Water-resistant paper and packaging container

Abstract

Provided is a water-resistant paper from which removal of stain though washing with water after use is easy and which can, because removal of stain therefrom is easy, suppress odor generation after being stored for a certain period of time since being washed with water after use.　The water-resistant paper according to the present invention comprises, on one surface of a paper base material, an undercoat layer 1 and a water-resistant layer 1 in this order from the paper base material side. The water-resistant paper exhibits a wedge wick value of 0.80 g / 1000 mm2 or less with respect to water at 70°C in a contact time of 20 minutes. The kit value in the surface having the water-resistant layer 1 of the water-resistant paper is 10 or more. The Oken-type smoothness on the surface having the water-resistant layer 1 of the water-resistant paper is 80 seconds or more.

Description

Water-resistant paper and packaging

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

[0002] Plastic products have traditionally been used for various containers for beverages, 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.

[0003] 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. However, there has been a problem in that the polyethylene film is difficult to remove during recycling, making it poorly recyclable. To address this problem, attempts have been made to impart properties such as water resistance to the paper by imparting properties during the papermaking process or by coating.

[0004] Furthermore, Japanese Patent No. 6580291 discloses a packaging paper having at least one heat seal layer on at least one side of a paper substrate, with the aim of providing a packaging paper that can reduce the amount of plastic used, wherein the heat seal layer contains an ionomer, and the dry coating amount of the heat seal layer is 2 to 10 g / m2 in total. ２ and a packaging paper characterized in that two or more heat seal layers are formed on at least one surface of the packaging paper.

[0005] When the water-resistant paper described in Japanese Patent No. 6580291 is used as a packaging container such as a paper cup or paper plate, stains such as beverage or food residue adhering to the container may be difficult to remove with water, and even if the container is washed with water after use, odors may be generated from the stains, making it difficult to efficiently recycle the pulp that makes up the paper base material. Therefore, the present invention aims to provide water-resistant paper that is easy to remove stains from by washing with water after use, and that, because of the easy removal of stains, can also suppress the generation of odors even after storage for a certain period of time after washing with water after use, and to provide a packaging container made using this water-resistant paper.

[0006] The inventors discovered that the above problem can be solved by controlling the Edgewick value in water at 70°C to a specific value or less in waterproof paper having a primer layer and a waterproof layer, in that order, on one side of a paper substrate, and controlling the Kitt value and Oken smoothness on the side having the waterproof layer to specific values ​​or more, and thus completed the present invention.

[0007] That is, the present invention relates to the following items <1> to <14>. <1> A waterproof paper having an undercoat layer 1 and a water-resistant layer 1 on one side of a paper substrate, in this order from the paper substrate side, wherein the Edgewick value in water at 70°C after a contact time of 20 minutes is 0.80 g / 1000 mm ２ a Kit value of 10 or more on the side of the water-resistant paper having the water-resistant layer 1, and an Oken smoothness of 80 seconds or more on the side of the water-resistant paper having the water-resistant layer 1. <2> The water-resistant paper according to <1>, wherein the pulp constituting the paper base has an average Runkel ratio of 0.51 or less. <3> The water-resistant paper according to <1> or <2>, wherein the pulp raw material constituting the paper base contains at least one selected from the group consisting of hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP), and the mass ratio of the hardwood bleached kraft pulp (LBKP) to the softwood bleached kraft pulp (NBKP) (LBKP / NBKP) is 60 / 40 or more and 100 / 0 or less. <4> The waterproof paper according to any one of <1> to <3>, wherein the undercoat layer 1 contains latex and a pigment, and the mass ratio of the latex to the pigment (latex / pigment) is 10 / 90 or more and 40 / 60 or less. <5> The waterproof paper according to any one of <1> to <4>, wherein the other surface of the paper substrate has at least one of the undercoat layer 2 and the water-resistant layer 2. <6> The waterproof paper according to any one of <1> to <4>, wherein the coating amount of the undercoat layer 1 is 4 g / m ２ <7> The water-resistant paper according to any one of <1> to <6>, wherein the water-resistant layer 1 contains at least one resin selected from the group consisting of polyolefin-based resins and acrylic-based resins. <8> The water-resistant paper according to any one of <1> to <7>, wherein the paper base contains a starch-based dry strength agent. <9> The paper base has a basis weight of 200 g / m ２<10> The waterproof paper according to any one of <1> to <8>, wherein the Cobb water absorbency of the surface of the waterproof paper having the water-resistant layer 1 in water at 20°C after a contact time of 30 minutes is 10 g / m or more. ２ <11> The waterproof paper according to any one of <1> to <9>, wherein the Cobb water absorbency of the surface of the waterproof paper having the water-resistant layer 1 is 20 g / m or less at 90°C for a contact time of 30 minutes. ２ <12> The water-resistant paper according to any one of <1> to <11>, which has an air permeability of 30,000 seconds or more. <13> The water-resistant paper according to any one of <1> to <12>, which is for use in a packaging container. <14> A packaging container made using the water-resistant paper according to any one of <1> to <13>.

[0008] [Water-resistant paper] The water-resistant paper of this embodiment has a primer layer 1 and a water-resistant layer 1 on one side of a paper substrate, in this order from the paper substrate side, and has an Edgewick value of 0.80 g / 1000 mm in water at 70° C. after a contact time of 20 minutes. ２ The water-resistant paper has a surface having the water-resistant layer 1 with a Kit value of 10 or more, and an Oken smoothness of 80 seconds or more on the surface having the water-resistant layer 1. The water-resistant paper of this embodiment is easily cleaned by rinsing with water after use, and the ease of cleaning reduces odor generation even after storage for a certain period of time after rinsing with water after use. The pulp obtained by disintegrating such water-resistant paper is less likely to be dirty or smelly, making it suitable for recycling as waste paper. In this embodiment, the surface on which the water-resistant layer 1 is formed is preferably the surface that comes into contact with the contents (liquid-contacting surface, front surface) when used as a packaging container, etc., and the opposite surface is preferably the surface on which printing is performed (printing surface, back surface). In the following description, for convenience, the surface on which the water-resistant layer 1 of the water-resistant paper is formed (one side) will be referred to as the liquid-contacting surface or front surface, and the other side will be referred to as the printing surface or back surface.

[0009] The mechanism by which the above effect is achieved is unknown, but is presumed to be as follows: The Edge Wick value in water at 70°C after a contact time of 20 minutes is 0.80 g / 1000 mm ２By controlling the following, it is believed that the penetration of beverages and other contaminants from the edge of the waterproof paper is suppressed, and by controlling the Kit value of the surface of the waterproof paper having the waterproof layer 1 to 10 or more, the oil resistance is enhanced, and by making this surface the liquid-contact surface, the adhesion of contaminants themselves can be suppressed. Furthermore, by setting the Oken smoothness of the surface of the waterproof paper having the waterproof layer 1 to 80 seconds or more, it is believed that adhering contaminants can be easily washed off with water. Since the penetration of beverages and other contaminants from the edge of the waterproof paper is suppressed, contaminants are less likely to adhere to the surface of the waterproof paper having the waterproof layer 1, and even if they do adhere, they are easily removed with water, it is believed that the generation of odors caused by food residues themselves and odors caused by bacteria that grow using food residues as a nutrient source can also be suppressed. Note that the effects of the present invention are not limited by the above mechanism. The configuration and physical properties of the waterproof paper of this embodiment are described in more detail below.

[0010] 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.

[0011] <Paper Base> The paper base constituting the waterproof paper of this embodiment may be a single-layer structure or a multi-layer structure. In the case of a multi-layer paper, the number of paper layers is not particularly limited, but is, for example, preferably 3 to 7 layers, more preferably 4 or more layers, and even more preferably 5 or more layers. By using three or more paper layers, the desired basis weight and paper thickness can be achieved, and the basis weight, freeness, etc. of each layer can be adjusted to adjust the physical properties of the waterproof paper to a desired range. The upper limit of the number of paper layers is more preferably 6 layers or less.

[0012] In this embodiment, the average Runkel ratio of the pulp constituting the paper base is preferably 0.51 or less. When the average Runkel ratio of the pulp constituting the paper base is 0.51 or less, the smoothness of the resulting paper base is superior, resulting in lower breathability of the water-resistant layer formed via the primer layer (higher air resistance). In other words, the occurrence of pinholes on the surface of the water-resistant layer is suppressed, and thickness unevenness of the water-resistant layer is also suppressed, resulting in a waterproof paper that is excellent in water resistance and oil resistance and is resistant to stain adhesion. The average Runkel ratio of the pulp constituting the paper base is preferably 0.20 or more and 0.51 or less, more preferably 0.48 or less, even more preferably 0.45 or less, even more preferably 0.42 or less, and more preferably 0.26 or more, even more preferably 0.32 or more. The average Runkel ratio of the pulp constituting the paper base material is preferably not more than the upper limit from the viewpoint of increasing the smoothness of the water-resistant layer, suppressing pinholes in the water-resistant layer, and obtaining water-resistant paper that is excellent in water resistance and oil resistance and has low air permeability, and is preferably not less than the lower limit from the viewpoint of obtaining the paper strength required for water-resistant paper and ease of production.

