Method for manufacturing paper-made barrier material

Abstract

To provide a paper-made barrier material which is excellent in barrier property, compared to a paper-made barrier material obtained by a conventional manufacturing method.SOLUTION: A method for manufacturing a paper-made barrier material includes a barrier base paper manufacturing step of forming a barrier coating layer on a coating surface as at least one surface of a paper base material, and a laminate step of providing a laminate layer composed of a thermoplastic resin film on the barrier coating layer by dry laminate through an adhesive, wherein the barrier coating layer is not subjected to smoothing treatment under a linear pressure of 20 kg / cm or more, and the adhesive is coated onto the barrier coating layer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a paper barrier material. [Background technology]

[0002] It is important to impart gas barrier properties (particularly oxygen barrier properties) to paper materials, particularly paper packaging materials, in order to protect various packaged products from deterioration due to gases, such as oxidation due to oxygen. Conventionally, the main method of imparting gas barrier properties to paper packaging materials has been to extrusion laminate or attach to the paper base a gas barrier layer made of a metal foil or metal vapor-deposited film made of a metal such as aluminum, a resin film such as polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, or polyacrylonitrile, or a film coated with one of these resins, or a ceramic vapor-deposited film vapor-deposited with an inorganic oxide such as silicon oxide or aluminum oxide. It is also important to impart water resistance (particularly water vapor barrier properties) to paper packaging materials in order to protect the various products packaged from deterioration due to water vapor.

[0003] The present applicant has proposed a paper barrier packaging material with gas barrier properties and water vapor barrier properties, which has 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 base material (Patent Document 1). Furthermore, among such paper barrier packaging materials, there are known those that enable heat sealing by providing a sealant layer on at least one of the outermost layers. For example, Patent Document 2 proposes providing a laminate layer (corresponding to a sealant layer) by melt extrusion lamination, dry lamination, or direct melt coating. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2013 / 069788 [Patent Document 2] International Publication No. 2017 / 170462 Summary of the Invention [Problem to be solved by the invention]

[0005] The dry lamination method is a method of bonding thermoplastic resin films together via an adhesive, and can produce laminates with excellent adhesive strength and heat seal strength. It is common technical knowledge that in dry lamination, the surface of the adherend should be as smooth as possible to enhance adhesion. Furthermore, when dry laminating paper and a thermoplastic resin film, the adhesive is usually applied to the film side. This is because, when the adhesive is applied to the paper, it penetrates into the paper, causing unevenness on the adhesive surface and making the adhesion poor. However, the present inventors have found that when a barrier coating layer is provided on a paper substrate, applying an adhesive to the barrier coating layer and then dry laminating a thermoplastic resin film provides superior barrier properties, leading to the completion of the present invention. That is, an object of the present invention is to provide a paper barrier material that has excellent barrier properties compared to those obtained by conventional manufacturing methods. [Means for solving the problem]

[0006] The means for solving the problems of the present invention are as follows. 1. A barrier base paper manufacturing process in which a barrier coating layer is formed on at least one coated surface of a paper substrate; a laminating step of providing a laminate layer made of a thermoplastic resin film on the barrier coating layer by dry lamination using an adhesive; and The barrier coating layer is not subjected to a smoothing treatment at a linear pressure of 20 kg / cm or more, A method for producing a paper barrier material, characterized in that the adhesive is applied to the barrier coating layer. 2. The arithmetic mean height (Sap) of the coated surface of the paper substrate is 2.0 μm or more and 30 μm or less, 1. The method for producing a paper barrier material according to 1, wherein the arithmetic mean height (Sac) of the barrier coating layer is 3.0 μm or more and 35 μm or less, and is at least 1 μm greater than the arithmetic mean height (Sap) of the coated surface. 3. Oxygen permeability at 23℃ and 0%RH is 20cc / m 2 3. The method for producing a paper barrier material according to 1. or 2., wherein the temperature is 100°C / day atm or less. 4. The coating amount (solid content) of the adhesive is 2.0 g / m 2 More than 5.0g / m 2 A method for producing a paper barrier material according to any one of 1. to 3., characterized in that: [Effects of the Invention]

[0007] The manufacturing method of the present invention can provide a paper barrier material with excellent barrier properties, with small gaps between the barrier base paper and the barrier coating layer, and between the barrier coating layer and the thermoplastic resin film. The manufacturing method of the present invention prevents cracking of the barrier coating layer and a decrease in barrier properties by not subjecting the barrier coating layer to a smoothing treatment at a linear pressure of 20 kg / cm or more. The manufacturing method of the present invention can provide a paper barrier material with excellent barrier properties even if the surface of the paper substrate is not smooth, thereby reducing manufacturing costs. Furthermore, paper with a rough surface that could not previously be used as a substrate for barrier paper can be used as the paper substrate for the paper barrier material. DETAILED DESCRIPTION OF THE INVENTION

[0008] The method for producing the paper barrier material of the present invention comprises the steps of: a barrier base paper manufacturing process in which a barrier coating layer is formed on at least one coated surface of a paper substrate; a lamination step in which a laminate layer made of a thermoplastic resin film is provided on the barrier coating layer by dry lamination using an adhesive; and The barrier coating layer is not subjected to a smoothing treatment at a linear pressure of 20 kg / cm or more, The adhesive is applied to the barrier coating layer.

[0009] Barrier base paper manufacturing process In the barrier base paper manufacturing process, a barrier coating layer is formed on at least one coated surface of the paper substrate. "Barrier base paper" Barrier base paper has a paper substrate with at least one coated surface and a barrier coating layer applied to the coated surface.

