JP7729009B2 - Paper barrier packaging materials - Google Patents

Description

The present invention relates to a paper barrier packaging material.

It is important to impart gas barrier properties (particularly oxygen barrier properties) to paper packaging materials in order to protect various packaged products from deterioration due to gases, such as oxidation due to oxygen.
Conventionally, gas barrier properties have been imparted to paper packaging materials mainly by extrusion laminating or pasting onto a paper substrate 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.

Other paper packaging materials with gas barrier properties have been disclosed, including paper gas barrier materials with a gas barrier layer made of a water-soluble polymer and an inorganic layered compound (Patent Documents 1 and 2). It is also important to impart water resistance (particularly water vapor barrier properties) to paper packaging materials in order to protect the various packaged products from deterioration due to water vapor. One paper packaging material with gas barrier and water vapor barrier properties has been disclosed as having a paper base material, a water vapor barrier layer containing a water vapor barrier resin and a pigment, and a gas barrier layer containing a polyvinyl alcohol resin and a pigment (Patent Document 3).

Such paper barrier packaging materials can bend when processed into packaging containers, or when the product is transported or used, which can significantly reduce their barrier properties. Therefore, there is a demand for paper barrier packaging materials with excellent bending resistance.

JP 2009-184138 A Japanese Patent Application Laid-Open No. 2003-094574 Patent No. 5331265

The present invention aims to provide a paper barrier packaging material with excellent bending resistance.

The means for solving the problems of the present invention are as follows.
1. A paper substrate having a water vapor barrier layer and a gas barrier layer,
the water vapor barrier layer contains a water vapor barrier resin and a pigment,
the water vapor barrier resin contains a styrene-based resin having a glass transition temperature of −20 to 95° C.,
1. A paper barrier packaging material characterized in that the gas barrier layer contains a gas barrier resin, and the pigment content is 90 parts by weight or less per 100 parts by weight of the gas barrier resin.
2. The paper barrier packaging material according to 1., characterized in that it has the water vapor barrier layer and the gas barrier layer in this order on the paper substrate.
3. The water vapor barrier layer contains an ethylene-based resin,
3. The paper barrier packaging material according to 1. or 2., characterized in that the styrene-based resin and the ethylene-based resin are contained in a weight ratio (dry weight) of 99/1 to 1/99.
4. The paper barrier packaging material according to 3., characterized in that the ethylene-based resin has a glass transition temperature of -20 to 95°C.
5. The paper barrier packaging material according to any one of 1. to 4., characterized in that the pigment content in the gas barrier layer is 5 to 80 parts by weight per 100 parts by weight of the gas barrier resin, on a dry weight basis.
6. The paper barrier packaging material according to any one of 1. to 5., wherein the water vapor barrier layer contains a pigment with an average particle size of 5 μm or more and an aspect ratio of 10 or more.
7. The paper barrier packaging material according to any one of 1. to 6., wherein the gas barrier resin contains a polyvinyl alcohol-based resin.
8. The paper barrier packaging material according to any one of 1. to 7., wherein the gas barrier layer contains a plasticizer.
9. The paper barrier packaging material according to any one of 1. to 8., wherein the gas barrier layer contains an adhesive aid.

The paper barrier packaging material of the present invention has excellent bending resistance and exhibits little deterioration in barrier properties when bent. The paper barrier packaging material of the present invention can be suitably used for flexible packaging bags that are prone to bending.

The present invention provides a paper substrate having a water vapor barrier layer and a gas barrier layer thereon,
the water vapor barrier layer contains a water vapor barrier resin and a pigment, and the water vapor barrier resin contains a styrene-based resin having a glass transition temperature of -20 to 95°C;
The present invention relates to a paper barrier packaging material in which the gas barrier layer contains a gas barrier resin, and the pigment content per 100 parts by weight of the gas barrier resin is 90 parts by weight or less.
In this specification, the expression "A to B (A and B are numbers)" means a numerical range including the values of A and B, that is, A or more and B or less.