[0013] Here, the Runkel ratio is expressed by the following formula, where R is the fiber diameter of the pulp fiber and r is the lumen diameter. Runkel ratio = (R - r) / r Here, the fiber diameter R and lumen diameter r of the pulp fiber are calculated from the following formula using circular approximation. If the outer periphery length of the fiber wall is X and the cross-sectional area of ​​the fiber wall is S, the radius A of the pulp fiber (i.e., R / 2) and the fiber lumen radius B (i.e., r / 2) are expressed by the following formulas. A = X / (2π) B = {(πA ２ −S) / π} １／２ In other words, a small Runkel ratio means that the fiber wall thickness is thin relative to the pulp fiber diameter, and it is thought that pulp with a small Runkel ratio is more easily crushed by external forces and produces a smoother paper base material. Therefore, when a paper base material is produced from a pulp raw material with a small average Runkel ratio, a paper base material with excellent smoothness is produced.

[0014] The average Runkel ratio is the average Runkel ratio of the pulp constituting the paper base material of the waterproof paper, and is measured using the pulp after disintegration of the obtained waterproof paper. Since the average Runkel ratio of the pulp constituting the paper base material hardly changes during papermaking and disintegration, it may be approximated by the average Runkel ratio of the raw material pulp. The Runkel ratio varies depending on the type and origin of the pulp. Generally, the Runkel ratio of hardwood bleached kraft pulp (LBKP) tends to be smaller than that of softwood bleached kraft pulp (NBKP). The raw material pulps to be used can be appropriately selected and combined to achieve the desired average Runkel ratio. The average Runkel ratio is the mass-weighted average value of pulps having the respective Runkel ratios. The Runkel ratio is measured by the method described in the Examples.

[0015] 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; synthetic pulp; etc. These pulps may be used alone or in combination of two or more. Among these, from the viewpoint of obtaining the desired Runkel ratio and paper strength, it is preferable that the pulp raw material constituting the paper base material contains at least one selected from the group consisting of LBKP and NBKP, it is more preferable to use LBKP alone or in combination with LBKP and NBKP, and it is even more preferable to use LBKP and NBKP in combination. Examples of raw materials for LBKP include eucalyptus and acacia. Examples of raw materials for NBKP include radiata pine and Douglas fir.

[0016] From the viewpoint of obtaining a strength suitable for use as a waterproof paper for packaging containers, the Canadian Standard Freeness (CSF) of the LBKP is preferably 300 mL or more and 600 mL or less, more preferably 325 mL or more, even more preferably 350 mL or more, even more preferably 380 mL or more, and more preferably 550 mL or less, even more preferably 500 mL or less, and even more preferably 480 mL or less. Furthermore, from the viewpoint of obtaining a strength suitable for use as a waterproof paper for packaging containers, the Canadian Standard Freeness (CSF) of the NBKP is preferably 350 mL or more and 700 mL or less, more preferably 400 mL or more, even more preferably 450 mL or more, even more preferably 480 mL or more, and more preferably 675 mL or less, even more preferably 650 mL or less, and even more preferably 625 mL or less. The 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.

[0017] As described above, the pulp raw material constituting the paper base preferably contains at least one selected from the group consisting of LBKP and NBKP, more preferably contains at least LBKP and further contains NBKP, and even more preferably uses LBKP and NBKP in combination. The mass ratio of LBKP to NBKP (LBKP / NBKP) in the pulp raw material constituting the paper base is preferably 60 / 40 or more and 100 / 0 or less, more preferably 70 / 30 or more, even more preferably 75 / 25 or more, and more preferably 90 / 10 or less, even more preferably 85 / 15 or less, from the viewpoint of setting the average Runkel ratio of the pulp constituting the paper base in the desired range and obtaining appropriate paper strength.

[0018] Examples of additives to paper substrates include pH adjusters (sodium bicarbonate, sodium hydroxide, etc.), dry strength agents, wet strength agents, internal sizing agents, drainage retention 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 commonly used.

[0019] 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. From the viewpoint of obtaining waterproof paper with excellent water resistance, air permeability, and oil resistance, it is preferable that the dry strength agent contains a starch-based dry strength agent. When the paper substrate has multiple paper layers, some of the layers may contain the dry strength agent, but it is preferable that each layer contains the dry strength agent, 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.

[0013] Note that the use of a polyacrylamide-based dry strength agent as the dry strength agent tends to reduce flexibility and top curl formability, and therefore the content of the polyacrylamide-based dry strength agent in the dry strength agent is preferably 50% by mass or less, more preferably 20% by mass or less, even more preferably 5% by mass or less, and it is particularly preferred that the dry strength agent be free of the polyacrylamide-based dry strength agent. 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, from the viewpoint of water resistance, the amount of cationic starch blended is preferably 0.05 to 2.0 parts by mass, more preferably 0.2 parts by mass or more, even more preferably 0.5 parts by mass or more, and 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 pulp (solids content).

[0020] Examples of wet strength agents include polyamidepolyamine epichlorohydrin resin (PAE), melamine-formaldehyde resin, and urea-formaldehyde resin, with polyamidepolyamine epichlorohydrin resin being preferred. When the paper substrate has multiple layers, the wet strength agent may be contained in some of the layers, but it is preferred that each layer contain it, and it is more preferred that the content of each layer be 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 and 1 part by mass or less, more preferably 0.03 part by mass or more, even more preferably 0.05 part by mass or more, still more preferably 0.1 part by mass or more, and more preferably 0.5 parts by mass or less, and even more preferably 0.3 parts by mass or less. Examples of internal sizing agents include rosin-based agents and alkyl ketene dimers, with rosin-based sizing agents being preferred. Examples of rosin-based sizing agents that can be used include acidic rosin-based sizing agents, weakly acidic rosin-based sizing agents, and neutral rosin-based sizing agents. When the paper substrate has multiple paper layers, some of the layers may contain the internal sizing 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. Note that, since the use of alkyl ketene dimer as the internal sizing agent tends to reduce edge wick resistance in water at 70°C, the content of alkyl ketene dimer in the internal sizing agent is preferably 10% by mass or less, more preferably 7% by mass or less, even more preferably 4% by mass or less, and even more preferably 0% by mass. The content of the internal sizing agent per 100 parts by mass of raw pulp is preferably 0.1 parts by mass or more and 5 parts by mass or less, more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, and more preferably 3 parts by mass or less, and even more preferably 1 part by mass or less.

[0021] The basis weight of the paper substrate is not particularly limited, but for example, in the case of packaging containers, preferably food containers, more preferably paper cups, it is preferably 180 g / m ２ More than 430g / m ２ More preferably, 200 g / m or less. ２More preferably, 220 g / m ２ More preferably, it is 380 g / m or more. ２ More preferably 330 g / m or less ２ Particularly preferably 280 g / m ２ The basis weight of the paper substrate is preferably equal to or greater than the lower limit from the viewpoint of obtaining sufficient paper strength as a packaging container, and is preferably equal to or less than the upper limit from the viewpoint of ease of manufacturing and formability of the waterproof paper. The basis weight of the paper substrate is measured in accordance with JIS P 8124:2011. The thickness of the paper substrate is also not particularly limited, but for example, for packaging containers, preferably food containers, and more preferably paper cups, it is preferably 210 μm or more and 480 μm or less, more preferably 230 μm or more, even more preferably 240 μm or more, more preferably 410 μm or less, even more preferably 380 μm or less, and even more preferably 330 μm or less. The thickness of the paper substrate is preferably equal to or greater than the lower limit from the viewpoint of obtaining sufficient paper strength as a packaging container, and is preferably equal to or less than the upper limit from the viewpoint of ease of manufacturing and formability of the waterproof paper. The thickness of the paper substrate is measured in accordance with JIS P 8118:2014. The density of the paper substrate is not particularly limited, but for example, in the case of packaging containers, preferably paper cups, it is preferably 0.4 g / cm ３ 1.1g / cm or more ３ or less, more preferably 0.6 g / cm ３ More preferably, 0.7 g / cm ３ More preferably, it is 1.0 g / cm or more. ３ More preferably, 0.95 g / cm or less ３ The density of the paper substrate is preferably equal to or greater than the lower limit from the viewpoint of obtaining sufficient paper strength as a packaging container, and is preferably equal to or less than the upper limit from the viewpoint of flexibility during molding. The density of the paper substrate is calculated from the basis weight and thickness of the paper substrate obtained by the above-mentioned measurement method.