[0010] (Paper base material) In the present invention, the paper substrate is a sheet made of pulp, filler, and various auxiliary agents. Pulp that can be used includes chemical pulps such as bleached hardwood kraft pulp (LBKP), bleached softwood kraft pulp (NBKP), unbleached hardwood kraft pulp (LUKP), unbleached softwood kraft pulp (NUKP), and sulfite pulp; mechanical pulps such as stone-ground pulp and thermomechanical pulp; wood fibers such as deinked pulp and recycled paper pulp; and non-wood fibers obtained from kenaf, bamboo, hemp, etc., and these can be used alone or in combination of two or more. Among these, chemical pulp and mechanical pulp made from wood fibers are preferred, and chemical pulp is more preferred, for reasons such as the low likelihood of foreign matter being mixed into the paper base material, the low likelihood of discoloration over time when used paper containers are recycled as recycled paper materials, and the high whiteness that results in a good surface appearance when printed, making them particularly valuable when used as packaging materials.

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

[0012] The paper substrate of the present invention has at least one coated surface. The arithmetic mean height (Sap) of the coated surface of the paper substrate of the present invention is preferably 2.0 μm or more and 30 μm or less. The manufacturing method of the present invention can obtain a laminate with excellent interlayer adhesion even if the surface of the paper substrate does not have a high degree of smoothness. In order to omit a high-level smoothing treatment for the coated surface of the paper substrate, the arithmetic mean height (Sap) of the coated surface of the paper substrate is preferably 5.0 μm or more, more preferably 8.0 μm or more, even more preferably 11 μm or more, even more preferably 14 μm or more, and even more preferably 17 μm or more. On the other hand, since the smoother the coated surface of the paper substrate, the more improved the barrier property tends to be, the arithmetic mean height (Sap) of the coated surface of the paper substrate is more preferably 28 μm or less, even more preferably 26 μm or less, and even more preferably 24 μm or less.

[0013] The PPS smoothness (hard backing, 1 MPa) of the coated surface is preferably 2.0 μm or more and 15 μm or less. The manufacturing method of the present invention can produce a laminate with excellent interlayer adhesion even if the surface of the paper substrate does not have a high level of smoothness. However, if the PPS smoothness (hard backing, 1 MPa) of the coated surface of the paper substrate exceeds 15 μm, there is a risk of reduced barrier properties. Therefore, the PPS smoothness (hard backing, 1 MPa) of the coated surface of the paper substrate is more preferably 4.0 μm or more, and even more preferably 7.0 μm or more. In this specification, PPS smoothness (Parker Print Surf smoothness) refers to the Parker Print Surf smoothness (μm) measured in accordance with Appendix A of JIS-P8151 (2004). The PPS smoothness of the present invention is a value measured using a hard-type backing at a clamp pressure of 1.0 MPa. In the paper barrier material of the present invention, the PPS smoothness is closely related to the surface condition of the pulp exposed on the measurement surface.

[0014] At least one of the coated surfaces of the paper substrate can be made smoother by, for example, smoothing the surface with an on-machine or off-machine calender in a dry state. However, since the manufacturing method of the present invention does not require a high degree of smoothness on the coated surface of the paper substrate, it is preferable not to perform a smoothing treatment.

[0015] The basis weight of the paper substrate can be selected appropriately depending on the desired qualities and handling properties of the paper barrier material, but is usually 20 g / m 2 More than 500g / m 2 For paper barrier materials used for packaging purposes such as food packaging, containers, and cups, a minimum of 25 g / m 2 More than 400g / m 2 The following is more preferable, especially for paper barrier materials used in flexible packaging bags described below: 2 More than 110g / m 2 The following is more preferred: The thickness of the paper substrate can be selected as appropriate depending on the desired qualities and handleability of the paper barrier material, but is preferably from 30 μm to 600 μm, and more preferably from 45 μm to 125 μm.

[0016] (Barrier coating layer) The barrier coating layer is formed on at least one coated surface of the paper substrate. The barrier coating 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 coating layer has both water vapor barrier property and gas barrier property, it is preferable to have both a water vapor barrier coating layer and a gas barrier coating layer, as this will result in a paper barrier material that has both gas barrier property and water vapor barrier property. Hereinafter, the water vapor barrier coating layer will also be referred to as the water vapor barrier layer, and the gas barrier coating layer will also be referred to as the gas barrier layer.

[0017] While there are no particular limitations on the stacking order of the water vapor barrier layer and the gas barrier layer, it is preferable that they be stacked in the order of paper substrate, water vapor barrier layer, and gas barrier layer, as this further improves the 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 both superior water vapor barrier and gas barrier properties is presumed to be as follows. As described below, polymers such as water-soluble polymers and water-dispersible polymers are generally used as resins with gas barrier properties used in the gas barrier layer. Therefore, when the gas barrier layer and water vapor barrier layer are provided on the paper substrate in this order, the polymers such as water-soluble polymers and water-dispersible polymers in the gas barrier layer are prone to degradation due to moisture in the paper substrate and moisture in the air that permeates via the paper substrate. Meanwhile, the water vapor barrier layer contains a resin with good water resistance to block water vapor, and by providing the water vapor barrier layer and gas barrier layer in this order on the paper substrate, the water vapor barrier layer can effectively suppress the impact (deterioration) of the gas barrier layer due to moisture from the paper substrate side. For this reason, paper barrier materials that have a water vapor barrier layer and a gas barrier layer in this order in particular can exhibit good water vapor barrier properties and gas barrier properties.

