Paper barrier material

Abstract

The present invention addresses the problem of providing a paper barrier material having excellent flex resistance. Provided as a solution is a paper barrier material that comprises, on a paper substrate, a barrier coating layer having water vapor barrier properties or gas barrier properties, and a heat-seal coating layer, in this order. After being folded into quarters with the heat-seal coating layer on the outside, the material satisfies at least one of the following (1) and (2): (1) the oxygen permeability at a temperature of 23°C and a relative humidity of 0% is 20 ml / m2∙day∙atm or less; and (2) the water vapor permeability at a temperature of 40°C and a relative humidity of 90% is 20 g / m2∙day or less.

Description

Paper barrier material

[0001] The present invention relates to a paper barrier material.

[0002] It is important to impart gas barrier properties (particularly oxygen barrier properties) to paper materials, particularly paper packaging materials, in order to protect various packaged products from gas-induced deterioration, for example, oxidation by oxygen, etc. Conventionally, gas barrier properties have been imparted to paper packaging materials mainly by extrusion laminating or bonding a gas barrier layer, such as a metal foil or metal-deposited film made of a metal such as aluminum, a resin film such as polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, or polyacrylonitrile, or a film coated with such a resin, or a ceramic-deposited film on which an inorganic oxide such as silicon oxide or aluminum oxide is vapor-deposited, onto the paper substrate.

[0003] As a paper packaging material to which gas barrier properties have been imparted without using a vapor-deposited film, a paper gas barrier material having a gas barrier layer made of a water-soluble polymer and an inorganic layered compound has been disclosed (Patent Document 1 and Patent Document 2). Furthermore, imparting water resistance (particularly water vapor barrier properties) to paper packaging materials is also important in order to protect various packaged products from deterioration due to water vapor, and as a paper packaging material with gas barrier and water vapor barrier properties, a paper barrier packaging material has been disclosed that has, on a paper substrate, a water vapor barrier layer containing a water vapor barrier resin and a pigment, and a gas barrier layer containing a polyvinyl alcohol-based resin and a pigment (Patent Document 3).

[0004] Paper barrier materials equipped with such a barrier coating layer may experience a significant decrease in barrier properties when bent. Paper barrier materials may be folded when processed into packaging, or may be partially bent due to impacts during transportation or storage, so there is a demand for paper barrier materials that experience minimal deterioration in barrier properties when bent.

[0005] JP 2009-184138 A JP 2003-094574 A Japanese Patent No. 5331265 A

[0006] An object of the present invention is to provide a paper barrier material that has excellent flex resistance.

[0007] The means for solving the problems of the present invention are as follows: 1. A paper barrier material having, on a paper substrate, a barrier coating layer having water vapor barrier properties or gas barrier properties and a heat seal coating layer in this order, and which satisfies at least one of the following (1) and (2) after being folded crosswise with the heat seal coating layer on the outside: (1) an oxygen permeability of 20 ml / m at a temperature of 23°C and a relative humidity of 0%; ２ (2) Water vapor permeability of 20 g / m at a temperature of 40°C and a relative humidity of 90% ２ 2. The coating amount of the heat seal coating layer is 5 g / m or less. ２ 20g / m or more ２ 1. The paper barrier material according to 1., characterized in that the heat seal coating layer has an elongation at break of 200% or more and a Young's modulus of 15 MPa or less when evaluated as a 50 μm thick film. 2. The paper barrier material according to 1. or 2., characterized in that the heat seal coating layer has an elongation at break of 200% or more and a Young's modulus of 15 MPa or less when evaluated as a 50 μm thick film. 3. The paper barrier material according to any one of 1. to 3., characterized in that the heat seal coating layer has a water vapor barrier coating layer and a gas barrier coating layer, in this order, on a paper substrate. 4. The paper barrier material according to any one of 1. to 4., characterized in that the heat seal coating layer comprises one or more selected from the group consisting of polyolefin resins, polyester resins, ethylene copolymers, and styrene copolymers. 5. The paper barrier material according to any one of 1. to 4., characterized in that the heat seal coating layer comprises one or more selected from the group consisting of polyolefin resins, polyester resins, ethylene copolymers, and styrene copolymers. 6. The paper substrate has a basis weight of 25 g / m ２ 70g / m or more ２The paper barrier material according to any one of 1. to 5., characterized in that it is: 7. The paper barrier material according to any one of 1. to 6., characterized in that the heat seal coating layer contains two or more resins selected from the group consisting of polyolefin-based resins, polyester-based resins, ethylene-based copolymers, and styrene-based copolymers. 8. The paper barrier material according to 7., characterized in that the heat seal coating layer contains an ethylene-vinyl acetate-based resin. 9. The paper barrier material according to 7. or 8., characterized in that the ethylene-vinyl acetate-based resin is contained in an amount of 1 to 30 parts (solid content) relative to 100 parts (solid content) of the total thermoplastic resin content in the heat seal coating layer. 10. The paper barrier material according to 8. or 9., characterized in that the Tg of the ethylene-vinyl acetate-based resin is 0°C or lower. 11. The paper barrier material according to any one of 8. to 10., characterized in that the ethylene-vinyl acetate-based resin contains a vinyl versatate structure.

[0008] The paper barrier material of the present invention has excellent flex resistance and can maintain high barrier properties even when flexed. The paper barrier material of the present invention is suitable for use in flexible packaging bags, which are prone to flexing due to their thinness.

[0009] The paper barrier material of the present invention has, on a paper substrate, a barrier coating layer having water vapor barrier properties or gas barrier properties, and a heat seal coating layer, in that order, and satisfies at least one of the following (1) and (2) after being folded crosswise with the heat seal coating layer on the outside: (1) an oxygen permeability of 20 ml / m at a temperature of 23°C and a relative humidity of 0%; ２ (2) Water vapor permeability of 20 g / m at a temperature of 40°C and a relative humidity of 90% ２ ・Less than day

[0010] (Paper Base Material) In the present invention, the paper base material is a sheet made of pulp, fillers, various auxiliaries, etc. Examples of pulp that can be used include chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood kraft pulp (NUKP), and sulfite pulp, mechanical pulps such as stone-ground pulp and thermomechanical pulp, wood fibers such as deinked pulp and recycled paper pulp, and non-wood fibers obtained from kenaf, bamboo, hemp, etc., and these can be used alone or in combination of two or more. Among these, it is preferable to use chemical pulp or mechanical pulp made from wood fibers, and it is more preferable to use chemical pulp, for reasons such as the fact that foreign matter is less likely to be mixed into the paper base material, that discoloration is less likely to occur over time when used paper containers are recycled as waste paper raw materials, and that the high whiteness results in a good surface appearance when printed, making the paper highly useful, particularly when used as a packaging material.

