JP7215635B1 - Water-resistant paper and packaging containers - Google Patents

Abstract

[PROBLEMS] To provide water-resistant paper excellent in water resistance, blocking resistance, moldability and heat-sealability, and a packaging container using the water-resistant paper. A water-resistant paper having a water-resistant layer as the uppermost layer on at least one surface of a paper substrate, wherein the water-resistant layer has at least two melting points, the first melting point being 75° C. or higher. It is less than 100° C., the second melting point is 100° C. or more and 120° C. or less, and the water-resistant layer is an ethylene-(meth)acrylic acid copolymer and a copolymer of ethylene and an unsaturated hydrocarbon other than ethylene. It contains a polymer, and the 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 coalescence/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 or more, A water-resistant paper having a pigment-coated layer containing a pigment and a binder between the paper base and the water-resistant layer. [Selection figure] None

Description

TECHNICAL FIELD The present invention relates to water-resistant paper and a packaging container using the same.

Conventionally, plastic products have been used as various containers for beverages, food, etc. and their lids.
Conventionally, polyethylene-laminated paper, in which a polyethylene film is laminated on one side of the base paper (paper base material), has been used for various containers for beverages, food, etc. However, it is difficult to remove the polyethylene film during recycling, making it difficult to recycle. There was a problem that it was inferior to
In order to deal with such problems, water resistance and the like have been imparted by imparting performance in the papermaking process and imparting performance by coating.
Patent Document 1 discloses a cup base paper and a cup that have processing aptitudes such as water resistance, heat sealability, top curl aptitude, and gravure printing aptitude equivalent to polyethylene-laminated paper, and that are highly recyclable for effective use of resources. For the purpose of providing base paper for paper containers such as base paper for lids and base paper for paper plates, base paper for paper containers is provided with an undercoat layer for filling and a topcoat layer consisting of a waterproof and oil-resistant layer on at least one side of the base paper. Consisting of a binder resin layer, the coating amount per side is 4 to 15 g/m ² , the resin coating amount of the water- and oil-resistant layer of the topcoat layer is 2 g/m ² or more per side, and the requirements A to D below are satisfied. A paper container base paper characterized by:
A. Cobb of the base paper has a water absorbency of 50 g/m ² or less and a smoothness of 10 seconds or more.
B. The pigment used in the undercoat layer has an aspect ratio of 5 to 30 and an average particle size of 0.5 to 30 μm.
C. The mixing ratio of the undercoat layer is 10 to 100 parts by weight of the binder resin per 100 parts by weight of the pigment.
D. A water- and oil-resistant resin used in the overcoat layer has a gel fraction of 70% or more, and a water-dispersible resin having a critical surface tension of 25 dyn/cm or more in the coating layer is used.

Further, Patent Document 2 discloses a packaging paper having at least one heat-seal layer on at least one surface of a paper substrate for the purpose of providing a packaging paper that can reduce the amount of plastic used. The heat seal layer contains an ionomer, the dry coating amount of the heat seal layer is 2 to 10 g/m ² in all layers, and the heat seal layer is formed in two or more layers on at least one surface. A packaging paper characterized by

JP-A-9-158089 Japanese Patent No. 6580291

In the case of continuous production, water-resistant paper is produced while being wound on a roll, but at that time, the coated surface of the wound water-resistant paper sticks to the back surface of the water-resistant paper, causing peeling. (blocking) was a problem. In addition, water-resistant paper is heat-sealed when it is formed into a packaging container, etc. At this time, there is a problem that sticking to the forming machine (for example, a mandrel in the case of paper cups) occurs, resulting in poor formability. there were. Regarding these problems, Patent Documents 1 and 2 have room for improvement.
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 inventors have found that in a water-resistant paper having a water-resistant layer as the uppermost layer of at least one of the paper substrates, the water-resistant layer has at least two melting points, and the first melting point and the second melting point is within a specific range, a specific resin is contained in a specific content ratio, the amount of coating per side of the water-resistant layer is set to a specific value or more, and the paper substrate and the water-resistant layer It has been found that a water-resistant paper having excellent water resistance, blocking resistance, moldability and heat-sealability can be obtained by having a pigment coating layer therebetween. The present invention relates to the following <1> to <9>.
<1> A water-resistant paper having a water-resistant layer as the uppermost layer on at least one surface of a paper substrate,
The water-resistant layer has at least two melting points, the first melting point being 75° C. or higher and lower than 100° C., the second melting point being 100° C. or higher and 120° C. or lower,
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 other than ethylene (copolymer with unsaturated hydrocarbon) is 50/50 or more and 90/10 or less,
The amount of coating per side of the water-resistant layer is 3.0 g/m ² or more,
Having a pigment coating layer containing a pigment and a binder between the paper base 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 waterproof paper according to <1> or <2>, wherein the unsaturated hydrocarbon other than ethylene contains an α-olefin having 4 to 20 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 1. Water-resistant paper according to one.
<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 per one side of the pigment coating layer is 1 g/m ² or more and 20 g/m ² or less.
<9> A packaging container using the waterproof paper according to any one of <1> to <8>.

ADVANTAGE OF THE INVENTION According to this invention, while being excellent in water resistance, the water resistant paper excellent in blocking resistance, moldability, and heat-sealing property, and the packaging container which uses this water resistant paper can be provided.

[Water resistant paper]
The water-resistant paper of the present embodiment is a water-resistant paper having a water-resistant layer as the uppermost layer on at least one surface of the paper base material, and the water-resistant layer has at least two melting points. The 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, and the water-resistant layer comprises an ethylene-(meth)acrylic acid copolymer and ethylene and unsaturated other than ethylene. It contains a copolymer with a hydrocarbon, and the weight 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/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 substrate and the water-resistant layer.
According to the embodiments, it is possible to provide water-resistant paper that is excellent in water resistance, blocking resistance, moldability, and heat-sealability (particularly, side-sealability when forming a paper cup).
Although the detailed reason why the above effect is obtained is unknown, part of it is considered as follows. In general, from the viewpoint of heat-sealability, it is preferable that the heat-seal layer is easily melted by 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 be melted by heat. That is, it can be said that the former and the latter are in a trade-off relationship. In the present embodiment, the water-resistant layer has at least two melting points within the above range and contains a specific resin, so that the easiness (difficulty) of melting by heat becomes appropriate. As a result, while ensuring heat sealability (especially side sealability during paper cup molding), blocking does not easily occur during winding (that is, excellent blocking resistance), and the molding machine (mandrel) during heat sealing It is thought that sticking to the paper was suppressed, and a water-resistant paper with excellent moldability was obtained.
In addition, a pigment-containing layer is provided between the paper base material and the water-resistant layer, and the coating amount per one side of the water-resistant layer is 3.0 g/m ² or more. It is considered that a water-resistant paper having excellent properties was obtained.
Note that the effects of the present invention are not limited by the above mechanism.
The present embodiment will be described in further detail below.

