Waterproof paper and packaging container

Abstract

To provide waterproof paper having heat sealability, excellent waterproof property, and excellent top curling workability.SOLUTION: Waterproof paper having a waterproof layer on at least a liquid contact surface of a paper substrate, has a tensile modulus in a longitudinal direction of 7.5 GPa or under, a short span compression strength in the longitudinal direction of 7.5 kN / m or under, and a heat seal peel strength when one surface and the other surface of the waterproof paper are heat-sealed in a condition of 130°C and a pressure of 2 kgf / cm2, for 2 seconds, of 7.0 kN / m or over.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Plastic products have traditionally been used for various containers for drinks, food, etc., and food cutlery (e.g., chopsticks, spoons, forks, etc.), but there is a desire to switch to paper products in order to reduce the environmental impact.

[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. In order to address these problems, attempts have been made to impart water resistance and other properties to the paper by imparting properties during the papermaking process or by coating.

[0004] Furthermore, Patent Document 1 discloses a packaging paper having at least one heat seal layer on at least one side of a paper substrate, with the aim of providing a packaging paper that can reduce the amount of plastic used, wherein the heat seal layer contains an ionomer and the dry coating weight of the heat seal layer is 2 to 10 g / m2 in total. 2 and a packaging paper characterized in that two or more heat seal layers are formed on at least one surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6580291 Summary of the Invention [Problem to be solved by the invention]

[0006] The waterproof paper described in Patent Document 1 has a problem with top curl processability when the waterproof paper is processed into various containers and the like. Therefore, an object of the present invention is to provide a waterproof paper that has heat sealing properties, excellent water resistance, and excellent top curl processability, and to provide a packaging container made using the waterproof paper. [Means for solving the problem]

[0007] The inventors discovered that the above-mentioned problems can be solved by setting the longitudinal tensile modulus and short span compressive strength to specific values or less and the heat seal peel strength to specific values or more in a waterproof paper having a waterproof layer on at least the liquid-contacting surface of a paper substrate, and thus completed the present invention.

[0008] That is, the present invention provides the following: <1> ~ <15> Regarding. <1> A waterproof paper having a waterproof layer on at least the liquid-contacting surface of the paper base, with a longitudinal tensile modulus of elasticity of 7.5 GPa or less and a longitudinal short span compressive strength of 7.5 kN / m or less, and one side of the waterproof paper and the other side are heated at 130°C under a pressure of 2 kgf / cm. 2 A waterproof paper having a heat seal peel strength of 7.0 kN / m or more when heat sealed for 2 seconds. <2> The total coating amount of the water-resistant layer is 7 g / m 2 That's all. <1> The water-resistant paper described in <3> The paper substrate has an undercoat layer and the water-resistant layer in this order on the liquid-contacting surface thereof. <1> or <2> The water-resistant paper described in <4> the undercoat layer contains latex and a pigment, and the mass ratio of the latex to the pigment in the undercoat layer (latex / pigment) is 10 / 90 or more and 40 / 60 or less; <3> The water-resistant paper described in <5> The pulp raw materials constituting the paper base material contain hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP), and the Canadian standard freeness of the hardwood bleached kraft pulp is 310 mL or more and 550 mL or less, and the Canadian standard freeness of the softwood bleached kraft pulp is 420 mL or more and 550 mL or less, <1> ~ <4> 1. The waterproof paper according to any one of the preceding items. <6> The pulp raw material constituting the paper base material contains hardwood bleached kraft pulp (LBKP) and softwood bleached kraft pulp (NBKP), and the mass ratio (LBKP / NBKP) of the hardwood bleached kraft pulp (LBKP) to the softwood bleached kraft pulp (NBKP) in the pulp raw material is 60 / 40 or more and 100 / 0 or less; <1> ~ <5> 1. The waterproof paper according to any one of the preceding items. <7> The paper substrate contains a starch-based dry paper strength agent. <1> ~ <6> 1. The waterproof paper according to any one of the preceding items. <8> The paper base has a basis weight of 200 g / m 2 That's all. <1> ~ <7> 1. The waterproof paper according to any one of the preceding items. <9> the water-resistant layer contains at least one resin selected from the group consisting of polyolefin-based resins and acrylic-based resins; <1> ~ <8> 1. The waterproof paper according to any one of the preceding items. <10> The paper substrate has the water-resistant layer as an uppermost layer on at least one surface thereof. <1> ~ <9> 1. The waterproof paper according to any one of the preceding items. <11> The paper substrate has the water-resistant layer on both sides thereof. <1> ~ <10> 1. The waterproof paper according to any one of the preceding items. <12> The Cobb water absorbency of the water-resistant paper surface at 20°C after 30 minutes of contact is 15 g / m 2 Below is the <1> ~ <11> 1. The waterproof paper according to any one of the preceding items. <13> The Cobb water absorbency of the water-resistant paper surface at 90°C for 30 minutes is 20 g / m 2 Below is the <1> ~ <12> 1. The waterproof paper according to any one of the preceding items. <14> For packaging containers, <1> ~ <13> 1. The waterproof paper according to any one of the preceding items. <15> <1> ~ <14> A packaging container made using the waterproof paper described in any one of the above. [Effects of the Invention]

[0009] The present invention provides a waterproof paper that has heat-sealing properties, excellent water resistance, and excellent top-curl processability. The present invention also provides a packaging container made from the waterproof paper. DETAILED DESCRIPTION OF THE INVENTION

[0010] [Waterproof paper] The waterproof paper of this embodiment is a waterproof paper having a waterproof layer on at least the liquid-contacting surface (also referred to as the surface) of a paper substrate, and has a longitudinal tensile modulus of elasticity of 7.5 GPa or less, a longitudinal short span compressive strength of 7.5 kN / m or less, and is capable of being heated by heating one side of the waterproof paper to the other side at 130°C under a pressure of 2 kgf / cm. 2 The heat seal peel strength when heat sealed under the conditions of 1.5 seconds and 2 seconds is 7.0 kN / m or more. The waterproof paper of this embodiment has heat sealability, excellent water resistance, and excellent top curl processability.

[0011] The mechanism by which the above-mentioned effects are achieved is unknown, but is speculated as follows. It is believed that by setting the longitudinal tensile modulus to 7.5 GPa or less and the longitudinal short-span compressive strength to 7.5 kN / m or less, the flexibility of the waterproof paper is high and top curl processability is excellent. Generally, when manufacturing a packaging container with a top curl portion, the longitudinal direction of the waterproof paper is the vertical direction of the container (i.e., the direction in which it is rolled during top curl processing) and the transverse direction is the horizontal direction, so the longitudinal tensile strength and short-span compressive strength are specified. It is also believed that by setting the heat seal peel strength to 7.0 kN / m or more, peeling and cracking of the heat-sealed portion during top curl processing are suppressed. The effects of the present invention are not limited by the above-mentioned mechanism. The longitudinal direction of waterproof paper means the direction corresponding to the papermaking direction (MD direction) of the paper base material, and the transverse direction of waterproof paper means the direction corresponding to the width direction (CD direction) of the paper base material. The structure and properties of the waterproof paper of this embodiment will be described in more detail below.

[0012] In this specification, the numerical range represented by "X to Y" means a numerical range including X as the lower limit and Y as the upper limit. When the numerical range is described in stages, the upper and lower limits of each numerical range can be combined arbitrarily. Furthermore, "(meth)acrylic" is a generic term including both acrylic and methacrylic.

[0013] <Paper base material> The paper base material constituting the waterproof paper of this embodiment may be a single-layer or multi-layer structure. In the case of multi-layer paper, the number of paper layers is not particularly limited, but is preferably three or more, more preferably four or more, and even more preferably five or more. By using three or more paper layers, the desired basis weight and paper thickness can be achieved, and the physical properties of the waterproof paper can be adjusted to the desired range by adjusting the basis weight, freeness, etc. of each layer. The upper limit of the number of paper layers is not particularly limited, but is preferably seven or fewer, more preferably six or fewer.

