Paper barrier materials

Abstract

To provide a paper barrier material excellent in flex resistance.SOLUTION: A paper barrier material includes: barrier base paper having a barrier coating layer containing a pigment on a paper substrate; and a protective layer having nylon 6 or nylon 66 as a main constituent, laminated on a side of the barrier coating layer of the barrier base paper.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a paper-based barrier material. [Background technology]

[0002] Imparting gas barrier properties (particularly oxygen barrier properties) to paper-based materials, especially paper-based packaging materials, is important for protecting the various products being packaged from deterioration caused by gases, such as oxidation by oxygen. Conventionally, methods for imparting gas barrier properties to paper packaging materials have mainly involved extruding and laminating or bonding a gas barrier layer onto a paper substrate. This layer typically consists of metal foil or metal vapor-deposited film made of metals such as aluminum, resin films such as polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, or polyacrylonitrile, or films coated with these resins, or ceramic vapor-deposited films with inorganic oxides such as silicon dioxide or aluminum oxide.

[0003] Other paper-based packaging materials that provide gas barrier properties besides those mentioned above include paper-based gas barrier materials having a gas barrier layer composed of a water-soluble polymer and an inorganic layered compound (Patent Documents 1 and 2). Furthermore, providing water resistance (especially water vapor barrier properties) to paper-based packaging materials is also important for protecting the various products being packaged from deterioration due to water vapor. As a paper-based packaging material possessing both gas barrier and water vapor barrier properties, a paper-based barrier packaging material has been disclosed having 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 on a paper substrate (Patent Document 3).

[0004] In such paper-based barrier materials, the barrier properties can be significantly reduced when bent. Our investigation revealed that this reduction in barrier properties due to bending occurs because the layer around the rigid pigment is broken down, allowing gases to pass through more easily. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2009-184138 [Patent Document 2] Japanese Patent Publication No. 2003-094574 [Patent Document 3] Patent No. 5331265 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to provide a paper barrier material with excellent flexibility. [Means for solving the problem]

[0007] The means for solving the problems of the present invention are as follows. 1. A barrier base paper having a barrier coating layer containing pigment on a paper substrate, A paper-based barrier material characterized by having a protective layer mainly composed of nylon 6 or nylon 66 laminated on the barrier coating layer side of the barrier base paper. 2. The paper-based barrier material according to 1, characterized in that the barrier base paper comprises a water vapor barrier coating layer and a gas barrier coating layer on a paper substrate in that order. 3. The basis weight of the paper substrate is 30 g / m². 2 More than 110g / m 2 The paper barrier material according to 1. or 2., characterized in that it is as follows: [Effects of the Invention]

[0008] The paper barrier material of the present invention has excellent flexibility and exhibits minimal reduction in barrier properties when bent. Because of its flexibility, the paper barrier material of the present invention can be suitably used in flexible packaging bags that are prone to bending. [Modes for carrying out the invention]

[0009] The paper barrier material of the present invention comprises a barrier base paper having a barrier coating layer containing a pigment on a paper base material, and has a protective layer mainly composed of nylon 6 or nylon 66 laminated on the barrier coating layer side of the barrier base paper.

[0010] The barrier base paper has a barrier coating layer containing a pigment on a paper base material. (Paper base material) In the present invention, the paper base material is a sheet composed of pulp, filler, and various additives. As the pulp, chemical pulps such as hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), softwood unbleached kraft pulp (NUKP), sulfite pulp, mechanical pulps such as stone ground pulp, thermomechanical pulp, recycled pulp, wood fibers such as wastepaper pulp, and non-wood fibers obtained from kenaf, bamboo, hemp, etc. can be used, and one or more of these can be blended and used. Among these, it is preferable to use chemical pulp or mechanical pulp of wood fiber, and more preferably chemical pulp, because it is difficult for foreign matter to混入 into the paper base material, it is difficult for discoloration to occur over time when the used paper container is recycled using waste paper raw materials, it has a high whiteness and thus has a good surface feeling during printing, and especially the use value when used as a packaging material is high.

[0011] As the filler, known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, zeolite, synthetic resin filler, etc. can be used as needed. In addition, internal additives such as sulfuric acid bands and various anionic, cationic, nonionic or amphoteric retention improvers, drainage improvers, paper strength enhancers, and internal sizing agents can be used as needed. Furthermore, dyes, fluorescent whitening agents, pH adjusters, defoamers, pitch control agents, slime control agents, etc. can also be added as needed.

[0012] The method for manufacturing (papermaking) paper substrates is not particularly limited, and paper substrates can be manufactured by papermaking using known methods such as acidic papermaking, neutral papermaking, and alkaline papermaking, using known screen formers, on-top hybrid formers, gap former machines, etc. Furthermore, the paper substrate may consist of one layer or two or more layers. Furthermore, the surface of the paper substrate 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-retaining agents, thickeners, and lubricants, which can be used individually or in combination of two or more. In addition, these various chemicals may be used in combination with pigments. 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 dense, hollow, or core-shell types, which can be used individually or in combination of two or more.