Paper barrier packaging materials preferably have a water vapor barrier layer and a gas barrier layer, in this order, on a paper substrate. Paper barrier packaging materials having a water vapor barrier layer and a gas barrier layer, in this order, on a paper substrate have excellent water vapor barrier properties and gas barrier properties. The reason for this is presumed to be as follows: When a gas barrier layer and a water vapor barrier layer are provided on a paper substrate in this order, the gas barrier resin in the gas barrier layer is prone to degradation due to moisture in the paper substrate and moisture in the air that permeates through the paper substrate. On the other hand, by providing a water vapor barrier layer and a gas barrier layer, in this order, on a paper substrate, which contain resins with good water resistance, the water vapor barrier layer can effectively suppress the impact (deterioration) of the gas barrier layer due to moisture in the paper substrate and other factors. For this reason, paper barrier base paper, particularly those having a water vapor barrier layer and a gas barrier layer, in this order, has excellent water vapor barrier properties and gas barrier properties.

(Paper base material)
In the present invention, the paper substrate is a sheet made of pulp, fillers, various auxiliaries, and the like.
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 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 can be used in appropriate combinations. Among these, chemical pulp and mechanical pulp made from wood fibers are preferred, and chemical pulp is more preferred, for reasons such as the fact that foreign matter is less likely to be mixed into the paper base material, that discoloration is less likely to occur over time when used paper containers are recycled as recycled paper raw materials, and that the high whiteness results in a good surface appearance when printed, thereby increasing the useful value, particularly when used as a packaging material.

Fillers that can be used include well-known fillers such as white carbon, talc, kaolin, clay, heavy calcium carbonate, light calcium carbonate, titanium oxide, zeolite, and synthetic resin fillers. Fillers are optional, and the paper may contain no fillers. Internal papermaking aids such as aluminum sulfate and various anionic, cationic, nonionic, or amphoteric retention aids, drainage aids, paper strength agents, and internal sizing agents can also be used as needed. Furthermore, dyes, fluorescent brighteners, pH adjusters, defoamers, pitch control agents, slime control agents, and other additives can also be added as needed.

The method for producing the paper base material (papermaking) is not particularly limited, and the paper base material can be produced by acidic papermaking, neutral papermaking, or alkaline papermaking using a known Fourdrinier former, on-top hybrid former, gap former machine, etc. The paper base material may be composed 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 retention agents, thickeners, and lubricants. These can be used alone or in combination of two or more. Furthermore, these various chemicals can 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 solid, hollow, and core-shell pigments, which can be used alone or in combination of two or more.

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

The basis weight of the paper substrate can be selected as appropriate depending on the various qualities and handleability desired for the paper barrier packaging material, but is usually preferably about 20 g/ ^m2 or more and 500 g/ ^m2 or less. In the case of paper barrier packaging materials used for packaging purposes such as packaging materials for food, containers, cups, etc., a basis weight of 25 g/ ^m2 or more and 400 g/ ^m2 or less is more preferred, and in the case of paper barrier packaging materials used for flexible packaging bags, which will be described later in particular, a basis weight of 30 g/m2 or ^more and 140 g/ ^m2 or less is more preferred.

(Water vapor barrier layer)
The water vapor barrier layer contains a water vapor barrier resin and a pigment.
The water vapor barrier resin includes a styrene-based resin having a glass transition temperature (Tg) of -20°C or higher and 95°C or lower. The styrene-based resin refers to a resin obtained by copolymerizing a styrene monomer with other monomers such as acrylic acid, methacrylic acid, acrylonitrile, or butadiene. However, it may also be a resin obtained by copolymerizing various comonomers for the purpose of modification. Examples of comonomers include methyl methacrylate, acrylonitrile, acrylamide, hydroxyethyl acrylate, and unsaturated carboxylic acids such as itaconic acid and maleic acid. Examples of styrene-based resins include styrene-acrylic resins, styrene-butadiene resins, and styrene-butadiene-acrylic resins, with styrene-acrylic resins being preferred. The glass transition temperature of the styrene-based resin is preferably -20°C or higher, more preferably -10°C or higher, and even more preferably 0°C or higher, and preferably 50°C or lower, more preferably 40°C or lower, and even more preferably 30°C or lower. The styrene-based resins can be used alone or in combination of two or more types.

