JP7632152B2 - Paper laminate - Google Patents

Description

The present invention relates to a paper laminate.

Packages that use the heat seal method are widely used for packaging general industrial products, as well as for packaging food, medicine, and medical equipment. For example, Patent Document 1 describes a packaging material that is made of a laminate containing at least a film substrate and a sealant, in which the parallel transmitted light at a specific wavelength of the laminate is equal to or less than a specific value, and in which a transparent gas barrier layer is provided in the laminate.

In recent years, the problem of plastic waste has become more serious. Of the total amount of plastic produced worldwide, a large amount is produced in the packaging container sector, which is the cause of plastic waste. Plastic does not decompose for a long time, and the waste breaks down into microplastics in the natural environment, causing serious damage to the ecosystem. As a countermeasure, it has been proposed to replace plastic with paper.

For example, Patent Document 2 describes a wrapping paper that includes a paper base material, a coating layer coated on one side of the paper base material, and a thermally adhesive resin layer disposed on the other side of the paper base material via an adhesive layer, in which the coating layer has gas barrier properties and the adhesive layer is formed from a gas barrier adhesive.

JP 2020-132263 A JP 2020-196529 A

However, the wrapping paper described in Patent Document 2 does not consider impact resistance and processability, and there is a need to develop wrapping paper with excellent impact resistance and processability.

Therefore, the present invention aims to provide a paper laminate with excellent impact resistance and processability.

The object of the present invention can be achieved by the following configuration.
<1> A paper laminate having a barrier film layer, a paper base layer, and a heat seal layer laminated in this order, wherein, when the tensile energy absorption in the longitudinal direction measured in accordance with JIS P 8113:2006 is _X1 , the tensile energy absorption in the transverse direction _{is Y1} , the specific tensile energy absorption in the longitudinal direction measured in accordance with JIS P 8113:2006 is _X2 , and the specific tensile energy absorption in the transverse direction is _Y2 , the geometric mean of _X1 and _Y1 is 120 J/ ^m2 or more, and the geometric mean of _X2 and _Y2 is 1.8 J/g or more.
<2> The paper laminate according to <1>, wherein the paper base material has a basis weight of 50 g/ ^m2 or more and 120 g/ ^m2 or less.
<3> The paper laminate according to <1> or <2>, in which the ratio of the basis weight of the paper base material to the basis weight of the paper laminate is 0.5 or more.
<4> The paper laminate according to any one of <1> to <3>, wherein the geometric mean of tear strength in the machine direction and the cross direction measured in accordance with JIS P 8116:2000 is 1000 mN or more.
<5> The paper laminate according to any one of <1> to <4>, having an oxygen permeability measured at 23°C and 50% RH of 10 mL/ ^m2 ·atm·day or less.
<6> The paper laminate according to any one of <1> to <5>, having a water vapor transmission rate measured at 40°C and 90% RH of 50 g/ ^m2 ·day or less.
<7> The paper laminate according to any one of <1> to <6>, wherein the basis weight of the paper laminate is 80 g/ ^m2 or more and 200 g/ ^m2 or less.
<8> The paper laminate according to any one of <1> to <7>, wherein the barrier film layer has a thickness of 5 μm or more and 30 μm or less.
<9> The paper laminate according to any one of <1> to <8>, wherein the barrier film layer has, from the paper substrate layer side, a substrate film, a vapor deposition layer, and an overcoat layer in this order.
<10> The paper laminate according to any one of <1> to <9>, wherein the heat seal layer has a thickness of 70 μm or less.
<11> The paper laminate according to any one of <1> to <10>, wherein the heat seal layer contains at least one selected from the group consisting of polyolefin resins and water-dispersible resin binders.
<12> A packaging bag made using the paper laminate according to any one of <1> to <11>.

The present invention provides a paper laminate with excellent impact resistance and processability.

The preferred embodiments of the present invention are described below. In this specification, the range "X to Y" means "X or more and Y or less." In this specification, unless otherwise specified, operations and measurements of physical properties are performed at room temperature (20 to 25°C) and a relative humidity of 40 to 50%. In addition, "(meth)acrylic" is a general term that includes both acrylic and methacrylic.

[Paper laminate]
The paper laminate according to this embodiment (hereinafter also simply referred to as the paper laminate) is a paper laminate formed by laminating a barrier film layer, a paper base layer, and a heat seal layer in this order, in which, when the longitudinal tensile energy absorption amount measured in accordance with JIS P 8113:2006 is _X1 , the transverse tensile energy absorption amount is _Y1 , the longitudinal tensile energy absorption ratio is _X2 , and the transverse tensile energy absorption ratio is _Y2 , measured in accordance with JIS P 8113:2006, the geometric mean of _X1 and _Y1 is 120 J/ ^m2 or more, and the geometric mean of _X2 and _Y2 is 1.8 J/g or more. The paper laminate according to this embodiment has excellent impact resistance and processability because the geometric mean of _X1 and _Y1 is 120 J/ ^m2 or more, and the geometric mean of _X2 and _Y2 is 1.8 J/g or more.

<Paper base material>
(Raw pulp)
The paper base material (hereinafter also simply referred to as the paper base material) constituting the paper base material layer used in the paper laminate according to this embodiment is preferably made of raw material pulp mainly composed of softwood pulp. "Raw material pulp mainly composed of softwood pulp" refers to raw material pulp in which the content of softwood pulp is more than 50% by mass, and the content of softwood pulp is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass. Softwood pulp has a long average fiber length, and paper base materials using softwood pulp as raw material pulp tend to have excellent impact resistance and processability.

