Paper barrier materials

Abstract

To provide a paper-based barrier material that minimizes the environmental impact associated with the treatment of wastewater (filtrate) generated during re-dissociation. [Solution] A paper substrate has a barrier layer which is a coating layer and a heat-seal layer which is a laminate layer, and when the slurry after disintegration is filtered, the ratio of coarse selection % (content of residue remaining on the screen plate when the slurry after disintegration is coarsely selected using a screen plate with a circular hole of 5 mm in diameter) to fine selection % (content of residue remaining on the screen plate when the slurry after disintegration of coated paper is finely selected using a screen plate with a slit width of 0.15 mm) is 80:20 to 100:0. Paper-based barrier material with a COD of 350 ppm or less in wastewater after pulp recovery.

Description

[Technical Field]

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

[0002] In recent years, driven by environmental issues such as plastic waste and global warming, there has been a growing trend towards reducing reliance on petroleum and plastics. There is a strong desire to minimize the use of fossil fuel-derived and non-biodegradable resin materials in industrial products. As a result, paper is attracting attention as an alternative to plastic. For example, Patent Document 1 describes a paper substrate having a water vapor barrier layer and a gas barrier layer in that order on a base paper, a resin layer on at least one surface of the paper substrate, the water vapor barrier layer and the gas barrier layer being coating layers, the resin layer mainly composed of a biodegradable resin or bio-derived resin, and having an oxygen permeability of 10 ml / m² at a temperature of 23°C and relative humidity of 0%. 2 A barrier material has been proposed in which pulp fibers are dispersed when the resin layer is a heat-sealable coating layer, the material is cut into 1cm x 1cm square pieces, immersed in a 2% by weight aqueous solution of sodium hydroxide at a liquid temperature of 60°C to a sample concentration of 2% by weight, and disintegrated for 60 minutes using a Tappi standard disintegrator.

[0003] The paper barrier material described in Patent Document 1, etc., can be heat-sealed and therefore can be used as a substitute for packaging films having a plastic film. Furthermore, the paper barrier material described in Patent Document 1, etc., has only a coating layer and no laminate layer, resulting in a high pulp recovery rate during re-disintegration. This makes it an environmentally friendly product because the recovered pulp (waste paper pulp) can be recycled as a papermaking material.

[0004] Here, recycled paper pulp is recovered by agitating paper products such as paper barrier materials with chemicals such as deinking agents in water to break down the pulp, and then filtering it. The filtrate contains fine pulp that cannot be recovered, as well as organic compounds such as starches and PVAs, which are papermaking chemicals. As a result, the COD and BOD are high, and it cannot be released as is. Therefore, it is treated as wastewater to meet environmental standards before being released. Wastewater treatment is generally carried out using the activated sludge process. However, treating wastewater with high COD and BOD using this process generates a large amount of excess sludge. This leads to the problem that drying, transporting, and landfilling this large amount of excess sludge consumes a large amount of energy and generates a large amount of carbon dioxide. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 7157069 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Further reductions in the environmental impact of paper-based barrier materials are required. The present invention aims to provide a paper-based barrier material that minimizes the environmental impact associated with the treatment of wastewater (filtrate) generated during redissociation. [Means for solving the problem]

[0007] The means for solving the problems of the present invention are as follows. 1. The paper substrate has a barrier layer which is a coating layer and a heat-seal layer which is a laminate layer. When the slurry after dissociation is filtered, the ratio of coarse selection % (the content rate of the residue remaining on the screen plate when the slurry after dissociation is coarsely selected using a screen plate having a round hole with a diameter of 5 mm): fine selection % (the content rate of the residue remaining on the screen plate when the slurry after dissociation of the coated paper is finely selected using a screen plate with a slit width of 0.15 mm) is 80:20 to 100:0, A paper barrier material characterized in that the COD of the wastewater after recovering the pulp is <350 ppm. 2. The coating amount of the barrier layer is 3 g / m 2 or more and 5 g / m 2 or less, The paper barrier material according to 1.

