CN116134193A

CN116134193A - Water-resistant paper, and wrapping paper or container using same

Info

Publication number: CN116134193A
Application number: CN202180061331.4A
Authority: CN
Inventors: 榎本肇; 菊池�浩; 田中克则
Original assignee: DIC Graphics Corp
Current assignee: DIC Graphics Corp
Priority date: 2020-10-01
Filing date: 2021-09-28
Publication date: 2023-05-16
Also published as: JPWO2022071261A1; JP7130168B1; WO2022071261A1

Abstract

The present invention relates to a water-resistant paper having a paper base, a water-resistant coating layer provided on at least a part of the paper base, and a heat-sealable coating layer provided on a part different from the part having the water-resistant coating layer. According to the present invention, there are provided a water-resistant paper having a water-resistant coating layer capable of imparting excellent water resistance and moisture resistance to paper only by coating and capable of improving the recyclability of the paper by becoming a substitute for paper laminated with a plastic film, and a packaging paper or container using the water-resistant paper.

Description

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

Technical Field

The present invention relates to water-resistant paper, and a packaging paper or container using the same.

Background

Paper packaging materials such as paper bags, cartons, paper cups and the like have been conventionally used for various purposes and purposes. In recent years, in order to replace plastic materials, there has been a growing trend in the use of "paper" using "wood" as a renewable resource as one of the materials having functions such as "recyclability" and "biodegradability", as a substitute for marine plastic waste, which is typified by microplastic.

One of the paper containers widely used in the past is paper cups used as containers for beverages, ice cream, yogurt, and the like. Paper cups are provided with water resistance by using a polyethylene film as a part of the raw material of paper. Such paper cups are obtained by bonding a polyethylene film, a polypropylene film, or the like, which is obtained by extruding a polyethylene resin, a polypropylene resin, or the like, which is melted by heat, into a film shape, to a paper base material. The polyethylene film functions as an adhesive by heat fusion under indirect heating such as a burner or hot air during paper cup molding, and the polyethylene film is present inside the paper cup, so that the paper substrate is not directly in contact with the contents, and is imparted with water repellency, moisture resistance, and strength.

However, the attached polyethylene film is not dissolved in the alkali solution used in the paper recycling process at the time of paper recycling, and thus needs to be physically removed, resulting in a decrease in recycling efficiency. In addition, marine pollution caused by outflow of plastic waste to the ocean becomes a worldwide problem. The following and the like are important topics worldwide: as an index of sustainable development targets (SDGs), a target of "preventing and greatly reducing all kinds of marine pollution including marine waste and eutrophication, particularly pollution caused by land activities, etc." has been proposed by 2025, and an agreement of enhanced cooperation has been achieved also at a peak (major national head office). Accordingly, there is a need for polyethylene film alternatives that can be applied to these uses without reducing the paper recycling efficiency.

On the other hand, as a substance that functions as an adhesive at the time of molding of bags, boxes, paper cups, and the like, an aqueous heat sealing agent is known. For example, patent document 1 discloses the following: an aqueous dispersion of an olefin- α, β -unsaturated carboxylic acid copolymer neutralized with ammonia or an amine and an olefin-based thermoplastic resin other than the above-mentioned copolymer are mixed and dispersed in a specific ratio, and can be used as a heat sealing agent.

Patent document 2 discloses the following: an aqueous dispersion containing a polyolefin resin comprising an unsaturated carboxylic acid unit, a vinyl hydrocarbon, and an acrylic acid ester or 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 disclose only so-called heat-sealing properties such as heat-sealing strength and blocking resistance, but do not describe any water resistance, moisture resistance, strength and recyclability that are desired as alternatives to polyethylene films.

Prior art literature

Patent literature

Patent document 1: japanese patent laid-open No. 2000-7860

Patent document 2: japanese patent laid-open No. 2006-45313

Disclosure of Invention

Problems to be solved by the invention

The present invention provides a water-resistant paper having a water-resistant coating layer capable of imparting excellent water resistance and moisture resistance to paper only by coating and capable of improving the recyclability of paper by replacing paper laminated with a plastic film, and a packaging paper or container using the water-resistant paper. Further, the coated paper of the present invention has a heat-sealable coating layer, and thus provides a water-resistant paper having a heat-sealing function in addition to water resistance and moisture resistance, and a packaging paper or container using the water-resistant paper.

Means for solving the problems

Namely, the present invention provides a water-resistant paper having:

a paper base material,

A water-resistant coating layer provided on at least a part of the paper base material, and a method for producing the same

And a heat-sealable coating layer provided on a portion different from the portion having the water-resistant coating layer.

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

Effects of the invention

The water-resistant paper of the present invention has a water-resistant coating layer that imparts excellent water resistance and moisture resistance to the paper only by coating, and therefore is excellent in water resistance and moisture resistance, and can improve recyclability. Further, the coated paper of the present invention has a heat-sealable coating layer, and thus can realize a water-resistant paper having a heat-sealing function in addition to water resistance and moisture resistance. The water-resistant layer and the heat-sealable coating layer provided on the water-resistant paper of the present invention may be formed of a material having 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 can be used in packaging and containers.

Detailed Description

The coated paper of the present invention comprises: a water-resistant coating layer provided on at least a part of the paper base material, and a heat-sealable coating layer provided on a part different from the part having the water-resistant coating layer.

In the present invention, (meth) acrylate means a generic term of acrylate and methacrylate, and (meth) acrylic acid means a generic term of acrylic acid and methacrylic acid.

[ Heat-sealable coating ]

In the water-resistant paper, the heat-sealable coating layer is provided at an appropriate portion on the paper base material according to the final packaging material, the shape of the container, and the use, but for example, in the paper base material, it is more preferable to provide the heat-sealable coating layer on the surface opposite to the surface on which the water-resistant coating layer is provided.

The water-resistant paper of the present invention has a heat-sealing function by the coating layer having heat-sealability, and has improved water resistance. Further, by attaching the heat-sealed portion, various packaging materials such as bags and boxes can be produced according to the application, and the workability improves.

The heat-sealable coating layer may be formed by a known heat-sealable coating agent, but in order to improve water resistance, an aqueous heat-sealing agent (HS) containing an aqueous solvent, an olefin- α, β -unsaturated carboxylic acid copolymer, and a wax (W1) is preferably used. The aqueous heat sealing agent (HS) can be used as a heat sealing agent for manufacturing paper containers and the like, and the coating portion other than the sealing (bonding) portion also functions as a coating agent for imparting water repellency to paper.

< Water-based Heat Sealant (HS) >)

The aqueous Heat Sealer (HS) contains at least an aqueous solvent, an olefin-alpha, beta unsaturated carboxylic acid copolymer, and a wax (W1).

