as "X or more and Y or less" or "X to Y" means a numerical range including the lower and upper limits, which are the endpoints, unless otherwise specified. When a numerical range is described in stages, the upper and lower limits of each numerical range can be arbitrarily combined.
The machine direction is the machine direction (MD) of the paper base material, which is the same as the direction in which the fibers are oriented, and the cross direction is the direction perpendicular to the machine direction (CD).

As mentioned above, Clupak processing is a process that gives the paper stretchability by minutely shrinking it on the papermaking machine. Specifically, for example, a Clupak device equipped with an endless thick elastic rubber blanket with nip rolls is installed in a part of the papermaking machine dryer. The wet paper web is introduced into the Clupak device and compressed by the nip rolls and blanket. At this time, the blanket, which has been stretched beforehand, contracts, shrinking the running paper web (imparting crepe), thereby increasing the breaking elongation. The resulting shrinkage is dried and fixed so that it does not stretch in the subsequent process.

The inventors have found that the above problem can be solved by controlling the specific tensile stiffness ratio and breaking elongation through Clupak treatment during the production of the paper base material. The tensile stiffness ratio indicates the stiffness of the paper, and the breaking elongation indicates how easily the paper stretches. The fact that Clupak paper has the above specific tensile stiffness ratio and breaking elongation indicates that it has a moderate stiffness and is somewhat easy to stretch. Therefore, the inventors believe that it is possible to obtain Clupak paper that has high stretchability, sufficient conformability even when molded into complex three-dimensional shapes, and is less likely to cause wrinkles in the molded parts.

The tensile stiffness ratio of the Clupak paper in the machine direction, measured in accordance with ISO/DIS 1924-3, should be between 2.0 kN.m/g and 3.9 kN.m/g, and the tensile stiffness ratio of the Clupak paper in the cross direction should be between 1.5 kN.m/g and 2.9 kN.m/g.
If the tensile stiffness ratio is less than the lower limit, too much stress is applied during molding, making the material prone to wrinkles and tears. On the other hand, if the tensile stiffness ratio is more than the upper limit, the pressure required for molding becomes too high, making molding difficult, and if molding is attempted too forcefully, wrinkles and tears are likely to occur.

The tensile stiffness ratio can be controlled by the speed difference before and after Clupak treatment, adjusting the density by the nip pressure in calendaring, the type of pulp, etc. In order to increase the tensile stiffness, there are methods such as decreasing the speed difference before and after Clupak treatment, increasing the density by increasing the nip pressure in calendaring, and increasing the fiber length of the pulp. On the other hand, in order to decrease the tensile stiffness, there are methods such as increasing the speed difference before and after Clupak treatment, decreasing the density by decreasing the nip pressure in calendaring, and decreasing the fiber length of the pulp.

The tensile stiffness index in the machine direction of the Clupak paper is preferably 3.0 kN·m/g to 3.9 kN·m/g, and more preferably 3.1 kN·m/g to 3.7 kN·m/g.
The tensile stiffness index in the cross direction of the Clupak paper is preferably 2.0 kN·m/g to 2.9 kN·m/g, more preferably 2.3 kN·m/g to 2.8 kN·m/g.

The ratio of the longitudinal tensile stiffness ratio of Clupak paper to the transverse tensile stiffness ratio (longitudinal/transverse) is preferably 1.10 or more, more preferably 1.20 or more, and even more preferably 1.25 or more. On the other hand, the upper limit is preferably 1.50 or less, more preferably 1.40 or less, and even more preferably 1.35 or less.

It is necessary that the breaking elongation of the Clupak paper in the machine direction is 5.0% to 10.0%, and the breaking elongation of the Clupak paper in the cross direction is 5.0% to 10.0%, as measured in accordance with JIS P 8113:2006.
If the breaking elongation is below the lower limit, the paper will not stretch enough during molding, making it difficult to mold. If molding is attempted too forcefully, the paper will tear. On the other hand, if the breaking elongation exceeds the upper limit, the paper will be able to be molded due to its large elongation, but it will be more likely to move and wrinkle, which will then cause the paper to tear.

The breaking elongation can be controlled by the basis weight, the speed difference before and after Clupak treatment, the nip pressure during Clupak treatment, etc. Methods for increasing the breaking elongation include increasing the basis weight, increasing the speed difference before and after Clupak treatment, and decreasing the nip pressure during Clupak treatment. On the other hand, methods for decreasing the breaking elongation include decreasing the basis weight, decreasing the speed difference before and after Clupak treatment, and increasing the nip pressure during Clupak treatment.