From the viewpoint of obtaining a paper laminate having excellent impact resistance and processability, the coniferous pulp is preferably pulp obtained from one or more species selected from the group consisting of Douglas fir and pine, and more preferably pulp obtained from Douglas fir.

The raw pulp constituting the paper base material is preferably one or more types selected from the group consisting of bleached kraft pulp and unbleached kraft pulp, and is more preferably unbleached kraft pulp.

(Kappa number)
From the viewpoint of obtaining a paper laminate having excellent impact resistance and processability, the kappa number of the pulp constituting the paper base material, measured in accordance with JIS P 8211:2011, is preferably 30 or more, and preferably 60 or less, more preferably 55 or less, and even more preferably 50 or less. The kappa number of the pulp constituting the paper base material is measured in accordance with JIS P 8211:2011 using a paper base pulp disintegrated in accordance with JIS P 8220-1:2012 as a sample.

(Tensile Energy Absorption (TEA))
When the tensile energy absorption in the machine direction measured in accordance with JIS P 8113:2006 is x ₁ and the tensile energy absorption in the cross direction is y ₁ , the geometric mean of x ₁ and y ₁ (the square root of the product of x ₁ and y ₁ ) is preferably 150 J/m 2 or more, more preferably 200 J/m ² or more, even more preferably 230 J/m ² or more, and even more preferably 250 J/m ² or more from the viewpoint of obtaining a paper laminate having excellent impact resistance and processability, and is preferably 800 J/m ² or less, more preferably 700 J/m ² or ^less , even more preferably 600 J/m ² or less, even more preferably 530 J/m ² or less, even more preferably 460 J/m ² or less, and even more preferably 420 J/m ² or less from the viewpoint of processability. When a paper base material having TEA properties within the above range is used, a paper laminate having the TEA properties of this embodiment can be obtained.
The paper substrate has a ratio of _X1 to _Y1 ( _X1 / _Y1 ) of preferably 0.4 or more, more preferably 0.5 or more, and preferably 2.0 or less, more preferably 1.8 or less.

(Tensile Energy Absorption Index (TEAI))
When the specific tensile energy absorption in the machine direction _{is x2} and the specific tensile energy absorption in the cross direction is _y2 , the geometric mean of _x2 and _y2 is preferably 1.9 J/g or more, more preferably 2.5 J/g or more, and even more preferably 3.0 J/g or more, from the viewpoint of obtaining a paper laminate having excellent impact resistance and processability, and the upper limit is not particularly limited, but is preferably 8.0 J/g or less, more preferably 7.0 J/g or less. When a paper base material having a TEAI property within the above range is used, a paper laminate having the TEAI property of this embodiment can be obtained.

(grammage)
From the viewpoint of obtaining a paper laminate having excellent impact resistance and processability, the basis weight of the paper base material is preferably 50 g/m ² or more, more preferably 60 g/m ² or more, even more preferably 70 g/m ² or more, and preferably 120 g/m ² or less, more preferably 110 g/m ² or less, even more preferably 105 g/m ² or less. The basis weight of the paper base material is measured in accordance with JIS P 8124:2011.
From the viewpoint of recyclability, the ratio of the basis weight of the paper base material to the basis weight of the paper laminate described below is preferably 0.5 or more, and although there is no particular upper limit, it is preferably 0.9 or less.

(Thickness)
From the viewpoint of impact resistance and processability of the paper laminate, the thickness of the paper substrate is preferably 20 μm or more, more preferably 30 μm or more, even more preferably 60 μm or more, still more preferably 80 μm or more, still more preferably 100 μm or more, and preferably 200 μm or less, more preferably 170 μm or less, still more preferably 150 μm or less, still more preferably 140 μm or less. The thickness of the paper substrate is measured in accordance with JIS P 8118:2014.

(density)
From the viewpoint of moldability, the density of the paper substrate is preferably 0.3 g/ ^cm3 or more, more preferably 0.5 g/ ^cm3 or more, and preferably 1.2 g/ ^cm3 or less, more preferably 1.0 g/ ^cm3 or less. The density of the paper substrate is calculated from the basis weight and thickness of the paper substrate obtained by the above-mentioned measurement method.

(Tear strength)
From the viewpoint of impact resistance, the paper base material has a geometric mean of longitudinal and transverse tear strengths measured in accordance with JIS P 8116:2000 of preferably 1000 mN or more, more preferably 1100 mN or more, and preferably 1700 mN or less, more preferably 1600 mN or less.

(Optional ingredients)
The paper base material may contain optional components as necessary, such as anionic, cationic or amphoteric retention agents, drainage improvers, dry strength agents, wet strength agents, sizing agents, internal additives such as fillers, water-resistant agents, dyes, and fluorescent whitening agents.
Examples of the dry strength agent include cationic starch, polyacrylamide, carboxymethyl cellulose, etc. The content of the dry strength agent is not particularly limited, but is preferably 3.0% by mass or less based on the raw pulp (bone dry mass).
Examples of the wet strength agent include polyamide polyamine epichlorohydrin, urea formaldehyde resin, and melamine formaldehyde resin.
Examples of the sizing agent include internal sizing agents such as rosin sizing agents, synthetic sizing agents, and petroleum resin-based sizing agents, and surface sizing agents such as styrene/acrylic acid copolymers and styrene/methacrylic acid copolymers. The content of the sizing agent is not particularly limited, but is preferably 3.0% by mass or less based on the raw pulp (bone dry mass).
Examples of the fixing agent include aluminum sulfate, polyethyleneimine, etc. The content of the fixing agent is not particularly limited, but is preferably 3.0% by mass or less based on the raw pulp (bone dry mass).
Examples of the filler include inorganic fillers such as talc, kaolin, calcined kaolin, calcium carbonate, calcium sulfate, barium sulfate, titanium dioxide, zinc oxide, alumina, magnesium carbonate, magnesium oxide, silica, white carbon, bentonite, zeolite, sericite, and smectite, and organic fillers such as acrylic resins and vinylidene chloride resins.