(aqueous solvent)

As the aqueous solvent used for the aqueous heat sealing agent HS, water, a water-soluble organic solvent dissolved in water, or the like can be used. As the water, pure water such as ion-exchanged water, ultrafiltration water, reverse osmosis water, distilled water, or ultrapure water can be used. The water is preferably sterilized by ultraviolet irradiation, hydrogen peroxide addition, or the like, because it can prevent the generation of mold or bacteria when the aqueous pigment dispersion is stored for a long period of time, or when an ink using the pigment dispersion is used.

Examples of the water-soluble organic solvent 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 ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, and carbitol; glycol ethers such as cellosolve 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, and pentanol; and various other solvents known as aqueous organic solvents, such as lactones, e.g., sulfolane, ester, ketone, and γ -butyrolactone, lactams, e.g., N- (2-hydroxyethyl) pyrrolidone, and glycerin and polyoxyalkylene adducts thereof. These aqueous organic solvents may be used singly or in combination of two or more. Among them, water is most preferable.

(olefin-alpha, beta unsaturated carboxylic acid copolymer)

Examples of the olefin- α, β -unsaturated carboxylic acid copolymer used in the aqueous heat-sealing agent HS include copolymers of an olefin and at least 1 monomer selected from the group consisting of α, β -unsaturated carboxylic acids, metal salts of α, β -unsaturated carboxylic acids, and esters of α, β -unsaturated carboxylic acids. Specifically, examples of the metal salt of an α, β -unsaturated carboxylic acid, an α, β -unsaturated carboxylic acid or a copolymer of an α, β -unsaturated carboxylic acid ester and an olefin include an olefin- α, β -unsaturated carboxylic acid copolymer, an ethylene-acrylic acid ester 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 ester-maleic anhydride copolymer, and metal salts thereof. These copolymers may be used alone or in a mixture of 2 or more.

Among them, olefin- α, β unsaturated carboxylic acid copolymers are preferable. Examples of the olefin- α, β -unsaturated carboxylic acid copolymer include random copolymers or block copolymers of ethylene and α, β -unsaturated carboxylic acid.

Examples of the olefin include ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 4-methyl-1-pentene, butadiene, dicyclopentadiene, and 5-ethylidene-2-norbornene. Among them, ethylene is preferable.

Examples of the α, β -unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid, itaconic acid, and the like. Among these, acrylic acid and methacrylic acid are suitably used. These α, β -unsaturated carboxylic acids may be used singly or in combination of 2 or more.

The α, β -unsaturated carboxylic acid esters are not particularly limited, and known alkyl esters, hydroxyalkyl esters, alkoxyalkyl esters, and the like of acrylic acid or methacrylic acid can be used. For example, specific examples thereof include acrylic 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, 2-methoxyethyl acrylate, 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, 2-ethoxyethyl methacrylate, and the like. These may be used in 1 kind or in combination of 2 or more kinds.

The method for producing the olefin- α, β unsaturated carboxylic acid copolymer can be obtained by a known method, for example, radical copolymerization at high temperature and high pressure.

The content of the α, β -unsaturated carboxylic acid in the above-mentioned olefin- α, β -unsaturated carboxylic acid copolymer is desirably 8 to 24% by weight, preferably 18 to 23% by weight. When the content of the α, β -unsaturated carboxylic acid is less than 8% by weight, the dispersibility in an aqueous dispersion medium is poor due to the nonpolar nature derived from the ethylene unit, and there is a concern that it is difficult to obtain an excellent aqueous dispersion of the olefin- α, β -unsaturated carboxylic acid copolymer resin. 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 film may be deteriorated.

The olefin- α, β unsaturated carboxylic acid copolymer used in the aqueous heat sealer HS is used in the form of an aqueous dispersion dispersed in an aqueous solvent. The method of dispersing in the aqueous solvent is not particularly limited and may be carried out by a known method. Examples of the method include a method of dispersing an olefin- α, β unsaturated carboxylic acid copolymer in an aqueous solvent by emulsifying the copolymer with a surfactant, and a method of neutralizing the copolymer with a basic compound and dispersing the neutralized copolymer in an aqueous solvent.

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

Examples of the basic compound 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 singly or in combination of 2 or more.

The degree of neutralization by the basic compound may be any degree as long as the olefin- α, β -unsaturated carboxylic acid copolymer is stably present in the aqueous solvent. For example, the carboxyl group of the copolymer may be desirably 30 to 100 mol%, more preferably 40 to 90 mol%.

As the above-mentioned dispersing method, for example, as a dispersing device using a medium, a paint stirrer, a ball MILL, an attritor, a basket MILL, a sand MILL, a DYNO-MILL (DYNO-MILL), a DISPERMAT dispersing machine, an SC MILL, a nail crusher, a stirring MILL, etc. may be used, and dispersion may be performed using an ultrasonic homogenizer, a high-pressure homogenizer, a nano-zer crusher, a dissolver, a disperser, a high-speed impeller dispersing machine, etc. as a dispersing device not using a medium.

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 viscosity desired when it is applied as a heat sealer, the drying condition after the application of the heat sealer, the film thickness of the coating film, and the like. Generally, the present invention is generally applied in a range of 10 to 40 mass% in solid content concentration.

(wax (W1) for aqueous Heat Sealant (HS))

The wax (W1) is added to the aqueous Heat Sealer (HS), whereby blocking resistance can be maintained. Examples of the wax (W1) include waxes such as fatty acid amide wax, carnauba wax, polyolefin wax, paraffin wax, fischer-tropsch wax, beeswax, microcrystalline wax, oxidized polyethylene wax, and amide wax, coconut oil fatty acid, and soybean oil fatty acid. These may be used alone or in combination.

Among these, fatty acid amide waxes, carnauba waxes and Fischer-Tropsch waxes are preferable, and fatty acid amide waxes and carnauba waxes are particularly preferable.

Specific examples of the fatty acid amide wax include pelargonic acid amide, capric acid amide, undecanoic acid amide, lauric acid amide, tridecanoic acid amide, myristic acid amide, pentadecanoic acid amide, palmitic acid amide, margaric acid amide, stearic acid amide, nonadecanoic acid amide, arachic acid amide, behenic acid amide, lignoceric acid amide, oleic acid amide, hexadecenoic acid amide (Japanese, melissic acid amide), linoleic acid amide, linolenic acid amide, a mixture thereof, and animal and vegetable fat fatty acid amide.

Specific examples of the carnauba WAX include MICROKLEAR 418 (manufactured by MicroPowrers, inc.), refined carnauba WAX No. 1 powder (NIPPON WAX Co., ltd.), and the like.