[0014] Pulps constituting the paper base material include chemical pulps such as bleached hardwood kraft pulp (LBKP) and bleached softwood kraft pulp (NBKP); mechanical pulps such as groundwood pulp (GP), pressure groundwood pulp (PGW), refiner mechanical pulp (RMP), thermomechanical pulp (TMP), chemi-thermomechanical pulp (CTMP), chemi-mechanical pulp (CMP), and chemi-ground pulp (CGP); recycled paper pulp; non-wood fiber pulps such as kenaf, bagasse, bamboo, and cotton; and synthetic pulp. These pulps may be used alone or in combination of two or more. Among these, the combined use of LBKP and NBKP is preferred.

[0015] From the viewpoint of achieving the desired ranges of tensile modulus and short span compressive strength of the waterproof paper, and of obtaining appropriate paper strength as waterproof paper for packaging containers, the Canadian Standard Freeness (CSF) of the LBKP is preferably 310 mL or more and 550 mL or less, more preferably 330 mL or more, even more preferably 350 mL or more, particularly preferably 380 mL or more, and more preferably 500 mL or less, even more preferably 480 mL or less, particularly preferably 450 mL or less. Furthermore, from the viewpoint of achieving the desired range of tensile modulus and short span compressive strength of the waterproof paper, and obtaining appropriate paper strength as waterproof paper for packaging containers, the Canadian Standard Freeness (CSF) of NBKP is preferably 420 mL or more and 550 mL or less, more preferably 450 mL or more, even more preferably 470 mL or more, and more preferably 530 mL or less, even more preferably 510 mL or less. Canadian standard freeness is measured in accordance with JIS P 8121-2:2012 "Pulp - Testing method for freeness - Part 2: Canadian standard freeness method." It is preferred that LBKP and NBKP are used in combination as the pulp constituting the paper base material, and that the Canadian Standard Freeness (CSF) of each is within the above range.

[0016] When LBKP and NBKP are used in combination as the pulp constituting the paper base material, the mass ratio of LBKP to NBKP (LBKP / NBKP) in the pulp raw materials constituting the paper base material is preferably 60 / 40 or more and 100 / 0 or less, more preferably 70 / 30 or more, even more preferably 75 / 25 or more, and more preferably 90 / 10 or less, even more preferably 85 / 15 or less.

[0017] Examples of additives to paper substrates include pH adjusters (sodium bicarbonate, sodium hydroxide, etc.), dry strength agents, wet strength agents, internal sizing agents, drainage retention aids, antifoaming agents, fillers (calcium carbonate, talc, etc.), dyes, and fixing agents (aluminum sulfate). These additives may be used alone or in combination of two or more. The content of the additives is not particularly limited and may be within the range commonly used.

[0018] Examples of dry strength agents generally include polyacrylamide (PAM)-based dry strength agents, starch-based dry strength agents, CMC (carboxymethylcellulose) or its salts such as sodium carboxymethylcellulose, calcium carboxymethylcellulose, and zinc carboxymethylcellulose. From the viewpoint of achieving the desired ranges of tensile modulus and short span compressive strength, it is preferable that the dry strength agent contains a starch-based dry strength agent. When the paper base material has multiple paper layers, some of the layers may contain the dry strength agent, but it is preferable that each layer contains it, and it is more preferable that the content of each layer be within the preferred content range described below. The content of the starch-based dry strength agent in the dry strength agent is preferably 50% by mass or more, more preferably 75% by mass or more, even more preferably 90% by mass or more, and 100% by mass or less. Note that, since the use of a polyacrylamide-based dry strength agent as the dry strength agent tends to increase the short span compressive strength, the content of the polyacrylamide-based dry strength agent in the dry strength agent is preferably 50% by mass or less, more preferably 20% by mass or less, even more preferably 5% by mass or less, and it is particularly preferred that no polyacrylamide-based dry strength agent is contained. An example of a starch-based dry strength agent is cationic starch. When a starch-based dry strength agent is used as the dry strength agent, the amount of the cationic starch to be blended is preferably 0.05 parts by mass or more, more preferably 0.2 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of raw pulp (solid content equivalent), from the viewpoint of top curl processability, and is preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, and even more preferably 1.0 part by mass or less.

[0019] Examples of wet strength agents include polyamidepolyamine epichlorohydrin resin (PAE), melamine-formaldehyde resin, and urea-formaldehyde resin, and among these, polyamidepolyamine epichlorohydrin resin is preferred. When the paper base material has multiple paper layers, the wet strength agent may be contained in some of the layers, but it is preferable that each layer contains the agent, and it is more preferable that the content of each layer is within the preferred content range described below. The content of the wet strength agent per 100 parts by mass of raw pulp is preferably 0.01 part by mass or more, more preferably 0.03 part by mass or more, even more preferably 0.05 part by mass or more, particularly preferably 0.1 part by mass or more, and is preferably 1 part by mass or less, more preferably 0.5 part by mass or less, even more preferably 0.3 part by mass or less. Examples of internal sizing agents include rosin-based sizing agents and alkyl ketene dimers, and among these, rosin-based sizing agents are preferred. Examples of rosin-based sizing agents that can be used include acidic rosin-based sizing agents, weakly acidic rosin-based sizing agents, and neutral rosin-based sizing agents. When the paper base material has multiple paper layers, some of the layers may contain the internal sizing agent, but it is preferable that each layer contains it, and it is more preferable that the content of each layer be within the preferred content range described below. The content of the internal sizing agent per 100 parts by mass of raw material pulp is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, and is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, even more preferably 1 part by mass or less.

[0020] The basis weight of the paper substrate is not particularly limited, but for example, in the case of a packaging container, preferably a food container, more preferably a paper cup, it is preferably 180 g / m from the viewpoint of obtaining the paper strength required for the packaging container. 2 More preferably, 200 g / m 2 More preferably, 220 g / m 2 From the viewpoint of top curl processability, it is preferably 430 g / m 2 or less, more preferably 380 g / m2 or less, more preferably 330 g / m 2 Below 280 g / m, particularly preferably 2 The basis weight of the paper substrate is measured in accordance with JIS P 8124:2011. The thickness of the paper substrate is not particularly limited, but for example, in the case of packaging containers, preferably food containers, more preferably paper cups, from the viewpoint of obtaining sufficient paper strength as a packaging container, it is preferably 210 μm or more, more preferably 230 μm or more, even more preferably 240 μm or more, and from the viewpoint of top curl processability, it is preferably 480 μm or less, more preferably 410 μm or less, even more preferably 380 μm or less, particularly preferably 330 μm or less. The thickness of the paper substrate is measured in accordance with JIS P 8118:2014.

[0021] [Method for manufacturing paper substrate] An example of a method for producing a paper base material is a method of making a stock containing pulp. The stock may further contain additives. Examples of additives include those listed above. The stock can be prepared by adding the additives to a pulp slurry. The pulp slurry is obtained by beating pulp in the presence of water. The pulp beating method and beating device are not particularly limited, and may be the same as known beating methods and beating devices. The pulp content in the stock is not particularly limited, and may be within a commonly used range. For example, it is 60% by mass or more and less than 100% by mass relative to the total mass of the stock (solid content).

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

[0023] <Water resistant layer> The waterproof paper of this embodiment has a waterproof layer at least on the liquid-contacting surface. The liquid-contacting surface is the surface that comes into contact with the liquid, and when the waterproof paper is used for a packaging container, for example, it means the surface that comes into contact with the contents. In the waterproof paper of this embodiment, the waterproof layer may be formed directly on the paper substrate or may be formed via an undercoat layer (described later) and is not particularly limited, but from the viewpoint of water resistance and oil resistance, it is preferable to form the waterproof layer via an undercoat layer on the paper substrate. Furthermore, from the viewpoint of heat sealability, the waterproof layer is preferably formed as the uppermost layer on at least one side of the paper substrate, and more preferably as the uppermost layer on at least the liquid-contacting surface.

