Water-resistant paper and liquid containers

Abstract

To provide a waterproof paper having excellent water resistance, blocking resistance and heat sealing properties. [Solution] This is water-resistant paper having a water-resistant layer as the top layer on at least one side of a paper base material, the water-resistant layer containing ethylene-methacrylic acid copolymer and organic particles, the melting point or softening point of the organic particles being 100°C or higher, and the content of organic particles in the water-resistant layer being 40 mass% or less.

Description

[Technical field]

[0001] The present invention relates to a waterproof paper and a liquid container using the same. [Background technology]

[0002] Conventionally, plastic products have been used as various containers for beverages, foods, etc., but there is a demand for a shift 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 deal with such problems, attempts have been made to impart properties such as water resistance by imparting properties during the papermaking process or by imparting properties through coating. Patent Document 1 describes a paper container base paper for cups, cup lids, paper plates, etc., which has processing suitability such as water resistance, heat sealability, top curl suitability, and gravure print suitability equivalent to that of polyethylene laminated paper and has excellent recyclability for effective use of resources, and which has an undercoat layer for sealing and a topcoat layer consisting of a water-resistant and oil-resistant layer on at least one side of a base paper, and in which the undercoat layer is made of a pigment / binder resin layer and has a coating amount of 4 to 15 g / m per side. 2 The amount of resin applied to the water- and oil-resistant topcoat layer is 2g / m per side. 2 The paper container base paper is as described above and is characterized by satisfying the following requirements A to D. A. The absorbency of the base paper Cobb is 50g / m 2 Below, the smoothness is 10 seconds or more. B. The pigment used in the undercoat layer has an aspect ratio of 5 to 30 and an average particle size of 0.5 to 30 μm. C. The blending ratio of the undercoat layer is 10 to 100 parts by mass of the binder resin per 100 parts by mass of the pigment. D. The water- and oil-resistant resin used in the topcoat layer has a gel fraction of 70% or more and is a water-dispersible resin with a critical surface tension of 25 dyn / cm or more.

[0003] In addition, Patent Document 2 discloses a packaging paper having at least one heat seal layer on at least one side of a paper base material, the heat seal layer containing an ionomer, and the dry coating amount of the heat seal layer is 2 to 10 g / m2 in total, for the purpose of providing a packaging paper that can reduce the amount of plastic used. 2 and a packaging paper characterized in that the heat seal layer is formed in two or more layers on at least one surface. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 9-158089 [Patent Document 2] Patent No. 6580291 Summary of the Invention [Problem to be solved by the invention]

[0005] When waterproof paper is continuously produced, it is produced while being wound up on a roll, but during this process, there is a problem that the coated surface of the wound waterproof paper sticks to the back surface of the waterproof paper, causing peeling (blocking). Patent documents 1 and 2 leave room for improvement in regard to such a problem. An object of the present invention is to provide a waterproof paper which is excellent in water resistance, blocking resistance and heat sealability. [Means for solving the problem]

[0006] The present inventors have found that by blending an ethylene-methacrylic acid copolymer in the water-resistant layer and further blending a specific amount of organic particles having a specific melting point or softening point, it is possible to obtain a water-resistant paper that is excellent in water resistance, blocking resistance and heat sealability. <1> ~ <16> Regarding. <1> A water-resistant paper having a water-resistant layer on the uppermost layer on at least one side of a paper base material, the water-resistant layer containing an ethylene-methacrylic acid copolymer and organic particles, the melting point or softening point of the organic particles being 100°C or higher, and the content of the organic particles in the water-resistant layer being 40 mass% or less. <2> The average particle size of the organic particles is 0.01 μm or more and 50 μm or less. <1> The water-resistant paper described in <3> The organic particles are polyolefin particles; <1> or <2> The water-resistant paper described in <4> The organic particles are at least one selected from the group consisting of polypropylene particles, polyethylene particles, and propylene-ethylene copolymer resin particles; <1> ~ <3> 2. A waterproof paper according to any one of the preceding claims. <5> The content of organic particles in the water-resistant layer is 0.5% by mass or more. <1> ~ <4> 2. A waterproof paper according to any one of the preceding claims. <6> The organic particles are water-dispersible organic particles. <1> ~ <5> 2. A waterproof paper according to any one of the preceding claims. <7> The coating weight of the water-resistant layer is 0.1 g / m 2 More than 20g / m 2 Below is the <1> ~ <6> 2. A waterproof paper according to any one of the preceding claims. <8> At least one undercoat layer and a water-resistant layer are provided on at least one surface of the paper substrate in this order. <1> ~ <7> 2. A waterproof paper according to any one of the preceding claims. <9> The undercoat layer contains an ethylene-methacrylic acid copolymer. <8> The water-resistant paper described in <10> Air permeability is 1,000 seconds or more. <1> ~ <9> 2. A waterproof paper according to any one of the preceding claims. <11> The Cobb water absorption of the surface with the water-resistant layer in water at 20°C for 30 minutes is 40 g / m 2 Below is the <1> ~ <10> 2. A waterproof paper according to any one of the preceding claims. <12> The Cobb water absorption of the surface with the water-resistant layer in 90°C water for 30 minutes is 100g / m 2 Below is the <1> ~ <11> 2. A waterproof paper according to any one of the preceding claims. <13> Has heat sealability, <1> ~ <12> 2. A waterproof paper according to any one of the preceding claims. <14> For liquid containers or their lids, <1> ~ <13> 2. A waterproof paper according to any one of the preceding claims. <15> <1> ~ <14> A liquid container or a lid thereof, comprising the waterproof paper described in any one of the above. <16> The liquid container is a paper cup; <15> A liquid container according to claim 1, or a lid thereof. Effect of the Invention

[0007] According to the present invention, it is possible to provide a waterproof paper which is excellent in water resistance, blocking resistance and heat sealability. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] [Waterproof paper] The waterproof paper of this embodiment is a waterproof paper having a waterproof layer as the uppermost layer on at least one side of a paper base material, the waterproof layer containing an ethylene-methacrylic acid copolymer and organic particles, the melting point or softening point of the organic particles being 100°C or higher, and the content of the organic particles in the waterproof layer being 40 mass% or less. According to the embodiment, it is possible to provide a waterproof paper that is excellent in water resistance, blocking resistance and heat sealability. The detailed reasons why the above-mentioned effects are obtained are unclear, but part of the reason is thought to be as follows. In this embodiment, an ethylene-methacrylic acid copolymer is blended in the water-resistant layer, which is thought to provide excellent water resistance and heat sealability. In addition, by blending a specific amount of organic particles having a specific melting point or softening point in the water-resistant layer, the surface of the water-resistant layer is roughened without deteriorating the water resistance and heat sealability, and when the water-resistant paper is superimposed, the water-resistant layer is prevented from sticking to the back surface of the water-resistant paper, resulting in a water-resistant paper with excellent blocking resistance. In addition, in the manufacturing process of waterproof paper, when coating layers are provided on the front and back sides of a paper substrate, it is common to coat and dry one side to provide a coating layer, wind it up, unwind it, and coat and dry the other side to provide a coating layer. In this case, there is a problem that the coating layer coated in the previous stage is rubbed by a metal roll in the subsequent coating and drying process, causing roll contamination. In this embodiment, by making the top layer of the coating layer provided in the previous stage a waterproof layer, it is also possible to have the effect of suppressing the occurrence of roll contamination during double-sided coating. This embodiment will be described in further detail below.

[0009] <Water resistant layer> In this embodiment, the waterproof paper has a waterproof layer containing an ethylene-methacrylic acid copolymer and organic particles on the uppermost layer on at least one surface of a paper substrate. The waterproof paper of this embodiment may have waterproof layers on both sides of the paper base.