In this specification, the numerical range represented by "X to Y" means a numerical range including X as a lower limit and Y as an upper limit. When numerical ranges are stated stepwise, the upper and lower limits of each numerical range can be combined arbitrarily. Moreover, "(meth)acryl" is a generic term including both acryl and methacryl.

<Paper substrate>
The paper substrate constituting the water-resistant paper of the present embodiment may have a single-layer structure or a multi-layer structure. In the case of multi-layered paper, the number of paper layers is not particularly limited, but is preferably 3 or more layers, more preferably 4 or more layers, still more preferably 5 or more layers, for example. By using three or more paper layers, the desired basis weight and paper thickness can be achieved, and the physical properties of the water-resistant paper can be adjusted within the desired range by adjusting the basis weight, freeness, etc. of each layer. . Although the upper limit of the number of paper layers is not particularly limited, it is preferably 7 layers or less, more preferably 6 layers or less.

Pulp constituting the paper substrate includes chemical pulp such as bleached hardwood kraft pulp (LBKP) and bleached softwood kraft pulp (NBKP); groundwood pulp (GP), pressurized groundwood pulp (PGW), and refiner mechanical pulp (RMP). , thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), chemi-mechanical pulp (CMP), chemi-grand pulp (CGP); waste paper pulp; non-wood fiber pulp such as kenaf, bagasse, bamboo, cotton, etc. ; Synthetic pulp and the like can be mentioned. These pulps may be used individually by 1 type, and may be used in combination of 2 or more type. Among them, it is preferable to use LBKP and NBKP together.

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

The content of broadleaf bleached kraft pulp (LBKP) relative to the total amount of pulp constituting the paper base is preferably 30% by mass or more, more preferably 40% by mass or more, and more preferably 40% by mass or more, from the viewpoint of moldability, smoothness and water resistance. is 45% by mass or more, more preferably 50% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 80% by mass or less, and even more preferably 70% by mass or less is.

The beating degree of the pulp is not particularly limited, but is preferably 200 mL or more, more preferably 350 mL or more, still more preferably 400 mL or more, and preferably 800 mL or less, in terms of Canadian Standard Freeness (CSF). 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 suitable 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, further preferably 380 mL or more, It is particularly preferably 410 mL or more, more preferably 480 mL or less, and particularly preferably 470 mL or less.
From the viewpoint of obtaining suitable 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, still more preferably 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 both LBKP and NBKP are used as the pulp constituting the paper substrate, and that the Canadian Standard Freeness (CSF) of each is within the above range.

Examples of additives to the paper substrate include pH adjusters (sodium hydrogen carbonate, sodium hydroxide, etc.), dry paper strength agents (polyacrylamide, starch, etc.), wet paper strength agents (polyamide polyamine epichlorohydrin resin, melamine-formaldehyde resin, or urea-formaldehyde resin), internal sizing agent (rosin type, alkylketene dimer, etc.), drainage retention improver, antifoaming agent, filler (calcium carbonate, talc, etc.), dye , a fixing agent (aluminum sulfate), and the like. These additives may be used singly or in combination of two or more. In addition, it is preferable to use the internal sizing agent and the wet paper strength enhancer in combination, since the water resistance of the paper substrate is improved. The content of the additive is not particularly limited, and may be within a commonly used range.

Although the basis weight of the paper base is not particularly limited, for example, in the case of packaging containers, preferably food containers, and more preferably paper cup applications, from the viewpoint of obtaining paper strength as packaging containers, it is preferably 150 g. /m ² or more, more preferably 180 g/m ² or more, still more preferably 200 g/m ² or more, still more preferably 220 g/m ² or more, and from the viewpoint of moldability, preferably 500 g/m ² or less , more preferably 430 g/m ² or less, still more preferably 380 g/m ² or less, even more preferably 330 g/m ² or less, and particularly preferably 280 g/m ² or less. The basis weight of the paper substrate is measured according to JIS P 8124:2011.

The thickness of the paper substrate is not particularly limited. For example, in the case of a packaging container, preferably a food container, and more preferably a paper cup, it is preferably 150 μm from the viewpoint of obtaining paper strength as a packaging container. Above, preferably 210 µm or more, more preferably 230 µm or more, still more preferably 240 µm or more, and from the viewpoint of moldability, preferably 650 µm or less, more preferably 480 µm or less, still more preferably 410 µm or less, and even more preferably 410 µm or less. 380 μm or less, particularly preferably 330 μm or less. The thickness of the paper substrate is measured according to JIS P 8118:2014.

The density of the paper substrate is preferably 0.4 g/cm ³ or more, more preferably 0.6 g/cm ³ or more, still more preferably 0.7 g/cm ³ or more, from the viewpoint of obtaining the desired strength, and , preferably 1.0 g/cm ³ or less, more preferably 0.9 g/cm ³ or less. The density of the paper base is calculated from the basis weight and thickness of the paper base obtained by the above-described measuring method.

[Method for producing paper substrate]
As a method for producing a paper substrate, there is a method of making paper from a pulp-containing stock. The paper material may further contain additives. Examples of the additive include those listed above. Stock can be prepared by adding additives to the pulp slurry. Pulp slurry is obtained by beating pulp in the presence of water. The pulp beating method and beating apparatus are not particularly limited, and may be the same as known beating methods and beating apparatus. The content of pulp in the stock is not particularly limited, and may be within a range commonly used. For example, it is 60% by mass or more and less than 100% by mass with respect to the total mass of the stock (solid content).

Papermaking of stock can be carried out by a conventional method. For example, there is a method in which a paper stock is cast on a wire or the like, dewatered to obtain a wet paper web, a plurality of wet paper webs are stacked as necessary, and this single-layer or multi-layer wet paper web is pressed and dried. . At this time, when a plurality of wet paper webs are not stacked, a single-layer paper is obtained, and when a plurality of wet paper webs are stacked, a multi-layer paper is obtained. When stacking a plurality of wet paper webs, an adhesive may be applied to the surface of the wet paper web (the surface on which other wet paper webs are stacked).

<Water resistant layer>
In this embodiment, the water-resistant paper has a water-resistant layer as the uppermost layer on at least one surface of the paper substrate.
The water-resistant paper of this embodiment may have water-resistant layers on both sides of the paper substrate.
The water-resistant layer has at least a resin component, and may contain various additives in addition to the resin component. The water-resistant layer is preferably formed by applying a coating liquid containing at least the resin component to the paper substrate, and the coating liquid is preferably a water-based coating liquid.