Furthermore, as the water vapor barrier resin, ethylene-based resins copolymerized with ethylene monomers and other monomers, such as ethylene-acrylic resins and ethylene-vinyl acetate resins, paraffin (wax)-based resins, various copolymers such as butadiene-methyl methacrylate-based and vinyl acetate-butyl acrylate-based resins, synthetic adhesives such as maleic anhydride copolymers and acrylic acid-methyl methacrylate copolymers, or paraffin (wax)-blended synthetic adhesives of these can be used in combination. Of these, ethylene-based resins are preferred, and ethylene-acrylic resins are more preferred. The glass transition temperature of the ethylene-based resin is preferably -20°C or higher and 95°C or lower, more preferably -15°C or higher, even more preferably -10°C or higher, and preferably 50°C or lower, even more preferably 40°C or lower. When an ethylene-based resin is used in combination, the weight ratio of the styrene-based resin to the ethylene-based resin (dry weight, styrene/ethylene) is preferably 99/1 to 1/99, more preferably 90/10 to 10/90, still more preferably 70/30 to 30/70, and even more preferably 65/35 to 45/55.

In addition, as long as the water vapor barrier properties are not affected, it is also possible to use the following in combination with the above water vapor barrier resins: polyvinyl alcohols 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; and water-soluble polymers such as polyvinylpyrrolidone and sodium alginate.

Examples of pigments include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, and organic pigments such as solid, hollow, and core-shell pigments, which can be used alone or in combination of two or more.
Among these pigments, from the viewpoint of improving the water vapor barrier property and improving adhesion with adjacent layers, flat inorganic pigments such as kaolin, mica, and talc are preferred, with kaolin or mica being more preferred. Furthermore, it is preferred to use a single inorganic pigment, or a mixture of two or more inorganic pigments, with a 50% volume average particle size (D50) (hereinafter also referred to as "average particle size") of 5 μm or more and an aspect ratio of 10 or more. 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 takes within the water vapor barrier layer decreases, shortening the distance it travels, which may result in a reduced effect in improving the water vapor barrier property.

In the present invention, from the perspective of improving water vapor barrier properties and improving adhesion with adjacent layers, it is preferable to further incorporate a pigment with an average particle size of 5 μm or less into a water vapor barrier layer containing an inorganic pigment with an average particle size of 5 μm or more and an aspect ratio of 10 or more. The combined use of a pigment with an average particle size of 5 μm or less reduces the voids in the water vapor barrier layer formed by the inorganic pigment with an average particle size of 5 μm or more and an aspect ratio of 10 or more, thereby achieving even better water vapor barrier properties. In other words, when pigments with different average particle sizes are incorporated into a water vapor barrier layer, the pigment with a smaller average particle size fills the voids formed by the inorganic pigment with a larger average particle size in the water vapor barrier layer, allowing water vapor to bypass the pigment and pass through. This is presumably why the layer has higher water vapor barrier properties than a water vapor barrier layer that does not contain a pigment with a different average particle size.

In the present invention, pigments with an average particle size of 5 μm or less that can be used in combination with inorganic pigments with an average particle size of 5 μm or more and an aspect ratio of 10 or more include inorganic pigments such as kaolin, clay, engineered kaolin, delaminated clay, heavy calcium carbonate, light calcium carbonate, mica, talc, titanium dioxide, barium sulfate, calcium sulfate, zinc oxide, silicic acid, silicates, colloidal silica, and satin white, as well as organic pigments such as solid, hollow, and core-shell pigments, which can be used alone or in combination of two or more. Of these pigments, heavy calcium carbonate is preferred.

The blending amount of the pigment in the water vapor barrier layer is preferably from 50 parts by weight to 1,000 parts by weight, more preferably from 120 parts by weight to 1,000 parts by weight, and particularly preferably from 150 parts by weight to 300 parts by weight, per 100 parts by weight of the water vapor barrier resin, in dry weight terms.
In the present invention, when an inorganic pigment having an average particle size of 5 μm or more and an aspect ratio of 10 or more is used in combination with a pigment having an average particle size of 5 μm or less, the blending ratio of the inorganic pigment having an average particle size of 5 μm or more and an aspect ratio of 10 or more to the pigment having 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 having 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 reduce the effect of improving the water vapor barrier property. On the other hand, if the blending ratio is greater than the above range, the pigment having 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, and no further improvement in the water vapor barrier property will be seen.