[0022] [Method for manufacturing paper base material] Methods for manufacturing a paper base material include a method of making a stock containing pulp. The stock may further contain additives. Examples of additives include those listed above. The stock can be prepared by adding additives to a pulp slurry. The pulp slurry is obtained by beating pulp in the presence of water. The pulp beating method and beating device are not particularly limited, and may be the same as known beating methods and beating devices. The pulp content in the stock is not particularly limited, and may be within a commonly used range. For example, it is 60% by mass or more and less than 100% by mass relative to the total mass of the stock (solid content).

[0023] Papermaking from the stock can be carried out by a conventional method. For example, the stock can be cast onto a wire or the like, dewatered to obtain a wet paper, and multiple wet papers can be stacked as needed. This single-layer or multi-layer wet paper can be pressed and dried. In this case, if multiple wet papers are not stacked, a single-layer paper can be obtained, and if multiple wet papers are stacked, a multi-layer paper can be obtained. When multiple wet papers are stacked, an adhesive can be applied to the surface of the wet paper (the surface on which other wet papers will be stacked). The resulting paper substrate may have a difference in smoothness between one side and the other side. In this embodiment, from the viewpoint of obtaining a waterproof paper with excellent water resistance, air permeability, and oil resistance, it is preferable to provide the primer layer 1 and the water-resistant layer 1 in this order on the smoother side of the paper substrate, making it the liquid-contact surface (surface).

[0024] <Undercoat Layer> The waterproof paper of this embodiment has, from the paper substrate side, an undercoat layer 1 and a water-resistant layer 1 in this order on one side of the paper substrate, for example, the liquid-contacting surface (front surface). Here, the liquid-contacting surface refers to the surface that comes into contact with the liquid. For example, when the waterproof paper is used for a packaging container, it means the surface that comes into contact with the contents. In this case, the contents may be either liquid or non-liquid. The undercoat layer 1 preferably contains latex and a pigment. The waterproof paper of this embodiment may also have at least one of an undercoat layer 2 and a water-resistant layer 2 on the other side of the paper substrate, for example, the surface opposite the liquid-contacting surface (printing surface, back surface). Alternatively, the waterproof paper may have an undercoat layer 2 and a water-resistant layer 2 in this order from the paper substrate side, or the water-resistant layer 2 without an undercoat layer 2 in between. Alternatively, the paper substrate may be exposed on the other side of the paper substrate.

[0025] By providing the primer layer 1 on the surface, water-resistant paper with superior water resistance can be obtained. Furthermore, by providing the primer layer 2 on the back surface, printability is improved. On the surface, the primer layer 1 is provided between the paper substrate and the water-resistant layer 1. When the primer layer 2 is provided on the back surface, a water-resistant layer 2 may or may not be laminated on the primer layer 2. The water-resistant paper of this embodiment only needs to have the primer layer 1 on at least one surface (liquid-contacting surface), and the other surface (printing surface, back surface) does not necessarily need to have the primer layer 2. For paper cup applications, from the viewpoint of water resistance, it is necessary for at least the liquid-contacting surface to have the primer layer 1 and the water-resistant layer 1 from the paper substrate side. Furthermore, for paper cup applications for cold beverages, from the viewpoint of condensation prevention and printability, it is preferable for the printed surface to also have the water-resistant layer 2. On the other hand, for paper cup applications for hot beverages, condensation resistance is not required, and therefore the printed surface does not necessarily need to have a water-resistant layer. Therefore, the waterproof paper according to one embodiment of the present invention has a primer layer 1 and a water-resistant layer 1, in this order, on one side (front surface, liquid-contacting surface) of the paper substrate, and does not have a water-resistant layer 2 on the other side (back surface, printing surface) of the paper substrate. When used for paper cups for hot beverages, the primer layer 2 may be present on the other side (back surface, printing surface) of the paper substrate from the viewpoint of printability. That is, the waterproof paper according to another embodiment of the present invention has a primer layer 1 and a water-resistant layer 1, in this order, on one side (front surface, liquid-contacting surface) of the paper substrate, and a primer layer 2 on the other side (back surface, printing surface) of the paper substrate. Note that, from the viewpoint of improving heat-sealing properties, it is preferable to have a water-resistant layer on both the front surface and the back surface. The primer layer may be one layer or two or more layers per side. When the waterproof paper has a primer layer, it is preferable to have one primer layer from the viewpoint of productivity, but two or more layers are acceptable from the viewpoint of improving water resistance. When two or more undercoat layers are present on one side of the paper substrate, the composition and coating amount of each undercoat layer may be the same or different. When undercoat layers are present on one side and the other side of the paper substrate, the composition and coating amount of each undercoat layer may be the same or different.In the following description, primer layer 1 refers to the primer layer provided on the surface (front surface, liquid-contacting surface) having water-resistant layer 1, and primer layer 2 refers to the primer layer provided on the opposite surface (back surface, printing surface). When the distinction between primer layer 1 and primer layer 2 is not specified, the terms primer layer 1 and primer layer 2 are used collectively.

[0026] In this embodiment, the undercoat layer preferably contains latex and a pigment. The latex and pigment contained in the undercoat layer will be described in detail below. [Latex] In this embodiment, latex refers to a polymer that is stably dispersible in water. Latex is generally emulsified and dispersed with a surfactant or the like. Specific examples of latex are not particularly limited as long as the effects of the present invention are achieved, but include, for example, conjugated diene polymers such as styrene-butadiene copolymer and acrylonitrile-butadiene copolymer; acrylic polymers such as homopolymers of (meth)acrylic acid esters and copolymers of such homopolymers with monomers copolymerizable therewith (e.g., styrene-acrylic copolymer and methyl methacrylate-butadiene copolymer); vinyl polymers such as ethylene-vinyl acetate copolymer and vinyl chloride-vinyl acetate; polyurethane resin; 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 oil resistance, at least one selected from the group consisting of styrene-butadiene copolymers and acrylic polymers is preferred, an acrylic polymer is more preferred, and a styrene-acrylic copolymer is even more preferred. The styrene-acrylic copolymer is preferably a copolymer of styrene and an alkyl (meth)acrylate ester. As the latex, either a commercially available product or a synthetic product may be used. Examples of commercially available products include Acronal S728ap, Acronal S504ap, and Joncryl HPB-4110 manufactured by BASF Corporation, Luckstar 3307BE manufactured by DIC Corporation, and AQUEENCE EPIX BC900F, BC905F, and BC910F manufactured by Henkel Japan.

[0027] The glass transition temperature of the latex is not particularly limited either, but from the viewpoint of the adhesive strength between the water-resistant layer and the undercoat layer, it is preferably −50° C. or higher and 60° C. or lower, more preferably −20° C. or higher, even more preferably 0° C. or higher, and more preferably 40° C. or lower. The glass transition temperature of the latex is a value measured by differential scanning calorimetry (DSC).

[0028] In the undercoat layer, the mass ratio of latex to pigment (latex / pigment) is preferably 10 / 90 or more and 40 / 60 or less, more preferably 12 / 88 or more, and more preferably 35 / 65 or less, from the viewpoint of obtaining waterproof paper excellent in water resistance, air permeability, and oil resistance.

[0029] [Pigment] The pigment is not particularly limited, and examples thereof include 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, and satin white; and organic pigments such as solid, hollow, and core-shell pigments. These pigments may be used alone or in combination of two or more. Among these, from the viewpoint of further improving water resistance and / or oil resistance, at least one pigment selected from the group consisting of kaolin and calcium carbonate is preferred, and it is more preferred to contain at least kaolin, and it is even more preferred to use calcium carbonate and kaolin in combination. When calcium carbonate and kaolin are used in combination, the mass ratio of calcium carbonate to kaolin (calcium carbonate / kaolin) is not particularly limited, but is preferably 50 / 50 or more and 90 / 10 or less, more preferably 60 / 40 or more and 80 / 20 or less.

[0030] The average particle size of the pigment is not particularly limited, but is preferably 0.1 μm or more and 20 μm or less, more preferably 0.5 μm or more, and 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.

[0031] It is preferable to use a pigment (pigment 1) having an aspect ratio of 5 or more and a pigment (pigment 2) having an aspect ratio of less than 5 as pigments, from the viewpoints of improving the water resistance of the undercoat layer, adjusting the viscosity of the undercoat layer coating liquid, and reducing costs. The aspect ratio of pigment 1 is preferably 5 or more and 500 or less, more preferably 50 or more, and 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 1 or more. An example of a pigment having the above aspect ratio is heavy 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 the pigment diluted with a solvent or the like onto a glass substrate, allowing it to dry naturally, and measuring the thickness of each of 20 points of the oriented pigment on the glass substrate using a transmission electron microscope. Of the 20 thicknesses measured, the upper and lower three thicknesses are excluded, and the average of the remaining 14 thicknesses is calculated, and this average is designated as the average thickness.

[0032] In the undercoat 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 viewpoints of water resistance and heat sealability.