[Melting point]
The water resistant layer has at least two melting points. It may have two or more melting points, and may have three or more melting points, but it preferably has two melting points.
The first melting point is 75° C. or higher and lower than 100° C., preferably 78° C. or higher, more preferably 80° C. or higher, and even more preferably 82° C. from the viewpoints of improving heat sealability, blocking resistance, and moldability. °C or higher, and preferably 96 °C or lower, more preferably 92 °C or lower, and even more preferably 90 °C or lower.
In addition, from the same viewpoint, the second melting point is 100° C. or higher and 120° C. or lower, preferably 105° C. or higher, more preferably 108° C. or higher, still more preferably 110° C. or higher, and preferably 118° C. °C or less, more preferably 116°C or less, and even more preferably 114°C or less.
In addition, as described above, it is sufficient that the water-resistant layer has a melting point of 75° C. or more and less than 100° C. and at least two melting points of 100° C. or more and 120° C. or less. and may further 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 the water-resistant layer is thinly scraped off with a razor from the surface of the water-resistant paper provided with the water-resistant layer. About 5 mg of the scraped water-resistant layer is enclosed in an aluminum pan and measured using a differential scanning calorimeter (NEXTA DSC600, manufactured by Hitachi High-Tech Science Co., Ltd.). After raising the temperature from 30 ° C. to 150 ° C. at 10 ° C./min under a nitrogen atmosphere (first run), cooling to 30 ° C. at 10 ° C./min, and again from 30 ° C. to 150 ° C. at 10 ° C./min ( second run). The endothermic peak temperature of the second run is read and taken as the melting point.
As will be 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 points of the resins used may be approximated.

〔resin〕
By containing two or more resins having different melting points in the water-resistant layer, a plurality of melting points is imparted to the water-resistant layer. The resin is preferably a water-dispersible resin because the water-resistant layer is preferably formed by applying a water-based coating liquid to the paper substrate.
The resin contained in the water-resistant layer is not particularly limited. copolymers with unsaturated hydrocarbons other than ethylene), (meth)acrylic acid-based polymers (for example, acrylic acid 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, water-dispersible polymers such as polyether, and modified products thereof. .
Among these, at least ethylene-(meth)acrylic acid copolymer and ethylene and unsaturated hydrocarbons other than ethylene are used from the viewpoint of obtaining water-resistant paper excellent in water resistance, blocking resistance, moldability and heat sealability. It contains a copolymer with In addition to the above two resins, other resins such as ethylene-vinyl acetate copolymer may be contained.

(Ethylene-(meth)acrylic acid copolymer)
In this embodiment, the water-resistant layer contains an ethylene-(meth)acrylic acid copolymer. The ethylene-(meth)acrylic acid copolymer is believed to mainly contribute to the first melting point.
Here, the ethylene-(meth)acrylic acid copolymer may be blended as an ionomer. Note that the phrase "blended as an ionomer" means that an ionomer is used as a raw material at least when the water-resistant layer is produced, and after production, the water-resistant layer contains a resin in the form of an ionomer. It does not have to be contained.
Ionomers are polymers neutralized with cations. That is, all resins obtained by neutralizing ethylene-(meth)acrylic acid copolymers with cations correspond to 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 ions (Li ⁺ ), sodium ions (Na ⁺ ) and potassium ions (K ⁺ ); alkaline earth metal ions such as magnesium ions (Mg ²⁺ ) and calcium ions (Ca ²⁺ ); ions, zinc ions (Zn ²⁺ ), copper ions (Cu ²⁺ ) and other transition metal ions, and the like. Among these, the sodium ion is preferable as the metal ion from the viewpoint of availability and the like.
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, more preferably 60% by mass or more, still more preferably 65% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, further preferably 85% by mass. % by mass or less. The content of structural units derived from ethylene in the ethylene-(meth)acrylic acid copolymer can be confirmed by, for example, ¹³ C-NMR analysis.

As the ethylene-(meth)acrylic acid copolymer, commercially available products may be used. (registered trademark) A, Zaixen (registered trademark) AC, Chemipearl series (S-100, S-300, S-500) manufactured by Mitsui Chemicals, Inc., BC-212F manufactured by Henkel Japan Co., Ltd., Maruyoshi Chemical Co., Ltd. MYE-30ER, MYE-30MAZ manufactured by the company, Surlyn series manufactured by DuPont, Himilan series manufactured by Mitsui Dow Polychemical Co., Ltd., HYPOD2000 manufactured by Dow Chemical Japan Co., Ltd., RHOBARR320 manufactured by Toho Chemical Industry Co., Ltd. Hitech manufactured by Toho Chemical Industry Co., Ltd. Examples include SC-100 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, more preferably 78° C. or higher, more preferably 78° C. or higher, from the viewpoints of improving water resistance and heat-sealing properties, blocking resistance and moldability. 80° C. or higher, more preferably 82° C. or higher, and preferably lower than 100° C., more preferably 96° C. or lower, even more preferably 92° C. or lower, and even more preferably 90° C. or lower.

(Copolymer of ethylene and unsaturated hydrocarbon other than ethylene)
In this embodiment, the water-resistant layer contains, as a resin, a copolymer of ethylene and an unsaturated hydrocarbon other than ethylene together with the ethylene-(meth)acrylic acid copolymer. Copolymers of ethylene and unsaturated hydrocarbons other than ethylene are believed to primarily contribute 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, or a tetraene having four. It may also 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 to 20 carbon atoms, and 6 or more carbon atoms. More preferably, it contains an α-olefin of 16 or less, and more preferably contains an α-olefin of 6 or more and 12 or less carbon atoms.
The types of ethylene and unsaturated hydrocarbons other than ethylene and the copolymerization ratio thereof may be appropriately selected so that the melting point is within the desired range. The content of structural units derived from ethylene in the coalescence is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 65% by mass or more, and even more preferably 68% by mass or more, and It is preferably 95% by mass or less, 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 the copolymer of ethylene and 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 higher, more preferably 105° C. or higher, and still more preferably 105° C. or higher, from the viewpoints of improving heat sealability, blocking resistance, and moldability. is 108° C. or higher, even more preferably 110° C. or higher, and is preferably 120° C. or lower, more preferably 118° C. or lower, even more preferably 116° C. or lower, and even more preferably 114° C. or lower.

A copolymer of ethylene and an unsaturated hydrocarbon other than ethylene may be either a commercial product or a synthetic product. In the case of a commercial product, for example, DIC Graphics Co., Ltd. (Dick Seal E-806LV) or the like 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. Moreover, the obtained copolymer may be used by dispersing it in an aqueous medium by a known method.