[0013] The surface treatment method for the paper substrate is not particularly limited, but known coating equipment such as rod metering size presses, pound-type size presses, gate roll coaters, spray coaters, blade coaters, and curtain coaters can be used. Examples of paper substrates obtained in this manner include various known types such as fine paper, medium-quality paper, coated paper, glossy paper on one side, kraft paper, glossy kraft paper on one side, bleached kraft paper, glassine paper, cardboard, white cardboard, and linerboard.

[0014] The basis weight of the paper substrate can be appropriately selected depending on the various qualities and handling requirements for the paper barrier material, but it is typically 20 g / m². 2 More than 500g / m 2 The following is preferable: For paper barrier materials used for packaging purposes such as food packaging, containers, and cups, 25 g / m² is preferred. 2 More than 400g / m 2The following are more preferable, and in particular, for paper barrier materials used in flexible packaging bags as described later, 30 g / m² is preferred. 2 More than 110g / m 2 The following are more preferable.

[0015] (Barrier coating layer) The barrier base paper of the present invention comprises a barrier coating layer containing a pigment. The barrier coating layer can be formed by applying a paint for forming a barrier coating layer using various coating devices and then drying it. The barrier coating layer preferably has either water vapor barrier properties or gas barrier properties, more preferably has at least gas barrier properties, and even more preferably has both water vapor barrier and gas barrier properties. When the barrier coating layer has both water vapor barrier and gas barrier properties, it is preferable to have both a water vapor barrier coating layer and a gas barrier coating layer, as this yields a paper barrier material that achieves both gas barrier and water vapor barrier properties. 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 limitations on the lamination order of the water vapor barrier layer and the gas barrier layer, it is preferable that they be laminated in the order of paper substrate, water vapor barrier layer, and gas barrier layer in order to further improve both water vapor barrier and gas barrier properties. The reason why a paper barrier material having a paper substrate, water vapor barrier layer, and gas barrier layer in this order possesses superior water vapor barrier and gas barrier properties is presumed to be as follows: As the resin with gas barrier properties used in the gas barrier layer, polymers such as water-soluble polymers and water-dispersible polymers are generally used, as will be described later. 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 deterioration due to moisture in the paper substrate and moisture in the air that penetrates through the paper substrate. On the other hand, the water vapor barrier layer contains a resin with good water resistance to prevent 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 influence (deterioration) of moisture from the paper substrate side on the gas barrier layer. Therefore, paper-based barrier materials having a water vapor barrier layer and a gas barrier layer in this order can exhibit good water vapor barrier and gas barrier properties.

[0017] When the barrier paper of the present invention comprises a water vapor barrier coating layer and a gas barrier coating layer, it is sufficient for either one of the barrier coating layers to contain a pigment. It is preferable that at least the barrier coating layer furthest from the paper substrate contains the pigment, as this improves flexibility and prevents a decrease in barrier properties due to bending, etc. That is, in the case of barrier paper having a water vapor barrier coating layer and a gas barrier coating layer on a paper substrate in that order, it is preferable that the gas barrier coating layer contains a pigment. Furthermore, from the viewpoint of barrier properties, it is even more preferable that both the gas barrier coating layer and the water vapor barrier coating layer contain a pigment.

[0018] (Water vapor barrier coating layer) The water vapor barrier coating layer contains at least a water vapor barrier resin. As the water vapor barrier resin, various copolymers such as styrene-butadiene, styrene-acrylic, ethylene-vinyl acetate, paraffin (wax), butadiene-methyl methacrylate, vinyl acetate-butyl acrylate, etc., synthetic adhesives such as maleic anhydride copolymers, acrylic acid-methyl methacrylate copolymers, etc., or paraffin (wax)-containing synthetic adhesives thereof can be used individually or in combination of two or more types. Among these, styrene-butadiene synthetic adhesives are preferred from the viewpoint of water vapor barrier properties. In the present invention, the styrene-butadiene synthetic adhesive is an emulsion polymerized adhesive in which styrene and butadiene are the main constituent monomers, and various comonomers for modification are combined with them. Examples of comonomers include methyl methacrylate, acrylonitrile, acrylamide, hydroxyethyl acrylate, and unsaturated carboxylic acids such as itaconic acid, maleic acid, and acrylic acid. Furthermore, anionic surfactants such as sodium oleate, rosinate soap, alkylallyl sulfonate sodium, and dialkyl sulfosuccinate sodium can be used alone or in combination with nonionic surfactants as emulsifiers. Depending on the purpose, amphoteric or cationic surfactants may also be used.

[0019] Furthermore, if there are no issues with water vapor barrier properties, polyvinyl alcohols such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and ethylene copolymerized polyvinyl alcohol; 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 carboxymethylcellulose, hydroxymethylcellulose, and hydroxyethylcellulose; and water-soluble polymers such as polyvinylpyrrolidone and sodium alginate can be used in combination with water vapor barrier resins.

