Water-resistant paper, and wrapping paper or container using the same

Abstract

The present invention relates to waterproof paper having a paper substrate, a waterproof coating provided on at least a portion of the paper substrate, and a heat-sealable coating provided on a portion different from the portion having the waterproof coating. According to the present invention, there are provided waterproof paper having a waterproof coating capable of imparting excellent water resistance and moisture resistance to paper simply by coating, and capable of improving the recyclability of paper by becoming an alternative to paper laminated with a plastic film, and a packaging paper or a container using the waterproof paper.

Description

Technical Field

[0001] The present invention relates to water-resistant paper, and packaging paper or a container using the water-resistant paper. Background Art

[0002] Paper packaging materials such as paper bags, paper boxes, and paper cups have been used for various purposes. In recent years, the problem of marine plastic waste represented by microplastics has come into focus, and as one of the raw materials with functions such as "recyclability" and "biodegradability", the trend of using "paper" made from "wood", a renewable resource, as a raw material to replace plastic materials has gradually increased.

[0003] As one of the most popular paper containers nowadays, there are paper cups used as containers for beverages, ice cream, yogurt, etc. Paper cups are given water resistance by using polyethylene film as a part of the raw material of paper. Such paper cups are obtained by attaching polyethylene film, polypropylene film, etc., which are extruded into a film shape by heat-melting polyethylene resin, polypropylene resin, etc., to a paper base material. When the paper cup is formed, the polyethylene film is melted by heat under indirect heating such as a burner and hot air, and acts as an adhesive. In addition, since the polyethylene film exists on the inside of the paper cup, the paper base material does not directly contact the contents, and is given waterproofness, moisture resistance, and strength.

[0004] However, the polyethylene film applied does not dissolve in the alkaline solution used in the paper recycling process when the paper is recycled, so it needs to be physically removed, resulting in a decrease in recycling efficiency. In addition, marine pollution caused by the outflow of plastic waste into the ocean has become a global problem. The following has become an important global theme: As an indicator of the Sustainable Development Goals (SDGs), the goal of "preventing and significantly reducing all types of marine pollution, including marine debris, eutrophication, and pollution caused by land-based activities, by 2025" has been proposed, and an agreement to strengthen cooperation has also been reached at the summit (head of state meeting of major countries). Therefore, there is a need for a polyethylene film substitute that can be applied to these uses and does not reduce paper recycling efficiency.

[0005] On the other hand, aqueous heat sealants are known as substances that function as adhesives when molding bags, boxes, paper cups, etc. For example, Patent Document 1 discloses that an aqueous dispersion of an ethylene resin obtained by mixing and dispersing an olefin-α,β-unsaturated carboxylic acid copolymer neutralized with ammonia or amine and another olefin-based thermoplastic resin at a specific ratio can be used as a heat sealant.

[0006] Patent Document 2 discloses that an aqueous dispersion containing a polyolefin resin composed of an unsaturated carboxylic acid unit, a vinyl hydrocarbon, and an acrylate or methacrylate, a natural wax, and an aqueous medium at a specific ratio can be used as a heat sealant.

[0007] However, these documents only disclose so-called properties as heat sealants, such as heat seal strength and blocking resistance, but do not describe water resistance, moisture resistance, strength, and recyclability that are expected as a substitute for polyethylene films.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Publication No. 2000-7860

[0011] Patent Document 2: Japanese Patent Application Publication No. 2006-45313 Summary of the invention

[0012] Problems to be solved by the invention

[0013] The problem to be solved by the present invention is to provide a waterproof paper having a waterproof coating that can impart excellent water resistance and moisture resistance to paper only by coating, and can improve the recyclability of paper by replacing paper laminated with a plastic film, and a wrapping paper or container using the waterproof paper. In addition, the coated paper of the present invention has a heat-sealable coating, so that in addition to water resistance and moisture resistance, a waterproof paper having a heat-sealable function, and a wrapping paper or container using the waterproof paper are provided.

[0014] Means for solving problems

[0015] That is, the present invention provides a water-resistant paper having:

[0016] Paper substrate,

[0017] a water-resistant coating provided on at least a portion of the paper substrate; and

[0018] A heat-sealable coating is provided on a portion different from the portion having the water-resistant coating.

[0019] The present invention also provides a package or a container using the water-resistant paper.

[0020] Effects of the Invention

[0021] The waterproof paper of the present invention has a waterproof coating that can impart excellent water resistance and moisture resistance to the paper only by coating, so it has excellent water resistance and moisture resistance, and can improve recyclability. In addition, the coated paper of the present invention has a heat-sealable coating, so it can be realized as a waterproof paper having a heat-sealable function in addition to water resistance and moisture resistance. The waterproof layer and the heat-sealable coating provided on the waterproof paper of the present invention can be formed of materials with high safety to the environment and the human body. The coated paper of the present invention is useful as a substitute for paper laminated with a plastic film, and the coated paper can be used in a packaging body or a container. DETAILED DESCRIPTION

[0022] The coated paper of the present invention comprises a water-resistant coating layer provided on at least a portion of a paper substrate, and a heat-sealable coating layer provided on a portion different from the portion having the water-resistant coating layer.

[0023] In addition, in this invention, (meth)acrylate is a general term for acrylate and methacrylate, and (meth)acrylic acid is a general term for acrylic acid and methacrylic acid.

[0024] [Heat seal coating]

[0025] In water-resistant paper, a heat-sealable coating is provided on an appropriate portion of the paper substrate depending on the final packaging material, shape of the container and purpose, but for example, in the paper substrate, it is more preferred to provide a heat-sealable coating on the surface opposite to the surface provided with the water-resistant coating.

[0026] The water-resistant paper of the present invention has a heat-sealable coating, thereby having a heat-sealable function and improving water resistance. In addition, by laminating the heat-sealable portion, various packaging materials such as bags and boxes can be made according to the purpose, and the processability is improved.

[0027] The heat-seal coating can use a known heat-seal coating agent, but in order to improve water resistance, it is preferable to use an aqueous heat-seal agent (HS) containing an aqueous solvent, an olefin-α,β-unsaturated carboxylic acid copolymer and a wax (W1). The aqueous heat-seal agent (HS) can be used as a heat-seal agent when manufacturing paper containers, etc., and the coating portion other than the sealing (bonding) portion also functions as a coating agent that imparts water resistance to paper.

[0028] <Water-based heat sealant (HS)>

[0029] The aqueous heat sealant (HS) contains at least an aqueous solvent, an olefin-α,β-unsaturated carboxylic acid copolymer and a wax (W1).

[0030] (Aqueous solvent)

[0031] As the aqueous solvent used for the aqueous heat sealant HS, water, a water-soluble organic solvent dissolved in water, etc. can be used. As the water, pure water such as ion exchange water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water can be used. In addition, as the above-mentioned water, water sterilized by ultraviolet irradiation or addition of hydrogen peroxide is used, which can prevent the generation of mold or bacteria when the aqueous pigment dispersion or the ink using the pigment dispersion is stored for a long time, so it is suitable.

[0032] As water-soluble organic solvents, for example, glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, polyethylene glycol, and polypropylene glycol can be cited; glycols such as butanediol, pentanediol, and hexanediol; glycol esters such as propylene glycol laurate; diethylene glycol ethers such as diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, and carbitol; glycol ethers such as cellosolves including propylene glycol ether, dipropylene glycol ether, and triethylene glycol ether; alcohols such as methanol, ethanol, isopropanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, butanol, and pentanol; lactones such as sulfolane, esters, ketones, and γ-butyrolactone, lactams such as N-(2-hydroxyethyl)pyrrolidone, glycerol and its polyoxyalkylene adducts, and other various solvents known as aqueous organic solvents. These aqueous organic solvents can be used alone or in combination of two or more. Among them, water is most preferred.