As a paper base material, for example, Clupak paper that has been treated with Clupak to shrink the paper web can be used.

<Barrier film layer>
The paper laminate according to this embodiment has at least one barrier film layer on one side of a paper substrate, so as to have a barrier film layer, a paper substrate layer, and a heat seal layer in this order. The barrier film layer preferably has, from the paper substrate layer side, a substrate film, a vapor deposition layer, and an overcoat layer in this order.

(Thickness)
The thickness of the barrier film layer is preferably 5 μm or more, more preferably 8 μm or more, even more preferably 10 μm or more, and is preferably 30 μm or less, more preferably 25 μm or less, even more preferably 20 μm or less. The thickness of the barrier film layer is measured in accordance with JIS P 8118:2014.

(Base film)
Examples of the substrate film include resin films formed by stretching polymers such as polyethylene, polypropylene, polyester, polystyrene, acrylic resin, polycarbonate, polyurethane, polyvinyl chloride, polysulfone, polyamide, polyimide, and polyamideimide as necessary to form a film. These polymers may be used alone or in combination of two or more. Among these, the polymer constituting the substrate film is preferably one or more selected from the group consisting of polyester and polyamide, and more preferably one or more selected from the group consisting of polyethylene terephthalate (PET) and nylon. Examples of nylon include nylon 6, nylon 11, nylon 12, and nylon 66, with nylon 6 being preferred.

The thickness of the substrate film is not particularly limited, but is, for example, preferably 1 μm or more, more preferably 5 μm or more, and preferably 300 μm or less, more preferably 150 μm or less, even more preferably 50 μm or less, and even more preferably 25 μm or less.

(Deposition layer)
The vapor deposition layer is at least one of a layer made of metal and a layer made of ceramic. That is, the vapor deposition layer may be any of a layer made of metal, a layer made of ceramic, and a laminate of a metal layer and a ceramic layer. When the vapor deposition layer is a laminate of a metal layer and a ceramic layer, the metal layer may be on the substrate film side, or the ceramic layer may be on the substrate film side, and is not particularly limited.

The vapor-deposited layer may be any of a layer made of a metal, a layer made of a ceramic, and a laminate of these, but a layer made of a ceramic is preferred.
When the vapor-deposited layer is a layer made of a metal, specific examples of the metal include aluminum, magnesium, silicon, titanium, zinc, etc. These may be used alone or in combination of two or more. Among these, aluminum is preferred.
When the deposition layer is a layer made of ceramic, specific examples of the ceramic include silicon oxide, titanium oxide, aluminum oxide, magnesium oxide, zinc oxide, etc. These may be used alone or in combination of two or more. Among these, it is preferable to use one or more selected from the group consisting of silicon oxide, aluminum oxide, and magnesium oxide, more preferable to use one or more selected from the group consisting of aluminum oxide and silicon oxide, and even more preferable to use one or more selected from the group consisting of aluminum oxide and silica alumina.

The thickness of the deposition layer is not particularly limited, but from the viewpoint of gas barrier properties, it is preferably 5 nm or more, more preferably 7 nm or more, and from the viewpoint of ease of handling, it is preferably 500 nm or less, more preferably 200 nm or less, even more preferably 100 nm or less, even more preferably 70 nm or less, and even more preferably 50 nm or less.

The method for forming a deposition layer on a substrate film is not particularly limited, and examples of the method include known methods such as direct vacuum deposition of the metal or ceramic that constitutes the deposition layer, sputtering, and ion plating. Among these, the vacuum deposition method is preferred.

(Overcoat Layer)
The overcoat layer is a layer for protecting the deposition layer. The overcoat layer is not particularly limited and may contain an organic compound, an inorganic compound, or both. That is, the overcoat layer may be any of an organic layer, an inorganic layer, and an organic-inorganic hybrid layer. Examples of the organic compound include vinyl alcohol resins such as polyvinyl alcohol, polyurethane resins, (meth)acryloyl compounds, and/or reaction products thereof. Examples of the inorganic compound include oxides of silicon, aluminum, and the like. The overcoat layer is preferably a layer containing, for example, polyvinyl alcohol and silicon oxide, (meth)acryloyl compounds, and/or reaction products thereof.

When the overcoat layer is a layer containing a (meth)acryloyl compound and/or a reaction product thereof, it may have, for example, the following embodiment, but is not particularly limited thereto.
Examples of the (meth)acryloyl compound include a compound obtained by cross-linking copolymerization of a compound having a (meth)acryloyl group but not a silane coupling agent and a (meth)acryloyl group-containing silane coupling agent, etc. The (meth)acryloyl compound preferably has two or more (meth)acryloyl groups per molecule.
The (meth)acryloyl group-containing silane coupling agent refers to an organosilicon compound having at least a (meth)acryloyl group and a hydrolyzable group.

Methods for forming an overcoat layer on a vapor deposition layer include, for example, a method of applying and drying a coating liquid for the overcoat layer that constitutes the overcoat layer, a method of adhering the overcoat layer with an adhesive, and a vapor deposition method such as flash vapor deposition.