[0011] As fillers, known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, zeolite, and synthetic resin fillers can be used as needed. Aluminum sulfate and various anionic, cationic, nonionic, or amphoteric retention aids, drainage aids, paper strength agents, internal sizing agents, and other internal additives can also be used as needed. Furthermore, dyes, fluorescent whitening agents, pH adjusters, antifoaming agents, pitch control agents, slime control agents, and the like can also be added as needed.

[0012] The method for producing the paper base (papermaking) is not particularly limited, and the paper base can be produced by acidic, neutral, or alkaline papermaking using a known Fourdrinier former, on-top hybrid former, gap former, or other machine. The paper base may be composed of a single layer or two or more layers. Furthermore, the surface of the paper base can be treated with various chemicals. Examples of chemicals that can be used include oxidized starch, hydroxyethyl etherified starch, enzyme-modified starch, polyacrylamide, polyvinyl alcohol, surface sizing agents, water-resistant agents, water-retention agents, thickeners, and lubricants. These can be used alone or in combination of two or more types. Furthermore, these various chemicals can be used in combination with pigments. Examples of pigments that can be used include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as organic pigments such as solid, hollow, and core-shell pigments, which can be used alone or in combination of two or more.

[0013] The method for surface treatment of the paper substrate is not particularly limited, and known coating devices such as a rod metering size press, a pond type size press, a gate roll coater, a spray coater, a blade coater, a curtain coater, etc. Examples of paper substrates obtained in this manner include various known types such as fine paper, medium quality paper, coated paper, one-side glossy paper, kraft paper, one-side glossy kraft paper, bleached kraft paper, glassine paper, paperboard, white paperboard, and liner.

[0014] The basis weight of the paper substrate can be selected appropriately depending on the desired qualities and handling properties of the paper barrier material, but is usually 20 g / m ２ More than 500g / m ２ In the case of paper barrier materials used for packaging applications such as food packaging, containers, cups, etc., a barrier strength of 25 g / m or less is preferred. ２ More than 400g / m ２ The following is more preferred, and in particular in the case of a paper barrier material used for flexible packaging bags described below, 25 g / m２ 70g / m or more ２ The following is more preferred:

[0015] (Barrier Coating Layer) The barrier coating layer can be formed by applying a coating liquid for forming the barrier coating layer using various types of coating equipment and drying it. The barrier coating layer has water vapor barrier property or gas barrier property, and more preferably has both water vapor barrier property and gas barrier property. When the barrier coating layer has both water vapor barrier property and gas barrier property, it is preferable to have both a water vapor barrier coating layer and a gas barrier coating layer, as this will result in a paper barrier material that has both gas barrier property and water vapor barrier property. Hereinafter, the water vapor barrier coating layer will also be referred to as the water vapor barrier layer, and the gas barrier coating layer will also be referred to as the gas barrier layer.

[0016] While there are no particular restrictions on the stacking order of the water vapor barrier layer and the gas barrier layer, it is preferable that they be stacked in the order of paper substrate, water vapor barrier layer, and gas barrier layer, as this further improves both the water vapor barrier property and the gas barrier property. The reason why a paper barrier material having a paper substrate, water vapor barrier layer, and gas barrier layer in this order possesses both superior water vapor barrier property and gas barrier property is presumed to be as follows. As will be described later, polymers such as water-soluble polymers and water-dispersible polymers are generally used as resins with gas barrier property used in the gas barrier layer. Therefore, when the gas barrier layer and water vapor barrier layer are provided on the paper substrate in this order, the polymers such as water-soluble polymers and water-dispersible polymers in the gas barrier layer are prone to degradation due to moisture in the paper substrate and moisture in the air that permeates via the paper substrate. On the other hand, the water vapor barrier layer contains a resin with good water resistance to block water vapor, but by having the water vapor barrier layer and gas barrier layer on the paper substrate in this order, the water vapor barrier layer can effectively suppress the impact (deterioration) of the gas barrier layer due to moisture from the paper substrate side. For this reason, paper barrier materials that have a water vapor barrier layer and a gas barrier layer in this order in particular can exhibit good water vapor barrier properties and gas barrier properties.

[0017] (Water Vapor Barrier Coating Layer) The water vapor barrier coating layer contains at least a water vapor barrier resin. Examples of water vapor barrier resins include polyurethane resins, styrene-butadiene, styrene-acrylic, ethylene-vinyl acetate, paraffin (wax), butadiene-methyl methacrylate, and vinyl acetate-butyl acrylate copolymers, synthetic adhesives such as maleic anhydride copolymers and acrylic acid-methyl methacrylate copolymers, and paraffin (wax)-blended synthetic adhesives thereof, which can be used alone or in combination of two or more. Among these, polyurethane resins or styrene-butadiene synthetic adhesives are preferred from the viewpoint of water vapor barrier properties, and polyurethane resins are more preferred.

[0018] The polyurethane resin can be obtained by reacting a polyol with a polyisocyanate and, if necessary, a chain extender or the like. The polyurethane resin of the present invention may be a polyurethane urea having a urea bond. The polyol may be any polyether polyol, polyester polyol, polycarbonate polyol, or other polyol used as a raw material for polyurethane, without any particular limitation. The polyisocyanate is also not particularly limited, and any aliphatic isocyanate, alicyclic isocyanate, aromatic isocyanate, or other polyol used as a raw material for polyurethane may be used without any particular limitation. However, from the viewpoint of water vapor barrier properties, cyclic isocyanates are preferred, and specific examples thereof include MDI, hydrogenated MDI, XDI, and hydrogenated XDI. In the present invention, the polyurethane resin may be used alone or in combination of two or more types.