[0033] The undercoat layer may further contain components other than the latex and the pigment. Examples of such other components 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.

[0034] The coating amount of the undercoat layer is preferably 1 g / m per side. ２ 30g / m or more２ More preferably, it is 3 g / m or less. ２ More preferably, 4 g / m ２ More preferably, 7 g / m ２ More preferably, it is 20 g / m or more. ２ More preferably, 12 g / m or less ２ The coating amount of the undercoat layer per side is preferably equal to or greater than the above-mentioned lower limit from the viewpoint of obtaining waterproof paper excellent in water resistance, air permeability, and oil resistance, and is preferably equal to or less than the above-mentioned upper limit from the viewpoint of economy.

[0035] The method for forming the undercoat layer is not particularly limited, but for example, a coating liquid for the undercoat layer containing latex, pigment, and other components as necessary is prepared, and the coating liquid is applied to the paper substrate and dried. It is preferable that the smoother side of the paper substrate has the undercoat layer 1 and the water-resistant layer 1, and it is preferable that the undercoat layer 1 and the water-resistant layer 1 are formed in this order on the smoother side of the paper substrate as the liquid-contacting surface (surface).

[0036] When the waterproof paper of this embodiment has an undercoat layer, the basis weight of the laminate of the paper substrate and the undercoat layer (hereinafter also referred to as "undercoat paper") is not particularly limited, but for example, when used for packaging containers, preferably paper cups, it is preferably 200 g / m ２ 450g / m or more ２ More preferably, 220 g / m or less. ２ More preferably, 240 g / m ２ More preferably, it is 400 g / m or more. ２ More preferably 350 g / m or less ２ More preferably, 300 g / m or less ２or less. From the viewpoint of obtaining the paper strength required for a packaging container, the basis weight of the primer paper is preferably equal to or greater than the lower limit, and from the viewpoints of ease of manufacturing and formability of the waterproof paper, it is preferably equal to or less than the upper limit. The basis weight of the primer paper is measured in accordance with JIS P 8124:2011. The thickness (paper thickness) of the primer paper is also not particularly limited, but for example, when used for packaging containers, preferably paper cups, it is preferably 230 μm or more and 500 μm or less, more preferably 250 μm or more, even more preferably 260 μm or more, and more preferably 430 μm or less, even more preferably 400 μm or less, and even more preferably 350 μm or less. From the viewpoint of obtaining the paper strength required for a packaging container, the thickness of the primer paper is preferably equal to or greater than the lower limit, and from the viewpoints of ease of manufacturing and formability of the waterproof paper, it is preferably equal to or less than the upper limit. The thickness of the primer paper is measured in accordance with JIS P 8118:2014.

[0037] The density of the undercoat paper is not particularly limited, but for example, in the case of a packaging container, preferably a paper cup, it is preferably 0.4 g / cm from the viewpoint of obtaining paper strength as a packaging container and flexibility during molding. ３ 1.1g / cm or more ３ or less, more preferably 0.6 g / cm ３ More preferably, 0.7 g / cm ３ More preferably, it is 1.0 g / cm or more. ３ More preferably, 0.95 g / cm or less ３ The density of the primer paper is calculated from the basis weight and thickness of the primer paper obtained by the above-mentioned measurement method.

[0038] The Oken smoothness of the surface of the primer paper on which the water-resistant layer 1 is formed (liquid-contacting surface, front surface) is preferably 20 seconds or more, more preferably 25 seconds or more, and even more preferably 30 seconds or more, with no particular upper limit, but for example, 500 seconds or less. When the Oken smoothness of the surface is equal to or greater than the above-mentioned lower limit, the Oken smoothness of the surface of the waterproof paper having the water-resistant layer 1 can be kept within the desired range. The Oken smoothness is measured in accordance with JIS P 8115:2010.

[0039] <Water-Resistant Layer> The waterproof paper of this embodiment has a waterproof layer 1 on one surface (e.g., the liquid-contacting surface) of the paper substrate. In the waterproof paper of this embodiment, the waterproof layer 1 is formed on the paper substrate via an undercoat layer 1. From the viewpoint of heat-sealability, the waterproof layer is preferably provided as the uppermost layer on at least one surface of the paper substrate, and more preferably as the uppermost layer on at least the liquid-contacting surface.

[0040] The waterproof paper of this embodiment has one or more waterproof layers on at least one side of the paper substrate, and may have two or more waterproof layers on at least one side. From the viewpoint of productivity, a single waterproof layer is preferable, and from the viewpoint of improving water resistance, two or more waterproof layers are preferable. Furthermore, the waterproof layer only needs to be provided on at least the liquid-contacting surface (hereinafter, the liquid-contacting surface is also referred to as the front surface), and may also be provided on the back surface, which is the opposite side via the paper substrate. Furthermore, when used in applications where condensation occurs, such as paper cups for cold water, it is preferable to have one or more waterproof layers on the outer surface (the surface opposite the liquid-contacting surface, also referred to as the back surface or printed surface), and two or more waterproof layers may be provided. That is, the waterproof paper of this embodiment preferably has waterproof layers on both sides of the paper substrate, and preferably has a waterproof layer 2 on the other side of the paper substrate. When two or more water-resistant layers are present on one side of the paper substrate, the compositions and coating amounts of the respective water-resistant layers may be the same or different, and when water-resistant layers are present on both sides of the paper substrate, the compositions and coating amounts of the respective water-resistant layers may be the same or different. In the following description, unless water-resistant layer 1 or water-resistant layer 2 is specified, water-resistant layer 1 and water-resistant layer 2 are collectively referred to.

[0041] The water-resistant layer preferably contains an aqueous resin. An aqueous resin refers to 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. Among these, from the viewpoints of water resistance and heat sealability, it is preferable to contain at least one selected from the group consisting of ethylene-(meth)acrylic acid copolymers, styrene-acrylic copolymers, and ethylene-α-olefin copolymers, with ethylene-(meth)acrylic acid copolymers or styrene-acrylic copolymers being more preferred, and ethylene-(meth)acrylic acid copolymers being even more preferred. The aqueous resins may be used alone or in combination of two or more. The water-resistant layer 1 may contain an ethylene-(meth)acrylic acid copolymer, and when the waterproof paper of this embodiment has a water-resistant layer 2, both the water-resistant layer 1 and the water-resistant layer 2 may contain an ethylene-(meth)acrylic acid copolymer.

[0042] From the viewpoint of heat sealability, when water-resistant layers are present on both the front surface (liquid-contacting surface) and the back surface (printing surface), it is preferable that the water-resistant layers on both surfaces contain the same type of aqueous resin. The same type of aqueous resin on the front and back surfaces tends to improve heat sealability. Therefore, for example, when the water-resistant layer on the front surface contains an ethylene-(meth)acrylic acid copolymer as the aqueous resin and the back surface has a water-resistant layer, it is preferable that the water-resistant layer on the back surface contains an ethylene-(meth)acrylic acid copolymer as the aqueous resin. While the water-resistant layers on both surfaces may contain different types of aqueous resins, it is preferable that the polarities of the resins are similar from the viewpoint of heat sealability.

[0043] The ethylene-(meth)acrylic acid copolymer may be an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer. The styrene-acrylic copolymer may be a styrene-(meth)acrylic acid alkyl ester copolymer. As the aqueous resin, commercially available products may be used, such as AQUENCE EPIX BC 9220HS manufactured by Henkel Japan Co., Ltd., and MP498345N, MP4983R, MP4990R, and 201103PX manufactured by Michelman Japan LLC. Examples include S, MFHS1279, ZAIKXEN (registered trademark) A and ZAIKXEN (registered trademark) AC manufactured by Sumitomo Seika Chemicals Co., Ltd., the Chemipearl series (S100, S300, 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 Mitsui-Dow Polychemicals Co., Ltd., HYPOD2000, RHOBAR R320, and RHOBAR R325 manufactured by Dow Chemical Japan Ltd., Hitec SC-100 manufactured by Toho Chemical Industry Co., Ltd., AQUATEX AC-3100 manufactured by Chuo Rika Kogyo Co., Ltd., AQUEENCE EPIX BC900F, BC905F, and BC910F manufactured by Henkel Japan, and Joncryl HPB-4110 manufactured by BASF.

[0044] From the viewpoint of water resistance, the content of the aqueous resin in the water-resistant layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, still more preferably 90% by mass or more, and even more preferably 95% by mass or more, but not more than 100% by mass, of the resin component of the water-resistant layer. Here, the resin component of the water-resistant layer means a polymer component contained in the water-resistant layer, i.e., a compound having a weight-average molecular weight of 1,000 or more.

[0045] The water-resistant layer may contain other components in addition to the aqueous resin described above. 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 anti-blocking agents such as inorganic pigments and synthetic resins. From the viewpoint of ensuring water resistance and heat sealability, the total content of these 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.

