Paper barrier materials

Abstract

To provide a paper-made barrier material having superior flex resistance.SOLUTION: A paper-made barrier material includes: barrier base paper where a barrier coating layer containing a pigment is provided on a paper substrate; and a polyethylene layer that is laminated on the barrier coating layer side of the barrier base paper and has a thickness of 20 μm or more, wherein the polyethylene layer is composed of polyethylene with a density of 0.920 g / cm3 or more.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

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

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

Means for Solving the Problems

[0007] Means for solving the problems of the present invention are as follows. 1. A barrier base paper having a barrier coating layer containing a pigment on a paper base material, a polyethylene layer having a thickness of 20 μm or more laminated on the barrier coating layer side of the barrier base paper, and having the polyethylene layer being made of polyethylene having a density of 0.920 g / cm 3 or more, a paper barrier material characterized in that. 2. Having a second polyethylene layer having a thickness of 10 μm or more laminated directly on the polyethylene layer, the second polyethylene layer being made of polyethylene having a lower density than the polyethylene of the polyethylene layer, the paper barrier material according to 1. 3. The barrier base paper is provided with a water vapor barrier coating layer and a gas barrier coating layer on the paper base material in this order, the paper barrier material according to 1. or 2. 4. The basis weight of the paper base material is 30 g / m 2 or more and 110 g / m 2 or less, the paper barrier material according to or 2. 5. A flexible packaging bag made of the paper barrier material according to 4.

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 substrate, A polyethylene layer with a thickness of 20 μm or more is laminated on the barrier coating layer side of this barrier paper, It has, The polyethylene layer has a density of 0.920 g / cm³. 3 The material is characterized by being made of polyethylene as described above.

[0010] The barrier paper comprises a barrier coating layer containing pigment on a paper substrate. (Paper base material) In this invention, the paper substrate is a sheet consisting of pulp, filler, and various auxiliary agents. As pulp, 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 can be used, as can 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. One or more of these can be used in combination. Among these, chemical pulps and mechanical pulps made from wood fibers are preferred, and chemical pulps are more preferred, for reasons such as the reduced likelihood of foreign matter contamination into the paper substrate, the reduced likelihood of discoloration over time when recycled paper containers are used as recycled paper raw materials after use, and the high whiteness resulting in a good surface texture when printed, which in turn increases the value of the material, especially when used as packaging material.

[0011] As fillers, known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium dioxide, zeolite, and synthetic resin fillers can be used as needed. Furthermore, aluminum sulfate and various anionic, cationic, nonionic, or amphoteric yield enhancers, water drainage enhancers, paper strength enhancers, and internal sizing agents can be used as needed. In addition, dyes, fluorescent whitening agents, pH adjusters, defoamers, pitch control agents, slime control agents, etc., can 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 the paper base material obtained in this way include various known materials such as high-quality paper, medium-quality paper, coated paper, single-sided coated paper, kraft paper, single-sided coated kraft paper, bleached kraft paper, glassine paper, cardboard, white cardboard, and liner.

[0014] The basis weight of the paper base material can be appropriately selected according to various qualities and handling properties desired for the paper barrier material. Usually, it is preferably 20 g / m 2 or more and 500 g / m 2 or less. In the case of a paper barrier material used for packaging purposes such as packaging materials, containers, cups, etc. for food, etc., it is more preferably 25 g / m 2 or more and 400 g / m 2 or less. Particularly in the case of a paper barrier material used for the soft packaging bag application described later, it is more preferably 30 g / m 2 or more and 110 g / m 2 or less.

[0015] (Barrier coating layer) The barrier base paper of the present invention has a barrier coating layer containing a pigment. The barrier coating layer can be formed by applying a coating material for forming the barrier coating layer with various coating apparatuses and drying it. The barrier coating layer preferably has either a water vapor barrier property or a gas barrier property, more preferably has at least a gas barrier property, and even more preferably has both a water vapor barrier property and a gas barrier property. When the barrier coating layer has both a water vapor barrier property and a gas barrier property, it is preferable to have a water vapor barrier coating layer and a gas barrier coating layer because a paper barrier material that achieves both gas barrier property and water vapor barrier property can be obtained. Hereinafter, the water vapor barrier coating layer is also referred to as a water vapor barrier layer, and the gas barrier coating layer is also referred to as a 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, shortening the distance they travel. As a result, the improvement in water vapor barrier properties may be reduced.