[0019] The polyurethane resin preferably has a glass transition temperature of -20°C or higher and 150°C or lower, more preferably -10°C or higher and 140°C or lower, and even more preferably 0°C or higher and 135°C or lower. The glass transition temperature refers to the midpoint glass transition temperature measured in accordance with JIS K 7121-1987. Commercially available polyurethane resins can also be used, such as "Takelac W series," "Takelac WPB series," and "Takelac WS series" manufactured by Mitsui Chemicals, Inc., and a specific example is Takelac WPB-341 (trade name).

[0020] Styrene-butadiene synthetic adhesives are emulsion-polymerized with styrene and butadiene as the primary monomers, combined with various comonomers for modification. Examples of comonomers include methyl methacrylate, acrylonitrile, acrylamide, hydroxyethyl acrylate, and unsaturated carboxylic acids such as itaconic acid, maleic acid, and acrylic acid. Anionic surfactants such as sodium oleate, rosin acid soap, sodium alkylarylsulfonate, and sodium dialkylsulfosuccinate can be used alone or in combination with nonionic surfactants as emulsifiers. Depending on the purpose, amphoteric or cationic surfactants may also be used.

[0021] Furthermore, provided that the water vapor barrier property is not affected, it is also possible to use in combination with the water vapor barrier resin water-soluble polymers such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, ethylene copolymer polyvinyl alcohol, and other polyvinyl alcohols; proteins such as casein, soy protein, and synthetic protein; starches such as oxidized starch, cationized starch, urea phosphate esterified starch, and hydroxyethyl etherified starch; cellulose derivatives such as carboxymethyl cellulose, hydroxymethyl cellulose, and hydroxyethyl cellulose; polyvinylpyrrolidone; and sodium alginate.

[0022] The water vapor barrier layer may contain a pigment. Examples of pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as organic pigments such as solid, hollow, and core-shell pigments, which may be used alone or in combination of two or more. Among these, from the viewpoints of both improving water vapor barrier properties and suppressing penetration of the coating material used to form the gas barrier layer, flat inorganic pigments such as kaolin, mica, and talc are preferred, with swellable mica, a type of synthetic mica, or kaolin being more preferred, and swellable mica being even more preferred. Specific examples of swellable mica include synthetic mica (product name: NTS-10) manufactured by Topy Industries, Ltd. and synthetic mica (product name: ME300B-4T) manufactured by Katakura Co-op Agri Co., Ltd.

[0023] The pigment preferably has a 50% volume average particle size (D50) (hereinafter also referred to as "average particle size") of 5 μm or more and an aspect ratio of 10 or more. The pigment's average particle size is more preferably 10 μm or more, more preferably 50 μm or less, and even more preferably 25 μm or less. The pigment's aspect ratio is more preferably 100 or more, even more preferably 200 or more, even more preferably 300 or more, even more preferably 400 or more, and even more preferably 450 or more. Here, the aspect ratio is a value calculated from an electron microscope magnified image of the pigment, and is the average value of the average particle size divided by the thickness.

[0024]

[0023] When the water vapor barrier layer contains a polyurethane resin and swellable mica, the polyurethane resin content is preferably 65 to 88 parts by weight, and the polyurethane resin content is more preferably 70 parts by weight or more, and more preferably 85 parts by weight or less, per 100 parts by weight of the total water vapor barrier layer. Furthermore, the swellable mica content is preferably 5 to 35 parts by weight, and more preferably 10 parts by weight or more, and even more preferably 15 parts by weight or more, per 100 parts by weight of the total water vapor barrier layer. Furthermore, in addition to the water vapor barrier resin, water-soluble polymer, and pigment described above, the water vapor barrier layer can also contain various commonly used auxiliaries, such as water-soluble polymers, pigments, crosslinking agents, water repellents, dispersants, thickeners, water retention agents, defoamers, water-resistant agents, dyes, and fluorescent dyes.

[0025] (Gas Barrier Coating Layer) The gas barrier coating layer contains at least a gas barrier resin. Examples of the gas barrier resin include water-soluble polymers or water-dispersible polymers, such as polyvinyl alcohol-based resins (e.g., fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and ethylene copolymer polyvinyl alcohol); proteins (e.g., casein, soybean protein, and synthetic protein); starches (e.g., oxidized starch, cationized starch, urea phosphate esterified starch, and hydroxyethyl etherified starch); cellulose derivatives (e.g., carboxymethyl cellulose, hydroxymethyl cellulose, and hydroxyethyl cellulose); polyvinylpyrrolidone; and sodium alginate. These may be used alone or in combination of two or more. Among these, from the viewpoint of gas barrier properties, polyvinyl alcohol-based resins and cellulose derivatives are preferred, polyvinyl alcohol-based resins are more preferred, polyvinyl alcohol-based resins having a degree of polymerization of 400 to 1700 are even more preferred, and polyvinyl alcohol-based resins having a degree of polymerization of 800 to 1400 are even more preferred.

[0026] The gas barrier layer may contain a pigment. Examples of pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, and organic pigments such as solid, hollow, and core-shell pigments, which may be used alone or in combination. Among these, the pigment is preferably a flat pigment having an average particle size of 3 μm or more and an aspect ratio of 10 or more, and more preferably a flat pigment having an average particle size of 5 μm or more and an aspect ratio of 30 or more.