[0020] The water vapor barrier layer may contain pigments. Pigments can 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 dense, hollow, or core-shell types, which can be used individually or in combination of two or more. Among these, from the viewpoint of improving water vapor barrier properties and suppressing the penetration of paint to form the gas barrier layer, inorganic pigments with a flattened shape, such as kaolin, mica, and talc, are preferred, with kaolin being more preferred. Furthermore, it is preferable to use inorganic pigments with a volume 50% average particle diameter (D50) (hereinafter also referred to as "average particle diameter") of 5 μm or more and an aspect ratio of 10 or more, either individually or in combination of two or more. If the average particle size or aspect ratio of the inorganic pigment used is smaller than the above range, the number of times water vapor molecules can bypass the water vapor barrier layer decreases, and the distance they travel becomes shorter, which may result in a reduced improvement in water vapor barrier properties.

[0021] In the present invention, from the viewpoint of improving water vapor barrier properties and adhesion to the gas barrier layer, it is preferable that the water vapor barrier layer contains an inorganic pigment with an average particle diameter of 5 μm or more and an aspect ratio of 10 or more, as well as a pigment with an average particle diameter of 5 μm or less. As the pigment with an average particle diameter of 5 μm or less, inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicate, colloidal silica, and satin white, as well as organic pigments such as dense, hollow, or core-shell types, can be used individually or in mixtures of two or more. Among these pigments, it is preferable to use heavy calcium carbonate.

[0022] By including pigments with an average particle size of 5 μm or less, the voids in the water vapor barrier layer formed by inorganic pigments with an average particle size of 5 μm or more and an aspect ratio of 10 or more can be more effectively filled, resulting in even better water vapor barrier properties. In other words, when pigments with different average particle sizes are included in the water vapor barrier layer, the voids formed by inorganic pigments with larger average particle sizes are filled with pigments with smaller average particle sizes. As a result, water vapor has to travel a longer distance to bypass these pigments, and it is presumed that this will result in higher water vapor barrier properties compared to a water vapor barrier layer that does not contain pigments with different average particle sizes. When using inorganic pigments with an average particle diameter of 5 μm or more and an aspect ratio of 10 or more in combination with pigments with an average particle diameter of 5 μm or less, the mixing ratio of the inorganic pigment with an average particle diameter of 5 μm or more and an aspect ratio of 10 or more to the pigment with an average particle diameter of 5 μm or less is preferably 50 / 50 to 99 / 1 by dry weight. If the mixing ratio of inorganic pigments with an average particle diameter of 5 μm or more and an aspect ratio of 10 or more is less than the above range, the number of times water vapor bypasses the water vapor barrier layer decreases and the distance it travels becomes shorter, which may reduce the effect of improving water vapor barrier properties. On the other hand, if the mixing ratio of inorganic pigments with an average particle diameter of 5 μm or more and an aspect ratio of 10 or more is more than the above range, the voids formed by the large average particle diameter inorganic pigments in the water vapor barrier layer cannot be sufficiently filled with pigments with an average particle diameter of 5 μm or less, and therefore improvement in water vapor barrier properties cannot be expected.

[0023] When a pigment is included in the water vapor barrier layer, the amount of pigment is preferably in the range of 5 to 200 parts by weight of the water vapor barrier resin and water-soluble polymer combined, per 100 parts by weight of pigment, and more preferably 10 to 150 parts by weight of the water vapor barrier resin and water-soluble polymer combined. Note that the pigment is an optional component of the water vapor barrier layer and may be omitted (0 parts by weight). Furthermore, in addition to the water vapor barrier resin, water-soluble polymer, and pigment mentioned above, the water vapor barrier layer can also contain various commonly used auxiliary agents such as dispersants, thickeners, water-retaining agents, defoaming agents, water-resistant agents, dyes, and fluorescent dyes.

[0024] Crosslinking agents, such as polyvalent metal salts, can be incorporated into the water vapor barrier layer. These crosslinking agents react with the water vapor barrier resin and water-soluble polymer contained within the water vapor barrier layer, increasing the number of bonds (crosslinking points) within the layer. This results in a denser structure and improved water vapor barrier properties. The type of crosslinking agent is not particularly limited, and one or more types of polyvalent metal salts (compounds formed by the bonding of polyvalent metals such as copper, zinc, silver, iron, potassium, sodium, zirconium, aluminum, calcium, barium, magnesium, and titanium with ionic substances such as carbonate ions, sulfate ions, nitrate ions, phosphate ions, silicate ions, nitrogen oxides, and boron oxides), amine compounds, amide compounds, aldehyde compounds, hydroxy acids, etc., can be used depending on the type of water vapor barrier resin and water-soluble polymer contained in the water vapor barrier layer. When using styrene-based water vapor barrier resins such as styrene-butadiene-based or styrene-acrylic-based resins that exhibit excellent water vapor barrier properties, it is preferable to use polyvalent metal salts, and more preferably potassium alum, from the viewpoint of exhibiting a crosslinking effect. The amount of crosslinking agent can be added without particular limitations as long as it is within the range of paint concentration and viscosity that can be applied. Preferably, the amount of crosslinking agent is 1 part by weight or more and 10 parts by weight or less per 100 parts by weight of pigment, and more preferably 3 parts by weight or more and 5 parts by weight or less. If the amount is less than 1 part by weight, the effect of adding the crosslinking agent may not be sufficiently obtained. Also, if the amount is more than 10 parts by weight, the viscosity of the paint will increase significantly, which may make application difficult.