[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, from the viewpoint of adhesion with the water vapor barrier layer, it is preferable to adjust the surface tension of the paint for the gas barrier layer 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. 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 paint for the gas barrier layer to ±20 mN / m relative to the wetting tension of the surface of the water vapor barrier layer.

[0033] (Coating of water vapor barrier layer and gas barrier layer) The method for applying coatings for forming water vapor barrier layers and gas barrier layers to paper substrates is not particularly limited and can be done using known coating apparatus and coating systems. For example, coating apparatuses include blade coaters, bar coaters, roll coaters, air knife coaters, reverse roll coaters, curtain coaters, spray coaters, size press coaters, and gate roll coaters. Coating systems include water-based coatings using solvents such as water and solvent-based coatings using solvents such as organic solvents, but water-based coatings are preferred. Conventional methods such as steam heaters, gas heaters, infrared heaters, electric heaters, hot air heaters, microwaves, and cylinder dryers are used to dry the water vapor barrier layer and gas barrier layer.

[0034] In this invention, the amount of water vapor barrier layer applied is 3 g / m² by dry weight. 2 More than 50g / m 2 The following is preferable: 5 g / m 2 More than 40g / m 2 The following is more preferable: 7 g / m 2 More than 30g / m 2 The following is even more preferable: The amount of water vapor barrier layer coating is 3 g / m². 2 If the amount is less than 50 g / m², it becomes difficult to completely coat the paper substrate with the paint, resulting in insufficient water vapor barrier properties. Alternatively, the paint for the gas barrier layer may not penetrate to the paper substrate, preventing the formation of a uniform gas barrier coating layer and resulting in insufficient gas barrier properties. On the other hand, a water vapor barrier layer coating amount of 50 g / m² is acceptable. 2 A higher concentration increases the drying load during coating. The water vapor barrier layer may be a single layer or a multilayer structure of two or more layers. When the water vapor barrier layer is a multilayer structure of two or more layers, it is preferable that the total coating amount of all water vapor barrier layers be within the above range.

[0035] In this invention, the coating amount of the gas barrier layer is 0.2 g / m² by dry weight. 2 More than 20g / 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] (Polyethylene layer) The polyethylene layer is laminated on the barrier coating layer side of the barrier base paper. By placing the polyethylene layer near the barrier coating layer, it is possible to prevent damage around the pigment of the barrier coating layer when it is bent, thereby improving the bending resistance of the paper barrier material. The polyethylene layer can be laminated directly on the barrier coating layer or laminated via other layers. As for other layers, an adhesive layer capable of connecting the barrier coating layer and the polyethylene layer to prevent peeling at the interface is preferred. The material of the adhesive layer is not particularly limited as long as it has excellent adhesion to both the barrier coating layer and the polyethylene layer, and can be a modified resin (solid) such as maleic acid-modified polyethylene, or a one-component curing type or a two-component curing type liquid adhesive, either alone or in mixture. 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.

[0037] The polyethylene layer has a density of 0.920 g / cm³. 3 The present invention consists of the above polyethylene. In this specification, "consists of" means that it is the main component, and it may also contain additives such as plasticizers, ultraviolet absorbers, and lubricants. Furthermore, in this invention, polyethylene can be derived from either fossil resources or biomass such as plants. As for the type of polyethylene, different types with varying side chain branching and lengths can be selected as appropriate. For example, in the case of low-density polyethylene, in addition to ordinary low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE) and others can be selected as appropriate. Furthermore, polyethylene polymerized using different polymerization catalysts can be appropriately selected. For example, polyethylene polymerized using conventional catalysts such as the Ziegler-Natta catalyst, as well as metallocene catalysts, can be used.

[0038] The polyethylene layer becomes more rigid as the polyethylene density increases, and therefore, the bending resistance improves with higher density. For this reason, the density of polyethylene is 0.925 g / cm³. 3 Preferably, it should be 0.930 g / cm³ or more. 3 It is more preferable that the value be greater than or equal to 0.935 g / cm³. 3 The above is even more preferable. The density of polyethylene in the polyethylene layer is 0.970 g / cm³ because the higher the density, the more likely the paper barrier material after the polyethylene layer is formed is to curl the polyethylene layer inward. 3 Preferably, it is 0.960 g / cm³. 3 It is more preferable that the following is the case: 0.955 g / cm³ 3 The following is even more preferable: The polyethylene layer thickness is 20 μm or more. If the polyethylene layer thickness is less than 20 μm, the improvement in flexural resistance may be insufficient. The polyethylene layer thickness is preferably 25 μm or more, and more preferably 30 μm or more. There is no particular upper limit to the polyethylene layer thickness, but it is around 100 μm. Further improvement in flexural resistance cannot be expected even if the polyethylene layer is thicker than this, and it will be costly.