The thickness of the overcoat layer is preferably 50 nm or more, more preferably 60 nm or more, from the viewpoint of protecting the deposition layer, and is preferably 500 nm or less, more preferably 400 nm or less, and even more preferably 350 nm or less, from the viewpoint of adhesion.
As the barrier film layer, a commercially available barrier film may be used, for example, GL-AE and GL-AEY-W manufactured by Toppan Printing Co., Ltd., VA607 and VN508 manufactured by Toyobo Co., Ltd., and 1011HG-CR manufactured by Toray Advanced Film Co., Ltd.

<Heat seal layer>
The paper laminate according to this embodiment has at least one heat seal layer on one side of the paper substrate, with a barrier film layer, a paper substrate layer, and a heat seal layer in this order. The heat seal layer is a layer that melts and adheres by heating, ultrasonic waves, etc. From the viewpoint of forming a heat seal layer on the paper substrate uniformly without defects, the paper laminate according to this embodiment preferably has two or more heat seal layers on one side of the paper substrate. In this case, the compositions of the two or more heat seal layers may be the same or different.

(Thickness)
From the viewpoint of heat sealability and recyclability, for example, when the heat seal layer is formed by laminating using melt extrusion or an adhesive, the thickness of the heat seal layer is preferably 5 μm or more, more preferably 10 μm or more, and preferably 70 μm or less, more preferably 60 μm or less. Also, for example, when the heat seal layer is formed by preparing a coating liquid for the heat seal layer and applying the coating liquid, the thickness is preferably 1 μm or more, more preferably 2 μm or more, even more preferably 3 μm or more, and preferably 30 μm or less, more preferably 20 μm or less. The thickness of the heat seal layer can be measured by taking an enlarged photograph of the vertical cross section of the paper laminate using a scanning electron microscope (for example, S-3600N, manufactured by Hitachi High-Tech Corporation).

The heat seal layer preferably contains at least one selected from the group consisting of polyolefin resins and water-dispersible resin binders. A water-dispersible resin binder is a resin binder that is not water-soluble but is finely dispersed in water, such as an emulsion or suspension. If a water-dispersible resin binder also falls under the category of a lubricant as described below, it is classified as a lubricant.

(Polyolefin resin)
Examples of polyolefin resins include polyethylene (PE) such as very low density polyethylene (VLDPE), low density polyethylene (LDPE), medium density polyethylene (MDPE), high density polyethylene (HDPE), linear low density polyethylene, polypropylene (PP), ethylene/propylene copolymer, etc. Among these, polyethylene is preferred, and low density polyethylene is more preferred.

(Water-dispersible resin binder)
The water-dispersible resin binder is, for example, preferably at least one selected from the group consisting of ethylene/vinyl acetate copolymers and olefin/unsaturated carboxylic acid copolymers, more preferably at least one selected from the group consisting of ethylene/vinyl acetate copolymers, ethylene/(meth)acrylic acid copolymers, and ethylene/(meth)acrylic acid alkyl ester copolymers, and even more preferably at least one selected from the group consisting of ethylene/vinyl acetate copolymers and ethylene/(meth)acrylic acid copolymers.

As the ethylene/(meth)acrylic acid copolymer, either a synthetic product or a commercially available product may be used. Examples of commercially available products include MP498345N, MP4983R, and MP4990R manufactured by Michaelman Japan LLC, ZAIXXEN (registered trademark) A and ZAIXXEN (registered trademark) AC manufactured by Sumitomo Seika Chemicals Co., Ltd., and the Chemipearl S series manufactured by Mitsui Chemicals, Inc.

The content of the water-dispersible resin binder in the heat seal layer is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 45% by mass or more, and even more preferably 50% by mass or more, and is 100% by mass or less, preferably 90% by mass or less, and more preferably 80% by mass or less. If it is within the above range, a paper laminate with high heat seal strength can be obtained.

The heat seal layer may further contain other components in addition to the above resins. Examples of other components include pigments, lubricants, and silane coupling agents.

[Physical properties of paper laminate]
<Tensile Energy Absorption (TEA)>
In the paper laminate, when the tensile energy absorption in the longitudinal direction measured in accordance with JIS P 8113:2006 _{is X1} and the tensile energy absorption in the transverse direction is _Y1 , the geometric mean of _X1 and _Y1 (the square root of the product of _X1 and _Y1 ) is 120 J/m2 or more, preferably 160 J/ ^m2 or more, more preferably 200 J/m2 or ^more , even more preferably 230 J/ ^m2 or more, and even more preferably 250 J/m2 or ^more , from the viewpoint of obtaining a paper laminate having excellent impact resistance and processability, and from the viewpoint of processability, it is preferably 800 J/ ^m2 or ^less , more preferably 700 J/ ^m2 or less, even more preferably 600 J/m2 or ^less , and even more preferably 550 J/ ^m2 or less.

<Tensile Energy Absorption Index (TEAI)>
When the specific tensile energy absorption in the longitudinal direction of the paper laminate _{is X2} and the specific tensile energy absorption in the transverse direction is _Y2 , as measured in accordance with JIS P 8113:2006, the geometric mean of _X2 and _Y2 is 1.8 J/g or more, preferably 2.0 J/g or more, more preferably 2.2 J/g or more, from the viewpoint of obtaining a paper laminate having excellent impact resistance and processability, and the upper limit is not particularly limited, but is preferably 8.0 J/g or less, more preferably 7.0 J/g or less.