[0025] When adding a crosslinking agent to a paint for a water vapor barrier layer, it is preferable to dissolve the crosslinking agent in a polar solvent such as ammonia before adding it to the paint. Dissolving the crosslinking agent in a polar solvent creates a bond between the crosslinking agent and the polar solvent, so even after adding it to the paint, a crosslinking reaction with the water vapor barrier resin or water-soluble polymer does not occur immediately, and the viscosity of the paint can be suppressed. In that case, after coating the paper substrate and drying, the polar solvent component volatilizes, and a crosslinking reaction with the water vapor barrier resin or water-soluble polymer occurs, forming a dense water vapor barrier layer.

[0026] From the viewpoint of improving water vapor barrier properties, it is preferable to include a water repellent in the water vapor barrier layer. Examples of water repellents include paraffin-based water repellents mainly composed of alkane compounds, natural oil-based water repellents derived from plants and animals such as carnauba and lanois, silicone-containing water repellents containing silicone or silicone compounds, and fluorine-containing water repellents containing fluorine compounds. These can be used individually or in combination of two or more types. Among these, paraffin-based water repellents are preferred from the viewpoint of achieving water vapor barrier performance.

[0027] The amount of water repellent is not particularly limited, but it is preferable that the amount of water repellent is 1 part by weight or more and 100 parts by weight or less per 100 parts by weight of the total of the water vapor barrier resin and water-soluble polymer by dry weight. If the amount of water repellent is less than 1 part by weight, the effect of improving water vapor barrier properties may not be sufficiently obtained. On the other hand, if it exceeds 100 parts by weight, it may become difficult to form a uniform gas barrier layer when a gas barrier layer is provided on the water vapor barrier layer, which may reduce the gas barrier properties. The wetting tension of the water vapor barrier layer surface is preferably 10 mN / m to 60 mN / m, and more preferably 15 mN / m to 50 mN / m, for improved water vapor barrier properties and adhesion with the gas barrier layer.

[0028] (Gas barrier coating layer) The gas barrier coating layer contains at least a gas barrier resin. As the gas barrier resin, water-soluble polymers or water-suspendable polymers can be used. Examples include polyvinyl alcohol-based resins such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and ethylene copolymerized polyvinyl alcohol; 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 carboxymethylcellulose, hydroxymethylcellulose, and hydroxyethylcellulose; polyvinylpyrrolidone; and sodium alginate. These can be used individually 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 with a degree of polymerization of 400 to 1700 are even more preferred, and polyvinyl alcohol-based resins with a degree of polymerization of 800 to 1400 are even more preferred.

[0029] The gas barrier layer may contain pigments. These pigments may 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 dense, hollow, or core-shell types, which can be used individually or in combination of two or more. Among these, the pigments are preferably flattened pigments with an average particle diameter of 3 μm or more and an aspect ratio of 10 or more, and more preferably flattened pigments with an average particle diameter of 5 μm or more and an aspect ratio of 30 or more.

[0030] When a gas barrier layer contains pigments, especially flattened pigments, gases such as oxygen have to travel a longer distance to bypass the pigments. Therefore, a gas barrier layer containing pigments has superior gas barrier properties compared to a gas barrier layer without pigments, and exhibits particularly excellent gas barrier properties in high-humidity atmospheres. The amount of pigment in the gas barrier layer is preferably 90 parts by weight or less of pigment per 100 parts by weight of gas barrier resin, based on dry weight. Note that the pigment is an optional component of the gas barrier layer and can be omitted (0 parts by weight). By keeping the pigment content within this range, excellent flexibility can be achieved. Furthermore, the inclusion of pigment in the gas barrier layer improves adhesion to the layer in contact with it. If the pigment content is reduced, flexibility improves, but gas barrier properties decrease. Therefore, the pigment content can be adjusted according to the balance between the gas barrier properties and flexibility required for the paper barrier material; for example, it can be between 5 and 80 parts by weight per 100 parts by weight of gas barrier resin. In addition to the water-soluble polymers and pigments mentioned above, the gas barrier layer can also contain various commonly used auxiliary agents such as dispersants, thickeners, water-retaining agents, defoaming agents, water-resistant agents, dyes, and fluorescent dyes.

[0031] Crosslinking agents, such as polyvalent metal salts, can be added to the gas barrier layer. The crosslinking agent undergoes a crosslinking reaction with the water-soluble polymers contained in the gas barrier layer, increasing the number of bonds (crosslinking points) within the gas barrier layer. This results in a denser structure in the gas barrier layer, enabling it to exhibit excellent gas barrier properties. The type of crosslinking agent is not particularly limited, and depending on the type of water-soluble polymer contained in the gas barrier layer, polyvalent metal salts (compounds formed by the bonding of polyvalent metals such as copper, zinc, silver, iron, potassium, sodium, zirconium, aluminum, calcium, barium, magnesium, and titanium with ionic substances such as carbonate ions, sulfate ions, nitrate ions, phosphate ions, silicate ions, nitrogen oxides, and boron oxides), amine compounds, amide compounds, aldehyde compounds, hydroxy acids, etc., can be appropriately selected and used. From the viewpoint of exhibiting a crosslinking effect, the use of polyvalent metal salts is preferred, and the use of potassium alum is more preferred. The amount of crosslinking agent can be added without particular limitations as long as it is within the range of paint concentration and viscosity that can be applied. Preferably, the amount of crosslinking agent is 1 part by weight or more and 10 parts by weight or less per 100 parts by weight of pigment, and more preferably 3 parts by weight or more and 5 parts by weight or less. If the amount is less than 1 part by weight, the effect of adding the crosslinking agent may not be sufficiently obtained. Also, if the amount is more than 10 parts by weight, the viscosity of the paint will increase significantly, which may make application difficult.

