Water-resistant paper, food containers, paper cups, paper lids, and method for manufacturing water-resistant paper

Abstract

The present invention addresses the problem of providing waterproof paper having waterproof performance and exhibiting excellent processing suitability. The problem is solved by this waterproof paper that has at least one waterproof layer on at least one surface of a paper base material and that has a tensile strength of not more than 19.0 kN / m in a transverse direction.

Description

[Technical field]

[0001] The present invention relates to water-resistant paper and food containers, paper cups, and paper lids made using the same. It also relates to a method for producing the water-resistant paper. [Background technology]

[0002] Plastic products have traditionally been used for various containers for beverages and food (trays, cups, etc.) and their lids, as well as 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., but there has been a problem in that it is difficult to remove the polyethylene film when recycling, making it poorly recyclable.

[0004] 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.

[0005] In addition, Patent Document 1 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 a dry coating weight 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]

[0006] [Patent Document 1] Patent No. 6580291 Summary of the Invention

[0007] The waterproof paper described in Patent Document 1 had a problem with its suitability for processing, as cracks occurred in the top curl portion when the paper was processed into a paper cup.

[0008] Therefore, an object of the present invention is to provide a waterproof paper that has water resistance and is excellent in processability.

[0009] The present inventors have found that the above problems can be solved by adjusting the tensile strength of the waterproof paper within a certain range, and have thus completed the present invention.

[0010] That is, the present invention provides the following: <1> ~ <20> Regarding. <1> A waterproof paper having at least one waterproof layer on at least one side of a paper base, and having a tensile strength in the transverse direction of 19.0 kN / m or less. <2> The transverse elongation at break is 5.3% or more. <1> The water-resistant paper described in <3> The tensile modulus in the transverse direction is 3.7 GPa or less. <1> or <2> The water-resistant paper described in <4> The lateral Taber stiffness is 10 mN·m or less. <1> ~ <3> 2. The water-resistant paper according to claim 1 . <5> The content of softwood bleached kraft pulp relative to the total amount of pulp constituting the paper base material is 5 to 50 mass%. <1> ~ <4> 2. The water-resistant paper according to claim 1 . <6> The paper base material has three or more paper layers. <1> ~ <5> 2. The water-resistant paper according to claim 1 . <7> The ratio of tensile strength in the longitudinal direction to that in the transverse direction is 1.40 or more and 3.00 or less. <1> ~ <6> 2. The water-resistant paper according to claim 1 . <8> The total coating amount of the water-resistant layer is 4 to 50 g / m 2 That is, <1> ~ <7> 2. The water-resistant paper according to claim 1 . <9> The paper base material has at least three water-resistant layers on at least one side thereof. <1> ~ <8> 2. The water-resistant paper according to claim 1 . <10> The paper base material has a water-resistant layer on both sides thereof. <1> ~ <9> 2. The water-resistant paper according to claim 1 . <11> The water-resistant layer contains an ethylene-(meth)acrylic acid copolymer. <1> ~ <10> 2. The water-resistant paper according to claim 1 . <12> Heat sealable, <1> ~ <11> 2. The water-resistant paper according to claim 1 . <13> Cobb water absorption of 20g / m2 at 20°C after 30 minutes of contact 2 Below is the <1> ~ <12> 2. The water-resistant paper according to claim 1 . <14> Cobb water absorption of 50g / m2 in 90°C water after 30 minutes of contact 2 Below is the <1> ~ <13> 2. The water-resistant paper according to claim 1 . <15> The oil resistance measured according to JAPAN TAPPI No. 41 is 6 or higher. <1> ~ <14> 2. The water-resistant paper according to claim 1 . <16> For food containers, <1> ~ <15> 2. The water-resistant paper according to claim 1 . <17> <1> ~ <15> 2. A food container comprising the water-resistant paper according to claim 1. <18> <1> ~ <15> A paper cup made using the water-resistant paper described in any one of the above. <19> <1> ~ <15> A paper lid made using the water-resistant paper described in any one of the above. <20> A coating process includes a coating liquid for a water-resistant layer applied onto a paper substrate by an on-machine method, and the coating process has a coating width of 2000 mm or more and a coating speed of 100 m / min or more. <1> ~ <16> 13. A method for producing waterproof paper according to any one of claims 1 to 12. <21> At least one of the following (i) and (ii) is satisfied: <1> ~ <16> Water-resistant paper according to any of the following: (i) The Taber stiffness in the longitudinal direction is 7.0 mN m or less. (ii) The longitudinal tensile strength is 15.0 kN / m or more and 20.0 kN / m or less. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The waterproof paper of this embodiment is a waterproof paper having at least one waterproof layer on at least one side of a paper base material, and has a tensile strength in the transverse direction of 19.0 kN / m or less. The waterproof paper of this embodiment is waterproof and has excellent processability. A paper cup usually has a top curl part at its end from the viewpoint of mouthfeel and fitting with a lid to be attached. In addition, in the case of a paper lid that is used assuming that a beverage is drunk while attached to the paper cup, a top curl part may also be provided at the end of the paper lid. In forming such a paper cup or paper lid, the lateral direction of the water-resistant paper is formed to be the horizontal direction of the paper cup or paper lid. In this case, although the detailed mechanism is unknown, it is speculated that by adjusting the lateral tensile strength of the water-resistant paper to 19.0 kN / m or less, the flexibility of the part to be processed (for example, the part to be top curled when formed into a paper cup or paper lid) is increased, and the processing suitability is improved (cracks and wrinkles are less likely to occur in the top curl part). However, the above mechanism is based on speculation, and the mechanism by which the effects of the present invention are achieved is not limited to this. In this specification, the "lateral direction" in the water-resistant paper means the CD direction (direction perpendicular to the paper-making direction) of the constituent paper base material. In addition, the "longitudinal direction" of the waterproof paper means the MD direction (papermaking direction) of the paper substrate. Furthermore, in a preferred embodiment of the present invention, the waterproof paper has an appropriate Taber stiffness, thereby obtaining excellent side sealing properties. In a further preferred embodiment, the coating liquid for the waterproof layer is applied on the paper substrate by the on-machine method, thereby obtaining excellent production efficiency.

[0012] The structure and properties of the waterproof paper of this embodiment will be described in more detail below.

[0013] 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 arbitrarily combined. In addition, "(meth)acrylic" is a generic term including both acrylic and methacrylic.

[0014] <Paper base material> The paper base material constituting the waterproof paper of this embodiment preferably has three or more paper layers, more preferably has four or more paper layers, and even more preferably has five or more paper layers. By having three or more paper layers, the desired basis weight and paper thickness can be achieved, and the physical properties of the waterproof paper can be adjusted to the desired range by adjusting the basis weight, freeness, etc. of each layer. The upper limit of the paper layers is not particularly limited, but is preferably seven or less, more preferably six or less.

[0015] Examples of pulp 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); recycled 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. Among them, it is preferable to use LBKP and NBKP in combination.

[0016] The content of softwood bleached kraft pulp (NBKP) relative to the total amount of pulp constituting the paper base material is, from the standpoints of processability, smoothness and water resistance, preferably 5 mass% or more, more preferably 10 mass% or more, even more preferably 15 mass% or more, even more preferably 20 mass% or more, and is preferably 60 mass% or less, more preferably 55 mass% or less, even more preferably 50 mass% or less, even more preferably 45 mass% or less, even more preferably 40 mass% or less, and may be 35 mass% or less or 30 mass% or less.

[0017] From the viewpoints of processability, smoothness and water resistance, the content of hardwood bleached kraft pulp (LBKP) relative to the total amount of pulp constituting the paper base material is preferably 40% by mass or more, more preferably 45% by mass or more, even more preferably 50% by mass or more, even more preferably 55% by mass or more, even more preferably 60% by mass or more, and may be 65% by mass or more or 70% by mass or more, and is preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and even more preferably 80% by mass or less.

[0018] When the paper base has three or more layers, the content of softwood bleached kraft pulp (NBKP) relative to the total amount of pulp constituting the outer layers (front and back layers) of the paper base is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 15% by mass or more, even more preferably 20% by mass or more, and preferably 60% by mass or less, more preferably 55% by mass or less, even more preferably 50% by mass or less, even more preferably 45% by mass or less, even more preferably 40% by mass or less, and may be 35% by mass or 30% by mass or less, from the viewpoint of processability, smoothness, and water resistance. When the paper base has three or more layers, the content of softwood bleached kraft pulp (NBKP) relative to the total amount of pulp constituting the middle layer may be 0% by mass or more, and may be within the same numerical range as the outer layer.

[0019] When the paper base has three or more layers, the content of hardwood bleached kraft pulp (LBKP) relative to the total amount of pulp constituting the outer layers (front and back layers) of the paper base is preferably 40% by mass or more, more preferably 45% by mass or more, even more preferably 50% by mass or more, even more preferably 55% by mass or more, even more preferably 60% by mass or more, and may be 65% by mass or 70% by mass or more, and preferably 95% by mass or less, more preferably 90% by mass or less, even more preferably 85% by mass or less, and even more preferably 80% by mass or less, from the viewpoint of processing suitability, smoothness, and water resistance. When the paper base has three or more layers, the content of hardwood bleached kraft pulp (LBKP) relative to the total amount of pulp constituting the middle layer may be 100% by mass or less, and may be within the same numerical range as the outer layer.