Advantages of the Invention

[0008] The paper barrier material of the present invention has a low COD in the wastewater generated during redissociation. Therefore, the amount of excess sludge generated when this wastewater is treated by activated sludge can be reduced compared to the conventional method, and the amount of carbon dioxide emissions generated during the treatment of excess sludge can be reduced. Since the slurry after dissociation of the paper barrier material of the present invention mainly contains large residues, it is easy to remove the residues. Therefore, it is easy to recover waste paper pulp from the dissociated slurry. In addition, since the waste paper pulp recovered from the paper barrier material of the present invention has few impurities, it is possible to reduce the operation troubles when using this waste paper pulp and obtain high-quality recycled paper. The paper barrier material of the present invention has a small amount of carbon dioxide emissions throughout the product life cycle, and can further reduce the environmental load.

Brief Description of the Drawings

[0009] [Figure 1] Schematic diagram of the screen plate used during the coarse selection process.

Embodiments for Carrying Out the Invention

[0010] The paper barrier material of the present invention has a barrier layer which is a coating layer and a heat-seal layer which is a laminate layer on a paper substrate. When the slurry after disintegration is filtered, the ratio of coarse selection % (content of residue remaining on the screen plate when the slurry after disintegration is coarsely selected using a screen plate with a 5 mm diameter circular hole) to fine selection % (content of residue remaining on the screen plate when the slurry after disintegration of coated paper is finely selected using a screen plate with a slit width of 0.15 mm) is 80:20 to 100:0. The COD of the wastewater after pulp recovery is 350 ppm or less. In this specification, the notation "A to B (where A and B are numerical values ​​or ratios)" refers to a numerical range that includes both ends of that range.

[0011] (Paper base material) In this invention, the paper substrate is a sheet made of pulp, filler, various auxiliary agents, etc. 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.

[0012] 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.

[0013] 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.

[0014] 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.

[0015] The basis weight of the paper substrate can be appropriately selected according to various qualities and handling properties desired for the paper barrier material, etc., but usually it is 20 g / m 2 or more and 500 g / m 2 or less, and such are preferable. In the case of a paper barrier material used for packaging purposes such as packaging materials, containers, cups, etc. for food, etc., 25 g / m 2 or more and 400 g / m 2 or less are more preferable, and particularly in the case of a paper barrier material used for the soft packaging bag application described later, 30 g / m 2 or more and 110 g / m 2 or less are more preferable.

[0016] (Barrier layer) The paper barrier base paper of the present invention includes a barrier layer which is a coating layer. The barrier layer can be formed by applying a paint for forming the barrier layer with various coating apparatuses and drying. The barrier layer preferably has either water vapor barrier property or gas barrier property, more preferably has at least gas barrier property, and even more preferably has both water vapor barrier property and gas barrier property. When the barrier layer has both water vapor barrier property and gas barrier property, it is preferable to have a water vapor barrier layer and a gas barrier layer because a paper barrier material that achieves both gas barrier property and water vapor barrier property can be obtained.

[0017] 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.

[0018] (Water vapor barrier layer) The water vapor barrier 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 layer) The gas barrier 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 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: 40 g / m 2 The following is more preferable: 30g / m 2 The following is even more preferable: 20 g / m 2 The following is even more preferable: 10 g / m 2 The following is even more preferable: 7 g / m 2 The following is even more preferable: 5 g / m 2 The following is even more preferable: A water vapor barrier layer coating amount of 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 3 g / m² by dry weight. 2 More than 20g / m 2 The following is preferable: 15 g / m 2 The following is more preferable: 10 g / m 2 The following is even more preferable: 7 g / m 2 The following is even more preferable: 5 g / m 2 The following is even more preferable: A gas barrier layer coating amount of 3 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] (Heat seal layer) The heat-seal layer is formed on the barrier layer by lamination. The material of the film forming the heat seal layer can be any material used for heat sealing applications without particular limitations. For example, a thermoplastic resin with a glass transition temperature of 100°C or less 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 preferred in terms of reducing the environmental burden when they are released as waste. In this specification, the glass transition temperature refers to the intermediate glass transition temperature measured in accordance with JIS K 7121-1987.

