Waterproof paper and packaging container

Abstract

To provide waterproof paper having sufficient waterproof property to cold water and hot water and having excellent edge wick resistance to not only hot water but also to an aqueous lactic acid solution, and a packaging container using the waterproof paper.SOLUTION: The waterproof paper has, on one surface of a paper substrate, an undercoat layer (1) and a waterproof layer (1) in this order, and has, on the other surface of the paper substrate, an undercoat layer (2) and a waterproof layer (2) in this order. In the waterproof paper, the paper substrate contains a rosin-based size agent, the undercoat layer (1) and the undercoat layer (2) include a pigment-containing layer, or the undercoat layer (1) includes a pigment-containing layer and the undercoat layer (2) includes a polyethyleneimine-containing layer. The waterproof paper shows a specified Cobb water absorbency on a surface having the undercoat layer (1) and the waterproof layer (1) and shows a specified edge wick value.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to waterproof paper and packaging containers made using the same. [Background technology]

[0002] Plastic products have traditionally been used for various containers for drinks, food, etc., and food cutlery (e.g., chopsticks, spoons, forks, etc.), but there is a desire to switch to paper products in order to reduce the environmental impact. Conventionally, polyethylene-laminated paper, which has a polyethylene film laminated on one side of a base paper, has been used for various containers for beverages, foods, etc., but there has been a problem in that it is difficult to remove the polyethylene film when recycling, making it poorly recyclable. In order to address these problems, attempts have been made to impart water resistance and other properties to the paper by imparting properties during the papermaking process or by coating. Patent Document 1 discloses a paper having at least one water-resistant layer containing an ethylene-acrylic acid copolymer ionomer on at least one side of a paper substrate, with the aim of providing a waterproof paper that is water-resistant not only to cold water but also to hot water and has excellent edge wick resistance. The paper has an edge wick value of 2.0 g / 1000 mm for 1% by mass octylphenol ethoxylate (average number of moles of oxyethylene groups added: 9.5) at 70°C after immersion for 10 minutes. 2 The following waterproof paper is described. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2022-11686 Summary of the Invention [Problem to be solved by the invention]

[0004] Through investigations by the present inventors, it was found that the waterproof paper described in Patent Document 1 has sufficient water resistance to cold water and hot water, and further has sufficient edge wicking resistance to hot water, but there is room for improvement in edge wicking resistance to lactic acid aqueous solution. The present invention aims to provide water-resistant paper that has sufficient water resistance to cold water and hot water and also has excellent edge wicking resistance not only to hot water but also to an aqueous lactic acid solution, and to provide a packaging container made using said water-resistant paper. [Means for solving the problem]

[0005] The inventors discovered that the above-mentioned problems can be solved by providing a water-resistant paper having a paper base containing a rosin-based sizing agent and a primer layer and a water-resistant layer, in that order, on both sides of the paper base, wherein the primer layers on both sides of the paper base contain a pigment-containing layer, or the primer layer on one side of the paper base contains a pigment-containing layer and the primer layer on the other side of the paper base contains a polyethyleneimine-containing layer, and wherein the ``one side of the paper base'' has a specific Cobb water absorbency and the water-resistant paper has specific edge wick resistance, and thus completed the present invention. That is, the present invention provides the following: <1> ~ <12> Regarding. <1> A paper substrate having an undercoat layer (1) and a water-resistant layer (1) in this order on one side thereof, A waterproof paper having a primer layer (2) and a waterproof layer (2) in this order on the other side of the paper substrate, The paper base material contains a rosin-based sizing agent, The undercoat layer (1) and the undercoat layer (2) comprise a pigment-containing layer, or the undercoat layer (1) comprises a pigment-containing layer, and the undercoat layer (2) comprises a polyethyleneimine-containing layer; The surface of the waterproof paper having the undercoat layer (1) and the waterproof layer (1) has a Cobb water absorption of 20 g / m2 in water at 90°C for a contact time of 30 minutes. 2 is as follows: Edgewick value in 70°C water after 20 minutes of contact is 0.80g / 1000mm 2 is as follows: The Edgewick value for a 20% by weight aqueous solution of lactic acid at 23°C after a contact time of 30 minutes is 0.70 g / 1000 mm 2 Below is the Water resistant paper. <2> The coating weight of the pigment-containing layer is 2 g / m per side. 2 That's all. <1> The water-resistant paper described in <3> The coating amount of the polyethyleneimine-containing layer is 0.1 g / m 2 That's all. <1> or <2> The water-resistant paper described in <4> the pigment-containing layer contains a pigment and latex, and the mass ratio of the latex to the pigment in the pigment-containing layer (latex / pigment) is 10 / 90 or more and 50 / 50 or less; <1> ~ <3> 1. The waterproof paper according to any one of the preceding items. <5> The glass transition temperature of the latex is -10°C or higher and 40°C or lower. <4> The water-resistant paper described in <6> The latex comprises a styrene-acrylic copolymer latex. <4> or <5> The water-resistant paper described in <7> the polyethyleneimine-containing layer contains at least one selected from the group consisting of polyvinyl alcohol and starch; <1> ~ <6> 1. The waterproof paper according to any one of the preceding items. <8> The paper substrate contains a polyamide polyamine epichlorohydrin resin. <1> ~ <7> 1. The waterproof paper according to any one of the preceding items. <9> The paper substrate contains a starch-based dry strength agent. <1> ~ <8> 1. The waterproof paper according to any one of the preceding items. <10> The film has at least one of a water-resistant layer (1) and a water-resistant layer (2) as the uppermost layer. <1> ~ <9> 1. The waterproof paper according to any one of the preceding items. <11> For packaging containers, <1> ~ <10> 1. The waterproof paper according to any one of the preceding items. <12> <1> ~ <11> A packaging container made using the waterproof paper described in any one of the above. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide water-resistant paper that has sufficient water resistance to cold water and hot water, and also has excellent edge wicking resistance not only to hot water but also to an aqueous lactic acid solution, and to provide a packaging container made using said water-resistant paper. DETAILED DESCRIPTION OF THE INVENTION

[0007] The waterproof paper of this embodiment has a primer layer (1) and a water-resistant layer (1) in this order on one side of a paper base, and a primer layer (2) and a water-resistant layer (2) in this order on the other side of the paper base, wherein the paper base contains a rosin-based sizing agent, and the primer layer (1) and the primer layer (2) comprise pigment-containing layers, or the primer layer (1) comprises a pigment-containing layer and the primer layer (2) comprises a polyethyleneimine-containing layer, and the Cobb water absorbency of water at 90°C on the side of the waterproof paper having the primer layer (1) and the water-resistant layer (1) for a contact time of 30 minutes is 20 g / m 2 The Edgewick value in 70°C water after a contact time of 20 minutes is 0.80g / 1000mm or less. 2 The Edgewick value for a 20% by mass aqueous solution of lactic acid at 23°C after a contact time of 30 minutes is 0.70 g / 1000 mm 2 The following is the result. The water-resistant paper of this embodiment has sufficient water resistance to both cold water and hot water, and has excellent edge wicking resistance not only to hot water but also to lactic acid aqueous solution. Because of its excellent edge wicking resistance to hot water, it can be used favorably for foods containing hot water, such as hot coffee and ramen. Furthermore, because of its excellent edge wicking resistance to lactic acid aqueous solution, it can be used favorably for dairy products, such as yogurt and ice cream. In other words, the water-resistant paper of this embodiment can be used for a wide range of food applications. The mechanism by which the above effects are achieved is unclear, but is speculated as follows. Because the rosin-based sizing agent contained in the paper substrate has excellent heat resistance and water repellency, the inclusion of the rosin-based sizing agent improves the water resistance of the paper substrate itself against cold and hot water. Furthermore, the water-resistant paper of this embodiment has a water-resistant layer on the paper substrate via an undercoat layer containing a pigment-containing layer or an undercoat layer containing a polyethyleneimine-containing layer, thereby enhancing adhesion between the paper substrate and the water-resistant layer and / or improving the smoothness of the water-resistant layer. These factors are speculated to be some of the reasons why the water-resistant paper of this embodiment has sufficient water resistance against cold and hot water and excellent edge wicking resistance not only to hot water but also to lactic acid aqueous solutions. The effects of the present invention are not limited by the above mechanism. The structure and properties of the waterproof paper of this embodiment will be described in more detail below.