[0018] (Water vapor barrier coating layer) The water vapor barrier coating layer contains at least a water vapor barrier resin. As water vapor barrier resins, synthetic adhesives such as styrene-butadiene, styrene-acrylic, ethylene-vinyl acetate, paraffin (wax), butadiene-methyl methacrylate, vinyl acetate-butyl acrylate copolymers, maleic anhydride copolymers, acrylic acid-methyl methacrylate copolymers, or paraffin (wax)-blended synthetic adhesives can be used alone or in combination of two or more. Of these, styrene-butadiene synthetic adhesives are preferred in terms of water vapor barrier properties. In this invention, styrene-butadiene synthetic adhesives are emulsion-polymerized using styrene and butadiene as the primary monomers, combined with various comonomers for modification. Examples of comonomers include methyl methacrylate, acrylonitrile, acrylamide, hydroxyethyl acrylate, and unsaturated carboxylic acids such as itaconic acid, maleic acid, and acrylic acid. Anionic surfactants such as sodium oleate, rosin acid soap, sodium alkylarylsulfonate, and sodium dialkylsulfosuccinate can be used alone or in combination with nonionic surfactants as emulsifiers. Depending on the purpose, amphoteric or cationic surfactants may also be used.

[0019] Furthermore, provided that the water vapor barrier property is not affected, it is also possible to use in combination with the water vapor barrier resin water-soluble polymers such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, ethylene copolymer polyvinyl alcohol, and other polyvinyl alcohols; proteins such as casein, soy protein, and synthetic protein; starches such as oxidized starch, cationized starch, urea phosphate esterified starch, and hydroxyethyl etherified starch; cellulose derivatives such as carboxymethyl cellulose, hydroxymethyl cellulose, and hydroxyethyl cellulose; polyvinylpyrrolidone; and sodium alginate.

[0020] The water vapor barrier layer can contain a pigment. Examples of pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as solid, hollow, and core-shell organic pigments, which can be used alone or in combination. Among these, flat inorganic pigments such as kaolin, mica, and talc are preferred, with kaolin being more preferred, from the perspectives of both improving water vapor barrier properties and suppressing the penetration of paint used to form the gas barrier layer. Furthermore, inorganic pigments with a volume 50% average particle size (D50) (hereinafter also referred to as "average particle size") of 5 μm or more and an aspect ratio of 10 or more are preferably used alone or in combination. If the average particle size or aspect ratio of the inorganic pigment used is smaller than the above range, the number of detours that water vapor molecules take within the water vapor barrier layer will decrease, shortening the distance they travel, which may result in a smaller effect of improving the water vapor barrier property.

[0021] In the present invention, from the viewpoint of improving water vapor barrier properties and adhesion to the gas barrier layer, the water vapor barrier layer preferably contains a pigment having an average particle size of 5 μm or less in addition to an inorganic pigment having an average particle size of 5 μm or more and an aspect ratio of 10 or more. Pigments having an average particle size of 5 μm or less include 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, silicates, colloidal silica, and satin white, as well as solid, hollow, or core-shell organic pigments, which can be used alone or in combination of two or more. Of these pigments, heavy calcium carbonate is preferred.

[0022] By including a pigment 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, thereby achieving 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 in the water vapor barrier layer are filled with pigments with smaller average particle sizes, and the water vapor has to travel a longer distance to bypass these pigments, which is presumably why the layer exhibits better water vapor barrier properties than a water vapor barrier layer that does not include pigments with different average particle sizes. When an inorganic pigment with an average particle size of 5 μm or more and an aspect ratio of 10 or more is used in combination with a pigment with an average particle size of 5 μm or less, the blending ratio of the inorganic pigment with an average particle size of 5 μm or more and an aspect ratio of 10 or more to the pigment with an average particle size of 5 μm or less is preferably 50 / 50 to 99 / 1 by dry weight. If the blending ratio of the inorganic pigment with an average particle size of 5 μm or more and an aspect ratio of 10 or more is less than the above range, the number of detours that water vapor takes within the water vapor barrier layer will decrease, shortening the distance it travels, which may result in a smaller improvement in water vapor barrier property. On the other hand, if the blending ratio of the inorganic pigment with an average particle size of 5 μm or more and an aspect ratio of 10 or more is more than the above range, the pigment with an average particle size of 5 μm or less will not be able to sufficiently fill the voids formed by the inorganic pigment with a large average particle size in the water vapor barrier layer, making it difficult to expect improvement in water vapor barrier property.

[0023] When a pigment is contained in the water vapor barrier layer, the blending amount of pigment is preferably in the range of 5 to 20 parts by weight of the total of the water vapor barrier resin and water-soluble polymer per 100 parts by weight of the pigment on a dry weight basis, and more preferably 10 to 150 parts by weight of the total of the water vapor barrier resin and water-soluble polymer. Note that the pigment is an optional component of the water vapor barrier layer, and it is possible to not include it (0 part by weight).

[0043] Furthermore, in addition to the water vapor barrier resin, water-soluble polymer, and pigment described above, the water vapor barrier layer may contain various commonly used auxiliary agents such as dispersants, thickeners, water retention agents, antifoaming agents, water-resistant agents, dyes, and fluorescent dyes.