[0010] [Ethylene-methacrylic acid copolymer] In this embodiment, the water-resistant layer contains an ethylene-methacrylic acid copolymer. As a result of intensive research, the present inventors have found that excellent water resistance can be obtained by including an ethylene-methacrylic acid copolymer in the water-resistant layer. In addition, as another effect, by blending an ethylene-methacrylic acid copolymer, a water-resistant paper with excellent heat sealability can be obtained. Here, the ethylene-methacrylic acid copolymer may be blended as an ionomer. Note that "blended as an ionomer" means that an ionomer is used as a raw material at least when the water-resistant layer is produced, and the water-resistant layer does not necessarily contain a resin in the form of an ionomer after production. An ionomer is a polymer neutralized with a cation. In other words, any resin made by neutralizing an ethylene-methacrylic acid copolymer with a cation is an ionomer. In addition to metal ions, ammonium ions (NH 4+ ), and organic ammonium ions. Metal ions include lithium ions (Li + ), sodium ion (Na + ), potassium ion (K + ), magnesium ions (Mg 2+ ), calcium ion (Ca 2+ ), alkaline earth metal ions such as zinc ions (Zn 2+ ), copper ions (Cu 2+ Among these, sodium ions are preferred as the metal ions from the viewpoint of availability and the like.

[0011] As the ethylene-methacrylic acid, commercially available products may be used, and examples thereof include the Chemipearl series (S-100, S-300, S-500) manufactured by Mitsui Chemicals, MYE-30ER and MYE-30MAZ manufactured by Maruyoshi Chemical Co., Ltd., the Surlyn series manufactured by DuPont, the Himilan series manufactured by Mitsui-DuPont Polychemicals, Hi-Tec SC-100 manufactured by Toho Chemical Industry Co., Ltd., and Aquatex AC-3100 manufactured by Chuo Rika Kogyo Co., Ltd.

[0012] The content of ethylene methacrylic acid in the water-resistant layer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more, from the viewpoint of water resistance, particularly water resistance to hot water, and heat sealability, and is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less, from the viewpoint of blocking resistance.

[0013] [Organic particles] In this embodiment, the water-resistant layer contains organic particles in addition to the ethylene-methacrylic acid copolymer. The organic particles have a melting point or softening point of 100°C or higher. When the melting point or softening point of the organic particles is 100°C or higher, the organic particles do not melt or soften during drying, and excellent blocking properties are obtained. Furthermore, the above-mentioned roll staining can be suppressed. In addition, when organic particles having a melting point or softening point of 100°C or higher are contained, water resistance is improved. Although the reason for this is unclear, it is believed that due to the difference in melting point (or softening point) between the ethylene-methacrylic acid copolymer and the organic particles, cracks that occur during film formation of the ethylene-methacrylic acid copolymer are filled with the organic particles that melt later, reducing cracks and pinholes in the water-resistant layer. However, the effects of the present invention are not limited by the above mechanism. The melting point or softening point is preferably 110°C or higher, more preferably 120°C or higher, and even more preferably 125°C or higher. There is no upper limit, but it is preferably 240°C or lower, more preferably 200°C or lower, and even more preferably 160°C or lower. The melting point or softening point of the organic particles is measured by the ring and ball softening point method, JIS K2207:2006.

[0014] The organic particles are preferably water-dispersible organic particles, from the viewpoint that the coating liquid for the water-resistant layer is preferably an aqueous coating liquid. That is, the organic particles are preferably blended in the coating liquid for the water-resistant layer as an aqueous dispersion. In addition, from the viewpoint of improving the heat sealability and water resistance, it is preferable that the aqueous dispersion of the organic particles contains little or no surfactant, dispersant, etc. Examples of the organic particles include polyester particles, acrylic particles, polystyrene particles, nylon particles, silicone particles, and polyolefin particles, and from the above-mentioned viewpoint, polyolefin particles are preferred. Examples of the polyolefin resin constituting the polyolefin particles include polymers of olefins such as ethylene, propylene, 1-butene, 1-pentene, and 1-hexene. The polyolefin resin may be a homopolymer or copolymer of the olefins listed above. The polyolefin resin may be modified. Examples of the modification include anion modification and cation modification, and it is also preferable to use polyolefin particles whose dispersibility in water is improved by modification. The polyolefin particles are more preferably at least one selected from the group consisting of polyethylene particles, polypropylene particles, and propylene-ethylene copolymer resin particles. The polyethylene may be high density polyethylene or low density polyethylene, and the polypropylene may be high density polypropylene or low density polypropylene, and there is no particular limitation.

[0015] The shape of the organic particles is not particularly limited, but is preferably spherical. The average particle size of the organic particles is preferably 0.01 μm or more, more preferably 0.02 μm or more, and even more preferably 0.03 μm or more from the viewpoint of blocking resistance, and is preferably 50 μm or less, more preferably 30 μm or less, even more preferably 15 μm or less, and even more preferably 10 μm or less from the viewpoint of maintaining heat sealability. In addition, when the average particle size of the organic particles is larger than or approximately the same as the thickness of the water-resistant layer, unevenness is formed on the coating surface, resulting in excellent blocking resistance and suppression of roll staining. For the above reasons, the average particle size of the organic particles is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more. In addition, if the average particle size of the organic particles is smaller than the film thickness, for example, less than 1.0 μm, when the water-resistant layer is provided, the organic particles are oriented on the coating film surface as the water contained in the coating liquid for the water-resistant layer evaporates, protecting the surface of the water-resistant layer, resulting in excellent blocking resistance and suppressing roll staining. For the above reasons, the average particle size of the organic particles is preferably 0.5 μm or less, more preferably 0.3 μm or less, and even more preferably 0.1 μm or less. The average particle size of the organic particles is measured by a laser diffraction particle size distribution measuring device based on the principle of the laser diffraction method or by a cole counter method.

[0016] From the viewpoint of blocking resistance, the content of organic particles in the water-resistant layer is preferably 0.5% by mass or more, more preferably 1.0% by mass or more, and even more preferably 1.5% by mass or more, and from the viewpoint of heat sealability, it is 40% by mass or less, preferably 35% by mass or less, more preferably 30% by mass or less, even more preferably 25% by mass or less, still more preferably 15% by mass or less, and particularly preferably 10% by mass or less. From the viewpoint of improving blocking resistance and water resistance, the mass ratio of the ethylene-methacrylic acid copolymer to the organic particles in the water-resistant layer (ethylene-methacrylic acid copolymer / organic particles) is preferably 60 / 40 or more, more preferably 70 / 30 or more, even more preferably 75 / 25 or more, and is preferably 99.5 / 0.5 or less, more preferably 99 / 1 or less, even more preferably 98 / 2 or less.

[0017] In addition to the above-mentioned ethylene-methacrylic acid copolymer and organic particles, other components may be added to the water-resistant layer. Examples of other components include antifoaming agents, viscosity modifiers, leveling agents such as surfactants and alcohols, and colorants such as coloring dyes. Among these, from the viewpoint of suppressing the incorporation of air bubbles into the layer due to foaming, it is preferable to contain a defoaming agent as another component. The defoaming agent may be appropriately selected from commercially available products, and specific examples thereof include various defoaming agents manufactured by Nissin Chemical Laboratory Co., Ltd. The amount of the antifoaming agent to be added is not particularly limited, but is preferably 0.1 parts by mass or more and 3.0 parts by mass or less based on 100 parts by mass of the ethylene-methacrylic acid copolymer (solid content). Since these other components tend to deteriorate water resistance and heat sealability, the total content of the other components is preferably 50 mass % or less, more preferably 30 mass % or less, and even more preferably 10 mass % or less, of the solid content of the water-resistant layer.

[0018] The water-resistant layer is obtained by preparing a coating liquid for the water-resistant layer containing an ethylene-methacrylic acid copolymer and organic particles, and coating this on at least one surface of the paper base material. The coating solution for the water-resistant layer is preferably a self-emulsifying dispersion, i.e., the coating solution for the water-resistant layer preferably does not contain an emulsifier such as a surfactant or a dispersant.

[0019] The method for applying the coating solution for the water-resistant layer is not particularly limited, and may be appropriately selected from commonly used coating devices, such as an air knife coater, a blade coater, a gravure coater, a rod blade coater, a roll coater, a reverse roll coater, a bar coater, a curtain coater, a die slot coater, a champlex coater, a metering blade type size press coater, a short dwell coater, a spray coater, a gate roll coater, and a lip coater.