In addition to the water vapor barrier resins, water-soluble polymers, and pigments mentioned above, the water vapor barrier layer can also contain various commonly used auxiliary agents such as plasticizers, crosslinking agents, water repellents, dispersants, thickeners, water retention agents, defoamers, water-resistant agents, dyes, and fluorescent dyes.

In the present invention, a plasticizer can be added to the water vapor barrier layer. The addition of a plasticizer improves the flexibility of the water vapor barrier layer, making it less likely to crack when bent, resulting in improved flex resistance. Glycol-based plasticizers such as glycerin and ethylene glycol are preferably used as the plasticizer.
The amount of plasticizer blended is not particularly limited, but the amount of plasticizer blended is preferably 0.1 part by weight or more and 50 parts by weight or less, more preferably 1 part by weight or more, and even more preferably 20 parts by weight or less, relative to 100 parts by weight of the water vapor barrier resin on a dry weight basis. If the amount of plasticizer blended is less than 0.1 part by weight, there is a possibility that the effect of improving flexibility and flexibility of the water vapor barrier property will not be sufficiently obtained. On the other hand, if it exceeds 50 parts by weight, there is a possibility that sufficient water vapor barrier property will not be obtained.

In the present invention, a crosslinking agent, such as a polyvalent metal salt, can be added to the water vapor barrier layer. The crosslinking agent undergoes a crosslinking reaction with the water vapor barrier resin and water-soluble polymer contained in the water vapor barrier layer, thereby increasing the number of bonds (crosslinking points) in the water vapor barrier layer. In other words, the water vapor barrier layer has a dense structure, allowing it to exhibit good water vapor barrier properties.
[0033] In the present invention, the type of crosslinking agent is not particularly limited, and can be appropriately selected and used according to the type of water vapor barrier resin and water-soluble polymer contained in the water vapor barrier layer, including 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, and hydroxy acids. Of these, from the perspective of achieving a crosslinking effect in the styrene-based resin contained in the water vapor barrier resin, it is preferable to use polyvalent metal salts, and it is more preferable to use potassium alum.
The amount of crosslinking agent blended is not particularly limited as long as it is within the range of coatable coating concentration and coating viscosity, but preferably the amount of crosslinking agent is 1 part by weight to 10 parts by weight, and more preferably 3 parts by weight to 5 parts by weight, per 100 parts by weight of the water vapor barrier resin. If the amount is less than 1 part by weight, the effect of adding the crosslinking agent may not be fully obtained. If the amount is more than 10 parts by weight, the viscosity of the coating may increase significantly, making coating difficult.

When adding a crosslinking agent to the coating material for the water vapor barrier layer in the present invention, 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 when the crosslinking agent is added to the coating material, a crosslinking reaction with the water vapor barrier resin or water-soluble polymer does not immediately occur, thereby preventing the coating material from thickening. In this case, it is believed that the polar solvent components volatilize upon drying after application to the paper substrate, causing a crosslinking reaction with the water vapor barrier resin or water-soluble polymer, resulting in the formation of a dense water vapor barrier layer.

In the present invention, a water repellent can be incorporated into the water vapor barrier layer from the perspective of improving water vapor barrier properties. Examples of water repellents include paraffin-based water repellents primarily composed of alkane compounds, natural oil-based water repellents derived from plants and animals such as carnauba and lanolin, silicone-containing water repellents containing silicone or silicone compounds, and fluorine-containing water repellents containing fluorine compounds. Of these, paraffin-based water repellents are preferred from the perspective of achieving water vapor barrier performance. These water repellents can be used alone or in combination of two or more types.