[0024] The water vapor barrier layer can be blended with a crosslinking agent, such as a polyvalent metal salt. The crosslinking agent undergoes a crosslinking reaction with the water vapor barrier resin or water-soluble polymer contained in the water vapor barrier layer, increasing the number of bonds (crosslinking points) in the water vapor barrier layer, giving the water vapor barrier layer a denser structure and enabling it to exhibit better water vapor barrier properties. There are no particular restrictions on the type of crosslinking agent, and one or more of the following may be used depending on the type of water vapor barrier resin and water-soluble polymer contained in the water vapor barrier layer: polyvalent metal salts (compounds in which a polyvalent metal such as copper, zinc, silver, iron, potassium, sodium, zirconium, aluminum, calcium, barium, magnesium, or titanium is bonded to an ionic substance such as carbonate ions, sulfate ions, nitrate ions, phosphate ions, silicate ions, nitrogen oxides, or boron oxides), amine compounds, amide compounds, aldehyde compounds, hydroxy acids, etc. When using styrene-based water vapor barrier resins such as styrene-butadiene and styrene-acrylic resins, which exhibit excellent water vapor barrier properties, it is preferable to use a polyvalent metal salt, and it is more preferable to use potassium alum, from the perspective of exhibiting a crosslinking effect. The amount of crosslinking agent to be added is not particularly limited as long as it is within the range of coatable paint concentration and paint viscosity, but preferably the amount of crosslinking agent is 1 part by weight to 10 parts by weight, more preferably 3 parts by weight to 5 parts by weight, per 100 parts by weight of pigment. If the amount is less than 1 part by weight, the effect of adding the crosslinking agent may not be fully obtained. On the other hand, if the amount is more than 10 parts by weight, the viscosity of the paint may increase significantly, making coating difficult.

[0025] When adding a crosslinking agent to a coating material for a water vapor barrier layer, it is preferable to dissolve the crosslinking agent in a polar solvent such as ammonia and then add it to the coating material. When the crosslinking agent is dissolved in a polar solvent, the crosslinking agent and the polar solvent form a bond, so that adding the crosslinking agent to the coating material does not immediately cause a crosslinking reaction with the water vapor barrier resin or water-soluble polymer, thereby preventing the coating material from thickening. In this case, the polar solvent components volatilize when the coating material is dried after application to the paper substrate, causing a crosslinking reaction with the water vapor barrier resin or water-soluble polymer, forming a dense water vapor barrier layer.

[0026] From the viewpoint of improving the water vapor barrier property, it is preferable that the water vapor barrier layer contain a water repellent. 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 lanoinn, silicone-containing water repellents containing silicone or silicone compounds, and fluorine-containing water repellents containing fluorine compounds, and these can be used alone or in combination of two or more. Of these, it is preferable to use a paraffin-based water repellent from the viewpoint of expressing water vapor barrier performance.

[0027] The amount of water repellent added is not particularly limited, but is preferably 1 part by weight to 100 parts by weight of water repellent added per 100 parts by weight of the combined total of the water vapor barrier resin and water-soluble polymer, in dry weight terms. If the amount of water repellent added is less than 1 part by weight, the effect of improving water vapor barrier property may not be sufficiently achieved. On the other hand, if the amount exceeds 100 parts by weight, it may be difficult to form a uniform gas barrier layer when forming a gas barrier layer on the water vapor barrier layer, which may result in a decrease in gas barrier property. The wetting tension of the surface of the water vapor barrier layer is preferably 10 mN / m or more and 60 mN / m or less, and more preferably 15 mN / m or more and 50 mN / m or less, in order to improve the water vapor barrier property and adhesion to the gas barrier layer.

[0028] (gas barrier coating layer) The gas barrier coating layer contains at least a gas barrier resin. The gas barrier resin may be a water-soluble resin or a water-suspendable resin, with water-soluble resins being preferred. Examples of gas barrier resins include polyvinyl alcohol resins such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and ethylene copolymer 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 carboxymethyl cellulose, hydroxymethyl cellulose, and hydroxyethyl cellulose; polyvinylpyrrolidone; and sodium alginate. These may be used alone or in combination of two or more. Among these, from the viewpoint of gas barrier properties, polyvinyl alcohol resins and cellulose derivatives are preferred, and polyvinyl alcohol resins are more preferred. Polyvinyl alcohol resins having a degree of polymerization of 400 to 1700 are even more preferred, and polyvinyl alcohol resins having a degree of polymerization of 800 to 1400 are even more preferred.

[0029] The gas barrier layer may contain a pigment. Examples of pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as solid, hollow, and core-shell organic pigments, which may be used alone or in combination. Among these, the pigment is preferably a flat pigment having an average particle size of 3 μm or more and an aspect ratio of 10 or more, and more preferably a flat pigment having an average particle size of 5 μm or more and an aspect ratio of 30 or more.

[0030] When a gas barrier layer contains a pigment, particularly a flat pigment, gases such as oxygen have to bypass the pigment, which increases the distance they travel, and therefore the gas barrier layer containing the pigment exhibits superior gas barrier properties compared to gas barrier layers that do not contain a pigment, and exhibits superior gas barrier properties particularly in high-humidity atmospheres. The amount of pigment in the gas barrier layer is preferably 90 parts by weight or less per 100 parts by weight of the gas barrier resin, on a dry weight basis. The pigment is an optional component of the gas barrier layer, and it is possible to not include it (0 part by weight). By setting the pigment amount in the gas barrier layer within this range, excellent flex resistance can be exhibited. Furthermore, the inclusion of a pigment in the gas barrier layer improves adhesion between the gas barrier layer and the layer in contact with it. A lower pigment amount improves flex resistance but decreases gas barrier properties. Therefore, the pigment amount can be adjusted depending on the balance between gas barrier properties and flex resistance desired for the paper barrier material; for example, it can be set to 5 to 80 parts by weight per 100 parts by weight of the gas barrier resin. In addition to the water-soluble polymers and pigments described above, the gas barrier layer may contain various commonly used auxiliary agents such as dispersants, thickeners, water retention agents, antifoaming agents, water-resistant agents, dyes, and fluorescent dyes.