[0039] (Second polyethylene layer) The paper barrier material of the present invention may have a second polyethylene layer with a thickness of 10 μm or more that is directly laminated on a polyethylene layer. The melting point of polyethylene increases with increasing density. Therefore, the higher the density of polyethylene contained in the polyethylene layer, the higher the heat sealing temperature required when heat sealing this polyethylene layer to form a package. This requires the packaged material to have high heat resistance, limiting the types of items that can be packaged. By directly laminating a second polyethylene layer made of lower-density polyethylene onto the polyethylene layer, it is possible to lower the heat sealing temperature while maintaining flexibility. This reduces the heat resistance required of the packaged material, allowing for the packaging of a wider variety of items. Furthermore, enabling heat sealing at lower temperatures reduces the time required for heat sealing and lowers manufacturing costs.

[0040] The polyethylene used in the second polyethylene layer can also be appropriately selected and used, similar to the polyethylene used in the aforementioned polyethylene layer, by using polyethylene with different side chain branching and lengths, polyethylene synthesized using various polymerization catalysts, polyethylene derived from fossil resources, polyethylene derived from biomass such as plants, etc. The density of polyethylene contained in the second polyethylene layer is the same as the density of polyethylene contained in the polyethylene layer (0.920 g / cm³). 3 (The above) is better than 0.05 g / cm³ 3 It is preferable that the amount is smaller than 0.10 g / cm³. 3 It is more preferable that the amount is smaller than 0.15 g / cm³. 3 It is even more preferable that it be smaller than 0.20 g / cm³. 3 It is even more preferable if the density is smaller than the above. Also, the density of polyethylene contained in the second polyethylene layer is 0.920 g / cm³. 3 It is preferable that it be less than [a certain value].

[0041] The thickness of the second polyethylene layer is 10 μm or more. If the thickness of the second polyethylene layer is less than 10 μm, the reduction in heat seal temperature may be insufficient. There is no particular upper limit to the thickness of the second polyethylene layer, but since the second polyethylene layer is formed directly on the polyethylene layer and functions as a single unit, a thickness of about 40 μm is sufficient. The method for forming the polyethylene layer and the second polyethylene layer is not particularly limited and can be formed by known methods such as extrusion lamination, sand lamination, and dry lamination.

[0042] 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.

[0043] 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 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]

[0044] 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.

[0045] (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 15 cc / m³. 2 Less than 1 day at a meter NG: The oxygen permeability of the folded sample is 15 cc / m³. 2 ·day · atm or more (2) Heat seal temperature Two rectangular test pieces, 60 mm long and 50 mm wide, were cut from the obtained paper barrier material. These were stacked with the polyethylene layers facing each other and subjected to a pressurized pressure of 2 kgf / cm² at different temperatures (100°C, 110°C, and 120°C). 2 The seal was then heat-sealed in the lateral direction with a seal width of 10 mm, after applying pressure for 0.5 seconds. A heat-sealed test specimen was cut to a width of 15 mm. At the boundary between the heat-sealed and unheated portions, the unheated portions of the specimen were folded outward by 90° to form a T-shape. These portions were then pulled outward (180° direction) at 200 mm / min to perform a peel test. The heat seal temperature was defined as the lowest heating temperature in the sample at which the barrier paper was destroyed, rather than the heat seal interface.

[0046] [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.

[0047] (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%.

[0048] (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.

[0049] (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.

[0050] (Preparation of paper barrier materials) The obtained barrier base paper is coated with a two-component curing aromatic ester adhesive (main component: Takelac A-3210, manufactured by Mitsui Chemicals; hardener: Takenate A-3075, manufactured by Mitsui Chemicals; diluent: ethyl acetate) diluted in a ratio of main component / hardener / diluent = 3 / 1 / 28 (by weight), mixed, and then applied by roll coating at a rate of 0.2 g / m². 2 (Dry weight) Apply to form an adhesive layer, dry at 80°C for 1 second, then density 0.937 g / cm³ 3 A polyethylene layer (Sumitomo Chemical Co., Ltd., Sumikasen L5721) was laminated by extrusion lamination to a thickness of 30 μm to obtain a paper barrier material.