[0032] The gas barrier layer preferably contains a surfactant because it improves adhesion between the gas barrier layer and the water vapor barrier layer, thereby improving barrier performance. The ionicity of the surfactant is not limited; it can be anionic, cationic, amphoteric, or nonionic surfactant, and can be used alone or in combination of two or more types. Examples of surfactants include silicone-based surfactants, fluorine-based surfactants, alcohol-based surfactants, acetylene-based surfactants having an acetylene group, acetylenediol-based surfactants having an acetylene group and two hydroxyl groups, alkylsulfonic acid-based surfactants having an alkyl group and a 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, it is preferable to use an acetylenediol-based surfactant, which has a significant effect on improving the leveling properties of the paint. When the leveling properties of the paint are improved, the uniformity of the gas barrier layer is improved, and thus the gas barrier performance is improved. When a gas barrier layer is provided on top of a water vapor barrier layer, it is preferable to adjust the surface tension of the gas barrier layer coating to 10 mN / m or more and 60 mN / m or less, and more preferably to 15 mN / m or more and 50 mN / m or less, from the viewpoint of adhesion with the water vapor barrier layer. Furthermore, from the viewpoint of adhesion between the water vapor barrier layer and the gas barrier layer, it is preferable to set the surface tension of the gas barrier layer coating to ±20 mN / m relative to the wetting tension of the water vapor barrier layer surface.

[0033] (Coating of water vapor barrier layer and gas barrier layer) The method of coating the paper substrate with the paint for forming the water vapor barrier layer and the gas barrier layer is not particularly limited, and it can be coated with known coating devices and coating systems. For example, as the coating device, a blade coater, a bar coater, a roll coater, an air knife coater, a reverse roll coater, a curtain coater, a spray coater, a size press coater, a gate roll coater, etc. can be mentioned. Further, as the coating system, an aqueous coating using a solvent such as water, a solvent-based coating using a solvent such as an organic solvent, etc. can be mentioned, but an aqueous coating is preferable. As a method for drying the water vapor barrier layer and the gas barrier layer, for example, ordinary methods such as a steam heater, a gas heater, an infrared heater, an electric heater, a hot air heater, a microwave, a cylinder dryer, etc. are used.

[0034] In the present invention, the coating amount of the water vapor barrier layer is 3 g / m in terms of dry weight 2 or more and 50 g / m 2 or less, preferably 5 g / m 2 or more and 40 g / m 2 or less, more preferably 7 g / m 2 or more and 30 g / m 2 or less. When the coating amount of the water vapor barrier layer is less than 3 g / m 2 , it becomes difficult to completely cover the paper substrate with the paint, and sufficient water vapor barrier properties cannot be obtained, or the paint for the gas barrier layer may penetrate to the paper substrate and a uniform gas barrier coating layer cannot be formed, resulting in insufficient gas barrier properties. On the other hand, when the coating amount of the water vapor barrier layer is more than 50 g / m 2 , the drying load during coating increases. The water vapor barrier layer may be a single layer or may be composed of two or more layers. When the water vapor barrier layer is composed of two or more layers, it is preferable that the total coating amount of all the water vapor barrier layers is within the above range.

[0035] In the present invention, the coating amount of the gas barrier layer is 0.2 g / m in terms of dry weight 2 or more and 20 g / m 2The following is preferable: The amount of gas barrier layer coating is 0.2 g / m². 2 If the concentration is less than 20 g / m², it becomes difficult to form a uniform gas barrier layer, and sufficient gas barrier properties may not be obtained. 2 A higher concentration increases the drying load during coating.

[0036] (protective layer) The protective layer is primarily composed of nylon 6 or nylon 66. "Primary component" means that it accounts for 50% or more by weight of the entire protective layer, and other additives such as plasticizers, UV absorbers, and lubricants may be included. Nylon 6 or nylon 66 can be used as a uniaxially or biaxially oriented nylon film, or as unoriented nylon directly extruded. Furthermore, when used as a film, laminated nylon films with other resins, such as polyethylene, can also be used. Paper barrier materials using a protective layer primarily composed of nylon 6 or nylon 66 can achieve both suppression of elongation of the barrier coating layer, flexibility due to resilience against bending, and sufficient sealing strength, despite the protective layer being a thin film. Furthermore, due to its sufficient strength, it can be used not only for filling lightweight materials such as powders and bulk materials, but also for filling heavier materials such as liquids and viscous substances, thus expanding the range of materials that can be filled. Although MX nylon is a type of nylon, it is not part of the present invention. While it offers better stretch suppression and resilience against bending, it is more expensive than other nylons. Furthermore, MX nylon itself is a resin with very high barrier properties, and simply laminating it onto paper provides sufficient barrier properties. Therefore, there is little point in laminating it onto a barrier base paper that already has a barrier coating layer, and thus it has been excluded from the present invention.