The amount of the wax (W1) to be blended is preferably 1.5 to 20% by mass based on 100% by mass of the total amount of the solid components of the aqueous heat-sealing agent (HS). If the total amount of the wax (W1) is 3 mass% or more relative to the total 100% of the solid content of the aqueous heat-sealing agent (HS), the blocking resistance tends to be maintained, and if the total amount of the wax (W1) is 15 mass% or less relative to the total 100% of the solid content of the aqueous heat-sealing agent (HS), the heat-sealing property tends to be maintained.

In the wax (W1), the fatty acid amide wax and the carnauba wax are used in combination, and the blocking resistance is further improved, more preferably. In the case of the combination, the ratio thereof is not particularly limited, and preferably, a fatty acid amide wax: carnauba wax = 1:1 to 1: the range of 10 is preferred, and the range of 1:1 to 1:5 is more preferred.

The wax (W1) may be directly added to the aqueous dispersion of the olefin- α, β -unsaturated carboxylic acid copolymer and mixed and dispersed, or may be simultaneously added to and mixed and dispersed in dispersing the olefin- α, β -unsaturated carboxylic acid copolymer in an aqueous solvent. The dispersion method may be appropriately used as the method used in the above-mentioned dispersion method of the above-mentioned olefin- α, β -unsaturated carboxylic acid copolymer in an aqueous solvent.

When a plurality of waxes (W1) are used in combination, the plurality of waxes (W1) may be added simultaneously or may be added in a plurality of steps. For example, an aqueous Heat Sealant (HS) may be obtained by: after the first wax (W1) is added when the olefin- α, β unsaturated carboxylic acid copolymer is dispersed in an aqueous solvent, the second wax (W1) is further added to the aqueous dispersion of the obtained first wax (W1) and the olefin- α, β unsaturated carboxylic acid copolymer.

The aqueous heat sealing agent (HS) may contain additives such as silica, alumina, defoaming agent, viscosity modifier, leveling agent, thickener, preservative, antimicrobial agent, rust inhibitor, antioxidant, silicone oil, and the like, in addition to the above components, within a range that does not hinder the object of the present invention.

In addition, in the aqueous heat sealing agent (HS), in order to prevent foaming when coating using various coating machines, a polymer-based defoaming agent, a silicon-based defoaming agent, and a fluorine-based defoaming agent are preferably used. As these antifoaming agents, any of an emulsion dispersion type, a soluble type, and the like can be used. Among them, polymer-based antifoaming agents are preferable. The amount of the defoaming agent is preferably 0.005 to 0.1% by weight based on the total amount of the aqueous heat-sealing agent.

The aqueous heat sealing agent (HS) can be used as a heat sealing agent in the production of paper packaging materials such as bags and boxes, and as a coating agent for imparting water repellency to paper, the coating portion other than the sealing (bonding) portion is used.

< method for producing Heat-sealable coating layer >

The heat-sealable coating is provided by coating on, for example, a paper substrate using a known heat-seal coating or heat-seal (HS). As a coating method at the time of coating, a known method can be used. For example, roll coaters, gravure coaters, flexible coaters, air knife coaters, doctor blade coaters, air knife coaters, extrusion coaters, impregnating coaters, transfer roll coaters, kiss coaters, curtain coaters, cast coaters, spray coaters, die coaters, offset printers, screen printers, and the like can be used. In addition, a drying step may be provided by an oven or the like after the application.

In the case of using an aqueous heat sealing agent (HS), the film thickness of the solid component after coating may be a desired film thickness, for example, in the case of using it in a paper container for food, if it is 2 to 12g/m ² In the above range, water resistance and heat sealability can be sufficiently obtained. Of these, more preferably 5 to 10g/m ² Is not limited in terms of the range of (a).

The aqueous heat sealing agent (HS) has a function as an adhesive for bonding 2 portions of the paper substrate coated with the aqueous heat sealing agent in a superimposed state. Specifically, the aqueous heat sealing agent of the present invention is applied to at least one (or two) of 2 portions of the paper base material, and then softened by heating. The aqueous heat sealing agent is easily softened by heating with a burner or hot air, and can bond papers or papers with other raw materials, and thereafter, the bonding portion is solidified by cooling, whereby the papers or papers and other raw materials can be firmly sealed.

As the heating method, conventionally known means such as a heat source such as a burner, hot air, electric heat, infrared rays, and electron beams can be used, and specifically, a method of heating with a burner or hot air, a heat fusion sealing method according to a molded shape, an ultrasonic sealing method, or a high-frequency sealing method is preferable. The heating temperature in this case is preferably 200 to 500℃and the heating time is preferably 0.1 to 3 seconds.

In addition, the aqueous heat sealing agent (HS) is easily softened by heating without contact, and the heat sealing function is continued for a certain period of time even when it is separated from the heat source, in addition to the method of melting by contact with a direct heat source such as a heat sealing rod. In the case where the base material is paper, there is a possibility that the paper burns when in contact with a direct heat source, but the heat sealing agent of the present invention exhibits a heat sealing function under non-contact heating and the function is continued, and therefore, is particularly useful as a heat sealing agent for industrial production of paper containers, which requires a high line speed.

The aqueous heat sealing agent (HS) is applied and the applied portion is softened by heating, and then the applied portion is pressure-bonded in a state of being overlapped with another portion, whereby the aqueous heat sealing agent can be used as a heat sealing agent. The pressure bonding method is not particularly limited, and may be performed by a hot plate method, ultrasonic sealing, or high-frequency sealing. Of course, the aqueous heat sealing agent (HS) may be used as a paper coating agent without heat sealing. In this case, the film is coated to have a desired film thickness by the coating method, and then dried by a drying method such as heat drying or normal temperature drying.

[ Water-resistant coating ]

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

The water-resistant coating layer is preferably formed of a water-resistant Overcoating Composition (OCM) for paper containing an aqueous solvent, a styrene acrylic copolymer (a) and a wax (W2).

< Water-resistant Overcoat Composition (OCM) >)

The water-resistant Overcoating Composition (OCM) contains at least an aqueous solvent, a styrene acrylic copolymer (A) and a wax (W2).

(aqueous solvent)

As the aqueous solvent, the same solvent as that used in the above-mentioned aqueous heat sealing agent (HS) can be used.

(styrene acrylic copolymer (A))

Regarding the styrene acrylic copolymer (a), a copolymer of styrene and (meth) acrylate is preferable to form a core-shell structure, and a copolymer of styrene and (meth) acrylate and (meth) acrylic acid are more preferable to form a core-shell structure.

The styrene used as the constituent of the styrene-acrylic copolymer (a) is a polymerizable compound having a styrene skeleton, such as styrene, alpha-methylstyrene (either o-methylstyrene, m-methylstyrene, or p-methylstyrene, or a mixture thereof), a styrene dimer, a styrene trimer, and a styrene derivative (p-dimethylsilylstyroxystyrene, p- ヅ, p-tert-butyldimethylsilyloxy styrene, or p-tert-butylstyrene). The number of styrenes may be 1 or 2 or more. Among these, styrene is preferably used, and when 2 or more kinds of styrenes are used, styrene is preferably used as a main component, and for example, the mass ratio of styrene in the whole of styrenes is set to the maximum.