[0033] (Olefin-α,β-unsaturated carboxylic acid copolymer)

[0034] As the olefin-α,β-unsaturated carboxylic acid copolymer used in the water-based heat sealant HS, there can be mentioned copolymers of olefin and at least one monomer selected from α,β-unsaturated carboxylic acid, metal salt of α,β-unsaturated carboxylic acid and α,β-unsaturated carboxylic acid ester. Specifically, it is a copolymer of α,β-unsaturated carboxylic acid, metal salt of α,β-unsaturated carboxylic acid or α,β-unsaturated carboxylic acid ester and olefin, and there can be mentioned olefin-α,β-unsaturated carboxylic acid copolymer, ethylene-acrylate copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid-maleic anhydride copolymer, ethylene-acrylate-maleic anhydride copolymer, ethylene-methacrylic acid-maleic anhydride copolymer, ethylene-methacrylic acid-maleic anhydride copolymer, ethylene-methacrylate-maleic anhydride copolymer, and metal salts thereof. These copolymers may be used alone or as a mixture of two or more.

[0035] Among them, olefin-α,β-unsaturated carboxylic acid copolymers are preferred. Examples of olefin-α,β-unsaturated carboxylic acid copolymers include random copolymers or block copolymers of ethylene and α,β-unsaturated carboxylic acid.

[0036] 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 them, ethylene is preferred.

[0037] As the above-mentioned α, β-unsaturated carboxylic acid, for example, acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, etc. can be mentioned. Among these, acrylic acid and methacrylic acid are preferably used. These α, β-unsaturated carboxylic acids can be used alone or in combination of two or more.

[0038] As the above-mentioned α, β-unsaturated carboxylic acid ester, known acrylic acid or methacrylic acid alkyl ester, hydroxyalkyl ester, alkoxyalkyl ester, etc. can be used without particular limitation. For example, specifically, 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, 2-methoxyethyl acrylate and other acrylates, 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, methacrylates such as 2-ethoxyethyl methacrylate can be exemplified. These can be used alone or in combination of two or more.

[0039] 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.

[0040] The content of α,β-unsaturated carboxylic acid in the above-mentioned olefin-α,β-unsaturated carboxylic acid copolymer is expected to be 8 to 24% by weight, preferably 18 to 23% by weight. When the content of α,β-unsaturated carboxylic acid is less than 8% by weight, due to the non-polar nature of the ethylene unit, the dispersibility relative to the aqueous dispersion medium is poor, and there is a concern that it is difficult to obtain an excellent olefin-α,β-unsaturated carboxylic acid copolymer resin aqueous dispersion. In addition, when the content of α,β-unsaturated carboxylic acid exceeds 24% by weight, there is a concern that the blocking resistance of the obtained coating will deteriorate.

[0041] The olefin-α,β-unsaturated carboxylic acid copolymer used in the water-based heat sealant HS is used in the form of an aqueous dispersion dispersed in an aqueous solvent. The method of dispersing in an aqueous solvent is not particularly limited and may be carried out by a known method. For example, there may be mentioned a method of dispersing in an aqueous solvent by emulsifying with a surfactant, a method of dispersing in an aqueous solvent after neutralizing the olefin-α,β-unsaturated carboxylic acid copolymer with an alkaline compound, and the like.

[0042] As the surfactant used in the emulsification, various known anionic, cationic, and nonionic surfactants, or various water-soluble polymers may be used in combination as appropriate.

[0043] In addition, as the basic compound used in the above neutralization, for example, 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 can be mentioned. These basic compounds can be used alone or in combination of two or more.

[0044] The degree of neutralization with the basic compound may be such that the olefin-α,β-unsaturated carboxylic acid copolymer can be stably present in an aqueous solvent, for example, desirably 30 to 100 mol %, more preferably 40 to 90 mol % of the carboxyl groups of the copolymer.

[0045] Regarding the above-mentioned dispersion method, as a well-known method, for example, as a dispersion device using a medium, a paint stirrer, a ball mill, a grinder, a basket mill, a sand mill, a grinder, a DYNO-MILL, a DISPERMAT disperser, an SC mill, a nail crusher, a stirring mill, etc. can be used, and an ultrasonic homogenizer, a high-pressure homogenizer, a NANOMIZER pulverizer, a dissolver, a disperser, a high-speed impeller disperser, etc. can be used as a dispersion device not using a medium for dispersion.

[0046] 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 can be appropriately determined according to the desired viscosity when used as a heat sealant, the drying conditions after the heat sealant is applied, the film thickness of the coating, etc. Generally speaking, it is often used within the range of 10 to 40% by mass of the solid content concentration.

[0047] (Wax (W1) for water-based heat sealants (HS))

[0048] By adding wax (W1) to the water-based heat sealant (HS), the blocking resistance can be maintained. Examples of the wax (W1) include fatty acid amide wax, carnauba wax, polyolefin wax, paraffin wax, Fischer-Tropsch wax, beeswax, microcrystalline wax, oxidized polyethylene wax, amide wax, coconut oil fatty acid, soybean oil fatty acid, etc. These can be used alone or in combination.

[0049] Among these, fatty acid amide wax, carnauba wax, and Fischer-Tropsch wax are preferably used, and fatty acid amide wax and carnauba wax are particularly preferably used.

[0050] Specific examples of fatty acid amide waxes include nonanoic acid amide, capric acid amide, undecanoic acid amide, lauric acid amide, tridecanoic acid amide, myristic acid amide, pentadecanoic acid amide, palmitic acid amide, heptadecanoic acid amide, stearic acid amide, nonadecanoic acid amide, arachidic acid amide, behenic acid amide, tetracosanoic acid amide, oleic acid amide, hexadecenoic acid amide (Japanese: セトレインアミド), linoleic acid amide, linolenic acid amide, mixtures thereof, and animal and plant oil fatty acid amides.

[0051] Specific examples of the carnauba wax include MICROKLEAR 418 (manufactured by Micro Powders, Inc.) and purified carnauba wax No. 1 powder (manufactured by NIPPON WAX Co., Ltd.).

[0052] Regarding the amount of the wax (W1) blended, the total amount of the wax (W1) is preferably 1.5 to 20% by mass relative to 100% by mass of the total solid content of the water-based heat sealant (HS). If the total amount of the wax (W1) is 3% by mass or more relative to 100% by mass of the total solid content of the water-based heat sealant (HS), there is a tendency to maintain anti-blocking properties, and if the total amount of the wax (W1) is 15% by mass or less relative to 100% by mass of the total solid content of the water-based heat sealant (HS), there is a tendency to maintain heat sealing properties.

[0053] Among the waxes (W1), the fatty acid amide wax and the carnauba wax are preferably used together, because the blocking resistance is further improved. When used together, the ratio is not particularly limited, but preferably, the fatty acid amide wax: the carnauba wax = 1:1 to 1:10 is preferred, and the range of 1:1 to 1:5 is more preferred.

[0054] The wax (W1) can be directly added to the aqueous dispersion of the olefin-α,β-unsaturated carboxylic acid copolymer and mixed and dispersed, or can be added and mixed and dispersed simultaneously when the olefin-α,β-unsaturated carboxylic acid copolymer is dispersed in an aqueous solvent. The dispersion method can appropriately use the method used in the above-mentioned dispersion method of the olefin-α,β-unsaturated carboxylic acid copolymer in an aqueous solvent.

[0055] When multiple waxes (W1) are used in combination, the multiple waxes (W1) may be added simultaneously or in multiple steps. For example, the aqueous heat sealant (HS) may be obtained by adding a first wax (W1) when dispersing the above-mentioned olefin-α,β-unsaturated carboxylic acid copolymer in an aqueous solvent, and then adding a second wax (W1) to the obtained aqueous dispersion of the first wax (W1) and the above-mentioned olefin-α,β-unsaturated carboxylic acid copolymer.

