Aqueous heat sealing agent, paper base material for paper container, paper container, and method for manufacturing paper container

Abstract

The problem to be solved by the present invention is to improve the polyethylene used in paper containers such as paper cups. It has the heat sealing function desired as a replacement for the polypropylene film and the anti-theft function desired for the coating agent on the inside of the cup. Water-based heat seal that is both water-based and strong, and can be recycled without sorting when recycling paper. and a paper container using the aqueous heat-sealing agent. [Solution] The solution to the problem of the present invention is an aqueous heat-sealing agent containing an aqueous solvent, an olefin-α,β-unsaturated carboxylic acid copolymer, and a wax, in which the content of the α,β-unsaturated carboxylic acid in the olefin-α,β-unsaturated carboxylic acid copolymer is 8 to 24 mass%, and the wax is one or more waxes selected from fatty acid amide wax, carnauba wax, and Fischer-Tropsch wax.

Description

[Technical Field]

[0001] The present invention relates to an aqueous sheet sealing agent for use in paper containers, a paper base material for paper containers using the aqueous heat sealing agent, a paper container, and a method for manufacturing a paper container. [Background technology]

[0002] Paper food containers were originally developed as ice cream containers, but they have since been improved upon to be used as paper cups for various beverages in response to changes in social phenomena and living environments, such as the spread of vending machines, the increase in convenience stores and fast food restaurants, the popularity of outdoor leisure activities, and the introduction of tea dispensers in the workplace, and demand for these has skyrocketed. In Japan, the advantages of paper containers began to be reconsidered in the 1970s as a measure to combat pollution caused by plastic waste, and paper cups for tea and coffee have since been used for a wider range of purposes, including desserts such as yogurt, pudding, and jelly, as well as natto and prepared foods. Furthermore, in recent years, as the issue of marine plastic waste, including microplastics, has come to the forefront once again, interest has been growing in paper, which is made from wood, a renewable resource, as a material with functional properties such as being reusable and biodegradable.

[0003] Paper cups, one of the most widely used paper food containers today, are made of paper but contain polyethylene film as part of their raw material, which reduces recycling efficiency. Paper cups are typically made by extruding polyethylene or polypropylene resins that have been melted under heat into a film-like shape, and laminating the film to a paper base. When the polyethylene film is molded into the paper cup, it acts as an adhesive when heated with indirect heat from a burner or hot air, and the presence of the polyethylene film inside the paper cup prevents the paper base from coming into direct contact with the contents, thereby providing waterproofing and strength. However, the laminated polyethylene film does not dissolve in the alkaline solution used in paper recycling, so it must be physically removed, reducing recycling efficiency. Furthermore, marine pollution caused by plastic waste flowing into the oceans is a global problem. One of the targets of the Sustainable Development Goals (SDGs) is to "by 2025 prevent and significantly reduce marine pollution of all kinds, especially from land-based activities, including marine litter and eutrophication." This goal has become a globally important theme, with summits of the major industrialized nations agreeing to strengthen efforts. Therefore, there is a need for polyethylene film substitutes that can be used in these applications without reducing paper recycling efficiency. There is also a need for paper containers that do not use plastic film.

[0004] Water-based heat-sealing agents are known to act as adhesives when molding paper cups. For example, Patent Document 1 discloses that an aqueous dispersion of an ethylene-based resin, in which an olefin-α,β-unsaturated carboxylic acid copolymer neutralized with ammonia or an amine and another olefin-based thermoplastic resin are mixed and dispersed in a specific ratio, can be used as a heat-sealing agent. Patent Document 2 discloses that an aqueous dispersion containing a polyolefin resin composed of an unsaturated carboxylic acid unit, an ethylene-based hydrocarbon, and an acrylic acid ester or a methacrylic acid ester, a natural wax, and an aqueous medium in a specific ratio can be used as a heat sealing agent. However, these documents only disclose the performance of the material as a heat sealing agent, such as heat sealing strength and blocking resistance, and make no mention of the compatibility of the heat sealing function desired as an alternative to the polyethylene film used in paper cups with the waterproofness and strength desired for a cup inner surface coating agent, or recyclability. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-7860 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-45313 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide an aqueous heat-sealing agent that can be used as an alternative to polyethylene films used in paper containers such as paper cups, that combines the desired heat-sealing function with the waterproofness and strength required for a cup inner surface coating agent, and that can be recycled without separation when recycling paper, and a paper container using the aqueous heat-sealing agent. [Means for solving the problem]