[0008] 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 the numerical range is described in stages, the upper and lower limits of each numerical range can be combined arbitrarily. Furthermore, "(meth)acrylic" is a generic term including both acrylic and methacrylic.

[0009] <Paper base material> The paper base material constituting the waterproof paper of this embodiment may be a single-layer or multi-layer structure. In the case of multi-layer paper, the number of paper layers is not particularly limited, but is preferably three or more, more preferably four or more, and even more preferably five or more. By using three or more paper layers, the desired basis weight and paper thickness can be achieved, and the physical properties of the waterproof paper can be adjusted to the desired range by adjusting the basis weight, freeness, etc. of each layer. The upper limit of the number of paper layers is not particularly limited, but is preferably seven or fewer, more preferably six or fewer.

[0010] Pulps constituting the paper base material include chemical pulps such as bleached hardwood kraft pulp (LBKP) and bleached softwood kraft pulp (NBKP); mechanical pulps such as groundwood pulp (GP), pressure groundwood pulp (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), chemi-mechanical pulp (CMP), and chemi-ground pulp (CGP); recycled paper pulp; non-wood fiber pulps such as kenaf, bagasse, bamboo, and cotton; and synthetic pulp. These pulps may be used alone or in combination of two or more. Among these, the combined use of LBKP and NBKP is preferred.

[0011] From the viewpoint of water resistance and / or edge wick resistance, the content of softwood bleached kraft pulp (NBKP) relative to the total amount of pulp constituting the paper base material is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, and is preferably 60% by mass or less, more preferably 55% by mass or less, even more preferably 50% by mass or less, even more preferably 40% by mass or less, and even more preferably 35% by mass or less.

[0012] From the viewpoint of water resistance and / or edge wick resistance, the content of hardwood bleached kraft pulp (LBKP) relative to the total amount of pulp constituting the paper base material is preferably 40% by mass or more, more preferably 45% by mass or more, even more preferably 50% by mass or more, even more preferably 60% by mass or more, even more preferably 65% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less.

[0013] In order to obtain a paper strength suitable for use as waterproof paper for packaging containers, the Canadian Standard Freeness (CSF) of LBKP is preferably 310 mL or more and 550 mL or less, more preferably 330 mL or more, even more preferably 350 mL or more, particularly preferably 380 mL or more, and more preferably 500 mL or less, even more preferably 480 mL or less, particularly preferably 450 mL or less. Furthermore, from the viewpoint of obtaining suitable paper strength as a waterproof paper for packaging containers, the Canadian Standard Freeness (CSF) of NBKP is preferably 420 mL or more and 550 mL or less, more preferably 450 mL or more, even more preferably 470 mL or more, and more preferably 530 mL or less, even more preferably 510 mL or less. Canadian standard freeness is measured in accordance with JIS P 8121-2:2012 "Pulp - Testing method for freeness - Part 2: Canadian standard freeness method." It is preferred that LBKP and NBKP are used in combination as the pulp constituting the paper base material, and that the Canadian Standard Freeness (CSF) of each is within the above range.

[0014] The paper base material contains a rosin-based sizing agent from the viewpoint of improving edge wick resistance. When the paper base material has multiple paper layers, the rosin-based sizing agent may be contained in some of the layers, but it is preferable that the rosin-based sizing agent be contained in each layer, and it is more preferable that the content of each layer be within the preferred content range described below. As the rosin-based sizing agent, for example, an acidic rosin-based sizing agent and a neutral rosin-based sizing agent can be used, with the acidic rosin-based sizing agent being preferred. From the viewpoint of improving edge wick resistance, the content of the rosin-based sizing agent in the paper base material is preferably 0.2 parts by mass or more, more preferably 0.4 parts by mass or more, even more preferably 0.6 parts by mass or more, per 100 parts by mass of pulp, and is preferably 1.4 parts by mass or less, more preferably 1.2 parts by mass or less, even more preferably 1.0 part by mass or less.

[0015] Other additives to the paper base (including sizing agents other than rosin-based sizing agents) include, for example, pH adjusters (sodium bicarbonate, sodium hydroxide, etc.), dry strength agents, wet strength agents, drainage yield aids, antifoaming agents, fillers (calcium carbonate, talc, etc.), dyes, and fixing agents (aluminum sulfate). These additives may be used alone or in combination of two or more. The content of the additives is not particularly limited and may be within the range of common use.

[0016] Examples of wet strength agents include polyamidepolyamine epichlorohydrin resin (PAE), melamine-formaldehyde resin, and urea-formaldehyde resin, and among these, polyamidepolyamine epichlorohydrin resin is preferred. When the paper base material has multiple paper layers, the wet strength agent may be contained in some of the layers, but it is preferable that each layer contains the agent, and it is more preferable that the content of each layer is within the preferred content range described below. The content of the wet strength agent per 100 parts by mass of raw pulp is preferably 0.01 part by mass or more, more preferably 0.03 part by mass or more, even more preferably 0.05 part by mass or more, particularly preferably 0.1 part by mass or more, and is preferably 1 part by mass or less, more preferably 0.5 part by mass or less, even more preferably 0.3 part by mass or less.

[0017] Examples of dry strength agents generally include polyacrylamide (PAM)-based dry strength agents, starch-based dry strength agents, CMC (carboxymethylcellulose) or its salts such as sodium carboxymethylcellulose, calcium carboxymethylcellulose, and zinc carboxymethylcellulose, but from the viewpoint of water resistance and / or edge wick resistance, it is preferable that the dry strength agent contains a starch-based dry strength agent. When the paper base material has multiple paper layers, some of the layers may contain the dry strength agent, but it is preferable that each layer contains it, and it is more preferable that the content of each layer be within the preferred content range described below. The content of the starch-based dry strength agent in the dry strength agent is preferably 50% by mass or more, more preferably 75% by mass or more, and even more preferably 90% by mass or more, and 100% by mass or less. An example of a starch-based dry strength agent is cationic starch. When a starch-based dry strength agent is used as the dry strength agent, the amount of cationic starch added is preferably 0.05 parts by mass or more, more preferably 0.2 parts by mass or more, even more preferably 0.5 parts by mass or more, and preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, even more preferably 1.0 part by mass or less, per 100 parts by mass of raw material pulp (solid content), from the viewpoint of water resistance and / or edge wick resistance.

[0018] The amount of fixing agent to be added is preferably 0.01 part by mass or more, more preferably 0.03 part by mass or more, even more preferably 0.05 part by mass or more, and preferably 1.0 part by mass or less, more preferably 0.6 part by mass or less, even more preferably 0.2 part by mass or less, per 100 parts by mass of raw pulp (solid content equivalent). When the paper substrate has multiple paper layers, the fixing agent is preferably contained in the layer containing the rosin-based sizing agent, and when there are two or more layers containing the rosin-based sizing agent, it is more preferable that the fixing agent content in each layer be within the above-mentioned preferred content range.

[0019] The basis weight of the paper substrate is not particularly limited, but for example, in the case of a packaging container, preferably a paper cup, it is preferably 180 g / m from the viewpoint of obtaining the paper strength required for the packaging container. 2 More preferably, 200 g / m 2 More preferably, 220 g / m 2 From the viewpoint of formability, it is preferably 430 g / m 2 or less, more preferably 380 g / m 2 or less, more preferably 330 g / m 2 Below 280 g / m, particularly preferably 2 The basis weight of the paper substrate is measured in accordance with JIS P 8124:2011. The thickness of the paper base material is not particularly limited, but for example, in the case of a packaging container, preferably a paper cup, from the viewpoint of obtaining the paper strength required for the packaging container, it is preferably 210 μm or more, more preferably 230 μm or more, and even more preferably 240 μm or more, and from the viewpoint of formability, it is preferably 480 μm or less, more preferably 410 μm or less, even more preferably 380 μm or less, and particularly preferably 330 μm or less. The thickness of the paper base material is measured in accordance with JIS P 8118:2014.

