WO2023248981A1 - Water-resistant paper and packaging container - Google Patents

Abstract

The present invention addresses the problem of providing: water-resistant paper that has excellent water resistance, anti-blocking properties, moldability, and heat-sealing properties; and a packaging container obtained by using the water-resistant paper.　A water-resistant paper according to the present invention has a water-resistant layer as the uppermost layer on at least one surface of a paper base. The water-resistant layer has at least two melting points. The first melting point is not lower than 75°C but lower than 100°C. The second melting point is 100-120°C. The water-resistant layer contains an ethylene-(meth)acrylic acid copolymer and a copolymer of ethylene and an unsaturated hydrocarbon other than ethylene. The mass ratio (ethylene-(meth)acrylic acid copolymer/copolymer of ethylene and n unsaturated hydrocarbon other than ethylene) of the ethylene-(meth)acrylic acid copolymer with respect to the copolymer of ethylene and an unsaturated hydrocarbon other than ethylene in the water-resistant layer is 50/50 to 90/10. The coated amount of the water-resistant layer per surface is at least 3.0 g/m². A pigment coating layer containing a pigment and a binder is provided between the paper base and the water-resistant layer.

Description

Waterproof paper and packaging containers

The present invention relates to waterproof paper and packaging containers made using the same.

Plastic products have traditionally been used for containers and lids for beverages, foods, etc., but there is a desire to switch to paper products for the purpose of reducing environmental impact.
Conventionally, polyethylene laminated paper, which is made by laminating a polyethylene film on one side of a base paper (paper base material), has been used for various containers for beverages, foods, etc., but it is difficult to remove the polyethylene film during recycling, and the recyclability has been limited. There was a problem that it was inferior to
In order to address such problems, efforts have been made to impart water resistance and the like by imparting performance during the papermaking process or by imparting performance through coating.
Patent Document 1 (Japanese Unexamined Patent Publication No. 9-158089) states that it has processing suitability such as water resistance, heat sealability, top curl suitability, and gravure printing suitability that is equivalent to that of polyethylene laminate paper, and that it is suitable for effective use of resources. For the purpose of providing paper container base paper such as cup base paper, cup lid base paper, paper plate base paper, etc. with excellent recyclability (recyclability), the base paper is composed of an undercoat layer for sealing and a water- and oil-resistant layer on at least one side of the base paper. In paper carton base paper provided with an overcoat layer, the undercoat layer consists of a pigment/binder resin layer and the coating amount is 4 to 15 g/m ² per side, and the resin coating amount of the water and oil resistant layer of the overcoat layer is 2 g/m ² per side. A folding carton base paper is described which is characterized by the above and also satisfies the following requirements A to D.
A. The cob water absorption of the base paper is 50 g/m ² or less, and the smoothness is 10 seconds or more.
B. The pigment used in the undercoat layer has an aspect ratio of 5 to 30 and an average particle diameter of 0.5 to 30 μm.
C. The blending ratio of the undercoat layer is 10 to 100 parts by weight of the binder resin to 100 parts by weight of the pigment.
D. The water- and oil-resistant resin used for the top coat layer has a gel fraction of 70% or more, and the critical surface tension of the coating layer is a water-dispersed resin of 25 dyn/cm or more.

Furthermore, in Patent Document 2 (Japanese Patent No. 6580291), for the purpose of providing packaging paper that can reduce the amount of plastic used, at least one layer of heat sealing is provided on at least one surface of a paper base material. A packaging paper having a layer, wherein the heat seal layer contains an ionomer, the dry coating amount of the heat seal layer is 2 to 10 g/m ² for the entire layer, and the heat seal layer is on at least one side. A packaging paper characterized by having two or more layers is described.

When manufacturing water-resistant paper continuously, it is manufactured by winding it into rolls, but at this time, the coated side of the rolled-up water-resistant paper sticks to the back side of the water-resistant paper, causing it to peel off. There was a problem with (blocking). In addition, heat sealing is performed when forming water-resistant paper into packaging containers, etc., but at this time, there is a problem that it sticks to the forming machine (for example, the mandrel in the case of paper cups), resulting in poor formability. there were. Regarding these problems, there is room for improvement in Patent Documents 1 and 2.
An object of the present invention is to provide a water-resistant paper that is excellent in water resistance, blocking resistance, moldability, and heat sealability, and a packaging container using the water-resistant paper.

The present inventor provides a water-resistant paper having a water-resistant layer on at least one uppermost layer of a paper base material, wherein the water-resistant layer has at least two melting points, and the first melting point and the second melting point be in a specific range, contain a specific resin at a specific content ratio, make the coating amount per side of the water-resistant layer more than a specific value, and It has been found that by having a pigment coating layer in between, it is possible to obtain a water-resistant paper that has excellent water resistance, blocking resistance, moldability, and heat sealability.
The present invention relates to the following <1> to <9>.
<1> A water-resistant paper having a water-resistant layer on the top layer of at least one side of the paper base material,
The water-resistant layer has at least two melting points, the first melting point is 75°C or more and less than 100°C, the second melting point is 100°C or more and 120°C or less,
The water-resistant layer contains an ethylene-(meth)acrylic acid copolymer and a copolymer of ethylene and an unsaturated hydrocarbon other than ethylene,
Mass ratio of the ethylene-(meth)acrylic acid copolymer and the copolymer of ethylene and an unsaturated hydrocarbon other than ethylene in the water-resistant layer (ethylene-(meth)acrylic acid copolymer/ethylene and non-ethylene copolymer with an unsaturated hydrocarbon) is 50/50 or more and 90/10 or less,
The coating amount per side of the water-resistant layer is 3.0 g/m ² or more,
A pigment coating layer containing a pigment and a binder is provided between the paper base material and the water-resistant layer.
Water resistant paper.
<2> In <1>, the total content of the ethylene-(meth)acrylic acid copolymer and the copolymer of ethylene and an unsaturated hydrocarbon other than ethylene in the water-resistant layer is 60% by mass or more. Water resistant paper as described.
<3> The water-resistant paper according to <1> or <2>, wherein the unsaturated hydrocarbon other than ethylene includes an α-olefin having 4 or more and 20 or less carbon atoms.
<4> Any one of <1> to <3>, wherein in the pigment coating layer, the mass ratio of the pigment content to the binder content (pigment/binder) is 50/50 or more and 90/10 or less. The water-resistant paper described in 1.
<5> The water-resistant paper according to any one of <1> to <4>, wherein the binder contains a styrene-acrylic copolymer.
<6> The water-resistant paper according to any one of <1> to <5>, wherein the pigment has an average particle size of 0.1 μm or more and 4 μm or less.
<7> The pigment contains calcium carbonate and kaolin, and the mass ratio of the content of calcium carbonate to the content of kaolin in the pigment coating layer (calcium carbonate/kaolin) is 40/60 or more and 80/20 or less. , the water-resistant paper according to any one of <1> to <6>.
<8> The water-resistant paper according to any one of <1> to <7>, wherein the coating amount of the pigment coating layer per side is 1 g/m ² or more and 20 g/m ² or less.
<9> A packaging container made of the water-resistant paper according to any one of <1> to <8>.

[Waterproof paper]
The water-resistant paper of this embodiment is a water-resistant paper having a water-resistant layer on the uppermost layer of at least one surface of a paper base material, the water-resistant layer having at least two melting points, and the first The melting point is 75°C or more and less than 100°C, the second melting point is 100°C or more and less than 120°C, and the water-resistant layer is composed of an ethylene-(meth)acrylic acid copolymer and ethylene and an unsaturated material other than ethylene. The mass ratio of the ethylene-(meth)acrylic acid copolymer and the copolymer of ethylene and an unsaturated hydrocarbon other than ethylene (ethylene-(meth)acrylic acid copolymer) in the water-resistant layer ) acrylic acid copolymer/copolymer of ethylene and unsaturated hydrocarbon other than ethylene) is 50/50 or more and 90/10 or less, and the coating amount per one side of the water-resistant layer is 3.0 g/ m ² or more, and has a pigment coating layer containing a pigment and a binder between the paper base material and the water-resistant layer.
According to the embodiment, a water-resistant paper that has excellent water resistance, blocking resistance, moldability, and heat-sealability (particularly side-sealability when forming a paper cup), and a paper made using the water-resistant paper A packaging container can be provided.
Although the detailed reason for the above-mentioned effects is unknown, some of them are thought to be as follows. Generally, from the viewpoint of heat-sealing properties, it is preferable that the heat-sealing layer melts easily with heat. On the other hand, from the viewpoint of suppressing blocking during winding and preventing sticking to a molding machine, it is preferable that the heat seal layer is less likely to melt due to heat. In other words, the former and the latter can be said to be in a trade-off relationship. In this embodiment, the water-resistant layer has at least two melting points within the above range and contains a specific resin, so that the degree of melting due to heat is appropriate. This ensures heat-sealability (especially side-sealability during paper cup molding), prevents blocking during winding (that is, excellent blocking resistance), and allows the molding machine (mandrel) during heat-sealing to be It is thought that a water-resistant paper with excellent moldability and suppressed adhesion to the paper was obtained.
In addition, by having a pigment-containing layer between the paper base material and the water-resistant layer, and by setting the coating amount per side of the water-resistant layer to 3.0 g/m2 or ^more , water resistance and heat sealability are improved. It is thought that a water-resistant paper with excellent properties was obtained.
Note that the effects of the present invention are not limited to the above mechanism.
This embodiment will be described in more detail below.