[0046] The water-resistant layer is obtained by preparing a coating liquid for the water-resistant layer containing an aqueous resin and applying the coating liquid. 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.

[0047] The ethylene-(meth)acrylic acid copolymer blended in the coating solution for the water-resistant layer may be in the form of an ionomer. Here, an ionomer is a copolymer neutralized with a cation. That is, ethylene-methacrylic acid copolymers and synthetic resins obtained by neutralizing ethylene-acrylic acid copolymers with a cation all fall under the category of ionomers. Ionomers may be used alone or in combination of two or more. Examples of cations include metal ions such as sodium ions, potassium ions, calcium ions, and magnesium ions, and ammonium ions (NH ４ ＋ ), and organic ammonium ions.

[0048] The method for applying the coating liquid for the water-resistant layer is not particularly limited, and a coating device appropriately selected from commonly used coating devices may be used. Examples include various known coating devices 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, and lip coater. From the viewpoint of improving 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). Furthermore, from the same viewpoint, 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.

[0049] The coating amount of the water-resistant layer 1 is preferably 5 g / m ２ 20g / m or more ２ More preferably, 6 g / m or less ２ More preferably, 7 g / m ２ More preferably, it is 15 g / m or more. ２ More preferably, 12 g / m or less ２ The coating weight of the water-resistant layer 1 is preferably equal to or greater than the above-mentioned lower limit from the viewpoint of improving water resistance and oil resistance, and is preferably equal to or less than the above-mentioned upper limit from the viewpoints of formability, cost, and recyclability. When the water-resistant layer 1 is two or more layers, the coating weight of the water-resistant layer 1 refers to the total coating weight of the layers.

[0050] The coating amount of the water-resistant layer 2 is preferably 2 g / m ２ 15g / m or more ２ More preferably, it is 3 g / m or less. ２ More preferably, it is 10 g / m or more. ２ More preferably, 5 g / m or less ２The coating amount of the water-resistant layer 2 is preferably equal to or greater than the above-mentioned lower limit from the viewpoint of improving water resistance and heat sealability, and is preferably equal to or less than the above-mentioned upper limit from the viewpoint of formability and cost. When the water-resistant layer 2 comprises two or more layers, the coating amount of the water-resistant layer 2 refers to the total coating amount of the layers.

[0051] The total coating amount of the water-resistant layer 1 and the water-resistant layer 2, i.e., the total coating amount of the water-resistant layers on the front and back surfaces, is preferably 6 g / m from the viewpoints of water resistance, air permeability, and oil resistance. ２ 20g / m or more ２ More preferably, 7 g / m or less ２ More preferably, 7.5 g / m ２ More preferably, it is 17 g / m or more. ２ More preferably 14 g / m or less ２ or less. Therefore, when the waterproof paper of this embodiment is used for a packaging container (preferably a food container, for example, a paper cup) and has a water-resistant layer on only one side (the liquid-contacting side), the total coating weight of the waterproof layer on the liquid-contacting side is preferably within the above-mentioned range. Furthermore, when the waterproof paper of this embodiment is used for a packaging container (preferably a food container, for example, a paper cup) and has a water-resistant layer on both sides (the liquid-contacting side and the printed side), the total coating weight of the waterproof layer on the liquid-contacting side and the total coating weight of the waterproof layer on the printed side are preferably within the above-mentioned ranges, and the total coating weight of the waterproof layers on both sides is preferably within the above-mentioned range.

[0052] The waterproof paper of this embodiment may have other layers in addition to the undercoat layer and water-resistant layer. Examples of such other layers include a printed layer, a water vapor barrier layer, an oxygen barrier layer, an oxygen-absorbing layer, and an adhesion-imparting 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 printed surface). The printed content may be a pattern, a design, or information (ingredients, expiration date, QR Code (registered trademark), etc.). Furthermore, in paper cup applications for hot beverages, the waterproof layer 1 may be provided on one surface (liquid-contacting surface) of the paper substrate, and the paper substrate may be exposed on the other surface (printed surface, back surface) of the paper substrate; however, this may result in poor heat-sealing properties (side-sealing properties) when forming the body of the paper cup. Therefore, from the viewpoint of improving heat sealability (side sealability), an adhesion-imparting layer may be provided on the other surface (printed surface, back surface) of the paper substrate. The adhesion-imparting layer can be formed using a known resin such as an olefin resin, a vinyl alcohol resin, an amide resin, or an amine resin. The water-resistant paper of this embodiment preferably has, on at least one surface of the paper substrate, one or more (preferably only one) primer layer provided in direct contact with the paper substrate, and one or more (preferably only one) water-resistant layer provided in direct contact with the primer layer, in this order. It is more preferable that the paper be composed of only the paper substrate, primer layer, and water-resistant layer. The other surface is not particularly limited, but for example, in paper cup applications for cold beverages, it is preferable to have one or more (preferably only one) undercoat layers provided so as to be in direct contact with the paper substrate, and one or more (preferably only one) water-resistant layers provided so as to be in direct contact with the undercoat layers, in that order; and in paper cup applications for hot beverages, it may have one or more (preferably only one) undercoat layers provided so as to be in direct contact with the paper substrate.

[0053] [Basis Weight] The basis weight of the waterproof paper is not particularly limited, but for example, when used for packaging containers, preferably food containers, more preferably paper cups, it is preferably 220 g / m２ More than 500g / m ２ More preferably, 240 g / m or less. ２ More preferably, 250 g / m ２ More preferably, it is 450 g / m or more. ２ More preferably 400 g / m or less ２ More preferably, 350 g / m or less ２ More preferably, 300 g / m or less ２ The basis weight of the waterproof paper is preferably equal to or greater than the lower limit from the viewpoint of water resistance and strength as a packaging container, and is preferably equal to or less than the upper limit from the viewpoint of ease of production of the waterproof paper, formability, and recyclability of the pulp that constitutes the paper base material. The basis weight of the waterproof paper is measured in accordance with JIS P 8124:2011.

[0054] [Thickness] The thickness of the waterproof paper (paper thickness) is not particularly limited, but for example, for packaging containers, preferably food containers, and more preferably paper cups, it is preferably 230 μm or more and 500 μm or less, more preferably 250 μm or more, even more preferably 270 μm or more, and more preferably 430 μm or less, even more preferably 400 μm or less, and even more preferably 350 μm or less. From the viewpoint of water resistance and strength as a packaging container, the thickness of the waterproof paper is preferably equal to or greater than the lower limit, and from the viewpoint of ease of manufacturing the waterproof paper, moldability, and recyclability of the pulp constituting the paper base, it is preferably equal to or less than the upper limit. The thickness of the waterproof paper is measured in accordance with JIS P 8118:2014.

[0055] [Density] The density of the waterproof paper is not particularly limited, but for example, in the case of a packaging container, preferably a paper cup, the density is preferably 0.4 g / cm from the viewpoint of obtaining paper strength as a packaging container and flexibility during molding. ３ 1.1g / cm or more ３ or less, more preferably 0.6 g / cm ３ More preferably, 0.7 g / cm ３ More preferably, it is 1.0 g / cm or more. ３More preferably, 0.95 g / cm or less ３ The density of the waterproof paper is calculated from the basis weight and thickness of the waterproof paper obtained by the above-mentioned measurement method.

[0056] <Physical Properties of Water-Resistant Paper> [Edgewick Value] In terms of Edgewick resistance to cold water, the water-resistant paper of the present embodiment preferably has an Edgewick value of 0.70 g / 1000 mm in water at 20° C. after a contact time of 60 minutes. ２ or less, more preferably 0.60 g / 1000 mm ２ More preferably, 0.50 g / 1000 mm or less ２ More preferably, 0.40 g / 1000 mm or less ２ The lower limit of the Edgewick value in water at 20° C. is not particularly limited, but from the viewpoint of ease of production, it is, for example, 0.10 g / 1000 mm ２ The Edge Wick value in cold water can be adjusted to a desired range by adjusting the type and amount of sizing agent, the type and amount of wet strength agent, etc. The Edge Wick value is measured in accordance with JIS P 8118:2014.

[0057] Furthermore, in terms 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 water at 70° C. after immersion for 20 minutes. ２ Preferably, it is 0.70 g / 1000 mm or less. ２ or less, more preferably 0.60 g / 1000 mm ２ More preferably, 0.50 g / 1000 mm or less ２ The lower limit of the Edgewick value in water at 70° C. is not particularly limited, but from the viewpoint of ease of production, it is, for example, 0.10 g / 1000 mm ２ The Edge Wick value in hot water can be adjusted to a desired range by adjusting the type and amount of sizing agent, the type and amount of wet strength agent, etc. The Edge Wick value is measured in accordance with JIS P 8118:2014.