[0024] The waterproof paper of this embodiment has one or more waterproof layers on at least one side of the paper base material, and may have two or more waterproof layers on at least one side. From the viewpoint of productivity, one waterproof layer is preferred, and from the viewpoint of improving water resistance, two or more waterproof layers are preferred. The water-resistant layer is sufficient as long as it is provided on at least the liquid-contacting surface (hereinafter, the liquid-contacting surface may also be referred to as the front surface), and may also be provided on the back surface, which is the opposite surface via the paper substrate. Furthermore, when used in applications where condensation occurs, such as paper cups for cold water, it is preferable that the outer surface (the surface opposite to the liquid-contacting surface, also referred to as the back surface or printed surface) have one or more water-resistant layers, and two or more layers may be provided. In other words, the waterproof paper of this embodiment preferably has water-resistant layers on both sides of the paper base material. When two or more water-resistant layers are present on one side of the paper substrate, the composition and coating amount of each water-resistant layer may be the same or different. When two or more water-resistant layers are present on one side and the other side of the paper substrate, the composition and coating amount of each water-resistant layer may be the same or different.

[0025] The water-resistant layer preferably contains a water-based resin, which means a resin that can be dispersed or suspended in water. Examples of aqueous resins include polyolefin resins and acrylic resins, such as ethylene-(meth)acrylic acid copolymers, styrene-acrylic copolymers, and ethylene-α-olefin copolymers. The carbon number of the α-olefin is preferably 4 to 20, more preferably 6 to 16, and even more preferably 6 to 12. The aqueous resins may be used alone or in combination of two or more.

[0026] From the viewpoint of obtaining a desired heat seal peel strength, when the water-resistant layer is provided on both the front surface (liquid-contacting surface) and the back surface (printing surface), it is preferable that the water-resistant layers on both surfaces contain the same type of aqueous resin. When the water-based resins on the front surface and the back surface are the same type, the heat seal peel strength tends to be improved. Therefore, when the water-resistant layer on the front surface contains an ethylene-(meth)acrylic acid copolymer as an aqueous resin, and when the back surface has a water-resistant layer, the water-resistant layer may contain an ethylene-(meth)acrylic acid copolymer as an aqueous resin. Although the water-resistant layers on both sides may contain different types of aqueous resins, it is preferable that the polarities of the resins are similar from the viewpoint of heat seal peel strength. Therefore, when the water-resistant layer on the front side contains a polyolefin-based resin, it is preferable that the water-resistant layer on the back side also contains a polyolefin-based resin. Similarly, when the water-resistant layer on the front side contains an acrylic-based resin, it is preferable that the water-resistant layer on the back side also contains an acrylic-based resin.

[0027] The ethylene-(meth)acrylic acid copolymer may be an ethylene-acrylic acid copolymer or an ethylene-methacrylic acid copolymer, and the styrene-acrylic copolymer may be a styrene-(meth)acrylic acid alkyl ester copolymer. As the water-based resin, commercially available products may be used, for example, Aquence EPIX manufactured by Henkel Japan Co., Ltd. Examples include BC-212F, BC900F, BC905F, BC910F, MP498345N, MP4983R, MP4990R, 201103PX.S, and MFHS1279 manufactured by Michelman Japan LLC, ZAIKSEN (registered trademark) A and ZAIKSEN (registered trademark) AC manufactured by Sumitomo Seika Chemicals Co., Ltd., the Chemipearl series (S100, S300, and S500) manufactured by Mitsui Chemicals, Inc., MYE-30ER and MYE-30MAZ manufactured by Maruyoshi Chemical Co., Ltd., the Surlyn series manufactured by DuPont, the Himilan series manufactured by Dow Mitsui Polychemicals Co., Ltd., HYPOD2000, RHOBARR320, and RHOBARR325 manufactured by Dow Chemical Japan Ltd., Hi-Tec SC-100 manufactured by Toho Chemical Industry Co., Ltd., Aquatex AC-3100 manufactured by Chuo Rika Kogyo Co., Ltd., and Joncryl HPB-4110 manufactured by BASF.

[0028] From the viewpoint of water resistance, the content of the aqueous resin in the water-resistant layer is preferably 50% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more, but not more than 100% by mass, of the resin components of the water-resistant layer. 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.

[0029] The water-resistant layer may contain other components in addition to the above-mentioned aqueous resin. Examples of other components include viscosity modifiers; antifoaming agents; leveling agents such as surfactants and alcohols; colorants such as color pigments and color dyes; and antiblocking agents such as inorganic pigments and synthetic resins. From the viewpoint of ensuring water resistance and heat sealability, the total content of these components and other components is preferably 50% by mass or less, more preferably 30% by mass or less, and even more preferably 10% by mass or less, of the solid content of the water-resistant layer, with the lower limit being 0% by mass.

[0030] The water-resistant layer can be obtained by preparing a coating liquid for the water-resistant layer containing a water-based resin and coating the coating liquid. The coating liquid for the water-resistant layer is preferably an aqueous dispersion. Furthermore, the coating liquid for the water-resistant layer is more preferably a self-emulsifying and dispersing coating liquid that does not contain an emulsifier such as a surfactant or a dispersant. The absence of an emulsifier such as a surfactant or a dispersant is preferred because it provides better water resistance.

[0031] The aqueous resin blended in the coating solution for the water-resistant layer may be in the form of an ionomer. Here, the ionomer is a copolymer neutralized with a cation. Examples of the cation include metal ions such as sodium ions, potassium ions, calcium ions, and magnesium ions, and ammonium ions (NH4 + ) and organic ammonium ions are examples.

[0032] The method for applying the coating liquid for the water-resistant layer is not particularly limited, and any commonly used coating device may be appropriately selected and used, such as an air knife coater, blade coater, gravure coater, rod blade coater, roll coater, reverse roll coater, bar coater, curtain coater, die slot coater, champlex coater, metering blade type size press coater, short dwell coater, spray coater, gate roll coater, or lip coater. To improve the quality of the water-resistant layer, it is preferable to use an air knife coater to form at least the water-resistant layer on the front surface (liquid-contacting surface).For the same reason, it is preferable to use an air knife coater to form the water-resistant layer on the back surface, but a gravure coater may also be used.

[0033] The coating amount of the water-resistant layer is preferably 2 g / m per side from the viewpoint of heat sealing property and water resistance. 2 More preferably, 3 g / m 2 More preferably, 4 g / m 2The upper limit of the coating amount of the water-resistant layer per side is not particularly limited, but from the viewpoint of top curl processability and cost, it is set to, for example, 20 g / m 2 The following is the result. The total coating amount of the water-resistant layer, i.e., the total coating amount of the front and back surfaces, is preferably 7 g / m from the viewpoint of water resistance and heat sealability. 2 More preferably, 8g / m 2 More preferably, 9 g / m 2 and preferably 24 g / m 2 Less than 20 g / m, more preferably 2 or less, more preferably 16 g / m 2 The following is the result. Therefore, when the waterproof paper of this embodiment is used for a packaging container (preferably a food container, e.g., a paper cup) and has a water-resistant layer on only one side (the liquid-contacting side), the total coating weight of the waterproof layer on the liquid-contacting side is preferably within the above-mentioned range. Furthermore, when the waterproof paper of this embodiment is used for a packaging container (preferably a food container, e.g., a paper cup) and has a water-resistant layer on both sides (the liquid-contacting side and the printed side), the total coating weight of the waterproof layer on the liquid-contacting side and the total coating weight of the waterproof layer on the printed side are preferably within the above-mentioned ranges. Furthermore, the total coating weight of the waterproof layer on both sides is preferably within the above-mentioned range. In this case, the total coating weight (A) of the waterproof layer on the printed side (rear side) may be equal to or less than the total coating weight (B) of the waterproof layer on the liquid-contacting side (front side); specifically, A / B may be 1.0 or less, 0.8 or less, or 0.6 or less.