[0020] The basis weight of the laminate of the paper substrate and the undercoat layers (1) and (2) (hereinafter also referred to as "undercoat paper") is not particularly limited, but for example, in the case of packaging containers, preferably food containers, more preferably paper cups, it is preferably 200 g / m from the viewpoint of obtaining the paper strength required for the packaging container. 2 More preferably, 220 g / m 2 More preferably, 240 g / m 2 and from the viewpoint of water resistance and / or edge wicking resistance, it is preferably 450 g / m 2 Less than 400 g / m 2 or less, more preferably 350 g / m 2 Below 300 g / m, particularly preferably 2 The basis weight of the primer paper is measured in accordance with JIS P 8124:2011. The thickness of the primer paper is not particularly limited, but for example, in the case of packaging containers, preferably food containers, more preferably paper cups, from the viewpoint of obtaining the paper strength required for the packaging container, it is preferably 230 μm or more, more preferably 250 μm or more, even more preferably 260 μm or more, and from the viewpoint of formability, it is preferably 500 μm or less, more preferably 430 μm or less, even more preferably 400 μm or less, particularly preferably 350 μm or less. The thickness of the primer paper is measured in accordance with JIS P 8118:2014.

[0021] [Method for manufacturing paper substrate] A method for producing a paper base material includes making a paper stock containing pulp and a rosin-based sizing agent. The paper stock may further contain additives other than the rosin-based sizing agent (the above-mentioned "other additives"). The paper stock can be prepared by adding a rosin-based sizing agent and, if necessary, additives other than the rosin-based sizing agent to the pulp slurry. The pulp slurry can be obtained by beating pulp in the presence of water. The method and apparatus for beating the pulp are not particularly limited, and may be the same as known beating methods and apparatuses. The pulp content in the stock is not particularly limited and may be in a commonly used range, for example, 60% by mass or more and less than 100% by mass relative to the total mass of the stock.

[0022] Papermaking from stock can be carried out by standard methods. For example, the stock is cast onto a wire or the like, dewatered to obtain a wet paper, and multiple wet papers are stacked as necessary, and this single-layer or multi-layer wet paper is pressed and dried. In this case, if multiple wet papers are not stacked, a single-layer paper is obtained, and if multiple wet papers are stacked, a multi-layer paper is obtained. When multiple wet papers are stacked, an adhesive may be applied to the surface of the wet paper (the surface on which other wet papers are stacked).

[0023] <Undercoat layer> In the waterproof paper of this embodiment, the primer layer (1) is provided on one side (front side, liquid-contacting surface) of the paper substrate, between the paper substrate and the waterproof layer (1) described later, and the primer layer (2) is provided on the other side (back side, printing surface) of the paper substrate, between the paper substrate and the waterproof layer (2) described later. In the waterproof paper of this embodiment, the undercoat layer (1) and the undercoat layer (2) each include a pigment-containing layer, or the undercoat layer (1) includes a pigment-containing layer and the undercoat layer (2) includes a polyethyleneimine-containing layer. When the undercoat layer (1) and the undercoat layer (2) each include a pigment-containing layer, the undercoat layer (1) and the undercoat layer (2) do not necessarily include a polyethyleneimine-containing layer. When the undercoat layer (1) includes a pigment-containing layer and the undercoat layer (2) includes a polyethyleneimine-containing layer, the undercoat layer (1) does not necessarily include a polyethyleneimine-containing layer, and the undercoat layer (2) does not necessarily include a pigment-containing layer. The undercoat layer (1) may be one layer or two or more layers. The undercoat layer (2) may be one layer or two or more layers. From the viewpoint of productivity, it is preferable that each of the undercoat layer (1) and the undercoat layer (2) is one layer, but from the viewpoint of improving water resistance, they may be two or more layers. The pigment-containing layer may be one layer or two or more layers per side. From the viewpoint of productivity, the pigment-containing layer is preferably one layer per side, but from the viewpoint of improving water resistance, it may be two or more layers. The polyethyleneimine-containing layer may be one layer or two or more layers. From the viewpoint of productivity, the polyethyleneimine-containing layer is preferably one layer, but from the viewpoint of improving water resistance, it may be two or more layers. When the pigment-containing layer has two or more layers, the pigment-containing layers may be the same as or different from one another in composition, coating amount, etc. When the polyethyleneimine-containing layer has two or more layers, the polyethyleneimine-containing layers may be the same as or different from one another in composition, coating amount, etc.

[0024] [Pigment-containing layer] The pigment-containing layer contains at least a pigment.

[0025] [Pigment] The pigment contained in the pigment-containing layer is not particularly limited and may be, for example, inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, calcined clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, or satin white; or organic pigments such as solid, hollow, or core-shell pigments. These pigments may be used alone or in combination. From the viewpoint of further improving water resistance and / or edge wicking resistance, at least one pigment selected from the group consisting of calcium carbonate and kaolin is preferred. When calcium carbonate and kaolin are used in combination, the mass ratio (calcium carbonate / kaolin) is not particularly limited and is preferably 50 / 50 or more and 90 / 10 or less, more preferably 60 / 40 or more and 80 / 20 or less.

[0026] 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. The average particle size of the pigment can be determined using a laser diffraction particle size distribution analyzer based on the principles of laser diffraction, and the value measured from the measured particle size distribution is used.

[0027] It is preferable to use a pigment having an aspect ratio of 5 or more (pigment 1) in combination with a pigment having an aspect ratio of less than 5 (pigment 2) as pigments, from the viewpoints of improving the water resistance of the pigment-containing layer, adjusting the viscosity of the coating liquid for the pigment-containing layer, and reducing costs. The aspect ratio of pigment 1 is 5 or more, preferably 50 or more, and preferably 500 or less, more preferably 300 or less. An example of a pigment having the above aspect ratio is kaolin. The aspect ratio of pigment 2 is less than 5, preferably 4 or less, more preferably 3.5 or less, and is at least 1. An example of a pigment having the above aspect ratio is calcium carbonate. The aspect ratio of a pigment is a shape factor obtained by dividing the average particle diameter by the average thickness. The average thickness is measured by dropping several drops of pigment diluted with a solvent onto a glass substrate, allowing it to dry naturally, and then measuring the thickness of 20 samples of the pigment oriented on the glass substrate using a transmission electron microscope. Of the 20 thickness measurements, the top three and bottom three are excluded, and the remaining 14 thicknesses are averaged to determine the average thickness.

[0028] From the viewpoint of water resistance and / or edge wicking resistance, the pigment content in the pigment-containing layer is 95% by mass or less, preferably 92% by mass or less, more preferably 89% by mass or less, and even more preferably 87% by mass or less. From the viewpoint of operability (prevention of contamination of coating equipment), the pigment content in the pigment-containing layer is preferably 30% by mass or more, more preferably 40% by mass or more, even more preferably 50% by mass or more, and particularly preferably 60% by mass or more.

[0029] [latex] The pigment-containing layer preferably contains a latex in addition to a pigment. In the present embodiment, latex refers to a polymer that can be stably dispersed in water. Latex is generally emulsified and dispersed with a surfactant or the like. Specific examples of latexes are not particularly limited as long as they achieve the effects of the present invention, but include conjugated diene polymers such as styrene-butadiene copolymers and acrylonitrile-butadiene copolymers; styrene-acrylic copolymers such as homopolymers of (meth)acrylic acid esters and copolymers of monomers copolymerizable therewith (e.g., styrene-(meth)acrylic acid ester copolymers); vinyl polymers such as ethylene-vinyl acetate copolymers and vinyl chloride-vinyl acetate; polyurethane resins; and natural rubber. These may be used alone or in combination of two or more. Among these, from the viewpoint of further improving water resistance and / or edge wick resistance, at least one selected from the group consisting of styrene-butadiene copolymers and styrene-acrylic copolymers is preferred, and styrene-acrylic copolymers are more preferred. An example of the styrene-acrylic copolymer is a copolymer of styrene and an alkyl (meth)acrylate ester. The latex may be either a commercially available product or a synthetic product, and examples of commercially available products include Acronal S728ap manufactured by BASF Ltd. and Acronal S 504ap manufactured by BASF Ltd.