[0058] [Oil Resistance] The waterproof paper of this embodiment has a Kit value of 10 or more, preferably 11 or more (maximum value 12), on the side having the waterproof layer 1, measured in accordance with JAPAN TAPPI No. 41 (Kit method). A higher Kit value indicates better oil resistance. A Kit value of 10 or more is suitable for use in food packaging applications. The Kit value of the waterproof paper can be adjusted within a desired range by adjusting the average Runkel ratio of the pulp constituting the paper base, the type of resin used in the waterproof layer 1 and the coating amount of the waterproof layer 1, the type of pigment used in the primer layer 1 and the amount of latex, the coating amount of the primer layer 1, etc.

[0059] [Oken Smoothness] In the waterproof paper of this embodiment, from the viewpoint of water resistance, the Oken Smoothness on the side having the waterproof layer 1 is 80 seconds or more, preferably 90 seconds or more, and more preferably 100 seconds or more. The upper limit of the Oken Smoothness is not particularly limited, but from the viewpoint of ease of manufacturing, it is, for example, 500 seconds or less. The Oken Smoothness on the side having the waterproof layer 1 of the waterproof paper can be adjusted within the desired range by adjusting the average Runkel ratio of the pulp constituting the paper base, the type of resin used in the waterproof layer 1 and the coating amount of the waterproof layer 1, the type of pigment used in the primer layer 1 and the amount of latex, the coating amount of the primer layer 1, and the like. The Oken Smoothness of the waterproof paper is a value measured in accordance with JIS P 8155:2010.

[0060] [Cobb Water Absorbency] In terms of water resistance to cold water, the waterproof paper of the present embodiment has a Cobb water absorbency of 12 g / m2 or more in water at 20°C on the side having the water-resistant layer 1 after a contact time of 30 minutes. ２ or less, more preferably 10 g / m ２ Less than 8 g / m, more preferably ２ More preferably, 6 g / m or less ２ More preferably, 4 g / m or less ２ or less (the lower limit is 0 g / m ２The Cobb water absorbency at 20°C can be adjusted within a desired range by adjusting the average Runkel ratio of the pulp constituting the paper base, the type of resin used in the water-resistant layer 1 and the coating amount of the water-resistant layer 1, the type of pigment used in the primer layer 1 and the amount of latex, the coating amount of the primer layer 1, etc. The Cobb water absorbency is a value 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 / m2 or less in water at 90°C for a contact time of 30 minutes on the side having the water-resistant layer 1. ２ or less, more preferably 12 g / m ２ More preferably, 10 g / m or less ２ More preferably, 8 g / m or less ２ Below 6 g / m, particularly preferably ２ or less (the lower limit is 0 g / m ２ The Cobb water absorbency at 70°C can be adjusted within a desired range by adjusting the Runkel ratio of the average pulp constituting the paper base, the type of resin used in the water-resistant layer 1 and the coating amount of the water-resistant layer 1, the type of pigment used in the primer layer 1 and the amount of latex, the coating amount of the primer layer 1, etc. The Cobb water absorbency is a value measured in accordance with JIS P 8140:1998.

[0062] [Oken Air Permeability] The waterproof paper of this embodiment preferably has an Oken air permeability of 30,000 seconds or more, more preferably 50,000 seconds or more, even more preferably 70,000 seconds or more, and even more preferably 90,000 seconds or more. The higher the Oken air permeability, the smoother and less breathable the waterproof paper's surface (higher air permeability resistance) is, i.e., the fewer surface defects (pinholes) in the waterproof layer 1. Within the above range, the waterproof paper has excellent water and oil resistance and is less susceptible to staining, making it suitable for use in food packaging. The Oken air permeability can be adjusted within the desired range by adjusting the average Runkel ratio of the pulp constituting the paper substrate, the type of resin used in the waterproof layer 1 and the coating weight of the waterproof layer 1, the type and amount of pigment and latex used in the primer layer 1, and the coating weight of the primer layer 1. The Oken air permeability is measured in accordance with JIS P 8117:2009.

[0063] <Uses of Water-Resistant Paper> The water-resistant paper of this embodiment is easily cleaned by rinsing with water after use, and the easy removal of stains also suppresses odor generation. Therefore, it 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 surface of the water-resistant 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 paper cups) made using the above-described water-resistant paper. Furthermore, the water-resistant paper of this embodiment has excellent oil resistance, making it suitable for use in food packaging applications. The contents of the packaging container may be either food or non-food. Furthermore, the contents of the packaging container may be liquid, solid, or gel. The contents of the packaging container are not particularly limited, and 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. Packaging containers made from the water-resistant paper of this embodiment use less plastic than packaging containers made from conventional laminated paper. Furthermore, while packaging containers made from conventional laminated paper require a pulper with high repulping performance to be recycled as waste paper, packaging containers made from the water-resistant paper of this embodiment can be repulped with a pulper with normal repulping performance, resulting in excellent recyclability. Packaging containers made from the water-resistant paper of this embodiment can be washed, cut, repulped, etc. to prepare a pulp slurry, and paper can be produced using the obtained pulp slurry. The type of paper to be produced is not particularly limited, and examples include printing paper, packaging paper, sanitary paper, cardboard, etc. The produced paper can also be processed to produce packaging containers (e.g., tissue boxes, paper cup sleeves, etc.).

[0064] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, 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, unless otherwise specified, the operations in the examples and comparative examples were carried out under conditions of room temperature (20 to 25°C) and normal humidity (40 to 50% RH (relative humidity)).

[0065] The raw materials used in the Examples and Comparative Examples are as follows. <Raw Material Pulp> LBKP1: Hardwood bleached kraft pulp (LBKP) made from eucalyptus and acacia. Runkel ratio: 0.29. The detailed blending ratios are as follows: Eucalyptus A and B are from different tree species and origins: Eucalyptus A: Runkel ratio: 0.24, blended at 15% by mass Eucalyptus B: Runkel ratio: 0.31, blended at 75% by mass Acacia A: Runkel ratio: 0.25, blended at 10% by mass LBKP2: Hardwood bleached kraft pulp (LBKP) made from acacia. Runkel ratio: 0.60. The detailed blending ratios are as follows: Acacia A, B, and C are from different tree species and origins: Acacia B: Runkel ratio 0.60, 50% by mass blend Acacia C: Runkel ratio 0.60, 50% by mass blend NBKP: Softwood bleached kraft pulp made from Radiata pine and Douglas fir. Runkel ratio 0.85. The detailed blend ratios are as follows: Radiata pine: Runkel ratio 0.80, 40% by mass Douglas fir: Runkel ratio 0.88, 60% by mass <Wet strength agents> Polyamide polyamine epichlorohydrin resin (PAE): trade name "WS4038", manufactured by Seiko PMC Corporation <Dry strength agents> Cationic starch: trade name "OptiBOND3005", manufactured by Ingredion Japan Inc. <Sizing agents> Weakly acidic rosin sizing agent: trade name "NeuRoz CF50", manufactured by Harima Chemicals Co., Ltd. (Hereinafter, the weakly acidic rosin sizing agent may be simply referred to as "rosin".) Alkyl ketene dimer sizing agent: trade name "AD1612", manufactured by Seiko PMC Corporation (Hereinafter, the alkyl ketene dimer sizing agent may be simply referred to as "AKD".) <Pigment> Heavy calcium carbonate: trade name "FMT-90", average particle size 1.15 μm, aspect ratio 1.0 to 3.0, Fimatec Co., Ltd. Kaolin: trade name "Barisurf HX", manufactured by Imerys Co., Ltd., average particle size 9.0 μm, aspect ratio 80 to 100 <Latex> Styrene-acrylic copolymer latex (trade name "Acronal S728ap", manufactured by BASF Corporation, glass transition temperature 23°C) <Antifoaming agent> Trade name "Bismar KS-38E", manufactured by Nissin Chemical Laboratory Co., Ltd. <Aqueous resin dispersion> Trade name "AQUENCE EPIX BC 9220HS", manufactured by Henkel Japan Ltd., solid content concentration 23% by mass, polyolefin resin dispersion - Product name "RHOBARR320", manufactured by Dow, solid content concentration 43 mass%, polyolefin resin dispersion - Product name "RHOBARR325", manufactured by Dow, solid content concentration 47 mass%, polyolefin resin dispersion.

[0066] <Preparation of Coating Liquid for Undercoat Layer> A pigment dispersion with a solids concentration of 70% by mass was prepared using 70 parts by mass of heavy calcium carbonate and 30 parts by mass of kaolin as the pigment. A styrene-acrylic copolymer latex was blended with this pigment dispersion to prepare a pigment / styrene-acrylic copolymer latex mixture such that the pigment content in the solids was 85.0% by mass and the styrene-acrylic copolymer latex content was 15.0% by mass. A defoamer was blended with this mixture to prepare a coating liquid for undercoat layer with a solids concentration of 62% by mass, with a pigment / styrene-acrylic copolymer latex content of 99.5% by mass and an defoamer content of 0.5% by mass.