The (meth) acrylic ester used as the constituent of the styrene-acrylic copolymer (A) is not particularly limited, and for example, 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, n-lauryl (meth) acrylate, n-tridecyl (meth) acrylate, n-stearyl (meth) acrylate, phenyl (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate, 4-t-butylcyclohexyl (meth) acrylate, isobornyl (meth) acrylate, tricyclodecyl (meth) acrylate, dicyclopentadiene (meth) acrylate, adamantyl (meth) acrylate, glycidyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, 2-ethoxyethyl (meth) acrylate And (meth) acrylic acid monomers containing polyoxyalkylene groups such as diethylaminoethyl (meth) acrylate, trifluoroethyl methacrylate, tetrafluoropropyl methacrylate, pentafluoropropyl methacrylate, octafluoropentyl methacrylate, pentadecafluorooctyl methacrylate, heptadecafluorodecyl methacrylate, N-dimethyl (meth) acrylamide, acryloylmorpholine, (meth) acrylonitrile, polyethylene glycol (meth) acrylate, polypropylene glycol (meth) acrylate, polyethylene glycol-polytetramethylene glycol (meth) acrylate, polypropylene glycol-polytetramethylene glycol (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, ethoxypolyethylene glycol (meth) acrylate, butoxypolyethylene glycol (meth) acrylate, octoxypolyethylene glycol (meth) acrylate, lauroxypolyethylene glycol (meth) acrylate, stearoxypolyethylene glycol (meth) acrylate, phenoxypolyethylene glycol (meth) acrylate, methoxypolypropylene glycol (meth) acrylate, octoxypolyethylene glycol-polypropylene glycol (meth) acrylate, and the like.

Among them, the homopolymer having an acrylic acid ester exhibits a low glass transition temperature, and therefore, it is preferable to use an acrylic acid ester having an alkyl group having 1 to 20 carbon atoms as a main component, and it is preferable to use an acrylic acid ester having an alkyl group having 1 to 12 carbon atoms as a main component. Examples of such an acrylic acid ester having an alkyl group having 1 to 12 carbon atoms include methyl acrylate, ethyl acrylate, isopropyl acrylate, allyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl (meth) acrylate, t-butyl acrylate, n-pentyl acrylate, isopentyl acrylate, n-hexyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, and n-lauryl (meth) acrylate. The (meth) acrylic acid ester used as the constituent of the styrene acrylic copolymer (A) of the present invention may be 1 kind or 2 or more kinds.

The styrene acrylic copolymer (a) may contain a known polymerizable compound other than styrene, (meth) acrylate, and (meth) acrylic acid.

The core-shell structure of the styrene-acrylic copolymer CA) is formed by having a region where "copolymer of styrene and (meth) acrylic acid ester" is present in a large amount and a region where "copolymer of styrene and (meth) acrylic acid ester and (meth) acrylic acid" is present in a large amount. In this core-shell structure, for example, in a region where "a copolymer of a styrene and a (meth) acrylic acid ester" is present in a large amount, "a copolymer of a styrene and a (meth) acrylic acid ester and (meth) acrylic acid ester" may be present, and these copolymers may be polymerized with each other. In order to improve the stability in an aqueous medium, it is preferable that the "copolymer of styrene and (meth) acrylate and (meth) acrylic acid having an acidic group" is used as a shell component, but a part of the "copolymer of styrene and (meth) acrylate and (meth) acrylic acid" may be present in the core portion.

The styrene acrylic copolymer (a) may contain a wax (W2) described later. By adding the wax (W2) to the styrene acrylic copolymer (a), the water resistance can be further improved. The wax (W2) may be present in the core portion or the shell portion. May be present on the surface of the styrene acrylic copolymer (A).

In the styrene acrylic copolymer (A), the ratio of the "copolymer of styrene and (meth) acrylic acid ester" to the "copolymer of styrene and (meth) acrylic acid ester" 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.

In the copolymer of styrene and (meth) acrylate, the ratio of styrene to (meth) acrylate 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 in terms of mass ratio.

In the copolymer of styrene and (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 the copolymer of styrene and (meth) acrylate and (meth) acrylic acid, the ratio 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 the copolymer of styrene and (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.

When other known polymerizable compounds other than styrene, (meth) acrylic acid esters and (meth) acrylic acid are contained in the styrene-acrylic copolymer (a), the proportion of the other polymerizable compounds in the styrene-acrylic copolymer (a) is preferably 10 mass% or less, and more preferably 5 mass% or less.

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

The styrene acrylic copolymer (a) can be produced by a known method. For example, the method can be obtained by the following steps (i) and (ii), wherein the step (i) is: supplying a monomer mixture forming a shell polymer, and polymerizing the monomer mixture in the presence of an initiator to form the shell polymer; the step (ii) is as follows: the monomer mixture forming the core polymer is supplied to the shell polymer of step (i), and the monomer mixture is polymerized in the presence of an initiator to form a shell on the core polymer. The method can be obtained by the following steps (1) and (2), wherein the step (1) is: supplying a monomer mixture forming a core polymer, and polymerizing the monomer mixture in the presence of an initiator to form the core polymer; the process (2) comprises the following steps: the monomer mixture forming the shell polymer is supplied to the core polymer of step (1), and the monomer mixture is polymerized in the presence of an initiator to form a shell on the core polymer.

The initiator is not particularly limited, and peroxides, persulfates, azo compounds, redox systems, or mixtures thereof used in emulsion polymerization methods and the like can be used. Examples of the peroxide include hydrogen peroxide, ammonium peroxide, sodium peroxide, potassium peroxide, t-butyl hydroperoxide, cumene hydroperoxide, and benzene peroxide. Examples of the persulfate include ammonium persulfate, sodium persulfate, and potassium persulfate. Examples of the azo compound include 2, 2-azobisisobutyronitrile and 4,4' - (4-cyanovaleric acid). The redox system is composed of an oxidizing agent and a reducing agent, and examples of the oxidizing agent include 1 peroxide, persulfate, or azo compound, sodium chloride or potassium chloride, or sodium bromide or potassium bromide among those mentioned above. Examples of the reducing agent include ascorbic acid, glucose, ammonium, sodium or potassium bisulfate, sodium or potassium thiosulfate, sodium or potassium sulfide, or ammonium iron (II) sulfate.

Among them, persulfate is preferable, and ammonium persulfate is more preferable.