The water-resistant layer contains, as resin components, an ethylene-(meth)acrylic acid copolymer and a copolymer of ethylene and an unsaturated hydrocarbon other than ethylene, and the ethylene-(meth)acrylic acid copolymer and The mass ratio of copolymers of ethylene and unsaturated hydrocarbons other than ethylene (ethylene-(meth)acrylic acid copolymer/copolymer of ethylene and unsaturated hydrocarbons other than ethylene) From the viewpoint of blocking property, moldability and heat sealability, it is 50/50 or more, preferably 60/40 or more, more preferably 70/30 or more, and 90/10 or less, preferably 85/ It is 15 or less, more preferably 80/20 or less, still 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, and the ethylene-(meth)acrylic acid copolymer and ethylene in the water-resistant layer and an unsaturated hydrocarbon other than ethylene, the total content of the copolymer is preferably 60% by mass or more, more preferably 65% by mass, from the viewpoint of water resistance, blocking resistance, moldability and heat sealability. % by mass or more, more preferably 70% by mass or more, even more preferably 75% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and still more Preferably, it is 80% by mass or less.

[Organic particles]
In the present embodiment, the water-resistant layer may contain organic particles in addition to the above resin from the viewpoint of improving blocking properties and moldability.
When the melting point or softening point of the organic particles is higher than the melting point of the resin component of the water-resistant paper, the organic particles do not melt or soften during the production and molding of the water-resistant paper, resulting in excellent blocking properties and moldability. is preferable from the viewpoint of being obtained.
The organic particles are preferably water-dispersible organic particles from the viewpoint that the water-resistant layer coating liquid is preferably an aqueous coating liquid. That is, the organic particles are preferably blended in the water-resistant layer coating liquid as an aqueous dispersion. From the viewpoint of improving heat-sealing properties and water resistance, it is preferable that the aqueous dispersion of organic particles contain little or no surfactant, dispersant, or the like.
Examples of organic particles include polyester particles, acrylic particles, polystyrene particles, nylon particles, silicone particles, polyolefin particles, etc. From the above viewpoints, polyolefin particles are preferred.
Examples of polyolefin resins constituting polyolefin particles include polymers of olefins such as ethylene, propylene, 1-butene, 1-pentene and 1-hexene. The polyolefin resin may be a homopolymer or a copolymer of the olefins exemplified above. Moreover, the polyolefin resin may be modified. Modification includes, for example, anion modification and cation modification, and it is also preferable to use polyolefin particles improved in dispersibility in water by modification.
More preferably, the polyolefin particles are at least one selected from the group consisting of polyethylene particles, polypropylene particles, and propylene-ethylene copolymer resin particles.
Polyethylene may be high-density polyethylene or low-density polyethylene, polypropylene may be high-density polypropylene or low-density polypropylene, and is not particularly limited. Also, the polyethylene and the polypropylene may be modified as described above.

Although the shape of the organic particles is not particularly limited, it is preferably spherical.
The average particle size of the organic particles is preferably 4 µm or more, more preferably 6 µm or more, and still more preferably 8 µm or more from the viewpoint of blocking resistance and moldability, and preferably 100 µm from the viewpoint of maintaining heat sealability. Below, it is more preferably 60 μm or less, still more preferably 40 μm or less, still more preferably 30 μm or less, and particularly preferably 15 μm or less.
If the average particle diameter of the organic particles is larger than or about the same as the film thickness of the water-resistant layer, unevenness is formed on the coating film surface, resulting in excellent blocking resistance and reducing the mandrel during molding. Sticking to is suppressed, and moldability is improved. The average particle diameter of the organic particles is preferably 0.8 to 7 times the film thickness of the water-resistant layer, more preferably 0.9 to 5 times, still more preferably 0.9 to 2.5 times. Below, it is more preferably 0.9 times or more and 1.5 times or less.
The average particle size of the organic particles is measured by a laser diffraction particle size distribution analyzer or a Coal counter method based on the principle of laser diffraction.

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

The water-resistant layer may contain other components in addition to the resins described above. For example, amine additives (aminomethylpropanol, dimethylaminomethylpropanol, dimethylaminoethanol, diethylaminoethanol etc.), higher fatty acids (oleic acid, stearic acid, palmitic acid, etc.), anti-sagging agents/anti-settling agents, anti-foaming agents, viscosity modifiers, leveling agents, wetting agents, dispersing agents, pigments, colorants such as coloring dyes etc. are exemplified.

The water-resistant layer is obtained by preparing a water-resistant layer coating solution containing a resin component and applying this to at least one surface of the paper substrate.
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 apparatuses 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 the present embodiment may have a water-resistant layer as the uppermost layer on at least one side of the paper base material, and preferably both sides of the paper base material.
By having water-resistant layers on both sides, for example, it can be suitably applied to applications where dew condensation occurs (for example, paper cups for cold water, etc.).

The water-resistant paper has a water-resistant layer as the top layer on at least one side. By having the water-resistant layer as the uppermost layer of the paper substrate, it is possible to impart water resistance and heat-sealing properties, as well as blocking resistance.
The amount of coating per side of the water-resistant layer is preferably 3.0 g/m ² or more, from the viewpoint of a water-resistant layer having excellent water resistance, heat sealability, blocking resistance, and moldability, and from the viewpoint of recyclability. is 3.5 g/m ² or more, more preferably 4.0 g/m ² or more, still more preferably 4.5 g/m ² or more, and preferably 20 g/m ² or less, more preferably 16 g/m ² 12 g/m 2 or less, more preferably 12 g/m ² or less.

In addition, you may measure the coating amount of a water resistant layer as follows.
A piece of water-resistant paper is cut into a size of 5 cm×5 cm, conditioned at 23° C. and 50% RH for 24 hours, and then weighed. 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. Then, the sample is immersed in a 1.0 mol/L ethylenediamine copper (II) solution for 12 hours to remove the remaining pulp (and pigment coating layer components if it has a pigment coating layer). The sample thus obtained from which the pulp and pigment components have been removed is air-dried at 23° C. and 50% RH for 24 hours, and then the mass is measured. By dividing the measured mass by the area of the water-resistant paper, the coating amount of the water-resistant layer is calculated. However, if the sample is too small to measure, observe the cross section of the water-resistant paper with a scanning electron microscope to determine the thickness of the water-resistant layer. may be calculated.

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

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

[Pigment]
Pigments are not particularly limited, and examples include kaolin, clay, engineered kaolin, delaminated clay, calcined clay, ground calcium carbonate, ground calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, Inorganic pigments such as silicic acid, silicates, colloidal silica, and satin white; solid-type, hollow-type, or core-shell-type organic pigments; These may be used individually by 1 type, and may use 2 or more types together. Among them, from the viewpoint of further improving water resistance and/or heat-sealing properties, it is preferably at least one selected from the group consisting of kaolin and calcium carbonate, more preferably containing at least kaolin, and kaolin and carbonate It is more preferable to use together with calcium.