[0067] <Preparation of Coating Liquid for Water-Resistant Layer> (a) Preparation of Coating Liquid A An antifoaming agent was blended into an aqueous resin dispersion (AQUENCE EPIX BC 9220HS, manufactured by Henkel Japan Ltd.), and water was added to adjust the solid content, thereby preparing Coating Liquid A having a solid content of 19 mass% and a water-based resin content of 99.5 mass% and an antifoaming agent content of 0.5 mass% in the solid content.

[0068] (b) Preparation of Coating Solution B An antifoaming agent was blended into an aqueous resin dispersion (RHOBAR R320, manufactured by Dow), and water was added to adjust the solid content, thereby preparing Coating Solution B having a solid content of 16 mass%, with the aqueous resin content being 99.5 mass% and the antifoaming agent content being 0.5 mass% in the solid content.

[0069] (c) Preparation of Coating Solution C An antifoaming agent was blended into an aqueous resin dispersion (RHOBAR R325, manufactured by Dow), and water was added to adjust the solid content, thereby preparing Coating Solution C, which had a solid content of 16 mass% and contained 99.5 mass% of aqueous resin and 0.5 mass% of antifoaming agent in the solid content.

[0070] Example 1 A stock for the outer layers (first layer, fifth layer) was prepared by adding 0.85 parts by mass of a weakly acidic rosin sizing agent, 0.15 parts by mass of a wet strength agent, and 0.70 parts by mass of a dry strength agent (cationized starch) to 100 parts by mass (solid content equivalent) of a pulp slurry prepared by mixing beaten LBKP1 (CSF 400 mL) and beaten NBKP (CSF 500 mL) in a ratio of 90% by mass and 10% by mass. Similarly, 0.85 parts by mass of a weakly acidic rosin sizing agent, 0.15 parts by mass of a wet strength agent, and 0.70 parts by mass of a dry strength agent (cationized starch) were added to 100 parts by mass (solids content) of a pulp slurry prepared by mixing beaten LBKP1 (CSF 425 mL) and beaten NBKP (CSF 525 mL) in proportions of 80% by mass and 20% by mass, to prepare paper stock for the inner layers (second and fourth layers). Similarly, 0.85 parts by mass of a weakly acidic rosin sizing agent, 0.15 parts by mass of a wet strength agent, and 0.70 parts by mass of a dry strength agent (cationized starch) were added to 100 parts by mass (solid content equivalent) of a pulp slurry prepared by mixing beaten LBKP1 (CSF 475 mL) and beaten NBKP (CSF 600 mL) at a ratio of 70% by mass and 30% by mass, to prepare a stock for the inner layer (third layer). Using these stocks, the first to fifth layers were made in order on a five-layer papermaking Fourdrinier machine, with a weight of 40 g / m. ２ , 40 g / m ２ , 90 g / m ２ , 40 g / m ２ , 40 g / m ２Next, the coating liquid for the undercoat layer was applied to the surface (liquid contact surface) of the paper substrate with a rod blade coater in a coating amount (solid content) of 5 g / m ２ The paper substrate was then coated with Coating Solution A in an amount (solid content) of 8.0 g / m and dried to form Undercoat Layer 1. The smoother side of the paper substrate was used as the liquid-contacting surface. ２ The coating was then applied using an air knife coater so that the coating amount (solid content) was 4.0 g / m, and the resultant was dried to form a water-resistant layer 1. Next, Coating Solution A was applied to the printing surface side in an amount (solid content) of 4.0 g / m. ２ The resulting mixture was coated using an air knife coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer 2, thereby obtaining water-resistant paper.

[0071] Example 2 Waterproof paper was obtained in the same manner as in Example 1, except that the composition of the raw pulp in Example 1 was changed as shown in Table 1 and a paper stock prepared in this manner was used.

[0072] Example 3: The coating amount (solid content) of the undercoat layer 1 was 10 g / m ２ A waterproof paper was obtained in the same manner as in Example 1, except that the above-mentioned step was changed to the above.

[0073] Example 4 A waterproof paper was obtained in the same manner as in Example 1, except that the waterproof layers 1 and 2 were formed using Coating Solution B.

[0074] Example 5 A waterproof paper was obtained in the same manner as in Example 1, except that the waterproof layer 2 was not formed.

[0075] Example 6 A waterproof paper was obtained in the same manner as in Example 1, except that the coating liquids for the waterproof layers 1 and 2 were changed to the coating liquid C.

[0076] Example 7 The paper substrate obtained in Example 1 was coated with a coating liquid for an undercoat layer on the surface (liquid-contacting surface) of the paper substrate using a rod blade coater in a coating amount (solid content) of 5 g / m ２ The coating solution for the undercoat layer was applied to the back surface (printing surface) of the paper substrate with a rod blade coater so that the coating amount (solid content) was 5 g / m ２The paper substrate was then coated with Coating Solution A in an amount (solid content) of 8.0 g / m and dried to form Undercoat Layer 2. The smoother side of the paper substrate was used as the liquid-contacting surface. ２ The coating was then applied using an air knife coater so that the coating amount (solid content) was 4.0 g / m, and the resultant was dried to form a water-resistant layer 1. Next, Coating Solution A was applied onto the undercoat layer 2 in an amount (solid content) of 4.0 g / m. ２ The resulting mixture was coated using an air knife coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer 2, thereby obtaining water-resistant paper.

[0077] Example 8 A waterproof paper was obtained in the same manner as in Example 7, except that the waterproof layer 2 was not provided.

[0078] Comparative Example 1 Waterproof paper was obtained in the same manner as in Example 1, except that a paper stock prepared by changing LBKP1 to LBKP2 was used.

[0079] <Comparative Example 2> A waterproof paper was obtained in the same manner as in Example 1, except that the composition of the raw pulp in Example 1 and the coating amount of the water-resistant layer 1 were changed as shown in Table 1 and a paper stock prepared using the same was used.

[0080] <Comparative Example 3> Waterproof paper was obtained in the same manner as in Example 3, except that the sizing agent was changed to an alkyl ketene dimer (AKD) sizing agent, and 0.20 parts by mass of this sizing agent was added to 100 parts by mass (solid content equivalent) of the pulp slurry to prepare paper stock for all layers (first layer, second layer, third layer, fourth layer, and fifth layer).

[0081] Comparative Example 4: The coating amount (solid content) of the undercoat layer 1 was 1.9 g / m ２ A waterproof paper was obtained in the same manner as in Example 1 except for changing the above.

[0082] [Measurements and evaluations of the pulp constituting the paper base, the primer paper, and the waterproof paper] The following measurements and evaluations were carried out on the pulp constituting the paper base, and the primer paper and waterproof paper obtained in Examples 1 to 8 and Comparative Examples 1 to 4 above.

[0083] <Runkel ratio> The fiber width, fiber coarseness, and lumen diameter of the pulp were measured using a fiber length measuring device (Valmet Fiber Image Analyzer Valmet FS5, manufactured by Valmet). The Runkel ratio of each pulp was calculated using the following formula: Runkel ratio = fiber wall thickness × 2 / lumen diameter The fiber wall thickness was calculated using the following formula (circular approximation).

[0084]

[0085] In the above formula, Wa = fiber wall thickness (μm), Wi = fiber width (μm), C = fiber roughness (mg / m), d = density (kg / dm) ３ The density d was calculated by the following formula using the water retention value WRV of the pulp measured in accordance with JIS P 8228:2018.

[0086]

[0087] The average Runkel ratio of the pulp constituting the paper base material was calculated from the Runkel ratio of each pulp (LBKP1, LBKP2, NBKP) and the pulp blend. When measuring the Runkel ratio from waterproof paper, the waterproof paper is disintegrated in accordance with JIS P 8220-1:2012, and the above measurement is carried out on the obtained pulp, whereby the average Runkel ratio constituting the paper base material can be calculated.

[0088] <CSF of pulp raw material constituting paper base material> The CSF of the raw pulp of the paper base material was measured in accordance with JIS P 8121-2:2012 "Pulp - Freeness test method - Part 2: Canadian standard freeness method."

[0089] <Basis weight, thickness, and density of primer paper and waterproof paper> The basis weight of the primer paper and waterproof paper was measured in accordance with JIS P 8124: 2011. The thickness of the primer paper and waterproof paper was measured in accordance with JIS P 8118: 2014. The density of the primer paper and waterproof paper was calculated from the basis weight and thickness obtained by the above-mentioned measurement methods.

[0090] <Smoothness (Oken Smoothness)> Measured in accordance with JIS P 8155:2010.

[0091] <Water resistance (Cobb water absorbency)> The obtained waterproof paper was cut into a 10 cm square, and the surface (liquid-contacting surface) of the obtained sample was brought into contact with ion-exchanged water at 20°C or 90°C for 30 minutes in accordance with JIS P 8140: 1998, and the Cobb water absorbency was calculated from the difference in mass of the sample before and after contact. A lower value indicates higher water resistance.