[0007] That is, the present invention provides a composition containing an aqueous solvent, an olefin-α,β-unsaturated carboxylic acid copolymer, and a wax. The content of the α,β-unsaturated carboxylic acid in the olefin-α,β-unsaturated carboxylic acid copolymer is 8 to 24 mass %, and the wax is at least one selected from fatty acid amide wax, carnauba wax, and Fischer-Tropsch wax. A water-based heat sealant is provided.

[0008] The present invention also provides a paper substrate for a paper container having the aqueous heat-sealing agent according to claim 1 or 2 on at least one surface of the paper substrate.

[0009] The present invention also provides a paper container using a paper base material for paper containers having the aqueous heat-sealing agent according to claim 1 or 2 on at least one side of the paper base material.

[0010] The present invention also provides a cylindrical body member (1) made of a paper base material having a resin layer provided on at least the inner surface of the container and on the bonding surface when assembling the container, the bonding surfaces of both ends of the paper base material rolled and overlapped being heat-welded; A method for manufacturing a paper container having a plate-shaped bottom member (2) made of a paper base material having a resin layer provided on at least the inner surface of the container and the bonding surface when assembling the container, and heat-welded to the lower end of the body member (1), The present invention provides a method for producing a paper container, wherein the resin layer is made of a dried coating film of the above-described aqueous heat-sealing agent. [Effects of the Invention]

[0011] The aqueous heat-sealing agent of the present invention can be used as a substitute for polyethylene film used in paper containers such as paper cups, and can achieve both the heat-sealing function desired and the waterproofness and strength desired for a cup inner surface coating agent, and can be recycled without sorting paper. Therefore, the aqueous heat-sealing agent of the present invention is useful as a substitute for polyethylene film in paper containers such as paper cups. DETAILED DESCRIPTION OF THE INVENTION

[0012] The aqueous heat-sealing agent of the present invention is characterized by containing an aqueous solvent, an olefin-α,β-unsaturated carboxylic acid copolymer, and a wax.

[0013] (water-based solvent) The aqueous solvent used in the present invention may be water, a water-soluble organic solvent that dissolves in water, or the like. As the water, pure water such as ion-exchanged water, ultrafiltered water, reverse osmosis water, or distilled water, or ultrapure water, may be used. Furthermore, it is preferable to use water that has been sterilized by ultraviolet irradiation or the addition of hydrogen peroxide, for example, because this can prevent the growth of mold or bacteria when the aqueous pigment dispersion or the ink using the same is stored for a long period of time. Examples of water-soluble organic solvents include glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol; diols such as butanediol, pentanediol, and hexanediol; glycol esters such as propylene glycol laurate; diethylene glycol ethers such as diethylene glycol monoethyl, diethylene glycol monobutyl, diethylene glycol monohexyl, and carbitol; glycol ethers such as cellosolves containing propylene glycol ether, dipropylene glycol ether, and triethylene glycol ether; alcohols such as methanol, ethanol, isopropyl alcohol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, butyl alcohol, and pentyl alcohol; lactones such as sulfolane, esters, ketones, and γ-butyrolactone; lactams such as N-(2-hydroxyethyl)pyrrolidone; and various other solvents known as aqueous organic solvents, such as glycerin and its polyalkylene oxide adducts. These aqueous organic solvents can be used alone or in combination. Of these, water is most preferred.