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 is preferably 20 μm or less, more preferably 10 μm or less, further preferably 4 μm or less, and even more preferably 4 μm or less. It is preferably 3 μm, particularly preferably 2.5 μm or less. When the average particle diameter of the pigment is within the above range, a water-resistant layer having excellent smoothness can be obtained, and water-resistant paper having excellent water resistance and heat-sealing properties can be obtained, which is preferable. The average particle size of the pigment can be obtained using a laser diffraction particle size distribution analyzer based on the principle of laser diffraction, and the value measured from the measured particle size distribution is adopted.

As pigments, a pigment having an aspect ratio of 3 or more (pigment 1) and a pigment having an aspect ratio of less than 3 (pigment 2) can be used in combination from the viewpoint of improving the water resistance of the undercoat layer, and It is preferable from the viewpoint of adjusting the viscosity of the working fluid and the 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 Pigment 2 is less than 3, preferably 2 or less, and 1 or more. A pigment having the above aspect ratio is exemplified by ground calcium carbonate.
The aspect ratio of the pigment is the shape factor obtained by dividing the average particle size by the average thickness. For the average thickness, a few drops of a pigment diluted with a solvent or the like are dropped on a glass substrate, dried naturally, and 20 points of the pigment oriented on the glass substrate are extracted using a transmission electron microscope. Measure. Then, among the thicknesses measured at 20 points, the average value of the thicknesses at the remaining 14 points, excluding the thicknesses at the three upper and lower values, is obtained, and the average value is taken as the average thickness.

When calcium carbonate and kaolin are used together as pigments, the mass ratio of calcium carbonate content to 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, and 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, water-resistant paper with excellent water resistance and heat-sealing properties can be obtained. preferable. On the other hand, the coating liquid for the pigment coating layer containing kaolin (coating liquid for the pigment coating layer) tends to have a high viscosity. Since it becomes necessary to lower the concentration and the amount of coating per application decreases, a large number of applications are required, which tends to lower the efficiency of application.
By using both calcium carbonate and kaolin as pigments and using the above mass ratio, a pigment coating layer with excellent smoothness can be obtained, and the coating property is excellent, and the amount of coating per application is large. Since the pigment coating layer can be formed with a small number of coatings, the coating efficiency is excellent, which is preferable.

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

<Binder>
The binder contained in the pigment coating layer is not particularly limited, but styrene-butadiene resins; acrylic resins such as methyl (meth)acrylate copolymers and styrene-acrylic copolymers; ethylene-acrylic acid copolymers; Polymers, ethylene-unsaturated carboxylic acid copolymers such as methacrylic acid copolymer; -Butadiene-based resins are more preferred, and styrene-acrylic copolymers are even more preferred.
The styrene-acrylic copolymer is preferably a copolymer of styrene and (meth)acrylic ester, more preferably a copolymer of styrene and acrylic ester, and a copolymer of styrene and alkyl acrylate. Polymers are more preferred. In this case, it is particularly preferable that the alkyl portion of the alkyl ester has from 1 to 8 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, and even more preferably 18% by mass, from the viewpoint of water resistance and heat sealability. % by mass or more, and from the viewpoint of suppressing roll contamination during coating, preferably 80% by mass or less, more preferably 60% by mass or less, even more preferably 40% by mass or less, and even more preferably 30% by mass. That's it.

In the pigment coating layer, the weight ratio of the pigment to the content of the binder (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 and the binder is equal to or higher than the above lower limit, since roll contamination during production is suppressed and the workability is excellent. If the binder content is high, roll contamination may occur during production.
On the other hand, when the mass ratio of the pigment and the binder exceeds the above upper limit, that is, when the pigment content in the pigment coating layer is too large, pores derived from the pigment are generated in the pigment coating layer, resulting in may enter into the pigment-coated layer, resulting in non-uniformity in the film thickness of the water-resistant layer. If the film thickness of the water-resistant layer becomes non-uniform, water may permeate through a portion with a small film thickness, resulting in a decrease in water resistance. In addition, if the film thickness of the water-resistant layer becomes non-uniform, it may be difficult to adhere to the portions where the film thickness is small, and the desired heat-sealing property may not be obtained. On the other hand, when the pigment/binder mass ratio is within the above range, that is, when the pigment content in the pigment coating layer is appropriately low, the above phenomenon is suppressed, so that the film thickness of the water-resistant layer is uniform. It is preferable because it has good properties, and as a result, a water-resistant paper having excellent water resistance and heat-sealing properties 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, still 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 the solid content 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 8 g/m ² or less.
A method for forming the pigment coating layer is not particularly limited, but a method of coating a paper base material with a dispersion containing a pigment and a binder and drying the layer is preferable.
Aqueous dispersions are preferred as dispersions containing pigments and resin binders.
In addition to the pigment and the binder, the pigment-coated layer may contain the components exemplified as other components for the water-resistant layer, and preferably contains an antifoaming agent.

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, water resistance agents, colorants, surfactants, and the like. Examples of adhesives include proteins such as casein, soybean protein, and synthetic proteins; Examples thereof include cellulose derivatives such as ethyl cellulose and hydroxymethyl cellulose.

The water-resistant paper of the present embodiment may have water-resistant layers on both sides of the paper base material. For example, the paper base material, the pigment coating layer, and the water-resistant layer are laminated in this order. It may have a structure in which the first water-resistant layer, the pigment coating layer, the paper substrate and the second water-resistant layer are laminated in this order. It may also have a configuration in which a first water-resistant layer, a water-resistant undercoat layer, a pigment coating layer, a paper substrate and a second water-resistant layer are 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 print layer, a water vapor barrier layer, an oxygen barrier layer, an oxygen absorption layer, and the like. The printed layer may be formed using known inks such as oil-based inks, water-based inks, and biomass inks. The print layer may be formed on one surface of the water-resistant paper, or may be formed on a part of the surface. That is, the water-resistant paper of this embodiment may be printed on at least one surface (for example, the printed surface) in whole or in part. The contents to be printed may be patterns, designs, information (ingredients, expiration date, QR code (registered trademark), etc.).

<Physical properties of water-resistant paper>
(air permeability)
The water-resistant paper of the present embodiment preferably has an air permeability (Oken type air permeability) of 1,000 seconds or more, more preferably 10,000 seconds or more, and still more preferably 25,000 seconds or more. Even more preferably, it is 99,999 seconds or longer. Although the upper limit of air permeability is not particularly limited, it is, for example, 1,000,000 seconds or less.
By setting the air permeability within the above range, the air-imperviousness of the paper is increased, and a water-resistant paper having even better water resistance can be obtained. In particular, when two or more water-resistant layers are provided, or when a pigment layer is provided as a lower layer of the water-resistant layer, the air permeability can be increased.
Air permeability is measured according to JIS P 8117:2009.