[0037] The protective layer is laminated on the barrier coating side of the barrier base paper. By placing the protective layer near the barrier coating layer, it is possible to prevent damage around the pigment in the barrier coating layer when it is bent, thereby improving the bending resistance of the paper barrier material. The thickness of the protective layer is not particularly limited, but for example, it is about 5 μm to 20 μm. The protective layer can be laminated directly onto the barrier coating layer, or it can be laminated via another layer. A preferred other layer is an adhesive layer that connects the barrier coating layer and the protective layer, preventing peeling at the interface. The material of the adhesive layer is not particularly limited as long as it exhibits excellent adhesion to both the barrier coating layer and the protective layer. Modified resins (solids) such as maleic acid-modified polyethylene, as well as one-component or two-component liquid adhesives, can be used alone or in combination. The method for forming other layers, such as adhesive layers, is not particularly limited and can be formed by known methods such as coating, extrusion lamination, sand lamination, and dry lamination.

[0038] (thermoplastic resin layer) The paper barrier material of the present invention can have a thermoplastic resin layer on at least one of its outermost surfaces. By providing a thermoplastic resin layer on at least one of its outermost surfaces, heat sealing becomes possible. The thermoplastic resin material used to form the thermoplastic resin layer can be any thermoplastic resin used for heat sealing applications without particular limitations. For example, a thermoplastic resin with a glass transition temperature of 100°C or lower can be used. Preferably, the glass transition temperature of the thermoplastic resin is between -20°C and 85°C. Preferably, the melting point of the thermoplastic resin is between 80°C and 120°C. As the thermoplastic resin, for example, any thermoplastic resin used for heat sealing applications such as ethylene-vinyl acetate resin, styrene-acrylic ester copolymer resin, acrylic resin, ethylene-acrylic resin, polyolefin resin (polyethylene, polypropylene, etc.), polyester resin (polyethylene terephthalate, polyethylene succinate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyvinyl alcohol resin, polyvinyl acetate resin, and polylactic acid resin can be used without particular limitations. Among these, ethylene-vinyl acetate resin, styrene-acrylic ester copolymer resin, acrylic resin, ethylene-acrylic resin, and polyolefin resin (polyethylene, polypropylene, etc.) are preferred in terms of heat seal strength. Furthermore, biodegradable resins such as polyvinyl alcohol, polylactic acid, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH) are preferable in terms of reducing the environmental burden if they are released as waste. The thermoplastic resin layer may contain additives such as antiblocking agents and silane coupling agents. Pigments, waxes, metal soaps, etc., can be used as antiblocking agents without particular limitations.

[0039] The method for forming the protective layer and the optional thermoplastic resin layer is not particularly limited and can be formed by known methods such as extrusion lamination, sand lamination, and dry lamination. Furthermore, when the thermoplastic resin layer is provided on the protective layer of the paper substrate, an adhesive layer can be provided between the protective layer and the thermoplastic resin layer to bond them together, if necessary.

[0040] The paper barrier material of the present invention can be used as a paper barrier material as is, or laminated with various resins, or laminated with various general-purpose films, barrier films, aluminum foil, etc., to form a paper barrier packaging material used for packaging food products, containers, cups, etc., or a laminate 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 food products, containers, cups, etc., and can be particularly suitably used as a flexible packaging bag for food products. A flexible packaging bag is a packaging material composed of a highly flexible material, and generally refers to a packaging material made of thin, flexible materials such as paper, film, or aluminum foil, either individually or laminated. 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, stand-up pouches, etc.

[0041] The paper barrier material of the present invention, when used as packaging material for food and other products, particularly as flexible packaging bags, can protect the contents from oxidation by oxygen and deterioration due to moisture, thereby extending the shelf life. Furthermore, because flexible packaging materials are thin and flexible, they are prone to bending during manufacturing, transportation, storage, and sales. However, the paper barrier material of the present invention has excellent bending resistance, and even when bending occurs, the reduction in barrier properties is suppressed, thus preventing the quality of the contents from being compromised due to unexpected bending. Furthermore, when the paper barrier material of the present invention is used as a laminate for industrial materials, it can prevent decay and deterioration 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. [Examples]

[0042] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, parts and % in the examples refer to parts by weight and weight %, respectively. The obtained paper barrier material was tested based on the evaluation method described below.