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

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

The surfactant is not particularly limited, and examples thereof include disodium dodecyl diphenyl ether and disulfonate. The chain transfer agent is not particularly limited, and examples thereof include α -methylstyrene dimer, thioglycolic acid, sodium hydrogen sulfite, 2-mercaptoethanol, N-dodecyl mercaptan, and t-dodecyl mercaptan. The chelating agent is not particularly limited, and examples thereof include ethylenediamine tetraacetic acid.

In addition, when neutralization is required, as the neutralizing agent, ammonia, triethylamine, aminomethylpropanol, monoethanolamine, diethylaminoethanol, sodium hydroxide, potassium hydroxide and other bases can be used.

(wax (W2))

The water-resistant Overcoating Composition (OCM) can further improve water resistance by containing the wax (W2). The wax (W2) is preferably at least one wax selected from paraffin wax, microcrystalline wax, oxidized polyethylene wax, and amide wax, and more preferably paraffin wax or microcrystalline wax. These may be used alone or in combination.

The melting point of the wax (W2) is preferably in the range of 30℃to 130℃and more preferably in the range of 50℃to 100 ℃.

The blending amount of the wax (W2) is preferably 0.5 to 20 mass%, and more preferably 1 to 15 mass% relative to 100 mass% of the styrene acrylic copolymer (a).

The wax (W2) may be present as dispersed in the water-resistant coating layer, and is preferably present integrally with the styrene acrylic copolymer (a) by being present in the core portion and/or the shell portion of the styrene acrylic copolymer (a), as described above. In the water-resistant coating, as to the wax (W2), there may be mixed a wax present in the form of being contained in the styrene acrylic copolymer (a) and a wax present not being contained in the styrene acrylic copolymer (a).

The wax (W2) may be directly added to the emulsion containing the styrene acrylic copolymer (a) and mixed and dispersed, or may be mixed with the emulsion after the dispersion of the wax (W2) is produced. As a known method, for example, as a dispersing device using a medium, a paint stirrer, a ball MILL, an attritor, a basket MILL, a sand MILL, a DYNO-MILL (DYNO-MILL), a DISPERMAT dispersing machine, an SC MILL, a nail MILL, a stirring MILL, etc. may be used, and dispersion may be performed using an ultrasonic homogenizer, a high pressure homogenizer, a NANOMIZER MILL, a dissolver, a disperser, a high-speed impeller dispersing machine, etc. as a dispersing device not using a medium.

In the case of using a powder wax, in order to uniformly disperse the wax, grinding is preferably performed using a medium (japanese:

meat) or blended after making a dispersion of wax. The grinding method can be carried out by a known method.

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.

When the wax (W2) is contained in the styrene acrylic copolymer (a), polymerization of the monomer mixture constituting the styrene acrylic copolymer (a) may be performed in the presence of the wax (W2) as described above.

(other additives)

The water-resistant Overcoating Composition (OCM) may further contain additives such as silica, alumina, wax, defoamer, leveling agent, thickener, preservative, antibacterial agent, and rust inhibitor in addition to the above components within a range that does not hinder the object of the present invention. In addition, other resins than the styrene acrylic copolymer (a) may be blended.

Among them, a leveling agent and/or wax is preferably further blended.

The wax to be blended further is a wax (W3) added in addition to the wax (W2). By containing the wax (W3), the blocking resistance, scratch resistance, and slidability of the coated paper coated with the water-resistant overcoating of the present invention can be improved when the coated paper is laminated.

Examples of the wax (W3) include waxes such as fatty acid amide wax, carnauba wax, polyolefin wax, paraffin wax, fischer-tropsch wax, beeswax, microcrystalline wax, oxidized polyethylene wax, and amide wax, which may be used alone or in combination.

Among these, 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.

Specific examples of the fatty acid amide wax include pelargonic acid amide, capric acid amide, undecanoic acid amide, lauric acid amide, tridecanoic acid amide, myristic acid amide, pentadecanoic acid amide, palmitic acid amide, margaric acid amide, stearic acid amide, nonadecanoic acid amide, arachic acid amide, behenic acid amide, lignoceric acid amide, oleic acid amide, hexadecenoic acid amide, linoleic acid amide, linolenic acid amide, and mixtures thereof, and animal and vegetable oil fatty acid amide.

Specific examples of the olefin wax include polyethylene wax and polypropylene wax, and examples thereof include MPP-635VF (MicroPowrers, inc.), MP-620VF XF (MicroPowrers, inc.), CHEMIPEARL W-400 (manufactured by Mitsui chemical Co., ltd.).

The amount of the wax (W3) to be blended is preferably 0.3 to 10% by mass based on 100% by mass of the total amount of the solid components in the composition of the present invention. If the total amount of the wax (W3) is 0.3 mass% or more relative to 100% of the total amount of the solid content in the composition of the present invention, the blocking resistance tends to be maintained, and more preferably 0.5 mass% or more. Further, if the total amount of the wax (W3) is 10 mass% or less relative to 100% of the total amount of the solid content of the aqueous heat-sealing agent, the slip angle does not become excessively large, and therefore workability tends to be well maintained, and is preferably 5 mass% or less, more preferably 3 mass% or less.

From the viewpoints of oil resistance and heat resistance, the melting point of the wax (W3) is preferably in the range of 80 to 130 ℃.

The wax (W3) may be directly added to the emulsion of the resin containing the styrene acrylic copolymer (a) and mixed and dispersed, or may be mixed with the emulsion after the wax dispersion is produced. In order to improve blocking resistance, it is preferable that the wax (W3) is not incorporated into the styrene acrylic copolymer (a) but dispersed so as to be present in the vicinity of the surface of the water-resistant coating layer.

The type of leveling agent is not particularly limited, and an alkyne-based surfactant is preferably used. Specific examples of the alkyne-based surfactant include 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, and 2-butyne-1, 4-diol. Examples of the commercial Products include alkylene oxide non-modified alkyne diol surfactants such as Surfynol 61, 82, 104 (all manufactured by Air Products Co., ltd.), alkylene oxide modified alkyne diol surfactants such as [0037]Surfynol 420, 440, 465, 485, TG, 2502, DYNOL 604, 607 (all manufactured by Air Products Co., ltd.), surfynol SE, MD-20, OLFINE E1004, E1010, PD-004, EXP4300, PD-501, PD-502, SPC (all manufactured by Japanese chemical industry Co., ltd.), and Acetylenol EH, E40, E60, E81, E100, E200 (all manufactured by KaWaken Fine Chemicals Co., ltd.).

The amount of the leveling agent to be added is preferably 0.01 to 0.1% by weight based on the total amount of the paper overcoat composition.

By using the wax (W3) and the leveling agent in combination, leveling property can be maintained and blocking property can be improved.