[0030] The average particle size of the latex is not particularly limited, but from the viewpoint of adhesive strength with the water-resistant layer, it is preferably 0.01 μm or more, more preferably 0.05 μm or more, and preferably 1.0 μm or less, more preferably 0.5 μm or less. The average particle size of the latex can be determined 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.

[0031] The glass transition temperature of the latex is not particularly limited, but from the viewpoint of adhesive strength with the water-resistant layer, it is preferably −10° C. or higher, more preferably 0° C. or higher, even more preferably 10° C. or higher, and preferably 50° C. or lower, more preferably 40° C. or lower, even more preferably 30° C. or lower. The glass transition temperature of the latex is a value measured by differential scanning calorimetry (DSC).

[0032] From the viewpoint of water resistance and / or edge wicking resistance, the content of latex in the pigment-containing layer is preferably 3% by mass or more, more preferably 6% by mass or more, even more preferably 9% by mass or more, and particularly preferably 12% by mass or more. From the viewpoint of operability (prevention of contamination of coating equipment), the content of latex in the undercoat layer is preferably 50% by mass or less, more preferably 45% by mass or less, and even more preferably 40% by mass or less.

[0033] In the pigment-containing layer, the mass ratio of latex to pigment (latex / pigment) is not particularly limited, but from the viewpoint of water resistance and / or edge wick resistance, it is preferably 10 / 90 or more, more preferably 20 / 80 or more, and even more preferably 25 / 75 or more. Furthermore, from the viewpoint of runnability (prevention of contamination of coating equipment), the mass ratio of latex to pigment (latex / pigment) in the pigment-containing layer is preferably 60 / 40 or less, more preferably 50 / 50 or less, and even more preferably 40 / 60 or less.

[0034] In the pigment-containing layer, the total content of the pigment and latex is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be 100% by mass, from the viewpoint of water resistance and edge wick resistance.

[0035] The pigment-containing layer may further contain components other than the latex and the pigment. Examples of the components other than the latex and the pigment include adhesives, dispersants, thickeners, water retention agents, antifoaming agents, waterproofing agents, colorants, surfactants, etc. Examples of adhesives include proteins such as casein, soy protein, and synthetic protein; starches such as oxidized starch, cationic starch, urea phosphate esterified starch, and etherified starch such as hydroxyethyl etherified starch, and dextrin; and cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxymethyl cellulose.

[0036] The coating amount of the pigment-containing layer is preferably 1 g / m per side from the viewpoint of edge wick resistance. 2 More preferably, 2 g / m 2 More preferably, 3 g / m 2 From the viewpoint of heat sealing property and cost, it is preferably 40 g / m 2 Less than 35g / m 2 or less, more preferably 25 g / m 2 Below 20 g / m, particularly preferably 2 The following is the result. When the undercoat layer (1) and the undercoat layer (2) include a pigment-containing layer, the coating amount of the pigment-containing layer is preferably 2 g / m per side from the viewpoint of water resistance and / or edge wick resistance. 2 More preferably, 3 g / m 2 More preferably, 4 g / m 2 More preferably, 6 g / m 2 More preferably, 8 g / m 2 From the viewpoint of heat sealing property and cost, it is preferably 20 g / m 2 Less than 15 g / m, more preferably 2 or less, more preferably 12 g / m 2 The following is the result. When the undercoat layer (1) includes a pigment-containing layer and the undercoat layer (2) includes a polyethyleneimine-containing layer, the coating amount of the pigment-containing layer is preferably 8 g / m per side from the viewpoint of water resistance and / or edge wick resistance. 2 More preferably, 12 g / m 2 More preferably, 16 g / m 2 From the viewpoint of heat sealing property and cost, it is preferably 40 g / m 2 Less than 30 g / m, more preferably 2 or less, more preferably 25 g / m 2 The following is the result.

[0037] The method for forming the pigment-containing layer is not particularly limited, but for example, the pigment-containing layer can be obtained by preparing a coating liquid for the pigment-containing layer containing latex, pigment, and, if necessary, other components, applying the coating liquid onto a paper substrate, and drying the coating liquid.

[0038] [Polyethyleneimine-containing layer] The polyethyleneimine-containing layer contains polyethyleneimine. The number average molecular weight of the polyethyleneimine is not particularly limited, but is preferably 30,000 or more, more preferably 60,000 or more, and is preferably 100,000 or less, more preferably 150,000 or less. The number average molecular weight of polyethyleneimine is a value determined by a viscosity method. As the polyethyleneimine, commercially available products may be used, for example, "Epomin P-1000," "Epomin P-3000," and "Epomin HM-2000" (all trade names, manufactured by Nippon Shokubai Co., Ltd.).

[0039] From the viewpoint of water resistance and / or edge wick resistance, the content of polyethyleneimine in the polyethyleneimine-containing layer is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, even more preferably 25% by mass or more, and particularly preferably 30% by mass or more, and is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less.

[0040] From the viewpoint of water resistance and / or edge wicking resistance, the polyethyleneimine-containing layer preferably contains at least one selected from the group consisting of polyvinyl alcohol and starch, and more preferably contains polyvinyl alcohol.

[0041] The degree of polymerization of polyvinyl alcohol is not particularly limited, but is preferably 1,000 or more, more preferably 1,500 or more, and is preferably 4,000 or less, more preferably 2,000 or less. The degree of saponification of polyvinyl alcohol is not particularly limited, but is preferably 85 mol % or more, more preferably 90 mol % or more, and 100 mol % or less. The degree of polymerization and the degree of saponification are measured in accordance with JIS K 6726-1994 (Testing method for polyvinyl alcohol).

[0042] Commercially available polyvinyl alcohol products may be used, such as "J-Poval JM-17" (trade name) and "J-Poval JF-17" (trade name) manufactured by Nippon Vinyl Acetate & Poval Co., Ltd., and "Kuraray Poval PVA-117" (trade name) and "Exeval RS-2117" (trade name) manufactured by Kuraray Co., Ltd. Similarly, commercially available starch products may be used, such as "GRS-T110, Ace K, Cornstarch K, Ace A, Ace D" (trade names) manufactured by Oji Cornstarch Co., Ltd., and "Film Coat 370" (trade name) manufactured by Ingredion Inc.

[0043] In the polyethyleneimine-containing layer, the mass ratio of polyvinyl alcohol and starch to polyethyleneimine (polyvinyl alcohol and starch (total) / polyethyleneimine) is not particularly limited, but from the viewpoint of water resistance and edge wick resistance, it is preferably 30 / 70 or more, more preferably 40 / 60 or more, even more preferably 50 / 50 or more, and preferably 80 / 20 or less, more preferably 75 / 25 or less, even more preferably 70 / 30 or less. In addition, in the polyethyleneimine-containing layer, it is also preferable that the mass ratio of polyvinyl alcohol to polyethyleneimine (polyvinyl alcohol / polyethyleneimine) is within the above range.

[0044] In the polyethyleneimine-containing layer, the total content of polyethyleneimine, polyvinyl alcohol, and starch is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be 100% by mass, from the viewpoint of water resistance and edge wick resistance.

[0045] The polyethyleneimine-containing layer may contain, in addition to polyethyleneimine and, if necessary, polyvinyl alcohol and / or starch, other components such as melamine resin, urea resin, epoxy resin, and polyacrylamide (also referred to as PAM).