In this specification, the numerical range represented by "X to Y" means a numerical range including X as the lower limit and Y as the upper limit. When numerical ranges are described in stages, the upper and lower limits of each numerical range can be combined arbitrarily. Furthermore, "(meth)acrylic" is a generic term that includes both acrylic and methacrylic.

<Paper base material>
The paper base material constituting the waterproof paper of this embodiment may have a single layer structure or a multilayer structure. In the case of multilayer paper, the number of paper layers is not particularly limited, but is, for example, preferably 3 or more layers, more preferably 4 or more layers, even more preferably 5 or more layers. By having three or more paper layers, the desired basis weight and paper thickness can be achieved, and by adjusting the basis weight, freeness, etc. of each layer, the physical properties of the water-resistant paper can be adjusted to the desired range. . The upper limit of the number of paper layers is not particularly limited, but is preferably 7 layers or less, more preferably 6 layers or less.

Pulps constituting the paper base material include chemical pulps such as hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP); groundwood pulp (GP), pressurized groundwood pulp (PGW), and refiner mechanical pulp (RMP). , thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), chem-mechanical pulp (CMP), chemi-ground pulp (CGP), etc.; waste paper pulp; non-wood fiber pulp such as kenaf, bagasse, bamboo, cotton, etc. ; Examples include synthetic pulp. These pulps may be used alone or in combination of two or more. Among these, it is preferable to use LBKP and NBKP in combination.

The content of bleached softwood kraft pulp (NBKP) with respect to the total amount of pulp constituting the paper base material is preferably 5% by mass or more and 70% by mass or less, more preferably 10% by mass or less, from the viewpoint of moldability, smoothness, and water resistance. % by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and more preferably 60% by mass or less, still more preferably 55% by mass or less, even more preferably 50% by mass or less. be.

The content of hardwood bleached kraft pulp (LBKP) with respect to the total amount of pulp constituting the paper base material is preferably 30% by mass or more and 95% by mass or less, more preferably 40% by mass or less, from the viewpoint of moldability, smoothness, and water resistance. At least 45% by mass, even more preferably at least 50% by mass, and more preferably at most 90% by mass, even more preferably at most 80% by mass, even more preferably at most 70% by mass. be.

The freeness of the pulp is not particularly limited, but it is preferably 200 mL or more and 800 mL or less, more preferably 350 mL or more, and even more preferably is 400 mL or more, and more preferably 750 mL or less, still more preferably 700 mL or less. If the CSF of the pulp is within the above range, it is easy to obtain the paper strength necessary for a packaging container. CSF is measured according to JIS P 8121-2:2012 "Pulp - Freeness Test Method - Part 2: Canadian Standard Freeness Method".
From the viewpoint of obtaining appropriate paper strength as water-resistant paper for packaging containers, the Canadian standard freeness (CSF) of LBKP is preferably 310 mL or more and 500 mL or less, more preferably 360 mL or more, and even more preferably 380 mL or more. It is particularly preferably 410 mL or more, and more preferably 480 mL or less, and may be 470 mL or less.
From the viewpoint of obtaining appropriate paper strength as water-resistant paper for packaging containers, the Canadian Standard Freeness (CSF) of NBKP is preferably 500 mL or more and 700 mL or less, more preferably 520 mL or more, and still more preferably 550 mL or more. Yes, and more preferably 680 mL or less, and may be 660 mL or less.
Canadian standard freeness is measured according to JIS P 8121-2:2012 "Pulp - Freeness test method - Part 2: Canadian standard freeness method".
It is preferable that LBKP and NBKP are used together as the pulp constituting the paper base material, and that the Canadian standard freeness (CSF) of each is within the above range.

Examples of additives to paper base materials include pH adjusters (sodium bicarbonate, sodium hydroxide, etc.), dry paper strength agents (polyacrylamide, starch, etc.), wet paper strength agents (polyamide polyamine epichlorohydrin, etc.). resin, melamine-formaldehyde resin, urea-formaldehyde resin), internal sizing agent (rosin type, alkyl ketene dimer, etc.), drainage retention improver, antifoaming agent, filler (calcium carbonate, talc, etc.), dye , a fixing agent (sulfuric acid band), and the like. These additives may be used alone or in combination of two or more. Note that it is preferable to use the internal sizing agent and the wet paper strength enhancer together, since this improves the water resistance of the paper base material. The content of the additive is not particularly limited, and may be within a commonly used range.

The basis weight of the paper base material is not particularly limited, but for example, if it is used for packaging containers, preferably food containers, more preferably paper cups, the basis weight of the paper base material is determined from the viewpoint of obtaining paper strength as a packaging container and from the viewpoint of formability. , preferably 150 g/m ² or more and 500 g/m ² or less, more preferably 180 g/m ² or more, even more preferably 200 g/m ² or more, even more preferably 220 g/m ² or more, and even more It is preferably 430 g/m ² or less, more preferably 380 g/m ² or less, even more preferably 330 g/m ² or less, even more preferably 280 g/m ² or less, particularly preferably 250 g/m ² or less. The basis weight of the paper base material is measured in accordance with JIS P 8124:2011.

The thickness of the paper base material is not particularly limited, but for example, if it is used for packaging containers, preferably food containers, more preferably paper cups, the thickness of the paper base material is determined from the viewpoint of obtaining paper strength as a packaging container and from the viewpoint of formability. , preferably 150 μm or more and 650 μm or less, more preferably 210 μm or more, even more preferably 230 μm or more, even more preferably 240 μm or more, and still more preferably 480 μm or less, still more preferably 410 μm or less, and even more preferably It is 380 μm or less, more preferably 330 μm or less, particularly preferably 280 μm or less. The thickness of the paper base material is measured in accordance with JIS P 8118:2014.

From the viewpoint of obtaining desired strength, the density of the paper base material is preferably 0.4 g/cm ³ or more and 1.0 g/cm ³ or less, more preferably 0.6 g/cm ³ or more, and even more preferably 0.4 g/cm 3 or more. It is 7 g/cm ³ or more, and more preferably 0.9 g/cm ³ or less. The density of the paper base material is calculated from the basis weight and thickness of the paper base material obtained by the above-mentioned measuring method.

[Manufacturing method of paper base material]
Examples of the method for manufacturing the paper base material include a method of making paper from a paper stock containing pulp. In addition, the paper stock may further contain an additive. Examples of the additive include the additives listed above. Paper stocks can be prepared by adding additives to pulp slurry. Pulp slurry is obtained by beating pulp in the presence of water. The pulp beating method and beating device are not particularly limited, and may be the same as known beating methods and beating devices. The content of pulp in the paper stock is not particularly limited, and may be within a commonly used range. For example, it is 60% by mass or more and less than 100% by mass with respect to the total mass of paper stock (solid content).

Paper making can be carried out using standard methods. For example, there is a method in which paper stock is cast on a wire or the like, dehydrated to obtain a wet paper, and if necessary, multiple wet papers are stacked, and this single-layer or multi-layer wet paper is pressed and dried. . At this time, if a plurality of wet papers are not stacked, a single-layer paper will be obtained, and if a plurality of wet papers are stacked, a multi-layer paper will be obtained. When stacking a plurality of wet papers, an adhesive may be applied to the surface of the wet paper (the surface on which other wet papers are stacked).

<Water resistant layer>
In this embodiment, the water-resistant paper has a water-resistant layer on the top layer of at least one side of the paper base material.
Note that the water-resistant paper of this embodiment may have water-resistant layers on both sides of the paper base material.
The water-resistant layer has at least a resin component, and may contain various additives in addition to the resin component. Further, the water-resistant layer is preferably formed by coating a paper base material with a coating liquid containing at least the resin component, and it is also preferable that the coating liquid is a water-based coating liquid.

[Melting point]
The water-resistant layer has at least two melting points. The water-resistant layer only needs to have a melting point of two or more points, and may have a melting point of three or more points, but preferably has a melting point of two points.
The first melting point is 75°C or higher and lower than 100°C, and from the viewpoint of improving heat sealability, blocking resistance, and moldability, it is preferably 78°C or higher, more preferably 80°C or higher, and even more preferably 82°C or higher. ℃ or higher, and preferably 96℃ or lower, more preferably 92℃ or lower, and still more preferably 90℃ or lower.
Further, from the same viewpoint, the second melting point is 100°C or more and 120°C or less, preferably 105°C or more, more preferably 108°C or more, even more preferably 110°C or more, and preferably 118°C or more. The temperature is preferably 116°C or lower, more preferably 114°C or lower.
As mentioned above, it is sufficient that the water-resistant layer has at least two melting points, one of 75°C or more and less than 100°C and one of 100°C or more and 120°C or less, and multiple melting points that fall within the above temperature range are sufficient. It may have a melting point that does not correspond to the above melting point.

The melting point of the water-resistant layer is measured by the following method.
Specifically, only a thin layer of the water-resistant layer is scraped off using a razor from the surface of the water-resistant paper on which the water-resistant layer is provided. About 5 mg of the scraped water-resistant layer is sealed in an aluminum pan, and measured using a differential scanning calorimeter (NEXTA DSC600, manufactured by Hitachi High-Tech Science Co., Ltd.). After heating at 10°C/min from 30°C to 150°C in a nitrogen atmosphere (first run), cooling at 10°C/min to 30°C, and increasing the temperature again from 30°C to 150°C at 10°C/min (first run). second run). Read the endothermic peak temperature of the second run and use it as the melting point. As used herein, "the water-resistant layer has at least two melting points" means that at least two endothermic peaks are observed when the water-resistant layer is subjected to the above measurement.
In addition, as described later, when the water-resistant layer has a plurality of melting points by containing two or more resins having different melting points, the melting point of the resin used may be used for approximation.