[0014] (olefin-α,β-unsaturated carboxylic acid copolymer) The olefin-α,β-unsaturated carboxylic acid copolymer used in the present invention may be a copolymer of an olefin with at least one monomer selected from the group consisting of an α,β-unsaturated carboxylic acid, a metal salt of an α,β-unsaturated carboxylic acid, and an α,β-unsaturated carboxylic acid ester. Specific examples include copolymers of an α,β-unsaturated carboxylic acid, a metal salt of an α,β-unsaturated carboxylic acid, or an α,β-unsaturated carboxylic acid ester with an olefin, such as an olefin-α,β-unsaturated carboxylic acid copolymer, an ethylene-acrylic acid ester copolymer, an ethylene-methacrylic acid copolymer, an ethylene-methacrylic acid ester copolymer, an ethylene-acrylic acid-maleic anhydride copolymer, an ethylene-acrylic acid ester-maleic anhydride copolymer, an ethylene-methacrylic acid-maleic anhydride copolymer, an ethylene-methacrylic acid ester-maleic anhydride copolymer, and metal salts thereof. These copolymers may be used alone or in combination of two or more. Among these, olefin-α,β-unsaturated carboxylic acid copolymers are preferred. Examples of the olefin-α,β-unsaturated carboxylic acid copolymer include random copolymers or block copolymers of ethylene and α,β-unsaturated carboxylic acid.

[0015] Examples of the olefin include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 4-methyl-1-pentene, butadiene, dicyclopentadiene, 5-ethylidene-2-norbornene, etc. Among these, ethylene is preferred.

[0016] Examples of the α,β-unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, and itaconic acid. Among these, acrylic acid and methacrylic acid are preferred. These α,β-unsaturated carboxylic acids may be used alone or in combination.

[0017] The α,β-unsaturated carboxylic acid ester can be any known alkyl ester, hydroxyalkyl ester, alkoxyalkyl ester, or the like of acrylic acid or methacrylic acid, without any particular limitation. Specific examples include acrylic acid esters such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, n-octyl acrylate, 2-hydroxyethyl acrylate, and 2-methoxyethyl acrylate, and methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, 2-ethylhexyl methacrylate, n-lauryl methacrylate, 2-hydroxyethyl methacrylate, and 2-ethoxyethyl methacrylate. These can be used alone or in combination of two or more.

[0018] The olefin-α,β-unsaturated carboxylic acid copolymer can be produced by a known method, for example, by radical copolymerization under high temperature and high pressure.

[0019] The α,β-unsaturated carboxylic acid content in the olefin-α,β-unsaturated carboxylic acid copolymer is desirably 8 to 24% by weight, preferably 18 to 23% by weight. If the α,β-unsaturated carboxylic acid content is less than 8% by weight, the non-polar nature of the ethylene unit may result in poor dispersibility in aqueous dispersion media, making it difficult to obtain an excellent aqueous dispersion of the olefin-α,β-unsaturated carboxylic acid copolymer resin. Furthermore, if the α,β-unsaturated carboxylic acid content exceeds 24% by weight, the resulting coating may have poor blocking resistance.

[0020] The olefin-α,β-unsaturated carboxylic acid copolymer used in the present invention is used as an aqueous dispersion in an aqueous solvent. The method for dispersing in an aqueous solvent is not particularly limited and may be any known method. For example, a method of emulsifying with a surfactant and dispersing in an aqueous solvent, or a method of neutralizing the olefin-α,β-unsaturated carboxylic acid copolymer with a basic compound and then dispersing in an aqueous solvent, etc., may be mentioned.

[0021] As the surfactant used in the emulsification, various known anionic, cationic, and nonionic surfactants, or various water-soluble polymers can be used in combination as appropriate.

[0022] Examples of basic compounds used in the neutralization include organic amines such as ammonia, methylamine, ethylamine, diethylamine, dimethylethanolamine, diethanolamine, and triethanolamine, and alkali metal hydroxides such as sodium hydroxide, potassium hydroxide, and lithium hydroxide. These basic compounds may be used alone or in combination of two or more. The degree of neutralization by the basic compound may be such that the olefin-α,β-unsaturated carboxylic acid copolymer is stable in an aqueous solvent, for example, 30 to 100 mol %, more preferably 40 to 90 mol %, of the carboxyl groups in the copolymer.