In the present invention, the amount of water repellent blended is not particularly limited, but the amount of water repellent blended is preferably 1 part by weight to 100 parts by weight per 100 parts by weight of the total of the water vapor barrier resin and water-soluble polymer, on a dry weight basis. If the amount of water repellent blended is less than 1 part by weight, the effect of improving water vapor barrier property may not be fully 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 one on the water vapor barrier layer, which may result in a decrease in gas barrier property.

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

(Gas barrier layer)
The gas barrier layer contains a gas barrier resin.
Examples of gas barrier resins that can be used include water-soluble polymers or water-dispersible polymers, such as polyvinyl alcohol-based resins such as fully saponified polyvinyl alcohol, partially saponified polyvinyl alcohol, and ethylene copolymer polyvinyl alcohol; proteins such as casein, soybean 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. Among these, from the viewpoint of gas barrier properties, polyvinyl alcohol-based resins and cellulose derivatives are preferred, polyvinyl alcohol-based resins are more preferred, polyvinyl alcohol-based resins having a degree of polymerization of 400 to 1700 are even more preferred, and polyvinyl alcohol-based resins having a degree of polymerization of 800 to 1400 are even more preferred.

The gas barrier layer contains 90 parts by weight or less of pigment per 100 parts by weight of gas barrier resin, on a dry basis. The pigment is an optional component in the gas barrier layer, and it can be absent (0 parts by weight). By ensuring that the pigment content of the gas barrier layer is within this range, the paper barrier packaging material of the present invention can exhibit excellent flex resistance. Furthermore, the inclusion of a pigment in the gas barrier layer improves adhesion between the gas barrier layer and the layer in contact with it. The lower the pigment content, the better the flex resistance, but the lower the gas barrier properties. Therefore, the pigment content can be adjusted depending on the flex resistance and gas barrier properties desired for the paper barrier packaging material; for example, it can be set to between 5 and 80 parts by weight per 100 parts by weight of gas barrier resin.

Pigments that can be incorporated into the gas barrier layer 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, satin white, etc., and organic pigments such as solid, hollow, and core-shell pigments, which can be used alone or in combination of two or more. The pigment is preferably a flat pigment with an average particle size of 3 μm or more and an aspect ratio of 10 or more, and more preferably a flat pigment with an average particle size of 5 μm or more and an aspect ratio of 30 or more.
When a gas barrier layer contains a pigment, particularly a flat pigment, gases such as oxygen bypass the pigment, resulting in superior gas barrier properties, particularly in high-humidity environments, compared to gas barrier layers that do not contain a pigment.

In the present invention, in addition to the gas barrier resins and pigments described above, the gas barrier layer may contain various commonly used additives such as crosslinking agents, surfactants, adhesion aids, plasticizers, dispersants, thickeners, water retention agents, antifoaming agents, water-resistant agents, dyes, and fluorescent dyes.

In the present invention, a crosslinking agent, such as a polyvalent metal salt, can be added to the gas barrier layer. The crosslinking agent undergoes a crosslinking reaction with the polymer contained in the gas barrier layer, thereby increasing the number of bonds (crosslinking points) in the gas barrier layer. In other words, the gas barrier layer has a dense structure, allowing it to exhibit good gas barrier properties.
In the present invention, 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 coating concentration and 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 the gas barrier resin. If the amount is less than 1 part by weight, the effect of adding the crosslinking agent may not be fully obtained. If the amount is more than 10 parts by weight, the viscosity of the coating may increase significantly, making coating difficult.

When a gas barrier layer is provided on a coating layer, it is preferable to include a surfactant in the gas barrier layer from the viewpoint of adhesion to the coating layer. The ionic nature of the surfactant is not limited, and any of anionic, cationic, amphoteric, and nonionic surfactants may be used, either alone or in combination. Specific surfactants include silicone-based surfactants, fluorine-based surfactants, alcohol-based surfactants, acetylene-based surfactants with an acetylene group, acetylene diol-based surfactants with an acetylene group and two hydroxyl groups, alkylsulfonic acid-based surfactants with 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 significantly improve the leveling properties of the coating. Improved coating leveling improves the uniformity of the gas barrier layer, thereby improving gas barrier properties.