[0027] When a gas barrier layer contains a pigment, particularly a flat pigment, gases such as oxygen travel a longer distance because they bypass the pigment. Therefore, a gas barrier layer containing a pigment has superior gas barrier properties compared to a gas barrier layer that does not contain a pigment, and exhibits excellent gas barrier properties, particularly under high-humidity atmospheres. The amount of pigment in the gas barrier layer is preferably 90 parts by weight or less per 100 parts by weight of the gas barrier resin, on a dry weight basis. The pigment is an optional component of the gas barrier layer, and the gas barrier layer may not contain any pigment (0 parts by weight). By maintaining the pigment amount in this range, the gas barrier layer can exhibit excellent flex resistance. Furthermore, the inclusion of a pigment in the gas barrier layer improves adhesion between the gas barrier layer and the adjacent layer. A smaller pigment amount improves flex resistance but decreases gas barrier properties. Therefore, the amount of pigment can be adjusted depending on the balance between gas barrier properties and flex resistance desired for the paper barrier material; for example, it can be 5 to 80 parts by weight per 100 parts by weight of the gas barrier resin. In addition to the water-soluble polymers and pigments described above, the gas barrier layer may contain various commonly used auxiliary agents such as dispersants, thickeners, water retention agents, antifoaming agents, water-resistant agents, dyes, and fluorescent dyes.

[0028] A crosslinking agent, such as a polyvalent metal salt, can be added to the gas barrier layer. The crosslinking agent undergoes a crosslinking reaction with the water-soluble polymer contained in the gas barrier layer, thereby increasing the number of bonds (crosslinking points) in the gas barrier layer. This means that the gas barrier layer has a dense structure, allowing for excellent gas barrier properties to be achieved. The type of crosslinking agent is not particularly limited, and polyvalent metal salts (compounds in which a polyvalent metal, such as copper, zinc, silver, iron, potassium, sodium, zirconium, aluminum, calcium, barium, magnesium, or titanium, is bonded to an ionic substance, such as carbonate ion, sulfate ion, nitrate ion, phosphate ion, silicate ion, nitrogen oxide, or boron oxide), amine compounds, amide compounds, aldehyde compounds, or hydroxy acids can be appropriately selected and used depending on the type of water-soluble polymer contained in the gas barrier layer. From the perspective of achieving a crosslinking effect, the use of polyvalent metal salts is preferred, and potassium alum is more preferred. The amount of crosslinking agent to be added is not particularly limited as long as it is within the range of coatable coating concentration and coating viscosity, but preferably the amount of crosslinking agent is 1 part by weight to 10 parts by weight, more preferably 3 parts by weight to 5 parts by weight, per 100 parts by weight of pigment. If the amount is less than 1 part by weight, the effect of adding the crosslinking agent may not be fully obtained. On the other hand, if the amount is more than 10 parts by weight, the viscosity of the coating may increase significantly, making coating difficult.

[0029] When a gas barrier layer is provided on a water vapor barrier layer, it is preferable for the gas barrier layer to contain a surfactant, as this improves adhesion between the gas barrier layer and the water vapor barrier layer and improves barrier properties. The ionicity of the surfactant is not limited, and any of anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants may be used alone or in combination of two or more. Examples of surfactants include silicone-based surfactants, fluorine-based surfactants, alcohol-based surfactants, acetylene-based surfactants having an acetylene group, acetylene diol-based surfactants having an acetylene group and two hydroxyl groups, alkylsulfonic acid-based surfactants having an alkyl group and sulfonic acid, ester-based surfactants, amide-based surfactants, amine-based surfactants, alkyl ether-based surfactants, phenyl ether-based surfactants, sulfate ester-based surfactants, and phenol-based surfactants. Among these, acetylene diol-based surfactants are preferred, as they have a significant effect in improving the leveling properties of the coating material. Improved leveling properties of the coating material improve the uniformity of the gas barrier layer, thereby improving gas barrier properties.

[0030]

[0033] When a gas barrier layer is provided on top of a water vapor barrier layer, from the viewpoint of adhesion to the water vapor barrier layer, the surface tension of the paint for the gas barrier layer is preferably adjusted to between 10 mN / m and 60 mN / m, and more preferably between 15 mN / m and 50 mN / m. Furthermore, from the viewpoint of adhesion between the water vapor barrier layer and the gas barrier layer, it is preferable to adjust the surface tension of the paint for the gas barrier layer to between ±20 mN / m and the wetting tension of the surface of the water vapor barrier layer.

[0031] (Heat-seal coating layer) The paper barrier material of the present invention has a barrier coating layer and a heat-seal coating layer, in this order, on a paper substrate. The thermoplastic resin material contained in the heat-seal coating layer can be any thermoplastic resin used in heat-sealing applications without any particular restrictions, and for example, a thermoplastic resin with a glass transition temperature of 100°C or lower can be used. The glass transition temperature of the thermoplastic resin is preferably −20°C or higher and 85°C or lower. Furthermore, the melting point of the thermoplastic resin is preferably 80°C or higher and 120°C or lower. Examples of thermoplastic resins that can be used include thermoplastic resins used in heat sealing applications, such as polyolefin resins (polyethylene, polypropylene, etc.), polyester resins (polyethylene terephthalate, polyethylene succinate, polybutylene terephthalate, polyethylene naphthalate, polylactic acid resins, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), etc.), ethylene copolymers (ethylene-vinyl acetate resins, ethylene-acrylic resins, etc.), styrene copolymers (styrene-acrylate copolymer resins, etc.), acrylic resins, polyvinyl alcohol resins, and polyvinyl acetate resins, without particular limitation. One or more of these may be used in combination. Among these, one or more selected from the group consisting of polyolefin resins, polyester resins, ethylene copolymers, and styrene copolymers are preferred, and two or more are even more preferred. Note that ethylene copolymers and styrene copolymers refer to copolymers containing ethylene and styrene as monomers, respectively.

[0032] In particular, it is preferable for the heat-seal coating layer to contain an ethylene-vinyl acetate resin, since this facilitates adjusting the elongation at break to 200% or more and the Young's modulus to 15 MPa or less. When the total content of the thermoplastic resins in the heat-seal coating layer is taken as 100 parts (solid content), it is more preferable for the ethylene-vinyl acetate resin to be contained in an amount of 1 to 30 parts (solid content), and even more preferable for it to contain 5 to 20 parts (solid content). Furthermore, from the viewpoint of suppressing a decrease in barrier property due to flexing, the glass transition temperature of the ethylene-vinyl acetate resin is preferably 0°C or less, and even more preferably -5°C or less. Furthermore, it is preferable for the ethylene-vinyl acetate resin to contain a vinyl versatate structure. In this specification, the glass transition temperature refers to the midpoint glass transition temperature measured in accordance with JIS K 7121-1987.