[0023] The dispersion method may be a known method, for example, a media-based dispersion device such as a paint shaker, ball mill, attritor, basket mill, sand mill, sand grinder, Dyno Mill, Dispermat, SC mill, spike mill, or agitator mill, or a media-free dispersion device such as an ultrasonic homogenizer, high-pressure homogenizer, Nanomizer, Dissolver, Disper, or high-speed impeller disperser.

[0024] The solid content of the aqueous dispersion of the olefin-α,β-unsaturated carboxylic acid copolymer used in the present invention is not particularly limited, and may be appropriately determined depending on the desired viscosity when used as a heat-sealing agent, the drying conditions after application of the heat-sealing agent, the film thickness, etc. Generally, a solid content concentration in the range of 10 to 40 mass% is often used.

[0025] (wax) The aqueous heat-sealing agent of the present invention can maintain blocking resistance by adding a wax. Examples of the wax include fatty acid amide wax, carnauba wax, polyolefin wax, paraffin wax, Fischer-Tropsch wax, beeswax, microcrystalline wax, polyethylene oxide wax, amide wax, coconut oil fatty acid, soybean oil fatty acid, etc. These waxes may be used alone or in combination. Among these, it is preferable to use fatty acid amide wax, carnauba wax, and Fischer-Tropsch wax, and it is particularly preferable to use fatty acid amide wax and carnauba wax. Specific examples of fatty acid amide waxes include pelargonic acid amide, capric acid amide, undecylic acid amide, lauric acid amide, tridecylic acid amide, myristic acid amide, pentadecylic acid amide, palmitic acid amide, heptadecylic acid amide, stearic acid amide, nonadecanoic acid amide, arachidic acid amide, behenic acid amide, lignoceric acid amide, oleic acid amide, cetoleic acid amide, linoleic acid amide, linolenic acid amide, mixtures thereof, and animal and vegetable oil fatty acid amides.

[0026] Specific examples of the carnauba wax include MICROKLEAR 418 (manufactured by Micro Powders, Inc.) and refined carnauba wax No. 1 powder (Nippon Wax Co., Ltd.).

[0027] The amount of wax blended is preferably 1.5 to 20% by mass relative to the total solid content of the aqueous heat-sealing agent (100% by mass). If the total wax content is 3% by mass or more relative to the total solid content of the aqueous heat-sealing agent (100% by mass), blocking resistance tends to be maintained, and if the total wax content is 15% by mass or less relative to the total solid content of the aqueous heat-sealing agent (100% by mass), heat sealability tends to be maintained.

[0028] Among the waxes, the fatty acid amide wax and the carnauba wax are preferably used in combination to further improve blocking resistance. When used in combination, the ratio of fatty acid amide wax to carnauba wax is not particularly limited, but is preferably in the range of 1:1 to 1:10, and more preferably 1:1 to 1:5.

[0029] The wax may be added directly to the aqueous dispersion of the olefin-α,β-unsaturated carboxylic acid copolymer and mixed therein for dispersion, or may be added simultaneously with the dispersion of the olefin-α,β-unsaturated carboxylic acid copolymer in an aqueous solvent for dispersion for dispersion. The dispersion method may be any of the methods used in the above-mentioned method for dispersing the olefin-α,β-unsaturated carboxylic acid copolymer in an aqueous solvent.

[0030] When multiple types of waxes are used in combination, the multiple types of waxes may be added simultaneously or in multiple separate steps. For example, the aqueous heat-sealing agent of the present invention can be obtained by adding a first wax when dispersing the olefin-α,β-unsaturated carboxylic acid copolymer in an aqueous solvent, and then adding a second wax to the resulting aqueous dispersion of the first wax and the olefin-α,β-unsaturated carboxylic acid copolymer.