[0046] The coating amount of the polyethyleneimine-containing layer is preferably 0.1 g / m from the viewpoint of water resistance and / or edge wick resistance. 2 More preferably, 0.2 g / m 2 More preferably, 0.3 g / m 2 From the viewpoint of heat sealing property and cost, it is preferably 4 g / m 2 Less than 3g / m, more preferably 2 More preferably, 2 g / m or less 2 More preferably, 1 g / m or less 2 The following is the result.

[0047] The method for forming the polyethyleneimine-containing layer is not particularly limited, but for example, the polyethyleneimine-containing layer can be obtained by preparing a coating liquid for the polyethyleneimine-containing layer containing polyethyleneimine, polyvinyl alcohol, and, if necessary, other components, applying the coating liquid onto a paper substrate, and drying the coating liquid.

[0048] As the undercoat layer other than the pigment-containing layer contained in the undercoat layer (1), and as the undercoat layer other than the pigment-containing layer and the polyethyleneimine-containing layer contained in the undercoat layer (2), for example, a layer obtained by removing the pigment from the pigment-containing layer can be used.

[0049] <Water resistant layer> In the waterproof paper of this embodiment, the waterproof layer (1) is formed on one side of the paper base material via an undercoat layer (1), and the waterproof layer (2) is formed on the other side of the paper base material via an undercoat layer (2). In the waterproof paper of this embodiment, from the viewpoint of heat-sealability, it is preferable that at least one of the waterproof layers (1) and (2) is provided as the uppermost layer. In the waterproof paper of this embodiment, the waterproof layer (1) may be one layer or two or more layers. The waterproof layer (2) may be one layer or two or more layers. From the viewpoint of productivity, it is preferable that each of the waterproof layer (1) and the waterproof layer (2) is one layer, and from the viewpoint of improving water resistance, it is preferable that each of the waterproof layer (1) and the waterproof layer (2) is two or more layers. When the water-resistant layer (1) and / or the water-resistant layer (2) is two or more layers, the compositions and coating amounts of the respective water-resistant layers may be the same or different. Furthermore, the composition and coating amount of the water-resistant layer constituting the water-resistant layer (1) may be the same or different from the composition and coating amount of the water-resistant layer constituting the water-resistant layer (2).

[0050] The water-resistant layers (1) and (2) preferably contain a water-based resin, which means a resin that can be dispersed or suspended in water. Examples of aqueous resins include polyolefin resins and acrylic resins, such as ethylene-(meth)acrylic acid copolymers, styrene-acrylic copolymers, and ethylene-α-olefin copolymers. The carbon number of the α-olefin is preferably 4 to 20, more preferably 6 to 16, and even more preferably 6 to 12. The aqueous resins may be used alone or in combination of two or more. The ethylene-(meth)acrylic acid copolymer may be an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer, and the styrene-acrylic copolymer may be a styrene-(meth)acrylic acid alkyl ester copolymer. The water-resistant layers (1) and (2) may contain different types of aqueous resins, but from the viewpoint of heat seal peel strength, it is preferable that the resins have similar polarities. Therefore, when the water-resistant layer (1) contains a polyolefin-based resin, it is preferable that the water-resistant layer (2) also contains a polyolefin-based resin. As the water-based resin, commercially available products may be used, for example, Aquence EPIX manufactured by Henkel Japan Co., Ltd. Examples include BC-212F, BC900F, BC905F, BC910F, MP498345N, MP4983R, MP4990R, 201103PX.S, and MFHS1279 manufactured by Michelman Japan LLC, ZAIKSEN (registered trademark) A and ZAIKSEN (registered trademark) AC manufactured by Sumitomo Seika Chemicals Co., Ltd., the Chemipearl series (S100, S300, and S500) manufactured by Mitsui Chemicals, Inc., MYE-30ER and MYE-30MAZ manufactured by Maruyoshi Chemical Co., Ltd., the Surlyn series manufactured by DuPont, the Himilan series manufactured by Dow Mitsui Polychemicals Co., Ltd., HYPOD2000, RHOBARR320, and RHOBARR325 manufactured by Dow Chemical Japan Ltd., Hi-Tec SC-100 manufactured by Toho Chemical Industry Co., Ltd., Aquatex AC-3100 manufactured by Chuo Rika Kogyo Co., Ltd., and Joncryl HPB-4110 manufactured by BASF.

[0051] From the viewpoint of water resistance and / or edge wicking resistance, the content of each aqueous resin in the water-resistant layers (1) and (2) is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, but not more than 100% by mass, of the resin components of the water-resistant layers. Here, the resin component of the water-resistant layers (1) and (2) means a polymer component contained in the water-resistant layer, that is, a compound having a weight-average molecular weight of 1,000 or more.

[0052] The water-resistant layers (1) and (2) may contain other components in addition to the above-mentioned aqueous resin. Examples of other components include viscosity modifiers; antifoaming agents; leveling agents such as surfactants and alcohols; colorants such as color pigments and color dyes; and antiblocking agents such as inorganic pigments and synthetic resins. Since these components tend to deteriorate water resistance and heat sealability, the total content of other components is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10% by mass or less, of the solid content of the water-resistant layer, with the lower limit being 0% by mass.

[0053] The water-resistant layer (1) is obtained by preparing a coating liquid for the water-resistant layer containing a water-based resin and applying the coating liquid onto the undercoat layer. The water-resistant layer (2) is obtained in the same manner as the water-resistant layer (1).

[0054] The coating liquid for the water-resistant layer is preferably an aqueous dispersion. Furthermore, the coating liquid for the water-resistant layer is more preferably a self-emulsifying and dispersing coating liquid that does not contain an emulsifier such as a surfactant or a dispersant. The absence of an emulsifier such as a surfactant or a dispersant is preferred because it provides better water resistance.

[0055] The aqueous resin blended in the coating solution for the water-resistant layer may be in the form of an ionomer. Here, the ionomer is a copolymer neutralized with a cation. Examples of the cation include metal ions such as sodium ions, potassium ions, calcium ions, and magnesium ions, and ammonium ions (NH4 + ) and organic ammonium ions are examples.

[0056] The method for applying the coating liquid for the water-resistant layer is not particularly limited, and any commonly used coating device may be appropriately selected and used, such as an 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 coater, gate roll coater, or lip coater. To improve the quality of the water-resistant layer, it is preferable to use an air knife coater to form at least the water-resistant layer on the front surface (liquid-contacting surface).For the same reason, it is preferable to use an air knife coater to form the water-resistant layer on the back surface, but a gravure coater may also be used.

[0057] The coating amount of each of the water-resistant layers (1) and (2) (coating amount per side) is preferably 1.0 g / m from the viewpoint of water resistance and / or edge wicking resistance. 2 More preferably, 2.0 g / m 2 More preferably, 3.0 g / m 2 The upper limit of the coating amount of each of the water-resistant layers (1) and (2) is not particularly limited, but from the viewpoint of achieving both water resistance and cost, it is, for example, 10 g / m 2 When the water-resistant layer (1) is two or more layers, the total coating weight is preferably within the above-mentioned preferred range. When the water-resistant layer (2) is two or more layers, the total coating weight is preferably within the above-mentioned preferred range.

[0058] The waterproof paper of this embodiment may have other layers in addition to the undercoat layer (1), undercoat layer (2), water-resistant layer (1), and water-resistant layer (2). Examples of other layers include a printed layer, a water vapor barrier layer, an oxygen barrier layer, and an oxygen absorbing layer. The printed layer may be formed using a known ink such as an oil-based ink, a water-based ink, or a biomass ink. The printed layer may be formed on one surface of the waterproof paper, or on a portion of the surface. That is, the waterproof paper of this embodiment may be printed on all or part of at least one surface (e.g., the printing surface). The printed content may be a pattern, a design, or information (such as ingredients, expiration date, or QR code (registered trademark)). The waterproof paper of this embodiment preferably has, on one side of the paper substrate, one or more (preferably only one) primer layer (1) (pigment-containing layer) provided so as to be in direct contact with the paper substrate, and one or more (preferably only one) water-resistant layer (1) provided so as to be in direct contact with the primer layer (1), in this order; and, on the other side of the paper substrate, one or more (preferably only one) primer layer (2) (pigment-containing layer or polyethyleneimine-containing layer) provided so as to be in direct contact with the paper substrate, and one or more (preferably only one) water-resistant layer (2) provided so as to be in direct contact with the primer layer (2), in this order; and more preferably, the waterproof paper is composed only of the paper substrate, primer layer (1), primer layer (2), water-resistant layer (1) and water-resistant layer (2).