<Basance weight>
The basis weight of the paper laminate is preferably 80 g/m ² or more, more preferably 100 g/m ² or more, even more preferably 105 g/m ² or more, and preferably 200 g/m ² or less, more preferably 180 g/m ² or less, even more preferably 170 g/m ² or less. The basis weight of the paper laminate is measured in accordance with JIS P 8124:2011.

<Thickness>
From the viewpoint of impact resistance and processability of the paper laminate, the thickness of the paper laminate is preferably 100 μm or more, more preferably 120 μm or more, even more preferably 140 μm or more, and is preferably 500 μm or less, more preferably 300 μm or less, even more preferably 250 μm or less. The thickness of the paper laminate is measured in accordance with JIS P 8118:2014.

<Density>
From the viewpoint of processability, the density of the paper laminate is preferably 0.4 g/ ^cm3 or more, more preferably 0.5 g/ ^cm3 or more, even more preferably 0.6 g/ ^cm3 or more, and preferably 1.5 g/ ^cm3 or less, more preferably 1.2 g/cm3 or ^less , even more preferably 1.0 g/ ^cm3 or less. The density of the paper laminate is calculated from the basis weight and thickness of the paper laminate obtained by the above-mentioned measurement method.

<Tear strength>
From the standpoint of impact resistance, the paper laminate preferably has a geometric mean of longitudinal and transverse tear strengths measured in accordance with JIS P 8116:2000 of 1000 mN or more, more preferably 1100 mN or more, and preferably 1900 mN or less, more preferably 1800 mN or less.

<Oxygen permeability>
The paper laminate has an oxygen permeability measured at 23°C and 50% RH of preferably 10mL/m2· ^atm ·day or less, more preferably 5.0mL/m2· ^atm ·day or less, even more preferably 2.0mL/m2· ^atm ·day or less, even more preferably 1.0mL/m2· ^atm ·day or less, and even more preferably 0.5mL/ ^m2 ·atm·day or less. There is no particular limit to the lower limit of the oxygen permeability. The oxygen permeability of the paper laminate is measured by the method described in the examples.

<Water vapor permeability>
The water vapor permeability of the paper laminate measured at 40°C and 90% RH is preferably 50 g/ ^m2 ·day or less, more preferably 30 g/ ^m2 ·day or less, even more preferably 10 g/ ^m2 ·day or less, even more preferably 5.0 g/ ^m2 ·day or less, even more preferably 3.0 g/ ^m2 ·day or less, even more preferably 2.0 g/ ^m2 ·day or less, even more preferably 1.8 g/ ^m2 ·day or less. The lower limit of the water vapor permeability is not particularly limited. The water vapor permeability of the paper laminate is measured by the method described in the examples.

[Method of manufacturing paper laminate]
The method for producing the paper laminate of this embodiment is not particularly limited. For example, a production method including a barrier film layer lamination step of laminating at least one barrier film layer on one side of a paper base obtained by a method including a cooking step of cooking raw pulp to have a kappa number of 30 to 60, a beating step of beating a dispersion containing 20% to 45% by mass of the cooked raw pulp, and a papermaking step of making paper from the beaten raw pulp, and a heat seal layer formation step of forming at least one heat seal layer by lamination or coating on the other side of the paper base. Note that either the barrier film layer lamination step or the heat seal layer formation step may be performed first, and for example, when the heat seal layer formation step is performed twice or more, it may be performed in the order of a first heat seal layer formation step, a barrier film layer lamination step, and a second heat seal layer formation step, and is not particularly limited. Each step of the production method is described below.

<Manufacturing method of paper base material>
(Digestion process)
The cooking step is a step of cooking the raw pulp so that the kappa number of the raw pulp is preferably 30 or more and 60 or less. Although not particularly limited, raw chips used as a material for the raw pulp are treated with a chemical solution containing sodium hydroxide to obtain raw pulp having a kappa number of 30 or more and 60 or less. As a treatment method with a chemical solution containing sodium hydroxide, a known treatment method using a known chemical solution can be used.
By making the kappa number of the raw material pulp 30 or more and 60 or less, a paper base material and a paper laminate using the paper base material that satisfy the above-mentioned TEA physical properties and TEAI physical properties and have impact resistance and processability can be obtained. From this viewpoint, the kappa number of the raw material pulp is preferably 50 or less, and more preferably 45 or less.

The raw chips used as the raw material pulp preferably contain coniferous pulp as the main component. "Raw chips containing coniferous pulp as the main component" refers to raw chips containing more than 50% by mass of coniferous wood, and the coniferous wood content is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass.

The raw material pulp may or may not be bleached. The raw material pulp is preferably one or more selected from the group consisting of bleached kraft pulp and unbleached kraft pulp, and more preferably unbleached kraft pulp.

(Beating process)
The beating step is a step of beating a dispersion containing preferably 20% by mass or more and 45% by mass or less of the digested raw pulp. The method of beating is not particularly limited, but it is preferable to disperse the digested raw pulp in water to prepare a dispersion having the above-mentioned raw pulp concentration, and then beat the dispersion. The method of beating is not particularly limited, but it can be performed using a beater such as a double disc refiner, a single disc refiner, or a conical refiner.
By beating a dispersion containing 20% by mass or more and 45% by mass or less of cooked raw pulp, a paper base material that satisfies the above-mentioned TEA physical properties and TEAI physical properties and has excellent impact resistance and processability, and a paper laminate using said paper base material can be obtained, which also has excellent productivity.