[0031] In addition to the above-mentioned components, the heat-sealing agent of the present invention may contain additives such as silica, alumina, antifoaming agents, viscosity modifiers, leveling agents, tackifiers, preservatives, antibacterial agents, rust inhibitors, antioxidants, and silicone oils, as long as the object of the present invention is not impaired. In addition, in the aqueous heat-sealing agent of the present invention, polymer-based defoaming agents, silicone-based defoaming agents, and fluorine-based defoaming agents are preferably used to prevent foaming during coating using various coaters. These defoaming agents can be either emulsion-dispersion type or solubilized type. Among these, polymer-based defoaming agents are preferred. The amount of the defoaming agent added is preferably 0.005 to 0.1% by weight of the total amount of the aqueous heat-sealing agent.

[0032] (Paper container) The aqueous heat-sealing agent of the present invention can be used as a heat-sealing agent when producing paper containers, and the coated areas other than the sealed (adhesive) areas function as a coating agent that imparts waterproofing to the paper. The aqueous heat sealing agent of the present invention can be easily softened by heating with a burner or hot air, allowing it to bond papers together or paper to other materials, and then cooled to solidify the bonded portions, allowing it to firmly seal papers together or paper to other materials.

[0033] Materials that can be bonded (sealed) with the aqueous heat-sealing agent of the present invention include paper, nonwoven fabrics, plastics, etc., with paper being preferred. The paper used in the present invention is produced using natural fibers for papermaking, such as wood pulp, on a known papermaking machine, but the papermaking conditions are not particularly specified. Natural fibers for papermaking include wood pulp such as softwood pulp and hardwood pulp, non-wood pulp such as Manila hemp pulp, sisal hemp pulp, and flax pulp, as well as pulps obtained by chemically modifying these pulps. Pulp types that can be used include chemical pulp produced by sulfate cooking, acidic, neutral, or alkaline sulfite cooking, soda cooking, etc., ground pulp, chemi-ground pulp, thermomechanical pulp, etc.

[0034] The type and thickness of the paper substrate can be selected according to the purpose. For example, for a burger wrap, the paper thickness is 20 grams per square meter. 2 For paper cups, the weight is 200-300g / m². 2 For paper plates, spoons, stirrers, etc., the weight should be 50-500 grams per square meter.2 In terms of recycling efficiency and cost reduction, it is preferable that these papers are not laminated with polyethylene film, aluminum, etc.

[0035] The aqueous heat-sealing agent of the present invention functions as an adhesive for bonding two overlapping portions of a paper substrate. Specifically, the aqueous heat-sealing agent of the present invention is applied to at least one portion (or both portions) of the two portions of the paper substrate, and then softened by heating.

[0036] The aqueous heat-sealing agent of the present invention can be applied by any known method, such as a roll coater, gravure coater, flexo coater, air doctor coater, blade coater, air knife coater, squeeze coater, impregnation coater, transfer roll coater, kiss coater, curtain coater, cast coater, spray coater, die coater, offset printing machine, screen printing machine, etc. After coating, a drying step in an oven or the like can be performed.

[0037] The heating method can be a conventional method such as a heat source such as a burner, hot air, electric heating, infrared rays, or electron beams, but specifically, a method using a burner or hot air, or depending on the shape of the mold, a heat welding sealing method, an ultrasonic sealing method, or a high-frequency sealing method is preferred. In this case, the heating temperature is preferably 200 to 500°C, and the heating time is preferably 0.1 to 3 seconds. The aqueous heat-sealing agent of the present invention can be easily heated and softened by non-contact heating, in addition to melting it by contacting it directly with a heat source such as a heat seal bar, and its heat-sealing function persists for a certain period of time even when it is removed from the heat source. When the substrate is paper, direct contact with a heat source can cause the paper to burn, but the heat-sealing agent of the present invention exhibits and maintains its heat-sealing function by non-contact heating, making it particularly useful as a heat-sealing agent for the industrial production of paper containers, which requires high line speeds.