[0033] In addition to the thermoplastic resin, the heat seal coating layer may contain additives such as an antiblocking agent, a silane coupling agent, etc. As the antiblocking agent, pigments, waxes, metal soaps, etc. can be used without any particular limitation.

[0034] The heat-seal coating layer is a layer obtained by coating and drying a composition containing at least a thermoplastic resin. When the composition forming this coating layer is evaluated as a 50 μm thick film, the heat-seal coating layer preferably has a breaking elongation of 200% or more and a Young's modulus of 15 MPa or less from the viewpoint of flex resistance. The breaking elongation is preferably 250% or more, more preferably 300% or more, even more preferably 350% or more, even more preferably 400% or more, even more preferably 450% or more, and even more preferably 500% or more. The upper limit of the breaking elongation is not particularly limited, but is about 1000%.

[0035] This Young's modulus is more preferably 14 MPa or less, even more preferably 13 MPa or less, even more preferably 12 MPa or less, even more preferably 11 MPa or less, even more preferably 10 MPa or less, even more preferably 9 MPa or less, even more preferably 8 MPa or less, even more preferably 7 MPa or less, even more preferably 6 MPa or less, even more preferably 5 MPa or less, even more preferably 4 MPa or less, even more preferably 3 MPa or less, even more preferably 2 MPa or less, and even more preferably 1.5 MPa or less. The lower limit of Young's modulus is not particularly limited, but is, for example, about 0.5 MPa. Young's modulus is the ratio of the force (stress) acting per unit cross-sectional area of ​​a sample when an external force is applied in one axial direction within the elastic range of the object to the deformation rate (strain), and is the initial slope of the stress-strain curve. Young's modulus is a value that represents the resistance to deformation of a material, and the higher the Young's modulus, the more difficult it is to deform.

[0036] (Coating) The method for applying the coating material for forming the water vapor barrier coating layer, gas barrier coating layer, and heat seal coating layer to the paper substrate is not particularly limited, and coating can be performed using known coating equipment and coating systems. Examples of coating equipment include blade coaters, bar coaters, roll coaters, air knife coaters, reverse roll coaters, curtain coaters, spray coaters, size press coaters, and gate roll coaters. Examples of coating systems include aqueous coating using a solvent such as water, and solvent-based coating using a solvent such as an organic solvent, with aqueous coating being preferred. Methods for drying the coating layer include conventional methods such as a steam heater, gas heater, infrared heater, electric heater, hot air heater, microwave, and cylinder dryer.

[0037] In the present invention, the coating amount of the water vapor barrier layer is 3 g / m2 in dry weight per side. ２ 50g / m or more ２ It is preferable that the density is 5 g / m or less. ２ 40g / m or more ２ More preferably, it is 7 g / m or less. ２ 30g / m or more ２It is more preferable that the coating amount of the water vapor barrier layer is 3 g / m or less. ２ If the coating weight of the water vapor barrier layer is less than 50 g / m, it may be difficult to completely coat the paper substrate with the coating material, resulting in insufficient water vapor barrier properties, or the coating material for forming the layer coated on the water vapor barrier layer may penetrate into the paper substrate, preventing the formation of a uniform coating layer. ２ If the amount is greater than this, the drying load during coating will be greater. The water vapor barrier layer may be a single layer, or may be configured as two or more layers. When the water vapor barrier layer is configured as two or more layers, it is preferable that the total coating amount of all the water vapor barrier layers be within the above range.

[0038] In the present invention, the coating amount of the gas barrier layer is 0.2 g / m2 in dry weight per side. ２ 20g / m or more ２ The coating weight of the gas barrier layer is preferably 0.2 g / m or less. ２ If the amount is less than 20 g / m, it may be difficult to form a uniform gas barrier layer, and sufficient gas barrier properties may not be obtained. ２ If the amount is larger, the drying load during coating increases.

[0039] In the present invention, the coating amount of the heat seal coating layer is 5 g / m2 in dry weight per side. ２ 20g / m or more ２ The coating weight of the heat seal coating layer is preferably 5 g / m or less. ２ If it is less than 20 g / m, the heat sealability may be insufficient. ２ If the coating amount of the heat seal coating layer exceeds 5 g / m, the heat sealability will saturate and will not improve any further, and the drying load during coating will increase. ２ 18g / m or more ２ More preferably, 7 g / m or less ２ 15g / m or more ２ More preferably, 8 g / m or less ２ 12g / m or more ２ Even more preferred are the following:

[0040] The paper barrier material of the present invention satisfies at least one of the following (1) and (2) after being folded crosswise with the heat seal coating layer on the outside: (1) The oxygen transmission rate at a temperature of 23°C and a relative humidity of 0% is 20 ml / m ２ (2) Water vapor permeability of 20 g / m at a temperature of 40°C and a relative humidity of 90% ２ ・Less than day

[0041] When the paper barrier material of the present invention satisfies (1), the oxygen permeability is 15 ml / m ２ ·day·atm or less is preferable, and 10 ml / m ２ ·day·atm or less is more preferable, and 8 ml / m ２ More preferably, it is 6 ml / m or less. ２ More preferably, the concentration is 4 ml / m or less. ２ More preferably, it is 2 ml / m ２ More preferably, it is 1 ml / m or less. ２ More preferably, it is 0.5 ml / m ２ More preferably, it is 0.3 ml / m or less. ２ More preferably, it is 0.2 ml / m or less. ２ More preferably, it is 0.1 ml / m or less. ２ ·day·atm or less is even more preferable.

[0042] Furthermore, the paper barrier material of the present invention has an oxygen permeability value before being folded crosswise, which is 20 ml / m less than the oxygen permeability value after being folded crosswise. ２ The oxygen permeability before folding is 15 ml / m ２ ·day·atm or less is preferable, and 10 ml / m ２ ·day·atm or less is more preferable, and 8 ml / m ２ More preferably, it is 6 ml / m or less. ２ More preferably, the concentration is 4 ml / m or less. ２ More preferably, it is 2 ml / m ２More preferably, it is 1 ml / m or less. ２ More preferably, it is 0.5 ml / m ２ More preferably, it is 0.3 ml / m or less. ２ More preferably, it is 0.2 ml / m or less. ２ More preferably, it is 0.1 ml / m or less. ２ ·day·atm or less is even more preferable.