In addition, in order to prevent foaming of the water-resistant Overcoating Composition (OCM) when the paper is coated with the composition, the water-resistant coating layer of the present invention preferably contains a polymer-based antifoaming agent, a silicon-based antifoaming agent, and a fluorine-based antifoaming agent. As these antifoaming agents, any of emulsion dispersion type, solubilizing type, and the like can be used. Among them, polymer-based antifoaming agents are preferable. The amount of the antifoaming agent added is preferably 0.005 to 0.1% by weight based on the total amount of the paper overcoat composition.

< method for Forming Water-resistant coating >

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

As a method for applying the water-resistant Overcoat Composition (OCM) on the paper substrate, a known method can be used. For example, any one or a combination of two or more coating methods 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 bar coater, a die coater, a lip coater, a dip coater, a knife coater, a brush coater, a curtain coater, a die slot coater, an offset printer, a screen printer, and the like can be used.

In addition, the water-resistant coating layer may be provided on the paper substrate by impregnating the paper substrate with the water-resistant overcoat composition of the present invention. In addition, a drying step may be provided by an oven or the like after the application.

The film thickness of the water-resistant Overcoating Composition (OCM) at the time of coating depends on the application, and when used in a food paper container, the effect of the present invention can be sufficiently obtained if it is in the range of 1 to 10g/m2, for example. Among them, the range of 2 to 6g/m2 is more preferable.

The water-resistant coating layer 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 after 30 minutes after the water drop is maintained at 70 degrees or more, preferably 75 degrees or more, more preferably 80 degrees or more. In addition, the contact angle of the water-resistant coating layer of the present invention after 40 minutes from the water drop is preferably maintained at 50 degrees or more, preferably 60 degrees or more, preferably 70 degrees or more, more preferably 75 degrees or more. The contact angle can be easily measured using a known contact angle measuring device (for example, an automatic contact angle measuring device manufactured by the company interface chemical Co., ltd.).

In addition, the water-resistant coating layer formed as described above has excellent moisture resistance, and can maintain the moisture resistance. The water-resistant coating of the present invention preferably has a water vapor transmission rate of 500g/m2·day or less, preferably 300g/m2·day or less, preferably 250g/m2·day or less, preferably 200g/m2·day or less when maintained at a temperature of 25 ℃ and a relative humidity of 50% rh for 7 days. The water vapor transmission rate when maintained at a temperature of 40℃for 7 days is preferably 1000 g/m2.multidot.day or less, more preferably 600 g/m2.multidot.day or less, still more preferably 500 g/m2.multidot.day or less, and still more preferably 400 g/m2.multidot.day or less.

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

The water-resistant paper having water resistance, moisture resistance and recycling properties can be obtained by applying the water-resistant Overcoat Composition (OCM) to a paper substrate and providing the paper substrate with a water-resistant coating layer. That is, the water-resistant coating layer of the present invention is excellent in water resistance, moisture resistance and recyclability, and therefore, can be used as a water-resistant paper by merely coating the water-resistant overcoat composition on a paper substrate without providing a heat-sealable coating layer. The paper base material and the coating method are the same as those of the water-resistant paper described later.

[ Water-resistant paper ]

The water-resistant paper of the present invention has a structure in which at least the above water-resistant coating layer and the heat-sealable coating layer are provided on a paper base material, and can be recycled directly after use.

The paper base material is made of natural fibers for paper making such as wood pulp by a known paper machine, and paper sheets thereof are not particularly limited. Examples of the natural fibers for paper production include wood pulp such as conifer pulp and hardwood pulp, non-wood pulp such as abaca pulp, sisal pulp and flax pulp, and pulp obtained by chemically modifying these pulps. As the kind of pulp, chemical pulp, grinding pulp, chemical grinding pulp, thermomechanical pulp, and the like based on sulfate hydrolysis, acid/neutral/alkaline sulfite hydrolysis, soda salt hydrolysis, and the like can be used. In addition, various commercially available high-quality papers, coated papers, liner papers, impregnated papers, cardboard, paperboard, and the like can be used.

The paper base material may be sequentially selected according to the purpose, for example, the type and thickness of paper. For example, if a hamburger is wrapped, it preferably corresponds to a grammage (Japanese: mild) of 20 g/m ² Food base paper such as left and right cup base paper, and in the case of paper cups, is preferably a paper cup having a gram weight of 200 to 300 g/m ² For food such as cup stock, if the food is a paper tray, a spoon, a stirring bar (japanese:

first, or the like, preferably corresponds to a gram weight of 50 to 500 g/m ² Base paper for food such as cup base paper. From the viewpoints of recycling efficiency and cost reduction, it is preferable that these papers are not laminated with a polyethylene film, aluminum or the like. The paper substrate may have a print layer.

[ packaging body or Container ]

The water-resistant paper of the present invention is excellent in water resistance and moisture resistance, and therefore can be used as a water-resistant paper and/or a moisture-resistant paper. The water-resistant paper of the present invention can be used as various packages or containers. Further, the heat-sealable coating portion can be used for heat sealing, and thus can be processed into boxes, bags, and containers.

Examples of the packaging material include a bag for packaging, a paper bag, a cardboard box, corrugated paper, wrapping paper, an envelope, a sleeve, and a lid. Examples of the container include a paper container, a paper tray, a tray, and a cup holder. The water-resistant paper of the present invention can be used for foods, sundries, living goods, etc. which require water resistance and moisture resistance, and can be used for packaging foods, sundries, living goods containing liquid or moisture. Examples thereof include cups and caps for desserts such as paper cups, cup noodles, various beverages, ice creams, puddings and jellies, snack bags and boxes such as rice snacks, potato chips, chocolate snack bags and boxes, snack bags and boxes such as biscuits, hamburgers, hot dog wrappers, hot snack containers such as pizza, dry fried foods, potatoes, cups for home dishes such as natto, food paper containers and wrappers such as bags for rice and miscellaneous cereals, and bags and boxes for sanitary products such as lotions and sanitary products. Depending on the application, the packaging material or container may have a water-resistant coating on the inner side, a water-resistant coating on the outer side, or both the inner and outer sides.

The water-resistant paper of the present invention is preferably used for labels for bottles and cans, paper tapes such as curing paper tapes and paper tapes, books such as books and magazines, posters, calendars, and the like. The water-resistant coating functions as an outer coating for the paper substrate with the printed layer.

Further, the heat-sealable coating portion is sealed with a water-resistant paper having both a water-resistant coating and a heat-sealable coating, whereby the bag, the box, and the wrapping paper can be formed. For example, a pillow-shaped bag for packaging snack foods and the like, an envelope-shaped bag, a bag for department stores, a cosmetic case, a bag or case for packaging pizza, doughnut and the like, an open-ended wrapper partially having a heat-sealed portion for packaging hamburgers, hotdogs and the like, a tubular container and the like can be cited.

The present invention will be described in detail with reference to examples, but the technical scope of the present invention is not limited to these embodiments.