[0056] The aqueous heat sealant (HS) may contain, in addition to the above components, additives such as silica, alumina, defoaming agents, viscosity modifiers, leveling agents, thickeners, preservatives, antibacterial agents, rust inhibitors, antioxidants, silicone oils, etc., within the range not hindering the purpose of the present invention.

[0057] In addition, in the water-based heat sealant (HS), in order to prevent foaming when applying using various coating machines, it is preferred to use a polymer defoamer, a silicon defoamer, or a fluorine defoamer. As these defoamers, any of an emulsified dispersion type and a soluble type can be used. Among them, a polymer defoamer is preferred. The amount of the above-mentioned defoamer added is preferably 0.005% by weight to 0.1% by weight of the total amount of the water-based heat sealant.

[0058] Aqueous heat sealants (HS) can be used as heat sealants when manufacturing paper packaging materials such as bags and boxes, and paper containers. The coated portion other than the sealed (bonded) portion functions as a coating agent that imparts water repellency to paper.

[0059] <Method for producing heat-sealable coating>

[0060] The heat seal coating is provided by coating, for example, a paper substrate using a known heat seal coating agent or heat sealant (HS). As a coating method during coating, a known method can be used. For example, a roll coater, a gravure coater, a flexible coater, an air knife coater, a knife coater, an air knife coater, an extrusion coater, an impregnation coater, a conveyor roll coater, a kiss coater, a curtain coater, a cast coater, a spray coater, a die coater, an offset printer, a screen printer, etc. can be used. In addition, a drying process can also be provided after coating using an oven, etc.

[0061] When using a water-based heat sealant (HS), the film thickness of the solid component after coating can be a desired film thickness. For example, when used in a paper container for food, it can be 2 to 12 g / m 2 The range of 5 to 10 g / m is more preferable. 2 range.

[0062] The water-based heat sealant (HS) has a function as an adhesive that bonds two places on a paper substrate coated with the water-based heat sealant in an overlapping state. Specifically, after the water-based heat sealant of the present invention is applied to at least one of the two places (or two places) of the paper substrate, it is softened by heating. The water-based heat sealant is easily softened by heating with a burner or hot air, and can bond paper to each other or paper to other raw materials. After cooling, the bonded part is solidified, and the paper can be firmly sealed to each other or paper to other raw materials.

[0063] As the heating method, a heat source such as a burner, hot air, electric heating, infrared rays, electron beams, and the like can be used. Specifically, a method of heating with a burner or hot air, a heat welding sealing method according to the formed shape, an ultrasonic sealing method, or a high-frequency sealing method is preferred. The heating temperature is preferably 200 to 500° C., and the heating time is preferably 0.1 to 3 seconds.

[0064] In addition, the water-based heat sealant (HS) can be easily softened by heating even by non-contact heating, in addition to the method of melting by contact with a direct heat source such as a heat seal rod, and the heat sealing function can be sustained for a certain period of time even when away from the heat source. In the case of paper as the substrate, if it is in contact with a direct heat source, there is a possibility that the paper will be burned, but the heat sealant of the present invention exhibits a heat sealing function under non-contact heating and the function is sustained, and therefore, it is particularly useful as a heat sealant for industrial production of paper containers requiring a high production line speed.

[0065] After applying a water-based heat sealant (HS) and heating and softening the applied part, the applied part is crimped while overlapping with another part, so that it can be used as a heat sealant. There is no particular limitation on the crimping method, and it can be performed by a hot plate method, ultrasonic sealing, or high-frequency sealing method. Of course, the water-based heat sealant (HS) can also be used as a paper coating agent without heat sealing. In this case, after applying it in a desired film thickness using the above-mentioned coating method, it can be dried using a drying method such as heat drying or room temperature drying.

[0066] [Water-resistant coating]

[0067] The water-resistant paper of the present invention has a water-resistant coating on a paper substrate. The water-resistant coating is provided on an appropriate portion of the paper substrate depending on the shape and use of the final packaging material or container, but as described above, it is preferably provided on a portion different from the portion of the paper substrate on which the heat-sealable coating is provided, and more preferably, the water-resistant coating is provided on the surface opposite to the surface on which the heat-sealable coating is provided.

[0068] The water-resistant coating layer is preferably formed from a water-resistant overcoat composition (OCM) for paper containing an aqueous solvent, a styrene acrylic copolymer (A) and a wax (W2).

[0069] <Water-resistant overcoat composition (OCM)>

[0070] The water-resistant overcoat composition (OCM) contains at least an aqueous solvent, a styrene acrylic copolymer (A), and a wax (W2).

[0071] (Aqueous solvent)

[0072] As the aqueous solvent, the same aqueous solvent as used in the above-mentioned aqueous heat sealant (HS) can be used.

[0073] (Styrene acrylic copolymer (A))

[0074] The styrene acrylic copolymer (A) preferably has a core-shell structure formed by a copolymer of styrene and (meth)acrylate, and more preferably has a core-shell structure formed by a copolymer of styrene and (meth)acrylate and a copolymer of styrene, (meth)acrylate and (meth)acrylic acid.

[0075] The styrenes used as the constituent components of the styrene acrylic copolymer (A) are polymerizable compounds having a styrene skeleton, such as styrene, α-methylstyrene (any one of o-methylstyrene, m-methylstyrene, and p-methylstyrene or a mixture), styrene dimer, styrene trimer, and styrene derivatives (p-dimethylsilylstyreneoxystyrene (Japanese: p-ヅメチルシリルスチキシスチレン), p-tert-butyldimethylsiloxystyrene, and p-tert-butylstyrene). The styrenes may be one or more. Among them, styrene is preferably used. When two or more styrenes are used, styrene is preferably used as the main component, for example, the mass proportion of styrene in all styrenes is set to the largest.

[0076] The (meth)acrylate used as a constituent component of the styrene acrylic copolymer (A) is not particularly limited, and examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, isopropyl (meth)acrylate, allyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, isopentyl (meth)acrylate, n-hexyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and (meth)acrylate. acrylate, n-lauryl (meth)acrylate, n-tridecyl (meth)acrylate, n-stearyl (meth)acrylate, phenyl (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate, 4-tert-butylcyclohexyl (meth)acrylate, isobornyl (meth)acrylate, tricyclodecyl (meth)acrylate, dicyclopentadienyl (meth)acrylate, adamantyl (meth)acrylate, glycidyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, 2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, trifluoroethyl methacrylate, tetrafluoropropyl methacrylate, pentafluoropropyl methacrylate, octafluoropentyl methacrylate, pentafluorooctyl methacrylate, heptadecafluorodecyl methacrylate, N,N-dimethyl (meth)acrylamide, acryloyl morpholine, (meth)acrylonitrile, polyethylene glycol (meth)acrylate, polypropylene glycol (meth)acrylate, polyethylene glycol-polypropylene glycol (meth)acrylate, polyethylene glycol-polybutylene glycol (meth)acrylate, polypropylene glycol-polybutylene glycol General-purpose (meth)acrylates such as (meth)acrylic monomers containing a polyoxyalkylene group, such as alcohol (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, ethoxypolyethylene glycol (meth)acrylate, butoxypolyethylene glycol (meth)acrylate, octyloxypolyethylene glycol (meth)acrylate, lauryloxypolyethylene glycol (meth)acrylate, stearyloxypolyethylene glycol (meth)acrylate, phenoxypolyethylene glycol (meth)acrylate, methoxypolypropylene glycol (meth)acrylate, and octyloxypolyethylene glycol-polypropylene glycol (meth)acrylate.