[0020] The degree of beating of the pulp is not particularly limited, but is preferably 200 to 800 mL, more preferably 350 to 700 mL, in terms of Canadian Standard Freeness (hereinafter also referred to as CSF or freeness). If the CSF of the pulp is within the above range, the paper strength required for food containers or cutlery is easily obtained. If it is 200 mL or more, the interfiber bond is not too high, and in the folding process in the molding process, the stress such as compression and tension is concentrated on the outermost layer of the folded part, and the occurrence of the phenomenon in which the resin layer is destroyed can be suppressed, and good processability can be maintained. In addition, if it is 800 mL or less, the smoothness of the paper surface is good, and printability can be maintained. Furthermore, from the viewpoint of setting the lateral tensile strength of the water-resistant paper within a desired range and improving processability, the degree of beating of the pulp is preferably 420 mL or more, more preferably 450 mL or more, in terms of CSF.

[0021] CSF is measured in accordance with JIS P 8121-2:2012 "Pulp - Test method for freeness - Part 2: Canadian standard freeness method".

[0022] Examples of additives to paper substrates 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 the range that is usually used.

[0023] The basis weight of the paper substrate is not particularly limited, but for example, for paper cups or paper lids, it is preferably 180 g / m 2 More preferably, 200 g / m 2 and preferably 350 g / m 2 Furthermore, from the viewpoint of improving side sealing properties, the basis weight of the paper base material is preferably 300 g / m 2 Less than 250 g / m 2 The thickness of the paper substrate is not particularly limited, but is preferably 220 μm or more, more preferably 300 μm or more, and preferably 450 μm or less, for example, for paper cups or paper lids. From the viewpoint of improving side sealing properties, the thickness of the paper substrate is preferably 350 μm or less, more preferably 300 μm or less. The basis weight of the paper substrate is measured in accordance with JIS P 8124:2011. The thickness of the paper substrate is measured in accordance with JIS P 8118:2014.

[0024] [Method of manufacturing paper base material] A method for producing a paper base material includes a method of making a paper stock containing pulp. The paper stock may further contain additives. Examples of additives include the additives listed above. The paper 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 paper stock is not particularly limited, and may be within a range that is usually used. For example, it is 60% by mass or more and less than 100% by mass with respect to the total mass of the paper stock (solid content).

[0025] The papermaking method is not particularly limited, and papermaking can be performed using various papermaking machines such as a Fourdrinier papermaking machine, a multi-layer Fourdrinier papermaking machine, a cylinder papermaking machine, a multi-layer cylinder papermaking machine, a multi-layer Fourdrinier cylinder papermaking machine, a twin-wire papermaking machine, etc. By performing papermaking using a papermaking machine mounted on an on-machine coater, the entire process from papermaking to coating of the water-resistant layer can be performed in an integrated manner, and production efficiency can be significantly improved. In papermaking, the papermaking width is preferably 2000 mm or more, more preferably 3000 mm or more, and even more preferably 4000 mm or more. The upper limit of the papermaking width is not particularly limited, but is, for example, 10000 mm or less. The papermaking speed is preferably 100 m / min or more, more preferably 200 m / min or more, and even more preferably 400 m / min or more. The upper limit of the papermaking speed is also not particularly limited, but is, for example, 2000 m / min or less.

[0026] The paper base material may be a single layer, a multi-layer, or a laminate of multiple layers. The papermaking of the paper stock can be carried out by a standard method. For example, the paper stock can be cast onto a wire or the like, dehydrated to obtain a wet paper, and multiple wet papers can be stacked as necessary, and this single or multi-layer wet paper can be pressed and dried. In this case, if multiple wet papers are not stacked, a single-layer paper is obtained, and if multiple wet papers are stacked, a multi-layer paper is obtained. When multiple wet papers are stacked, an adhesive can be applied to the front side of the wet paper (the side on which other wet papers are stacked). In addition, from the viewpoint of improving oil resistance, a pigment layer can be provided on the front side after pressing and drying.

[0027] <Water resistant layer> The waterproof paper of this embodiment has at least one waterproof layer on at least one surface of a paper base material. From the viewpoint of heat sealability, the waterproof layer is preferably provided as the uppermost layer.

[0028] The water-resistant paper of the present embodiment preferably has three or more water-resistant layers on at least one side of the paper base material. By adopting such a form, even if a coating defect such as a pinhole occurs in the lower water-resistant layer, it can be covered by the upper water-resistant layer, so that good water resistance can be exhibited. For example, when used for a paper cup or paper lid, it is preferable to have three or more water-resistant layers on the inner surface (also called the liquid-contacting surface). Furthermore, when used for an application where condensation occurs, such as a paper cup for cold water or a paper lid, it is preferable to have one or more water-resistant layers on the outer surface (the surface opposite to the liquid-contacting surface, also called the printed surface), more preferably two or more layers, and even more preferably three or more layers. Furthermore, in the case of a paper lid that is used assuming that a beverage is drunk while attached to a paper cup, the outer surface may be the drinking mouth surface, so it is preferable to have one or more water-resistant layers on that surface, more preferably two or more layers, and even more preferably three or more layers. That is, the water-resistant paper of the present embodiment preferably has water-resistant layers on both sides of the paper base material. It is also preferable to have a water-resistant layer on both sides of the paper base material in that the side sealability can be improved.

[0029] The water-resistant layer preferably contains an ethylene-(meth)acrylic acid copolymer from the viewpoint of water resistance and heat sealability, and more preferably contains an ethylene-methacrylic acid copolymer from the viewpoint of blocking suppression and facility fouling prevention. As the ethylene-(meth)acrylic acid copolymer, either a commercially available product or a synthetic product can be used, and specific examples of commercially available products include the Chemipearl series (S-100, S-300, S-500) manufactured by Mitsui Chemicals, Inc., the 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, the Hi-Tec SC-100 manufactured by Toho Chemical Industry Co., Ltd., the Joncryl HPB-4110 manufactured by BASF Japan, the RHOBARR320 manufactured by DOW Chemical Japan, the AQUENCE EPIX BC212F manufactured by Henkel Japan, and the Aquatex AC-3100 manufactured by Chuorika Kogyo Co., Ltd.

[0030] From the viewpoint of water resistance, the content of the ethylene-(meth)acrylic acid copolymer 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 particularly preferably 95% by mass or more and 100% by mass or less, of the resin components of the water-resistant layer.

[0031] Here, the resin component of the water-resistant layer means a polymer component contained in the water-resistant layer, that is, a compound having a weight-average molecular weight of 1,000 or more.

[0032] The water-resistant layer preferably contains organic particles in addition to the ethylene-(meth)acrylic acid copolymer. The organic particles preferably 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, roll contamination during coating 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 is unclear, it is considered that due to the difference in melting point (or softening point) between the ethylene-(meth)acrylic acid copolymer and the organic particles, cracks that occur during film formation of the ethylene-(meth)acrylic 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 of the organic particles 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.

[0033] 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.

[0034] 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.

[0035] The shape of the organic particles is not particularly limited and may be spherical or amorphous, but is preferably spherical. Note that spherical means an aspect ratio of 3 or less.

[0036] 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.

[0037] 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.

[0038] 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-(meth)acrylic acid copolymer to the organic particles in the water-resistant layer (ethylene-(meth)acrylic 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.

[0039] The water-resistant layer may contain other components in addition to the above-mentioned ethylene-(meth)acrylic acid copolymer and organic particles.

[0040] Examples of other components include viscosity modifiers; antifoaming agents; leveling agents such as surfactants and alcohols; colorants such as color pigments and color dyes; and antiblocking agents such as inorganic pigments and synthetic resins.

[0041] Since these components tend to deteriorate water resistance and heat sealability, the total content of 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, with the lower limit being 0 mass %.

[0042] The water-resistant layer is obtained by preparing a coating liquid for the water-resistant layer containing an ethylene-(meth)acrylic acid copolymer and, if necessary, organic particles, and coating this on at least one surface of the paper base material.

[0043] The coating liquid for the water-resistant layer is preferably an aqueous dispersion, i.e., the coating liquid for the water-resistant layer preferably does not contain an emulsifier such as a surfactant or a dispersant. The ethylene-(meth)acrylic acid copolymer blended in the coating liquid for the water-resistant layer may be in the form of an ionomer. Here, the ionomer is a copolymer neutralized with a cation. In other words, synthetic resins obtained by neutralizing an ethylene-methacrylic acid copolymer, an ethylene-acrylic acid copolymer, or an ethylene-urethane copolymer with a cation all fall under the category of ionomers. Ionomers may be used alone or in combination of two or more types. Examples of cations include metal ions such as sodium ions and potassium ions, ammonium ions (NH 4 + ) and organic ammonium ions.