Examples

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

< Synthesis of styrene acrylic copolymer (A) >

Production example 1

Into a nitrogen-substituted 4-neck flask, 100 parts of isopropyl alcohol was added, and after the temperature was raised to 80 to 82 ℃, it took 2 hours to drop 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, which was added to a dropping funnel. After completion of the dropwise addition, 0.5 part of benzoyl peroxide was added and the reaction was further carried out for 2 hours. The temperature was reduced to 40 ℃, and dimethylethanolamine and ion-exchanged water were added. Thereafter, the temperature of the reaction flask was raised to 80 to 82℃and steam stripping was performed to finally obtain a water-soluble resin having a solid content of 30%.

To the water-soluble resin obtained above, 2 parts by mass of paraffin wax (paraffin wax 155, manufactured by japan fine wax corporation) as wax (W2) was added and stirred to prepare a wax dispersion. Next, 10 parts of wax dispersion and ion-exchanged water were added to a reaction flask, the temperature was raised to 80 to 82 ℃, and then 2 parts of potassium persulfate was added thereto, and it took 2 hours to drop a mixture of 30 parts of styrene and 24 parts of 2-ethylhexyl acrylate. After completion of the dropwise addition, 0.2 part of potassium persulfate was added and the reaction was carried out for 2 hours. The solid content of the aqueous styrene-acrylic copolymer dispersion (A-1) thus obtained was 35%, and the glass transition point was-10 ℃.

Production example 2

An aqueous dispersion (A-2) of a styrene-acrylic copolymer was obtained in the same manner as in the synthesis of the styrene-acrylic copolymer (A-1), except that a microcrystalline wax (Hi-Mic-1080, manufactured by Japanese refined wax Co., ltd.) was added instead of paraffin wax in the synthesis of the styrene-acrylic copolymer (A-1). The solid content of the aqueous dispersion (A-2) was 35%, and the glass transition point was-10 ℃.

PREPARATION EXAMPLE 3

As the styrene-acrylic copolymer (A), a copolymer of styrene and (meth) acrylic acid ester and (meth) acrylic acid are used as the aqueous dispersion (A-3) of a commercially available styrene-acrylic copolymer having a core-shell structure and a glass transition temperature in the range of-30 to 10 ℃. The solid content of the aqueous dispersion (A-3) was 40%, and the glass transition point was-21 ℃.

< preparation of laminate >

Reference examples 1 to 4

Using the above aqueous dispersions (A-1) to (A-3), the compositions obtained by mixing the compositions according to Table 1 were sufficiently stirred with a disperser to prepare paper overcoat compositions. The thickness of the overcoat composition was 6g/m ² The resulting laminate was applied to unbleached kraft paper (70 g weight per unit area, manufactured by king paper making Co., ltd.) and dried at 150℃for 20 seconds using a dryer to prepare laminates of examples 1 to 4.

Comparative example 1

The kraft papers used in examples 1 to 4 were used without applying the overcoat composition.

Comparative example 2

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 nitrocotton, 55 parts of isopropyl alcohol and 32 parts of ethyl acetate was used in the paper overcoat composition.

Comparative example 3

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 parts of a styrene acrylic resin, 4 parts of isopropyl alcohol, and 68 parts of ion-exchanged water was used in the paper overcoat composition.

< evaluation item >

(Water resistance)

Tap water was collected into a dropper, and 0.1ml of tap water was added dropwise to the surface of the coated paper test piece for evaluation, which was provided with a water-resistant coating.

After tap water was added dropwise, tap water was wiped off at 25℃for each of 1 hour, 4 hours, 5 hours and 8 hours, and the front and back surfaces were visually evaluated according to the following evaluation criteria.

O: there was no trace of dripping on the surface, swelling by water, or penetration to the back.

Delta: there are marks of drops on the surface and penetration of water, but no penetration to the back.

X: there are marks of dripping on the surface, swelling due to water, and penetration to the back.

(contact angle)

Tap water was collected into a dropper, and the contact angle immediately after 0.1ml was added dropwise to the coated paper test piece for evaluation, and the contact angles after 30 minutes and after 40 minutes were measured.

An automatic contact angle meter manufactured by Kagaku Kogyo Co., ltd was used for the measurement of the contact angle.

(blocking resistance)

The coated surface of the prepared water-resistant paper was overlapped with the coated surface, a load of 10kgf/cm2 was applied thereto, the water-resistant paper was taken out after 48 hours at 40℃and the adhesion between the coated surface and the non-coated surface was visually evaluated in the following 4 stages.

(evaluation criterion)

And (3) the following materials: no blocking was observed at all.

O: a few blocking was observed in part.

Delta: blocking was partially observed.

X: blocking was observed across the entire face.

(sliding angle)

The coated surface of the produced water-resistant paper was overlapped with the coated surface, and the inclination angle at which the coated paper began to slide was measured as the sliding angle by the inclination method. The sliding angle was measured using a sliding angle inclination measuring device (HEIDON corporation). If the value of the slip angle is too small, load displacement (japanese: load collapse) is likely to occur at the time of the overlapping. If too large, there is a possibility of coating stacking. Therefore, when the slide angle is proper, the coated paper can be easily taken out one by one from the coated papers in the stacked state, and workability is improved.

TABLE 1

TABLE 2

As the wax (W3) in the table, CHEMIPEARL W-400 (Sanjingchu chemical Co., ltd.) was used.

The leveling agents in the tables were Surfynol420 (manufactured by Nissan chemical industries, ltd.).

According to reference examples 1 to 4 and comparative examples 1 to 3, the water resistance was improved by providing the water-resistant Overcoat Composition (OCM). In addition, according to reference example 4, further addition of wax (W3) improves blocking resistance, and also reduces sliding angle and improves workability.

(Water vapor permeability)

A stainless steel cup was prepared, and 7g of water was added to the cup. The upper part of the cup was sealed with water-resistant paper for evaluation using beeswax. Next, the portion protruding from the cup was cut off, and a sample bottle was fabricated. The initial weight of the sample bottle was measured, stored at the temperature and humidity shown in table 3, and the weight of the sample was measured every 1 day, and the amount of water evaporated was calculated. The humidity was not adjusted at 40 ℃.

As the water-resistant paper used for the evaluation of water vapor permeability, the laminate of reference example 1, kraft paper of comparative example 1, and laminate of comparative example 4 were used. The laminate of comparative example 4 was produced in the same manner as in 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 in place of the composition (OC-1) in example 1.

The results are shown in Table 3.

TABLE 3

According to reference example 1 and comparative examples 1 and 2, the water-resistant Overcoat Composition (OCM) was provided to significantly reduce the water vapor permeability. By providing the water-resistant Overcoat Composition (OCM), it was confirmed that moisture resistance could be imparted.