In the present invention, an adhesion promoter can be added to the gas barrier layer. The addition of an adhesion promoter improves adhesion to adjacent layers and can suppress the occurrence of interlayer delamination during bending or processing, thereby improving flex resistance. Examples of adhesion promoters that can be used include polyethyleneimine, organic titanium compounds, and polybutadiene compounds, with polyethyleneimine being particularly preferred.
The amount of the adhesive aid to be blended is not particularly limited, but the amount of the adhesive aid to be blended is preferably 0.1 parts by weight or more and 50 parts by weight or less, and more preferably 1 part by weight or more and 20 parts by weight or less, relative to 100 parts by weight of the gas barrier resin on a dry weight basis.

In the present invention, a plasticizer can be added to the gas barrier layer. The addition of a plasticizer improves the flexibility of the gas barrier layer, making it less likely to crack when bent, resulting in improved flex resistance. Glycol-based plasticizers such as glycerin, ethylene glycol, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylolpropane are preferably used as plasticizers. These can be used alone or in combination of two or more. Of these, glycerin, ethylene glycol, and diglycerin are preferred.
The amount of plasticizer to be blended is not particularly limited, but the amount of plasticizer to be blended is preferably 0.1 to 50 parts by weight, and more preferably 1 to 20 parts by weight, per 100 parts by weight of the gas barrier resin on a dry basis. If the amount of plasticizer to be blended is less than 0.1 part by weight, the effect of improving the flexibility and flexibility of the gas barrier properties may not be sufficiently obtained. On the other hand, if the amount exceeds 50 parts by weight, sufficient gas barrier properties may not be obtained.

(Coating of water vapor barrier layer and gas barrier layer)
In the present invention, the coating method for the water vapor barrier layer and the gas barrier layer is not particularly limited, and coating can be performed using known coating devices and coating systems. Examples of coating devices 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.
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.

[0033] In the present invention, the coating weight of the water vapor barrier layer is preferably 3 g/m2 or ^more and 50 g/m2 or ^less , more preferably 5 g/ ^m2 or more and 40 g/ ^m2 or less, and even more preferably 7 g/ ^m2 or more and 30 g/ ^m2 or less, in dry weight. If the coating weight of the water vapor barrier layer is less than 3 g/ ^m2 , it may be difficult to completely cover the paper substrate with the coating liquid, making it impossible to obtain sufficient water vapor barrier properties, or the gas barrier layer may penetrate into the paper substrate, making it impossible to obtain sufficient gas barrier properties. On the other hand, if it exceeds 50 g/ ^m2 , the drying load during coating increases.
In the present invention, the water vapor barrier layer may be a single layer, or may be configured as two or more layers. When the water vapor barrier layer is configured as two or more layers, it is preferable that the total coating weight of all the water vapor barrier layers is within the above-mentioned range.

In the present invention, the coating amount of the gas barrier layer is preferably 0.2 g/ ^m2 or more and 20 g/ ^m2 or less in dry weight. If the coating amount of the gas barrier layer is less than 0.2 g/ ^m2 , it is difficult to form a uniform gas barrier layer, and sufficient gas barrier properties may not be obtained. On the other hand, if it is more than 20 g/ ^m2 , the drying load during coating increases.
In the present invention, 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 the gas barrier layers is within the above range.

(protective layer)
The paper barrier packaging material of the present invention can have a protective layer on at least one surface. The protective layer prevents deterioration of the water vapor barrier layer and gas barrier layer due to moisture in the air, etc., and can also impart additional water vapor barrier properties and gas barrier properties to the paper barrier packaging material, or can impart oil resistance, solvent resistance, heat resistance, abrasion resistance, impact resistance, light resistance, etc. Furthermore, if the protective layer is a resin layer, it can also impart heat sealability. The protective layer can be provided on both sides of the paper barrier packaging material, but it is preferable to have a protective layer on at least the surface having the gas barrier layer.
Examples of the protective layer include a resin layer, a paper layer, and a metal foil, and among these, a resin layer is preferred.