[0077] Among them, homopolymers containing acrylates show a relatively low glass transition temperature, and therefore, it is preferred that the main component be an acrylate having an alkyl group with 1 to 20 carbon atoms, and preferably an acrylate having an alkyl group with 1 to 12 carbon atoms. Examples of such acrylates having an alkyl group with 1 to 12 carbon atoms include methyl acrylate, ethyl acrylate, isopropyl acrylate, allyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl (meth)acrylate, tert-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, and n-lauryl (meth)acrylate. The (meth)acrylate used as a constituent component of the styrene acrylic copolymer (A) of the present invention may be one kind or two or more kinds.

[0078] As a constituent component of the styrene acrylic copolymer (A), other known polymerizable compounds other than styrenes, (meth)acrylates, and (meth)acrylic acid may be contained.

[0079] The core-shell structure of the so-called styrene acrylic copolymer (CA) is formed by having a region where a large amount of "styrene-(meth)acrylate copolymer" exists and a region where a large amount of "styrene-(meth)acrylate-(meth)acrylic acid copolymer" exists. In this core-shell structure, for example, a "styrene-(meth)acrylate-(meth)acrylic acid copolymer" may exist in a region where a large amount of "styrene-(meth)acrylate copolymer" exists, and these copolymers may also be polymerized with each other. In order to improve the stability in an aqueous medium, it is preferred that the "styrene-(meth)acrylate-(meth)acrylic acid copolymer" having an acidic group becomes a shell component, but a part of the "styrene-(meth)acrylate-(meth)acrylic acid copolymer" may also exist in the core.

[0080] The styrene acrylic copolymer (A) may contain a wax (W2) described later. By containing the wax (W2) in the styrene acrylic copolymer (A), water resistance can be further improved. The wax (W2) may be present in the core portion or in the shell portion. It may also be present on the surface of the styrene acrylic copolymer (A).

[0081] In the styrene acrylic copolymer (A), the ratio of the "copolymer of styrenes and (meth)acrylate" to the "copolymer of styrenes, (meth)acrylate and (meth)acrylic acid" is preferably in the range of 20:80 to 95:5, more preferably in the range of 30:70 to 92:8, and most preferably in the range of 40:60 to 90:10 in terms of mass ratio.

[0082] In the copolymer of styrenes and (meth)acrylates, the mass ratio of styrenes to (meth)acrylates is preferably in the range of 20:80 to 80:20, more preferably in the range of 30:70 to 70:30, and most preferably in the range of 40:60 to 60:40.

[0083] In the copolymer of styrene, (meth)acrylate and (meth)acrylic acid, the proportion of styrene is preferably 10 to 90% by mass, more preferably 20 to 80% by mass, and most preferably 30 to 70% by mass. In addition, in the copolymer of styrene, (meth)acrylate and (meth)acrylic acid, the proportion of (meth)acrylate is preferably 10 to 80% by mass, more preferably 15 to 70% by mass, and most preferably 20 to 60% by mass. In addition, in the copolymer of styrene, (meth)acrylate and (meth)acrylic acid, the proportion of (meth)acrylic acid is preferably 10 to 70% by mass, more preferably 15 to 60% by mass, and most preferably 20 to 50% by mass.

[0084] When the styrene acrylic copolymer (A) contains other known polymerizable compounds other than styrenes, (meth)acrylates and (meth)acrylic acid, the proportion of other polymerizable compounds in the styrene acrylic copolymer (A) is preferably 10% by mass or less, and preferably 5% by mass or less.

[0085] The glass transition temperature (hereinafter sometimes referred to as Tg) of the styrene acrylic copolymer (A) is in the range of -30 to 10°C, preferably -25 to 5°C, more preferably -20 to 0°C. In the present invention, the glass transition temperature is obtained by measurement using a differential scanning calorimeter.

[0086] The styrene acrylic copolymer (A) can be produced by a known method. For example, it can be obtained by the following steps (i) and (ii), wherein the step (i) is: supplying a monomer mixture to form a shell polymer, and polymerizing the monomer mixture in the presence of an initiator to form a shell polymer; the step (ii) is: supplying a monomer mixture to form a core polymer to the shell polymer of the step (i), and polymerizing the monomer mixture in the presence of an initiator to form a shell on the core polymer. In addition, it can be obtained by the following steps (1) and (2), wherein the step (1) is: supplying a monomer mixture to form a core polymer, and polymerizing the monomer mixture in the presence of an initiator to form a core polymer; the step (2) is: supplying a monomer mixture to form a shell polymer to the core polymer of the step (1), and polymerizing the monomer mixture in the presence of an initiator to form a shell on the core polymer.

[0087] As the initiator, there is no particular limitation, and the peroxide, persulfate, azo compound, or redox system or mixture thereof used in the emulsion polymerization method etc. can be used. As the peroxide, for example, hydrogen peroxide, ammonium peroxide, sodium peroxide, or potassium peroxide, tert-butyl peroxide, tert-butyl hydroperoxide, cumene hydroperoxide, and benzene peroxide can be mentioned. In addition, as the persulfate, for example, ammonium persulfate, sodium persulfate, or potassium persulfate can be mentioned. In addition, as the azo compound, for example, 2,2-azobisisobutyronitrile and 4,4'-(4-cyanovaleric acid) can be mentioned. In addition, the redox system is composed of an oxidant and a reductant, and as the oxidant, for example, one of the peroxides, persulfate, or azo compound, or sodium chloride or potassium chloride, or sodium bromide or potassium bromide can be mentioned above. Examples of the reducing agent include ascorbic acid, glucose, or ammonium, sodium or potassium hydrogen sulfate, sodium or potassium hydrogen sulfite, sodium or potassium thiosulfate, sodium or potassium thiosulfate, or sodium or potassium sulfide, or ammonium iron (II) sulfate.

[0088] Among them, persulfates are preferred, and ammonium persulfate is more preferred.

[0089] The polymerization of the above-mentioned monomer mixture can be carried out in the presence of additives such as surfactants, chain transfer agents, chelating agents, etc., for example, in the presence of surfactants and chain transfer agents. These additives may be added in advance to the aqueous medium used in step (i) and / or step (ii), step (1) and / or step (2), or may be mixed with the monomer mixture supplied in step (i) and / or step (ii), step (1) and / or step (2).

[0090] Among them, the styrene acrylic copolymer (A) is preferably polymerized in the presence of a wax (W2) to form a monomer mixture. The wax (W2) may be added in advance to the aqueous medium used in step (i) and / or step (ii), step (1) and / or step (2), or mixed with the monomer mixture supplied in step (i) and / or step (ii), step (1) and / or step (2), thereby forming a core-shell structure in which the wax (W2) is incorporated into the styrene acrylic copolymer (A).

[0091] The surfactant is not particularly limited, and examples thereof include disodium dodecyl diphenyl ether and disulfonates. The chain transfer agent is also not particularly limited, and examples thereof include α-methylstyrene dimer, thioglycolic acid, sodium hydrogen phosphite, 2-mercaptoethanol, N-dodecyl mercaptan, and tert-dodecyl mercaptan. The chelating agent is not particularly limited, and examples thereof include ethylenediaminetetraacetic acid.

[0092] When neutralization is required, as the neutralizing agent, ammonia, triethylamine, aminomethylpropanol, monoethanolamine, diethylaminoethanol, a base such as sodium hydroxide and potassium hydroxide can be used.

[0093] (Wax(W2))

[0094] The water-resistant outer coating composition (OCM) can further improve water resistance by containing wax (W2). The wax (W2) is preferably selected from at least one of paraffin wax, microcrystalline wax, oxidized polyethylene wax, and amide wax, and more preferably paraffin wax or microcrystalline wax. These can be used alone or in combination.