[0034] <Undercoat layer> The water-resistant paper of this embodiment preferably has a primer layer and a water-resistant layer, in this order, on at least one side of the paper substrate. Having a primer layer is preferable because it results in water-resistant paper with superior water resistance. Furthermore, providing a primer layer improves printability. The primer layer is provided between the paper substrate and the water-resistant layer. The water-resistant paper of this embodiment does not necessarily have a primer layer. When used as a paper cup, from the viewpoint of water resistance, it is preferable that at least the liquid-contacting surface has a primer layer and a water-resistant layer. Furthermore, when used as a paper cup for cold beverages, it is preferable that the printing surface also has a primer layer and a water-resistant layer from the viewpoint of condensation prevention and printability. Therefore, the water-resistant paper according to one embodiment of the present invention has a primer layer and a water-resistant layer, in this order, on both sides of the paper substrate. On the other hand, when used as a paper cup for hot beverages, the above performance is not required, so the printing surface does not necessarily have to have a primer layer and a water-resistant layer. Therefore, the waterproof paper according to one embodiment of the present invention has a primer layer and a waterproof layer, in that order, on one side (front side, liquid-contacting surface) of the paper substrate, and the other side (back side, printing surface) of the paper substrate does not have a primer layer or a waterproof layer. The number of undercoat layers per side may be one or two or more. When the waterproof paper has an undercoat layer, it is preferable that the number of undercoat layers is one from the viewpoint of productivity, but two or more from the viewpoint of improving water resistance. When there are two or more undercoat layers on one side of the paper substrate, the composition and coating amount of each undercoat layer may be the same or different. When there are undercoat layers on one side and the other side of the paper substrate, the composition and coating amount of each undercoat layer may be the same or different. The primer layer preferably contains a latex and a pigment.

[0035] 〔latex〕 In the present embodiment, latex refers to a polymer that can be stably dispersed in water. Latex is generally emulsified and dispersed with a surfactant or the like. Specific examples of latexes are not particularly limited as long as they achieve the effects of the present invention, but include conjugated diene polymers such as styrene-butadiene copolymers and acrylonitrile-butadiene copolymers; acrylic polymers such as homopolymers of (meth)acrylic acid esters and copolymers of monomers copolymerizable therewith (e.g., styrene-acrylic copolymers and methyl methacrylate-butadiene copolymers); vinyl polymers such as ethylene-vinyl acetate copolymers and vinyl chloride-vinyl acetate; polyurethane resins; and natural rubber. These may be used alone or in combination of two or more. Among these, from the viewpoint of further improving water resistance and / or oil resistance, at least one selected from the group consisting of styrene-butadiene copolymers and acrylic polymers is preferred, acrylic polymers are more preferred, and styrene-acrylic copolymers are even more preferred. The styrene-acrylic copolymer is preferably a copolymer of styrene and an alkyl (meth)acrylate ester. The latex may be either a commercially available product or a synthetic product, and examples of commercially available products include Acronal S728ap and Acronal S504ap manufactured by BASF Ltd., and Luckstar 3307BE manufactured by DIC Corporation.

[0036] The average particle size of the latex is not particularly limited, but from the viewpoint of the adhesive strength between the resin layer and the undercoat layer, it is preferably 0.01 μm or more, more preferably 0.05 μm or more, and preferably 1.0 μm or less, more preferably 0.5 μm or less. The average particle size of the latex can be determined using a laser diffraction particle size distribution analyzer based on the principle of laser diffraction, and the value measured from the measured particle size distribution is adopted.

[0037] The glass transition temperature of the latex is not particularly limited, but from the viewpoint of the adhesive strength between the resin layer and the undercoat layer, it is preferably −50° C. or higher, more preferably −20° C. or higher, even more preferably 0° C. or higher, and preferably 60° C. or lower, more preferably 40° C. or lower. The glass transition temperature of the latex is a value measured by differential scanning calorimetry (DSC).

[0038] In the undercoat layer, the weight ratio of latex to pigment (latex / pigment) is preferably 10 / 90 or more, more preferably 12 / 88 or more, and preferably 40 / 60 or less, more preferably 35 / 65 or less.

[0039] [Pigments] The pigment is not particularly limited, and examples thereof include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, calcined clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white; and organic pigments such as solid, hollow, and core-shell pigments. These pigments may be used alone or in combination of two or more. Among these, from the viewpoint of further improving water resistance and / or oil resistance, at least one pigment selected from the group consisting of kaolin and calcium carbonate is preferred, and it is more preferred to contain at least kaolin, and it is even more preferred to use a combination of kaolin and calcium carbonate. When calcium carbonate and kaolin are used in combination, the mass ratio of calcium carbonate to kaolin (calcium carbonate / kaolin) is not particularly limited, but is preferably 50 / 50 or more and 90 / 10 or less, more preferably 60 / 40 or more and 80 / 20 or less.

[0040] The average particle size of the pigment is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.5 μm or more, and preferably 20 μm or less, more preferably 10 μm or less. The average particle size of the pigment can be determined using a laser diffraction particle size distribution analyzer based on the principles of laser diffraction, and the value measured from the measured particle size distribution is used.

[0041] It is preferable to use a pigment having an aspect ratio of 5 or more (pigment 1) in combination with a pigment having an aspect ratio of less than 5 (pigment 2) as pigments, from the viewpoint of improving the water resistance of the undercoat layer, adjusting the viscosity of the coating liquid for the undercoat layer, and reducing costs. The aspect ratio of pigment 1 is 5 or more, preferably 50 or more, and preferably 500 or less, more preferably 300 or less. An example of a pigment having the above aspect ratio is kaolin. The aspect ratio of pigment 2 is less than 5, preferably 4 or less, more preferably 3.5 or less, and is at least 1. An example of a pigment having the above aspect ratio is calcium carbonate. The aspect ratio of a pigment is a shape factor obtained by dividing the average particle diameter by the average thickness. The average thickness is measured by dropping several drops of pigment diluted with a solvent onto a glass substrate, allowing it to dry naturally, and then measuring the thickness of 20 samples of the pigment oriented on the glass substrate using a transmission electron microscope. Of the 20 thickness measurements, the top three and bottom three are excluded, and the remaining 14 thicknesses are averaged to determine the average thickness.

[0042] In the undercoat layer, the total content of the pigment and latex is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and may be 100% by mass, from the viewpoint of water resistance and heat sealability.

[0043] The undercoat layer may further contain components other than the latex and pigment. Examples of such other components include adhesives, dispersants, thickeners, water retention agents, antifoaming agents, waterproofing agents, colorants, surfactants, etc. Examples of adhesives include proteins such as casein, soy protein, and synthetic protein; starches such as oxidized starch, cationic starch, urea phosphate esterified starch, and etherified starch such as hydroxyethyl etherified starch, and dextrin; and cellulose derivatives such as carboxymethyl cellulose, hydroxyethyl cellulose, and hydroxymethyl cellulose.

[0044] The coating amount of the undercoat layer is preferably 1 g / m per side from the viewpoint of water resistance. 2 More preferably, 3 g / m 2 More preferably, 5 g / m 2 From the viewpoint of heat sealing property and cost, it is preferably 30 g / m 2 Less than 20 g / m, more preferably 2 or less, more preferably 12 g / m 2 The following is the result.

[0045] The method for forming the undercoat layer is not particularly limited, but for example, the undercoat layer can be obtained by preparing a coating liquid for the undercoat layer containing latex, pigment, and, if necessary, other components, applying the coating liquid onto a paper substrate, and drying the coating liquid.