[0037] The method for forming the heat seal layer is not particularly limited and can be formed by known lamination methods such as extrusion lamination, sand lamination, and dry lamination. Furthermore, the thickness of the heat seal layer is not particularly limited and can be, for example, 5 μm to 100 μm.

[0038] The paper barrier material of the present invention, when the slurry after disintegration is subjected to a screen, has a coarse sorting % (content of residue remaining on the screen plate when the slurry after disintegration is coarsely sorted using a screen plate with circular holes of 5 mm in diameter) to refined % (content of residue remaining on the screen plate when the slurry after disintegration of coated paper is refined using a screen plate with a slit width of 0.15 mm) of 80:20 to 100:0. The paper barrier material of the present invention has a coarse wire %:refined % ratio of 80:20 to 100:0, which means that there is a large amount of large residue, making it easy to remove the residue. Therefore, when recovering waste paper pulp from the disintegrated slurry using the paper barrier material of the present invention, the screen plate and the like are less likely to clog, making filtration easy and allowing filtration to be done in a short time. In the present invention, the coarse wire %:refined % ratio is preferably 85:15 to 100:0, more preferably 90:10 to 100:0, even more preferably 95:5 to 100:0, even more preferably 98:2 to 100:0, and even more preferably 99:1 to 100:0.

[0039] The paper barrier material of the present invention has a COD of 350 ppm or less in the wastewater after disintegration and pulp recovery. The paper barrier material of the present invention has a low COD in the wastewater because a large amount of residue is removed in the coarse sorting and fine sorting processes. The COD of the wastewater is preferably 330 ppm or less, more preferably 310 ppm or less, even more preferably 290 ppm or less, even more preferably 270 ppm or less, and even more preferably 250 ppm or less. Furthermore, because this wastewater contains a low amount of dissolved impurities such as evaporation residue, wastewater treatment is easy, and the amount of carbon dioxide generated during treatment can be reduced. The evaporation residue can be calculated by drying the wastewater used for COD measurement in a dryer and then using the weight after drying as a percentage of the weight of the raw materials used.

[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. [Examples]

[0041] 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-based barrier material was tested based on the evaluation method described below.

[0042] (Rough screening) A paper barrier material with an oven-dry weight of 37.5 g was cut into 4 cm squares. Warm water was added to achieve a concentration of 2.5% of the paper barrier material and a water temperature of 40°C. The material was then dissociated for 10 minutes at a rotation speed of 3000 rpm using a TAPPI standard dissociator (manufactured by Kumagai Riki Kogyo Co., Ltd.). The entire obtained pulp slurry was subjected to a standard test flat screen (manufactured by Kumagai Riki Kogyo Co., Ltd.) equipped with a Φ5 mm screen plate (a plate measuring 282 mm wide and 273 mm long, with holes of 5 mm diameter and a pitch of 6 mm wide x 7.5 mm high, resulting in 792 holes), as shown in Figure 1. The material was subjected to a rough screening process for 20 minutes in a water flow of 10 L / min. At this time, the material that passed through the screen (roughly accepted) and the residue remaining on the screen plate (roughly rejected) were collected separately. The rough rejected material was dried in an oven at 105°C and its oven-dry weight was measured.

[0043] (Selective screen processing) Next, the coarsely selected accepts were subjected to a standard test flat screen (manufactured by Kumagai Riki Kogyo Co., Ltd.) equipped with a screen plate with 6 cuts (slit width 0.15 mm), and refined screening was performed for 20 minutes in a water flow of 10 L / min. The material that passed through the screen (refined accepts) and the residue remaining on the screen plate (refined rejects) were collected separately. The refined rejects were dried in an oven at 105°C, and their oven-dry weight was measured.

[0044] (Method for calculating the content of residues) The percentages for rough selection and refinement were calculated according to the following formula. Rough selection % (%) = Absolute dry weight of rough selection rejects (BDg) / Absolute dry weight of paper barrier material used in the test (BDg) × 100 Rejection percentage (%) = Dry weight of rejected materials (BDg) / Dry weight of paper barrier material tested (BDg) × 100 BD stands for bone-dry.