[0043] When the paper barrier material of the present invention satisfies (2), the water vapor permeability is 18 g / m ２ ・day or less is preferable, 16 g / m ２ ・day or less is more preferable, 14 g / m ２ ・day or less is more preferable, and 12 g / m ２ day or less is even more preferable, and 10 g / m ２ ・day or less is even more preferable.

[0044] Furthermore, the water vapor permeability of the paper barrier material of the present invention before folding crosswise is 20 g / m less than the water vapor permeability after folding crosswise. ２ The water vapor permeability before cross folding is 18 g / m ２ ・day or less is preferable, 16 g / m ２ ・day or less is more preferable, 14 g / m ２ ・day or less is more preferable, and 12 g / m ２ day or less is even more preferable, and 10 g / m ２ ・day or less is even more preferable, 9 g / m ２ day or less is even more preferable, and 8 g / m ２ ・day or less is even more preferable.

[0045] The paper barrier material of the present invention can be used as is, or laminated with various resins, etc., or attached with various general-purpose films, barrier films, aluminum foil, etc., to form paper barrier packaging materials used for packaging applications such as food packaging, containers, cups, etc., or laminates used for industrial materials, etc. Among these, the paper barrier material of the present invention can be suitably used as a paper barrier packaging material used for packaging applications such as food packaging, containers, cups, etc., and can be particularly suitably used as a flexible packaging bag for food, etc. Note that a flexible packaging bag is a packaging material made of a highly flexible material, and generally refers to a packaging material made of thin, flexible materials such as paper, film, aluminum foil, etc., either alone or bonded together. The shape of the flexible packaging bag is not particularly limited, and examples include vertical pillow packaging bags, horizontal pillow packaging bags, side seal bags, two-side seal bags, three-side seal bags, gusset bags, bottom gusset bags, and stand-up bags.

[0046]

[0033] When used as packaging material for food and the like, particularly as flexible packaging bags, the paper barrier material of the present invention can protect the contents from oxidation by oxygen and deterioration due to moisture, enabling an extension of the storage period. Furthermore, because flexible packaging materials are thin and flexible, they are prone to bending during production, transportation, storage, sales, etc., but the paper barrier material of the present invention has excellent bending resistance and reduces the decline in barrier properties even when bending occurs, preventing the quality of the contents from being damaged by unexpected bending. Furthermore, when the paper barrier material of the present invention is used as a laminate for industrial materials, etc., it can prevent putrefaction, deterioration, rust, etc. by suppressing the intrusion of oxygen and moisture, and is also expected to have effects such as flavor barrier properties that prevent the leakage of solvent odors.

[0047] The present invention will be specifically described below using examples, but the present invention is not limited to these examples. Unless otherwise specified, parts and % in the examples indicate parts by weight and % by weight, respectively. The obtained paper barrier materials were tested based on the evaluation methods shown below.

[0048] (Evaluation Method) <Elongation at Break, Young's Modulus> A coating solution for forming a heat-seal coating layer was applied to a 20 μm PET film and dried at 105°C for 2 minutes to obtain a coating layer with a thickness of 50 μm. The PET film was peeled off to obtain a film with a thickness of 50 μm. In accordance with JIS K 7127:1999, test pieces cut into 15 mm wide strips were measured from the prepared film using a Tensilon tensile tester (chuck distance 50 mm, pulling speed 100 mm / min) to measure the elongation at break and Young's modulus.

[0049] <Heat seal strength> Two square test pieces measuring 100 mm on a side were cut from the obtained paper barrier material, and the heat seal coating layers were brought into contact with each other and heat sealed at a pressing temperature of 140°C, a pressing pressure of 2 kgf, and a pressing time of 0.5 seconds. The heat-sealed test pieces were peeled off using a Tensilon tensile tester, and the tensile strength was measured to determine the maximum value.

[0050] <Water Vapor Permeability and Oxygen Permeability> Water vapor permeability and oxygen permeability were measured on the sheet sample as is (unfolded) and on a sheet sample folded with the barrier layer side facing outward, with a rubber roller weighing approximately 400 g rolling back and forth five times at a speed of approximately 10 cm / sec under its own weight to create a cross crease (folded). For the folded sample, the cross was positioned in the center of the jig. Water vapor permeability was measured using a MOCON PERMATRAN W3 / 34 at 40°C and 90% RH. Oxygen permeability was measured using a MOCON OX-TRAN 2 / 21 at 23°C and 0% RH.

[0051] (Thermoplastic resins) Resin A: Styrene-acrylic resin (manufactured by Sakata Inx Corporation, B069 (640V)) Resin B: Ethylene-vinyl acetate resin (manufactured by Sumika Chemtex Corporation, Sumikaflex 400HQ, Tg = 0°C) Resin C: Acrylic resin (manufactured by VANORA Corporation, DXA.4081) Resin D: Mixture of 100 parts by weight of polyolefin resin (manufactured by Sakata Inx Corporation, Brightone HS-31-1) and 40 parts by weight of ethylene-vinyl acetate resin (manufactured by Sumika Chemtex Corporation, Sumikaflex 951HQ, having a vinyl versatate structure, Tg = -25°C) Resin E: Polyolefin resin (manufactured by Dow Chemical Company, Rhobarr 320) Resin F: Styrene-acrylic resin (manufactured by Daiichi Toryo Co., Ltd., Harvil HS-1) Resin G PHBH resin (Rezem W465, manufactured by Chukyo Yushi Co., Ltd.)