[0044] The method for applying the coating liquid for the water-resistant layer onto the paper base material is not particularly limited, and may be either a method performed continuously with the papermaking process (the so-called on-machine method), or a method in which the paper base material is once wound up and the coating liquid for the water-resistant layer is applied separately using a coating machine (the so-called off-machine method), but from the viewpoint of production efficiency, the on-machine method is preferred. When the coating liquid for the water-resistant layer is applied by the on-machine method (on-machine coater), the coating width is preferably 2000 mm or more, more preferably 3000 mm or more, and even more preferably 4000 mm or more. The upper limit of the coating width is not particularly limited, but is, for example, 10000 mm or less. The coating speed is preferably 100 m / min or more, more preferably 200 m / min or more, and even more preferably 500 m / min or more. The upper limit of the coating speed is also not particularly limited, but is, for example, 2000 m / min or less. By using an on-machine coater, the papermaking width and the coating width can be made wider, making it possible to make paper at a higher speed, and thus improving the production efficiency of water-resistant paper. 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.

[0045] The coating amount of each water-resistant layer is not particularly limited, but is preferably 1 to 10 g / m 2 The total coating weight of the water-resistant layer in the water-resistant paper is preferably 8 g / m 2 More than 10 g / m 2 More preferably, 15 g / m 2 More preferably, 20 g / m 2 The upper limit is not particularly limited, but is preferably 50 g / m 2 Less than 40 g / m 2 Less than 30 g / m, more preferably 30 g / m 2 When the waterproof paper is used as a paper cup or a paper lid, the total coating weight of the waterproof layer on the inner surface (liquid-contacting surface) is preferably 2 g / m 2 More preferably, 5 g / m 2More preferably, 8 g / m 2 The upper limit is not particularly limited, but is preferably 20 g / m 2 In addition, when a water-resistant layer is provided on the outer surface (printing surface), the total coating amount of the water-resistant layer on that side is preferably 2 g / m or less. 2 More preferably, 5 g / m 2 More preferably, 8 g / m 2 The upper limit is not particularly limited, but is preferably 20 g / m 2 The following is the result.

[0046] <Other layers> The waterproof paper of this embodiment may have other layers in addition to the waterproof layer described above. An example of the other layers is a pigment layer between the paper base material and the waterproof layer, which is preferable because the pigment layer functions as a sealing layer and improves waterproofness. The pigment layer contains a pigment and an adhesive (binder).

[0047] The adhesive is not particularly limited, and examples thereof include synthetic adhesives such as styrene-butadiene, styrene-acrylic, ethylene-vinyl acetate, butadiene-methyl methacrylate, vinyl acetate-butyl acrylate copolymers, polyvinyl alcohol, maleic anhydride copolymers, and acrylic acid-methyl methacrylate copolymers; proteins such as casein, soy protein, and synthetic protein; starches such as oxidized starch, cationic starch, urea phosphate esterified starch, etherified starch such as hydroxyethyl etherified starch, and dextrin; and cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxymethyl cellulose. The adhesive (binder) may be used alone or in combination of two or more. In addition, a preferred embodiment of the adhesive is a combination of a synthetic adhesive and starches.

[0048] The pigment used in the pigment layer 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; organic pigments such as solid, hollow, or core-shell type; etc. The pigments may be used alone or in combination of two or more.

[0049] The coating amount of the pigment layer is set to, for example, 2 g / m from the viewpoint of the function of sealing. 2 More than 40g / m 2 The following is the result.

[0050] The coating liquid for the pigment layer may be prepared by mixing the above-mentioned pigment, adhesive (binder), and aqueous medium, and in addition to the pigment and adhesive (binder), various components may be added to the above-mentioned coating liquid as necessary. Examples of the various components include various auxiliaries that are usually added to coating liquids, such as dispersants, thickeners, water retention agents, defoamers, water resistance agents, colorants, surfactants, etc. The coating method for the pigment layer is not particularly limited, and the coating methods described in the section on <Water-resistant layer> can be adopted.

[0051] <Water-resistant paper properties> [Tensile strength] The water-resistant paper of this embodiment has a lateral tensile strength of 19.0 kN / m or less. It is believed that the flexibility of the part to be processed (for example, the part to be top curled when molded into a paper cup or paper lid) is increased, and the processing suitability is improved (cracks and wrinkles are less likely to occur at the top curl part). From the viewpoint of further increasing the flexibility and further improving the processing suitability, the lateral tensile strength of the water-resistant paper is preferably 17.0 kN / m or less, more preferably 15.0 kN / m or less, and even more preferably 14.0 kN / m or less. Furthermore, from the viewpoint of achieving both processing suitability and other performance, it is preferably 13.0 kN / m or less, more preferably 12.0 kN / m or less, even more preferably 11.0 kN / m or less, and even more preferably 10.0 kN / m or less. The lower limit of the tensile strength in the transverse direction of the waterproof paper is not particularly limited, but from the viewpoint of processing suitability, it is preferably 6.0 kN / m or more, more preferably 6.5 kN / m or more, even more preferably 7.0 kN / m or more, even more preferably 8.0 kN / m or more, and may be 9.0 kN / m or more. The tensile strength in the transverse direction of the waterproof paper can be adjusted within the above range by adjusting the blending of the pulp constituting the paper base material, the beating degree (freeness) or fiber length, the amount of dry strength agent added, the papermaking speed, the J / W ratio, the shaking conditions in the CD direction of the papermaking wire (for example, shaking on / off, vibration frequency, vibration width), etc.

[0052] From the viewpoint of further improving processability, the tensile strength in the longitudinal direction of the waterproof paper is preferably 14.0 kN / m or more, more preferably 15.0 kN / m or more, and may be 18.0 kN / m or more, 20.0 kN / m or more, or 21.0 kN / m or more, and is preferably 30.0 kN / m or less, more preferably 28.0 kN / m or less, even more preferably 27.0 kN / m or less, even more preferably 26.0 kN / m or less, even more preferably 21.0 kN / m or less, and particularly preferably 20.0 kN / m or less. The tensile strength in the longitudinal direction can be adjusted within the above range by adjusting the blending of the pulp constituting the paper base material, the beating degree (freeness) or fiber length, the amount of dry strength agent added, the papermaking speed, the J / W ratio, the shaking conditions in the CD direction of the papermaking wire (e.g., shaking on / off, vibration frequency, vibration width), etc.

[0053] The ratio of the tensile strength in the longitudinal direction to the transverse direction (longitudinal direction / transverse direction) of the waterproof paper is preferably 1.40 or more, more preferably 1.45 or more, even more preferably 1.50 or more, even more preferably 1.60 or more, and is preferably 3.00 or less, more preferably 2.50 or less, and may be 2.30 or less, from the viewpoints of processability, smoothness, and waterproofness. The tensile strength ratio can be adjusted within the above range by adjusting the papermaking speed, J / W ratio, and the conditions of shaking the papermaking wire in the CD direction (e.g., shaking on / off, vibration frequency, vibration width), etc.

[0054] The tensile strength in the transverse and longitudinal directions of waterproof paper shall be the values ​​measured in accordance with JIS P 8113:2006.

[0055] [Elongation at break] The breaking elongation in the horizontal direction of the waterproof paper is preferably 4.5% or more, more preferably 5.0% or more, even more preferably 5.3% or more, even more preferably 5.4% or more, and may be 5.5% or more. By making the breaking elongation in the horizontal direction of the waterproof paper equal to or more than the above lower limit, it is considered that the elongation of the part to be processed (for example, the part to be top curled when molded into a paper cup or paper lid) is improved, and the processing suitability is improved (cracks and wrinkles are less likely to occur in the top curl part). In addition, the upper limit of the breaking elongation in the horizontal direction of the waterproof paper is not particularly limited, but from the viewpoint of processing suitability, it is preferably 8.0% or less, more preferably 7.5% or less, and may be 7.0% or less. The transverse breaking elongation can be adjusted to within the above range by adjusting the composition of the pulp that makes up the paper base material, the degree of beating (freeness) or fiber length, the amount of dry strength agent added, the papermaking speed, the J / W ratio, and the shaking conditions of the papermaking wire in the CD direction (e.g., shaking on / off, vibration frequency, vibration amplitude), etc.

[0056] The longitudinal breaking elongation of the waterproof paper is preferably 1.5% or more, more preferably 1.8% or more, and may be 2.0% or more or 2.1% or more, and is preferably 4.0% or less, more preferably 3.0% or less, and even more preferably 2.5% or less. The longitudinal breaking elongation can be adjusted to within the above range by adjusting the composition of the pulp constituting the paper base material, the beating degree (freeness) or fiber length, the amount of dry strength agent added, the papermaking speed, the J / W ratio, the shaking conditions of the papermaking wire in the CD direction (e.g., shaking on / off, vibration frequency, vibration width), etc.

[0057] The ratio of the longitudinal and transverse breaking elongation of the waterproof paper (longitudinal / transverse) is preferably 0.60 or less, more preferably 0.50 or less, and even more preferably 0.45 or less, from the viewpoint of processing suitability. The lower limit is not particularly limited, but is preferably 0.10 or more, more preferably 0.20 or more. The breaking elongation ratio can be adjusted to within the above range by adjusting the papermaking speed, J / W ratio, and the shaking conditions of the papermaking wire in the CD direction (e.g., shaking on / off, vibration frequency, vibration width), etc.