[0020] [Preferred embodiment of water-resistant layer] The waterproof paper of this embodiment only needs to have a waterproof layer as the uppermost layer on at least one side of the paper base material, and it is also preferable to have a waterproof layer on both sides of the paper base material. By providing water-resistant layers on both sides, the paper can be suitably used in applications where condensation occurs (such as paper cups for cold water, etc.).

[0021] The waterproof paper has a waterproof layer on the top layer of at least one side. By providing the waterproof layer containing ethylene-methacrylic acid copolymer and a pigment on the top layer of the paper base, waterproof paper can be provided with waterproof and heat sealability as well as blocking resistance. The coating amount of the water-resistant layer is preferably 0.1 g / m from the viewpoint of providing a water-resistant layer excellent in water resistance, heat sealability and blocking resistance. 2 More preferably, 0.5 g / m 2 More preferably, 1.0 g / m 2 More preferably, 3.0 g / m 2 and preferably 20 g / m 2 Less than 15g / m 2 More preferably, 10 g / m 2 The following is the result. From the viewpoint of providing a water-resistant layer having excellent water resistance, heat sealability and blocking resistance, the thickness of the water-resistant layer is preferably 0.1 μm or more, more preferably 0.5 μm or more, even more preferably 1.0 μm or more, and even more preferably 3.0 μm or more, and is preferably 20 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less.

[0022] <Other layers> In this embodiment, the waterproof paper preferably has an undercoat layer under the waterproof layer from the viewpoint of further improving the waterproofness. That is, the waterproof paper preferably has an undercoat layer and a waterproof layer in this order on a paper substrate. By providing an undercoat layer, the waterproofness can be further improved and the heat sealability can also be improved, which is preferable. In addition, by providing an undercoat layer, the adhesion to the paper substrate can be improved. Examples of the undercoat layer include a water-resistant undercoat layer intended to impart water resistance and heat sealability, and a pigment coating layer provided for the purposes of sealing and improving printability.

[0023] [Water-resistant undercoat layer] The water-resistant undercoat layer preferably contains an ethylene-methacrylic acid copolymer, and examples of the ethylene-methacrylic acid copolymer include those mentioned above as components of the water-resistant layer. That is, the ethylene-methacrylic acid blended in the water-resistant undercoat layer may be an ethylene-methacrylic acid copolymer ionomer, for example, a metal salt of an ethylene-methacrylic acid copolymer or an ammonium salt of an ethylene-methacrylic acid copolymer. The water-resistant undercoat layer may contain, in addition to ethylene methacrylic acid, other components exemplified above for the water-resistant layer. It is also preferable that the water-resistant undercoat layer is a composition that does not include organic particles from the above-mentioned water-resistant layer, but in that case, the poor stickiness may cause the roll to become dirty, making coating difficult. From the viewpoint of suppressing the above-mentioned phenomenon and improving the stability of operation, it is also preferable to incorporate organic particles in the water-resistant undercoat layer in addition to the ethylene-methacrylic acid copolymer. Examples of organic particles to be incorporated in the water-resistant undercoat layer include those mentioned above as components of the water-resistant layer. The preferred ranges of the average particle size, melting point or softening point of the organic particles are also as mentioned above. When the water-resistant undercoat layer contains an ethylene-methacrylic acid copolymer and organic particles, the mass ratio of the ethylene-methacrylic acid copolymer and the organic particles in the water-resistant undercoat layer (ethylene-methacrylic acid copolymer / organic particles) is, from the viewpoint of water resistance and blocking resistance, preferably 60 / 40 or more, more preferably 70 / 30 or more, even more preferably 75 / 25 or more, and is preferably 99.5 / 0.5 or less, more preferably 99 / 1 or less, even more preferably 98 / 2 or less, from the viewpoint of improving blocking resistance and water resistance.

[0024] The coating amount of the water-resistant undercoat layer is preferably 1.0 g / m from the viewpoint of improving water resistance and reducing the coating amount of the water-resistant layer. 2 More preferably, 2.0 g / m 2 More preferably, 2.5 g / m 2 and preferably 20 g / m 2 Less than 15g / m 2 More preferably, 10 g / m2 Less than 8.0 g / m 2 The following is the result.

[0025] [Pigment coating layer] The waterproof paper of the present embodiment may have a pigment coating layer between the paper substrate and the waterproof layer, or between the paper substrate and the waterproof undercoat layer. The pigment coating layer can seal and smooth the paper substrate. This allows the formation of a uniform waterproof undercoat layer and waterproof layer, improving the waterproofness and heat sealability.

[0026] The pigment coating layer is mainly composed of a pigment and a binder. The phrase "the pigment coating layer is mainly composed of a pigment and a binder" means that the total content of the pigment and the binder in the pigment coating layer is, for example, 50% by mass or more, preferably 60% by mass or more, more preferably 70% 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. The upper limit is not particularly limited, but is 100% by mass or less. The pigment coating layer may further contain any optional components other than the pigment and the binder. The pigment contained in the pigment coating layer is not particularly limited, but examples thereof include kaolin, talc, and mica. The average particle size of the pigment is not particularly limited, but is preferably 0.03 μm or more, more preferably 0.1 μm or more, even more preferably 0.5 μm or more, and is preferably 30 μm or less, more preferably 10 μm or less, even more preferably 4 μm or less. The average particle size of the pigment is a value measured by a sedimentation method. When the pigment is a layered inorganic compound, the average particle size means the average major axis. The aspect ratio of the pigment is preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more. There is no particular upper limit, but it is preferably 10,000 or less. The aspect ratio can be measured by observation with an electron microscope or X-ray diffraction measurement. The pigment content in the pigment coating layer is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 35% by mass or more, and preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 60% by mass or less.

[0027] The binder contained in the pigment coating layer is not particularly limited, but examples thereof include styrene-butadiene resins; acrylic resins such as methyl acrylate copolymers, methyl methacrylate copolymers, styrene-acrylic copolymers, and styrene-methacrylic copolymers; olefin-unsaturated carboxylic acid copolymers such as ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers; and the like, with styrene-butadiene resins being more preferred. The content of the binder in the pigment coating layer is preferably 10% by mass or more, more preferably 20% by mass or more, even more preferably 30% by mass or more, and preferably 80% by mass or less, more preferably 70% by mass or less, even more preferably 65% ​​by mass or less. The coating amount of the pigment coating layer is not particularly limited, but is preferably 1 g / m2 in terms of solid content. 2 More preferably, 2 g / m 2 and preferably 10 g / m 2 Less than 5g / m 2 The following is the result. The method for forming the pigment coating layer is not particularly limited, but a method in which a dispersion containing a pigment and a binder is applied onto a paper substrate and then dried to form the pigment coating layer is preferred. The dispersion containing the pigment and the resin binder is preferably an aqueous dispersion. The pigment coating layer may contain, in addition to the pigment and binder, the components exemplified as other components in the water-resistant layer, and preferably contains a defoaming agent.

[0028] The waterproof paper of this embodiment may have waterproof layers on both sides of a paper base material, and may have a configuration in which, for example, a first waterproof layer, a waterproof undercoat layer, a pigment coating layer, a paper base material, and a second waterproof layer are laminated in this order. Also, a layer not containing resin particles and having water resistance and heat sealability may be provided on the side opposite to the side having the water-resistant layer.

[0029] <Paper base material> The waterproof paper of the present embodiment has a waterproof layer on the uppermost layer of at least one surface of a paper substrate. When the waterproof paper is used for food containers, it is preferable that the paper be a multi-layer paper having a surface layer, a back layer, and at least one middle layer. 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), pressurized groundwood pulp (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), chemi-mechanical pulp (CMP), and chemi-ground pulp (CGP), waste paper pulp, non-wood fiber pulps such as kenaf, bagasse, bamboo, and cotton, and synthetic pulps. These pulps may be used alone or in combination of two or more.

[0030] The beating degree of the pulp is not particularly limited, but is preferably 200 mL or more and 650 mL or less, more preferably 350 mL or more and 600 mL or less, in terms of Canadian Standard Freeness (CSF). If the CSF of the pulp is within the above range, the necessary paper strength is easily obtained when the waterproof paper is used as a base paper for liquid containers. If it is 200 mL or more, the interfiber bond is not too high, and the stress such as compression and tension is concentrated on the outermost layer of the folded part during the folding process in the molding process, and the occurrence of the phenomenon in which the resin layer is destroyed can be suppressed, and good processability can be maintained. Also, if it is 650 mL or less, the smoothness of the paper surface is good, and printability can be maintained. CSF is measured in accordance with JIS P 8121-2:2012 "Pulp - Test method for freeness - Part 2: Canadian standard freeness method".