[0051] [Example 2] A paper barrier material was obtained in the same manner as in Example 1, except that the thickness of the polyethylene layer was set to 60 μm. [Example 3] The polyethylene layer has a density of 0.931 g / cm³. 3 A paper barrier material was obtained in the same manner as in Example 1, except that polyethylene (Sumitomo Chemical Co., Ltd., Sumikasen CE3506) was used. [Example 4] A paper barrier material was obtained in the same manner as in Example 3, except that the thickness of the polyethylene layer was set to 60 μm. [Example 5] On the polyethylene layer of the paper barrier material obtained in Example 1, a density of 0.916 g / cm³ was added. 3 A second polyethylene layer was created by extrusion lamination of polyethylene (Sumitomo Chemical Co., Ltd., Sumikasen Hiα XS764) to a thickness of 30 μm, thereby obtaining a paper-based barrier material.

[0052] [Comparative Example 1] A paper barrier material was obtained in the same manner as in Example 1, except that the thickness of the polyethylene layer was set to 15 μm. [Comparative Example 2] The polyethylene layer has a density of 0.919 g / cm³. 3 A paper barrier material was obtained in the same manner as in Example 1, except that polyethylene (Sumitomo Chemical Co., Ltd., Sumikasen L705) was used. [Comparative Example 3] The polyethylene layer has a density of 0.916 g / cm³. 3 A paper barrier material was obtained in the same manner as in Example 1, except that polyethylene (Sumitomo Chemical Co., Ltd., Sumikasen Hiα XS764) was used. [Comparative Example 4] On the polyethylene layer of the paper barrier material obtained in Comparative Example 1, a density of 0.916 g / cm³ was added. 3 A second polyethylene layer was created by extrusion lamination of polyethylene (Sumitomo Chemical Co., Ltd., Sumikasen Hiα XS764) to a thickness of 15 μm, thereby obtaining a paper-based barrier material.

[0053] [Table 1]

[0054] The paper barrier materials obtained in Examples 1 to 5 of the present invention exhibited excellent flexibility and maintained high oxygen barrier properties even in the presence of folds. From the evaluation results of the oxygen permeability of the paper barrier materials obtained in Examples 1 to 4, it was confirmed that flexibility improved as the density and thickness of the polyethylene layer increased. The paper barrier material obtained in Example 5, which had a second polyethylene layer made of lower-density polyethylene on top of the polyethylene layer, had the same flexibility as the paper barrier material obtained in Example 2, while also being heat-sealable at 110°C. The paper barrier materials obtained in Comparative Examples 1 and 4 had insufficient polyethylene layer thickness and poor bending resistance. The paper barrier materials obtained in Comparative Examples 2 and 3 had low-density polyethylene in the polyethylene layer and poor bending resistance.

Claims

1. A barrier base paper having a barrier coating layer containing pigment on a paper substrate, A polyethylene layer with a thickness of 20 μm or more is laminated on the barrier coating layer side of the barrier base paper, It has, The barrier coating layer containing the pigment and the polyethylene layer are either in direct contact or laminated with an adhesive layer in contact with both. The basis weight of the aforementioned paper substrate is 30 g / m². ２ 110g / m or more ２ The following: The polyethylene layer has a density of 0.925 g / cm³. ３ The above consists of polyethylene, The barrier coating layer is a water vapor barrier coating layer containing a water vapor barrier resin or a gas barrier coating layer containing a gas barrier resin. The water vapor barrier resin is one or more selected from the group consisting of a styrene-butadiene copolymer, a styrene-acrylic copolymer, an ethylene-vinyl acetate copolymer, a paraffin (wax) copolymer, a butadiene-methyl methacrylate copolymer, a vinyl acetate-butyl acrylate copolymer, a maleic anhydride copolymer, an acrylic acid-methyl methacrylate copolymer, or a paraffin (wax)-containing synthetic adhesive thereof. A paper-based barrier material characterized in that the gas barrier resin is one or more selected from the group consisting of polyvinyl alcohol-based resins, proteins, starches, cellulose derivatives, polyvinylpyrrolidone, and sodium alginate.

2. The polyethylene layer has a second polyethylene layer with a thickness of 10 μm or more that is directly laminated on the polyethylene layer, The paper barrier material according to claim 1, characterized in that the second polyethylene layer is made of polyethylene with a lower density than the polyethylene in the polyethylene layer.

3. 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.

4. A flexible packaging bag made of a paper barrier material according to any one of claims 1 to 3.

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