[0046] When the waterproof paper of this embodiment has an undercoat layer, the basis weight of the laminate of the paper base material and the undercoat layer (hereinafter also referred to as "undercoat paper") is not particularly limited. For example, in the case of packaging containers, preferably paper cups, the basis weight is preferably 200 g / m from the viewpoint of obtaining sufficient paper strength as a packaging container. 2 More preferably, 220 g / m 2 More preferably, 240 g / m 2 From the viewpoint of top curl processability, it is preferably 450 g / m 2 Less than 400 g / m 2 or less, more preferably 350 g / m 2 Below 300 g / m, particularly preferably 2The basis weight of the primer paper is measured in accordance with JIS P 8124:2011. The thickness of the primer paper (paper thickness) is not particularly limited, but for example, in the case of packaging containers, preferably paper cups, from the viewpoint of obtaining sufficient paper strength as a packaging container, it is preferably 230 μm or more, more preferably 250 μm or more, even more preferably 260 μm or more, and from the viewpoint of top curl processability, it is preferably 500 μm or less, more preferably 430 μm or less, even more preferably 400 μm or less, particularly preferably 350 μm or less. The thickness of the primer paper is measured in accordance with JIS P 8118:2014.

[0047] The waterproof paper of this embodiment may have other layers in addition to the undercoat layer and waterproof layer. Examples of other layers include a printed layer, a water vapor barrier layer, an oxygen barrier layer, and an oxygen absorbing layer. The printed layer may be formed using a known ink such as an oil-based ink, a water-based ink, or a biomass ink. The printed layer may be formed on one surface of the waterproof paper, or on a portion of the surface. That is, the waterproof paper of this embodiment may be printed on all or part of at least one surface (e.g., the printing surface). The printed content may be a pattern, a design, or information (such as ingredients, expiration date, or QR code (registered trademark)). The waterproof paper of this embodiment preferably has, on at least one side of the paper substrate, one or more (preferably only one) primer layers provided in direct contact with the paper substrate, and one or more (preferably only one) water-resistant layers provided in direct contact with the primer layers, in this order; more preferably, it is composed of only the paper substrate, primer layer, and water-resistant layer. The other side is not particularly limited, but preferably has one or more (preferably only one) primer layers provided in direct contact with the paper substrate, and one or more (preferably only one) water-resistant layers provided in direct contact with the primer layers, in this order.

[0048] <Water-resistant paper properties> [Basic weight] The basis weight of the waterproof paper is not particularly limited, but for example, in the case of a packaging container, preferably a food container, more preferably a paper cup, it is preferably 220 g / m from the viewpoint of obtaining the strength required for the packaging container. 2 More preferably, 240 g / m 2 More preferably, 250 g / m 2 From the viewpoint of top curl processability, it is preferably 500 g / m 2 or less, more preferably 450 g / m 2 More preferably, 400 g / m or less 2 or less, even more preferably 350 g / m 2 Below 300 g / m, particularly preferably 2 The following is the result. The basis weight of waterproof paper is measured in accordance with JIS P 8124:2011.

[0049] [Paper thickness] The thickness of the waterproof paper is not particularly limited, but for example, in the case of packaging containers, preferably food containers, and more preferably paper cups, from the viewpoint of obtaining the strength required for the packaging container, it is preferably 230 μm or more, more preferably 250 μm or more, and even more preferably 270 μm or more, and from the viewpoint of top curl processability, it is preferably 500 μm or less, more preferably 430 μm or less, even more preferably 400 μm or less, and particularly preferably 350 μm or less. The thickness of waterproof paper is measured in accordance with JIS P 8118:2014.

[0050] [Vertical tensile modulus] From the viewpoint of top curl processability, the waterproof paper of this embodiment has a longitudinal tensile modulus of 7.5 GPa or less, preferably 7.2 GPa or less, more preferably 7.0 GPa or less, even more preferably 6.9 GPa or less, and even more preferably 6.8 GPa or less. There is no particular lower limit, but from the viewpoint of obtaining paper strength suitable for, for example, packaging containers, preferably food containers, it is preferably 4.0 GPa or more, more preferably 5.0 GPa or more, and even more preferably 5.5 GPa or more. The longitudinal tensile modulus of the waterproof paper can be adjusted within the desired range by the type, beating degree, and blending ratio of the pulp constituting the paper base, the type and amount of internal chemicals added to the paper base, etc. The tensile modulus of elasticity in the machine direction of the waterproof paper is measured in accordance with JIS P 8113:2006.

[0051] [Vertical short-span compressive strength] From the viewpoint of top curl processability, the waterproof paper of this embodiment has a longitudinal short span compressive strength of 7.5 kN / m or less, preferably 7.2 kN / m or less, more preferably 7.0 kN / m or less. There is no particular lower limit, but from the viewpoint of obtaining paper strength suitable for, for example, packaging containers, preferably food containers, it is preferably 5.0 kN / m or more, more preferably 5.5 kN / m or more, even more preferably 6.0 kN / m or more, and particularly preferably 6.5 kN / m or more. The longitudinal short span compressive strength of the waterproof paper can be adjusted within the desired range by the type, beating degree, and blending ratio of the pulp constituting the paper base, the type and amount of internal chemicals added to the paper base, etc. The short span compressive strength in the machine direction of waterproof paper is measured in accordance with JIS P 8156:2012.

[0052] [Heat seal peel strength] From the viewpoint of top curl processability, the waterproof paper of this embodiment is heated on one side and the other side at 130°C under a pressure of 2 kgf / cm. 2The heat seal peel strength when heat sealed for 2 seconds is 7.0 kN / m or more, preferably 7.5 kN / m or more, more preferably 8.0 kN / m or more, even more preferably 9.0 kN / m or more, and even more preferably 10 kN / m or more, and although there is no particular upper limit, from the viewpoint of ease of production, it is preferably 20 kN / m or less, more preferably 17 kN / m or less, and even more preferably 14 kN / m or less. The heat seal peel strength of the waterproof paper can be adjusted within the desired range by the type of resin used in the water-resistant layer, the coating amount, etc. The heat seal peel strength of the waterproof paper is measured by the method described in the examples.

[0053] [Cobb water absorption] From the viewpoint of cold water resistance, the water-resistant paper of this embodiment has a Cobb water absorbency of 15 g / m2 at the liquid-contact surface in water at 20°C after a contact time of 30 minutes. 2 Less than 10 g / m, more preferably 2 Less than 8g / m, more preferably 2 Less than 6 g / m, more preferably 2 or less, even more preferably 4 g / m 2 or less (the lower limit is 0 g / m 2 The Cobb water absorbency at 20°C can be adjusted within the desired range by adjusting the type and coating amount of the resin used in the water-resistant layer, the type and amount of latex of the pigment used in the undercoat layer, and the coating amount of the undercoat layer. The Cobb water absorbency is measured in accordance with JIS P 8140:1998.

[0054] Furthermore, from the viewpoint of hot water resistance, the water-resistant paper of this embodiment has a Cobb water absorbency of 20 g / m2 or less in water at 90°C for a contact time of 30 minutes on the liquid-contact surface. 2 Less than 15 g / m, more preferably 2 or less, more preferably 12 g / m 2 or less, even more preferably 10 g / m 2 Below 8 g / m, particularly preferably 2 or less (the lower limit is 0 g / m 2The Cobb water absorbency at 90°C can be adjusted within the desired range by adjusting the type and coating amount of the resin used in the water-resistant layer, the type and amount of latex of the pigment used in the undercoat layer, and the coating amount of the undercoat layer. The Cobb water absorbency is measured in accordance with JIS P 8140:1998.

[0055] [Oil resistance] The waterproof paper of this embodiment has a Kit value of preferably 3 or more, more preferably 5 or more, and even more preferably 8 or more, at the liquid-contact surface, as measured in accordance with JAPAN TAPPI No. 41 (Kit method). A larger Kit value indicates better oil resistance. If the Kit value is within the above range, the paper can be suitably used for food packaging applications.