[0031] Examples of additives to paper base materials include pH adjusters (sodium bicarbonate, sodium hydroxide, etc.), dry strength agents (polyacrylamide, starch, etc.), wet strength agents (polyamide polyamine epichlorohydrin resin, melamine-formaldehyde resin, urea-formaldehyde resin), internal sizing agents (rosin-based, alkyl ketene dimer, etc.), drainage retention improvers, antifoaming agents, fillers (calcium carbonate, talc, etc.), dyes, etc. 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 a range that is commonly used.

[0032] The basis weight of the paper substrate is not particularly limited, but for example, for paper cup applications, it is 200 g / m 2 More than 350g / m 2 The following is preferred: The basis weight of the paper base material is measured in accordance with JIS P 8124:2011. The thickness of the paper base material is not particularly limited, but for example, for paper cup applications, it is preferably 250 μm or more and 450 μm or less. The thickness of the paper base material is measured in accordance with JIS P 8118:2014.

[0033] [Method of manufacturing paper base material] The method for producing the paper base material includes a method of making a paper stock containing pulp. The paper stock may further contain additives. Examples of the additives include the additives listed above. The stock can be prepared by adding additives 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 content of pulp in the paper stock is not particularly limited and may be within a range that is usually used, for example, 60% by mass or more and less than 100% by mass based on the total mass of the paper stock (solid content).

[0034] The papermaking process can be carried out by a standard method. For example, the papermaking process can be carried out by casting the paper onto a wire or the like, dehydrating the paper to obtain a wet paper, stacking multiple wet papers as necessary, pressing the single-layer or multi-layer wet paper, and drying the resulting paper. 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).

[0035] <Water-resistant paper properties> The waterproof paper of the present embodiment preferably has an air permeability of 1,000 seconds or more, more preferably 10,000 seconds or more, even more preferably 25,000 seconds or more, and even more preferably 99,999 seconds or more. The upper limit of the air permeability is not particularly limited, but is, for example, 1,000,000 seconds or less. By setting the air permeability within the above range, the barrier property in terms of blocking air is improved, and a waterproof paper with even better water resistance can be obtained. In particular, when the waterproof paper has two or more waterproof layers or when a pigment layer is provided as an underlayer of the waterproof layer, the air permeability can be increased. The air permeability is measured in accordance with JIS P 8117:2009.

[0036] From the viewpoint of cold water resistance, the waterproof paper of the present embodiment has a Cobb water absorbency in water at 20° C. for 30 minutes on the surface on which the waterproof layer is provided, of preferably 40 g / m 2 Less than 20 g / m, more preferably 20 g / m 2 More preferably, 15 g / m or less 2 More preferably, 10 g / m or less 2 The lower limit is not particularly limited. The Cobb water absorbency is measured in accordance with JIS P 8140:1998.

[0037] From the viewpoint of water resistance to hot water, the water-resistant paper of the present embodiment has a Cobb water absorbency in water at 90° C. for 30 minutes on the surface on which the water-resistant layer is provided, of preferably 100 g / m 2 Less than 60 g / m 2Less than 30 g / m, more preferably 30 g / m 2 More preferably, 20 g / m or less 2 The lower limit is not particularly limited. The Cobb water absorbency is measured in accordance with JIS P 8140:1998.

[0038] The waterproof paper of the present embodiment preferably has excellent blocking resistance, and after heating at 65° C. for 30 minutes, it can be applied with a pressure of 0.5 kg / cm 2 When the waterproof paper is peeled off after cooling, it is preferable that there is little or no resistance, and it is more preferable that it is peeled off without resistance.

[0039] In the waterproof paper of this embodiment, the waterproof layer preferably has heat sealability. The heat sealing conditions are not particularly limited, but the temperature during heat sealing is, for example, 60°C or higher and 300°C or lower, the pressure during heat sealing is, for example, 0.05 MPa or higher and 10 MPa or lower, and the pressure application time is, for example, 0.1 seconds or higher and 15 seconds or lower.

[0040] The water-resistant paper of the present embodiment is preferably used for liquid containers such as paper cups or their lids, and other paper containers that require water resistance (for example, paper trays). When used for liquid containers, it is preferable from the viewpoint of formability that the water-resistant layer has heat sealability. As an example of forming a liquid container, printing is applied to the front or back of waterproof paper as necessary, and the paper is punched out into a shape corresponding to the shape of the liquid container to be manufactured, folded, and the overlapping parts are heat sealed to form a liquid container. The waterproof paper of this embodiment has excellent water resistance and heat sealability, and therefore has excellent moldability. EXAMPLES

[0041] The features of this embodiment will be described in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, processing contents, processing 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. Note that % means mass % unless otherwise specified.

[0042] The raw materials used in the examples and comparative examples are as follows. [Resin component] Ethylene-methacrylic acid copolymer ionomer: Aqueous dispersion of metal salt of ethylene-methacrylic acid copolymer, product name "Chemipearl S-300", manufactured by Mitsui Chemicals, Inc., solid content concentration 35.0 mass% Ethylene-acrylic acid copolymer ionomer: Aqueous dispersion of ethylene-acrylic acid copolymer ammonium salt, product name "Zaixen AC", manufactured by Sumitomo Seika Chemicals Co., Ltd., solid content concentration 29.3% by mass, copolymerization ratio of acrylic acid 21.1% by mass

[0043] [Particle components (organic particles, inorganic particles (pigments))] Kaolin / SBR=4 / 6, product name "VB2160", kaolin particle size=0.1~4μm, manufactured by Michaelman Japan LLC High density PE (HDPE), product name "ME61335P (MICHEM EMULSION 61335P)", manufactured by Michaelman Japan LLC, particle size 30-60nm Low molecular weight PE + modified PO (modified polyolefin, low molecular weight PO), product name "Chemipearl W310", manufactured by Mitsui Chemicals, Inc., particle size 9.5 μm Engineered kaolin, product name "Balisurf HX", manufactured by Imerys Minerals Japan Co., Ltd., average particle size 2.0 μm, aspect ratio 100 [others] Defoamer: Product name "Bismar KS38-E", manufactured by Nisshin Chemical Laboratory Co., Ltd.

[0044] [Example 1] (a) Preparation of pigment layer coating solution A An antifoaming agent was added to VB2160 with a kaolin / SBR ratio of 4 / 6 to prepare pigment layer coating solution A (coating solution A) with a solids concentration of 40.0% by mass, where the VB2160 content in the solids was 98.9% by mass and the antifoaming agent content was 1.1% by mass. (b) Preparation of Coating Solution B The ethylene-methacrylic acid copolymer ionomer was mixed with HDPE and an antifoaming agent to prepare Coating Solution B having a solid content of 30 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 75.8 mass%, the HDPE content being 22.7 mass%, and the antifoaming agent content being 1.5 mass% in the solid content.

[0045] <Preparation of waterproof paper> Basis weight 224g / m 2 The coating solution A was applied to one side (front side) of a paper substrate having a thickness of 268 μm in a coating amount (solid content) of 2.5 g / m 2 The surface was coated with coating solution B using an air knife coater so that the coating amount (solid content) was 2.5 g / m. 2 The substrate was coated with a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the first layer on the surface, thickness approximately 2.5 μm). Coating solution B was then applied again to the same surface so that the coating amount (solid content) was 2.5 g / m2. 2 The coating solution B was applied to the same surface in an amount (solid content) of 5.0 g / m2 using a gravure coater and then dried to form a water-resistant undercoat layer (hereinafter referred to as the second layer on the surface, thickness: about 2.5 μm). 2 The mixture was coated using an air knife coater and dried to form a water-resistant layer (hereinafter referred to as the third layer in the table, film thickness approximately 5.0 μm), and one pigment coating layer, two undercoat water-resistant layers, and one water-resistant layer were formed in this order on the paper base material.