[0095] The melting point of the wax (W2) is preferably in the range of 30°C to 130°C, more preferably in the range of 50°C to 100°C.

[0096] The amount of the wax (W2) blended is preferably 0.5 to 20% by mass, more preferably 1 to 15% by mass, based on 100% by mass of the styrene acrylic copolymer (A).

[0097] The wax (W2) may be dispersed in the water-resistant coating layer, and as described above, it is preferably present in the core and / or shell of the styrene acrylic copolymer (A) so as to be integrated with the styrene acrylic copolymer (A). In the water-resistant coating layer, the wax (W2) may be a mixture of waxes present in the form of being contained in the styrene acrylic copolymer (A) and waxes present without being contained in the styrene acrylic copolymer (A).

[0098] The wax (W2) can be directly added to the emulsion containing the styrene acrylic copolymer (A) and mixed and dispersed, or it can be mixed with the emulsion after making the dispersion of the wax (W2). Regarding the dispersion method, as a known method, for example, as a dispersion device using a medium, a paint stirrer, a ball mill, a grinder, a basket grinder, a sand mill, a sand grinder, a DYNO-MILL, a DISPERMAT disperser, an SC mill, a nail crusher, a stirring mill, etc. can be used, and an ultrasonic homogenizer, a high-pressure homogenizer, a NANOMIZER pulverizer, a dissolver, a disperser, a high-speed impeller disperser, etc. can be used as a dispersion device without using a medium to disperse.

[0099] When using wax powder, it is preferable to grind with a medium in order to disperse the wax uniformly. Meat), or after preparing the dispersion of wax. The grinding method can be carried out by a known method.

[0100] When a plurality of waxes are used in combination, the plurality of waxes may be added simultaneously or may be added in a plurality of steps.

[0101] When the wax (W2) is contained in the styrene acrylic copolymer (A), as described above, the polymerization of the monomer mixture constituting the styrene acrylic copolymer (A) can be carried out in the presence of the wax (W2).

[0102] (Other additives)

[0103] The water-resistant outer coating composition (OCM) may further contain additives such as silica, alumina, wax, defoamer, leveling agent, tackifier, preservative, antibacterial agent, rust inhibitor, etc., in addition to the above-mentioned components, within the scope not hindering the purpose of the present invention. In addition, other resins other than the styrene acrylic copolymer (A) may also be contained.

[0104] Among them, it is preferred to further mix a leveling agent and / or a wax.

[0105] The further formulated wax is a wax (W3) added in addition to the above wax (W2). By including the wax (W3), the blocking resistance, scratch resistance and sliding property of the coated paper coated with the water-resistant outer coating of the present invention can be improved when laminating.

[0106] Examples of the wax (W3) include fatty acid amide wax, carnauba wax, polyolefin wax, paraffin wax, Fischer-Tropsch wax, beeswax, microcrystalline wax, oxidized polyethylene wax, amide wax and the like. These may be used alone or in combination.

[0107] Among them, fatty acid amide wax, carnauba wax, Fischer-Tropsch wax, polyolefin wax, and paraffin wax are preferably used, and carnauba wax, polyolefin wax, and paraffin wax are particularly preferably used.

[0108] Specific examples of fatty acid amide waxes include nonanoic acid amide, capric acid amide, undecanoic acid amide, lauric acid amide, tridecanoic acid amide, myristic acid amide, pentadecanoic acid amide, palmitic acid amide, heptadecanoic acid amide, stearic acid amide, nonadecanoic acid amide, arachidic acid amide, behenic acid amide, tetracosanoic acid amide, oleic acid amide, hexadecenoic acid amide, linoleic acid amide, linolenic acid amide, mixtures thereof, and animal and plant oil fatty acid amides.

[0109] Specific examples of the carnauba wax include MICROKLEAR 418 (manufactured by Micro Powders, Inc.) and purified carnauba wax No. 1 powder (manufactured by NIPPON WAX Co., Ltd.).

[0110] Specific examples of the olefin wax include polyethylene wax and polypropylene wax, for example, MPP-635VF (Micro Powders, Inc.), MP-620VF XF (Micro Powders, Inc.), CHEMIPEARL W-400 (manufactured by Mitsui Chemicals, Inc.), and the like.

[0111] Regarding the amount of wax (W3), the total amount of wax (W3) is preferably 0.3 to 10% by mass relative to the total amount of 100% by mass of the solid content in the composition of the present invention. If the total amount of wax (W3) is 0.3% by mass or more relative to the total amount of 100% by mass of the solid content in the composition of the present invention, there is a tendency to maintain anti-blocking properties, and more preferably 0.5% by mass or more. In addition, if the total amount of wax (W3) is 10% by mass or less relative to the total amount of 100% by mass of the solid content of the water-based heat sealant, the sliding angle will not become too large, so there is a tendency to maintain good workability, preferably 5% by mass or less, and more preferably 3% by mass or less.

[0112] In addition, from the viewpoint of oil resistance and heat resistance, the melting point of the wax (W3) is preferably in the range of 80°C to 130°C.

[0113] The wax (W3) may be directly added to the emulsion of the resin containing the styrene acrylic copolymer (A) and mixed and dispersed, or the wax dispersion may be prepared and mixed with the emulsion. In order to improve the blocking resistance, it is preferred that the wax (W3) is not incorporated into the styrene acrylic copolymer (A) but is dispersed so as to be present near the surface of the water-resistant coating.

[0114] The type of leveling agent is not particularly limited, and acetylene surfactants are preferably used. As acetylene surfactants, specifically, 2,5-dimethyl-3-hexyne-2,5-diol, 3,6-dimethyl-4-octyne-3,6-diol, 2,4,7,9-tetramethyl-5-decyne-4,7-diol, 3,5-dimethyl-1-hexyne-3-ol, 3-methyl-1-butyne-3-ol, 3-methyl-1-pentyne-3-ol, 3-hexyne-2,5-diol, 2-butyne-1,4-diol, etc. can be mentioned. Examples of commercially available products include oxyalkylene non-modified acetylene glycol surfactants such as Surfynol 61, 82, and 104 (all manufactured by Air Products), Surfynol 420, 440, 465, 485, TG, 2502, and DYNOL 604 and 607 (all manufactured by Air Products), Surfynol SE, MD-20, OLFINE E1004, E1010, PD-004, EXP4300, PD-501, PD-502, and SPC (all manufactured by Nissin Chemical Industries, Ltd.), and Acetylenol EH, E40, E60, E81, E100, and E200 (all manufactured by KaWaken Fine Chemicals Co., Ltd.).

[0115] The amount of the leveling agent added is preferably 0.01 to 0.1% by weight of the total amount of the paper outer coating composition.

[0116] By using wax (W3) and a leveling agent in combination, it is possible to improve adhesion while maintaining leveling properties.

[0117] In addition, in order to prevent the composition from bubbling when the water-resistant outer coating composition (OCM) is used to coat paper, the water-resistant coating of the present invention is preferably combined with a polymer defoamer, a silicon defoamer, or a fluorine defoamer. As these defoamers, any of an emulsified dispersion type and a solubilized type can be used. Among them, a polymer defoamer is preferred. As the addition amount of the above-mentioned defoamer, it is preferably 0.005% by weight to 0.1% by weight of the total amount of the outer coating composition for paper.

[0118] <Method for forming water-resistant coating>

[0119] The water-resistant coating of the present invention is preferably formed using a water-resistant outer coating composition containing at least a styrene acrylic copolymer (A), a wax (W2) and an aqueous solvent. The water-resistant coating is provided on a paper substrate, for example, by coating the paper substrate.