〔resin〕
The water-resistant layer contains two or more resins having different melting points, thereby imparting a plurality of melting points to the water-resistant layer. Since it is preferable to form the water-resistant layer by coating a paper base material with an aqueous coating liquid, the resin is preferably a water-dispersible resin.
The resin contained in the water-resistant layer is not particularly limited, and examples include polycarbonate, polyacrylonitrile, polystyrene polymers (e.g., styrene-butadiene copolymer), polyurethane, polyolefins (e.g., polyethylene, polypropylene, polybutadiene, ethylene). copolymers of (meth)acrylic acid and unsaturated hydrocarbons other than ethylene), (meth)acrylic acid polymers (e.g., acrylic esters, copolymers of (meth)acrylic acid and other unsaturated monomers, ethylene -(meth)acrylic acid copolymer), ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, polyester, polyamide, polyether, and their modified products. It will be done.
Among these, from the viewpoint of obtaining water-resistant paper with excellent water resistance, blocking resistance, moldability, and heat sealability, at least ethylene-(meth)acrylic acid copolymer and ethylene and unsaturated hydrocarbons other than ethylene are used. Contains a copolymer with In addition to the above two resins, it may contain the resins exemplified above (eg, ethylene-vinyl acetate copolymer, etc.).

(Ethylene-(meth)acrylic acid copolymer)
In this embodiment, the water-resistant layer contains an ethylene-(meth)acrylic acid copolymer (hereinafter also referred to as copolymer A). It is thought that the ethylene-(meth)acrylic acid copolymer mainly contributes to the first melting point.
Here, the ethylene-(meth)acrylic acid copolymer may be blended as an ionomer. Note that "blended as an ionomer" means that the ionomer is used as a raw material at least when producing the water-resistant layer, and the form of the ionomer does not need to be maintained after production. Therefore, the water-resistant layer does not need to contain resin in the form of an ionomer.
Ionomers are polymers neutralized with cations. That is, all resins obtained by neutralizing ethylene-(meth)acrylic acid copolymers with cations fall under the category of ionomers. Examples of cations include metal ions, ammonium ions (NH ₄ ⁺ ), and organic ammonium ions. Examples of metal ions include alkali metal ions such as lithium ion (Li ⁺ ), sodium ion (Na ⁺ ), and potassium ion (K ⁺ ), and alkaline earth metals such as magnesium ion (Mg ²⁺ ) and calcium ion (Ca ²⁺ ). ions, transition metal ions such as zinc ions (Zn ²⁺ ), copper ions (Cu ²⁺ ), and the like. Among these, from the viewpoint of availability and the like, it is preferable that the metal ions include sodium ions.
The copolymerization ratio of ethylene and (meth)acrylic acid may be appropriately selected so as to obtain the desired melting point. The content is preferably 50% by mass or more and 95% by mass or less, more preferably 60% by mass or more, even more preferably 65% by mass or more, and more preferably 90% by mass or less, even more preferably 85% by mass. % or less. The content of structural units derived from ethylene in the ethylene-(meth)acrylic acid copolymer can be confirmed, for example, by ¹³ C-NMR analysis.

As the ethylene-(meth)acrylic acid copolymer, commercially available products may be used, such as MP498345N, MP4983R, MP4990R, MFHS1279, 201103PX. S, Zaixen (registered trademark) A manufactured by Sumitomo Seika Co., Ltd., Zaixen (registered trademark) AC, Chemipearl series (S100, S300, S500) manufactured by Mitsui Chemicals Co., Ltd., BC-212F manufactured by Henkel Japan Co., Ltd. MYE-30ER, MYE-30MAZ manufactured by Maruyoshi Chemical Co., Ltd., Surlyn series manufactured by DuPont, Hymilan series manufactured by Mitsui Dow Polychemical Co., Ltd., HYPOD2000, RHOBARR320 manufactured by Dow Chemical Japan Co., Ltd., Toho Chemical Co., Ltd. Examples include Hitech SC-100 manufactured by the company and Aquatex AC-3100 manufactured by Chuo Rika Kogyo Co., Ltd.

The melting point of the ethylene-(meth)acrylic acid copolymer is preferably 75°C or higher and lower than 100°C, more preferably 78°C, from the viewpoint of improving water resistance and heat sealability, as well as blocking resistance and moldability. Above, the temperature is more preferably 80°C or higher, even more preferably 82°C or higher, and more preferably 96°C or lower, even more preferably 92°C or lower, even more preferably 90°C or lower.

(Copolymer of ethylene and unsaturated hydrocarbon other than ethylene)
In this embodiment, the water-resistant layer uses a copolymer of ethylene and an unsaturated hydrocarbon other than ethylene (hereinafter also referred to as copolymer B) in addition to the ethylene-(meth)acrylic acid copolymer as the resin. Contains. It is believed that the copolymer of ethylene and an unsaturated hydrocarbon other than ethylene mainly contributes to the second melting point.
The unsaturated hydrocarbon other than ethylene may be a monoolefin having one unsaturated double bond in the molecule, a diolefin having two unsaturated double bonds, a triene having three bonds, or a tetraene having four bonds. Moreover, it may have a conjugated double bond.
Among these, from the viewpoint of water resistance, blocking resistance, moldability, and heat sealability, the unsaturated hydrocarbon other than ethylene preferably contains an α-olefin having 4 or more and 20 or less carbon atoms, and 6 or more carbon atoms. It is more preferable to include an α-olefin having 16 or less carbon atoms, and even more preferably an α-olefin having 6 or more and 12 or less carbon atoms.
The type of unsaturated hydrocarbon other than ethylene and the copolymerization ratio of ethylene and unsaturated hydrocarbon other than ethylene may be selected appropriately so that the melting point is within the desired range. The content of structural units derived from ethylene in the copolymer with hydrocarbon is preferably 50% by mass or more and 95% by mass or less, more preferably 60% by mass or more, still more preferably 65% by mass or more, and more preferably 60% by mass or more, still more preferably 65% by mass or more. It is more preferably 68% by mass or more, more preferably 90% by mass or less, and even more preferably 88% by mass or less. The content of structural units derived from ethylene in a copolymer of ethylene and an unsaturated hydrocarbon other than ethylene can be confirmed, for example, by ¹³ C-NMR analysis.

The melting point of the copolymer of ethylene and an unsaturated hydrocarbon other than ethylene is preferably 100°C or more and 120°C or less, more preferably 105 The temperature is at least 108°C, more preferably at least 108°C, even more preferably at least 110°C, and more preferably at most 118°C, even more preferably at most 116°C, even more preferably at most 114°C.

The copolymer of ethylene and an unsaturated hydrocarbon other than ethylene may be either a commercially available product or a synthetic product. In the case of a commercially available product, for example, one manufactured by DIC Graphics Corporation (Dick Seal E-806LV) can be used. In the case of a synthetic product, it may be polymerized by a known method, and the synthesis method is not particularly limited. Further, the obtained copolymer may be used by dispersing it in an aqueous medium by a known method. As copolymer A and copolymer B, commercially available mixtures thereof may be used.

The water-resistant layer contains, as a resin, at least an ethylene-(meth)acrylic acid copolymer and a copolymer of ethylene and an unsaturated hydrocarbon other than ethylene; The mass ratio of the copolymer of ethylene and an unsaturated hydrocarbon other than ethylene (ethylene-(meth)acrylic acid copolymer/copolymer of ethylene and an unsaturated hydrocarbon other than ethylene) is determined by the water resistance and blocking resistance. From the viewpoint of properties, moldability and heat sealability, the ratio is 50/50 or more and 90/10 or less, preferably 60/40 or more, more preferably 70/30 or more, and preferably 85/15 or less, more Preferably it is 80/20 or less, more preferably 75/25 or less.

The water-resistant layer contains an ethylene-(meth)acrylic acid copolymer and a copolymer of ethylene and an unsaturated hydrocarbon other than ethylene. The total content of the copolymer with an unsaturated hydrocarbon other than ethylene is preferably 60% by mass or more and 95% by mass or less from the viewpoint of water resistance, blocking resistance, moldability, and heat sealability. Yes, more preferably 65% by mass or more, still more preferably 70% by mass or more, even more preferably 75% by mass or more, and still more preferably 90% by mass or less, even more preferably 85% by mass or less, even more preferably is 80% by mass or less.

The difference between the melting point of the ethylene-(meth)acrylic acid copolymer and the melting point of the copolymer of ethylene and an unsaturated hydrocarbon other than ethylene is determined from the viewpoint of improving heat sealability, blocking resistance, and moldability. From this point of view, the temperature is preferably 5°C or higher and 40°C or lower, more preferably 10°C or higher, even more preferably 15°C or higher, even more preferably 20°C or higher, and even more preferably 35°C or lower, even more preferably The temperature is below 30°C.