[0058] The breaking elongation in the transverse and longitudinal directions of waterproof paper shall be the values ​​measured in accordance with JIS P 8113:2006.

[0059] [Tensile modulus] The tensile modulus of the water-resistant paper in the transverse direction is preferably 3.7 GPa or less, more preferably 3.5 GPa or less, and even more preferably 3.2 GPa or less. By making the tensile modulus of the water-resistant paper in the transverse direction less than the above upper limit, the part to be processed (for example, the part to be subjected to top curl processing when molded into a paper cup or a paper lid) becomes easier to deform, and the processing suitability is improved. In addition, the lower limit of the tensile modulus of the water-resistant paper in the transverse direction is not particularly limited, but from the viewpoint of processing suitability, it is preferably 1.5 GPa or more, more preferably 1.7 GPa or more, and may be 2.0 GPa or more. The tensile modulus of the transverse direction can be adjusted within the above range by adjusting the blending of the pulp constituting the paper base material, the beating degree (freeness) or fiber length, the amount of dry paper strength agent added, the papermaking speed, the J / W ratio, the conditions of shaking in the CD direction of the papermaking wire (for example, shaking on / off, vibration frequency, vibration width), etc.

[0060] From the viewpoint of further improving processability, the waterproof paper of this embodiment has a tensile modulus in the machine direction of preferably 4.5 GPa or more, more preferably 5.0 GPa or more, and preferably 10.0 GPa or less, more preferably 9.0 GPa or less, and even more preferably 8.0 GPa or less. The tensile modulus in the machine direction can be adjusted to within the above range by adjusting the blending of the pulp constituting the paper base material, the papermaking speed, the J / W ratio, the shaking conditions of the papermaking wire in the CD direction (e.g., shaking on / off, vibration frequency, vibration width), etc.

[0061] From the viewpoint of further improving processability, the ratio of the tensile modulus in the longitudinal direction to the transverse direction of the waterproof paper (longitudinal direction / transverse direction) is preferably 1.60 or more, more preferably 1.80 or more, even more preferably 2.00 or more, and is preferably 4.00 or less, more preferably 3.50 or less, and may be 3.00 or less. The tensile modulus ratio can be adjusted to within the above range by adjusting the papermaking speed, J / W ratio, shaking conditions in the CD direction of the papermaking wire (e.g., shaking on / off, vibration frequency, vibration width), etc.

[0062] The tensile modulus of elasticity in the transverse and longitudinal directions of the waterproof paper shall be the value measured in accordance with JIS P 8113:2006.

[0063] [Taber stiffness] The Taber stiffness of the water-resistant paper in the horizontal direction is preferably 10 mN·m or less, more preferably 6.0 mN·m or less, and even more preferably 4.0 mN·m or less. By making the Taber stiffness of the water-resistant paper in the horizontal direction equal to or less than the above upper limit, excellent side sealing properties can be obtained when the water-resistant paper is rolled horizontally into a cylindrical shape. In other words, when a paper cup is formed using water-resistant paper that satisfies the above physical properties, a paper cup or paper lid that has excellent side sealing properties and is less likely to leak liquid from the side seal portion can be obtained. In addition, the lower limit of the Taber stiffness of the water-resistant paper in the horizontal direction is not particularly limited, but from the viewpoint of processing suitability, it is preferably 2.0 mN·m or more, more preferably 2.5 mN·m or more. The Taber stiffness in the lateral direction can be adjusted within the above range by adjusting the thickness of the paper base material, the composition of the pulp that makes up the paper base material, the degree of beating (freeness), the papermaking speed, the J / W ratio, and the shaking conditions of the papermaking wire in the CD direction (e.g., shaking on / off, vibration frequency, vibration amplitude), etc.

[0064] From the viewpoint of further improving processability, the Taber stiffness in the longitudinal direction of the water-resistant paper is preferably 25 mN·m or less, more preferably 15 mN·m or less, even more preferably 10 mN·m or less, even more preferably 9.0 mN·m or less, and even more preferably 7.0 mN·m or less. The lower limit of the Taber stiffness in the longitudinal direction of the water-resistant paper is not particularly limited, but is preferably 4.0 mN·m or more. The Taber stiffness in the longitudinal direction can be adjusted to within the above range by adjusting the thickness of the paper base material, the composition of the pulp constituting the paper base material, the beating degree (freeness), the papermaking speed, the J / W ratio, the shaking conditions of the papermaking wire in the CD direction (for example, shaking on / off, vibration frequency, vibration width), etc.

[0065] The ratio of the Taber stiffness in the longitudinal direction and the transverse direction of the waterproof paper (longitudinal direction / transverse direction) is preferably 1.5 or more, more preferably 1.8 or more, and may be 2.5 or more, 3.0 or more, or 3.5 or more, from the viewpoint of further improving the side sealability. The upper limit is preferably 5.0 or less, more preferably 4.0 or less, and even more preferably 3.0 or less, from the viewpoint of further improving the processing suitability. The Taber stiffness ratio can be adjusted within the above range by adjusting the papermaking speed, J / W ratio, the conditions of shaking of the papermaking wire in the CD direction (for example, shaking on / off, vibration frequency, vibration width), etc.

[0066] The Taber stiffness in the transverse and longitudinal directions of waterproof paper shall be values ​​measured in accordance with JIS P 8125:2000.

[0067] [Air permeability] The waterproof paper of this embodiment preferably has an air permeability of 1,000 seconds or more, more preferably 3,000 seconds or more, even more preferably 10,000 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.

[0068] By setting the air permeability within the above range, the air barrier property 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.

[0069] The air permeability shall be the value measured in accordance with JIS P 8117:2009.

[0070] [Cobb water absorption] From the viewpoint of cold water resistance, the water-resistant paper of the present embodiment has a Cobb water absorbency of preferably 20 g / m2 or less in water at 20° C. after a contact time of 30 minutes. 2 Less than 15g / m 2 More preferably, 10 g / m 2 Less than or equal to 8 g / m 2 More preferably, 5 g / m 2 (Lower limit is 0 g / m 2 The Cobb water absorbency shall be the value measured in accordance with JIS P 8140:1998.

[0071] In addition, from the viewpoint of hot water resistance, the water-resistant paper of the present embodiment has a Cobb water absorbency of preferably 50 g / m2 or less in water at 90° C. for a contact time of 30 minutes. 2 Less than or equal to 35 g / m 2 Less than 25 g / m, more preferably 2 or less, and even more preferably 15 g / m 2 or less, and even more preferably 10 g / m 2 (Lower limit is 0 g / m 2 The Cobb water absorbency shall be the value measured in accordance with JIS P 8140:1998.

[0072] [Oil resistance] From the viewpoint of application to foods containing oil (soup, coffee, etc.), the water-resistant paper of this embodiment preferably has an oil resistance of 6 or more, more preferably 8 or more, and even more preferably 10 or more (maximum oil resistance of 12). The oil resistance of the water-resistant paper is a value measured in accordance with JAPAN TAPPI No. 41 (kit method). The oil resistance can be adjusted to a desired value by providing a pigment layer between the paper base material and the water-resistant layer, or by adjusting the number and type of layers of the water-resistant layer.

[0073] [Recycling rate] From the viewpoint of environmental load, the recycle rate of the waterproof paper of the present embodiment is preferably 90% or more, more preferably 93% or more. The recycle rate is a value measured by the method described in the examples.

[0074] [Basic weight / paper thickness] The basis weight of the waterproof paper of the present embodiment is not particularly limited, but for example, for paper cups or paper lids, it is preferably 200 g / m 2 and preferably 400 g / m 2 Furthermore, from the viewpoint of improving side sealing performance, the basis weight of the waterproof paper is preferably 300 g / m 2 Less than 260 g / m 2 The basis weight of waterproof paper is measured in accordance with JIS P 8124:2011.

[0075] The thickness of the waterproof paper of this embodiment is not particularly limited, but is preferably 220 μm or more and 500 μm or less for use as a paper cup or paper lid. From the viewpoint of improving side sealing performance, the thickness of the waterproof paper is preferably 400 μm or less, more preferably 300 μm or less. The thickness of the waterproof paper is measured in accordance with JIS P 8118:2014.

[0076] <Uses of water-resistant paper> The water-resistant paper of the present embodiment is preferably used for liquid containers such as paper cups, etc. When used for paper containers, it is preferable from the viewpoint of formability that the water-resistant layer has heat sealability.

[0077] As an example of molding, the surface of the waterproof paper is printed as necessary, punched 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 also has excellent moldability.

[0078] The water-resistant paper of this embodiment has excellent processing suitability and is therefore suitable for use as a food container. More specifically, examples include paper cups (for iced drinks and hot drinks), paper plates, paper trays, paper food containers, paper lids, spoons, forks, knives, chopsticks, straws, and the like. In particular, the water-resistant paper of this embodiment has processing suitability that allows it to withstand high curvature processing such as top curl processing of paper cups and paper lids (particularly paper lids for paper cups), and is therefore suitable for use as paper cups and paper lids (particularly paper lids for paper cups). Therefore, as another aspect of the present invention, there is also provided a food container (particularly paper cups and paper lids) made of the above-mentioned water-resistant paper. EXAMPLES

[0079] The features of the present invention 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. Furthermore, unless otherwise specified, "%" and "parts" represent "% by mass" and "parts by mass", respectively. Furthermore, the operations of the examples and comparative examples were carried out under conditions of room temperature (20 to 25°C) and normal humidity (40 to 50% RH) unless otherwise specified.