[0059] <Water-resistant paper properties> [Basic weight] The basis weight of the waterproof paper is not particularly limited, but for example, in the case of a packaging container, preferably a food container, more preferably a paper cup, it is preferably 220 g / m from the viewpoint of obtaining the strength required for the packaging container. 2 More preferably, 240 g / m 2 More preferably, 260 g / m 2 From the viewpoint of water resistance and edge wicking resistance, it is preferably 500 g / m 2 or less, more preferably 450 g / m 2 or less, more preferably 400 g / m 2 or less, even more preferably 350 g / m 2 Below 300 g / m, particularly preferably 2 The following is the result. The basis weight of waterproof paper is measured in accordance with JIS P 8124:2011. The thickness of the waterproof paper is not particularly limited, but for example, in the case of packaging containers, preferably food containers, and more preferably paper cups, from the viewpoint of obtaining the strength required for the packaging container, it is preferably 230 μm or more, more preferably 250 μm or more, and even more preferably 270 μm or more, and from the viewpoint of water resistance and edge wick resistance, it is preferably 500 μm or less, more preferably 430 μm or less, even more preferably 400 μm or less, and particularly preferably 350 μm or less. The thickness of waterproof paper is measured in accordance with JIS P 8118:2014.

[0060] [Cobb water absorption] From the viewpoint of cold water resistance, the water-resistant paper of the present embodiment preferably has a Cobb water absorbency of 15 g / m2 in water at 20°C after a contact time of 30 minutes. 2 Less than 10 g / m, more preferably 2 Less than 9g / m 2 Less than 7 g / m, more preferably 2 or less, even more preferably 5 g / m 2 or less (the lower limit is 0 g / m 2 The Cobb water absorbency at 20°C can be adjusted within the desired range by adjusting the type of resin used in the water-resistant layers (1) and (2), the coating weight of the water-resistant layers (1) and (2), the ratio of pigment to latex in the undercoat layers (1) and (2), and the coating weight of the pigment coating layer. The Cobb water absorbency is measured in accordance with JIS P 8140:1998.

[0061] Furthermore, in terms of water resistance to hot water, the waterproof paper of this embodiment has a Cobb water absorbency of 20 g / m or more in 90°C water for a contact time of 30 minutes on the surface (surface) having the undercoat layer (1) and the waterproof layer (1). 2 Less than 15 g / m 2 or less, more preferably 12 g / m 2 Below, 9g / m 2 or less (the lower limit is 0 g / m 2The Cobb water absorbency at 90°C can be adjusted within the desired range by adjusting the type of resin used in the water-resistant layers (1) and (2), the coating weight of the water-resistant layers (1) and (2), the ratio of pigment to latex in the undercoat layers (1) and (2), and the coating weight of the pigment coating layer. The Cobb water absorbency is measured in accordance with JIS P 8140:1998.

[0062] [Edgewick resistance value] From the viewpoint of edge wick resistance in hot water, the waterproof paper of this embodiment has an edge wick value of 0.80 g / 1000 mm in 70°C water after immersion for 20 minutes. 2 Less than 0.70g / 1000mm, preferably 0.70g / 1000mm 2 Less than or equal to 0.60g / 1000mm, more preferably 0.60g / 1000mm 2 Less than 0.50g / 1000mm, more preferably 0.50g / 1000mm 2 The hot water edge wick value can be adjusted to within a desired range by adding a rosin-based sizing agent, the type and amount of wet strength agent, and the like. The Edgewick value is measured by the method described in the Examples.

[0063] Furthermore, in terms of edge wick resistance to a lactic acid aqueous solution, the waterproof paper of this embodiment has an edge wick value of 0.70 g / 1000 mm in a 20% by mass lactic acid aqueous solution at 23° C. after a contact time of 30 minutes. 2 Less than 0.60g / 1000mm, preferably 0.60g / 1000mm 2 Less than or equal to 0.50g / 1000mm 2 Less than 0.40g / 1000mm, more preferably 0.40g / 1000mm 2 The lactic acid edge wick value can be adjusted to within a desired range by providing a primer layer on both sides of the paper substrate as described above. The Edgewick value is measured by the method described in the Examples.

[0064] <Uses of water-resistant paper> The waterproof paper of this embodiment has excellent water resistance and edge wicking resistance, and therefore can be suitably used for packaging containers such as cups, plates, trays, lids, pouches, and tube-shaped containers; cutlery such as spoons, forks, knives, and chopsticks; straws; and flexible packaging materials such as wrapping paper, packaging bags, lids, and labels. Packaging containers can be formed, for example, by printing on the front and back surfaces of the waterproof paper as needed, punching into a shape corresponding to the shape of the packaging container to be manufactured, folding, and heat-sealing the overlapping portions. Therefore, the present invention also provides packaging containers (particularly food containers such as paper cups) made using the above-mentioned waterproof paper. The contents of the packaging container may be either food or non-food. The contents of the packaging container may also be liquid, solid, or gel. The contents of the packaging container are not particularly limited, and examples thereof include beverages such as coffee, tea, black tea, juice, and carbonated drinks; alcoholic beverages such as sake, shochu, and wine; dairy beverages such as milk; foods such as instant foods (instant ramen, etc.), microwaveable foods, beverages (yogurt, ice cream, jelly, pudding, etc.), and prepared dishes; pharmaceuticals; and chemical products such as car wax, shampoo, conditioner, detergent, bath additives, hair dye, and toothpaste. The water-resistant paper of this embodiment has excellent edge wicking resistance to hot water, and therefore can be suitably used as a packaging container (food container) for foods containing hot water, such as hot coffee, ramen, etc. Furthermore, the water-resistant paper of this embodiment has excellent edge wicking resistance to lactic acid aqueous solution, and therefore can be suitably used as a packaging container for dairy products, such as yogurt and ice cream. Packaging containers made from the waterproof paper of this embodiment use less plastic than packaging containers made from conventional laminated paper. Furthermore, while packaging containers made from conventional laminated paper must be disintegrated using a pulper with high disintegration performance when recycled into waste paper, packaging containers made from the waterproof paper of this embodiment can be disintegrated using a pulper with normal disintegration performance, making them highly recyclable. Packaging containers made from the waterproof paper of this embodiment can be washed, cut, disintegrated, etc. to prepare 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 include printing paper, packaging paper, sanitary paper, and cardboard. Furthermore, the paper made can be processed to manufacture packaging containers (e.g., tissue boxes, paper cup sleeves, etc.). [Example]

[0065] The features of this embodiment will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. Furthermore, the operations in the examples and comparative examples were carried out at room temperature (20-25°C) and normal humidity (40-50% RH) unless otherwise specified.