[Organic particles]
In this embodiment, the water-resistant layer may contain organic particles in addition to the resin described above, from the viewpoint of further improving blocking properties and moldability.
If the melting point or softening point of the organic particles is at least higher than the melting points of copolymers A and B, the organic particles will not melt or soften during the production and molding of waterproof paper, resulting in excellent blocking properties and moldability. This is preferable from the viewpoint of obtaining the following.
The organic particles are preferably water-dispersible organic particles from the viewpoint that the coating liquid for the water-resistant layer is preferably a water-based coating liquid. That is, the organic particles are preferably blended into the water-resistant layer coating solution as an aqueous dispersion. Further, from the viewpoint of improving heat sealability and water resistance, it is preferable that the aqueous dispersion of organic particles contains little or no surfactant, dispersant, or the like.
Examples of the organic particles include polyester particles, acrylic particles, polystyrene particles, nylon particles, silicone particles, polyolefin particles, etc., and it is preferable to include at least one selected from the group consisting of these particles. , more preferably contains polyolefin particles.
Examples of the polyolefin resin constituting the polyolefin particles include polymers of olefins such as ethylene, propylene, 1-butene, 1-pentene, and 1-hexene. These may be used alone or in combination of two or more. The polyolefin resin may be a homopolymer or a copolymer of the olefins listed above. Moreover, the polyolefin resin may be modified. Examples of modification include anionic modification and cationic modification, and it is also preferable to use polyolefin particles whose dispersibility in water has been improved by modification.
The polyolefin particles more preferably contain at least one selected from the group consisting of polyethylene particles, polypropylene particles, and propylene-ethylene copolymer resin particles, and two types of polyethylene particles and polypropylene particles may be used in combination. .
Polyethylene may be at least one of high-density polyethylene and low-density polyethylene, and polypropylene may be at least one of high-density polypropylene and low-density polypropylene, and is not particularly limited. Further, the polyethylene and the polypropylene may be modified as described above.

The shape of the organic particles is not particularly limited, and may be spherical, ellipsoidal, polygonal (polygonal pyramid, square, rectangular, etc.), plate-shaped, rod-shaped, irregular shape, etc., but must be spherical. is preferred. Here, spherical shape includes true spherical shape and approximately true spherical shape (for example, aspect ratio 0.9 to 1.1).
The average particle diameter of the organic particles is preferably 4 μm or more and 100 μm or less, more preferably 6 μm or more, and still more preferably 8 μm or more, from the viewpoint of blocking resistance and moldability, and maintaining heat sealability. , more preferably 60 μm or less, still more preferably 40 μm or less, even more preferably 30 μm or less, particularly preferably 15 μm or less.
Note that if the average particle size of the organic particles is larger than or about the same as the thickness of the water-resistant layer, unevenness will be formed on the coating surface, resulting in excellent blocking resistance, and This suppresses sticking to the surface and improves moldability. The average particle size of the organic particles is preferably 0.8 times or more and 7 times or less, more preferably 0.9 times or more and 5 times or less, and even more preferably 0.9 times or more and 2.5 times the thickness of the water-resistant layer. Hereinafter, it is even more preferably 0.9 times or more and 1.5 times or less. At this time, the thickness of the water-resistant layer is preferably 2 μm or more and 20 μm or less, more preferably 3 μm or more, even more preferably 4 μm or more, and still more preferably 15 μm or less, and still more preferably 12 μm or less.
The average particle size of the organic particles is measured by a laser diffraction type particle size distribution measuring device based on the principle of laser diffraction method or by a call counter method.

The content of organic particles in the water-resistant layer is preferably 0.5% by mass or more and 40% by mass or less, more preferably 1.0% by mass or more, from the viewpoint of blocking resistance and heat sealability. It is more preferably 3.0% by mass or more, more preferably 35% by mass or less, even more preferably 25% by mass or less, even more preferably 15% by mass or less, even more preferably 10% by mass or less.

[Other ingredients]
The water-resistant layer may contain other components in addition to the above-mentioned resins, such as amine additives that are neutralizing agents (aminomethylpropanol, dimethylaminomethylpropanol, dimethylaminoethanol, diethylaminoethanol, etc.). ), higher fatty acids (oleic acid, stearic acid, palmitic acid, etc.), anti-sagging agents/anti-settling agents, antifoaming agents, viscosity modifiers, leveling agents, wetting agents, dispersants, pigments, colorants such as colored dyes, etc. etc. are exemplified. The content of other components in the water-resistant layer is not particularly limited as long as it does not impair the effects of the invention.

The water-resistant layer can be obtained by preparing a coating solution for a water-resistant layer containing the above-mentioned resin and coating it on at least one surface of the paper base material.
The method for applying the water-resistant layer coating liquid is not particularly limited, and may be appropriately selected from commonly used coating apparatuses. For example, air knife coater, blade coater, gravure coater, rod blade coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, champlex coater, metering blade type size press coater, short dwell coater, spray Various known coating devices such as a coater, a gate roll coater, and a lip coater can be used.

[Preferred embodiment of water-resistant layer]
The water-resistant paper of this embodiment only needs to have a water-resistant layer on the uppermost layer of at least one side of the paper base material, and preferably on both sides of the paper base material.
By having water-resistant layers on both sides, it can be suitably applied, for example, to applications where dew condensation occurs (for example, cold water paper cups, etc.).

Water-resistant paper has a water-resistant layer on the top layer on at least one side. By having a water-resistant layer on the uppermost layer of the paper base material, water resistance and heat-sealing properties can be imparted, and blocking resistance can also be imparted.
The coating amount per side of the water-resistant layer is preferably 3.0 g/m2 or ^more , from the viewpoint of providing a water-resistant layer with excellent water resistance, heat sealability, blocking resistance, and moldability, and from the viewpoint of recyclability. is 3.5 g/m ² or more and 20 g/m ² or less, more preferably 4.0 g/m ² or more, even more preferably 4.5 g/m ² or more, and even more preferably 16 g/m ² or less. , more preferably 12 g/m ² or less.

In addition, the coating amount of the water-resistant layer may be measured as follows.
A piece of water-resistant paper is cut into a size of 5 cm x 5 cm, and after being conditioned at 23° C. and 50% RH for 24 hours, the mass is measured. Subsequently, 2 mL of Viscamyl flow 150 (cellulase) manufactured by Genencore is immersed in an enzyme solution diluted to 50 mL with 50 mM acetate buffer of pH 5, and reacted overnight at 50° C. to decompose and remove the pulp. Next, the sample is immersed in a 1.0 mol/L ethylenediamine copper (II) solution for 12 hours to remove the remaining pulp (and if it has a pigment coating layer, the pigment coating layer components). The thus obtained sample from which the pulp and pigment have been removed is air-dried at 23° C. and 50% RH for 24 hours, and then its mass is measured. The coating amount of the water-resistant layer is calculated by dividing the measured mass by the area of the water-resistant paper. However, if the sample is too small to measure, the thickness of the water-resistant layer can be determined by observing the cross section of the water-resistant paper with a scanning electron microscope, and then multiplying this by the density of the solid content of the coating liquid. The coating amount may be calculated.

<Pigment coating layer>
The water-resistant paper of this embodiment has a pigment coating layer between the paper base material and the water-resistant layer. By having a pigment coating layer, the paper base material can be sealed and smoothed. Thereby, a uniform water-resistant layer can be formed, and water resistance and heat sealability are improved.
The pigment coating layer contains a pigment and a binder.

The pigment coating layer is mainly composed of a pigment and a binder. Note that "the pigment coating layer is mainly composed of a pigment and a binder" means that the total content of the pigment and binder in the pigment coating layer is, for example, 50% by mass or more, preferably 60% by mass or more, or more. It means preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more. The upper limit is not particularly limited, but is 100% by mass or less. In addition, the pigment coating layer may further contain arbitrary components in addition to the pigment and the binder.

[Pigment]
Pigments are not particularly limited and include, for example, kaolin, clay, engineered kaolin, delaminated clay, calcined clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, Examples include inorganic pigments such as silicic acid, silicate, colloidal silica, and satin white; organic pigments such as solid type, hollow type, and core-shell type. These may be used alone or in combination of two or more. Among these, from the viewpoint of further improving water resistance and/or heat sealability, it is preferable to contain at least one selected from the group consisting of kaolin and calcium carbonate, more preferably to contain at least kaolin, and at least kaolin and calcium carbonate. It is further preferable to contain calcium carbonate.

The average particle size of the pigment is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.5 μm or more, and preferably 20 μm or less, more preferably 10 μm or less, even more preferably 4 μm or less, and even more preferably Preferably it is 3 μm, particularly preferably 2.5 μm or less. When the average particle size of the pigment is within the above range, a water-resistant layer with better smoothness can be obtained, and a water-resistant paper with better water resistance and heat sealability can be obtained, so it is preferable. The average particle size of the pigment can be determined using a laser diffraction particle size distribution measuring device based on the principle of laser diffraction, and the value determined based on the measured particle size distribution is used.

It is recommended to use a pigment with an aspect ratio of 3 or more (pigment 1) and a pigment with an aspect ratio of less than 3 (pigment 2) together as pigments, from the viewpoint of improving the water resistance of the undercoat layer and from the viewpoint of improving the undercoat layer coating. This is preferable from the viewpoint of adjusting the viscosity of the working solution and cost.
The aspect ratio of Pigment 1 is 3 or more, preferably 5 or more, and preferably 500 or less, more preferably 300 or less. Kaolin is exemplified as a pigment having the above aspect ratio.
The aspect ratio of the pigment 2 is less than 3, preferably 2 or less, and 1 or more. Calcium carbonate is exemplified as a pigment having the above aspect ratio.
Note that the aspect ratio of a pigment is a shape factor obtained by dividing the average particle size by the average thickness. To calculate the average thickness, drop a few drops of the pigment diluted with a solvent, etc. onto a glass substrate, let it dry naturally, extract 20 points of the pigment oriented on the glass substrate using a transmission electron microscope, and calculate the thickness of each. Measure. Then, among the 20 thicknesses measured, the average value of the remaining 14 thicknesses after excluding the three thicknesses of the upper and lower values is determined, and the average value is taken as the average thickness.