[0080] The raw materials used in the examples and comparative examples are as follows. Ethylene-methacrylic acid copolymer ionomer: Aqueous dispersion of ethylene-methacrylic acid copolymer metal salt, product name "Chemipearl S300", manufactured by Mitsui Chemicals, Inc. Defoamer: Product name "Bismar KS-38E", manufactured by Nisshin Chemical Laboratory Co., Ltd. ·Organic particle A: High-density PE (HDPE), product name "AQUACER 272N", manufactured by BYK, average particle size 30 μm Organic particles B: low molecular weight PE + modified PO (modified polyolefin, low molecular weight PO), product name "Chemipearl W400", manufactured by Mitsui Chemicals, Inc., average particle size 4 μm

[0081] [Example 1] <Preparation of paper substrate> To 100 parts by mass (solid content equivalent) of pulp slurry in which beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed at a ratio of 70% and 30%, 0.8 parts by mass of weak acidic rosin sizing agent, 0.15 parts by mass of wet strength agent, and 1.45 parts by mass of aluminum sulfate were added to prepare a stock for the outer layers (first layer, fifth layer). Similarly, to 100 parts by mass (solid content equivalent) of pulp slurry in which beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed at a ratio of 70% and 30%, 0.8 parts by mass of weak acidic rosin sizing agent, 0.15 parts by mass of wet strength agent, and 1.7 parts by mass of aluminum sulfate were added to prepare a stock for the middle layers (second layer to fourth layer). Using these stocks, paper was made using a five-layer papermaking Fourdrinier machine to obtain a paper base material. The papermaking speed was 600 m / min.

[0082] <Preparation of water-resistant coating liquid> (a) Preparation of coating solution A (coating solution for gravure coater) An antifoaming agent was added to the ethylene-methacrylic acid copolymer ionomer to prepare coating solution A having a solid content of 30 mass% with an ethylene-methacrylic acid copolymer ionomer content of 97.5 mass% and an antifoaming agent content of 2.5 mass% in the solid content.

[0083] (b) Preparation of coating fluid B (coating fluid for air knife coater) An ethylene-methacrylic acid copolymer ionomer and an antifoaming agent were mixed to prepare Coating Solution B having a solid content of 28 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 97.5 mass% and the antifoaming agent content being 2.5 mass% in the solid content.

[0084] <Preparation of waterproof paper> Basis weight 320g / m 2 The coating solution A was applied to one side (front side) of a paper substrate having a thickness of 415 μm in a coating amount (solid content) of 2.5 g / m 2 The coating liquid was then applied using a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and the coating liquid was then dried to form a water-resistant layer (hereinafter referred to as the first layer on the front surface). Then, Coating Solution A was 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 g / m2, and then dried to form a water-resistant layer (hereinafter referred to as the second surface layer). 2 The coating liquid was then applied using an air knife coater so that the coating amount (solid content) was 5 g / m2, and the coating liquid was then dried to form a water-resistant layer (hereinafter referred to as the third layer). 2 The mixture was applied using an air knife coater so as to obtain a coating composition as shown in the figure, and then dried to form a water-resistant layer (hereinafter, referred to as the fourth layer in the table), thereby forming a total of four water-resistant layers.

[0085] The coating solution A was applied to the other side (back side) of the paper substrate in an amount (solid content) of 2.5 g / m 2 The coating liquid was then applied using a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and the coating liquid was then dried to form a water-resistant layer (hereinafter referred to as the first back layer). Then, Coating Solution A was 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 g / m2, and then dried to form a water-resistant layer (hereinafter referred to as the second back layer). 2 The mixture was coated using an air knife coater so that the thickness of the coating layer was 120 mm and then dried to form a water-resistant layer (hereinafter referred to as the third back layer), thereby forming a total of three water-resistant layers. The coating speed was 120 m / min.

[0086] [Example 2] The stock for the outer layers (first layer, fifth layer) was prepared in the same manner as in Example 1, except that beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed in a ratio of 80% and 20%. Similarly, the stock for the middle layers (second to fourth layers) was prepared in the same manner as in Example 1, except that beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed in a ratio of 80% and 20%. Using these stocks, paper was made using a five-layer papermaking fourdrinier machine to obtain a paper base material. The coating liquid was applied to the front surface of the obtained paper base material up to the first to third layers in the same manner as in Example 1 to form water-resistant layers (first to third layers) to produce water-resistant paper.

[0087] [Example 3] A paper substrate was obtained in the same manner as in Example 2. The coating liquid was applied to the front surface of the paper substrate in the same manner as in Example 1 up to the 1st to 4th layers to form water-resistant layers (front 1st to 4th layers) to produce water-resistant paper.

[0088] [Example 4] A paper substrate was obtained in the same manner as in Example 2. A water-resistant layer (front 1st to 3rd layers) was formed on the front surface of the paper substrate in the same manner as in Example 1, and then a water-resistant layer (reverse 1st to 3rd layers) was formed on the reverse surface of the paper substrate to produce a water-resistant paper.

[0089] [Example 5] <Preparation of base paper> A paper substrate was obtained in the same manner as in Example 2. A water-resistant layer (front 1st to 4th layers) was formed on the front surface of the paper substrate in the same manner as in Example 1, and then a water-resistant layer (reverse 1st to 3rd layers) was formed on the reverse surface of the paper substrate to produce a water-resistant paper.

[0090] [Example 6] The stock for the outer layers (first layer, fifth layer) was prepared in the same manner as in Example 1, except that beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed in a ratio of 90% and 10%. Similarly, the stock for the middle layers (second to fourth layers) was prepared in the same manner as in Example 1, except that beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed in a ratio of 90% and 10%. Using these stocks, paper was made using a five-layer fourdrinier paper machine to obtain a paper base material. In the same manner as in Example 1, a water-resistant layer (front first to fourth layers) was formed on the front surface of the paper base material, and then a water-resistant layer (back first to third layers) was formed on the back surface of the paper base material to produce a water-resistant paper.

[0091] [Example 7] The stock for the outer layers (first layer, fifth layer) was prepared in the same manner as in Example 1, except that beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed in a ratio of 45% and 55%. Similarly, the stock for the middle layers (second to fourth layers) was prepared in the same manner as in Example 1, except that beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed in a ratio of 45% and 55%. Using these stocks, paper was made using a five-layer fourdrinier paper machine to obtain a paper base material. In the same manner as in Example 1, a water-resistant layer (front layers 1 to 4) was formed on the front surface of the paper base material, and then a water-resistant layer (back layers 1 to 3) was formed on the back surface of the paper base material to produce a water-resistant paper.

[0092] [Example 8] The stock for the outer layers (first layer, fifth layer) was prepared in the same manner as in Example 1, except that beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed in a ratio of 50%:50%. Similarly, the stock for the middle layers (second to fourth layers) was prepared in the same manner as in Example 1, except that beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed in a ratio of 50%:50%. Using these stocks, paper was made using a five-layer fourdrinier paper machine to obtain a paper base material. In the same manner as in Example 1, a water-resistant layer (front layers 1 to 4) was formed on the front surface of the paper base material, and then a water-resistant layer (back layers 1 to 3) was formed on the back surface of the paper base material to produce a water-resistant paper.

[0093] [Example 9] The stock for the outer layers (first layer, fifth layer) was prepared in the same manner as in Example 1, except that beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed in a ratio of 40% and 60%. Similarly, the stock for the middle layers (second to fourth layers) was prepared in the same manner as in Example 1, except that beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) were mixed in a ratio of 40% and 60%. These stocks were used to make paper using a five-layer fourdrinier paper machine to obtain a paper base material. In the same manner as in Example 1, a water-resistant layer (front layers 1 to 4) was formed on the front surface of the paper base material, and then a water-resistant layer (back layers 1 to 3) was formed on the back surface of the paper base material to produce a water-resistant paper.

[0094] [Comparative Example 1] The stock for the outer layers (first layer, fifth layer) was prepared in the same manner as in Example 1, except that the pulp slurry was prepared from 100% beaten LBKP (CSF 460 mL). Similarly, the stock for the middle layers (second to fourth layers) was prepared in the same manner as in Example 1, except that the beaten LBKP (CSF 460 mL) was mixed at a ratio of 100%. Using these stocks, paper was made using a five-layer fourdrinier paper machine to obtain a paper base material. In the same manner as in Example 1, a water-resistant layer (front layers 1 to 4) was formed on the front surface of the paper base material, and then a water-resistant layer (back layers 1 to 3) was formed on the back surface of the paper base material to produce a water-resistant paper.