[0046] [Example 2] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. (c) Preparation of coating solution C The ethylene-methacrylic acid copolymer ionomer was blended with HDPE and an antifoaming agent to prepare coating solution C having a solid content of 30 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 94.3 mass%, the HDPE content being 3.8 mass%, and the antifoaming agent content being 1.9 mass% in the solid content.

[0047] <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 1, except that Coating Liquid B was changed to Coating Liquid C described above in (c).

[0048] [Example 3] In the same manner as in Example 1, (a) pigment layer coating solution A and (b) coating solution B were prepared. (d) Preparation of Coating Solution D An antifoaming agent was added to the ethylene-methacrylic acid copolymer ionomer to prepare coating solution D having a solid content of 30 mass% with an ethylene-methacrylic acid copolymer ionomer content of 98.0 mass% and an antifoaming agent content of 2.0 mass% in the solid content.

[0049] <Preparation of waterproof paper> Basis weight 224g / m 2 The coating solution A was applied to one side (front side) of a paper substrate having a thickness of 268 μm in a coating amount (solid content) of 2.5 g / m 2 The resulting layer was coated with an air knife coater so that the coating amount (solid content) was 2.5 g / m2, and then dried to form a pigment coating layer (hereinafter referred to as the surface pigment layer). Then, Coating Solution D was applied to the same surface in an amount (solid content) of 2.5 g / m2. 2 The substrate was coated with a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the first layer on the surface, thickness approximately 2.5 μm). Coating solution D was then applied again to the same surface so that the coating amount (solid content) was 2.5 g / m2. 2 The coating solution B was applied to the same surface in an amount (solid content) of 5.0 g / m2 using a gravure coater and then dried to form a water-resistant undercoat layer (hereinafter referred to as the second layer on the surface, thickness: about 2.5 μm). 2The mixture was coated using an air knife coater and dried to form a water-resistant layer (hereinafter referred to as the third layer in the table, film thickness approximately 5.0 μm), and one pigment coating layer, two undercoat water-resistant layers, and one water-resistant layer were formed in this order on the substrate.

[0050] [Example 4] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 2, (c) Coating Solution C was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 3, except that Coating Liquid B was changed to Coating Liquid C described above in (c).

[0051] [Example 5] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. (e) Preparation of Coating Solution E The ethylene-methacrylic acid copolymer ionomer was mixed with low molecular weight PE and an antifoaming agent to prepare coating solution E having a solids concentration of 30 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 94.3 mass%, the low molecular weight PE content being 3.8 mass%, and the antifoaming agent content being 1.9 mass%.

[0052] <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 1, except that Coating Liquid B was changed to Coating Liquid E described above in (e).

[0053] [Example 6] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. (f) Preparation of coating solution F The ethylene-methacrylic acid copolymer ionomer was blended with low molecular weight PE and an antifoaming agent to prepare coating solution F having a solids concentration of 30 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 96.2 mass%, the low molecular weight PE content being 1.9 mass%, and the antifoaming agent content being 1.9 mass% in the solids.

[0054] <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 1, except that Coating Liquid B was changed to Coating Liquid F described above in (f).

[0055] [Example 7] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 5, (e) Coating Solution E was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 3, except that Coating Liquid B was changed to Coating Liquid E described above in (e).

[0056] [Example 8] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 6, (f) Coating Solution F was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 3, except that Coating Liquid B was changed to Coating Liquid F described above in (f).

[0057] [Example 9] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. (k) Preparation of coating solution K An antifoaming agent was added to the ethylene-methacrylic acid copolymer ionomer to prepare coating solution K having a solid content of 30 mass% and a solid content of 98.9 mass% of the ethylene-methacrylic acid copolymer ionomer and a defoaming agent content of 1.1 mass%. (l) Preparation of coating solution L The ethylene-methacrylic acid copolymer ionomer was mixed with low molecular weight PE and an antifoaming agent to prepare coating solution L having a solid content of 30 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 95.2 mass%, the low molecular weight PE content being 3.8 mass%, and the antifoaming agent content being 1.0 mass%. <Preparation of waterproof paper> Waterproof paper was prepared in the same manner as in Example 7, except that Coating Liquid D was changed to Coating Liquid K described above in (k) and Coating Liquid E was changed to Coating Liquid L described above in (l).

[0058] [Example 10] Basis weight 246g / m 2 A waterproof paper was prepared in the same manner as in Example 9, except that the paper base material was changed to a thickness of 274 μm.

[0059] [Example 11] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 9, (k) Coating Solution K was prepared. (m) Preparation of coating solution M The ethylene-methacrylic acid copolymer ionomer was blended with low molecular weight PE and an antifoaming agent to prepare coating solution M having a solid content of 30 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 91.7 mass%, the low molecular weight PE content being 7.3 mass%, and the antifoaming agent content being 1.0 mass% in the solid content. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 9, except that Coating Liquid L was changed to Coating Liquid M of (m) above.

[0060] [Example 12] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 9, (k) Coating Solution K was prepared. (n) Preparation of coating solution N The ethylene-methacrylic acid copolymer ionomer was blended with low molecular weight PE and an antifoaming agent to prepare coating solution N having a solid content of 30 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 82.6 mass%, the low molecular weight PE content being 16.5 mass%, and the antifoaming agent content being 0.9 mass%. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 9, except that Coating Liquid L was changed to Coating Liquid N of (n) above.

[0061] [Example 13] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 1, (b) Coating Solution B was prepared. <Preparation of waterproof paper> Coating solution B is applied to the back side at a coating amount (solid content) of 2.5 g / m 2 The substrate was coated with a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the first back layer, film thickness: approximately 2.5 μm). Coating solution B was then applied again to the same surface so that the coating amount (solid content) was 2.5 g / m2. 2 The coating solution B was applied to the same surface in an amount (solid content) of 5.0 g / m2 using a gravure coater and then dried to form a water-resistant undercoat layer (hereinafter referred to as the second back layer, film thickness: about 2.5 μm). 2 The resulting coating was carried out using an air knife coater so that the coating composition satisfies the above requirements, and then dried to form a water-resistant layer (hereinafter referred to as the back third layer, having a film thickness of approximately 5.0 μm). Furthermore, on the opposite side (front side), a layer having water resistance was formed on the front side in the same manner as in Example 1, except that Coating Liquid B was changed to Coating Liquid D of (d) above. Two undercoat water-resistant layers and one water-resistant layer were formed on one side (rear side), and one pigment coating layer and three water-resistant layers were formed on the opposite side (front side).

[0062] [Example 14] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 2, (c) Coating Solution C was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 13, except that Coating Liquid B was changed to Coating Liquid C described above in (c).

[0063] [Example 15] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 2, (b) Coating Solution B was prepared. <Preparation of waterproof paper> Coating solution D was applied to the back side at a coating weight (solid content) of 2.5 g / m 2 The substrate was coated with a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the first back layer, film thickness: approximately 2.5 μm). Coating solution D was then applied again to the same surface so that the coating amount (solid content) was 2.5 g / m2. 2 The coating solution B was applied to the same surface in an amount (solid content) of 5.0 g / m2 using a gravure coater and then dried to form a water-resistant undercoat layer (hereinafter referred to as the second back layer, film thickness: about 2.5 μm). 2 The resulting coating was carried out using an air knife coater so that the coating composition satisfies the above requirements, and then dried to form a water-resistant layer (hereinafter referred to as the back third layer, having a film thickness of approximately 5.0 μm). Furthermore, on the opposite side (front side), a layer having water resistance was formed on the front side in the same manner as in Example 1, except that Coating Liquid B was changed to Coating Liquid D of (d) above. Two water-resistant undercoat layers and one water-resistant layer were formed on one side (rear side), and one pigment coating layer was formed on the opposite side (front side), resulting in three water-resistant layers.

[0064] [Example 16] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 2, (c) Coating Solution C was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 15, except that Coating Liquid B was changed to Coating Liquid C described above in (c).

[0065] [Example 17] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 5, (e) Coating Solution E was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 13, except that Coating Liquid B was changed to Coating Liquid E described above in (e).

[0066] [Example 18] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 6, (f) Coating Solution F was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 13, except that Coating Liquid B was changed to Coating Liquid F described above in (f).