The breaking elongation of Clupak paper in the longitudinal direction is preferably 7.0% or more, more preferably 8.0% or more. The upper limit of the breaking elongation in the longitudinal direction is preferably 9.7% or less, more preferably 9.0% or less.
The breaking elongation of Clupak paper in the transverse direction is preferably 6.5% or more, more preferably 7.5% or more. The upper limit of the breaking elongation in the transverse direction is preferably 9.5% or less, more preferably 8.5% or less.

The ratio of the breaking elongation in the longitudinal direction of Clupak paper to the breaking elongation in the transverse direction (longitudinal direction/transverse direction) is preferably 1.01 or more, more preferably 1.03 or more, and even more preferably 1.05 or more. On the other hand, the upper limit is preferably 1.30 or less, more preferably 1.20 or less, and even more preferably 1.12 or less.

The length-weighted average fiber length of the pulp obtained by disintegrating Clupak paper, measured in accordance with ISO 16065-2:2007, is preferably 1.1 mm to 2.0 mm, more preferably 1.2 mm to 1.9 mm, and even more preferably 1.3 mm to 1.8 mm. If the length-weighted average fiber length is equal to or greater than the lower limit, the strength is high and breakage during molding is less likely to occur. On the other hand, if the length-weighted average fiber length is equal to or less than the upper limit, the strength is appropriately high and wrinkles during molding can be further suppressed. Therefore, within the above numerical range, moldability can be further improved. The length-weighted average fiber length of the pulp can be controlled by the type of pulp used, etc.

The basis weight of the paper base material is preferably 30 g/m ² to 120 g/m ² , more preferably 60 g/m ² to 110 g/m ² , and even more preferably 70 g/m ² to 90 g/m ^2. When the basis weight is equal to or greater than the lower limit, the strength is high and tearing during molding can be more effectively prevented. On the other hand, when the basis weight is equal to or less than the upper limit, the strength is adequately high and wrinkles during molding can be more effectively prevented. Therefore, within the above numerical range, moldability can be improved.

The thickness of the paper substrate is preferably 50 μm to 300 μm, more preferably 60 μm to 200 μm, even more preferably 70 μm to 150 μm, and even more preferably 100 μm to 140 μm.

The density of the paper base material is preferably 0.30 g/m ³ to 1.00 g/m ³ , more preferably 0.40 g/m ³ to 0.90 g/m ³ , even more preferably 0.50 g/m ³ to 0.80 g/m ³ , and even more preferably 0.60 g/m ³ to 0.70 μmg/m ³ .

Next, materials that can be used for Clupak paper 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 softwood kraft pulp, more preferably contains hardwood kraft pulp and softwood kraft pulp, and even more preferably contains hardwood unbleached kraft pulp and softwood unbleached kraft pulp.

The hardwood kraft pulp content in the pulp is preferably 0% by mass or more, more preferably 5% by mass or more, even more preferably 10% by mass or more, and even more preferably 13% by mass or more. On the other hand, the upper limit is preferably 75% by mass or less, more preferably 65% by mass or less, even more preferably 60% by mass or less, and even more preferably 57% by mass or less.

The content of softwood kraft pulp in the pulp is preferably 25% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, even more preferably 40% by mass or more, and even more preferably 43% by mass or more. On the other hand, the upper limit is preferably 100% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less, and even more preferably 87% by mass or less.

The degree of beating of the pulp is not particularly limited, but the Canadian standard freeness (CSF) is preferably 200 to 800 mL, and more preferably 450 to 700 mL. CSF is measured in accordance with JIS P 8121-2:2012 "Pulp - Freeness test method - Part 2: Canadian standard freeness method."

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-based, alkyl ketene dimer, etc.), drainage retention aids (polyacrylamide resin), antifoaming agents, fillers (calcium carbonate, talc, etc.), dyes, etc. These additives may be used alone or in combination of two or more. The content of the additives is not particularly limited and may be within the range of those usually used.

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

The solids concentration of the pulp slurry during beating is not particularly limited, but is preferably about 5 to 40% by mass, and more preferably about 10 to 30% by mass. The pulp content in the paper stock or paper base material is also not particularly limited, and may be within the range that is normally used. For example, it is preferably 60% by mass or more and 100% by mass or less, and more preferably 80% by mass or more and less than 100% by mass, based on the total mass of the paper stock (solids) or paper base material.