[0120] As a method for coating the water-resistant outer coating composition (OCM) on the paper substrate, a known method can be used. For example, any one of a comma coater, a roll coater, a reverse roll coater, a direct gravure coater, a reverse gravure coater, an offset gravure coater, a roll kiss coater, a reverse kiss coater, a kiss gravure coater, a reverse kiss gravure coater, an air knife coater, a knife coater, a rod coater, a wire rod coater, a die coater, a lip coater, a dip coater, a knife coater, a brush coater, a curtain coater, a slot coater, an offset printing press, a screen printing press, etc., or a combination of two or more coating methods can be used.

[0121] In addition, a water-resistant coating layer can be provided on a paper substrate by impregnating the paper substrate with the water-resistant outer coating composition of the present invention. In addition, a drying step using an oven or the like can be provided after coating.

[0122] The film thickness of the water-resistant outer coating composition (OCM) during coating depends on the application. When used in a paper food container, for example, a film thickness of 1 to 10 g / m2 can fully achieve the effects of the present invention, and a film thickness of 2 to 6 g / m2 is more preferred.

[0123] The water-resistant coating formed as described above has excellent water resistance and can maintain water resistance. Preferably, the contact angle of the water-resistant coating of the present invention is maintained at more than 70 degrees, preferably more than 75 degrees, and more preferably more than 80 degrees 30 minutes after water is added. In addition, preferably, the contact angle of the water-resistant coating of the present invention is maintained at more than 50 degrees, preferably more than 60 degrees, preferably more than 70 degrees, and more preferably more than 75 degrees 40 minutes after water is added. The contact angle can be easily measured using a known contact angle measuring device (for example, an automatic contact angle measuring device manufactured by Kyowa Interface Chemical Co., Ltd.).

[0124] In addition, the water-resistant coating formed as described above has excellent moisture resistance and can maintain moisture resistance. The water vapor permeability of the water-resistant coating of the present invention when maintained at a temperature of 25°C and a relative humidity of 50% RH for 7 days is preferably 500 g / m2·day or less, preferably 300 g / m2·day or less, preferably 250 g / m2·day or less, and preferably 200 g / m2·day or less. In addition, the water vapor permeability when maintained at a temperature of 40 degrees for 7 days is preferably 1000 g / m2·day or less, preferably 600 g / m2·day or less, preferably 500 g / m2·day or less, and preferably 400 g / m2·day or less.

[0125] In addition, the water-resistant coating of the present invention is excellent in abrasion resistance.

[0126] By applying the above-mentioned water-resistant outer coating composition (OCM) to a paper substrate and providing a water-resistant coating on the paper substrate, a water-resistant paper having water resistance, moisture resistance and recyclability can be obtained. That is, the water-resistant coating of the present invention has excellent water resistance, moisture resistance and recyclability. Therefore, in the case of not providing a heat-sealable coating, only applying the water-resistant outer coating composition on the paper substrate can be used as water-resistant paper. The paper substrate and the coating method are the same as those of the water-resistant paper described later.

[0127] [Water-resistant paper]

[0128] The water-resistant paper of the present invention has at least the above-mentioned water-resistant coating layer and heat-sealable coating layer on a paper substrate, and can be directly recycled after use.

[0129] As the paper substrate, natural fibers for papermaking such as wood pulp are used and manufactured by a known papermaking machine, and the papermaking conditions are not particularly specified. As natural fibers for papermaking, wood pulps such as conifer pulp and broadleaf pulp, non-wood pulps such as Manila hemp pulp, sisal pulp, and flax pulp, and pulps obtained by chemically modifying these pulps can be cited. As the type of pulp, chemical pulps, ground pulps, chemically ground pulps, thermomechanical pulps, etc. based on sulfate digestion, acid / neutral / alkaline sulfite digestion, soda salt digestion, etc. can be used. In addition, various commercially available high-quality papers, coated papers, lining papers, impregnated papers, thick paperboards, paperboards, etc. can also be used.

[0130] The paper substrate may be selected in accordance with the purpose, the type of paper, the thickness, etc. For example, if it is a hamburger package, it is preferably corresponding to a gram weight (Japanese: meter square) of 20 g / m 2 If it is a paper cup, it is preferably corresponding to a gram weight of 200 to 300 g / m 2 For paper plates, paper spoons, paper stirring sticks (Japanese: Madoka-), etc., preferably corresponds to a gram weight of 50 to 500 g / m 2 The paper base material is preferably not laminated with a polyethylene film, aluminum, etc. from the viewpoint of recycling efficiency and cost reduction. The paper base material may have a printed layer.

[0131] [Packaging or container]

[0132] The water-resistant paper of the present invention has excellent water resistance and moisture resistance, and can be used as water-resistant paper and / or moisture-proof paper. In addition, the water-resistant paper of the present invention can be used as various packaging bodies or containers. In addition, by heat-sealing the coating part with heat sealability, it can be processed into boxes, bags, and containers.

[0133] Examples of packaging bodies include bags, paper bags, cartons, corrugated paper, wrapping paper, envelopes, cup sleeves, covers, etc. for packaging. Examples of containers include paper containers, paper plates, trays, cup holders, etc. The water-resistant paper of the present invention can be used for foods, groceries, daily necessities, etc. that require water resistance and moisture resistance. In addition, it can also be used for packaging foods, groceries, and daily necessities that contain liquid or moisture. For example, paper cups, cup noodles, various beverages, cups or covers for desserts such as ice cream, pudding, and jelly, rice snacks, potato chips, chocolate snack bags or boxes, snack snack bags or boxes such as biscuits, wrapping paper for hamburgers and hot dogs, packaging containers for pizzas, etc., containers for hot snacks such as fried foods and potatoes, cups for home-cooked dishes such as natto, bags for rice and grains, and food paper containers or packaging materials, bags or boxes for sanitary products such as detergents and sanitary products, etc. Depending on the application, the packaging material or container may have a water-resistant coating on the inner side, the outer side, or both the inner side and the outer side.

[0134] The water-resistant paper of the present invention is also preferably used for labels of bottles and cans, protective tapes, paper tapes such as masking tapes, books such as books and magazines, posters, calendars, etc. The water-resistant coating functions as an outer coating of the paper substrate having a printed layer.

[0135] In addition, by using water-resistant paper having both a water-resistant coating and a heat-sealable coating, the heat-sealable coating portion is sealed to form a bag, a box, or a wrapping paper. For example, there can be mentioned pillow-shaped bags for packaging snacks, envelope-shaped bags, bags for general merchandise, cosmetic boxes, bags or boxes for packaging pizzas, donuts, etc., open-shaped wrapping paper for packaging hamburgers, hot dogs, etc., partially having a heat-sealable portion, and tube-shaped containers.

[0136] Hereinafter, the present invention will be described in detail based on Examples, but the technical scope of the present invention is not limited to these embodiments.

[0137] Example

[0138] In the following examples, "parts" means "parts by mass" and "%" means "% by mass".

[0139] <Synthesis of Styrene Acrylic Copolymer (A)>

[0140] (Production Example 1)

[0141] In a 4-necked flask replaced with nitrogen, 100 parts of isopropanol were added, and after the temperature was raised to 80-82°C, a mixture of 30 parts of styrene, 15 parts of 2-ethylhexyl acrylate, 20 parts of (meth)acrylic acid, 5 parts of methyl methacrylate, and 1 part of benzoyl peroxide added to the dropping funnel was added dropwise over 2 hours. After the addition was completed, 0.5 parts of benzoyl peroxide was added and the reaction was further carried out for 2 hours. The temperature was lowered to 40°C, and dimethylethanolamine and ion exchange water were added. Thereafter, the temperature of the reaction flask was raised to 80-82°C, and stripping was performed to finally obtain a water-soluble resin with a solid content of 30%.