[0095] [Comparative Example 2] The stock for the outer layers (first layer, fifth layer) was prepared in the same manner as in Example 1, except that the pulp slurry was prepared from 100% beaten LBKP (CSF 400 mL). Similarly, the stock for the middle layers (second to fourth layers) was prepared in the same manner as in Example 1, except that the beaten LBKP (CSF 400 mL) was mixed at a ratio of 100%. Using these stocks, paper was made using a five-layer fourdrinier paper machine to obtain a paper base material. In the same manner as in Example 1, a water-resistant layer (front layers 1 to 4) was formed on the front surface of the paper base material, and then a water-resistant layer (back layers 1 to 3) was formed on the back surface of the paper base material to produce a water-resistant paper.

[0096] [Evaluation method] The following measurements and evaluations were performed on the water-resistant papers of Examples 1 to 9 and Comparative Examples 1 to 2 above. The results are shown in Tables 1 and 2. <Grammage> The grammage of the water-resistant paper was measured in accordance with JIS P 8124:2011.

[0097] <Paper thickness> The paper thickness of the water-resistant paper was measured in accordance with JIS P 8118:2014.

[0098] <Air permeability> The air permeability of the water-resistant paper was measured in accordance with JIS P 8117:2009.

[0099] <Tensile strength, elongation at break, tensile elastic modulus> The tensile strength, elongation at break, and tensile elastic modulus of the water-resistant paper were measured in accordance with JIS P 8113:2006. Note that the longitudinal direction of the water-resistant paper represents the papermaking direction (MD direction) of the paper base material that constitutes it. Also, the transverse direction of the water-resistant paper represents the direction (CD direction) perpendicular to the papermaking direction of the paper base material that constitutes it. <Taber stiffness> The Taber stiffness of the water-resistant paper was measured in accordance with JIS P 8125:2000.

[0100] <Cobb sizing degree> For the Cobb sizing degree, the obtained water-resistant paper was cut into a 10 cm square, and ion-exchanged water at 20 °C or 90 °C was brought into contact with the surface of the water-resistant paper for 30 minutes in accordance with JIS P 8140:1998, and it was measured in accordance with JIS P 8140:1998 from the mass difference before and after the contact.

[0101] <Recyclability> The obtained waterproof paper was weighed out to about 50g in bone dry weight, cut by hand without using a blade into pieces of about 2cm each, added with tap water to make the concentration 3%, and processed for 10 minutes at 21℃ and 3000rpm using a disintegrator (Kumagaya Riki Kogyo Co., Ltd. No. 2532) to prepare a pulp slurry in which the pulp fibers were completely disintegrated. This pulp slurry was screened for 10 minutes with a slit width of 0.2mm (8 cuts) and a flow rate of 10L / min to obtain a residue. The ratio of the bone dry residue weight to the charged bone dry weight was defined as the residue rate, and the pulp transmittance was calculated by subtracting this from 100% to obtain the recycle rate.

[0102] <Processing suitability> The obtained waterproof paper was molded into a cup shape with the front side facing inward (liquid-contacting surface) and the back side facing outward (printed surface), and with the CD direction of the constituent paper substrate facing the horizontal direction of the cup. The moldability of the top curled part of the cup when top curled was evaluated based on the following criteria. The top curling was performed in the following manner. A die was placed on the periphery of the opening at the top end of the cup to widen the opening, and a die with a curl shape of about 3 mm in diameter was placed on it to curl it toward the outside of the cup. The cup was then pressed downward, and the substrate was rolled inward along the curved surface of the die with a curl shape set below. The processing suitability was evaluated based on the following criteria. Using the above method, 10,000 paper cups were molded and the top curl portion was inspected for defects (cracks, paper layer peeling, insufficient curl, wrinkles). The defect rate of the top curl portion was calculated using the formula: Defective rate = number of defective cups ÷ number of paper cups molded × 100. [Evaluation Criteria] A: The defect rate of the top curl part is 1% or less (no problem in practical use) B: The defect rate of the top curl portion is more than 1% and 2% or less (no problem in practical use) C: The defect rate of the top curl portion is more than 2% and 3% or less (no problem in practical use) D: The defect rate of the top curl portion is more than 3% and less than 10% (problematic in practical use) E: The defect rate of the top curl part exceeds 10% (problematic in practical use).

[0103] <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. [Evaluation Criteria] 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)

[0104] <Production efficiency> The production efficiency of waterproof paper was evaluated according to the following criteria. [Evaluation Criteria] It indicates the amount of waterproof paper produced per minute in m (meter) / min. A: The production speed is over 400m / min, and the production efficiency is very good. B: The production speed is 200 m / min or more and less than 400 m / min, and the production efficiency is somewhat good. C: The production speed is less than 200 m / min, and the production efficiency is very poor.

[0105] <Smoothness> The smoothness of the back surface (outer surface of the cup) of the obtained waterproof paper was visually evaluated based on the following criteria. [Evaluation Criteria] A: High smoothness, high printability, no coating unevenness B: Low smoothness, slightly poor printability, coating unevenness is observed C: Very low smoothness, poor printability, and very large coating unevenness.

[0106] <Side sealing performance> The obtained waterproof paper was cut into a length of 15 cm x width of 25 cm, and rolled horizontally with the surface facing inward to form a cylinder with a diameter of 7.5 cm. The heat sealability of the overlapping part of the waterproof paper (corresponding to the side of the body of the paper cup, side seal width 0.7 cm) was evaluated based on the following criteria. Heat sealing was performed using "CS-205" manufactured by Chubu Sogyo Co., Ltd., at a temperature of 250°C, a pressure of 0.1 MPa, and a bonding time of 2 seconds. [Evaluation Criteria] A: The adhesive strength is strong, and it will not easily peel off even if you press it with your hand from the outside of the tube and distort its shape. B: The adhesive strength is slightly weak, and when the tube is pushed by hand from the outside and the shape is distorted, part of the adhesive part peels off. C: The adhesive strength is weak, and when the tube is pushed by hand from the outside and distorted, about half of the adhesive part peels off.

[0107] <Oil resistance> The oil resistance of the waterproof paper surface was evaluated according to JAPAN TAPPI No. 41 (kit method). The higher the value (kit value), the higher the oil repellency.

[0108] [Table 1]

[0109] [Table 2]

[0110] As can be seen from the results in Tables 1 and 2, by having an appropriate value for the lateral tensile strength, the obtained waterproof paper had excellent processability without cracks or wrinkles at the top curl portion when molded into a cup shape. As a preferred embodiment, according to Examples 1 to 5 and 8 to 9 in which the NBKP content relative to the total amount of pulp constituting the paper base material was 20 to 50%, waterproof paper with further elongation and tensile modulus became appropriate values ​​and with better processability was obtained. On the other hand, in Example 6, in which the NBKP content relative to the total amount of pulp constituting the paper base material was 10%, the water-resistant paper had high tensile strength in the lateral direction and excellent processing suitability, but some cracks and wrinkles occurred in the top curl portion. In Example 7, in which the NBKP content was 55% relative to the total amount of pulp constituting the paper base material, the processing suitability was good, but the surface smoothness was slightly inferior, which tended to deteriorate the printability when used for cups. Furthermore, unevenness occurred during application of the coating liquid, and the Cobb water absorbency tended to deteriorate. On the other hand, in Comparative Example 1, where the NBKP content relative to the total amount of pulp constituting the paper base material was 0%, the lateral tensile strength and tensile modulus were too high, and the lateral breaking elongation was too low, causing large cracks and wrinkles in the top curl portion. Comparative Example 2 had the same formulation as Comparative Example 1 except that the beating degree of the LBKP was increased, but the lateral tensile strength was high, causing large cracks and wrinkles in the top curl portion.

[0111] [Example 10] <Preparation of paper substrate> To 100 parts by mass (solids content) of pulp slurry made of beaten LBKP (CSF 400 mL) and beaten NBKP (CSF 530 mL) mixed at a ratio of 75% and 25%, 0.67 parts by mass of weak acidic rosin sizing agent, 0.84 parts by mass of wet strength agent, and 1.9 parts by mass of aluminum sulfate were added to prepare stock for the outer layers (first and fifth layers). Similarly, to 100 parts by mass (solids content) of pulp slurry made of beaten LBKP (CSF 390 mL), 0.5 parts by mass of weak acidic rosin sizing agent, 0.3 parts by mass of wet strength agent, and 1.8 parts by mass of aluminum sulfate were added to prepare stock for the middle layers (second to fourth layers). These stocks were used to make paper using a five-layer Fourdrinier paper machine, and the basis weight was 224 g / m 2 The paper base material had a thickness of 268 μm. The papermaking speed was 600 m / min.