When calcium carbonate and kaolin are used together as pigments, the mass ratio of the calcium carbonate content to the kaolin content in the pigment coating layer (calcium carbonate/kaolin) is not particularly limited, but is preferably 40/60 or more and 80 /20 or less, more preferably 50/50 or more and 75/25 or less, still more preferably 60/40 or more and 75/25 or less, even more preferably 65/35 or more and 75/25 or less.
Kaolin is a layered inorganic compound, and by using kaolin as a pigment, a pigment coating layer with excellent smoothness can be obtained, and as a result, a water-resistant paper with excellent water resistance and heat sealability can be obtained. preferable. On the other hand, coating liquids for pigment coating layers that contain kaolin (coating liquids for pigment coating layers) tend to have high viscosity. Since it is necessary to lower the concentration and the amount of coating per time is reduced, a large number of coatings are required, which tends to reduce coating efficiency.
By using calcium carbonate and kaolin together as pigments and using the above mass ratio, it is possible to obtain a pigment coating layer with excellent smoothness, excellent coating properties, and a large amount of coating per application. This is preferable because the pigment coating layer can be formed with a small number of coatings, resulting in excellent coating efficiency.

The pigment content in the pigment coating layer is preferably 20% by mass or more and 95% by mass or less, more preferably 40% by mass, from the viewpoint of suppressing roll staining during coating, and from the viewpoints of water resistance and heat sealability. % or more, more preferably 60% by mass or more, even more preferably 70% by mass or more, and more preferably 90% by mass or less, still more preferably 85% by mass or less, even more preferably 82% by mass or less. .

〔binder〕
The binder contained in the pigment coating layer is not particularly limited, but includes styrene-butadiene resin; acrylic resin such as methyl (meth)acrylate copolymer, styrene-acrylic copolymer, and ethylene-acrylic acid copolymer. polymers, olefin/unsaturated carboxylic acid copolymers such as ethylene-methacrylic acid copolymers; etc., and contain at least one selected from the group consisting of acrylic resins and styrene-butadiene resins. It is more preferable that the resin contains at least one selected from the group consisting of a styrene-acrylic copolymer and a styrene-butadiene resin, and even more preferably a styrene-acrylic copolymer.
The styrene-acrylic copolymer is preferably a copolymer of styrene and a (meth)acrylic ester, more preferably a copolymer of styrene and an acrylic ester, and a copolymer of styrene and an alkyl acrylate. Polymers are more preferred. In this case, it is particularly preferable that the alkyl moiety of the alkyl ester has 1 or more and 8 or less carbon atoms.

The content of the binder in the pigment coating layer is preferably 5% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more, even more preferably 18% by mass or more, from the viewpoint of water resistance and heat sealability. % by mass or more, and from the viewpoint of suppressing roll staining during coating, preferably 80% by mass or less, more preferably 60% by mass or less, still more preferably 40% by mass or less, even more preferably 30% by mass. It is as follows.

In the pigment coating layer, the mass ratio of the pigment to the binder content (pigment/binder) is preferably 50/50 or more, more preferably 60/40 or more, still more preferably 70/30 or more, and preferably is 90/10 or less, more preferably 85/15 or less.
It is preferable that the mass ratio of the pigment to the binder is equal to or higher than the above lower limit because roll staining during production is suppressed and operability is excellent.
On the other hand, if the mass ratio of the pigment to the binder exceeds the above upper limit, that is, if the amount of binder in the pigment coating layer is too small, the fixation of the pigment to the paper base material becomes weak, resulting in partial drop-off of the pigment. may occur, and the thickness of the pigment coating layer may become uneven. As a result, the thickness of the water-resistant layer formed on the pigment coating layer may become non-uniform. If the thickness of the water-resistant layer becomes non-uniform, water may penetrate from areas where the film thickness is small, resulting in a decrease in water resistance. Furthermore, if the thickness of the water-resistant layer becomes non-uniform, it may be difficult to bond the thinner portions, and the desired heat-sealability may not be obtained. On the other hand, if the pigment/binder mass ratio is below the above upper limit, that is, if the pigment content in the pigment coating layer is moderately low, the above phenomenon will be suppressed, and the thickness of the water-resistant layer will be reduced. This is preferred because it has good uniformity and, as a result, a water-resistant paper with excellent water resistance and heat sealability can be obtained.

The total content of the pigment and binder in the pigment coating layer is preferably 60% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and the upper limit is It is 100% by mass or less.

The coating amount of the pigment coating layer is not particularly limited, but in terms of solid content, it is preferably 1 g/m ² or more, more preferably 3 g/m ² or more, and preferably 10 g/m ² or less, more preferably is 8g/ ^m2 or less.
The method of forming the pigment coating layer is not particularly limited, but it is preferably formed by coating a dispersion containing a pigment and a binder onto a paper base material and drying it.
The dispersion containing the pigment and resin binder is preferably an aqueous dispersion.
In addition to the pigment and the binder, the pigment coating layer may contain the components exemplified as other components in the water-resistant layer, and preferably contains an antifoaming agent.

[Other ingredients]
The pigment coating layer may further contain components other than the pigment and the binder. Other components include adhesives, dispersants, thickeners, water retention agents, antifoaming agents, waterproofing agents, colorants, surfactants, and the like. Adhesives include proteins such as casein, soy protein, and synthetic proteins; etherified starches such as oxidized starch, positive starch, urea phosphate starch, and hydroxyethyl etherified starch; starches such as dextrin; carboxymethyl cellulose, hydroxy Examples include cellulose derivatives such as ethyl cellulose and hydroxymethyl cellulose. The content of other components in the pigment coating layer is not particularly limited as long as the content is within a range that does not impair the effect.

The water-resistant paper of this embodiment may have a water-resistant layer on both sides of the paper base, for example, a structure in which the paper base, a pigment coating layer, and a water-resistant layer are laminated in this order. Alternatively, the first water-resistant layer, the pigment coating layer, the paper base material, and the second water-resistant layer may be laminated in this order. Alternatively, the first water-resistant layer, the undercoat water-resistant layer, the pigment coating layer, the paper base material, and the second water-resistant layer may be laminated in this order.
The water-resistant paper of this embodiment may have other layers in addition to the pigment coating layer and the water-resistant layer. Examples of other layers include a printed layer, a water vapor barrier layer, an oxygen barrier layer, an oxygen absorption layer, and the like. The printing layer may be formed using a known ink such as oil-based ink, water-based ink, or biomass ink. The printing layer may be formed on one surface of the waterproof paper, or may be formed on a part of the surface. That is, the waterproof paper of this embodiment may be printed on all or part of at least one surface (for example, the printing surface). The printed content may be a pattern, a design, information (ingredients, expiration date, QR code (registered trademark), etc.).

<Physical properties of water-resistant paper>
(Air permeability)
The water-resistant paper of this embodiment preferably has an air permeability (Oken type air permeability) of 1,000 seconds or more, more preferably 10,000 seconds or more, still more preferably 25,000 seconds or more, Even more preferably, it is 99,999 seconds or more. The upper limit of the air permeability is not particularly limited, but is, for example, 1,000,000 seconds or less.
By setting the air permeability within the above range, the air-blocking property in the sense of blocking air becomes high, and a water-resistant paper with further excellent water resistance can be obtained. In particular, when having two or more water-resistant layers or when providing a pigment layer as a lower layer of the water-resistant layer, the air permeability can be increased.
Air permeability is measured in accordance with JIS P 8117:2009.

(Cobb water absorption for water at 20°C)
From the viewpoint of water resistance to cold water, the water-resistant paper of this embodiment has a Cobb water absorption of 20° C. water at a measurement time of 30 minutes on the surface provided with the water-resistant layer, preferably 40 g/m ² or less, or more. It is preferably 20 g/m ² or less, more preferably 15 g/m ² or less, even more preferably 10 g/m ² or less. The lower limit is not particularly limited.
Cobb water absorption is measured in accordance with JIS P 8140:1998.

(Cobb water absorption for water at 90°C)
From the viewpoint of water resistance to hot water, the water-resistant paper of the present embodiment preferably has a Cobb water absorption of 90° C. water at a measurement time of 30 minutes on the surface provided with the water-resistant layer of 100 g/m ² or less, It is more preferably 60 g/m ² or less, still more preferably 30 g/m ² or less, even more preferably 20 g/m ² or less. The lower limit is not particularly limited.
Cobb water absorption is measured in accordance with JIS P 8140:1998.

(blocking resistance)
The water-resistant paper of this embodiment preferably has excellent blocking resistance, and after heating and pressurizing at 40°C and 90% relative humidity at a pressure of 2 kg/ ^cm2 for 24 hours, and cooling to room temperature, the water-resistant paper When it is peeled off, it is preferable that there is slight resistance or that it is peeled off without resistance, and it is more preferable that it be peeled off without resistance.

(Oil resistance)
The water-resistant paper of this embodiment has JAPPAN TAPPI No. 1 on the side provided with the water-resistant layer. The value (kit value, KIT value) measured in accordance with No. 41 (kit method) is preferably 6 or more, more preferably 8 or more, and still more preferably 10 or more. The upper limit of the KIT value is 12, and a KIT value of 12 is particularly preferred.

(Recycle rate (pulp recovery rate after re-disintegration))
The heat seal paper of this embodiment has a recycling rate expressed as a pulp recovery rate after re-disintegration, preferably 85% or more, more preferably 90% or more, and even more preferably 95% or more. If the recycling rate (pulp recovery rate after re-disintegration) is within the above range, the recyclability is excellent. The recycling rate (pulp recovery rate after re-disintegration) of the water-resistant paper is a value measured by the method described in the Examples below.