[0031] A cross-linking agent, such as a polyvalent metal salt, can be added to the gas barrier layer. The cross-linking agent undergoes a cross-linking reaction with the water-soluble polymer contained in the gas barrier layer, increasing the number of bonds (cross-linking points) in the gas barrier layer. This means that the gas barrier layer has a dense structure, allowing it to exhibit good gas barrier properties. The type of crosslinking agent is not particularly limited, and can be appropriately selected and used depending on the type of water-soluble polymer contained in the gas barrier layer, such as polyvalent metal salts (compounds in which a polyvalent metal such as copper, zinc, silver, iron, potassium, sodium, zirconium, aluminum, calcium, barium, magnesium, or titanium is bonded to an ionic substance such as carbonate ion, sulfate ion, nitrate ion, phosphate ion, silicate ion, nitrogen oxide, or boron oxide), amine compounds, amide compounds, aldehyde compounds, or hydroxy acids. From the viewpoint of exerting a crosslinking effect, it is preferable to use polyvalent metal salts, and it is more preferable to use potassium alum. The amount of crosslinking agent to be added is not particularly limited as long as it is within the range of coatable paint concentration and paint viscosity, but preferably the amount of crosslinking agent is 1 part by weight to 10 parts by weight, more preferably 3 parts by weight to 5 parts by weight, per 100 parts by weight of pigment. If the amount is less than 1 part by weight, the effect of adding the crosslinking agent may not be fully obtained. On the other hand, if the amount is more than 10 parts by weight, the viscosity of the paint may increase significantly, making coating difficult.

[0032] The gas barrier layer preferably contains a surfactant, as this improves adhesion between the gas barrier layer and the water vapor barrier layer and improves barrier properties. The ionic nature of the surfactant is not limited, and any of anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants may be used alone or in combination of two or more. Examples of surfactants include silicone-based surfactants, fluorine-based surfactants, alcohol-based surfactants, acetylene-based surfactants having an acetylene group, acetylene diol-based surfactants having an acetylene group and two hydroxyl groups, alkylsulfonic acid-based surfactants having an alkyl group and sulfonic acid, ester-based surfactants, amide-based surfactants, amine-based surfactants, alkyl ether-based surfactants, phenyl ether-based surfactants, sulfate ester-based surfactants, and phenol-based surfactants. Among these, acetylene diol-based surfactants are preferred, as they have a significant effect in improving the leveling properties of the coating material. Improved leveling properties of the coating material improve the uniformity of the gas barrier layer, thereby improving gas barrier properties. When a gas barrier layer is provided on top of a water vapor barrier layer, from the viewpoint of adhesion to the water vapor barrier layer, the surface tension of the paint for the gas barrier layer is preferably adjusted to between 10 mN / m and 60 mN / m, and more preferably between 15 mN / m and 50 mN / m. Furthermore, from the viewpoint of adhesion between the water vapor barrier layer and the gas barrier layer, it is preferable to adjust the surface tension of the paint for the gas barrier layer to between ±20 mN / m and the wetting tension of the surface of the water vapor barrier layer.

[0033] Here, the smaller the arithmetic mean height (Sac) of the barrier coating layer, i.e., the smoother the barrier coating layer, the better the adhesion to the dry-laminated thermoplastic resin film. However, to achieve a smooth barrier coating layer, a smoothing treatment such as calendering is necessary. When a high-pressure smoothing treatment such as calendering is performed on the barrier coating layer, the high pressure can cause cracks in the barrier coating layer, which can facilitate gas escape from the side edges of the paper barrier material and reduce the barrier properties. Cracks are particularly likely to occur when the barrier coating layer contains a pigment. Therefore, in the manufacturing method of the present invention, the coating layer is not subjected to a smoothing treatment with a line thickness of 20 kg / cm or more. It is preferable that a pressure of 15 kg / cm or more be applied to the coating layer with a line thickness of 15 kg / cm or more, and more preferably a pressure of 10 kg / cm or more be applied to the coating layer with a line thickness of 10 kg / cm or more.

[0034] The arithmetic mean height (Sac) of the barrier coating layer is preferably 3.0 μm to 35 μm, and is at least 1 μm greater than the arithmetic mean height (Sap) of the coated surface. A barrier coating layer that satisfies these conditions can be produced, for example, by forming a barrier coating layer on a paper substrate having an arithmetic mean height (Sap) of the coated surface of 2.0 μm to 30 μm, and not subjecting this barrier coating layer to a smoothing treatment with a line thickness of 20 kg / cm or more.

[0035] The manufacturing method of the present invention can produce a laminate with excellent interlayer adhesion even if the barrier coating layer does not have a high degree of smoothness. The arithmetic mean height (Sac) of the barrier coating layer is preferably 6.0 μm or more, more preferably 9.0 μm or more, even more preferably 12 μm or more, even more preferably 15 μm or more, and even more preferably 18 μm or more. On the other hand, since the smoother the barrier coating layer, the more improved the barrier properties tend to be, the arithmetic mean height (Sac) of the barrier coating layer is preferably 32 μm or less, more preferably 29 μm or less, and even more preferably 26 μm or less.