[0112] <Preparation of water-resistant coating liquid> (a) Preparation of coating solution C (coating solution for gravure coater) An antifoaming agent was added to the ethylene-methacrylic acid copolymer ionomer to prepare coating solution C having a solid content of 30 mass% with an ethylene-methacrylic acid copolymer ionomer content of 98.9 mass% and an antifoaming agent content of 1.1 mass% in the solid content. (b) Preparation of coating fluid D (coating fluid for air knife coater) An antifoaming agent was added to the ethylene-methacrylic acid copolymer ionomer to prepare coating solution D having a solid content of 28 mass% with an ethylene-methacrylic acid copolymer ionomer content of 98.9 mass% and an antifoaming agent content of 1.1 mass% in the solid content. (c) Preparation of coating solution E (pigment layer coating solution) An antifoaming agent was added to VB2160 (Michaelman Japan) with a kaolin / SBR (styrene butadiene rubber) ratio of 4 / 6 to prepare a pigment layer coating liquid (Coating Liquid E) with a solids concentration of 40.0% by mass, where the VB2160 content in the solids is 98.9% by mass and the antifoaming agent content is 1.1% by mass. (d) Preparation of Coating Fluid F (Pigment Layer Undercoat Coating Fluid) A pigment layer undercoat coating liquid (Coating Liquid F) was prepared with a kaolin / heavy carbon / latex / starch content of 25 / 75 / 10.5 / 4 and a solids concentration of 45.0 mass %. (e) Preparation of Coating Fluid G (Pigment Layer Top Coating Fluid) A pigment layer topcoat coating liquid (Coating Liquid G) was prepared with a kaolin / heavy carbon / latex / starch content of 24 / 76 / 12.5 / 1.0 and a solids concentration of 45.0 mass %. (f) Preparation of coating solution H (coating solution for gravure coater) An antifoaming agent was added to the ethylene-methacrylic acid copolymer ionomer to prepare Coating Solution H having a solid content of 28 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 98.9 mass% and the antifoaming agent content being 1.1 mass% in the solid content. (g) Preparation of coating fluid I (coating fluid for air knife coater) The ethylene-methacrylic acid copolymer ionomer was blended with organic particles B and an antifoaming agent to prepare coating solution I having a solids concentration of 28 mass%, with the ethylene-methacrylic acid copolymer ionomer content of 96.9 mass%, the low molecular weight PE + modified PO content of 2.0 mass%, and the antifoaming agent content of 1.1 mass% in the solids. (h) Preparation of Coating Solution J The ethylene-methacrylic acid copolymer ionomer was blended with organic particles B and an antifoaming agent to prepare coating solution J having a solid content of 28 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 92.9 mass%, the low molecular weight PE + modified PO content being 6.0 mass%, and the antifoaming agent content being 1.1 mass%. (i) Preparation of Coating Solution K The ethylene-methacrylic acid copolymer ionomer was blended with organic particles A and an antifoaming agent to prepare coating solution K having a solid content of 28 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 93.9 mass%, the high-density PE content being 5.0 mass%, and the antifoaming agent content being 1.1 mass% in the solid content. (j) Preparation of coating solution L The ethylene-methacrylic acid copolymer ionomer was mixed with organic particles A and an antifoaming agent to prepare coating solution L having a solid content of 28 mass%, with the ethylene-methacrylic acid copolymer ionomer content being 78.9 mass%, the high-density PE content being 20.0 mass%, and the antifoaming agent content being 1.1 mass% in the solid content.

[0113] <Preparation of waterproof paper> The coating solution C was applied to one side (front side) of the paper substrate in an amount (solid content) of 2.5 g / m 2 The coating liquid was then applied using a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and the coating liquid was then dried to form a water-resistant layer (hereinafter referred to as the first layer on the front surface). Then, Coating Solution C was applied again to the same surface so that the coating amount (solid content) was 2.5 g / m2. 2 The coating solution D was applied to the same surface in an amount (solid content) of 5 g / m2, and then dried to form a water-resistant layer (hereinafter referred to as the second surface layer). 2The mixture was coated using an air knife coater so that the coating speed was 120 m / min., and then dried to form a water-resistant layer (hereinafter referred to as the third layer in the table), forming a total of three water-resistant layers.

[0114] [Example 11] The coating liquid was applied to the front surface of the paper substrate produced in Example 10 in the same manner as in Example 10 to form water-resistant layers (1st to 3rd layers), thereby producing water-resistant paper. The above-mentioned coating liquid C was applied to the other surface (rear surface) of the paper substrate in an amount (solid content) of 2.5 g / m 2 The coating liquid was then applied using a gravure coater so that the coating amount (solid content) was 2.5 g / m2, and the coating liquid was then dried to form a water-resistant layer (hereinafter referred to as the first back layer). Then, Coating Solution C was applied again to the same surface so that the coating amount (solid content) was 2.5 g / m2. 2 The coating solution D was applied to the same surface in an amount (solid content) of 5 g / m2, and then dried to form a water-resistant layer (hereinafter referred to as the second back layer). 2 The resulting mixture was applied using an air knife coater so that the above-mentioned composition was adhered to the substrate, and then dried to form a water-resistant layer (hereinafter referred to as the back third layer), thereby forming a total of three water-resistant layers.

[0115] [Example 12] <Preparation of paper substrate> Beaten LBKP (CSF 400 mL) and beaten NBKP (CSF 530 mL) were mixed at a ratio of 60% and 40%, and 2.4 parts by mass of weak acid rosin sizing agent, 0.14 parts by mass of wet strength agent, and 1.25 parts by mass of aluminum sulfate were added to 100 parts by mass (solid content equivalent) of pulp slurry made of beaten LBKP (CSF 400 mL) and beaten NBKP (CSF 530 mL) to prepare a stock for the outer layers (first layer, fifth layer). Similarly, 1.5 parts by mass of weak acid rosin sizing agent, 0.14 parts by mass of wet strength agent, and 1.5 parts by mass of aluminum sulfate were added to 100 parts by mass (solid content equivalent) of pulp slurry made of beaten LBKP (CSF 330 mL) to prepare a stock for the middle layers (second layer to fourth layer). These stocks were used to make a five-layer paper using a Fourdrinier paper machine, and furthermore, coating liquid F was applied to the front surface at a coating amount (solid content) of 15 g / m. 2 Then, coating solution G was applied on top of the rod coater so that the coating amount (solid content) was 10 g / m2 The paper is coated with a blade coater so that the surface has a pigment layer and a basis weight of 229 g / m. 2 The paper base material had a thickness of 257 μm. The papermaking speed was 600 m / min. The coating speed was 120 m / min.

[0116] <Preparation of waterproof paper> The coating liquid was applied to one side (front side) of the above paper base material in the same manner as in Example 10 to form water-resistant layers (front first to third layers) to produce water-resistant paper.

[0117] [Example 13] Using the paper stock prepared in the same manner as in Example 12, paper was made using a 5-layer papermaking machine, and the basis weight of the paper base was 225 g / m 2 A paper substrate with a thickness of 263 μm was obtained. In the same manner as in Example 10, the coating liquid was applied to one side (front side) of the paper substrate up to the first to third layers to form water-resistant layers (front first to third layers) to produce water-resistant paper.

[0118] [Example 14] Using the paper stock prepared in the same manner as in Example 12, paper was made using a 5-layer papermaking machine, and the paper base had a basis weight of 225 g / m2 and had a pigment layer on the front surface. 2 A paper base material with a thickness of 263 μm was obtained. On one side (front side) of the paper substrate, the coating liquid was applied for the first to third layers to form water-resistant layers (front first to third layers) in the same manner as in Example 10. On the other side (reverse side) of the paper substrate, water-resistant layers (reverse first to third layers) were formed in the same manner as in Example 11 to produce water-resistant paper.

[0119] [Example 15] Using the paper stock prepared in the same manner as in Example 12, paper was made using a 5-layer papermaking machine, and the basis weight of the paper base was 220 g / m 2 A paper substrate having a thickness of 252 μm was obtained. The above-mentioned coating liquid E was applied to the front surface of the paper substrate in an amount (solid content) of 4.5 g / m 2The pigment layer was formed by coating using an air knife coater so as to obtain the above-mentioned composition, followed by drying to form a pigment layer. Then, water-resistant layers (front 1st to 3rd layers) were formed on the same surface in the same manner as in Example 10 to produce water-resistant paper.

[0120] [Example 16] <Preparation of waterproof paper> Using the paper stock prepared in the same manner as in Example 12, paper was made using a 5-layer papermaking machine, and the basis weight of the paper base was 228 g / m 2 A paper substrate having a thickness of 260 μm was obtained. The above-mentioned coating liquid E was applied to the front surface of the paper substrate in an amount (solid content) of 4.5 g / m 2 The coating was then applied to the same surface using an air knife coater so that the coating amount (solid content) was 2.0 g / m, and the resulting mixture was dried to form a pigment layer. 2 The coating liquid H was applied again to the same surface so that the coating amount (solid content) was 2.0 g / m. 2 The coating solution I was applied to the same surface in an amount (solid content) of 4 g / m2 and then dried to form a water-resistant layer (hereinafter referred to as the second layer on the front surface). 2 The mixture was applied using an air knife coater so as to obtain a water-resistant layer (hereinafter, referred to as the third front layer) by drying, thereby forming a total of three water-resistant layers.

[0121] [Example 17] Using the paper stock prepared in the same manner as in Example 12, paper was made using a 5-layer papermaking machine, and the basis weight of the paper base was 224 g / m 2 A paper substrate having a thickness of 268 μm was obtained. The above-mentioned coating solution E was applied to the front surface of the paper substrate in a coating amount (solid content) of 4.5 g / m 2 The resulting coating was performed using an air knife coater so that the pigment layer was formed as shown in the figure, followed by drying to form a pigment layer. Then, on the same surface, the above-mentioned Coating Liquid H and Coating Liquid J were used to form water-resistant layers (front 1st to 3rd layers) in the same manner as in Example 16 to produce water-resistant paper.