In making paper substrates, a known wet paper machine can be appropriately selected and used. Examples of paper machines include Fourdrinier paper machines, gap former paper machines, cylinder paper machines, and short wire paper machines. Clupak devices capable of carrying out the Clupak treatment can be provided in these paper machines, and the Clupak treatment can be carried out. For example, the Clupak treatment can be carried out after the paper stock is made and dehydrated by calendaring.

A known Clupak device can be used. For example, a Clupak device equipped with a nip roll and an endless thick elastic rubber blanket can be mentioned. As described above, in the Clupak process, the paper web is introduced between the nip roll and the blanket, and when the paper web is compressed by the nip roll and the blanket, the blanket, which has been stretched beforehand, is contracted to shrink the paper web and impart a crepe. The Clupak device is usually installed as part of the dryer device of a papermaking machine, and after creping, the paper is dried and fixed. In this manner, a paper base material can be obtained.

In papermaking using the Clupak device, the tensile stiffness index and breaking elongation can be controlled by the difference in papermaking speed before and after the Clupak treatment and the pressure of the nip rolls.
The papermaking speed is not particularly limited, but may be controlled, for example, within the range of preferably 200 to 1000 m/min, more preferably 300 to 800 m/min, and further preferably 400 to 700 m/min. The nip pressure between the nip roll and the blanket during the Clupac treatment is also not particularly limited. For example, it may be appropriately controlled within the range of preferably 5 kN/m to 50 kN/m, and more preferably 10 kN/m to 25 kN/m.
The speed difference before and after the Clupak treatment is not particularly limited, and may be controlled so as to obtain the desired tensile stiffness index and breaking elongation depending on the basis weight and pulp material. It is preferably -45.0% to -10.0%, more preferably -40.0% to -15.0%. Here, the minus sign "-" indicates that the speed after the Clupak treatment is slow.

The nip pressure in the calendar treatment is not particularly limited, and may be controlled to obtain the desired specific tensile stiffness depending on the basis weight, pulp material, speed difference before and after the Clupak treatment, etc. It is preferably 100 kN/m to 200 kN/m, and more preferably 130 kN/m to 170 kN/m.

The obtained paper base material can be used as Clupak paper as it is. 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 Clupak paper to the extent that the above effects are not impaired. The Clupak paper 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 3 μm or more, and even more preferably 5 μm or more. On the other hand, the upper limit of the thickness is preferably 50 μm or less, more preferably 30 μm or less, and even more preferably 20 μm or less.

The uses of the obtained Clupak paper are not particularly limited, and by forming it into an appropriate molded product, it can be used for paper products such as packaging materials such as wrapping paper, packaging bags, and packaging containers, and various containers such as cups and trays. For example, it can be formed into paper containers such as paper plates, paper cups, and paper trays, and bags for horizontal pillow packaging, vertical pillow packaging, three-sided sealed packaging, four-sided sealed packaging, bag-feeding filling packaging, tube packaging, and stick packaging. The molding method is not particularly limited, and known methods can be used. For example, it can be molded into the desired shape by press molding.

The measurement methods for each physical property are described below.
<Tensile strength>
The tensile stiffness ratios of Clupak paper in the machine direction and cross direction are measured in accordance with ISO/DIS 1924-3. Specifically, the procedure is as follows. A sample with a test piece length of 150 mm and a test piece width of 15 mm is prepared in each of the machine direction and cross direction, and is stored at 23±5°C and 50±10% Rh.
The sample is then placed in a tensile tester (model RTC-1210A, manufactured by A&D Co., Ltd.) with a chuck distance of 100 mm and tested at a speed of 100 mm/min.

<Breaking elongation>
The breaking elongation in the machine direction and the cross direction of Clupak paper is measured in accordance with JIS P 8113:2006 (Testing methods for tensile properties of paper and paperboard).
Specifically, Clupak paper is left to stand for at least one day in an environment of 23±5°C and 50±10% humidity as a temperature and humidity conditioning treatment, and then cut into a sample with a width of 15 mm and a length of 150 mm. The sample is attached to a tensile tester (model RTC-1210A, manufactured by A&D Co., Ltd.) with a chuck distance of 100 mm, and a tensile test is performed at a speed of 20 mm/min to measure the breaking elongation in both the MD (machine direction) and CD (cross direction).