(Cobb water absorbency for water at 20°C)
From the viewpoint of water resistance to cold water, the water-resistant paper of the present embodiment preferably has a Cobb water absorbency of 40 g/m ² or less, more than It is preferably 20 g/m ² or less, more preferably 15 g/m ² or less, still more preferably 10 g/m ² or less. The lower limit is not particularly limited.
Cobb water absorbency is measured according to JIS P 8140:1998.

(Cobb water absorbency 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 absorbency of 100 g/m ² or less for water at 90°C in a measurement time of 30 minutes on the surface provided with the water-resistant layer. It is more preferably 60 g/m ² or less, still more preferably 30 g/m ² or less, and even more preferably 20 g/m ² or less. The lower limit is not particularly limited.
Cobb water absorbency is measured according to JIS P 8140:1998.

(Blocking resistance)
The water-resistant paper of the present embodiment is preferably excellent in blocking resistance, and after heating and pressurizing for 24 hours at 40 ° C. and a relative humidity of 90% at a pressure of 2 kg / cm ² , after cooling to room temperature, the water-resistant paper When peeled off, it is preferable that there is little or no resistance, and that it is peeled off without resistance is more preferable.

(Oil resistance)
The water-resistant paper of the present embodiment is JAPPAN TAPPI No. 2 on the surface provided with the water-resistant layer. 41 (kit method) (kit value, KIT value) 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.

(Recycling rate (pulp recovery rate after re-disintegration))
The heat-sealable paper of the present embodiment preferably has a recycling rate represented by a pulp recovery rate after re-maceration of 85% or more, more preferably 90% or more, and still 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 of water-resistant paper (pulp recovery rate after re-maceration) is a value measured by the method described in Examples below.

(Heat sealability)
In the water-resistant paper of the present embodiment, the water-resistant layer preferably has heat-sealing properties.
The conditions for heat sealing are not particularly limited, but the temperature during heat sealing is, for example, 60° C. or higher and 300° C. or lower, the pressure during heat sealing is, for example, 0.05 MPa or higher and 10 MPa or lower, and the pressurization time is, for example, 0. .1 second or more and 15 seconds or less.

(basis weight)
The basis weight of the water-resistant paper of the present embodiment is not particularly limited. , preferably 150 g/m ² or more, more preferably 180 g/m ² or more, still more preferably 220 g/m ² or more, still more preferably 240 g/m ² or more, particularly preferably 250 g/m ² or more, and From the viewpoint of moldability, it is preferably 500 g/m ² or less, more preferably 450 g/m ² or less, even more preferably 400 g/m ² or less, even more preferably 350 g/m ² or less, and particularly preferably 300 g/m ² or less. is. The basis weight of water-resistant paper is measured according to JIS P 8124:2011.

(thickness)
The thickness of the water-resistant paper of the present embodiment is not particularly limited, but for example, a packaging container, preferably a food container, and more preferably a paper cup, from the viewpoint of obtaining strength as a packaging container. , preferably 150 μm or more, more preferably 180 μm or more, still more preferably 230 μm or more, still more preferably 250 μm or more, particularly preferably 270 μm or more, and from the viewpoint of moldability, preferably 650 μm or less, more preferably 500 μm Below, it is more preferably 430 μm or less, still more preferably 400 μm or less, and particularly preferably 350 μm or less. The thickness of the water resistant layer is measured according to JIS P 8118:2014.

(Application of water-resistant paper)
Since the water-resistant paper of the present embodiment has excellent heat-sealing properties and water resistance, it can be used in packaging containers such as cups, plates, trays, lids, pouches, and tube-shaped containers; cutlery such as spoons, forks, knives, and chopsticks; It can be suitably used for soft packaging materials such as straws, wrapping paper, packaging bags, lids and labels. The packaging container is formed, for example, by printing on the surface of water-resistant paper as necessary, punching into a shape corresponding to the shape of the packaging container to be manufactured, bending, and bonding the overlapping portions by 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 water-resistant paper. Moreover, since the water-resistant paper of the present embodiment is also excellent in oil resistance, it can be suitably used for food packaging applications.
The contents of the packaging container may be food or non-food. Moreover, the contents of the packaging container may be liquid, solid, or gel. The contents of the packaging container are not particularly limited. Ramen, etc.), microwaveable food, luxury food (yogurt, ice cream, jelly, pudding, etc.), foods such as prepared foods; pharmaceuticals; car wax, shampoo, rinse, detergent, bath powder, hair dye, toothpaste, etc. chemical products;
The water-resistant paper of the present embodiment is preferably used for liquid containers such as paper cups, their lids, and other paper containers that require water resistance (for example, paper trays). When used for liquid containers, the water-resistant layer preferably has heat-sealing properties (particularly, in the case of paper cups, side-sealing properties) from the viewpoint of formability.
To give an example of the molding of a liquid container (paper cup), printing is applied to the front or back of the water-resistant paper as needed, punching into a shape corresponding to the shape of the liquid container to be manufactured, and a mandrel mold. After winding and side-sealing to form a body, a paper cup is formed by bottom forming and top curling.
The water-resistant paper of this embodiment is excellent in water resistance, heat-sealability, and moldability.
The water-resistant paper of the present embodiment is not limited to the above applications, and may be used as packaging paper.
The packaging container made of water-resistant paper of this embodiment uses less plastic than conventional packaging containers made of laminated paper. Furthermore, when the packaging container made of conventional laminated paper is reused as waste paper, it is necessary to defiberize it using a pulper with high defiberization performance. It can be disintegrated even with high-performance pulpers, and has excellent recyclability. A packaging container made of the water-resistant paper of the present embodiment can be subjected to washing, cutting, macerating, etc. to prepare a pulp slurry, and paper can be manufactured using the obtained pulp slurry. 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. Moreover, it is also possible to manufacture packaging containers (for example, tissue boxes, sleeves of paper cups, etc.) by processing paper made into paper.

EXAMPLES The barrier laminate of the present invention will be described in more detail below with reference to Examples, but the present invention is not limited to these. "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. Unless otherwise specified, the measurement was performed in an environment of 23° C.±1° C. and 50±2% relative humidity as described in JIS P8111:1998.