(heat sealability)
In the water-resistant paper of this embodiment, it is preferable that the water-resistant layer has heat sealability.
The heat sealing conditions are not particularly limited, but the temperature during heat sealing is, for example, 60°C or more and 300°C or less, the pressure during heat sealing is, for example, 0.05 MPa or more and 10 MPa or less, and the pressurizing time is, for example, 0.05 MPa or more and 10 MPa or less. .1 second or more and 15 seconds or less.

(Basic weight)
The basis weight of the water-resistant paper of this embodiment is not particularly limited, but for example, if it is used for a packaging container, preferably a food container, more preferably a paper cup, for example, from the viewpoint of obtaining strength as a packaging container and From the viewpoint of moldability, it is preferably 150 g/m ² or more and 500 g/m ² or less, more preferably 180 g/m ² or more, even more preferably 220 g/m ² or more, and even more preferably 450 g/m ² Below, it is more preferably 400 g/m ² or less, even more preferably 350 g/m ² or less, even more preferably 300 g/m ² or less, particularly preferably 270 g/m ² or less. The basis weight of waterproof paper is measured in accordance with JIS P 8124:2011.

(thickness)
The thickness of the water-resistant paper of this embodiment is not particularly limited, but for example, if it is used for a packaging container, preferably a food container, more preferably a paper cup, for example, from the viewpoint of obtaining strength as a packaging container and From the viewpoint of moldability, it is preferably 150 μm or more and 650 μm or less, more preferably 180 μm or more, even more preferably 230 μm or more, even more preferably 250 μm or more, particularly preferably 270 μm or more, and still more preferably 500 μm or less, and even more preferably is 430 μm or less, even more preferably 400 μm or less, even more preferably 350 μm or less, particularly preferably 300 μm or less. The thickness of waterproof paper is measured in accordance with JIS P 8118:2014.

(Applications of water-resistant paper)
The water-resistant paper of this embodiment has excellent heat-sealability and water resistance, so it can be used for packaging containers such as cups, plates, trays, lids, pouches, and tube-shaped containers; for cutlery such as spoons, forks, knives, and chopsticks; Straw: Can be suitably used for soft packaging materials such as wrapping paper, packaging bags, lids, and labels. For example, packaging containers are formed by printing on the surface of water-resistant paper as necessary, punching it into a shape that corresponds to the shape of the packaging container to be manufactured, bending it, and pasting the overlapping parts together using heat sealing. be able to. Therefore, according to the present invention, there is also provided a packaging container (particularly a paper cup) using the above-mentioned water-resistant paper. Moreover, since the water-resistant paper of this embodiment also has excellent oil resistance, it can be suitably used for food packaging applications.
The contents of the packaging container may be either food or non-food. Furthermore, the contents of the packaging container may be liquid, solid, or gel. The contents of the packaging container are not particularly limited, and include, for example, recreational beverages such as coffee, tea, tea, juice, and carbonated drinks; alcoholic beverages such as sake, shochu, and wine; milk beverages such as milk; and instant foods (instant ramen noodles, etc.), microwaveable foods, luxury foods (yoghurt, ice cream, jelly, pudding, etc.), prepared foods; Pharmaceutical products; Car wax, shampoo, conditioner, detergents, bath additives, hair dye, toothpaste, etc. Chemical products; etc.
The water-resistant paper of this embodiment is preferably used for liquid containers such as paper cups, their lids, and other paper containers (for example, paper trays) that require water resistance. When used in liquid containers, it is preferable from the viewpoint of moldability that the water-resistant layer has heat-sealability (particularly side-sealability in the case of paper cups).
To give an example of molding a liquid container (paper cup), if necessary, print on the front or back side of waterproof paper, punch it into a shape that corresponds to the shape of the liquid container to be manufactured, and then insert it into a mandrel mold. After wrapping and sealing the sides to form the body, the bottom is formed and the top is curled to create a paper cup.
The water-resistant paper of this embodiment has excellent water resistance, heat sealability, and moldability.
Note that the water-resistant paper of this embodiment is not limited to the above-mentioned applications, but may also be used as packaging paper.
The packaging container made of waterproof paper of this embodiment uses less plastic than the packaging container made of conventional laminated paper. Furthermore, conventional packaging containers made of laminated paper need to be disintegrated using a pulper with high disintegration performance when reusing them as waste paper, but the packaging containers made of water-resistant paper of this embodiment can be disintegrated using normal disintegration. It can be disintegrated even with a high-performance pulper, and has excellent recyclability. A packaging container made of the waterproof paper of this embodiment is subjected to washing, cutting, disintegration, etc. to prepare a pulp slurry, and the obtained pulp slurry can be used to manufacture paper. The type of paper to be made is not particularly limited, and examples thereof include printing paper, packaging paper, sanitary paper, paperboard, and the like. It is also possible to manufacture packaging containers (for example, tissue boxes, paper cup sleeves, etc.) by processing the paper.

The barrier laminate of the present invention will be described in more detail with reference to Examples below, but the present invention is not limited thereto. Note that "parts" and "%" in Examples and Comparative Examples indicate "parts by mass" and "% by mass", respectively, unless otherwise specified.

[Measuring method]
The measurement method is shown below. Note that unless otherwise specified, measurements were performed in an environment at a temperature of 23° C.±1° C. and a relative humidity of 50±2% as described in JIS P 8111:1998.

<Measurement of viscosity>
The B-type viscosity was measured using a B-type viscometer (BM II, manufactured by Toki Sangyo Co., Ltd.). The rotational speed of the rotor was measured at 60 rpm.

<Measurement of melting point>
The melting point of the dried solidified aqueous resin emulsion was measured by the following procedure.
The water-based resin emulsion was applied onto a PET film using a bar coater and dried at 120°C to form a film. After repeating coating and drying until the thickness of the film became approximately 20 to 50 μm, the film was peeled off from the PET film to obtain a dried solidified water-based resin emulsion.
5 mg of the dried solidified product was sealed in an aluminum pan and measured using a differential scanning calorimeter (NEXTA DSC600, manufactured by Hitachi High-Tech Science Co., Ltd.). After heating at 10°C/min from 30°C to 150°C in a nitrogen atmosphere (first run), cooling at 10°C/min to 30°C, and increasing the temperature again from 30°C to 150°C at 10°C/min (first run). Second run). The endothermic peak temperature of the second run was read and taken as the melting point.

<Measurement of acid value>
The acid value was measured by the following procedure. About 0.5 g of the dried solidified sample obtained by the above method and 70 mL of xylene were put into a 100 mL Erlenmeyer flask, and after heating and dissolving it on a 135°C oil bath for about 20 minutes, the sample was mixed with a hot stirrer. Indicator titration was performed with a 0.1 mol/L sodium hydroxide benzyl alcohol solution while keeping the solution at about 100° C., and the end point of the titration was when the sample solution changed color from colorless to red and the red color did not disappear for 30 seconds. A blank test was also conducted in the same manner, and the acid value was calculated from the amount of sodium hydroxide benzyl alcohol solution required for titration.

[material]
The raw materials used in the examples and comparative examples are as follows.
<Water-based resin emulsion>
・Commercially available water-based resin emulsion A: solid content concentration 43% by mass, type B viscosity at 23°C 3000 mPa・s, specific gravity 0.97, melting point 1 of dry solidified product is 86.8°C, melting point 2 is 112.7°C , acid value of dry solidified product: 26.4mgKOH/g-solid
The components contained in water-based resin emulsion A were analyzed using the following procedure. Water-based resin emulsion A was dried at 120° C. for 2 hours to obtain a solidified product. The solidified product was immersed in a sufficient amount of heptane, heated at 120° C. for 1 hour, and separated into a soluble portion and an insoluble portion. The solvent was removed from the soluble portion by distillation under reduced pressure using an evaporator, and the solvent was dried under vacuum at 40° C. to obtain a hot heptane soluble portion. The insoluble portion was washed with a small amount of hot heptane and then vacuum dried at 40° C. to obtain a hot heptane insoluble portion.
The components were analyzed using a gas chromatography mass spectrometer (GCMS-QP2010, manufactured by Shimadzu Corporation) connected to a pyrolysis sample introduction device (FRONTIER LAB, PY-3030D). As a result of the analysis, the hot heptane soluble portion contained a copolymer of ethylene and an α-olefin having 6 to 10 carbon atoms, and the ethylene hot heptane insoluble portion contained an ethylene-acrylic acid copolymer and dimethylaminoethanol. was found to be included.
In addition, the mass ratio of ethylene-acrylic acid copolymer to a copolymer of ethylene and α-olefin having 6 to 10 carbon atoms (ethylene-acrylic acid copolymer: ethylene and copolymer having 6 to 10 carbon atoms) copolymer with α-olefin) was 73:27. Furthermore, the total content of the ethylene-acrylic acid copolymer and the copolymer of ethylene and an α-olefin having 6 to 10 carbon atoms in the solid content of the water-based resin emulsion A is 68.9% by mass, Further, the total content of the ethylene-acrylic acid copolymer and the copolymer of ethylene and an α-olefin having 6 to 10 carbon atoms in the resin component of water-based resin emulsion A was 78.1% by mass. As a result of ¹³ C-NMR analysis, the content of structural units derived from ethylene in the ethylene-(meth)acrylic acid copolymer was 65 to 85% by mass. Furthermore, as a result of ¹³ C-NMR analysis, the content of structural units derived from ethylene in the copolymer of ethylene and α-olefin having 6 to 10 carbon atoms was 68 to 88% by mass.