<Length-weighted average fiber length of pulp>
The length-weighted average fiber length of the pulp in Clupak paper is measured in accordance with ISO 16065-2:2007, specifically as follows:
The Clupak paper is cut into 40 cm square pieces, immersed in ion-exchanged water, and the solid content is adjusted to 2% by mass, and then soaked for 24 hours. After soaking for 24 hours, the paper is disintegrated for 30 minutes using a standard disintegrator (manufactured by Kumagai Riki Kogyo Co., Ltd.) to disintegrate the pulp into fibers. If the Clupak paper has a resin layer, the disintegrated slurry (dispersion of pulp fibers) from which the resin layer has been removed is separated.
Using the obtained pulp fiber sample, the "length-weighted average fiber length (ISO)" is measured using a fiber length measuring instrument (model FS-5 with UHD base unit, manufactured by Valmet Co., Ltd.). The "length-weighted average fiber length (ISO)" is the length-weighted average fiber length calculated by selecting fibers of 0.2 mm or more and 7.6 mm or less.

<Basance weight>
The basis weight of the paper base material is measured in accordance with JIS P 8124:2011.
In addition, when the Clupak paper has a resin layer in addition to the 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 by 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 Clupak 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 a cross section of the Clupak paper under a scanning 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 will be 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 to 25°C) unless otherwise specified.
The test was performed under normal humidity conditions (40 to 50% RH).

Example 1
Pulp was prepared by using NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood in a ratio (mass ratio) of NUKP:LUKP = 30:70, and beating the slurry to a CSF (Canadian Standard Freeness) of 600 mL at a slurry concentration of 2 mass% at the time of beating.
Using the above pulp, 0.15 parts of a synthetic sizing agent (SPS400, manufactured by Arakawa Chemical Industries, Ltd.), 1.2 parts of aluminum sulfate, 0.65 parts of a polyacrylamide resin (DS4433, manufactured by Seiko PMC Corporation) as a retention agent, and 0.035 parts of nonionic polyacrylamide (Percoll 47, manufactured by Allied Colloids) as a polymer flocculant (retention agent) were added per 100 parts of pulp in terms of solid content to prepare a paper stock.
Using the above-mentioned paper material, paper was made on a wet papermaking machine (Bellform III, manufactured by Mitsubishi Heavy Industries, Ltd.) equipped with an expansion device (manufactured by Clupak) at a papermaking speed of 600 m/min, a reel moisture content of 6.5%, a nip pressure by calendaring of 150 kN/m, a speed difference before and after Clupak treatment of -37.5%, and a nip pressure between the nip roll and blanket during Clupak treatment of 15 kN/m, to obtain a paper base material with a basis weight of 50 g/ ^m2 and a crepe applied to the paper surface. The paper base material was prepared in the following order: papermaking, dehydration by calendaring, and Clupak treatment (including drying). The obtained paper base material was designated as Clupak paper of Example 1.

Example 2
Clupak paper was obtained under the same conditions as in Example 1, except that the basis weight was changed to 80 g/ ^m2 by adjusting the discharge rate of pulp.

Example 3
Clupak paper was obtained under the same conditions as in Example 1, except that the basis weight was changed to 100 g/ ^m2 by adjusting the discharge rate of pulp.

Example 4
Clupak paper was obtained under the same conditions as in Example 1, except that the mass ratio of NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood was changed to NUKP:LUKP = 45:55.

Example 5
Clupak paper was obtained under the same conditions as in Example 1, except that the mass ratio of NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood was changed to NUKP:LUKP = 85:15.

Example 6
Clupak paper was obtained under the same conditions as in Example 1, except that the mass ratio of NUKP (softwood unbleached kraft pulp) and LUKP (hardwood unbleached kraft pulp) made by pulping (cooking) wood was changed to NUKP:LUKP = 100:0.

Example 7
Clupak paper was obtained under the same conditions as in Example 1, except that the paper was made with a speed difference of -18.0% before and after the Clupak treatment.

Example 8
Clupak paper was obtained under the same conditions as in Example 1, except that LDPE was melt-extrusion coated on one side of the paper base material so that the coating thickness after drying was 10 μm.

<Example 9>
Clupak paper was obtained under the same conditions as in Example 1, except that LDPE was melt-extrusion coated on both sides of the paper base so that the coating thickness after drying was 10 μm on each side.