[0045] (COD) The refined accept was filtered through filter paper (Whatman1; 11μm pore size) to recover the pulp. The filtrate (wastewater) that passed through the filter paper was heated to 23-25°C, and then the COD was measured using a Pack Test (Kyoritsu Chemical Laboratory, KR-COD-2, measurement range 0-100 mg / L).

[0046] (Oxygen permeability) Measurements were taken using MOCON's OX-TRAN2 / 21 under 23°C-0%RH conditions (dry), and evaluated according to the following criteria. ○: 20cc / m 2 ·day · atm or less △: 20cc / m 2 • Day • ATM exceeding 100cc / m 2 ·day · atm or less ×: 100cc / m 2 • Day • ATM exceeding

[0047] (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) as a sizing agent, 0.15% of polyamide epichlorohydrin (PAEH) resin as a wet strength enhancer, and 0.08% of polyacrylamide (PAM) with a molecular weight of 10 million was added as a yield enhancer. After this, the paper was made using a Duoformer FM type paper machine, resulting in a basis weight of 50 g / m². 2 A paper substrate was obtained.

[0048] (Preparation of coating liquid for gas barrier layer) An aqueous solution of polyvinyl alcohol (VC-10, manufactured by Nippon Vinegar & Polyvinyl Alcohol Co., Ltd.) with a solid content of 12% was prepared and used as a coating solution for the gas barrier layer.

[0049] (Preparation of paper barrier packaging materials) The resulting paper substrate was coated with a gas barrier layer coating liquid at a dry weight of 2.0 g / m². 2 A single-sided coating was applied to obtain a paper-based barrier base paper. A film (manufactured by Futamura Chemical Co., Ltd., LLDPE, 30 μm thick) and an adhesive (two-component curing polyurethane adhesive, curing agent: polyisocyanate, solvent: ethyl acetate) are applied to the gas barrier layer of a paper-based barrier base paper at a coating rate (solids content) of 4 g / m². 2 A paper barrier material was obtained by laminating the materials together using a dry lamination method.

[0050] Example 2 The coating liquid for gas barrier layers is 4.0 g / m² by dry weight. 2 A paper barrier material was obtained in the same manner as in Example 1, except as described above.

[0051] "Comparative Example 1" A water-based coating solution (solid content concentration 35%) was prepared by mixing a thermoplastic resin (Mitsui Chemicals, Inc.: ChemiPearl S500, ethylene methacrylate-based ionomer) and an antifoaming agent (BASF: Foamstar SI2213) in a solid content weight ratio of 99.8 / 0.2, and then adding water and stirring. On the gas barrier layer of the paper barrier base obtained in Example 1, this aqueous coating solution was applied using an air knife coating method to a target coating amount of 5.5 g / m². 2 The material was coated and dried at 150 degrees Celsius to form a heat-seal layer, thereby obtaining a paper barrier material. "Comparative Example 2" A paper barrier material was obtained in the same manner as in Comparative Example 1, except that the paper barrier base paper obtained in Example 2 was used.

[0052] [Table 1]

[0053] ·result The paper barrier materials obtained in Examples 1 and 2 of the present invention were found to have a low COD of wastewater after pulp recovery, resulting in a low environmental impact during wastewater treatment. Furthermore, the paper barrier materials obtained in Examples 1 and 2 of the present invention had a coarse sorting %: fine sorting % ratio of 100:0, making it easy to recover the disintegrated waste paper pulp.

Claims

1. The paper substrate has a barrier layer which is a coating layer and a heat-seal layer which is a laminate layer. When the slurry after disintegration is filtered, the ratio of coarse selection % (percentage of residue remaining on the screen plate when the slurry after disintegration is coarsely selected using a screen plate with 5 mm diameter circular holes) to refined selection % (percentage of residue remaining on the screen plate when the slurry after disintegration of coated paper is refined using a screen plate with a slit width of 0.15 mm) is 80:20 to 100:

0. A paper-based barrier material characterized by having a COD of 350 ppm or less in the wastewater after pulp recovery.

2. The coating amount of the barrier layer is 3 g / m ２ 5g / m or more ２ The paper barrier material according to claim 1, characterized in that it is as follows.

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