[0067] [Example 19] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 5, (e) Coating Solution E was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 15, except that Coating Liquid B was changed to Coating Liquid E described above in (e).

[0068] [Example 20] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 6, (f) Coating Solution F was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 15, except that Coating Liquid B was changed to Coating Liquid F described above in (f).

[0069] [Example 21] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 9, (k) Coating Solution K was prepared. (l) Coating liquid L was prepared in the same manner as in Example 9. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 15, except that Coating Liquid D was changed to Coating Liquid K described above in (k) and Coating Liquid B was changed to Coating Liquid L described above in (l).

[0070] [Example 22] Basis weight 246g / m 2 A waterproof paper was prepared in the same manner as in Example 21, except that the paper base material was changed to a thickness of 274 μm.

[0071] [Example 23] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 9, (k) Coating Solution K was prepared. In the same manner as in Example 11, (m) Coating Solution M was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 21, except that Coating Liquid L was changed to Coating Liquid M of (m) above.

[0072] [Example 24] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 9, (k) Coating Solution K was prepared. In the same manner as in Example 12, (n) Coating Solution N was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 21, except that Coating Liquid L was changed to Coating Liquid N of (n) above.

[0073] [Example 25] (o) Preparation of coating solution O The ethylene-methacrylic acid copolymer ionomer was blended with HDPE and an antifoaming agent to prepare coating solution O having a solid content of 30 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 76.3 mass%, the HDPE content being 22.9 mass%, and the antifoaming agent content being 0.8 mass% in the solid content. <Preparation of waterproof paper> Basis weight 224g / m 2 The coating solution O was applied to one side (front side) of a paper substrate having a thickness of 268 μm in a coating amount (solid content) of 2.5 g / m 2 The substrate was coated with a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the first layer on the surface, thickness approximately 2.5 μm). Then, the coating solution O was applied again to the same surface so that the coating amount (solid content) was 2.5 g / m2. 2 The coating solution O was applied to the same surface in an amount (solid content) of 5.0 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the second layer on the surface, thickness: about 2.5 μm). 2The mixture was applied using an air knife coater and dried to form a water-resistant layer (hereinafter referred to as the third layer in the table, film thickness approximately 5.0 μm), and two undercoat water-resistant layers and one water-resistant layer were formed in this order on the paper base material.

[0074] [Example 26] (p) Preparation of coating solution P Ethylene-methacrylic acid copolymer ionomer was blended with HDPE and an antifoaming agent to prepare coating solution P having a solid content of 30 mass%, with an ethylene-methacrylic acid copolymer ionomer content of 95.2 mass%, an HDPE content of 3.8 mass%, and an antifoaming agent content of 1.0 mass% in the solid content. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 25, except that Coating Solution O was changed to Coating Solution P of (p) above.

[0075] [Example 27] In the same manner as in Example 9, (k) Coating Solution K was prepared. (o) Coating Solution O was prepared in the same manner as in Example 25. <Preparation of waterproof paper> Basis weight 224g / m 2 Coating solution K was applied to one side (front side) of a paper substrate with a thickness of 268 μm at a coating weight (solid content) of 2.5 g / m 2 The substrate was coated with a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the first layer on the surface, thickness approximately 2.5 μm). Coating solution K was then applied again to the same surface so that the coating amount (solid content) was 2.5 g / m2. 2 The coating solution O was applied to the same surface in an amount (solid content) of 5.0 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the second layer on the surface, thickness: about 2.5 μm). 2 The mixture was applied using an air knife coater and dried to form a water-resistant layer (hereinafter referred to as the third layer in the table, film thickness approximately 5.0 μm), thereby forming two water-resistant undercoat layers and one water-resistant layer in that order on the substrate.

[0076] [Example 28] In the same manner as in Example 9, (k) Coating Solution K was prepared. (p) Coating solution P was prepared in the same manner as in Example 26. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 27, except that Coating Liquid O was changed to Coating Liquid P of (p) above.

[0077] [Example 29] (l) Coating liquid L was prepared in the same manner as in Example 9. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 25, except that Coating Liquid O was changed to Coating Liquid L in (l) above.

[0078] [Example 30] (q) Preparation of coating solution Q The ethylene-methacrylic acid copolymer ionomer was blended with low molecular weight PE and an antifoaming agent to prepare a coating solution P having a solids concentration of 30 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 97.0 mass%, the low molecular weight PE content being 1.9 mass%, and the antifoaming agent content being 1.1 mass% in the solids. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 25, except that Coating Solution O was changed to Coating Solution Q of (q) above.

[0079] [Example 31] In the same manner as in Example 9, (k) Coating Solution K was prepared. (l) Coating liquid L was prepared in the same manner as in Example 9. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 27, except that Coating Liquid O was changed to Coating Liquid L in (l) above.

[0080] [Example 32] In the same manner as in Example 9, (k) Coating Solution K was prepared. (q) Coating Solution Q was prepared in the same manner as in Example 30. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 27, except that Coating Solution O was changed to Coating Solution Q of (q) above.

[0081] [Example 33] In the same manner as in Example 9, (k) Coating Solution K was prepared. In the same manner as in Example 11, (m) Coating Solution M was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 27, except that Coating Solution O was changed to Coating Solution M of (m) above.

[0082] [Example 34] In the same manner as in Example 9, (k) Coating Solution K was prepared. In the same manner as in Example 12, (n) Coating Solution N was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 27, except that Coating Liquid O was changed to Coating Liquid N in (n) above.

[0083] [Example 35] Basis weight 246g / m 2 A waterproof paper was prepared in the same manner as in Example 31, except that the paper base material was changed to a thickness of 274 μm.

[0084] [Example 36] (o) Coating Solution O was prepared in the same manner as in Example 25. In the same manner as in Example 9, (k) Coating Solution K was prepared. <Preparation of waterproof paper> Coating solution O is applied to the back side at a coating amount (solid content) of 2.5 g / m 2 The substrate was coated with a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the first back layer, film thickness: approximately 2.5 μm). Then, coating solution O was applied again to the same surface so that the coating amount (solid content) was 2.5 g / m2. 2 The coating solution O was applied to the same surface in an amount (solid content) of 5.0 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the second back layer, film thickness: about 2.5 μm). 2 The resulting coating was carried out using an air knife coater so that the coating composition satisfies the above requirements, and then dried to form a water-resistant layer (hereinafter referred to as the back third layer, having a film thickness of approximately 5.0 μm). Moreover, on the opposite side (front side), a layer having water resistance was formed on the front side in the same manner as in Example 25, except that Coating Liquid O was changed to Coating Liquid K of (k) above. Two water-resistant undercoat layers and one water-resistant layer were formed on one side (rear side), and three water-resistant layers were formed on the opposite side (front side).

[0085] [Example 37] (p) Coating solution P was prepared in the same manner as in Example 26. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 36, except that Coating Solution O was changed to Coating Solution P of (p) above.

[0086] [Example 38] In the same manner as in Example 9, (k) Coating Solution K was prepared. (o) Coating Solution O was prepared in the same manner as in Example 25. <Preparation of waterproof paper> Coating solution K is applied to the back side at a coating weight (solid content) of 2.5 g / m 2 The substrate was coated with a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the first back layer, film thickness: approximately 2.5 μm). Then, Coating Solution K was applied again to the same surface so that the coating amount (solid content) was 2.5 g / m2. 2 The coating solution O was applied to the same surface in an amount (solid content) of 5.0 g / m2, and then dried to form a water-resistant undercoat layer (hereinafter referred to as the second back layer, film thickness: about 2.5 μm). 2 The resulting coating was carried out using an air knife coater so that the coating composition satisfies the above requirements, and then dried to form a water-resistant layer (hereinafter referred to as the back third layer, having a film thickness of approximately 5.0 μm). In addition, on the opposite side (front side), a layer having water resistance was formed on the front side in the same manner as in Example 25, except that Coating Liquid O was changed to Coating Liquid K of (k) above. Two water-resistant undercoat layers and one water-resistant layer were formed on one side (rear side), and three water-resistant layers were formed on the opposite side (front side).