[0036] Furthermore, the PPS smoothness (hardbacking, 1 MPa) of the barrier coating layer is preferably 1.0 μm or more and 14 μm or less. The manufacturing method of the present invention can produce a laminate with excellent interlayer adhesion even if the barrier coating layer does not have a high level of smoothness. However, if the PPS smoothness (hardbacking, 1 MPa) of the barrier coating layer exceeds 14 μm, the barrier properties may be reduced. Therefore, the PPS smoothness (hardbacking, 1 MPa) of the paper substrate is more preferably 3.0 μm or more, and even more preferably 5.0 μm or more. If the coated surface is not smoothed, the arithmetic mean height value for the barrier coating layer will be greater than the value for the coated surface of the paper substrate, and the PPS smoothness value for the barrier coating layer will be smaller than the value for the coated surface of the paper substrate. Arithmetic mean height is measured by non-contact measurement of the surface shape using laser light or a cantilever. PPS smoothness, on the other hand, is calculated by measuring the degree of air escape when a jig is pressed against the surface and air is passed through. The difference in the trends in the values ​​calculated for arithmetic mean height and PPS smoothness before and after smoothing treatment is presumably due to differences in factors that have a significant impact on the measured values ​​(such as the size of surface roughness (nano-size or micro-size) and surface shape (such as the period of irregularities)) due to the different measurement methods used for arithmetic mean height and PPS smoothness.

[0037] (Formation of barrier coating layer) The barrier coating layer can be formed by applying a coating material for forming the barrier coating layer using various coating devices and drying the applied coating material.

[0043] There are no particular limitations on the method for applying the coating material for forming the water vapor barrier layer and gas barrier layer to the paper substrate, and coating can be performed using known coating equipment and coating systems. Examples of coating equipment include blade coaters, bar coaters, roll coaters, air knife coaters, reverse roll coaters, curtain coaters, spray coaters, size press coaters, and gate roll coaters. Furthermore, examples of coating systems include aqueous coating using a solvent such as water, and solvent-based coating using a solvent such as an organic solvent, with aqueous coating being preferred. The water vapor barrier layer and the gas barrier layer can be dried using a conventional method such as a steam heater, gas heater, infrared heater, electric heater, hot air heater, microwave, or cylinder dryer.

[0038] In the present invention, the coating amount of the water vapor barrier layer is 3 g / m2 in dry weight. 2 More than 50g / m 2 It is preferable that the density is 5 g / m or less. 2 More than 40g / m 2 It is more preferable that the density is 7 g / m or less. 2 More than 30g / m 2 It is more preferable that the coating weight of the water vapor barrier layer is 3 g / m or less. 2 If the coating weight of the water vapor barrier layer is less than 50 g / m, it may be difficult to completely coat the paper substrate with the coating material, resulting in insufficient water vapor barrier properties, or the coating material for the gas barrier layer may penetrate into the paper substrate, preventing the formation of a uniform gas barrier coating layer and resulting in insufficient gas barrier properties. 2 If the amount is larger, the drying load during coating increases. The water vapor barrier layer may be a single layer, or may be configured as two or more layers. When the water vapor barrier layer is configured as two or more layers, the total coating weight of all the water vapor barrier layers is preferably within the above range.

[0039] In the present invention, the coating amount of the gas barrier layer is 0.2 g / m2 in terms of dry weight. 2 More than 20g / m 2 The coating weight of the gas barrier layer is preferably 0.2 / m or less. 2 If the density is less than 20 g / m, it may be difficult to form a uniform gas barrier layer, and sufficient gas barrier properties may not be obtained. 2 If the amount is larger, the drying load during coating increases. The gas barrier layer may be a single layer or may be configured as two or more layers. When the gas barrier layer is configured as two or more layers, it is preferable that the total coating weight of all gas barrier layers is within the above range. This is presumably because gas easily escapes from the side edges of the material.

[0040] Lamination process The laminating step is a step of providing a laminate layer made of a thermoplastic resin film on a barrier coating layer by dry lamination via an adhesive. In the manufacturing method of the present invention, the adhesive is applied to the barrier coating layer. When the paper substrate has a barrier coating layer on only one side, a thermoplastic resin film can also be laminated by dry lamination on the side of the paper substrate opposite the barrier coating layer. In this case, the adhesive is applied to the thermoplastic resin film.

[0041] (laminate layer) The laminate layer is made of a thermoplastic resin film. Examples of thermoplastic resin films that can be used to form the laminate layer include, without limitation, polyolefin resins (polyethylenes such as LDPE and LLDPE, polypropylene, etc.), ethylene-vinyl acetate resins, styrene-acrylate copolymer resins, acrylic resins, ethylene-acrylic resins, polyester resins (polyethylene terephthalate, polyethylene succinate, polybutylene terephthalate, polyethylene naphthalate, etc.), polyvinyl alcohol resins, polyvinyl acetate resins, and polylactic acid resins. Among these, polyolefin resins, ethylene-vinyl acetate resins, styrene-acrylate copolymer resins, acrylic resins, and ethylene-acrylic resins are preferred in terms of heat seal strength. Furthermore, biodegradable resins such as polyvinyl alcohol, polylactic acid, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBH), and polybutylene succinate are preferred in terms of reducing the environmental impact if they are disposed of as waste. Furthermore, from the standpoint of processability when the obtained paper barrier material is heat-sealed into packaging, it is preferable that the melting point is 90° C. or higher and 180° C. or lower. In this specification, melting point refers to the peak melting temperature according to JIS K7121-1987. The thickness of the laminate layer is not particularly limited, but is preferably 25 μm or more and 60 μm or less from the viewpoint of the balance between heat sealability and molding processability.