・Ethylene-methacrylic acid copolymer sodium salt ionomer emulsion: Trade name "Chemipearl S300", manufactured by Mitsui Chemicals, Inc., chemical concentration 35% by mass, type B viscosity at 23°C 105 mPa・s, chemical specific gravity 0.99, dry solidification Melting point of the product: 92.8°C, acid value of the dry solid: 16.6mgKOH/g-solid
- Ethylene-acrylic acid copolymer amine salt ionomer emulsion: Product name "201103PX.S", manufactured by Michael Mann Japan LLC, chemical concentration 20% by mass, type B viscosity at 23°C 100 mPa・s, chemical specific gravity 1.00, Melting point of dried solidified product: 91.5°C, acid value of dried solidified product: 47.2mgKOH/g-solid
・Ethylene-acrylic acid copolymer ammonium salt ionomer emulsion: Zaixen AC, manufactured by Sumitomo Seika Co., Ltd., chemical concentration 28% by mass, type B viscosity at 23°C 700 mPa・s, chemical specific gravity 1.00, melting point of dry solidified product 82.2℃, acid value of dry solidified product 62.2mgKOH/g-solid

<Defoaming agent>
・Defoaming agent: Product name “Bismer KS-38E”, manufactured by Nissin Kagaku Kenkyusho Co., Ltd.

<Organic particles>
- Organic particles A: mixture of low molecular weight PE particles and modified PO particles (modified polyolefin, low molecular weight PO), trade name "Chemipearl W310", manufactured by Mitsui Chemicals, Inc., chemical concentration 39% by mass, spherical, average particle size 9. 5 μm
・Organic particles B: High-density PE (HDPE), trade name "AQUACER 272N", manufactured by BYK, chemical concentration 55% by mass, spherical, average particle size 30 μm

[Preparation of coating liquid]
(a) Preparation of coating liquid A for pigment coating layer 70 parts of heavy calcium carbonate (average particle size 1.0 μm, aspect ratio 1.4), 30 parts of kaolin (average particle size 2.0 μm, aspect ratio 7) 0.1 solid part of a dispersant (sodium polyacrylate) was added to water with stirring to prepare a pigment slurry having a concentration of 70% by mass. Next, a 48% aqueous sodium hydroxide solution was added to adjust the pH to 11.5. Subsequently, 25 solid parts of styrene-acrylic copolymer latex (Acronal S 728ap manufactured by BASF, acrylic ester-styrene copolymer) and an antifoaming agent (Bismer KS38E manufactured by Nissin Kagaku Kenkyujo Co., Ltd.) were added. 0.31 part of solid was added, and water was added to adjust the coating solution concentration to 63% by mass. The B type viscosity of the completed coating liquid was 800 mPa·s (liquid temperature 20°C), and the pH was 9.5.

(b) Preparation of coating liquid B for pigment coating layer Coating for pigment coating layer except that the amount of styrene-acrylic copolymer latex (Acronal S 728ap manufactured by BASF) was 11.1 solid parts. Pigment coating layer coating liquid B was prepared in the same manner as liquid A. The B type viscosity of the completed coating liquid was 1,000 mPa·s (liquid temperature 20°C), and the pH was 9.0.

(c) Preparation of coating liquid C for pigment coating layer Coating liquid A for pigment coating layer except that the amount of styrene-acrylic copolymer latex (Acronal S 728ap manufactured by BASF) was 100 solid parts. Pigment coating layer coating liquid C was prepared in the same manner as above. The B-type viscosity of the completed coating liquid was 600 mPa·s (liquid temperature 20°C), and the pH was 9.5.

(d) Preparation of coating liquid D for pigment coating layer The styrene-acrylic copolymer latex was changed to styrene-butadiene copolymer latex (Nipol LX432M manufactured by Nippon Zeon Co., Ltd.), and the amount added was 25 solid parts. Pigment coating layer coating liquid D was prepared in the same manner as pigment coating layer coating liquid A except for the following. The B-type viscosity of the completed coating liquid was 800 mPa·s (liquid temperature 20°C), and the pH was 9.0.

(e) Preparation of topcoat coating liquid A Water-based resin emulsion A and an antifoaming agent are blended, and the content of the antifoaming agent in the solid content is 0.1% by mass, and the topcoat has a solid content concentration of 43% by mass. Coating liquid A was prepared.

(f) Preparation of top coating solution B Ethylene-methacrylic acid copolymer sodium salt ionomer emulsion (trade name "Chemipearl S300") and antifoaming agent are blended to form a solid content of ethylene-methacrylic acid copolymer sodium salt. A topcoat coating liquid B was prepared with an ionomer content of 99.9% by mass, an antifoaming agent content of 0.1% by mass, and a solid content concentration of 35% by mass.

(g) Preparation of top coating liquid C Ethylene-acrylic acid copolymer amine salt ionomer emulsion (product name "201103PX.S") is blended with an antifoaming agent to contain ethylene-acrylic acid copolymer amine in the solid content. A top coating liquid C was prepared in which the salt ionomer content was 99.9% by mass, the antifoaming agent content was 0.1% by mass, and the solid content concentration was 20% by mass.

(h) Preparation of topcoat coating solution D Ethylene-acrylic acid copolymer ammonium salt ionomer emulsion (Zaixen AC) and antifoaming agent are blended to determine the content of ethylene-acrylic acid copolymer ammonium salt ionomer in the solid content. was 99.9% by mass, the antifoaming agent content was 0.1% by mass, and the solid content concentration was 28% by mass.

(i) Preparation of top coating liquid E A water-based resin emulsion A, organic particles A, and an antifoaming agent are blended so that the content of organic particles A in the solid content is 4% by mass and the content of the antifoaming agent is 4% by mass. 0.1% by mass, and a coating liquid E having a solid content concentration of 42.8% by mass was prepared.

(j) Preparation of topcoat coating liquid F Water-based resin emulsion A, organic particles B, and antifoaming agent are blended, and the content of organic particles B in the solid content is 4% by mass and the content of antifoaming agent is 0. .1% by mass, and a coating liquid F having a solid content concentration of 43% by mass was prepared.

[Comparative example 1]
<Preparation of water-resistant paper>
0.8 parts by mass of a weakly acidic rosin sizing agent and wet paper per 100 parts by mass (in terms of solid content) of pulp slurry, which is a mixture of beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) at a ratio of 60% and 40%. A paper stock for the outer layer (first layer, fifth layer) was prepared by adding 0.15 parts by mass of a force enhancer and 1.45 parts by mass of band sulfate.
Similarly, 0.8 parts by mass of a weakly acidic rosin sizing agent was added to 100 parts by mass (in terms of solid content) of pulp slurry in which beaten LBKP (460 mL of CSF) and beaten NBKP (650 mL of CSF) were mixed at a ratio of 60% and 40%. , 0.15 parts by mass of a wet paper strength enhancer, and 1.7 parts by mass of aluminum sulfate were added to prepare a paper stock for the middle layer (second to fourth layers).
Using these paper stocks, paper was made using a 5-layer Fourdrinier paper machine. Coating was then performed on-machine using a rod blade coater located downstream of the paper machine. Coat coating liquid A for pigment coating layer on the front surface (liquid contact surface) of the paper base material using the first stage rod coater so that the coating amount (solid content) is 5 g/ ^m2 . It was then dried to form a pigment coating layer. Next, apply top coating liquid A onto the pigment coating layer on the front surface (liquid contact surface) using the second blade coater so that the coating amount (solid content) is 2.5 g/ ^m2 . This was coated and dried to form an overcoat layer (water-resistant layer) with a thickness of 2.4 μm, thereby producing water-resistant paper. Note that the paper making speed was 600 m/min.

[Example 1]
Comparative Example 1 except that the coating amount (solid content) of the top coat layer (water resistant layer) was changed to 3.0 g/m ² and a top coat layer (water resistant layer) with a film thickness of 2.9 μm was formed. Water-resistant paper was produced in the same manner.

[Example 2]
Comparative Example 1 except that the coating amount (solid content) of the top coat layer (water resistant layer) was changed to 4.0 g/m ² and a top coat layer (water resistant layer) with a film thickness of 3.8 μm was formed. Water-resistant paper was produced in the same manner.

[Example 3]
Comparative Example 1 except that the coating amount (solid content) of the top coat layer (water resistant layer) was changed to 5.0 g/m ² and a top coat layer (water resistant layer) with a film thickness of 4.8 μm was formed. Water-resistant paper was produced in the same manner.

[Example 4]
Comparative Example 1 except that the coating amount (solid content) of the top coat layer (water resistant layer) was changed to 6.0 g/m ² and a top coat layer (water resistant layer) with a film thickness of 5.8 μm was formed. Water-resistant paper was produced in the same manner.

[Example 5]
Comparative Example 1 except that the coating amount (solid content) of the top coat layer (water resistant layer) was changed to 8.0 g/m ² and a top coat layer (water resistant layer) with a film thickness of 7.7 μm was formed. Water-resistant paper was produced in the same manner.

[Example 6]
The procedure was the same as in Comparative Example 1, except that the coating amount (solid content) of the top coat layer (water resistant layer) was changed to 10 g/m ² and a top coat layer (water resistant layer) with a film thickness of 9.6 μm was formed. A water-resistant paper was produced.

[Example 7]
The procedure was the same as Comparative Example 1, except that the coating amount (solid content) of the top coat layer (water resistant layer) was changed to 12 g/m ² and a top coat layer (water resistant layer) with a film thickness of 11.5 μm was formed. A water-resistant paper was produced.

[Comparative example 2]
Water-resistant paper was produced in the same manner as in Example 6, except that the top coating solution was changed to coating solution B.

[Comparative example 3]
Water-resistant paper was produced in the same manner as in Example 6, except that the top coating liquid was changed to coating liquid C.