[0087] [Example 39] In the same manner as in Example 9, (k) Coating Solution K was prepared. (p) Coating solution P was prepared in the same manner as in Example 26. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 38, except that the coating solution O was changed to the coating solution P of (p) above.

[0088] [Example 40] (l) Coating liquid L was prepared in the same manner as in Example 9. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 36, except that Coating Liquid O was changed to Coating Liquid L in (l) above.

[0089] [Example 41] (q) Coating Solution Q was prepared in the same manner as in Example 30. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 36, except that Coating Solution O was changed to Coating Solution Q of (q) above.

[0090] [Example 42] In the same manner as in Example 9, (k) Coating Solution K was prepared. (l) Coating liquid L was prepared in the same manner as in Example 9. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 38, except that Coating Liquid O was changed to Coating Liquid L in (l) above.

[0091] [Example 43] In the same manner as in Example 9, (k) Coating Solution K was prepared. (q) Coating Solution Q was prepared in the same manner as in Example 30. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 38, except that Coating Solution O was changed to Coating Solution Q of (q) above.

[0092] [Example 44] In the same manner as in Example 9, (k) Coating Solution K was prepared. In the same manner as in Example 11, (m) Coating Solution M was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 38, except that Coating Solution O was changed to Coating Solution M of (m) above.

[0093] [Example 45] In the same manner as in Example 9, (k) Coating Solution K was prepared. In the same manner as in Example 12, (n) Coating Solution N was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 38, except that Coating Solution O was changed to Coating Solution N of (n) above.

[0094] [Example 46] Basis weight 246g / m 2 A waterproof paper was prepared in the same manner as in Example 42, except that the paper base material was changed to a thickness of 274 μm.

[0095] [Comparative Example 1] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 1, except that Coating Liquid B was changed to Coating Liquid D described above in (d).

[0096] [Comparative Example 2] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. (g) Preparation of coating solution G The ethylene-methacrylic acid copolymer ionomer was blended with HDPE and an antifoaming agent to prepare Coating Solution G, which had a solids concentration of 30 mass%, with an ethylene-methacrylic acid copolymer ionomer content of 54.9 mass%, an HDPE content of 44.0 mass%, and an antifoaming agent content of 1.1 mass% in the solids.

[0097] <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 1, except that Coating Liquid B was changed to Coating Liquid G (g) above.

[0098] [Comparative Example 3] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. Similarly to Comparative Example 2, (g) Coating Solution G was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 3, except that Coating Liquid B was changed to Coating Liquid G (g) above.

[0099] [Comparative Example 4] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. (h) Preparation of coating solution H Kaolin and an antifoaming agent were added to the ethylene-methacrylic acid copolymer ionomer to prepare Coating Solution H having a solid content of 30 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 78.7 mass%, the kaolin content being 19.7 mass%, and the antifoaming agent content being 1.6 mass% in the solid content. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 3, except that Coating Liquid B was changed to Coating Liquid H described above in (h).

[0100] [Comparative Example 5] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 9, (k) Coating Solution K was prepared. (r) Preparation of coating solution R The ethylene-methacrylic acid copolymer ionomer was blended with low molecular weight PE and an antifoaming agent to prepare coating solution R having a solid content of 30 mass%, with an ethylene-methacrylic acid copolymer ionomer content of 58.4 mass%, a low molecular weight PE content of 41.0 mass%, and an antifoaming agent content of 0.6 mass% in the solid content. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 9, except that Coating Liquid L was changed to Coating Liquid R (r) above.

[0101] [Comparative Example 6] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. (i) Preparation of Coating Solution I The ethylene-acrylic acid copolymer ionomer was blended with HDPE and an antifoaming agent to prepare Coating Solution I, which had a solids concentration of 20 mass% and contained 94.3 mass% ethylene-acrylic acid copolymer ionomer, 3.8 mass% HDPE, and 1.9 mass% antifoaming agent in the solids. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 1, except that Coating Liquid B was changed to Coating Liquid I described above in (i).

[0102] [Comparative Example 7] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Comparative Example 6, (i) Coating Solution I was prepared. (j) Preparation of Coating Solution J An antifoaming agent was added to the ethylene-acrylic acid copolymer ionomer to prepare coating solution J having a solid content of 20 mass% with an ethylene-acrylic acid copolymer ionomer content of 98.0 mass% and an antifoaming agent content of 2.0 mass% in the solid content.

[0103] <Preparation of waterproof paper> Waterproof paper was prepared in the same manner as in Example 3, except that Coating Liquid D was changed to Coating Liquid J in (j) above, and Coating Liquid B was changed to Coating Liquid I in (i) above.

[0104] [Comparative Example 8] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 13, except that Coating Liquid B was changed to Coating Liquid D described above in (d).

[0105] [Comparative Example 9] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 3, (g) Coating Solution G was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 13, except that Coating Liquid B was changed to Coating Liquid G described above in (g).

[0106] [Comparative Example 10] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. In the same manner as in Example 3, (g) Coating Solution G was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 15, except that Coating Liquid B was changed to Coating Liquid G described above in (g).

[0107] [Comparative Example 11] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 3, (d) Coating Solution D was prepared. Similarly to Comparative Example 4, (h) Coating Solution H was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 15, except that Coating Liquid B was changed to Coating Liquid H described above in (h).

[0108] [Comparative Example 12] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. In the same manner as in Example 9, (k) Coating Solution K was prepared. In the same manner as in Comparative Example 5, (r) Coating Solution R was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 21, except that Coating Liquid L was changed to Coating Liquid R (r) above.

[0109] [Comparative Example 13] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. (j) Coating Solution J was prepared in the same manner as in Comparative Example 7. In the same manner as in Comparative Example 6, (i) Coating Solution I was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 13, except that Coating Liquid D was changed to Coating Liquid J in (j) above, and Coating Liquid B was changed to Coating Liquid I in (i) above.

[0110] [Comparative Example 14] In the same manner as in Example 1, (a) pigment layer coating solution A was prepared. (j) Coating Solution J was prepared in the same manner as in Comparative Example 7. In the same manner as in Comparative Example 6, (i) Coating Solution I was prepared. <Preparation of waterproof paper> Waterproof paper was prepared in the same manner as in Example 15, except that the coating liquid D on the front side was changed to the coating liquid J described above in (j) and the coating liquid B on the back side was changed to the coating liquid I described above in (i).

[0111] [Comparative Example 15] In the same manner as in Example 3, (d) Coating Solution D was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 25, except that Coating Liquid O was changed to Coating Liquid D described above in (d).

[0112] [Comparative Example 16] Similarly to Comparative Example 2, (g) Coating Solution G was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 25, except that Coating Solution O was changed to Coating Solution G described above in (g).

[0113] [Comparative Example 17] In the same manner as in Example 3, (d) Coating Solution D was prepared. Similarly to Comparative Example 2, (g) Coating Solution G was prepared. <Preparation of waterproof paper> Waterproof paper was prepared in the same manner as in Example 27, except that Coating Liquid K was changed to Coating Liquid D in (d) above and Coating Liquid O was changed to Coating Liquid G in (g) above.

[0114] [Comparative Example 18] In the same manner as in Example 3, (d) Coating Solution D was prepared. Similarly to Comparative Example 4, (h) Coating Solution H was prepared. <Preparation of waterproof paper> Waterproof paper was prepared in the same manner as in Example 27, except that Coating Liquid K was changed to Coating Liquid D in (d) above and Coating Liquid O was changed to Coating Liquid H in (h) above.

[0115] [Comparative Example 19] In the same manner as in Example 9, (k) Coating Solution K was prepared. In the same manner as in Comparative Example 5, (r) Coating Solution R was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 27, except that Coating Solution O was changed to Coating Solution R (r) above.

[0116] [Comparative Example 20] In the same manner as in Comparative Example 13, (i) Coating Solution I was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 25, except that Coating Liquid O was changed to Coating Liquid I in (i) above.

[0117] [Comparative Example 21] In the same manner as in Comparative Example 6, (i) Coating Solution I was prepared. (j) Coating Solution J was prepared in the same manner as in Comparative Example 7. <Preparation of waterproof paper> Waterproof paper was prepared in the same manner as in Example 27, except that Coating Liquid K was changed to Coating Liquid J in (j) above, and Coating Liquid O was changed to Coating Liquid I in (i) above.