[0038] The aqueous heat sealing agent of the present invention may have a desired thickness as the solid content of the coating film after application. For example, when the aqueous heat sealing agent is used for a paper container for food, the thickness is 2 to 12 g / m 2 The effects of the present invention can be sufficiently obtained within this range. 2 It is more preferable that the range is:

[0039] The aqueous heat-sealing agent of the present invention is applied to a substrate, the coated portion is heated and softened, and then the coated portion is placed on another portion and pressure-bonded to the other portion. The pressure-bonding method is not particularly limited, and may be a hot plate method, ultrasonic sealing, or high-frequency sealing.

[0040] On the other hand, when the aqueous heat sealing agent of the present invention is used as a paper coating agent, the thickness of the solid content on the coated surface after coating may be any desired thickness. For example, when used for paper containers for food, the thickness is 2 to 12 g / m 2 The effects of the present invention can be sufficiently obtained within this range. 2 It is more preferable that the range is:

[0041] When the aqueous heat-sealing agent of the present invention is used as a paper coating agent, it may be coated to a desired thickness by the above-mentioned coating method, and then dried by a drying method such as heat drying or room temperature drying.

[0042] Paper containers that can use the aqueous heat sealing agent of the present invention are widely used for paper containers for food, including paper cups, instant noodles, various beverages, desserts such as ice cream, pudding, and jelly, snacks such as rice crackers, potato chips, chocolate confectionery, and biscuits, wraps for hamburgers and hot dogs, take-out containers for pizza and the like, containers for hot snacks such as fried chicken and potatoes, and cups for prepared foods such as natto.

[0043] (Paper container manufacturing method) As a specific embodiment of the method for producing a paper container using the aqueous heat-sealing agent of the present invention, a method for producing a paper container such as a paper cup will be specifically described. However, the present invention is not limited to this specific embodiment and can be applied to all heat-sealable paper containers.

[0044] In a specific embodiment, the container includes a cylindrical body member (1) made of a paper base material having a resin layer provided on at least the inner surface of the container and on the bonding surface when assembling the container, and the bonding surfaces at both ends of the rolled and overlapped paper base material are heat-welded; This describes a method for manufacturing a paper container having a paper base material with a resin layer on at least the inner surface of the container and the bonding surface when assembling the container, and a plate-shaped bottom member (2) heat-welded to the lower end of the body member (1).

[0045] Both the cylindrical body member (1) and the plate-like bottom member (2) are made by cutting out a paper base material having a resin layer in a desired shape, and the heat-sealing agent of the present invention is used for the resin layer. First, the heat-sealing agent of the present invention is applied to at least the bonding surface of the paper substrate, preferably the entire surface. The above-mentioned coating methods can be used as appropriate. After coating, the aqueous solvent on the heat-sealing agent-coated surface is removed using a dryer or the like, and then printing is performed as necessary. Printing is often performed on the surface opposite the heat-sealing agent.

[0046] Next, the cylindrical body member (1) is cut out into a fan shape, and the plate-like bottom member (2) is cut out into a circle. The bonding surfaces at both ends of the cylindrical body member (1) cut into a fan shape are heated with a heat source such as a burner or hot air to heat-soften the heat-sealing agent, and the bonding surfaces are then overlapped and pressure-bonded. The order of heating, overlapping, and pressure-bonding is not particularly limited. For example, the bonding surfaces may be heated with a heat source, then overlapped, and then pressure-bonded; the bonding surfaces may be overlapped, heated with a heat source, and then pressure-bonded; or the bonding surfaces may be overlapped and heated with a heat source while being pressure-bonded. The method of heating the bonding surfaces with a heat source, then overlapping, and then pressure-bonding is preferred because it ensures the heat-sealing agent is heated and softened. The heating temperature is preferably 200 to 500°C, and the heating time is preferably 0.1 to 3 seconds. This results in a cylindrical body member with the heat-sealing agent-coated surface facing inward. The fan-shaped paper substrate may be punched into a fan-shaped paper substrate using a machine called a blanker, which can be used to produce a blank (body) for a paper container.