[0043] (Evaluation method) (1) Oxygen permeability / flexural resistance Measurements were taken using a MOCON OX-TRAN2 / 21 under conditions of 23°C and 0%RH. Measurements were taken on both an unfolded sheet sample and a folded sheet sample (with a 370g rubber roller rolled back and forth 10 times under its own weight) to create a cross-shaped crease. For the folded sample, the measurement was taken with the cross positioned in the center of the jig. Furthermore, the flexural resistance was evaluated according to the following criteria. OK: The oxygen permeability of the folded sample is 10 cc / m³. 2 Less than 1 day at a meter NG: The oxygen permeability of the folded sample is 10 cc / m³. 2 ·day · atm or more

[0044] (2) Sealing strength The sealing strength was measured using a sealing strength meter manufactured by Sun Science Co., Ltd., employing the compressed air rupture method. Two test pieces measuring 150 mm in length and 165 mm in width were cut from the obtained paper barrier material, and they were placed on top of each other so that the outermost thermoplastic resin layer (polyethylene layer) faced each other. The test was then conducted at a temperature of 120°C and a pressure of 2 kgf / cm². 2 The four edges were heat-sealed with a seal width of 10 mm under the condition of pressurizing for 0.5 sec. The air injection needle of the measuring instrument was inserted into a heat-sealed test bag, and air was injected into the test bag at a rate of 100 mmHg per 10 seconds. The pressure at which air leakage or bag rupture occurred was then measured. ◎: Sealing strength is 300 mmHg (upper limit of measurement) or higher. ○: Sealing strength is 100 mmHg or more, and less than 300 mmHg. ×: Sealing strength is less than 100 mmHg

[0045] [Example 1] (Preparation of paper substrate) The raw pulp was prepared by blending hardwood bleached kraft pulp (LBKP) with a Canadian standard filtration efficiency (CSF) of 500 ml and softwood bleached kraft pulp (NBKP) with a CSF of 530 ml in a weight ratio of 80 / 20. To the raw pulp, 0.1% of polyacrylamide (PAM) with a molecular weight of 2.5 million was added as a dry strength enhancer, 0.35% of alkyl ketene dimer (AKD) with a molecular weight of 2.5 million was added as a sizing agent, 0.15% of polyamide epichlorohydrin (PAEH) resin with a molecular weight of 2.5 million was added as a wet strength enhancer, and 0.08% of polyacrylamide (PAM) with a molecular weight of 10 million was added as a yield enhancer. The paper was then made at a speed of 300 m / min using a Duoformer FM type paper machine, resulting in a basis weight of 45 g / m². 2 I obtained the paper. Next, polyvinyl alcohol (PVA117, manufactured by Kuraray Co., Ltd.), prepared to a solid content concentration of 2%, was applied to the resulting paper using a rod metering size press, with a total of 1.0 g / m² applied to both sides. 2 After coating and drying, the basis weight is 45 g / m². 2 A base paper was obtained. The obtained base paper was smoothed using a chilled calender at a speed of 300 m / min and a linear pressure of 50 kgf / cm in one pass to obtain a paper substrate.

[0046] (Preparation of coatings for water vapor barrier layers) Engineered kaolin (Imeris, Varisurf HX, average particle size 90 μm, aspect ratio 80-100) was mixed with sodium polyacrylate as a dispersant (0.2% relative to pigment) and dispersed in a Serie mixer to prepare a kaolin slurry with a solids content of 60%. To the obtained kaolin slurry, styrene-acrylic copolymer emulsion (Saiden Chemical Co., Ltd., X-511-374E) was added as a water vapor barrier resin at a ratio of 100 parts (solids) to 100 parts (solids) of pigment to obtain a water vapor barrier coating with a solids content of 45%.

[0047] (Preparation of paint for gas barrier layer) Engineered kaolin (Imeris, Varisurf HX, average particle size 90 μm, aspect ratio 80-100) was mixed with sodium polyacrylate as a dispersant (0.2% relative to pigment) and dispersed in a Serie mixer to prepare a kaolin slurry with a solid content of 55%. An aqueous solution of polyvinyl alcohol (Kuraray, PVA117) was adjusted to a solid content of 10% to obtain an aqueous PVA solution. The obtained kaolin slurry and the aqueous PVA solution were mixed so that the solid content ratio of pigment:PVA = 100:100 and the solid content was 10% to obtain a coating for a gas barrier layer.

[0048] (Preparation of barrier paper) On the resulting paper substrate, apply a water vapor barrier coating at a dry weight of 15 g / m². 2 The coating is applied to one side and allowed to dry. Then, the gas barrier layer coating is applied at a dry weight rate of 5.0 g / m². 2 The paper was coated on one side and dried to obtain a barrier base.

[0049] (Preparation of paper barrier materials) On the barrier coating layer of the obtained barrier paper, a two-component curing aromatic ester adhesive (main component: DIC LX-500, curing agent: DIC KW-75) is applied by roll coating at a rate of 1.0 g / m². 2 (Dry weight) The adhesive layer was applied and dried at 80°C for 1 second. A laminated film of polyethylene / nylon 6 / polyethylene = 10 μm / 10 μm / 10 μm (Gunze Heptax B type (#30), biaxially oriented) was then sand-laminated with 15 μm of polyethylene (Asahi Kasei Suntech L1850K). A further layer of 30 μm of polyethylene (Nippon Polyethylene Co., Ltd. Kernel KC577T) was laminated to the outermost surface of the laminated film by extrusion lamination to obtain a paper barrier material with a protective layer.

[0050] [Example 2] On the barrier coating layer of the obtained barrier paper, a two-component curing aromatic ester adhesive (main component: DIC LX-500, curing agent: DIC KW-75) is applied by roll coating at a rate of 3.0 g / m². 2A paper barrier material having a protective layer was obtained in the same manner as in Example 1, except that the nylon side of a film, which had been previously laminated with a nylon 6 film (Bonel W (#15), biaxially oriented, manufactured by Kojin Film & Chemical Co., Ltd.) and a polyethylene film (HR653H (#30), manufactured by Skyfilm Co., Ltd.) by dry lamination using the same adhesive and conditions, was laminated by dry lamination.