(Papermaking process)
The papermaking process is a process in which the beaten raw pulp is made into paper. The papermaking method is not particularly limited, and examples thereof include an acidic papermaking method in which papermaking is performed at a pH of about 4.5, and a neutral papermaking method in which papermaking is performed at a pH of about 6 to about 9. In the papermaking process, chemicals for the papermaking process such as a pH adjuster, a defoamer, a pitch control agent, and a slime control agent can be appropriately added as necessary. The papermaking machine is also not particularly limited, and examples thereof include a continuous papermaking machine such as a fourdrinier type, a cylinder type, or a tilt type, or a multi-layer papermaking machine that combines these.

The paper base material used in the paper laminate of this embodiment can be obtained by a method including the above-mentioned cooking process, beating process, and papermaking process. After the papermaking process, if necessary, a Clupak process may be performed in which the paper web is shrunk using Clupak equipment. Any known Clupak equipment can be used. The method for producing the paper base material used in the paper laminate of this embodiment is not limited to the above-mentioned method.

The method for producing the paper laminate of this embodiment may also include a surface treatment step in which the surface of the paper base material is treated with a chemical. Chemicals used in the surface treatment step include sizing agents, water-resistant agents, water retention agents, thickeners, lubricants, etc. Known devices can be used for the surface treatment step.

<Barrier film layer lamination process>
The method for producing a paper laminate of this embodiment includes a barrier film layer lamination step of laminating a barrier film layer on one side of the paper base material obtained as described above, so as to have a barrier film layer, a paper base material layer, and a heat seal layer in this order. For example, the barrier film layer can be adhered and laminated on the paper base material using an adhesive or the like. A known adhesive can be used as the adhesive. Two or more barrier film layers may be laminated.

<Heat seal layer forming step>
The manufacturing method of the paper laminate of this embodiment includes a heat seal layer formation step of forming a heat seal layer on one side of the paper base material obtained as described above so as to have a barrier film layer, a paper base material layer, and a heat seal layer in that order.
Examples of methods for forming the heat seal layer include a method of laminating the heat seal layer using melt extrusion, an adhesive, etc., and a method of forming the heat seal layer by preparing a coating liquid for the heat seal layer and applying the coating liquid. A known adhesive can be used as the adhesive. Two or more heat seal layers may be formed.

When forming multiple heat seal layers on a paper substrate, the above method of forming heat seal layers sequentially is preferred, but is not limited to this, and a simultaneous multi-layer coating method may also be used. The simultaneous multi-layer coating method is a method in which multiple types of coating liquids are ejected separately from a slit-shaped nozzle to form a liquid laminate, which is then coated onto the paper substrate to simultaneously form multiple heat seal layers.

The solvent of the heat seal layer coating liquid is not particularly limited, and water or organic solvents such as ethanol, isopropyl alcohol, methyl ethyl ketone, and toluene can be used. Among these, from the viewpoint of not causing problems with volatile organic solvents, an aqueous solvent (preferably water) is preferred as the dispersion medium of the heat seal layer coating liquid. That is, the heat seal layer coating liquid is preferably an aqueous composition for heat seal layers. In addition, forming the heat seal layer by aqueous coating is advantageous for recyclability, and further reduction in environmental load due to reduction in the amount of plastic used can be expected. In this specification, "aqueous" means that the content of water in the solvent is 50% by mass or more, preferably 80% by mass or more.
There are no particular limitations on the coating equipment used to apply the heat seal layer coating liquid to the paper substrate, and any known equipment may be used.
The drying equipment for drying the heat seal layer is not particularly limited, and known equipment can be used.

The total coating weight of the heat seal layer (after drying) is preferably 1 to 50 g/ ^m2 , more preferably 2 to 30 g/ ^m2 , and even more preferably 5 to 20 g/ ^m2 .

The paper laminate of this embodiment has excellent heat sealability, processability, and impact resistance, as well as excellent oxygen and water vapor barrier properties, making it suitable for use as packaging bags for food, household goods, daily necessities (soap, bath additives, powder detergent, wet tissues), medical drugs, electronics, etc.

The following examples are provided to specifically explain the present invention, but the present invention is not limited to these examples. Unless otherwise specified, the following operations were performed at 23°C and 50% RH. In the examples and comparative examples, "parts" and "%" refer to "parts by mass" and "% by mass," respectively, unless otherwise specified.

[Analysis and Evaluation]
The paper laminates of the examples and comparative examples were subjected to the following analyses and evaluations.

<Tensile energy absorption amount, specific tensile energy absorption amount>
The tensile energy absorption amount and the specific tensile energy absorption amount were measured in accordance with JIS P 8113:2006.

<Basance weight>
The basis weight was measured in accordance with JIS P 8124:2011.

<Thickness>
The thicknesses of the paper substrate and the barrier film layer were measured in accordance with JIS P 8118: 2014. The thickness of the heat seal layer was measured by taking an enlarged photograph of the vertical cross section of the paper laminate using a scanning electron microscope (S-3600N, manufactured by Hitachi High-Tech Corporation).

<Tear strength>
The tear strength was measured in accordance with JIS P 8116:2000.

<Oxygen permeability>
The oxygen permeability was measured using an oxygen permeability measuring device (OX-TRAN2/20, manufactured by MOCON) under conditions of 23° C. and 50% RH.

<Water vapor permeability>
The water vapor permeability was measured in accordance with JIS Z 0208:1976 using a moisture permeability cup prepared so that the barrier film-attached surface of the paper laminate was on the inside (Condition B: temperature 40±0.5° C., relative humidity 90±2%).