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

<Measurement of melting point>
The melting point of the dried and solidified water-based resin emulsion was measured by the following procedure.
The aqueous resin emulsion was applied onto a PET film using a bar coater and dried at 120° C. to form a film. After repeating the application and drying until the thickness of the film reached about 20 to 50 μm, the film was peeled off from the PET film to obtain a dried solidified product of the water-based resin emulsion.
5 mg of the dried solid was sealed in an aluminum pan and measured using a differential scanning calorimeter (NEXTA DSC600, manufactured by Hitachi High-Tech Science Co., Ltd.). After raising the temperature from 30 ° C. to 150 ° C. at 10 ° C./min under a nitrogen atmosphere (first run), cooling to 30 ° C. at 10 ° C./min, and again from 30 ° C. to 150 ° C. at 10 ° C./min ( 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 solid sample obtained by the above method and 70 mL of xylene are added to a 100 mL Erlenmeyer flask and dissolved by heating on an oil bath at 135 ° C. for about 20 minutes. While the solution was kept at about 100° C., titration with an indicator was performed with a 0.1 mol/L sodium hydroxide benzyl alcohol solution, 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]
Raw materials used in Examples and Comparative Examples are as follows.
<Water-based resin emulsion>
・Commercially available water-based resin emulsion A: Solid content concentration is 43% by mass, B-type viscosity at 23 ° C. is 3000 mPa s, specific gravity is 0.97, melting point 1 of dried solidified product is 86.8 ° C., melting point 2 is 112.7 ° C. , The acid value of the dry solidified product is 26.4 mg KOH / g-solid
The components contained in the aqueous resin emulsion A were analyzed by the following procedure. The aqueous 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 residue was vacuum dried 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 (PY-3030D, manufactured by FRONTIER LAB). 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 contain
In addition, the mass ratio of the ethylene-acrylic acid copolymer and the copolymer of ethylene and the α-olefin having 6 to 10 carbon atoms (ethylene-acrylic acid copolymer: ethylene and 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 the α-olefin having 6 to 10 carbon atoms in the solid content of the aqueous resin emulsion A is 68.9% by mass, Further, the total content of the ethylene-acrylic acid copolymer and the copolymer of ethylene and the α-olefin having 6 to 10 carbon atoms in the resin component of the aqueous 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. 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, B-type viscosity at 23 ° C. 105 mPa s, chemical specific gravity 0.99, dry solidification Melting point of solid: 92.8°C, acid value of dried solid: 16.6mgKOH/g-solid
Ethylene-acrylic acid copolymer amine salt ionomer emulsion: trade name "201103PX.S", manufactured by Michael Mann Japan LLC, chemical concentration 20 mass%, B-type viscosity at 23 ° C. 100 mPa s, chemical specific gravity 1.00, Melting point of dried solid: 91.5°C Acid value of dried solid: 47.2 mgKOH/g-solid
・ Ethylene-acrylic acid copolymer ammonium salt ionomer emulsion: Zaixen AC, manufactured by Sumitomo Seika Co., Ltd., chemical concentration 28% by mass, B-type viscosity at 23 ° C. 700 mPa s, chemical specific gravity 1.00, melting point of dry solidified product 82.2 ° C., acid value of dry solidified product 62.2 mg KOH / g-solid

<Antifoaming agent>
・ Antifoaming agent: trade name “Bismer KS-38E”, manufactured by Nisshin Chemical Laboratory Co., Ltd.

<Organic particles>
・Organic particles A: Low molecular weight PE + modified PO (modified polyolefin, low molecular weight PO), trade name “Chemipearl W310”, Mitsui Chemicals, Inc., chemical concentration 39% by mass, 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, 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 while stirring to prepare a pigment slurry having a concentration of 70% by mass. Next, a 48% aqueous sodium hydroxide solution was added to bring the pH to 11.5. Subsequently, 25 solid parts of acrylic latex (Acronal S 728ap manufactured by BASF) and 0.31 solid parts of an antifoaming agent (manufactured by Nisshin Chemical Laboratory Co., Ltd.: Bismer KS38E) were added, and the coating liquid concentration was 63 mass. % by adding water. The completed coating liquid had a B-type viscosity of 800 mPa·s (liquid temperature of 20° C.) and a pH of 9.5.

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

(c) Preparation of Pigment Coating Layer Coating Solution C In the same manner as the pigment coating layer coating solution A, pigment A coating liquid C for coating layer was prepared. The completed coating liquid had a B-type viscosity of 600 mPa·s (liquid temperature of 20° C.) and a pH of 9.5.

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

(e) Preparation of topcoat coating liquid A 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 solid content concentration is 43% by mass. A coating liquid A was prepared.

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

(g) Preparation of Topcoat Coating Liquid C Ethylene-acrylic acid copolymer amine salt ionomer emulsion (trade name “201103PX.S”) and an antifoaming agent are added to the ethylene-acrylic acid copolymer amine in the solid content. A top coating solution C containing a salt ionomer content of 99.9% by mass, an antifoaming agent content of 0.1% by mass, and a solid concentration of 20% by mass was prepared.

(h) Preparation of Topcoat Coating Liquid D Ethylene-acrylic acid copolymer ammonium salt ionomer emulsion (Zaichsen AC) and antifoaming agent are blended, and the content of ethylene-acrylic acid copolymer ammonium salt ionomer in the solid content was 99.9% by mass, the content of the antifoaming agent was 0.1% by mass, and a coating liquid D having a solid content concentration of 28% by mass was prepared.

(i) Preparation of topcoat coating liquid E Water-based resin emulsion A, organic particles A, and antifoaming agent are blended so that the content of organic particles A in the solid content is 4% by mass, and the content of antifoaming agent is A coating liquid E having a solid 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 so that 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, wet paper 0.15 parts by mass of a strength enhancer and 1.45 parts by mass of aluminum sulfate were added to prepare stock for outer layers (first layer and fifth layer).
Similarly, 0.8 parts by mass of a weakly acidic rosin sizing agent with respect to 100 parts by mass (in terms of solid content) of pulp slurry in which beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) are mixed at a ratio of 60% and 40% , 0.15 parts by mass of a wet strength agent, and 1.7 parts by mass of aluminum sulfate were added to prepare a stock for the middle layers (second to fourth layers).
Using these stocks, paper was made using a fourdrinier paper machine with five layers. As it was, coating was carried out by an on-machine method using a rod blade coater in the latter stage of the paper machine. Coat the front surface (wetted surface) of the paper substrate with the coating liquid A for the pigment coating layer with a first-stage rod coater so that the coating amount (solid content) is 5 g/m ² . and dried to form a pigment coating layer. Subsequently, topcoat coating liquid A was applied to the pigment coating layer on the front surface (wetted surface) so that the coating amount (solid content) was 2.5 g / m ² on the second stage blade coater. A topcoat layer (water-resistant layer) having a thickness of 2.4 μm was formed by coating and drying to form a water-resistant paper. The papermaking speed was 600 m/min.