[Comparative example 4]
Water-resistant paper was produced in the same manner as in Example 6, except that the top coating liquid was changed to coating liquid D.

[Example 8]
A water-resistant paper with a top coat layer (water-resistant layer) having a thickness of 4.8 μm was produced in the same manner as in Example 3 except that the top coat coating liquid was changed to E.

[Example 9]
The same procedure as in Example 8 was carried out except that the coating amount (solid content) of the top coat layer (water resistant layer) was changed to 10 g/m ² , and the top coat layer (water resistant layer) had a thickness of 9.5 μm. I made a paper.

[Example 10]
Water-resistant paper with a top coat layer (water-resistant layer) having a thickness of 4.8 μm was produced in the same manner as in Example 3 except that the top coat coating liquid was changed to F.

[Example 11]
The same procedure as in Example 10 was carried out except that the coating amount (solid content) of the top coat layer (water resistant layer) was changed to 10 g/m ² , except that the top coat layer (water resistant layer) had a thickness of 9.6 μm. I made a paper.

[Example 12]
Water-resistant paper was produced in the same manner as in Example 2 except that the coating solution for pigment coating layer was changed to coating solution B for pigment coating layer.

[Example 13]
Water-resistant paper was produced in the same manner as in Example 2 except that the coating solution for pigment coating layer was changed to coating solution C for pigment coating layer.

[Example 14]
Water-resistant paper was produced in the same manner as in Example 2 except that the coating solution for pigment coating layer was changed to coating solution D for pigment coating layer.

[Evaluation method]
The following measurements and evaluations were performed on the water-resistant papers of Examples 1 to 14 and Comparative Examples 1 to 4. The results are shown in Table 1.

<Basic weight>
The basis weight of the paper base material was measured in accordance with JIS P 8124:2011.

<Paper thickness>
The paper thickness of the paper base material was measured in accordance with JIS P 8118:2014.

<Air permeability (Ouken style air permeability)>
The air permeability of the waterproof paper was measured in accordance with JIS P 8117:2009.

<Cobb water absorption>
Cobb water absorption was measured by cutting the obtained water-resistant paper into 13 cm square pieces, and contacting ion-exchanged water at 20°C or 90°C with the surface of the water-resistant paper for 30 minutes in accordance with JIS P 8140:1998, before and after contact. It was measured based on the mass difference in accordance with JIS P 8140:1998.

<Recyclability>
Weigh out approximately 50 g of the obtained water-resistant paper on an absolute dry basis, cut it by hand without using a knife into approximately 2 cm square pieces, add tap water to make the concentration 3%, and use a disintegrator (manufactured by Kumagai Riki Kogyo Co., Ltd.). No. 2532) for 10 minutes at 21° C. and 3000 rpm to prepare a pulp slurry in which the pulp fibers were completely disintegrated. This pulp slurry was screened for 10 minutes at a slit width of 0.2 mm (8 cuts) and a flow rate of 10 L/min to obtain a residue. The ratio of the bone dry residue mass to the charged bone dry mass was defined as the residue rate, and this was subtracted from 100% to calculate the pulp passage rate, which was defined as the recycling rate.

<Adhesion to metal (formability)>
A SUS block (assumed to be a mandrel in paper cup molding) heated to 70°C was pressed against the front surface (liquid contact surface) of the water-resistant paper for 1 minute, and the condition when peeled off was evaluated according to the following criteria. A and B can be judged to be practically usable.
〔Evaluation criteria〕
A: Does not stick to the block B: Sticks to the block but peels off without resistance if removed by hand C: Sticks to the block and has some resistance when removed by hand D: Sticks to the block and peels off by hand there is great resistance

<Blocking resistance>
Cut the sample into 5 cm square pieces, stack them so that the front surface (liquid contact surface) and back surface are in close contact, sandwich them between blocking testers, pressurize them at a pressure of 2 kg/cm ² , and test them at a temperature of 40°C and a relative humidity of 90%. The pressurized state was maintained under these conditions for 24 hours. After 24 hours, it was taken out from the environment at a temperature of 40°C and a relative humidity of 90%, cooled to room temperature, peeled off by hand, and evaluated according to the following criteria. A and B can be judged to be practically usable.
〔Evaluation criteria〕
A: Peels off with no resistance B: Slight resistance C: Large resistance and coated surface peels off slightly D: Considerable resistance and coated surface peels off (paper peels off)

<Side sealability (heat sealability)>
The obtained water-resistant paper was cut into pieces of 15 cm in the vertical direction and 25 cm in the horizontal direction, and rolled into a cylinder shape with a diameter of 7.5 cm with the front surface (liquid-contacted surface) facing inside. The heat sealability of the overlapping portion of paper (corresponding to the side portion of the paper cup body, side seal width 0.7 cm) was evaluated based on the following criteria. Note that heat sealing was performed using "CS-205" manufactured by Chubu Sogyo Co., Ltd. under conditions of a temperature of 250° C., a pressure of 0.1 MPa, and a bonding time of 2 seconds. If it is A or B, it can be determined that it is practically usable.
〔Evaluation criteria〕
A: The adhesive strength is strong, and it does not peel off easily even if the shape is distorted by pushing from the outside of the cylinder by hand. When the adhesive part is torn and disassembled, it can be confirmed that all the adhesive parts are destroyed from the base material.
B: The adhesive strength is strong and does not peel off easily even if the shape is distorted by pressing from the outside of the cylinder by hand, but when the adhesive part is torn and disassembled, there is a small part that has not been broken from the base material.
C: The adhesive strength is somewhat strong, and it does not peel off easily even if you push it by hand from the outside of the cylinder and distort the shape, but when you tear the adhesive part and disassemble it, there are some parts that are not broken from the base material due to poor adhesion. .
D: Adhesive strength is somewhat weak, and if the shape is distorted by pressing from the outside of the cylinder by hand, more than half of the adhesive part will peel off.
E: No adhesion at all.

<Oil resistance>
JAPAN TAPPI No. 41 (kit method), the oil resistance of the front surface (liquid contact surface) was evaluated. The higher the value (kit value), the higher the oil repellency.

<Operability>
A probe of a tacking tester TAC-1000 (manufactured by Resca Co., Ltd.) was brought into contact with the back surface for measurement. The pressing speed was 0.5 mm/s, the pressing load was 200 gf, the pressing time was 1 s, the pulling speed was 1 mm/s, the stage temperature was 100°C, and the probe temperature was 80°C.
Note that if the adhesive strength is high, it tends to stick to the transfer roll of a coating machine during manufacturing, and also tends to cause roll staining.
〔Evaluation criteria〕
A: Average value of measurement is 20gf or less (no surface stickiness)
B: Measured average value is more than 20gf and less than 40gf (less surface stickiness)
C: Average value of measurement is more than 40gf and less than 60gf (the surface is a little sticky)
D: Average measurement value exceeds 60 gf (surface is sticky)

In the water-resistant papers of Examples 1 to 14, water-resistant papers with excellent water resistance, blocking resistance, moldability, and heat sealability were obtained.
The water-resistant paper of Comparative Example 1 in which the coating weight of the water-resistant layer was less than 3.0 g/m ² did not have sufficient water resistance and was also poor in formability. In addition, the water-resistant papers of Comparative Examples 2 to 4, in which the water-resistant layer has only one melting point, have excellent heat-sealability, but stick to the mandrel, have poor moldability, and have poor blocking resistance. It was also inferior to

Claims (9)

A water-resistant paper having a water-resistant layer on the top layer of at least one side of the paper base material,
The water-resistant layer has at least two melting points, the first melting point is 75°C or more and less than 100°C, the second melting point is 100°C or more and 120°C or less,
The water-resistant layer contains an ethylene-(meth)acrylic acid copolymer and a copolymer of ethylene and an unsaturated hydrocarbon other than ethylene,
Mass ratio of the ethylene-(meth)acrylic acid copolymer and the copolymer of ethylene and an unsaturated hydrocarbon other than ethylene in the water-resistant layer (ethylene-(meth)acrylic acid copolymer/ethylene and non-ethylene copolymer with an unsaturated hydrocarbon) is 50/50 or more and 90/10 or less,
The coating amount per side of the water-resistant layer is 3.0 g/m ² or more,
A pigment coating layer containing a pigment and a binder is provided between the paper base material and the water-resistant layer.
Water resistant paper. The water resistant layer according to claim 1, wherein the total content of the ethylene-(meth)acrylic acid copolymer and the copolymer of ethylene and an unsaturated hydrocarbon other than ethylene in the water resistant layer is 60% by mass or more. Sex paper. The water-resistant paper according to claim 1 or 2, wherein the unsaturated hydrocarbon other than ethylene includes an α-olefin having 4 or more and 20 or less carbon atoms. In the pigment coating layer, the mass ratio of the pigment content to the binder content (pigment/binder) is 50/50 or more and 90/10 or less, according to any one of claims 1 to 3. Water resistant paper. The water-resistant paper according to any one of claims 1 to 4, wherein the binder contains a styrene-acrylic copolymer. The water-resistant paper according to any one of claims 1 to 5, wherein the average particle size of the pigment is 0.1 μm or more and 4 μm or less. The pigment contains calcium carbonate and kaolin, and the mass ratio of the content of calcium carbonate to the content of kaolin in the pigment coating layer (calcium carbonate/kaolin) is 40/60 or more and 80/20 or less. Water-resistant paper according to any one of items 1 to 6. The water-resistant paper according to any one of claims 1 to 7, wherein the coating amount of the pigment coating layer per side is 1 g/m ² or more and 20 g/m ² or less. A packaging container made of the water-resistant paper according to any one of claims 1 to 8.