< method for producing olefin-alpha, beta-unsaturated carboxylic acid copolymer for Heat sealing agent >

Production example 4

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

25 parts of the obtained copolymer, ammonia having a neutralization rate of 100% relative to the acid value of the copolymer, water as an aqueous solvent, and 1.5 parts of a fatty acid amide wax as a wax were added and stirred to obtain an aqueous dispersion (H1) of an olefin- α, β -unsaturated carboxylic acid copolymer and a fatty acid amide wax.

< preparation of aqueous Heat sealing agent >

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-sealing agent.

< preparation of laminate >

Examples 1 to 12

The paper substrates shown in tables 4 to 7 were prepared, and the thickness of the paper substrate was set to 2g/m on one side of the paper substrate ² The water-resistant overcoating composition used in reference example 1 was coated and dried at 150℃for 20 seconds using a dryer. Next, the thickness of the film was set to 2g/m on the other surface of the paper base material ² The aqueous heat sealing agent was applied and dried at 100℃for 30 seconds using a dryer to prepare the laminates of examples 5 to 10.

In the same manner, the thickness of the film thickness of the paper overcoat composition and the aqueous heat sealer was 5g/m ² The laminate of examples 11 to 18 was produced by coating.

Comparative examples 5 to 18

Laminates of comparative examples 5 to 18 were produced in the same manner as in examples 1 to 12 except that the paper overcoat composition was not applied in examples 1 to 12.

< evaluation >

(Heat sealability)

The heat sealing sections were provided by overlapping the coated surfaces of the heat sealants of the laminates of examples 5 to 18 with each other, heating the laminate at a temperature in the range of 80℃to 140℃and immediately using a heat sealer under a pressure of 0.2MPa and a sealing condition of 1 second. Regarding the adhesion state, when the heat sealing portion is peeled off, the paper is broken according to paper peeling (japanese:

cutting) was evaluated for the adhesion strength, and the lowest temperature of the completely adhered hot plate was examined.

6: complete sealing at 80 ℃.

5: complete sealing at 90 ℃.

4: complete sealing at 100 ℃.

3: complete sealing at 110 ℃.

2: complete sealing at 120 ℃.

1: it is not adhered even at 130 ℃.

(Water resistance)

Tap water was collected into a dropper, and 0.1ml of tap water was added dropwise to the surface of the coated paper test piece for evaluation, which was provided with a water-resistant coating. The dropping is performed on each part of the seal portion provided in the convex folded portion, concave folded portion, planar portion, and sheet-sealed by the heat sealability evaluation method of the laminate. After tap water was added dropwise, tap water was wiped off at 25℃for each of 1 hour, 3 hours, 5 hours and 24 hours, and the front and back surfaces were visually evaluated according to the following evaluation criteria.

(recyclability)

The coated papers of examples 1 to 12 produced in the evaluation of heat sealability were cut to 3.0cm×5.0cm, and the resultant was put into a 1 mass% aqueous solution of sodium hydroxide, and the resultant was stirred with a paint stirrer (shallow Tian Tiegong Co., ltd.) for 30 minutes, whereby the papers were sufficiently dissociated, and no film-like substance was confirmed.

On the other hand, the commercial paper cup was cut into 3.0 cm. Times.5.0 cm pieces, and the same evaluation was performed, and as a result, it was confirmed that a film-like substance remained. Therefore, it was confirmed that the polyethylene film obtained in the examples remained in the form of a sheet.

Therefore, it is understood that the coated papers of examples 1 to 12 do not lower the paper recycling efficiency.

The evaluation results of the laminates of examples 1 to 12 and comparative examples 5 to 18 are shown in the following table. Tables 4 and 5 show the application of the water-resistant top coating composition (2 g/m ² ) Heat-sealing agent (2 g/m) ² ) Tables 6 and 7 show the results of applying the water-resistant top coating composition (5 g/m ² ) Heat-sealing agent (5 g/m) ² ) As a result of (a).

TABLE 4

TABLE 5

TABLE 6

TABLE 7

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

Silver bamboo: unbleached kraft paper (manufactured by japan paper products, inc., per unit area)Weight 50g/m ² )

East sea kraft paper: unbleached kraft paper (New east China sea paper Co., ltd., weight per unit area of 50 g/m) ² )

Double-layer kraft paper: double-layer unbleached kraft paper (manufactured by Japanese paper Co., ltd., weight per unit area of 50 g/m) ² )

Silver (a): single light kraft paper (manufactured by Japan paper Co., ltd., weight per unit area 24 g/m) ² )

Silver (b): single light kraft paper (manufactured by Japan paper Co., ltd., 50 g/m) ² )

Shan Guangbai kraft: single light kraft paper (manufactured by Japan paper Co., ltd., 50 g/m) ² )

From tables 4 to 7, it was confirmed that the laminate of examples had no water permeation and excellent water resistance. There is no penetration of water in any of the male, female, and heat seal portions. It was also confirmed that even when both the water-resistant coating and the heat-sealing agent were applied, sufficient heat-sealing properties could be exhibited. Although there is a slight difference depending on the paper, the coating is 2g/m ² In the case of the heat-sealing agent of (C), a high sealing strength can be obtained at about 110 to 120 ℃. At the time of coating 5g/m ² In the case of the heat-sealing agent of (C), good sealing strength can be obtained even at a low temperature of 90 ℃.

Claims

1. A water resistant paper, characterized by comprising:

a paper base material,

A water-resistant coating layer provided on at least a portion of the paper substrate, and

2. The water resistant paper of claim 1 wherein the heat sealable coating comprises an olefin- α, β unsaturated carboxylic acid copolymer and a wax W1.

3. The water-resistant paper according to claim 1 or 2, wherein the wax W1 is a fatty acid amide wax and/or carnauba wax.

4. The water-resistant paper according to claim 1 to 3, wherein,

the water-resistant coating contains a styrene acrylic copolymer A and wax W2,

for the styrene acrylic copolymer A, a copolymer of styrene and (meth) acrylate forms a core-shell structure, and the glass transition temperature of the styrene acrylic copolymer A is in the range of-30 to 10 ℃.

5. The water-resistant paper according to claim 4, wherein,

the wax W2 is at least one wax selected from polyolefin wax, paraffin wax, microcrystalline wax, oxidized polyethylene wax and amide wax.

6. The water-resistant paper according to claim 4 or 5, wherein,

the contact angle of the water-resistant coating after being added with water for 30 minutes is more than 70 ℃.

7. The water-resistant paper according to any one of claims 3 to 6, wherein,

the styrene acrylic copolymer a contains a wax W2.

8. A package or container using the water-resistant paper according to claim 1 to 7.

9. A package or container comprising the water-resistant paper according to claim 1 to 7, and a heat-sealable coating layer provided on the water-resistant paper.