<Comparative Example 1>
A paper base material (Clupak paper) was obtained under the same conditions as in Example 1, except that the nip pressure by the calendar was changed to 100 kN/m.

<Comparative Example 2>
A paper base material (Clupak paper) was obtained under the same conditions as in Example 1, except that the nip pressure by the calendar was changed to 180 kN/m.

<Comparative Example 3>
A paper base material (Clupak paper) was obtained under the same conditions as in Example 1, except that the nip pressure by the calendar was changed to 200 kN/m.

<Comparative Example 4>
A paper base was obtained under the same conditions as in Example 1, except that the Clupak treatment was not applied.

<Comparative Example 5>
A paper base material (Clupak paper) was obtained under the same conditions as in Example 1, except that the speed difference before and after the Clupak treatment was changed to -45.0%.

<Comparative Example 6>
A paper base material was obtained under the same conditions as in Example 1, except that the nip pressure by the calendar was changed to 100 kN/m and the Clupak treatment was not applied.

The obtained Clupak paper or paper base material was used to carry out the following evaluations.
The obtained Clupak paper or paper base material was cut out to obtain an A4 blank sheet 3 with the long side in the machine direction (MD). The blank sheet 3 was pressed using a molding die (1 and 2) and a press molding machine (FVT400, manufactured by Wakisaka Engineering Co., Ltd.) under conditions of a press pressure of 35 kgf/ ^cm2 , a press temperature of 150°C, and a press time of 5 seconds as shown in Figure 1 to form a tray shape as shown in Figure 2. The obtained tray was evaluated for the presence or absence of wrinkles and tears according to the following criteria. As shown in Figures 1 and 2, the edge of the opening of the tray was evaluated as the formed part 4. The higher the value, the better the result.
5: The molded portion has no tears or wrinkles, and the tray is not distorted.
4: The molded portion is not torn or wrinkled, but the tray is distorted.
3: The molded portion is not torn, but wrinkles are formed on one to three of the four sides of the molded portion.
2: The molded portion is not torn, but wrinkles are formed on all four sides of the molded portion.
1: The molded part is torn.

The physical properties and evaluation results of Examples 1 to 9 and Comparative Examples 1 to 6 are shown in Table 1.

1, 2: Molding die, 3: Blank sheet, 4: Molding part

Claims (8)

Clupak paper having a paper base containing pulp,
The Clupak paper has a longitudinal tensile stiffness ratio of 2.0 kN.m/g to 3.9 kN.m/g, and a transverse tensile stiffness ratio of 1.5 kN.m/g to 2.8 kN.m/g, measured in accordance with ISO/DIS 1924-3 (except when the transverse tensile stiffness ratio is 2.8 kN.m/g) ;
The Clupak paper has a breaking elongation in a longitudinal direction of 5.0% to 10.0%, and a breaking elongation in a transverse direction of 5.0% to 10.0%, as measured in accordance with JIS P 8113:2006. The Clupak paper has a tensile stiffness index in the longitudinal direction of 3.0 kN·m/g to 3.9 kN·m/g;
The tensile stiffness ratio in the transverse direction of the Clupak paper is 2.0 kN·m/g to 2.8 kN·m/g (excluding the case where the tensile stiffness ratio in the transverse direction is 2.8 kN·m/g).
Clupak paper as claimed in claim 1. The Clupak paper according to claim 1 or 2, wherein the length-weighted average fiber length of the pulp obtained by disintegrating the Clupak paper, as measured in accordance with ISO 16065-2:2007, is 1.1 mm to 2.0 mm. The Clupak paper according to any one of claims 1 to 3, wherein the basis weight of the paper base is between 30 g/m ² and 120 g/m ² . The Clupak paper according to any one of claims 1 to 4, wherein the Clupak paper has a thermoplastic resin layer on at least one surface of the paper base material. The breaking elongation in the longitudinal direction of the Clupak paper is 7.0% to 9.7%;
The Clupak paper according to any one of claims 1 to 5, wherein the breaking elongation in the transverse direction of the Clupak paper is 6.5% to 9.5%. The pulp contains softwood kraft pulp,
The Clupak paper according to any one of claims 1 to 6, wherein the content of softwood kraft pulp in the pulp is 25% by mass or more. A paper product which is a molded body of Clupak paper according to any one of claims 1 to 7.

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