[0047] On the other hand, the bottom member (2) cut out into a circle is placed inside the cylindrical body member so that the heat-sealing agent-coated surface faces the inside of the cup, and then the contact area between the bottom member and the body member is heated with a heat source to heat-soften and bond the heat-sealing agents on both the bottom member and the body member in the same manner as described above. At this time, the heat-sealing agent softens and fills the gap between the bottom member and the body member, preventing water leakage.

[0048] In the manufacture of paper cups, the paper cup can then be obtained by a known process, for example, by folding the bottom edge of the body member inward and pressing it with a rotating circular die to finish the bottom of the paper cup. If necessary, the heat-sealed portion may be heated with the heat source described above during finishing to further strengthen the connection between the body member and the bottom member. Finally, the portion of the body member at the top that corresponds to the drinking spout is subjected to a molding process called curling, in which the tool is rotated as necessary to curl it onto the outside of the paper cup.

[0049] The paper container of the specific embodiment is mainly a cup-shaped container with a disk-shaped bottom member, but the shape is not limited to this and may be, for example, a rectangular, polygonal, or cubic container with a rectangular plate-shaped bottom member. Furthermore, if necessary, the container may be sealed with a separately manufactured lid or the like, and the lid may be removed or partially opened when heating in a microwave oven or the like.

[0050] The present invention will be described in detail below based on examples, but the technical scope of the present invention is not limited to these embodiments. [Example]

[0051] <Method of producing olefin-α,β-unsaturated carboxylic acid copolymer> (Production Example 1) An ethylene-ethyl acrylate-acrylic acid copolymer was obtained by synthesizing 77.8 parts of ethylene, 11.1 parts of ethyl acrylate, and 11.2 parts of acrylic acid in a conventional manner. 25 parts of the obtained copolymer, ammonia with a neutralization rate of 100% relative to the acid value of the copolymer, and water as an aqueous solvent were charged and stirred to obtain an aqueous dispersion (A1) of an olefin-α,β-unsaturated carboxylic acid copolymer.

[0052] (Production Example 2) An ethylene-ethyl acrylate-acrylic acid copolymer was obtained by synthesizing 77.8 parts of ethylene, 11.1 parts of ethyl acrylate, and 11.2 parts of acrylic acid in a conventional manner. 25 parts of the obtained copolymer, ammonia with a neutralization rate of 100% relative to the acid value of the copolymer, water as an aqueous solvent, and 1.5 parts of fatty acid amide wax as a wax were charged and stirred to obtain an aqueous dispersion (A2) of an olefin-α,β-unsaturated carboxylic acid copolymer and fatty acid amide wax.

[0053] <Preparation of water-based heat sealant> (Examples 1 to 8 and Comparative Examples 1 to 7) Using the aqueous dispersion (A1) or (A2) obtained in Production Example 1 or Production Example 2, the aqueous heat-sealing agents of Examples or Comparative Examples were obtained according to the compositions in Tables 1 or 2.

[0054] <Evaluation> (heat sealability) Using a bar coater #16, the aqueous heat-sealing agent of the Example or Comparative Example was applied to cup base paper (manufactured by Nippon Paper Industries Co., Ltd.), which was then dried at 100°C for 30 seconds. The coated paper was then cut into 3.0cm x 5.0cm pieces, and the short sides were temporarily secured together with tape so that the coated and uncoated sides were in close contact with each other over a width of 5mm. One side was heated on a hot plate for 5 seconds, and then immediately dried at 1kgf / m without heating. 2 The samples were heat-sealed using a heat-sealing machine under one-second adhesion conditions, and the adhesion state was visually evaluated. The minimum temperature of the hot plate that resulted in complete adhesion was then investigated. 6: Complete adhesion at 200℃. 5: Complete adhesion at 210℃. 4: Complete adhesion at 220℃. 3: Complete adhesion at 230℃. 2: Complete adhesion at 240℃. 1: Does not adhere even at temperatures above 240°C.

[0055] (Water-resistant seal) In the evaluation of heat sealability, water was dropped onto the sealed portion of the sheet, and the degree of water leakage from the sealed portion was visually confirmed. 4: No water leakage at all. 3: There is a very slight water leak in some areas. 2: There is a slight water leak in some areas. 1: Water leaks are visible all over the surface.