[0092] <Air permeability (Oken air permeability)> Measured in accordance with JIS P 8117:2009.

[0093] <Oil Resistance> The oil resistance of the surface (liquid-contacting surface) was evaluated in accordance with JAPAN TAPPI No. 41 (kit method). A higher value (kit value) indicates higher oil resistance.

[0094] <Pinholes> A sufficient amount (approximately 5 mL) of dyeing solution (trade name: "Isodine Mouthwash", manufactured by Mundipharma Co., Ltd.) was applied to the surface (liquid-contacting surface) of an A5-size sample (water-resistant paper) using a Mayer bar to cover the entire sample, and left to stand for 1 minute. Thereafter, the dyeing solution on the surface was wiped clean, and the presence of pinholes was evaluated. [Evaluation criteria] A: No pinholes at all (0 pinholes in the A5-size sample) B: Some pinholes (1 to 9 pinholes in the A5-size sample) C: Many pinholes (10 or more pinholes in the A5-size sample) (An "A" rating indicates no practical problems.)

[0095] <Edgewick Value> First, the thickness of the waterproof paper was measured in accordance with JIS P 8118:2014. Then, commercially available polyethylene film was laminated on both sides of the waterproof paper, and a test piece of 60 mm x 90 mm was cut out so that the edge was exposed, and the mass of the test piece (mass before immersion) was measured. The test piece was immersed in ion-exchanged water at 20°C for 60 minutes or 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. The Edgewick value of the waterproof paper in ion-exchanged water was then calculated using the following formula. Edgewick value [g / 1000 mm ２ ] = (mass after immersion (g) - mass before immersion (g)) / paper thickness (mm) / circumference (mm)

[0096] <Staining after washing> The obtained waterproof paper was formed into a cup shape with the front surface facing inward (liquid-contacting surface) and the back surface facing outward (printed surface). Coffee at 70°C was poured into the cup up to 80% of its maximum capacity. After 30 minutes, the contents of the cup were discarded. Nescafé Excella coffee manufactured by Nestlé Japan Ltd. was used, with a concentration of 1.5% by mass. After 80% of the maximum capacity of 23°C ion-exchanged water was poured into the cup and immediately discarded (within 3 seconds) to wash the inside of the cup, the staining on the paper surface and edge of the cup (the edge through which the coffee passed when discarded) was visually evaluated. [Evaluation criteria for the paper surface] 1: Almost no coffee color remained on the paper surface inside the cup. 2: A faint coffee color remained on the paper surface inside the cup. 3: A clear coffee color remained on the paper surface inside the cup. [Evaluation criteria for edge surfaces] A: Width of coffee penetration from the paper edge surface inside the cup is 1 mm or less B: Width of coffee penetration from the paper edge surface inside the cup is more than 1 mm

[0097] <Odor after washing> After evaluating the stains after washing, the cups were stored for 7 days in an environment of 23°C and 25% relative humidity, and then the odor inside the cups was evaluated. Five panelists were selected who passed a panel selection test conducted by an odor judge using five standard odor liquids, and the evaluation was based on the following criteria, with the average of the five panelists' scores rounded to the nearest whole number to determine the evaluation score. [Evaluation criteria] 0: No odor 1: Barely detectable odor 2: Can identify what the odor is, but it is a weak odor 3: Easily detectable odor 4: Strong odor 5: Overpowering odor

[0098]

[0099] Regarding Oken air permeability, ">99999" means more than 99,999 seconds. Pulp freeness (CSF), types and amounts of internal additives are as follows: (Pulp Freeness) Outer layer (top and bottom) (5th layer and 1st layer): NBKP 500 mL, LBKP 400 mL (Examples 1 to 8, Comparative Examples 1 to 4) Inner layer (bottom top and bottom back layers) (4th layer and 2nd layer): NBKP 525 mL, LBKP 425 mL (Examples 1 to 8, Comparative Examples 1 to 4) Inner layer (middle layer) (3rd layer): NBKP 600 mL, LBKP 475 mL (Examples 1 to 8, Comparative Examples 1 to 4) (Types and Amounts of Internal Chemicals Added) Wet strength agent: PAE (polyamide polyamine epichlorohydrin resin), 0.15 parts by mass per 100 parts by mass of pulp (dry mass) (Examples 1 to 8, Comparative Examples 1 to 4) Dry paper strength agent: cationized starch, 0.70 parts by mass per 100 parts by mass of pulp (dry mass) (Examples 1 to 8, Comparative Examples 1 to 4) Sizing agent: rosin, 0.85 parts by mass per 100 parts by mass of pulp (dry mass) (Examples 1 to 8, Comparative Examples 1, 2, and 4) Sizing agent: AKD (alkyl ketene dimer), 0.20 parts by mass per 100 parts by mass of pulp (dry mass) (Comparative Example 3)

[0100] The waterproof papers obtained in Examples 1 to 8 were disintegrated, and the Runkel ratios of the pulps constituting the paper base were measured. All of the results were 0.51 or less. As can be seen from the results in Table 1, the waterproof papers had primer layer 1 and water-resistant layer 1 on one side of the paper base, in this order from the paper base side. The Edgewick value in water at 70°C after a contact time of 20 minutes was 0.80 g / 1000 mm. ２The paper cups made using the waterproof paper of Examples 1 to 8, in which the surface having the waterproof layer 1 of the waterproof paper had a Kit value of 10 or more and an Oken smoothness of 80 seconds or more on the surface having the waterproof layer 1 of the waterproof paper, were easy to remove stains by rinsing with water and the generation of odors was suppressed after storage for a certain period of time after rinsing. On the other hand, the paper cups made using the waterproof paper of Comparative Examples 1, 2, and 4, in which the surface having the waterproof layer 1 of the waterproof paper had an Oken smoothness of less than 80 seconds and a Kit value of less than 10 on the surface having the waterproof layer 1 of the waterproof paper, were difficult to remove stains by rinsing with water and generated odors after storage for a certain period of time after rinsing. In addition, the Edgewick value in 70°C water was 0.80 g / 1000 mm ２ The paper cups made using the waterproof paper of Comparative Example 3, which was above 100%, were difficult to remove stains from by washing with water, and emitted a strong odor after being stored for a certain period of time after washing.

Claims

1. A waterproof paper having a primer layer 1 and a waterproof layer 1 in this order from the paper substrate side on one side of the paper substrate, Edge wick value in 70°C water after 20 minutes of contact time: 0.80g / 1000mm ２ is as follows: The kit value on the side of the waterproof paper having the waterproof layer 1 is 10 or more, The Oken smoothness of the surface of the waterproof paper having the waterproof layer 1 is 80 seconds or more. Water resistant paper.

2. 2. The waterproof paper according to claim 1, wherein the pulp constituting the paper base has an average Runkel ratio of 0.51 or less.

3. 3. The waterproof paper according to claim 1, wherein the pulp raw material constituting the paper base material contains at least one selected from the group consisting of bleached hardwood kraft pulp (LBKP) and bleached softwood kraft pulp (NBKP), and the mass ratio of the bleached hardwood kraft pulp (LBKP) to the bleached softwood kraft pulp (NBKP) (LBKP / NBKP) is 60 / 40 or more and 100 / 0 or less.

4. 3. The waterproof paper according to claim 1, wherein the undercoat layer 1 contains latex and a pigment, and the mass ratio of the latex to the pigment (latex / pigment) is 10 / 90 or more and 40 / 60 or less.

5. 3. The waterproof paper according to claim 1, further comprising at least one of a primer layer 2 and a waterproof layer 2 on the other side of the paper substrate.

6. The coating amount of the undercoat layer 1 is 4 g / m ２ The waterproof paper according to claim 1 or 2, wherein the above-mentioned

7. 3. The waterproof paper according to claim 1, wherein the waterproof layer 1 contains at least one resin selected from the group consisting of polyolefin-based resins and acrylic-based resins.

8. 3. The waterproof paper according to claim 1, wherein the paper substrate contains a starch-based dry strength agent.

9. The basis weight of the paper base material is 200 g / m ２ The waterproof paper according to claim 1 or 2, wherein the above-mentioned

10. The surface of the waterproof paper having the waterproof layer 1 has a Cobb water absorption of 10 g / m2 at 20°C for a contact time of 30 minutes. ２ 3. The waterproof paper according to claim 1, wherein:

11. On the side of the waterproof paper having the waterproof layer 1, the Cobb water absorption of water at 90°C for a contact time of 30 minutes is 20 g / m ２ 3. The waterproof paper according to claim 1, wherein:

12. 3. The waterproof paper according to claim 1, having an Oken air permeability of 30,000 seconds or more.

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

14. A packaging container made using the waterproof paper according to claim 1 or 2.