[0052] Resin H: A mixture of 100 parts by weight of polyolefin resin (HS-31-1, manufactured by Sakata Inx Corporation) and 10 parts by weight of polyvinyl alcohol resin (JF-10, manufactured by Japan Vinyl Acetate & Poval Corporation) Resin I: Polyolefin resin (Brightone HS-31-1, manufactured by Sakata Inx Corporation) Resin J: Ethylene-acrylic resin (Chemipearl S500NW, manufactured by Mitsui Chemicals, Inc.) Resin K: Polyvinyl alcohol resin (PVA117, manufactured by Kuraray Co., Ltd.) Resin L: Ethylene-acrylic resin (Zaixen AC, manufactured by Sumitomo Seika Chemicals Co., Ltd.) Resin M: Polylactic acid resin (Landy PL3000, manufactured by Miyoshi Oil & Fats Co., Ltd.) Resin N: Polyvinyl alcohol resin (Exceval AQ-4104, manufactured by Kuraray Co., Ltd.) Resin O: Styrene-acrylic resin (Brightone FC-643V, manufactured by Sakata Inx Corporation) Resin P Resin Q: A mixture of 100 parts by weight of a styrene-acrylic resin (Brightone FC-643V, manufactured by Sakata Inx Corporation) and 10 parts by weight of an ethylene-vinyl acetate resin (Sumikaflex 951HQ, manufactured by Sumika Chemtex Corporation, having a vinyl versatate structure, Tg = -25°C). Resin Q: A mixture of 100 parts by weight of a styrene-acrylic resin (Brightone FC-643V, manufactured by Sakata Inx Corporation) and 20 parts by weight of an ethylene-vinyl acetate resin (Sumikaflex 951HQ, manufactured by Sumika Chemtex Corporation, having a vinyl versatate structure, Tg = -25°C).

[0053] [Example 1] (Preparation of Paper Base Material) A hardwood bleached kraft pulp (LBKP) with a Canadian Standard Freeness (CSF) of 500 ml and a softwood bleached kraft pulp (NBKP) with a CSF of 530 ml were blended in an 80 / 20 weight ratio to prepare a raw pulp. To the raw pulp, 0.1% of polyacrylamide (PAM) with a molecular weight of 2.5 million was added as a dry strength agent, 0.35% of alkyl ketene dimer (AKD) as a sizing agent, 0.15% of polyamide epichlorohydrin (PAEH) resin as a wet strength agent, and 0.08% of polyacrylamide (PAM) with a molecular weight of 10 million was added as a retention agent. The resulting pulp was then spun at a speed of 300 m / min using a Fourdrinier paper machine (manufactured by Suzuki Seikisho) equipped with a Yankee dryer, with a basis weight of 50 g / m. ２ A paper substrate having the following composition was obtained.

[0054] (Preparation of coating liquid for gas barrier layer) An aqueous solution of polyvinyl alcohol (VC-10, manufactured by Japan Vinyl Acetate & Poval Co., Ltd.) with a solids concentration of 12% was prepared to serve as the coating liquid for the gas barrier layer. (Preparation of coating liquid for heat seal layer) An aqueous dispersion of thermoplastic resin A with a solids concentration of 40% was prepared to serve as the coating liquid for the heat seal layer. (Production of paper barrier material) The coating liquid for the gas barrier layer was applied in a dry weight of 4.0 g / m to the surface of the obtained paper substrate that had come into contact with the mirror surface of the Yankee dryer (glossy surface). ２ The coating solution for the heat seal layer was applied to the gas barrier layer at 10.0 g / m ２ The paper barrier material was obtained by coating on one side of the paper.

[0055] [Example 2] A paper barrier material was obtained in the same manner as Example 1, except that an aqueous dispersion of thermoplastic resin C adjusted to a solids concentration of 50% was used as the coating solution for the heat-seal layer. [Example 3] A paper barrier material was obtained in the same manner as Example 1, except that an aqueous dispersion of thermoplastic resin B adjusted to a solids concentration of 55% was used as the coating solution for the heat-seal layer. [Example 4] A paper barrier material was obtained in the same manner as Example 1, except that an aqueous dispersion of thermoplastic resin D adjusted to a solids concentration of 42% was used as the coating solution for the heat-seal layer.

[0056] Example 5 (Preparation of coating liquid for water vapor barrier layer) A polyurethane resin emulsion (manufactured by Mitsui Chemicals, Inc., WPB-341, Tg 130°C) was blended into a slurry of swellable mica (manufactured by Topy Industries, Ltd., NTS-10) so that the pigment was 20 parts by weight and the polyurethane resin was 80 parts by weight, relative to a total amount of 100 parts by weight of the water vapor barrier layer, to obtain a coating liquid for water vapor barrier layer with a solids concentration of 22%. (Production of paper barrier material) Instead of a gas barrier layer, a water vapor barrier layer was formed at a dry weight of 5.0 g / m ２ A paper barrier material was obtained in the same manner as in Example 4, except that the paper barrier material was formed so as to have the following properties.

[0057] [Example 6] A gas barrier layer was formed on a water vapor barrier layer at a dry weight of 4.0 g / m ２ A paper barrier material was obtained in the same manner as in Example 5, except that the coating solution for the heat-seal layer was changed so that the solid content of the thermoplastic resin E was 42%. [Example 7] A paper barrier material was obtained in the same manner as in Example 6, except that an aqueous dispersion of thermoplastic resin E adjusted to a solid content of 42% was used as the coating solution for the heat-seal layer. [Example 8] A paper barrier material was obtained in the same manner as in Example 6, except that an aqueous dispersion of thermoplastic resin O adjusted to a solid content of 46% was used as the coating solution for the heat-seal layer. [Example 9] A paper barrier material was obtained in the same manner as in Example 6, except that an aqueous dispersion of thermoplastic resin P adjusted to a solid content of 46% was used as the coating solution for the heat-seal layer. [Example 10] A paper barrier material was obtained in the same manner as in Example 6, except that an aqueous dispersion of thermoplastic resin Q adjusted to a solid content of 46% was used as the coating solution for the heat-seal layer. [Example 11] A paper barrier material was obtained in the same manner as in Example 1, except that an aqueous dispersion of thermoplastic resin Q adjusted to a solid content of 46% was used as the coating solution for the heat-seal layer.