<Heat sealability>
The obtained paper laminate was cut to a width of 2.5 cm and a length of 15 cm, and the front and back sides were overlapped with an area of 14.85 ^cm2 . The laminate was then sealed for 2 seconds at a temperature of 150°C and a pressure of 0.2 MPa using a heat seal tester (manufactured by Tester Sangyo Co., Ltd.), cooled to room temperature, and peeled off by hand. The appearance of the laminate was evaluated according to the following criteria: If the laminate was rated A according to the following criteria, it was suitable for practical use.
A: Completely adhered and difficult to peel off by hand. B: At least some areas are not adhered. C: Not adhered at all.

<Evaluation of pillow molding processability>
The paper laminate was used to produce pillow bags measuring 15 cm in length and 11 cm in width using a vertical pillow molding machine (KBF6000X2, manufactured by Kawashima Seisakusho Co., Ltd.), and the quality of the bags was evaluated according to the following criteria.
A: Pillow bags can be formed without any problems. B: Although it is somewhat difficult to form, pillow bags can be formed without any problems. C: The bag shape can be formed, but there are problems such as wrinkles, deformation, and poor sealing. D: It is impossible to form a pillow bag shape.

<Evaluation of impact resistance>
A paper laminate cut to 400 mm long x 760 mm wide was folded in half with the heat-sealed layer surfaces facing each other to a size of 400 mm long x 380 mm wide, and 3 kg of gravel was placed inside and sealed with an impulse sealer (VG-400, manufactured by Fuji Impulse Co., Ltd.) with a seal width of 10 mm to produce five three-sided sealed bags. The three-sided sealed bags were dropped from a height of 60 cm onto a concrete floor in the order of "1: bottom corner → 2: bottom → 3: side → 4: side → 5: top → 6: front surface → 7: back surface," and the state of damage to the bags was visually evaluated according to the following criteria.
A: The above items 1 to 7 are considered as one set. Even if three sets are dropped, the bag will not be damaged (all five bags will be in three sets and will not be damaged)
B: The above steps 1 to 7 are considered as one set. The bag will not break within one set, but it may break after 2 to 3 sets (at least 1 out of 5 bags breaks after 2 to 3 sets).
C: The above steps 1 to 7 are considered as one set, and the bag may break within one set (one or more bags out of five break within one set)
D: The above steps 1 to 7 are considered as one set, and all five bags are damaged within one set.

Example 1
<Preparation of paper substrate>
Using Douglas fir, a coniferous tree, as raw material chips, a cooking treatment was performed using a chemical solution containing sodium hydroxide to obtain raw material pulp, which is unbleached kraft pulp with a kappa number of 45. Next, the raw material pulp obtained by the cooking treatment was dispersed in water to prepare a 30% by mass dispersion. Thereafter, the dispersion was beaten using a single disc refiner and a double disc refiner as a beater to obtain kraft pulp. To the obtained kraft pulp, 0.2% by mass of a synthetic sizing agent (Sizepine MXE2, manufactured by Arakawa Chemical Industries Co., Ltd.), 1.0% by mass of aluminum sulfate, 0.8% by mass of polyacrylamide (DS744, manufactured by Seiko PMC Co., Ltd.), and 0.8% by mass of cationic starch (OPTIBOND3922, manufactured by Ingredion Japan Co., Ltd.) were added based on the bone dry mass of the kraft pulp to obtain a paper material (paper base material). The obtained paper stock was made into paper using a papermaking machine equipped with Clupak equipment to produce a paper base material (ultra-stretch paper) with a target basis weight of 100 g/ ^m2 (the actual basis weight is shown in Table 1, and the same applies below).
<Preparation of Paper Laminate>
The stretched PET film surface of a barrier film (GL-AE, 12 μm thick, manufactured by Toppan Printing Co., Ltd.) consisting of a stretched PET film, an aluminum oxide vapor deposition layer, and an overcoat layer laminated in that order was bonded to one side of the paper substrate using an adhesive (Polysol AX505ZH, manufactured by Showa Denko K.K.). Furthermore, low-density polyethylene (L2340, manufactured by Asahi Kasei Corporation) was melt-extruded onto the opposite side of the paper substrate and laminated to a thickness of 50 μm to form a heat seal layer, thereby producing a paper laminate. The analysis and evaluation results are shown in Table 1.

Example 2
A paper laminate was obtained in the same manner as in Example 1, except that the paper base material was made to a target basis weight of 80 g/ ^m2 .

Example 3
A paper laminate was produced in the same manner as in Example 1, except that a paper base material (stretched paper cement) was used, which was prepared by dispersing the raw pulp obtained by the cooking process in Example 1 at 3% by mass, beating it, and making it into a paper base material with a target basis weight of 83 g/ ^m2 .

Example 4
A paper laminate was produced in the same manner as in Example 3, except that the paper base material was made to a target basis weight of 78 g/ ^m2 .

Example 5
A paper laminate was produced in the same manner as in Example 3, except that the paper base material was made to a target basis weight of 73 g/ ^m2 .

Example 6
A paper laminate was produced in the same manner as in Example 3, except that the paper base material obtained in the same manner as in Example 1 was made into a paper base material (heavy-duty packaging paper) with a target basis weight of 84 g/ ^m2 using a Fourdrinier continuous papermaking machine.