[0042] (glue) In the present invention, the barrier base paper and thermoplastic resin film are laminated by dry lamination, and the adhesive is applied to the barrier coating layer. Conventionally, when dry laminating paper and a film, it has been common technical knowledge to apply the adhesive to the film side to prevent a decrease in adhesion due to the adhesive soaking into the paper. In the present invention, the barrier base paper is provided with a barrier coating layer, which can prevent the adhesive from soaking in, so that even if an adhesive is applied on the barrier coating layer, a decrease in adhesion can be prevented. Furthermore, the adhesive has fluidity immediately after coating, and this fluidity fills in any irregularities on the surface of the barrier coating layer, making it possible to obtain a paper barrier material with better interlayer adhesion and high barrier properties.

[0043] The coating amount (solid content) of the adhesive is not particularly limited, but for example, 2.0 g / m 2 More than 5.0g / m 2 The coating weight (solid content) of the adhesive is 2.0 g / m or less. 2 If the adhesive is applied at a coating weight (solid content) of less than 5.0 g / m, the adhesive will not be able to fill in the unevenness of the coating layer, resulting in gaps between the adhesive layer and the laminate layer, and the expected barrier properties will not be achieved. 2 If the coating rate exceeds this, problems such as reduced productivity due to slower coating and drying speeds, increased residual solvents that cause odors, and increased costs due to increased material usage are likely to occur. From the perspective of barrier properties, the coating amount (solid content) of the adhesive should be 3.0 g / m 2 More than 4.0 g / m is preferable. 2 On the other hand, from the viewpoint of cost, 4.0 g / m 2 The following is preferred:

[0044] The adhesive can be any adhesive used in dry lamination without any particular limitations, and examples thereof include polyurethane-based (polyether polyol, polyester polyol, etc.), polyacrylic-based, polyester-based, epoxy-based, polyvinyl acetate-based, and cellulose-based adhesives, with polyurethane-based adhesives being preferred in terms of adhesive strength. In addition to the adhesive, the adhesive layer can also contain a curing agent, a solvent, etc. Among these, those using water as a solvent are preferred in terms of reducing emissions of volatile organic compounds into the atmosphere and improving the hygiene of the working environment.

[0045] In the manufacturing method of the present invention, by not subjecting the barrier coating layer to a smoothing treatment at a linear pressure of 20 kg / cm or more, cracks in the barrier coating layer are prevented, and extremely high barrier properties can be achieved. The paper barrier material manufactured by the present invention has an oxygen permeability of 20 cc / m or more at 23°C and 0% RH. 2 The oxygen permeability is preferably 10 cc / m 2 ·day·atm or less is preferable, 5cc / m 2 ·day·atm or less is preferable, 3cc / m 2 ·day·atm or less is even more preferable, 1cc / m 2 ·day·atm or less is even more preferable, 0.8cc / m 2 ·day·atm or less is even more preferable, 0.6cc / m 2 ·day·atm or less is even more preferable, 0.4cc / m 2 ·day·atm or less is even more preferable.

[0046] The paper barrier material of the present invention has a laminate layer made of a thermoplastic resin film on at least one surface and is heat-sealable, so it can be used as a packaging material after heat-sealing. The paper barrier material of the present invention can be used as is, or laminated with various resins, etc., or attached with various general-purpose films, barrier films, aluminum foil, etc., to form paper barrier packaging materials used for packaging applications such as food packaging, containers, cups, etc., or laminates used for industrial materials, etc. The paper barrier material of the present invention can be suitably used as a paper barrier packaging material used for packaging applications such as food packaging, containers, cups, etc., and is particularly suitably used as a flexible packaging bag for food, etc. A flexible packaging bag is a packaging material made of a highly flexible material, and generally refers to a packaging material made of thin, flexible materials such as paper, film, aluminum foil, etc., either alone or bonded together. The shape of the flexible packaging bag is not particularly limited, and examples include vertical pillow packaging bags, horizontal pillow packaging bags, side seal bags, two-side seal bags, three-side seal bags, gusset bags, bottom gusset bags, and stand-up bags. [Example]

[0047] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, parts and % in the examples represent parts by weight and % by weight, respectively. The resulting paper substrate, barrier base paper, and paper barrier material were tested using the evaluation methods described below. The results are shown in Table 1.

[0048] <Oxygen permeability (gas barrier properties)> For paper barrier materials, measurements were taken using the MOCON OX-TRAN2 / 21 at 23°C and 0% RH. <Arithmetic mean height (Sa)> In accordance with ISO25178-2:2012, a 3D microscope (KEYENCE, VR-3000) (ISO4287 compliant) was used to measure the surface area (0.4 cm ) of the obtained paper substrate and barrier base paper. 2 The arithmetic mean height (Sa) was calculated as the average distance from the reference surface of each point in the image. Distortion in the measured surface area was suppressed using a first-order Gaussian regression filter. Measurement conditions using a 3D microscope Filter type: Gaussian End effect correction (suppress distorted areas): Enabled S-filter (filter to remove small scale roughness components): None L-filter (filter to remove large-scale undulations): None

[0049] <PPS smoothness> The PPS smoothness of the obtained paper substrate and barrier base paper was measured in accordance with JIS P8151:2004 (Paper and paperboard - Surface roughness and smoothness test method (air leak method) - Print surf tester method).

[0050] [Example 1] (Preparation of paper substrate 1) The raw material pulp was prepared by blending hardwood bleached kraft pulp (LBKP) with a Canadian standard freeness (CSF) of 500 ml and softwood bleached kraft pulp (NBKP) with a CSF of 530 ml in a weight ratio of 80 / 20. The raw pulp was mixed with 0.1% of polyacrylamide (PAM) with a molecular weight of 2.5 million as a dry strength agent, based on the weight of the bone-dry pulp, 0.35% of alkyl ketene dimer (AKD) as a sizing agent, 0.15% of polyamide epichlorohydrin (PAEH) resin as a wet strength agent, and 0.08% of polyacrylamide (PAM) with a molecular weight of 10 million as a retention agent, and then the mixture was made into paper using a Duoformer FM papermaking machine to obtain the paper base material.