[0058] [Comparative Example 1] A paper barrier material was obtained in the same manner as in Example 1, except that an aqueous dispersion of thermoplastic resin F adjusted to a solids concentration of 40% was used as the coating solution for the heat-seal layer. [Comparative Example 2] A paper barrier material was obtained in the same manner as in Example 6, except that an aqueous dispersion of thermoplastic resin F adjusted to a solids concentration of 40% was used as the coating solution for the heat-seal layer. [Comparative Example 3] A paper barrier material was obtained in the same manner as in Example 1, except that an aqueous dispersion of thermoplastic resin G adjusted to a solids concentration of 50% was used as the coating solution for the heat-seal layer. [Comparative Example 4] A paper barrier material was obtained in the same manner as in Example 1, except that an aqueous dispersion of thermoplastic resin K adjusted to a solids concentration of 8% was used as the coating solution for the heat-seal layer.

[0059] [Comparative Example 5] A paper barrier material was obtained in the same manner as in Example 1, except that an aqueous dispersion of thermoplastic resin H adjusted to a solids concentration of 40% was used as the coating solution for the heat-seal layer. [Comparative Example 6] A paper barrier material was obtained in the same manner as in Example 1, except that an aqueous dispersion of thermoplastic resin I adjusted to a solids concentration of 45% was used as the coating solution for the heat-seal layer. [Comparative Example 7] A paper barrier material was obtained in the same manner as in Example 1, except that an aqueous dispersion of thermoplastic resin J adjusted to a solids concentration of 32% was used as the coating solution for the heat-seal layer. [Comparative Example 8] A paper barrier material was obtained in the same manner as in Example 5, except that an aqueous dispersion of thermoplastic resin J adjusted to a solids concentration of 32% was used as the coating solution for the heat-seal layer.

[0060] [Comparative Example 9] A paper barrier material was obtained in the same manner as Example 1, except that an aqueous dispersion of thermoplastic resin L adjusted to a solids concentration of 30% was used as the coating solution for the heat-seal layer. [Comparative Example 10] A paper barrier material was obtained in the same manner as Example 5, except that an aqueous dispersion of thermoplastic resin L adjusted to a solids concentration of 30% was used as the coating solution for the heat-seal layer. [Comparative Example 11] A paper barrier material was obtained in the same manner as Example 6, except that an aqueous dispersion of thermoplastic resin L adjusted to a solids concentration of 30% was used as the coating solution for the heat-seal layer. [Comparative Example 12] A paper barrier material was obtained in the same manner as Example 1, except that an aqueous dispersion of thermoplastic resin M adjusted to a solids concentration of 45% was used as the coating solution for the heat-seal layer.

[0061] [Comparative Example 13] A paper barrier material was obtained in the same manner as in Example 5, except that an aqueous dispersion of thermoplastic resin M adjusted to a solids concentration of 45% was used as the coating solution for the heat-seal layer. [Comparative Example 14] A paper barrier material was obtained in the same manner as in Example 6, except that an aqueous dispersion of thermoplastic resin M adjusted to a solids concentration of 45% was used as the coating solution for the heat-seal layer. [Comparative Example 15] A paper barrier material was obtained in the same manner as in Example 1, except that an aqueous dispersion of thermoplastic resin N adjusted to a solids concentration of 11% was used as the coating solution for the heat-seal layer.

[0062]

[0063]

[0064]

[0065]

[0066] The paper barrier material obtained in Example 1-11 of the present invention has, after being folded crosswise, (1) an oxygen transmission rate of 20 ml / m at a temperature of 23°C and a relative humidity of 0%. ２ (2) Water vapor permeability of 20 g / m at a temperature of 40°C and a relative humidity of 90% ２- One or both of the following conditions were satisfied, and the deterioration of barrier properties after bending was suppressed. The paper barrier material obtained in Comparative Example 1-15 did not satisfy both of the above (1) and (2), and the barrier properties after bending were significantly reduced.

Claims

1. A paper barrier material having, on a paper substrate, a barrier coating layer with water vapor barrier properties or gas barrier properties and a heat seal coating layer in that order, and which satisfies at least one of the following (1) and (2) after being folded crosswise with the heat seal coating layer on the outside: (1) an oxygen permeability of 20 ml / m at a temperature of 23°C and a relative humidity of 0%; ２ (2) Water vapor permeability of 20 g / m at a temperature of 40°C and a relative humidity of 90% ２ ・Less than day.

2. The coating amount of the heat seal coating layer is 5 g / m ２ 20g / m or more ２ 2. The paper barrier material according to claim 1, wherein:

3. The paper barrier material according to claim 1 or 2, characterized in that the heat-seal coating layer, when evaluated as a 50 μm thick film, has an elongation at break of 200% or more and a Young's modulus of 15 MPa or less.

4. The paper barrier material according to claim 1 or 2, characterized in that it has a water vapor barrier coating layer and a gas barrier coating layer in this order on a paper substrate.

5. The paper barrier material according to claim 1 or 2, characterized in that the heat-seal coating layer contains one or more materials selected from the group consisting of polyolefin-based resins, polyester-based resins, ethylene-based copolymers, and styrene-based copolymers.

6. The basis weight of the paper base material is 25 g / m ２ 70g / m or more ２ 3. The paper barrier material according to claim 1, wherein:

7. The paper barrier material according to claim 1 or 2, characterized in that the heat-seal coating layer contains two or more types selected from the group consisting of polyolefin-based resins, polyester-based resins, ethylene-based copolymers, and styrene-based copolymers.

8. The paper barrier material according to claim 7, wherein the heat seal coating layer contains an ethylene-vinyl acetate resin.

9. The paper barrier material according to claim 8, characterized in that it contains 1 to 30 parts (solid content) of ethylene-vinyl acetate resin, relative to 100 parts (solid content) of the total content of thermoplastic resins in the heat-seal coating layer.

10. The paper barrier material according to claim 8, wherein the Tg of the ethylene-vinyl acetate resin is 0°C or lower.

11. The paper barrier material according to claim 8, wherein the ethylene-vinyl acetate resin contains a vinyl versatate structure.

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