[0056] <Uses of water-resistant paper> The waterproof paper of this embodiment has excellent heat-sealing properties and water resistance, and therefore can be suitably used for packaging containers such as cups, plates, trays, lids, pouches, and tube-shaped containers; cutlery such as spoons, forks, knives, and chopsticks; straws; and flexible packaging materials such as wrapping paper, packaging bags, lids, and labels. Packaging containers can be formed, for example, by printing on the surface of the waterproof paper as needed, punching it into a shape corresponding to the shape of the packaging container to be manufactured, folding it, and heat-sealing the overlapping portions. Therefore, the present invention also provides packaging containers (particularly paper cups) made using the waterproof paper. Furthermore, the waterproof paper of this embodiment has excellent oil resistance, and therefore can be suitably used for food packaging applications. The waterproof paper of this embodiment has excellent top curl resistance and is therefore suitable for packaging containers that require top curl, such as paper cups, paper plates, and paper trays. The contents of the packaging container may be either food or non-food. The contents of the packaging container may also be liquid, solid, or gel. The contents of the packaging container are not particularly limited, and examples thereof include beverages such as coffee, tea, black tea, juice, and carbonated drinks; alcoholic beverages such as sake, shochu, and wine; dairy beverages such as milk; foods such as ready-to-eat foods (instant ramen, etc.), microwaveable foods, beverages (yogurt, ice cream, jelly, pudding, etc.), and prepared dishes; pharmaceuticals; and chemical products such as car wax, shampoo, conditioner, detergent, bath additives, hair dye, and toothpaste. Packaging containers made from the waterproof paper of this embodiment use less plastic than packaging containers made from conventional laminated paper. Furthermore, while packaging containers made from conventional laminated paper must be disintegrated using a pulper with high disintegration performance when recycled into waste paper, packaging containers made from the waterproof paper of this embodiment can be disintegrated using a pulper with normal disintegration performance, making them highly recyclable. Packaging containers made from the waterproof paper of this embodiment can be washed, cut, disintegrated, etc. to prepare pulp slurry, and paper can be manufactured using the obtained pulp slurry. The type of paper to be made is not particularly limited, and examples include printing paper, packaging paper, sanitary paper, and cardboard. Furthermore, the paper made can be processed to manufacture packaging containers (e.g., tissue boxes, paper cup sleeves, etc.). [Example]

[0057] The features of the present invention will be explained in more detail below with reference to examples and comparative examples. The materials, amounts used, ratios, treatment details, treatment procedures, etc. shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below. Furthermore, the operations in the examples and comparative examples were carried out at room temperature (20-25°C) and normal humidity (40-50% RH) unless otherwise specified.

[0058] The raw materials used in the examples and comparative examples are as follows. <Pigments> Heavy calcium carbonate (product name "FMT-90", Fimatec Co., Ltd., average particle size 1.1 μm, aspect ratio 1.0 to 3.0) Kaolin (product name "Balisurf HX", manufactured by Imerys Co., Ltd., average particle size 9.0 μm, aspect ratio 80-100) <Latex> Latex: Styrene-acrylic copolymer latex (product name "Acronal S728ap", manufactured by BASF Ltd., average particle size 0.16 μm, glass transition temperature 23°C), used in coating solutions A and B <Aqueous resin dispersion> Product name: AQUENCE EPIX BC-212F, manufactured by Henkel Japan Co., Ltd., solids concentration 25% by mass, polyolefin resin dispersion Product name: AQUENCE EPIX BC900F, manufactured by Henkel Japan Co., Ltd., solids concentration 45% by mass, acrylic resin dispersion <Other> Antifoaming agent: Product name "Bismar KS-38E", manufactured by Nissin Chemical Laboratory Co., Ltd.

[0059] <Preparation of coating liquid for undercoat layer> (a) Preparation of coating solution A A pigment dispersion was prepared by adjusting the pigment blending to a calcium carbonate content of 70.0% by mass and a kaolin content of 30.0% by mass based on the solid content. A styrene-acrylic copolymer latex was blended with this pigment dispersion to prepare a pigment / styrene-acrylic copolymer latex mixture with a pigment content of 85.0% by mass and a styrene-acrylic copolymer latex content of 15.0% by mass based on the solid content. A defoamer was blended with the pigment / styrene-acrylic copolymer latex mixture to prepare Coating Solution A with a solid content of 60% by mass and a pigment / styrene-acrylic copolymer latex content of 99.0% by mass and a defoamer content of 1.0% by mass based on the solid content.

[0060] (b) Preparation of coating solution B A pigment dispersion was prepared by adjusting the pigment formulation to a calcium carbonate content of 70.0% by mass and a kaolin content of 30.0% by mass based on the solid content. A styrene-acrylic copolymer latex was blended with this pigment dispersion to prepare a pigment / styrene-acrylic copolymer latex mixture with a pigment content of 70.0% by mass and a styrene-acrylic copolymer latex content of 30.0% by mass based on the solid content. A defoamer was blended with the pigment / styrene-acrylic copolymer latex mixture to prepare Coating Solution B with a solid content of 60% by mass and a pigment / styrene-acrylic copolymer latex content of 99.0% by mass and a defoamer content of 1.0% by mass based on the solid content.

[0061] <Preparation of coating liquid for water-resistant layer> (a) Preparation of coating solution C (coating solution for gravure coater) An antifoaming agent was added to an aqueous resin dispersion (AQUENCE EPIX BC-212F), and water was added to adjust the solid content, thereby preparing Coating Solution C, which had a solid content of 21 mass% and contained 99.0 mass% of aqueous resin and 1.0 mass% of antifoaming agent in the solid content.

[0062] (b) Preparation of coating solution D (air knife coater coating solution) An antifoaming agent was added to an aqueous resin dispersion (AQUENCE EPIX BC-212F), and water was added to adjust the solid content, thereby preparing Coating Solution D, which had a solid content of 20 mass% and contained 99.0 mass% of aqueous resin and 1.0 mass% of antifoaming agent in the solid content.

[0063] (c) Preparation of coating solution E (coating solution for gravure coater) An antifoaming agent was added to an aqueous resin dispersion (AQUENCE EPIX BC900F), and water was added to adjust the solid content, thereby preparing Coating Solution E, which had a solid content of 35 mass% and contained 99.0 mass% of aqueous resin and 1.0 mass% of antifoaming agent in the solid content.

[0064] (d) Preparation of coating solution F (air knife coater coating solution) An antifoaming agent was added to an aqueous resin dispersion (AQUENCE EPIX BC900F), and water was added to adjust the solid content, thereby preparing Coating Solution F, which had a solid content of 30 mass% and contained 99.0 mass% of aqueous resin and 1.0 mass% of antifoaming agent in the solid content.

[0065] Example 1 A pulp slurry (100 parts by weight (solids content)) was prepared by mixing 80% and 20% beaten LBKP (CSF 400 mL) and 500 mL beaten NBKP (CSF 500 mL), respectively. To this slurry, 0.85 parts by weight of an acidic rosin sizing agent (Sizepine N-811, manufactured by Arakawa Chemical Industries, Ltd.), 0.15 parts by weight of a wet strength agent (polyamide polyamine epichlorohydrin resin (PAE), manufactured by Seiko PMC Corporation, WS4020), 0.7 parts by weight of a dry strength agent (cationized starch, manufactured by Oji Cornstarch Co., Ltd., Ace K), and 1.5 parts by weight of aluminum sulfate were added to prepare a paper stock. This paper stock was used for papermaking on a five-layer Fourdrinier paper machine to obtain a paper base. The coating solution A was applied to both sides of the paper substrate in an amount (solid content) of 10.0 g / m per side. 2 The coating was carried out using a rod coater so that the coating weight was 250 g / m. The coating was then dried to form a primer layer. 2 Thus, a primer paper with a thickness of 290 μm was obtained. The coating solution D was applied to the highly smooth surface (surface, liquid-contacting surface) of the primer paper in an amount (solid content) of 8.0 g / m 2 The coating was then applied using an air knife coater so that the thickness of the coating liquid was 4.0 g / m2, and the coating liquid was dried to form a water-resistant layer 1. Then, the coating liquid C was applied to the other surface of the substrate in an amount (solid content) of 4.0 g / m2. 2 The resulting mixture was coated using a gravure coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer 2, thereby producing water-resistant paper.