[0051] (Preparation of coating solution for water vapor barrier layer) Large-particle engineered kaolin (Imerys Barrisurf HX, particle size 9.0 μm, aspect ratio 80-100) was mixed with sodium polyacrylate as a dispersant (0.2 parts relative to inorganic pigment) and dispersed in a Serie mixer to prepare a large-particle kaolin slurry with a solids concentration of 55%. Styrene-butadiene latex (Zeon PNT7868) was then blended into the resulting kaolin slurry at a solids concentration of 100 parts relative to pigment, yielding a coating solution for the water vapor barrier layer with a solids concentration of 50%. (Preparation of coating solution for gas barrier layer) An aqueous solution of polyvinyl alcohol (VC-10, manufactured by Nippon Vinyl Acetate & Poval Co., Ltd.) with a solids concentration of 12% was prepared as a coating solution for the gas barrier layer.

[0052] (Production of paper barrier packaging materials) The water vapor barrier layer coating solution was applied to the obtained paper substrate in a dry weight of 12.0 g / m 2 After coating and drying, the gas barrier layer coating solution was applied on top of it in a dry weight of 4.0 g / m 2 The barrier base paper was obtained by coating one side of the paper so that the thickness was 100 μm, and then drying it in an SCAF dryer. Note that no pressure of more than 20 kg / cm was applied to the coating layer during drying or transport. Furthermore, an adhesive (two-component curing polyurethane adhesive, curing agent: polyisocyanate, solvent: ethyl acetate) was applied to the gas barrier layer of the obtained barrier base paper at a coating amount (solid content) of 3 g / m 2 A film (Futamura Chemical Co., Ltd., LLDPE, thickness 30 μm, melting point 130°C) was then attached using the dry lamination method at a pressure of 0.4 MPa, a processing speed of 3.8 m / min and 90°C to obtain a paper barrier material.

[0053] "Example 2" A paper barrier material was obtained in the same manner as in Example 1, except that the wet paper was dried using a Yankee dryer and smoothed. "Comparative Example 1" A paper barrier material was obtained in the same manner as in Example 1, except that an adhesive was applied to the film during dry lamination.

[0054] "Example 3" A paper barrier material was obtained in the same manner as in Example 1, except that the dry lamination conditions were a pressure of 0.2 MPa, a processing speed of 3.8 m / min, and a temperature of 125°C. "Comparative Example 2" A paper barrier material was obtained in the same manner as in Example 3, except that an adhesive was applied to the film during dry lamination. Example 4 The adhesive coating amount (solid content) is 2g / m 2A paper barrier material was obtained in the same manner as in Example 1, except that the dry lamination conditions were a pressure of 0.4 MPa, a processing speed of 3.8 m / min, and 125°C. "Comparative Example 3" A paper barrier material was obtained in the same manner as in Example 4, except that an adhesive was applied to the film during dry lamination.

[0055] "Example 5" The adhesive coating amount (solid content) is 5g / m 2 A paper barrier material was obtained in the same manner as in Example 1, except that: "Comparative Example 4" A paper barrier material was obtained in the same manner as in Example 5, except that the barrier coating layer was subjected to a smoothing treatment (calender line thickness: 30 kg / cm).

[0056] [Table 1]

[0057] The results of Examples 1-2 and Comparative Example 1, Example 3 and Comparative Example 2, and Example 4 and Comparative Example 3 confirmed that by coating paper with an adhesive, a paper barrier material with superior barrier properties can be obtained compared to when the adhesive is coated on a film. The results of Example 5 and Comparative Example 4 show that when the barrier coating layer was subjected to high-pressure smoothing treatment, the barrier coating layer became smooth but its barrier properties deteriorated. This confirms that when the barrier coating layer was subjected to high-pressure smoothing treatment, cracks were generated in the coating layer, resulting in a deterioration of its barrier properties. Examples 1 and 3-5 confirmed that a paper barrier material with high barrier properties could be obtained by the very simple method of applying an adhesive onto the barrier coating layer, without having to apply a smoothing treatment to both the paper substrate and the barrier coating layer.

Claims

1. a barrier base paper manufacturing process in which a barrier coating layer is formed on at least one coated surface of a paper substrate; a laminating step of providing a laminate layer made of a thermoplastic resin film on the barrier coating layer by dry lamination using an adhesive; and The barrier coating layer is not subjected to a smoothing treatment at a linear pressure of 20 kg / cm or more, A method for producing a paper barrier material, characterized in that the adhesive is applied to the barrier coating layer.

2. The arithmetic mean height (Sap) of the coated surface of the paper substrate is 2.0 μm or more and 30 μm or less, 2. The method for producing a paper barrier material according to claim 1, wherein the arithmetic mean height (Sac) of the barrier coating layer is 3.0 μm or more and 35 μm or less, and is at least 1 μm greater than the arithmetic mean height (Sap) of the coated surface.

3. Oxygen permeability at 23°C and 0% RH is 20 cc / m ２ 3. The method for producing a paper barrier material according to claim 1 or 2, characterized in that the water content is 1000 ppm or less.

4. The coating amount (solid content) of the adhesive is 2.0 g / m ２ 5.0g / m or more ２ The method for producing a paper barrier material according to claim 1 or 2, characterized in that:

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