[0066] The raw materials used in the examples and comparative examples are as follows. Polyamide polyamine epichlorohydrin resin (PAE): WS4020 (product name), manufactured by Seiko PMC Corporation Cationic starch: Ace K (product name), manufactured by Oji Cornstarch Co., Ltd. Rosin-based sizing agent: Sizepine N-811 (product name), manufactured by Arakawa Chemical Industries, Ltd. Alkyl ketene dimer (AKD) sizing agent: Product name "AD1612", Seiko PMC Corporation, weak cation, solids content 20% by mass Pigment: Heavy calcium carbonate (product name "FMT-90", manufactured by Fimatec Co., Ltd., average particle size 1.1 μm, aspect ratio 1.0 to 3.0) Pigment: Kaolin (product name "Balisurf HX", manufactured by Imerys Co., Ltd., average particle size 9.0 μm, aspect ratio 80-100) Latex: Styrene-acrylic copolymer latex (product name "Acronal S728ap", manufactured by BASF Ltd., average particle size 0.16 μm, glass transition temperature 23°C, density 1.04 g / cm 3 ) Polyvinyl alcohol (PVA): Trade name "J-Poval JM-17", manufactured by Nippon Vinyl Acetate & Poval Co., Ltd., polymerization degree 1700, saponification degree 95.5-97.5 mol% Polyethyleneimine (PEI): Trade name "Epomin P-1000", manufactured by Nippon Shokubai Co., Ltd., solid content 30% by mass, number average molecular weight 70,000 Antifoaming agent: Product name "Bismar KS-38E", manufactured by Nissin Chemical Laboratory Co., Ltd. Water-based resin dispersion: Product name "AQUENCE EPIX BC-212F", manufactured by Henkel Japan Co., Ltd., solids concentration 25% by mass, polyolefin resin dispersion

[0067] <Preparation of coating liquid for undercoat layer> (a) Preparation of coating solution A A pigment dispersion was prepared by blending heavy calcium carbonate and kaolin (heavy calcium carbonate:kaolin (mass ratio) = 7 / 3) with water. Styrene-acrylic copolymer latex was blended with this pigment dispersion to prepare a pigment / styrene-acrylic copolymer latex mixture with a pigment content of 85.0 mass% and a styrene-acrylic copolymer latex content of 15.0 mass% based on the solids. An antifoaming agent was blended with the pigment / styrene-acrylic copolymer latex mixture to prepare Coating Solution A with a solids concentration of 60 mass%, with a pigment / styrene-acrylic copolymer latex content of 99.5 mass% and an antifoaming agent content of 0.5 mass% based on the solids.

[0068] (b) Preparation of coating solution B Coating Solution B was prepared in the same manner as Coating Solution A, except that in the preparation of Coating Solution A, the "pigment / styrene-acrylic copolymer latex mixture in which the pigment content in the solid content was 85.0 mass % and the styrene-acrylic copolymer latex content was 15.0 mass %" was changed to a "pigment / styrene-acrylic copolymer latex mixture in which the pigment content in the solid content was 70.0 mass % and the styrene-acrylic copolymer latex content was 30.0 mass %."

[0069] (c) Preparation of coating solution C PVA and PEI (PVA to PEI (mass ratio) = 66.6:33.4) were mixed with water to prepare a coating solution C with a solid content concentration of 4 mass %.

[0070] <Preparation of coating liquid for water-resistant layer> (a) Preparation of coating solution D (coating solution for gravure coater) An antifoaming agent was blended into the aqueous resin dispersion, and water was added to adjust the solid content, thereby preparing Coating Solution D, which had a solid content of 21 mass% and contained 99.0 mass% of the aqueous resin and 1.0 mass% of the antifoaming agent in the solid content.

[0071] (b) Preparation of coating solution E (air knife coater coating solution) An antifoaming agent was blended into the aqueous resin dispersion, and water was added to adjust the solid content, thereby preparing Coating Solution E, which had a solid content of 20 mass% and contained 99.0 mass% of aqueous resin and 1.0 mass% of antifoaming agent in the solid content.

[0072] Example 1 Beaten LBKP (CSF 400 mL) and beaten NBKP (CSF 500 mL) were mixed at 80% and 20% mass ratios to prepare 100 parts by mass (solids equivalent) of pulp slurry. 0.8 parts by mass of an acidic rosin-based sizing agent, 0.15 parts by mass of a wet strength agent (PAE), 0.7 parts by mass of a dry strength agent (cationized starch), and 1.5 parts by mass of aluminum sulfate were added to prepare a paper stock with a pH of 5.0. This paper stock was used to make a five-layer paper using a Fourdrinier paper machine, and a paper base was obtained. The coating solution A was applied to both sides of the paper substrate in an amount (solid content) of 5.0 g / m per side. 2 The coating is carried out using a rod coater so that the coating is in the range of 1000 to 2000 g / m², and then dried to form the undercoat layer (1) and the undercoat layer (2). 2 Thus, a primer paper with a thickness of 290 μm was obtained. The coating solution E was applied to the undercoat layer (1) (highly smooth surface) of the undercoated paper in a coating amount (solid content) of 8.0 g / m 2 The coating was then applied using an air knife coater so that the coating amount (solid content) was 4.0 g / m. 2 The resulting mixture was coated using a gravure coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer (2), thereby producing water-resistant paper.

[0073] <Example 2> Using the paper stock prepared in the same manner as in Example 1, paper was made using a five-layer Fourdrinier paper machine to obtain a paper base material. The coating solution A was applied to both sides of the paper substrate in an amount (solid content) of 10.0 g / m per side. 2 The coating is carried out using a rod coater so that the coating is in the range of 250 g / m2, and then dried to form the undercoat layer (1) and the undercoat layer (2). 2 Thus, a primer paper with a thickness of 290 μm was obtained. A water-resistant layer (1) and a water-resistant layer (2) were formed on both sides of the undercoated paper in the same manner as in Example 1 to prepare a water-resistant paper.

[0074] Example 3 Using the paper stock prepared in the same manner as in Example 1, paper was made using a five-layer Fourdrinier paper machine to obtain a paper base material. The coating solution A was applied to the highly smooth surface of the paper substrate in a coating amount (solid content) of 20.0 g / m 2 The coated layer was then dried using a rod coater to form an undercoat layer (1), and the coating solution C was applied to the opposite surface in an amount (solid content) of 0.5 g / m. 2 The coating was applied using a rod coater so that the coating was dried to form an undercoat layer (2), and the basis weight was 250 g / m 2 Thus, a primer paper with a thickness of 290 μm was obtained. A water-resistant layer (1) and a water-resistant layer (2) were formed on both sides of the undercoated paper in the same manner as in Example 1 to prepare a water-resistant paper.

[0075] Example 4 Using the paper stock prepared in the same manner as in Example 1, paper was made using a five-layer Fourdrinier paper machine to obtain a paper base material. The coating solution B was applied to both sides of the paper substrate in an amount (solid content) of 10.0 g / m per side. 2 The coating is carried out using a rod coater so that the coating is in the range of 250 g / m2, and then dried to form the undercoat layer (1) and the undercoat layer (2). 2 Thus, a primer paper with a thickness of 290 μm was obtained. A water-resistant layer (1) and a water-resistant layer (2) were formed on both sides of the undercoated paper in the same manner as in Example 1 to prepare a water-resistant paper.

[0076] <Comparative Example 1> Using the paper stock prepared in the same manner as in Example 1, paper was made using a five-layer Fourdrinier paper machine to obtain a paper base material. The coating solution A was applied to the highly smooth surface of the paper substrate in a coating amount (solid content) of 10.0 g / m 2 The coating was applied using a rod coater so that the coating was dried to form an undercoat layer (1), and the basis weight was 250 g / m 2 Thus, a primer paper with a thickness of 290 μm was obtained. The coating solution E was applied to the undercoat layer (1) (highly smooth surface) of the undercoated paper in a coating amount (solid content) of 8.0 g / m 2 The coating was then applied using an air knife coater so that the thickness of the coating was 4.0 g / m2, and the coating was then dried to form a water-resistant layer (1). Then, the coating solution D was applied to the opposite surface of the substrate in an amount (solid content) of 4.0 g / m2. 2 The resulting mixture was coated using a gravure coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer (2), thereby producing water-resistant paper.