[0066] <Example 2> The coating amount (solid content) of the water-resistant layer 2 on the opposite side is 2.0 g / m 2 Waterproof paper was prepared in the same manner as in Example 1, except that the above was changed.

[0067] Example 3 Using the paper stock prepared in the same manner as in Example 1, paper was made using a five-layer Fourdrinier paper machine, and the basis weight was 250 g / m 2 A paper substrate with a thickness of 290 μm was obtained. The coating solution D was applied to the highly smooth surface (surface, liquid-contacting surface) of the paper substrate in a coating amount (solid content) of 8.0 g / m 2 The coating was then applied using an air knife coater so that the thickness of the coating liquid was 7.0 g / m2, and the coating liquid was then dried to form a water-resistant layer 1. 2 The resulting mixture was coated using a gravure coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer 2, thereby producing water-resistant paper.

[0068] Example 4 Using the paper stock prepared in the same manner as in Example 1, paper was made using a five-layer Fourdrinier paper machine to obtain a paper base material. The coating solution A was applied to the highly smooth surface (surface, liquid-contacting surface) of the paper substrate in a coating amount (solid content) of 10.0 g / m 2 The coating was carried out using a rod coater so that the coating weight was 250 g / m. The coating was then dried to form a primer layer. 2 Thus, a primer paper with a thickness of 290 μm was obtained. The coating solution D was applied to the undercoated surface of the undercoated paper in a coating amount (solid content) of 10.0 g / m 2 The mixture was coated using an air knife coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer 1, thereby producing water-resistant paper.

[0069] <Example 5> Waterproof paper was prepared in the same manner as in Example 1, except that coating liquid F was used instead of coating liquid D and coating liquid E was used instead of coating liquid C for the water-resistant layer.

[0070] Example 6 Using the paper stock prepared in the same manner as in Example 1, paper was made using a five-layer Fourdrinier paper machine to obtain a paper base material. The coating solution B was applied to the highly smooth surface (surface, liquid-contacting surface) of the paper substrate A in a coating amount (solid content) of 10.0 g / m 2 The coating was carried out using a rod coater so that the coating weight was 250 g / m. The coating was then dried to form a primer layer. 2Thus, a primer paper with a thickness of 290 μm was obtained. The coating solution D was applied to the undercoated surface of the undercoated paper in a coating amount (solid content) of 10.0 g / m 2 The mixture was coated using an air knife coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer 1, thereby producing water-resistant paper.

[0071] <Comparative Example 1> A pulp slurry (100 parts by weight (solids content)) was prepared by mixing 80% and 20% beaten LBKP (CSF 300 mL) and 400 mL beaten NBKP (CSF 400 mL), respectively. To this slurry, 0.85 parts by weight of an acidic rosin sizing agent (Sizepine N-811, manufactured by Arakawa Chemical Industries, Ltd.), 0.15 parts by weight of a wet strength agent (polyamide polyamine epichlorohydrin resin (PAE), manufactured by Seiko PMC Corporation, WS4020), 0.7 parts by weight of a dry strength agent (cationized starch, manufactured by Oji Cornstarch Co., Ltd., Ace K), and 1.5 parts by weight of aluminum sulfate were added to prepare a paper stock. This paper stock was used for papermaking on a five-layer Fourdrinier paper machine to obtain a paper base. The coating solution A was applied to both sides of the paper substrate in a coating amount (solid content) of 10.0 g / m 2 The coating was carried out using a rod coater so that the coating weight was 250 g / m. The coating was then dried to form a primer layer. 2 Thus, a primer paper with a thickness of 290 μm was obtained. The coating solution D was applied to the highly smooth surface (surface, liquid-contacting surface) of the primer paper in an amount (solid content) of 8.0 g / m 2 The coating was then applied using an air knife coater so that the thickness of the coating liquid was 2.0 g / m2, and the coating liquid was then dried to form a water-resistant layer 1. Then, the coating liquid C was applied to the other surface of the substrate in an amount (solid content) of 2.0 g / m2. 2 The resulting mixture was coated using a gravure coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer 2, thereby producing water-resistant paper.

[0072] <Comparative Example 2> A pulp slurry (100 parts by weight (solids content)) was prepared by mixing 80% and 20% beaten LBKP (CSF 400 mL) and 500 mL beaten NBKP (CSF 500 mL), respectively. To this slurry, 0.85 parts by weight of an acidic rosin sizing agent (Sizepine N-811, manufactured by Arakawa Chemical Industries, Ltd.), 0.15 parts by weight of a wet strength agent (polyamide polyamine epichlorohydrin resin (PAE), manufactured by Seiko PMC Corporation, WS4020), 0.7 parts by weight of a dry strength agent (amphoteric PAM, manufactured by Seiko PMC Corporation, DS4433), and 1.5 parts by weight of aluminum sulfate were added to prepare a paper stock. This paper stock was used for papermaking on a five-layer Fourdrinier paper machine to obtain a paper base. The coating solution A was applied to both sides of the paper substrate in a coating amount (solid content) of 10.0 g / m 2 The coating was carried out using a rod coater so that the coating weight was 250 g / m. The coating was then dried to form a primer layer. 2 Thus, a primer paper with a thickness of 290 μm was obtained. The coating solution D was applied to the highly smooth surface (surface, liquid-contacting surface) of the primer paper in an amount (solid content) of 8.0 g / m 2 The coating was then applied using an air knife coater so that the thickness of the coating liquid was 2.0 g / m2, and the coating liquid was then dried to form a water-resistant layer 1. Then, the coating liquid C was applied to the other surface of the substrate in an amount (solid content) of 2.0 g / m2. 2 The resulting mixture was coated using a gravure coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer 2, thereby producing water-resistant paper.

[0073] <Comparative Example 3> Using the paper stock prepared in the same manner as in Example 1, paper was made using a five-layer Fourdrinier paper machine to obtain a paper base material. The coating solution A was applied to the highly smooth surface (surface, liquid-contacting surface) of the paper substrate in a coating amount (solid content) of 10.0 g / m 2 The coating was carried out using a rod coater so that the coating weight was 250 g / m. The coating was then dried to form a primer layer. 2 Thus, a primer paper with a thickness of 290 μm was obtained. The coating solution D was applied to the undercoated surface of the undercoated paper in a coating amount (solid content) of 8.0 g / m 2 The coating was then applied using an air knife coater so that the thickness of the coating liquid was 4.0 g / m2, and the coating liquid was dried to form a water-resistant layer 1. Then, the coating liquid E was applied to the other surface of the substrate in an amount (solid content) of 4.0 g / m2.2 The resulting mixture was coated using a gravure coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer 2, thereby producing water-resistant paper.

[0074] <Comparative Example 4> Using the paper stock prepared in the same manner as in Example 1, paper was made using a five-layer Fourdrinier paper machine to obtain a paper base material. The coating solution A was applied to the highly smooth surface (surface, liquid-contacting surface) of the paper substrate A in a coating amount (solid content) of 10.0 g / m 2 The coating was carried out using a rod coater so that the coating weight was 250 g / m. The coating was then dried to form a primer layer. 2 Thus, a primer paper with a thickness of 290 μm was obtained. The coating solution D was applied to the undercoated surface of the undercoated paper in a coating amount (solid content) of 6.0 g / m 2 The resulting mixture was coated using an air knife coater so that the thickness of the coating was as follows: and then dried to form a water-resistant layer 1, thereby preparing a water-resistant layer.

[0075] [Evaluation of primed and waterproof papers] The primer paper and waterproof paper obtained in the examples and comparative examples were evaluated. <Basis weight and thickness of primer paper and waterproof paper> The basis weights of the primer paper (paper substrate for Example 3) and the waterproof paper were measured in accordance with JIS P 8124:2011. The thicknesses of the primer paper (paper substrate for Example 3) and the waterproof paper were measured in accordance with JIS P 8118:2014.