[0142] 2 parts by mass of paraffin wax (paraffin 155, manufactured by Nippon Seira Co., Ltd.) as a wax (W2) were added to the water-soluble resin obtained above, and the mixture was stirred to prepare a wax dispersion. Next, the wax dispersion and 10 parts of ion exchange water were added to a reaction flask, and after the temperature was raised to 80°C to 82°C, 2 parts of potassium persulfate were added, and a mixture of 30 parts of styrene and 24 parts of 2-ethylhexyl acrylate was dripped over 2 hours. After the dripping was completed, 0.2 parts of potassium persulfate was added, and the reaction was carried out for 2 hours. The solid content of the aqueous dispersion (A-1) of the styrene acrylic copolymer obtained in this way was 35%, and the glass transition point was -10°C.

[0143] (Production Example 2)

[0144] In the synthesis of the styrene acrylic acid copolymer (A-1), except that microcrystalline wax (Hi-Mic-1080, manufactured by Nippon Seiro Co., Ltd.) was added instead of paraffin wax, the same operation as the synthesis of the styrene acrylic acid copolymer (A-1) was performed to obtain an aqueous dispersion (A-2) of a styrene acrylic acid copolymer. The aqueous dispersion (A-2) had a solid content of 35% and a glass transition point of -10°C.

[0145] <Production Example 3>

[0146] As the styrene acrylic copolymer (A), a copolymer of styrene and (meth) acrylic ester, and a copolymer of styrene, (meth) acrylic ester and (meth) acrylic acid, which forms a core-shell structure and has a glass transition temperature in the range of -30°C to 10°C, a commercially available aqueous dispersion (A-3) of a styrene acrylic copolymer was used. The aqueous dispersion (A-3) had a solid content of 40% and a glass transition point of -21°C.

[0147] <Production of Laminated Body>

[0148] (Reference Examples 1 to 4)

[0149] The above-mentioned aqueous dispersions (A-1) to (A-3) were used to prepare a paper outer coating composition by mixing the composition according to Table 1 and stirring the composition with a disperser. The outer coating composition was prepared to a film thickness of 6 g / m 2 The film was applied to unbleached kraft paper (manufactured by Daio Paper Co., Ltd., weight per unit area: 70 g) in a manner and dried at 150° C. for 20 seconds using a dryer to produce laminates of Examples 1 to 4, respectively.

[0150] (Comparative Example 1)

[0151] The kraft paper used in Examples 1 to 4 was used directly without applying the outer coating composition.

[0152] (Comparative Example 2)

[0153] A laminate of Comparative Example 2 was obtained in the same manner as in Reference Examples 1 to 4 except that a comparative solvent-based varnish containing 13 parts of industrial nitrocellulose, 55 parts of isopropyl alcohol and 32 parts of ethyl acetate was used for the paper outer coating composition.

[0154] (Comparative Example 3)

[0155] A laminate of Comparative Example 3 was obtained in the same manner as in Reference Examples 1 to 4 except that a comparative aqueous varnish containing 28% of a styrene acrylic resin, 4 parts of isopropyl alcohol, and 68 parts of ion-exchanged water was used in the paper outer coating composition.

[0156] <Evaluation Items>

[0157] (Water resistance)

[0158] Tap water was collected in a dropper, and 0.1 ml of the water was dropped onto the surface of the coated paper test piece for evaluation provided with the water-resistant coating layer.

[0159] After the tap water was dropped, the tap water was wiped off after 1 hour, 4 hours, 5 hours, and 8 hours at 25°C, and the front and back surfaces were visually evaluated according to the following evaluation criteria.

[0160] ○: There is no trace of dripping, no swelling due to water, and no penetration to the back surface.

[0161] △: There are traces of dripping on the surface, and water has penetrated, but there is no penetration to the back side.

[0162] ×: There are traces of dripping on the surface, swelling caused by water, and penetration to the back side.

[0163] (Contact angle)

[0164] Tap water was collected in a dropper, and 0.1 ml of the water was dropped onto a coated paper test piece for evaluation. The contact angle was measured immediately, 30 minutes later, and 40 minutes later.

[0165] The contact angle was measured using an automatic contact angle meter manufactured by Kyowa Interface Chemical Co., Ltd.

[0166] (Blocking resistance)

[0167] The coated surfaces of the prepared water-resistant paper were overlapped in contact with each other, a load of 10 kgf / cm2 was applied, and after 48 hours at 40°C, the adhesion between the coated surface and the non-coated surface was visually evaluated according to the following 4 stages.

[0168] (Evaluation Criteria)

[0169] ⊚: No blocking was observed at all.

[0170] ○: Slight blocking was partially observed.

[0171] △: Blocking was partially observed.

[0172] ×: Blocking was observed on the entire surface.

[0173] (Sliding angle)

[0174] The coated surface of the produced water-resistant paper is overlapped in a contacting manner with the coated surface, and the tilt angle at which the coated paper starts to slide is measured as the sliding angle by the tilt method. The sliding angle is measured using a sliding angle tilt measuring device (manufactured by HEIDON). It should be noted that if the value of the sliding angle is too small, it is easy to cause load displacement (Japanese: load collapse) when overlapping. If it is too large, there is a possibility of stacking of the coated objects. Therefore, if there is an appropriate sliding angle, it becomes easy to take out the coated paper one by one from the stacked coated paper, and the workability is improved.

[0175] [Table 1]

[0176]

[0177] [Table 2]

[0178]

[0179] As the wax (W3) in the table, CHEMIPEARL W-400 (manufactured by Mitsui Chemicals, Inc.) was used.

[0180] In addition, Surfynol 420 (made by Nissin Chemical Industry Co., Ltd.) was used as the leveling agent in the table.

[0181] According to Reference Examples 1 to 4 and Comparative Examples 1 to 3, the provision of a water-resistant outer coating composition (OCM) resulted in improved water resistance. In addition, according to Reference Example 4, the further addition of wax (W3) improved blocking resistance, reduced sliding angles, and improved workability.

[0182] (Water vapor permeability)

[0183] Prepare a stainless steel cup and add 7g of water to the cup. Seal the top of the cup with water-resistant paper for evaluation with beeswax. Next, cut off the part protruding from the cup to make a sample bottle. Measure the initial weight of the sample bottle, store it at the temperature and humidity described in Table 3, measure the sample weight every day, and calculate the amount of evaporated water. It should be noted that the humidity was not adjusted at 40°C.

[0184] The water-resistant paper used for the evaluation of water vapor permeability was the laminate of Reference Example 1, the kraft paper of Comparative Example 1, and the laminate of Comparative Example 4. The laminate of Comparative Example 4 was prepared in the same manner as Reference Example 1 except that an aqueous dispersion (solid content 30%) containing a commercially available styrene acrylic copolymer having a core-shell structure was used instead of the composition (OC-1) in Example 1.

[0185] The results are shown in Table 3.

[0186] [Table 3]

[0187]

[0188] According to Reference Example 1 and Comparative Examples 1 and 2, the water vapor permeability was significantly reduced by providing the water-resistant overcoat composition (OCM). It was confirmed that moisture resistance could be imparted by providing the water-resistant overcoat composition (OCM).

[0189] <Method for producing olefin-α,β-unsaturated carboxylic acid copolymer for heat sealant>

[0190] (Production Example 4)

[0191] 77.8 parts of ethylene, 11.1 parts of ethyl acrylate and 11.2 parts of acrylic acid were synthesized by a conventional method to obtain an ethylene ethyl acrylate acrylic acid copolymer.

[0192] 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 are added and stirred to obtain an aqueous dispersion (H1) of olefin-α, β unsaturated carboxylic acid copolymer and fatty acid amide wax.