[0056] (Slipperiness) Using a bar coater #16, the aqueous heat-sealing agent of the Example or Comparative Example was applied to cup base paper (manufactured by Nippon Paper Industries Co., Ltd.), which was then dried at 100°C for 30 seconds. The coated paper was then cut into 3.0 cm x 5.0 cm pieces to prepare test pieces. Several test pieces were stacked so that the coated and uncoated sides were in contact, and only the top one was taken as a sample, and the behavior of the test piece at that time was visually confirmed. 4: When test pieces are stacked, they can be removed one by one. 3: The lower test piece slightly adheres to the upper test piece. 2: Sometimes the lower test piece sticks to the upper test piece. 1: The lower test piece sticks to the upper test piece.

[0057] (blocking resistance) (blocking resistance) The coated and uncoated surfaces of the coated papers prepared for the heat sealability evaluation were placed in contact with each other and subjected to a pressure of 10 kgf / cm 2 After removal, the adhesion between the coated and uncoated surfaces was visually evaluated using the following four-point scale. (Evaluation criteria) 4: No blocking observed at all. 3: Slight blocking observed in some areas. 2: Partial blocking is observed. 1: Blocking is observed across the entire surface.

[0058] (Recyclability) The coated papers of Examples 1 to 8 prepared for the evaluation of heat sealing properties were cut into 3.0 cm x 5.0 cm pieces, placed in a 1% by mass aqueous solution of sodium hydroxide, and stirred for 30 minutes using a paint shaker (Asada Iron Works Co., Ltd.). After this, the condition was checked and the paper was found to have sufficiently disintegrated, with no film-like residue being observed. On the other hand, when a commercially available paper cup was cut into 3.0 cm x 5.0 cm pieces and subjected to the same evaluation, it was confirmed that a film-like substance remained. Therefore, it was confirmed that the polyethylene film obtained in the examples remained in a sheet form. Therefore, it is clear that the coated papers of Examples 1 to 8 do not reduce paper recycling efficiency.

[0059] The evaluation results of each of the laminates of Examples 1 to 8 and Comparative Examples 1 to 7 are shown in Tables 1 and 2.

[0060] [Table 1]

[0061] [Table 2]

[0062] In the table, the abbreviations are as follows: Styrene-acrylic resin: Neocryl A-2095 (Kusumoto Chemicals Co., Ltd.) Carnauba wax: MICROKLEAR 418 (Micro Powders, Inc.) Fischer Trofisch Wax (a): MP-22XF (Micro Powders, Inc.) Fischer Trofisch Wax (b): MP-28C (Micro Powders, Inc.) Fine powder polyethylene: FLOTHENE uF1.5N (Sumitomo Seika Chemicals Co., Ltd.)

Claims

1. A paper substrate for a paper container having a resin layer on at least one side of the paper substrate, the resin layer is a coating film of an aqueous heat-sealing agent containing an aqueous solvent, an olefin-α,β-unsaturated carboxylic acid copolymer, and a wax; the content of the α,β-unsaturated carboxylic acid in the olefin-α,β-unsaturated carboxylic acid copolymer is 8 to 24 mass%; the wax is at least one selected from fatty acid amide wax, carnauba wax, and Fischer-Tropsch wax; The paper substrate is an unlaminated paper substrate. A paper base material for a paper container characterized by:

2. A paper container comprising the paper base material for paper containers according to claim 1.

3. a cylindrical body member (1) made of a paper base material for a paper container having a resin layer provided on at least the inner surface of the container and on the bonding surface when assembling the container, the bonding surfaces of both ends of the paper base material for a paper container rolled and overlapped being heat-welded; A method for manufacturing a paper container having a paper base material for a paper container, the paper base material having a resin layer provided on at least the inner surface of the container and the surface to be joined when assembling the container, and a plate-shaped bottom member (2) heat-welded to the lower end of the body member (1), The method for manufacturing a paper container, wherein the paper base material for a paper container is the paper base material for a paper container according to claim 1.

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