[0076] <CSF of pulp raw materials that make up paper base material> The CSF of the raw pulp for the paper base material was measured according to JIS P 8121-2:2012 "Pulp - Freeness test method - Part 2: Canadian standard freeness method."

[0077] <Water resistance (Cobb water absorption)> The obtained waterproof paper was cut into 10 cm squares, and the surface (liquid-contacting surface) of the waterproof paper was brought into contact with ion-exchanged water at 20°C or 90°C for 30 minutes in accordance with JIS P 8140: 1998, and the Cobb water absorbency was measured from the difference in mass before and after contact in accordance with JIS P 8140: 1998. The Cobb water absorbency of the waterproof paper surface was measured, and a lower value indicates higher water resistance.

[0078] <Measurement of tensile modulus> The tensile modulus of the waterproof paper was measured in accordance with JIS P 8113: 2006. The tensile modulus was measured at 23°C.

[0079] <Short span compressive strength> The short span compressive strength of the waterproof paper was measured in accordance with JIS P 8156: 2012. The tensile modulus was measured at 23°C.

[0080] <Kit Value> The oil resistance of the surface (wetted surface) was evaluated in accordance with JAPAN TAPPI No. 41 (kit method). The higher the value (kit value), the higher the oil repellency.

[0081] <Heat seal peel strength> Two pieces of waterproof paper measuring 150 mm lengthwise and 105 mm widthwise were cut out and stacked so that the front side of the first piece faced the back side of the second piece. Next, using a heat seal tester (Tester Sangyo Co., Ltd., TP-701-B, seal width 10 mm), a heat seal tester was applied at 130°C and a pressure of 2 kgf / cm across the center of the lengthwise direction (75 ± 5 mm from the end in the lengthwise direction). 2The heat-sealed sheets were heat-sealed for 2 seconds. Next, the two sheets of water-resistant paper were cut horizontally into 15-mm increments, excluding regions within 7.5 mm of each end, to prepare six test samples (i.e., two-ply strips measuring 150 mm x 15 mm, with a 10-mm heat seal 75 ± 5 mm from the end). The six test samples were then chucked at the top end of only the first sheet and the bottom end of only the second sheet using a vertical tensile tester (A&D Co., Ltd., Tensilon Universal Testing Machine RTG-1310) with a chuck distance of 100 mm (i.e., the part of each end fixed to the tester was positioned 25 mm from the end). The test samples were then pulled at a speed of 300 mm / min. The recorded maximum loads were averaged to determine the heat-seal peel strength.

[0082] <Processing suitability (top curl processing suitability)> The obtained waterproof paper was molded into a cup shape with the front surface facing inward (liquid-contacting surface) and the back surface facing outward (printed surface), and with the CD direction of the constituent paper base material aligned horizontally with the cup. The formability of the top curled portion of the cup after top curling was evaluated based on the following criteria. The top curling was performed as follows: The opening was widened by placing a mold around the periphery of the opening at the top of the cup, and then a mold with a curl diameter of approximately 3 mm was placed on top to curl the material toward the outside of the cup. The cup was then pressed downward, and the substrate was curled inward along the curved surface of the mold with a curl shape set below. Processability was evaluated based on the following criteria. Using the above method, 10,000 paper cups were molded and inspected for defects in the top curl area (cracks, paper layer peeling, insufficient curl, wrinkles). The defect rate for the top curl area was calculated using the formula: defect rate (%) = (number of defective cups / number of paper cups molded) x 100.

[0083] [Evaluation criteria] A: The defect rate in the top curl area is less than 1% (no practical problems) B: The defect rate of the top curl portion is more than 1% and less than 2% (no practical problems) C: The defect rate of the top curl portion is more than 2% and less than 3% (no practical problem) D: The defect rate of the top curl portion is more than 3% and less than 10% (somewhat problematic in practical use). E: The defect rate of the top curl part exceeds 10% (problems in practical use)

[0084] [Table 1]

[0085] As can be seen from the results in Table 1, the waterproof papers of Examples 1 to 6, which had a waterproof layer on at least one side of the paper substrate, a longitudinal tensile modulus of 7.5 GPa or less, a longitudinal short-span compressive strength of 7.5 kN / m or less, and a heat-seal peel strength of 7.0 kN / m or more, had excellent water resistance against cold water and hot water, oil resistance, and top curl processability. In particular, the waterproof papers of Examples 1, 2, and 4 to 6, which had a primer layer, had excellent oil resistance. On the other hand, the waterproof paper of Comparative Example 1, in which the beating degree of the pulp raw material was increased, had a longitudinal tensile modulus of elasticity exceeding 7.5 GPa and a longitudinal short span compressive strength exceeding 7.5 kN / m, and was therefore poor in top curl processability. Furthermore, the waterproof paper of Comparative Example 2, which used amphoteric PAM (amphoteric polyacrylamide-based dry strength agent) as the dry strength agent, had a longitudinal tensile modulus of elasticity exceeding 7.5 GPa and a longitudinal short-span compressive strength exceeding 7.5 kN / m, and was therefore poor in top curl processability. The waterproof paper of Comparative Example 3, in which the waterproof layer on the front surface (liquid contact surface) contained a polyolefin resin and the waterproof layer on the back surface contained an acrylic resin, had a heat seal peel strength of less than 7.0 kN / m and was poor in top curl processability. The waterproof paper of Comparative Example 4, which had a small total coating amount of the waterproof layer on the front surface (liquid-contacting surface) and back surface, had a heat seal peel strength of less than 7.0 kN / m, poor water resistance, and poor top curl processability.

Claims

1. A waterproof paper having a waterproof layer on at least the liquid-contacting surface of a paper substrate, The tensile modulus in the longitudinal direction is 7.5 GPa or less, The short span compressive strength in the longitudinal direction is 7.5 kN / m or less, and One side of the waterproof paper was pressed against the other side at 130°C and a pressure of 2 kgf / cm ２ The heat seal peel strength when heat sealed under the conditions of 1.5 seconds and 2 seconds is 7.0 kN / m or more. Water resistant paper.

2. The total coating amount of the water-resistant layer is 7 g / m ２ The waterproof paper according to claim 1, wherein the above-mentioned

3. The waterproof paper according to claim 1, which has a primer layer and the waterproof layer in this order on at least the liquid-contacting surface of the paper substrate.

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

5. 2. The waterproof paper according to claim 1, wherein the pulp raw materials constituting the paper base material contain bleached hardwood kraft pulp (LBKP) and bleached softwood kraft pulp (NBKP), and the Canadian standard freeness of the bleached hardwood kraft pulp is 310 mL or more and 550 mL or less, and the Canadian standard freeness of the bleached softwood kraft pulp is 420 mL or more and 550 mL or less.

6. 2. The waterproof paper according to claim 1, wherein the pulp raw material constituting the paper base material contains bleached hardwood kraft pulp (LBKP) and bleached softwood kraft pulp (NBKP), and the mass ratio (LBKP / NBKP) of the bleached hardwood kraft pulp (LBKP) to the bleached softwood kraft pulp (NBKP) in the pulp raw material is 60 / 40 or more and 100 / 0 or less.

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

8. The paper base has a basis weight of 200 g / m ２ The waterproof paper according to claim 1, wherein the above-mentioned

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

10. The waterproof paper according to claim 1 , wherein the waterproof layer is an uppermost layer on at least one surface of the paper substrate.

11. The waterproof paper according to claim 1 , wherein the waterproof layer is provided on both sides of the paper substrate.

12. The water-resistant paper has a Cobb water absorbency of 15 g / m2 at 20°C for a contact time of 30 minutes. ２ 2. The waterproof paper of claim 1, wherein:

13. The water-resistant paper has a Cobb water absorbency of 20 g / m2 at 90°C for a contact time of 30 minutes. ２ 2. The waterproof paper of claim 1, wherein:

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

15. A packaging container made using the waterproof paper according to any one of claims 1 to 14.

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