[0051] [Example 3] A paper barrier material having a protective layer was obtained in the same manner as in Example 1, except that 15 μm of adhesive resin (Modic M545, manufactured by Mitsubishi Chemical Corporation) and 15 μm of nylon 6 (1022, manufactured by Ube Industries, Ltd.) were co-extruded and laminated onto the barrier coating layer of the obtained barrier base paper, and 15 μm of adhesive resin (Modic M545, manufactured by Mitsubishi Chemical Corporation) and 20 μm of polyethylene (Harmolex NH745N, manufactured by Nippon Polyethylene Co., Ltd.) were further laminated to the outermost surface of the nylon layer by co-extrusion lamination. The nylon layer was obtained by melting pellets and extruding them into a film from the T-die of a laminating machine, and was unstretched. [Example 4] A paper barrier material was obtained in the same manner as in Example 3, except that nylon 66 (E2001R, manufactured by Unitika Corporation) was used as the protective layer. The nylon layer was formed by melting pellets and extruding them into a film from the T-die of a laminating machine, and was not stretched.

[0052] [Comparative Example 1] An adhesive layer was formed on the barrier coating layer of the obtained barrier base paper in the same manner as in Example 1, and after drying, a 60 μm layer of polyethylene (kernel KC577T, manufactured by Nippon Polyethylene Co., Ltd.) was laminated by extrusion lamination to obtain a paper barrier material. [Comparative Example 2] On the surface of the obtained barrier paper, 15 μm of adhesive resin (Modic M545, manufactured by Mitsubishi Chemical Corporation) and 15 μm of nylon 6 (1022, manufactured by Ube Industries, Ltd.) were co-extruded and laminated in the same manner as in Example 3. Furthermore, 15 μm of adhesive resin (Modic M545, manufactured by Mitsubishi Chemical Corporation) and 20 μm of polyethylene (Harmolex NH745N, manufactured by Nippon Polyethylene Co., Ltd.) were co-extruded and laminated onto the barrier coating layer to obtain a paper barrier material having a protective layer on the paper surface side. The nylon layer was obtained by melting pellets and extruding them into a film from the T-die of a laminating machine, and was unstretched.

[0053] [Reference example] On one side of the obtained paper substrate, 15 μm of adhesive resin (Modic M545, manufactured by Mitsubishi Chemical Corporation) and 15 μm of MX nylon (S6007, manufactured by Mitsubishi Chemical Corporation) were co-extruded and laminated in the same manner as in Example 3. On the outermost surface, 15 μm of adhesive resin (Modic M545, manufactured by Mitsubishi Chemical Corporation) and 20 μm of polyethylene (Harmolex NH745N, manufactured by Nippon Polyethylene Co., Ltd.) were further laminated by co-extrusion to obtain a paper barrier material having a protective layer. The nylon layer was obtained by melting pellets and extruding them into a film from the T-die of a laminating machine, and was unstretched.

[0054] [Table 1]

[0055] The paper barrier materials obtained in Examples 1 to 4 of the present invention exhibited excellent flexural resistance regardless of whether the nylon layer was stretched or not, and were able to maintain high oxygen barrier properties even in the presence of folds. Moreover, the sealing strength when formed into a bag exceeded 300 mmHg, which was particularly excellent. The paper-based barrier materials obtained in Comparative Examples 1 and 2 lacked sufficient ability to protect the barrier coating layer and had poor flexibility. The paper-based barrier material obtained in the reference example, although lacking a barrier coating layer, was able to maintain high oxygen barrier properties even in the presence of folds because it contained a layer made of MX nylon, which has excellent barrier properties.

Claims

1. A barrier base paper having a barrier coating layer containing pigment on a paper substrate, The barrier paper has a protective layer laminated on the barrier coating layer side, which is mainly composed of nylon 6 or nylon 66. The barrier coating layer contains a water vapor barrier resin which is one or more of the following: styrene-butadiene, styrene-acrylic, ethylene-vinyl acetate, paraffin (wax), butadiene-methyl methacrylate, vinyl acetate-butyl acrylate copolymer, maleic anhydride copolymer, acrylic acid-methyl methacrylate copolymer, or paraffin (wax)-containing synthetic adhesives thereof; or a gas barrier resin which is one or more of the following: polyvinyl alcohol-based resin other than saponified ethylene-vinyl acetate copolymer, proteins, starches, cellulose derivatives, polyvinylpyrrolidone, sodium alginate. A paper-based barrier material characterized in that the paper substrate and the barrier coating layer are in direct contact.

2. The paper-based barrier material according to claim 1, characterized in that the barrier base paper comprises a water vapor barrier coating layer and a gas barrier coating layer on a paper substrate in that order.

3. The basis weight of the aforementioned paper substrate is 30 g / m². ２ 110g / m or more ２ The paper barrier material according to claim 1 or 2, characterized in that it is as follows:

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