Example 7
A paper laminate was prepared in the same manner as in Example 1, except that the PET film surface of a barrier film (VA607, manufactured by Toyobo Co., Ltd., thickness 12 μm) consisting of a PET film with aluminum oxide vapor-deposited and an overcoat layer laminated thereon was bonded to one side of the paper base material (ultra-stretch paper) prepared in Example 1 using an adhesive (Polysol AX505ZH, manufactured by Showa Denko K.K.).

Example 8
A paper laminate was prepared in the same manner as in Example 1, except that a PET film surface of a barrier film (VN508, manufactured by Toyobo Co., Ltd., thickness 15 μm) consisting of a nylon film with aluminum oxide vapor-deposited and an overcoat layer laminated thereon was attached to one side of the paper base material prepared in Example 1 using an adhesive (Polysol AX505ZH, manufactured by Showa Denko K.K.).

Example 9
A paper laminate was produced in the same manner as in Example 1, except that, instead of laminating low-density polyethylene on the surface of the paper substrate opposite to the surface to which the gas barrier film was attached, an ethylene-methacrylic acid copolymer ionomer (Mitsui Chemicals, Inc., Chemipearl S-300) was coated to a coating amount (solid content) of 16 g/ ^m2 .

Comparative Example 1
A paper laminate was produced in the same manner as in Example 6, except that the paper base material was made to a target basis weight of 75 g/m ^2. The analysis and evaluation results are shown in Table 2.

Comparative Example 2
A paper laminate was produced in the same manner as in Example 6, except that the paper base material was made to a target basis weight of 78 g/m ^2. The analysis and evaluation results are shown in Table 2.

Comparative Example 3
A paper laminate was produced in the same manner as in Example 1, except that unbleached kraft paper (manufactured by Oji Materia Co., Ltd., basis weight 80 g/m ² ) was used as the paper base material. The analysis and evaluation results are shown in Table 2.

Comparative Example 4
A paper laminate was produced in the same manner as in Example 1, except that unbleached kraft paper (manufactured by Oji Materia Co., Ltd., basis weight 100 g/m ² ) was used as the paper base material. The analysis and evaluation results are shown in Table 2.

Comparative Example 5
A paper laminate was produced in the same manner as in Example 1, except that unbleached kraft paper (manufactured by Oji Materia Co., Ltd., basis weight 120 g/m ² ) was used as the paper base material. The analysis and evaluation results are shown in Table 2.

Comparative Example 6
A paper laminate was produced in the same manner as in Example 1, except that unbleached kraft paper (manufactured by Oji Materia Co., Ltd., basis weight 130 g/m ² ) was used as the paper base material. The analysis and evaluation results are shown in Table 2.

As can be seen from Table 1, the paper laminates of Examples 1 to 9 were excellent in pillow-shaped formability and impact resistance. On the other hand, as can be seen from Table 2, the paper laminates of Comparative Examples 1 to 6 were poor in pillow-shaped formability and impact resistance.

The paper laminate of the present invention has excellent heat sealability, processability and impact resistance, as well as excellent oxygen and water vapor barrier properties, making it suitable for use as packaging bags for food, household goods, daily necessities (soap, bath additives, powder detergent, wet tissues), medical drugs, electronics, etc.

Claims (12)

1. A paper laminate comprising a barrier film layer, a paper base layer, and a heat seal layer laminated in this order, the barrier film layer having, from the paper base side, a base film, a vapor deposition layer, and an overcoat layer, the polymer constituting the base film being one or more selected from the group consisting of polyesters and polyamides, wherein, when the tensile energy absorption amount in the longitudinal direction of the paper laminate measured in accordance with JIS P 8113:2006 is _X1 , the tensile energy absorption amount in the lateral direction of the paper laminate _{is Y1} , the specific tensile energy absorption amount in the longitudinal direction of the paper laminate measured in accordance with JIS P 8113:2006 is _X2 , and the specific tensile energy absorption amount in the lateral direction of the paper laminate is Y2, the geometric mean of _X1 and _Y1 is 250 J/ ^m2 or more, and the geometric mean of _X2 and _Y2 is 1.8 J/g or more. The paper laminate according to claim 1 , wherein the paper base material has a basis weight of 50 g/m ² or more and 120 g/m ² or less. The paper laminate according to claim 1 or 2, in which the ratio of the basis weight of the paper base material to the basis weight of the paper laminate is 0.5 or more. 4. The paper laminate according to claim 1, wherein the geometric mean of the tear strength in the machine direction and the cross direction of the paper laminate, measured in accordance with JIS P 8116:2000, is 1000 mN or more. The paper laminate according to any one of claims 1 to 4, wherein the oxygen permeability of the paper laminate measured at 23°C and 50% RH is 10 mL/ ^m2 ·atm·day or less. 6. The paper laminate according to claim 1 , wherein the water vapor permeability of the paper laminate measured at 40° C. and 90% RH is 50 g/m ² ·day or less. The paper laminate according to any one of claims 1 to 6, wherein the basis weight of the paper laminate is 80 g/ ^m2 or more and 200 g/ ^m2 or less. The paper laminate according to any one of claims 1 to 7, wherein the thickness of the barrier film layer is 5 μm or more and 30 μm or less. The paper laminate according to any one of claims 1 to 8, wherein the kappa number of the pulp constituting the paper base material is 30 or more and 60 or less. The paper laminate according to any one of claims 1 to 9, wherein the thickness of the heat seal layer is 70 μm or less. The paper laminate according to any one of claims 1 to 10, wherein the heat seal layer contains at least one selected from the group consisting of polyolefin resins and water-dispersible resin binders. A packaging bag made using the paper laminate described in any one of claims 1 to 11.