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

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

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

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

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

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

[Example 7]
The same procedure as in Comparative Example 1 was performed except that the coating amount (solid content) of the topcoat layer (water-resistant layer) was changed to 12 g/m ² to form a topcoat layer (water-resistant layer) with a thickness of 11.5 µm. Then, a water resistant paper was produced.

[Comparative Example 2]
A water-resistant paper was prepared in the same manner as in Example 6, except that the coating liquid for the top coat was changed to the coating liquid B.

[Comparative Example 3]
A water-resistant paper was produced in the same manner as in Example 6, except that the coating solution C was used as the top coating solution.

[Comparative Example 4]
A water-resistant paper was produced in the same manner as in Example 6, except that the coating liquid for overcoating was changed to coating liquid D.

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

[Example 9]
In the same manner as in Example 8 except that the coating amount (solid content) of the topcoat layer (water-resistant layer) was changed to 10 g / m ² , the thickness of the topcoat layer (water-resistant layer) was 9.5 μm. A paper sheet was prepared.

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

[Example 11]
In the same manner as in Example 10 except that the coating amount (solid content) of the topcoat layer (water-resistant layer) was changed to 10 g / m ² , the thickness of the topcoat layer (water-resistant layer) was 9.6 μm. A paper sheet was prepared.

[Example 12]
A water-resistant paper was prepared in the same manner as in Example 2, except that the pigment coating layer coating liquid was changed to the pigment coating layer coating liquid B.

[Example 13]
A water-resistant paper was prepared in the same manner as in Example 2, except that the pigment coating layer coating liquid was changed to the pigment coating layer coating liquid C.

[Example 14]
A water-resistant paper was prepared in the same manner as in Example 2, except that the pigment coating layer coating solution was changed to the pigment coating layer coating solution D.

[Evaluation method]
The water-resistant papers of Examples 1 to 14 and Comparative Examples 1 to 4 were subjected to the following measurements and evaluations. Table 1 shows the results.

<Basis weight>
The basis weight of the paper substrate was measured according to JIS P 8124:2011.

<Paper thickness>
The paper thickness of the paper substrate was measured according to JIS P 8118:2014.

<Air permeability (Oken type air permeability)>
The air permeability of the water-resistant paper was measured according to JIS P 8117:2009.

<Cobb water absorption>
The Cobb water absorbency was measured by cutting the obtained water-resistant paper into 13 cm squares and contacting the surface of the water-resistant paper with deionized water at 20 ° C. or 90 ° C. for 30 minutes in accordance with JIS P 8140: 1998. was measured according to JIS P 8140:1998 from the difference in mass.

<Recyclability>
About 50 g of the resulting water-resistant paper was weighed out in absolute dry mass, cut into pieces of about 2 cm square by hand without using a knife, tap water was added to make the concentration 3%, and a disintegrator (manufactured by Kumagai Riki Kogyo Co., Ltd.) No. 2532) was treated at 21° C. and 3000 rpm for 10 minutes to prepare a pulp slurry in which the pulp fibers were completely disaggregated. 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 absolute dry residue mass to the charged absolute dry mass was defined as the residue rate, and the recycle rate was obtained by subtracting this from 100% to calculate the permeability of the pulp.

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

<Blocking resistance>
Cut the sample into 5 cm squares, stack them so that the front surface (wetted surface) and the back surface are in close contact, sandwiched between blocking testers and pressurized at a pressure of 2 kg / cm ² at a temperature of 40 ° C and a relative humidity of 90%. The pressure was maintained under these conditions for 24 hours. After 24 hours, the film was removed from the conditions of 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. If it is A and B, it can be judged that it can be practically used.
〔Evaluation criteria〕
A: Peeled off without resistance B: Slightly resisted C: Great resistance, the coated surface peeled off slightly D: Considerable resistance and the coated surface peeled off (paper peeling)

<Side sealability (heat sealability)>
The resulting water-resistant paper was cut into a size of 15 cm in the vertical direction and 25 cm in the horizontal direction, and rolled horizontally so that the front surface (wetted surface) was on the inside to form a cylinder with a diameter of 7.5 cm. The heat-sealing property of the portion where the paper overlaps (the side portion of the body of the paper cup, 0.7 cm in side seal width) was evaluated based on the following criteria. The 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 an adhesion time of 2 seconds. If it is A or B, it can be judged that it can be used practically.
〔Evaluation criteria〕
A: The adhesion strength is strong, and even if the shape is distorted by pushing from the outside of the cylinder by hand, it is not easily peeled off.
B: Adhesive strength is high, and even if the shape is distorted by pushing from the outside of the cylinder by hand, it does not peel off easily.
C: Adhesive strength is slightly strong, and even if the shape is distorted by pushing from the outside of the cylinder by hand, it does not peel off easily. .
D: Adhesive strength is slightly weak, and more than half of the adhered portion is peeled off when the shape is distorted by pushing from the outside of the cylinder by hand.
E: No adhesion at all.

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

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

The water-resistant papers of Examples 1 to 14 were excellent in water resistance, blocking resistance, moldability and heat-sealability.
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 , was insufficient in water resistance and inferior in moldability. 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-sealing properties, but sticking to the mandrel, poor moldability, and blocking resistance. was inferior to

Claims (9)

A water-resistant paper having a water-resistant layer as the uppermost layer on at least one surface of the paper substrate,
The water-resistant layer has at least two melting points, the first melting point being 75° C. or higher and lower than 100° C., the second melting point being 100° C. or higher and 120° C. or lower,
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 other than ethylene (copolymer with unsaturated hydrocarbon) is 50/50 or more and 90/10 or less,
The amount of coating per side of the water-resistant layer is 3.0 g/m ² or more,
Having a pigment coating layer containing a pigment and a binder between the paper base and the water-resistant layer,
water resistant paper. The water resistance 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 resistance layer is 60% by mass or more. nature paper. 2. The water-resistant paper according to claim 1, wherein the unsaturated hydrocarbon other than ethylene contains an α-olefin having 4 to 20 carbon atoms. 2. The water-resistant paper according to claim 1, wherein the pigment-coated layer has a weight ratio of pigment content to binder content (pigment/binder) of 50/50 or more and 90/10 or less. A water-resistant paper according to claim 1, wherein said binder contains a styrene-acrylic copolymer. 2. The water-resistant paper according to claim 1, wherein the pigment has an average particle size of 0.1 [mu]m or more and 4 [mu]m 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. 1. The water-resistant paper according to 1. 2. The water-resistant paper according to claim 1, wherein the coating amount per one side of the pigment coating layer is 1 g/m< ² > or more and 20 g/m< ² > or less. A packaging container using the water-resistant paper according to any one of claims 1 to 8.