[0077] <Comparative Example 2> Beaten LBKP (CSF 400 mL) and beaten NBKP (CSF 500 mL) were mixed at 80% and 20% by mass, respectively, to prepare a pulp slurry (100 parts by mass (solids content equivalent)). 0.2 parts by mass of AKD sizing agent, 0.15 parts by mass of wet strength agent (PAE), 0.7 parts by mass of dry strength agent (cationized starch), 1.5 parts by mass of aluminum sulfate, and 0.3 parts by mass of caustic soda were added as a pH adjuster to prepare a paper stock with a pH of 7.5. This paper stock was used to make a paper base using a five-layer Fourdrinier paper machine. The coating solution A was applied to the highly smooth surface of the paper substrate in a coating amount (solid content) of 20.0 g / m 2 The coating solution C was applied to the opposite surface in an amount (solid content) of 0.5 g / m using a rod coater and dried to form an undercoat layer (1). 2 The coating was applied using a rod coater so that the coating was dried to form an undercoat layer (2), and the basis weight was 250 g / m 2 Thus, a primer paper with a thickness of 290 μm was obtained. A water-resistant layer (1) and a water-resistant layer (2) were formed on both sides of the undercoated paper in the same manner as in Example 1 to prepare a water-resistant paper.

[0078] <Comparative Example 3> Beaten LBKP (CSF 400 mL) and beaten NBKP (CSF 500 mL) were mixed at 80% and 20% mass, respectively, to prepare a pulp slurry (100 parts by mass (solids content equivalent)). 0.3 parts by mass of AKD sizing agent, 0.15 parts by mass of wet strength agent (PAE), 0.7 parts by mass of dry strength agent (cationized starch), 1.5 parts by mass of aluminum sulfate, and 0.3 parts by mass of caustic soda were added as a pH adjuster to prepare a paper stock with a pH of 7.5. This paper stock was used to make a paper base using a five-layer Fourdrinier paper machine. The coating solution A was applied to the highly smooth surface of the paper substrate in a coating amount (solid content) of 20.0 g / m 2 The coating solution C was applied to the opposite surface in an amount (solid content) of 0.5 g / m using a rod coater and dried to form an undercoat layer (1). 2 The coating was applied using a rod coater so that the coating was dried to form an undercoat layer (2), and the basis weight was 250 g / m2 , a base paper with a paper thickness of 290 μm was obtained. On both sides of the base paper, a water-resistant layer (1) and a water-resistant layer (2) were formed in the same manner as in Example 1 to produce a water-resistant paper.

[0079] [Evaluation of base paper and water-resistant paper] The following evaluations were performed on the base paper and water-resistant paper obtained in the above Examples and Comparative Examples. <Basis weight and thickness of base paper and water-resistant paper> The basis weight of the base paper and water-resistant paper was measured in accordance with JIS P 8124:2011. Also, the thickness of the base paper and water-resistant paper was measured in accordance with JIS P 8118:2014.

[0080] <CSF of pulp raw material constituting paper base material> For the raw material pulp of the paper base material, CSF was measured in accordance with JIS P 8121-2:2012 "Pulp - Filterability test method - Part 2: Canadian standard filterability method".

[0081] <Cobb water absorption> The Cobb water absorption was measured in accordance with JIS P 8140:1998 at a contact time of 30 minutes. The water temperature was measured at 20 °C and 90 °C. More specifically, it was measured from the mass difference before and after contacting with water at 20 °C or 90 °C for 30 minutes.

[0082] <Edgewick value> First, in accordance with JIS P 8118:2014, the thickness (paper thickness) of the water-resistant paper was measured. Then, a commercially available polyethylene film was laminated on both sides of the water-resistant paper, and it was cut out into a 60 mm × 90 mm size so that the end faces were exposed to prepare a test piece, and the mass of the test piece (mass before immersion) was measured. This test piece was immersed in ion-exchanged water at 70 °C for 20 minutes, and after wiping off the surface moisture, the mass of the test piece (mass after immersion) was measured. And then, the Edgewick value of the water-resistant paper with respect to ion-exchanged water was determined by the following formula. The Edgewick value for coffee at 70° C. after an immersion time (contact time) of 10 minutes was also determined using the same measurement method. The coffee used was Nescafe Excella manufactured by Nestle Japan Ltd., and the concentration was 1.5% by mass. In addition, the Edgewick value was determined in a similar manner for a 20% by mass aqueous solution of lactic acid at 23° C. after an immersion time (contact time) of 30 minutes. Edgewick value [g / 1000mm 2 ] = (mass after immersion (g) - mass before immersion (g)) / paper thickness (mm) / circumference (mm)

[0083] [Table 1]

[0084] The results in Table 1 show that the waterproof papers of Examples 1, 2, and 4 have a base coat layer (1) and a water-resistant layer (1) in this order on one side of a paper base containing a rosin-based sizing agent, and a base coat layer (2) and a water-resistant layer (2) in this order on the other side of the paper base, with the base coat layer (1) and the base coat layer (2) containing pigments, and have sufficient water resistance to cold and hot water and excellent edge wick resistance not only to hot water but also to lactic acid aqueous solutions. The waterproof paper of Example 3 has a base coat layer (1) and a water-resistant layer (1) in this order on one side of a paper base containing a rosin-based sizing agent, and the base coat layer (1) contains a pigment-containing layer and the base coat layer (2) contains a polyethyleneimine-containing layer on the other side of the paper base, and has sufficient water resistance to cold and hot water and excellent edge wick resistance not only to hot water but also to lactic acid aqueous solutions. It is also clear that the waterproof papers of Examples 1 to 4 have excellent edge wicking resistance even when exposed to coffee at 70°C. In contrast, the waterproof paper of Comparative Example 1, which does not have a primer layer (2), is poor in edge wicking resistance to lactic acid. Also, the waterproof papers of Comparative Examples 2 and 3, which use AKD as a sizing agent, are poor in edge wicking resistance to hot water.

Claims

1. A paper substrate having an undercoat layer (1) and a water-resistant layer (1) in this order on one side thereof, A waterproof paper having a primer layer (2) and a waterproof layer (2) in this order on the other side of the paper substrate, The paper base material contains a rosin-based sizing agent, The undercoat layer (1) and the undercoat layer (2) comprise a pigment-containing layer, or the undercoat layer (1) comprises a pigment-containing layer and the undercoat layer (2) comprises a polyethyleneimine-containing layer; The water-resistant paper has a Cobb water absorption of 20 g / m2 at 90°C on the side having the undercoat layer (1) and the water-resistant layer (1) for a contact time of 30 minutes. ２ is as follows: Edge wick value in 70°C water after 20 minutes of contact time: 0.80g / 1000mm ２ is as follows: The Edgewick value for a 20% by mass aqueous solution of lactic acid at 23°C after a contact time of 30 minutes is 0.70 g / 1000 mm ２ Below is the Water resistant paper.

2. The coating amount of the pigment-containing layer is 2 g / m per side ２ The waterproof paper according to claim 1, wherein the above-mentioned

3. The coating amount of the polyethyleneimine-containing layer is 0.1 g / m ２ The waterproof paper according to claim 1, wherein the above-mentioned

4. 2. The waterproof paper according to claim 1, wherein the pigment-containing layer contains a pigment and a latex, and the mass ratio of the latex to the pigment (latex / pigment) in the pigment-containing layer is 10 / 90 or more and 50 / 50 or less.

5. 5. The waterproof paper according to claim 4, wherein the glass transition temperature of the latex is from -10°C to 40°C.

6. 5. The waterproof paper of claim 4, wherein the latex comprises a styrene-acrylic copolymer latex.

7. 2. The waterproof paper of claim 1, wherein the polyethyleneimine-containing layer comprises at least one selected from the group consisting of polyvinyl alcohol and starch.

8. 10. The waterproof paper of claim 1, wherein the paper substrate contains a polyamidepolyamine epichlorohydrin resin.

9. 2. The waterproof paper of claim 1, wherein the paper substrate contains a starch-based dry strength agent.

10. 2. The waterproof paper according to claim 1, which has at least one of the waterproof layer (1) and the waterproof layer (2) as the uppermost layer.

11. The waterproof paper according to claim 1, which is for use in packaging containers.

12. A packaging container made using the waterproof paper according to any one of claims 1 to 11.

Images