[0118] [Comparative Example 22] In the same manner as in Example 9, (k) Coating Solution K was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 36, except that Coating Liquid O was changed to Coating Liquid K described above in (k).

[0119] [Comparative Example 23] In the same manner as in Example 9, (k) Coating Solution K was prepared. Similarly to Comparative Example 2, (g) Coating Solution G was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 36, except that Coating Solution O was changed to Coating Solution G described above in (g).

[0120] [Comparative Example 24] In the same manner as in Example 9, (k) Coating Solution K was prepared. Similarly to Comparative Example 2, (g) Coating Solution G was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 38, except that Coating Solution O was changed to Coating Solution G (g) above.

[0121] [Comparative Example 25] In the same manner as in Example 9, (k) Coating Solution K was prepared. Similarly to Comparative Example 4, (h) Coating Solution H was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 38, except that Coating Liquid O was changed to Coating Liquid H described above in (h).

[0122] [Comparative Example 26] In the same manner as in Example 9, (k) Coating Solution K was prepared. In the same manner as in Comparative Example 13, (r) Coating Solution R was prepared. <Preparation of waterproof paper> A waterproof paper was prepared in the same manner as in Example 38, except that Coating Solution O was changed to Coating Solution R (r) above.

[0123] [Comparative Example 27] In the same manner as in Comparative Example 6, (i) Coating Solution I was prepared. (j) Coating Solution J was prepared in the same manner as in Comparative Example 7. <Preparation of waterproof paper> Waterproof paper was prepared in the same manner as in Example 36, except that Coating Liquid K was changed to Coating Liquid J in (j) above, and Coating Liquid O was changed to Coating Liquid I in (i) above.

[0124] [Comparative Example 28] In the same manner as in Comparative Example 6, (i) Coating Solution I was prepared. (j) Coating Solution J was prepared in the same manner as in Comparative Example 7. <Preparation of waterproof paper> Waterproof paper was prepared in the same manner as in Example 38, except that Coating Liquid K was changed to Coating Liquid J in (j) above, and Coating Liquid O was changed to Coating Liquid I in (i) above.

[0125] [Evaluation method] <Air permeability> The air permeability was measured in accordance with JIS P 8117:2009.

[0126] <Adhesion> The probe of the tackiness tester TAC-1000 (manufactured by Resca Co., Ltd.) was brought into contact with the back surface for measurement. The pressing speed was 0.5 mm / s, the pressing load was 200 gf, the pressing time was 1 s, the pulling-up speed was 1 mm / s, the stage temperature was 90°C, and the probe temperature was 25°C. Note that if the adhesion is high, it is likely to stick to the roll during manufacturing, etc., and it is also likely to cause roll contamination. A: The average value of the measurement is 20 gf or less, and there is no surface stickiness. B: The average value of the measurement exceeds 20 gf and is 40 gf or less, and there is little surface stickiness. C: The average value of the measurement exceeds 40 gf and is 60 gf or less, and the surface is slightly sticky. D: The average value of the measurement exceeds 60 gf, and the surface is sticky.

[0127] <Cobb water absorbency> The Cobb water absorbency was measured in accordance with JIS P 8140:1998 from the mass difference before and after bringing the obtained water-resistant paper into contact with water at 20°C or warm water at 90°C for 30 minutes.

[0128] <Heat sealability> The sample was cut into 2.5 cm × 15 cm, and after overlapping so that the coated surface (front surface) and the coated surface (back surface), or the coated surface (front surface) and the paper base material surface (back surface) were in close contact, it was heat-sealed at a temperature of 150°C or 250°C and a pressure of 0.2 MPa for 2 seconds using a heat seal tester (manufactured by Tester Sangyo Co., Ltd.), and then cooled to room temperature. Thereafter, the state when the overlapped samples were peeled off by hand was evaluated based on the following evaluation criteria. A: It is completely adhered, and it is difficult to peel it off easily by hand. B: It is adhered, but the adhesion strength is weak, and it can be easily peeled off by hand. C: There are non-adhered parts in at least a part.

[0129] <Blocking resistance> Cut the sample into a 5cm square, overlap it so that the front and back surfaces (paper substrate in the case of one-sided coating) are in close contact, place it in a blocking tester, heat it at 65℃ for 30 minutes, and then apply a pressure of 0.5kg / cm. 2 After cooling to room temperature, the samples were evaluated as follows. A: Peels off without resistance B: Slight resistance C: High resistance, slight peeling of the coated surface D: There is considerable resistance and the coated surface peels off (paper peels off)

[0130] [Table 1-1]

[0131] [Table 1-2]

[0132] [Table 1-3]

[0133] [Table 1-4]

[0134] [Table 1-5]

[0135] [Table 1-6]

[0136] [Table 1-7]

[0137] [Table 1-8]

[0138] In Examples 1 to 46, which have a water-resistant layer containing an ethylene-methacrylic acid copolymer and organic particles with an organic particle content of 40 mass % or less, water-resistant papers having high air permeability, excellent water resistance, excellent blocking resistance, and heat sealability were obtained. On the other hand, in Comparative Examples 1, 8, 15, and 22, in which the water-resistant layer does not contain organic particles, blocking resistance and adhesive strength were deteriorated. In Comparative Examples 2, 3, 5, 9, 10, 12, 16, 17, 19, 23, 24, and 26, in which the content of organic particles exceeds 40 mass%, sufficient heat sealability was not obtained. Furthermore, in Comparative Examples 4, 11, 18, and 25, in which kaolin, an inorganic particle, was used instead of organic particles, the water resistance was poor, and sufficient water resistance was not obtained, particularly against hot water at 90°C. In addition, the surface was more adhesive than in the Examples. In Comparative Examples 6, 7, 13, 14, 20, 21, 27, and 28, in which an ethylene-acrylic acid copolymer was used instead of an ethylene-methacrylic acid copolymer as the resin component, sufficient blocking resistance was not obtained.

Claims

1. A water-resistant paper having two or more undercoat water-resistant layers and a water-resistant layer, in that order, on at least one side of a paper base material, A water-resistant layer is provided on the uppermost layer of at least one surface of the paper substrate; the water-resistant layer contains an ethylene-methacrylic acid copolymer and organic particles; The melting point or softening point of the organic particles is 100° C. or higher, The content of organic particles in the water-resistant layer is 40% by mass or less. Water resistant paper.

2. 2. The waterproof paper according to claim 1, wherein the organic particles have an average particle size of 0.01 μm or more and 50 μm or less.

3. 3. The waterproof paper according to claim 1, wherein the organic particles are polyolefin particles.

4. 4. The waterproof paper according to claim 1, wherein the organic particles are at least one selected from the group consisting of polypropylene particles, polyethylene particles, and propylene-ethylene copolymer resin particles.

5. The waterproof paper according to any one of claims 1 to 4, wherein the content of organic particles in the waterproof layer is 0.5% by mass or more.

6. 6. The waterproof paper according to claim 1, wherein the organic particles are water-dispersible organic particles.

7. The coating weight of the water-resistant layer is 0.1 g / m ２ 20g / m or more ２ The waterproof paper according to any one of claims 1 to 6, wherein:

8. The waterproof paper according to any one of claims 1 to 7, wherein the undercoat waterproof layer contains an ethylene-methacrylic acid copolymer.

9. The waterproof paper according to any one of claims 1 to 8, which has an air permeability of 1,000 seconds or more.

10. The Cobb water absorbency of the surface provided with the water-resistant layer in water at 20°C for 30 minutes is 40 g / m ２ The waterproof paper according to any one of claims 1 to 9, wherein:

11. The Cobb water absorbency of the surface provided with the water-resistant layer in water at 90°C for 30 minutes is 100 g / m ２ The waterproof paper according to any one of claims 1 to 10, wherein:

12. The waterproof paper according to any one of claims 1 to 11, which has heat sealability.

13. The waterproof paper according to any one of claims 1 to 12, which is for a liquid container or a lid thereof.

14. A liquid container or a lid thereof, comprising the waterproof paper according to any one of claims 1 to 13.

15. A liquid container or its lid according to claim 14, wherein the liquid container is a paper cup.

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