[0122] [Example 18] Using the paper stock prepared in the same manner as in Example 12, paper was made using a 5-layer papermaking machine, and the basis weight of the paper base was 229 g / m 2 A paper substrate having a thickness of 257 μm was obtained. The above-mentioned coating liquid E was applied to the front surface of the paper substrate in a coating amount (solid content) of 4.5 g / m 2 The resulting paper was coated using an air knife coater and dried to form a pigment layer. Then, on the same surface, the above-mentioned Coating Liquid H and Coating Liquid K were used to form water-resistant layers (front 1st to 3rd layers) in the same manner as in Example 16 to produce water-resistant paper.

[0123] [Example 19] Using the paper stock prepared in the same manner as in Example 12, paper was made using a 5-layer papermaking machine, and the basis weight of the paper base was 225 g / m 2 A paper substrate having a thickness of 263 μm was obtained. The above-mentioned coating liquid E was applied to the front surface of the paper substrate in an amount (solid content) of 4.5 g / m 2 The resulting paper was coated using an air knife coater so that the pigment layer was formed as shown in the figure, and then dried to form a pigment layer. Then, on the same surface, the above-mentioned Coating Liquid H and Coating Liquid L were used to form water-resistant layers (front 1st to 3rd layers) in the same manner as in Example 16, to produce water-resistant paper.

[0124] [Example 20] The stock for the outer layers (first layer, fifth layer) was prepared in the same manner as in Example 12, except that the pulp slurry was prepared from 100% beaten LBKP (CSF 350 mL). Similarly, the stock for the middle layers (second to fourth layers) was prepared in the same manner as in Example 1, except that the beaten LBKP (CSF 350 mL) was mixed at a ratio of 100%. Using these stocks, paper was made using a five-layer fourdrinier papermaking machine to obtain a paper base material. At this time, the J / W ratio was adjusted to be high so that the aspect ratio of the tensile strength of the waterproof paper was 3.06. In the same manner as in Example 1, a waterproof layer (front layers 1 to 4) was formed on the front surface of the paper base material, and then a waterproof layer (back layers 1 to 3) was formed on the back surface of the paper base material to produce waterproof paper.

[0125] [Example 21] <Preparation of paper substrate> To 100 parts by mass (solids equivalent) of pulp slurry made by mixing beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) at a ratio of 60% and 40%, 0.8 parts by mass of weak acid rosin sizing agent, 0.15 parts by mass of wet strength agent, and 1.45 parts by mass of aluminum sulfate were added to prepare the stock for the outer layers (1st and 5th layers). Similarly, to 100 parts by mass (solids equivalent) of pulp slurry made by mixing beaten LBKP (CSF 460 mL) and beaten NBKP (CSF 650 mL) at a ratio of 60% and 40%, 0.8 parts by mass of weak acid rosin sizing agent, 0.15 parts by mass of wet strength agent, and 1.7 parts by mass of aluminum sulfate were added to prepare the stock for the middle layers (2nd to 4th layers). Using these paper materials, a paper was made using an on-machine coater (manufactured by Voith IHI Paper Technology Co., Ltd., model number: Fourdrinier multilayer) with a five-layer Fourdrinier papermaking machine at a papermaking width of 4200 mm and a papermaking speed of 200 m / min. Subsequently, using the on-machine coater, a water-resistant layer was coated as follows. Coating solution F was applied to the paper with a coating amount (solid content) of 4.5 g / m2 at a coating width of 4200 mm and a coating speed of 200 m / min. 2 A rod coater was used to simultaneously coat both sides of the substrate so that a pigment layer was formed, and then coating solution J was applied to the front surface of the pigment layer so that the coating amount (solid content) was 5.0 g / m. 2 Then, on the back side, coating solution J was applied at a coating amount (solid content) of 5.0 g / m. 2 The sheet is coated with a blade coater so that the surface has a water-resistant layer on both sides and a basis weight of 260 g / m 2 A waterproof paper with a thickness of 340 μm was produced.

[0126] [Example 22] Example 2 except that the papermaking speed and coating speed of the on-machine coater were changed to 400 m / min. 1 Similarly, the basis weight is 258 g / m 2 A waterproof paper with a thickness of 338 μm was produced.

[0127] [Example 23] Example 2 except that the papermaking speed and coating speed of the on-machine coater were changed to 600 m / min. 1 Similarly, the basis weight is 256 g / m2 A waterproof paper with a thickness of 337 μm was produced.

[0128] [Example 24] Example 2 except that the papermaking speed and coating speed of the on-machine coater were changed to 800 m / min. 1 Similarly, the basis weight is 263 g / m 2 A waterproof paper with a thickness of 344 μm was produced.

[0129] [Example 25] Example 2 except that the papermaking speed and coating speed of the on-machine coater were changed to 1000 m / min. 1 Similarly, the basis weight is 259 g / m 2 A waterproof paper with a thickness of 337 μm was produced.

[0130] [Example 26] The same procedure as in Example 21 was repeated except that the papermaking conditions were changed so that the basis weight and thickness of the waterproof paper were as follows: 2 A waterproof paper with a thickness of 327 μm was produced.

[0131] [Example 27] The same procedure as in Example 23 was repeated except that the papermaking conditions were changed so that the basis weight and thickness of the waterproof paper were as follows: 2 A waterproof paper with a thickness of 468 μm was produced.

[0132] Examples 10 to 27 were evaluated in the same manner as the above Examples 1 to 9 and Comparative Example 1. The results are shown in Tables 3 and 4, as well as Tables 5 and 6.

[0133] [Table 3]

[0134] [Table 4]

[0135] [Table 5]

[0136] [Table 6]

[0137] As can be seen from the results in Tables 3 and 4, in Examples 10 to 15, when the waterproof paper was rolled horizontally to form a tube, the waterproof paper had an appropriate Taber stiffness in the horizontal direction compared to Examples 1 to 9, and therefore had a small repulsive force, resulting in excellent side sealing properties. In addition, according to Examples 16 to 19, since the organic particles were contained, excellent blocking resistance was obtained. On the other hand, Example 20 had a higher failure rate in the top curl portion, probably because the Taber stiffness in the longitudinal direction was too high compared to the other Examples, and the processability was somewhat inferior. Furthermore, in Examples 21 to 27, the coating liquid was applied by an on-machine method, and therefore excellent production efficiency was obtained.

[0138] Although the present invention will be described in detail with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the present invention. [Industrial Applicability]

[0139] Water-resistant paper can be used for various containers for food (trays, cups, etc.) and their lids, food cutlery (for example, chopsticks, spoons, forks, etc.), and the like.

Claims

1. A waterproof paper having at least one waterproof layer on at least one surface of a paper substrate, The tensile strength in the transverse direction is 19.0 kN / m or less, The ratio of tensile strength in the longitudinal direction to that in the transverse direction (longitudinal direction / transverse direction) is 1.40 or more and 3.00 or less, The transverse elongation at break is 4.5% or more; The content of softwood bleached kraft pulp relative to the total amount of pulp constituting the paper base material is 20 to 50 mass%; The water-resistant paper has a hardwood bleached kraft pulp content of 50 to 80% by mass relative to the total amount of pulp constituting the paper base material.

2. A waterproof paper as described in claim 1, having a ratio of breaking elongation in the longitudinal direction to the transverse direction (longitudinal direction / transverse direction) of 0.60 or less.

3. 3. The waterproof paper according to claim 1, having a tensile modulus in the transverse direction of 3.7 GPa or less.

4. The waterproof paper according to any one of claims 1 to 3, having a Taber stiffness in the transverse direction of 10 mN·m or less.

5. A waterproof paper described in any one of claims 1 to 4, having a ratio of the tensile modulus in the longitudinal direction to the transverse direction (longitudinal direction / transverse direction) of 2.00 or more.

6. The waterproof paper according to any one of claims 1 to 5, wherein the paper base material has three or more paper layers.

7. The waterproof paper according to any one of claims 1 to 6, which satisfies at least one of the following (i) and (ii): (i) The Taber stiffness in the longitudinal direction is 7.0 mN·m or less. (ii) The tensile strength in the longitudinal direction is 15.0 kN / m or more and 20.0 kN / m or less.

8. The waterproof paper according to any one of claims 1 to 7, wherein the waterproof layer contains an ethylene-(meth)acrylic acid copolymer.

9. Cobb water absorption at 20°C for 30 minutes is 20 g / m ２ The waterproof paper according to any one of claims 1 to 8, wherein:

10. Cobb water absorption at 90°C for 30 minutes is 50 g / m ２ The waterproof paper according to any one of claims 1 to 9, wherein:

11. The waterproof paper according to any one of claims 1 to 10, which has an oil resistance of 6 or more as measured in accordance with JAPAN TAPPI No.

41.

12. A food container, a paper cup or a paper lid made using the waterproof paper according to any one of claims 1 to 11.

13. 12. The method for producing waterproof paper according to claim 1, further comprising a coating step of coating a coating liquid for a waterproof layer on a paper substrate by an on-machine method, the coating step having a coating width of 2000 mm or more and a coating speed of 100 m / min or more.

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