[0193] <Production of Water-Based Heat Sealant>

[0194] 67 parts of water and 3 parts of isopropyl alcohol were mixed with 30 parts of the aqueous dispersion (H1) obtained in Production Example 3 or Production Example 4 to prepare an aqueous heat sealant.

[0195] <Production of Laminated Body>

[0196] (Examples 1 to 12)

[0197] The paper substrates listed in Tables 4 to 7 were prepared, and a film having a thickness of 2 g / m was formed on one surface of the paper substrate. 2 The water-resistant outer coating composition used in Reference Example 1 was applied in a manner of 100° C. and dried at 150° C. for 20 seconds using a dryer. Next, a film having a thickness of 2 g / m 2 The aqueous heat sealant was applied in a manner of , and dried at 100° C. for 30 seconds using a dryer to produce laminates of Examples 5 to 10.

[0198] The same operation was performed to obtain a film thickness of 5 g / m2 of the paper outer coating composition and the aqueous heat sealant. 2 The coating was performed in a manner to produce the laminated bodies of Examples 11 to 18.

[0199] (Comparative Examples 5 to 18)

[0200] Laminated bodies of Comparative Examples 5 to 18 were prepared in the same manner as in Examples 1 to 12 except that the paper outer coating composition was not applied.

[0201] <Evaluation>

[0202] (Heat sealability)

[0203] The heat sealant coated surfaces of the laminates of Examples 5 to 18 were overlapped with each other, heated at a temperature range of 80°C to 140°C, and immediately used a heat sealer under the conditions of 0.2 MPa pressure and 1 second sealing to form a heat seal portion. The sealing condition was determined by peeling the heat seal portion and then determining the sealing condition according to the paper peeling and paper breaking (Japanese: The lowest temperature of the hot plate that achieves complete adhesion was investigated based on the evaluation of adhesion strength based on the occurrence of cuts.

[0204] 6: Completely sealed at 80°C.

[0205] 5: Completely sealed at 90°C.

[0206] 4: Completely sealed at 100°C.

[0207] 3: Completely sealed at 110℃.

[0208] 2: Completely sealed at 120°C.

[0209] 1: Not tight even at 130°C or above.

[0210] (Water resistance)

[0211] Tap water was collected in a dropper, and 0.1 ml was dripped onto the surface of the coated paper test piece for evaluation provided with the water-resistant coating. The dripping was performed on the convex folded portion, concave folded portion, flat portion provided on the laminate, and the sealed portion obtained by sheet sealing by the heat sealability evaluation method. After dripping the tap water, the tap water was wiped off at 25°C after 1 hour, 3 hours, 5 hours, and 24 hours, and the surface and back were visually evaluated according to the following evaluation criteria.

[0212] ○: There is no trace of dripping, no swelling due to water, and no penetration to the back surface.

[0213] △: There are traces of dripping on the surface, and water has penetrated, but there is no penetration to the back side.

[0214] ×: There are traces of dripping on the surface, swelling caused by water, and penetration to the back side.

[0215] (Recyclability)

[0216] The coated papers of Examples 1 to 12 produced in the evaluation of heat sealability were cut into pieces of 3.0 cm×5.0 cm, placed in a 1 mass % aqueous solution of sodium hydroxide, and stirred for 30 minutes using a paint shaker (Asada Iron Works Co., Ltd.). The state was then checked. As a result, the paper was fully dissociated and no film-like substance was confirmed.

[0217] On the other hand, a commercially available paper cup was cut into pieces of 3.0 cm×5.0 cm and the same evaluation was performed. As a result, it was confirmed that a film-like substance remained. Therefore, it was confirmed that the polyethylene film obtained in the example remained in a sheet-like state.

[0218] Therefore, it can be seen that the coated papers of Examples 1 to 12 do not reduce the paper recycling efficiency.

[0219] The evaluation results of each laminate of Examples 1 to 12 and Comparative Examples 5 to 18 are shown in the following table. Tables 4 and 5 are the results of the evaluation of the laminate of Examples 1 to 12 and Comparative Examples 5 to 18 after coating with the water-resistant outer coating composition (2 g / m 2 )、heat sealant (2g / m 2 ) results, Tables 6 and 7 are the results of coating the water-resistant outer coating composition (5g / m 2 ), heat sealant (5g / m 2 ) results.

[0220] [Table 4]

[0221]

[0222] [Table 5]

[0223]

[0224] [Table 6]

[0225]

[0226] [Table 7]

[0227]

[0228] The following materials were used as paper substrates in the table.

[0229] Silver Bamboo: Unbleached single-gloss kraft paper (manufactured by Nippon Paper Industries, Ltd., unit weight 50 g / m 2 )

[0230] Tokai Kraft Paper: Unbleached Kraft Paper (produced by Shin Tokai Paper Co., Ltd., with a unit weight of 50 g / m 2 )

[0231] Double-layer kraft paper: Double-layer unbleached kraft paper (made by Nippon Paper Industries, Ltd., unit weight 50g / m 2 )

[0232] Silver (a): Single gloss kraft paper (manufactured by Nippon Paper Industries, Ltd., unit weight 24 g / m 2 )

[0233] Silver (b): Single gloss kraft paper (manufactured by Nippon Paper Industries, Ltd., 50 g / m 2 )

[0234] Single gloss white kraft paper: Single gloss kraft paper (made by Nippon Paper Industries, Ltd., 50g / m 2 )

[0235] Tables 4 to 7 show that the laminated bodies of the examples have excellent water resistance and no water permeation. No water permeates any of the convex folds, concave folds, and heat-sealed parts. In addition, it can be confirmed that sufficient heat-sealing properties can be exhibited even when both the water-resistant coating and the heat-sealing agent are applied. Although there are slight differences depending on the paper used, when 2 g / m 2 When heat sealant is used, high sealing strength can be obtained at about 110℃ to 120℃. 2 When using a heat sealant, good sealing strength can be obtained even at a low temperature of 90°C.

Claims

1. A water-resistant paper, characterized in that: have: Paper substrate, a water-resistant coating disposed on at least a portion of the paper substrate, and A heat-sealable coating is provided on a portion different from the portion having the water-resistant coating, The water-resistant coating contains styrene acrylic copolymer A and wax W2, The wax W2 is at least one wax selected from polyolefin wax, paraffin wax, microcrystalline wax, oxidized polyethylene wax, and amide wax. The styrene acrylic copolymer A comprises a copolymer of styrene and (meth)acrylate, and a copolymer of styrene, (meth)acrylate and (meth)acrylic acid to form a core-shell structure. The glass transition temperature of the styrene acrylic copolymer A is in the range of -30°C to 0°C.

2. The water-resistant paper according to claim 1, wherein: The heat-sealable coating contains an olefin-α,β-unsaturated carboxylic acid copolymer and a wax W1. The wax W1 is at least one selected from fatty acid amide wax, carnauba wax, polyolefin wax, paraffin wax, Fischer-Tropsch wax, beeswax, microcrystalline wax, oxidized polyethylene wax, amide wax, coconut oil fatty acid, and soybean oil fatty acid.

3. The water-resistant paper according to claim 2, wherein: The wax W1 is fatty acid amide wax and / or carnauba wax.

4. The water-resistant paper according to any one of claims 1 to 3, wherein The glass transition temperature of the styrene acrylic copolymer A is in the range of -25°C to 0°C.

5. The water-resistant paper according to any one of claims 1 to 3, wherein The contact angle of the water-resistant coating 30 minutes after water is dropped is 70° C. or more.

6. The water-resistant paper according to any one of claims 1 to 3, wherein The styrene acrylic copolymer A contains the wax W2.

7. A package or container using the water-resistant paper according to any one of claims 1 to 6.

8. A package or container, which is assembled by using the water-resistant paper according to any one of claims 1 to 6 and laminating a heat-sealable coating layer provided on the water-resistant paper.

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