(Resin layer)
Resins for the resin layer include fossil resource-derived resins such as polyester, polyvinyl alcohol, polypropylene, polyethylene, polystyrene, polyethylene terephthalate, polybutylene terephthalate, polymethylpentene, polyvinyl chloride, acrylonitrile butadiene styrene, acrylonitrile styrene, polymethyl methacrylic, polyvinylidene chloride, polyamide (nylon), polyacetal, and polycarbonate, and biologically derived resins such as polylactic acid (PLA), esterified starch, cellulose acetate, polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), biopolyethylene, biopolyethylene terephthalate, and biopolyurethane.
The bio-based resin refers to a polymeric material with a number average molecular weight (Mn) of 1,000 or more, which includes substances derived from renewable organic resources as raw materials and is obtained by chemical or biological synthesis.
In addition, as fossil resource-derived resins and bio-derived resins, any of biodegradable resins such as polylactic acid (PLA), esterified starch, cellulose acetate, polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), etc., and non-biodegradable resins such as polyethylene, polypropylene, polyester, polyethylene terephthalate, polyamide (nylon), biopolyethylene, etc. Biodegradable resins are resins that can be decomposed to the molecular level by the action of microorganisms, ultimately becoming carbon dioxide and water that are circulated into nature.

In the present invention, the resin layer is preferably a resin laminate layer, and examples of the resin laminate layer include an extrusion laminate layer and a film attachment layer such as a barrier film or a vapor-deposited film.
When the resin laminate layer is an extrusion laminate layer, the various resins mentioned above are laminated as a resin laminate layer by extrusion lamination on at least one side of the paper barrier base paper. When the resin laminate layer is a film attachment layer, a film made from the various resins mentioned above is attached as a resin laminate layer on at least one side of the paper barrier base paper by dry lamination, sand lamination or the like. The resin layer can be provided on both sides of the paper barrier base paper, but it is preferable that it is provided at least on the side that has the gas barrier layer. Furthermore, it is preferable that a resin layer be provided on the gas barrier layer of the paper barrier base paper.

In the present invention, films used for the film attachment layer include films made from the various resins listed above. Among these films, preferred are barrier films such as films whose main component is a resin such as polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, or polyacrylonitrile; films made from the various resins listed above coated with a resin such as polyvinyl alcohol; films made from the various resins listed above attached with a metal foil made from various metals such as aluminum; and vapor-deposited films made from the various resins listed above vapor-deposited with various metals such as aluminum or inorganic oxides such as silicon oxide or aluminum oxide, with vapor-deposited films being more preferred. Depending on the purpose, these films can be used by attaching one or more layers together.

The paper barrier packaging material of the present invention can be used as is, or laminated with various resins, etc., or attached to various general-purpose films, barrier films, aluminum foil, etc., to form paper barrier packaging materials used for packaging applications such as food packaging, containers, cups, etc., or laminates used for industrial materials, etc. Among these, the paper barrier packaging material of the present invention is suitable for use as a paper barrier packaging material used for packaging applications such as food packaging, containers, cups, etc., and is particularly suitable for use as flexible packaging bags for food, etc. 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 alone or laminated 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.

When the paper barrier packaging material of the present invention is used as a packaging material for food and the like, in particular as a flexible packaging bag, laminating it with a resin having heat-sealing properties can improve the airtightness of the packaging material, protect the contents from oxidation by oxygen and deterioration due to moisture, etc., and enable an extension of the storage period. Furthermore, because flexible packaging materials are thin and flexible, they are prone to bending during production, transportation, storage, sales, etc., but the paper barrier packaging material of the present invention has excellent bending resistance and reduces the decline in barrier properties even when bending occurs, so it is possible to prevent the quality of the contents from being damaged by unexpected bending.
Furthermore, when used as a laminate for industrial materials, etc., it is possible to prevent decay and deterioration by suppressing the intrusion of oxygen and moisture, and it is also expected to have effects such as flavor barrier properties that prevent the leakage of solvent odors.

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 obtained metallized paper substrate and metallized paper were subjected to tests based on the evaluation methods shown below.

(Evaluation method)
Oxygen permeability: Measured using OX-TRAN2/21 manufactured by MOCON under conditions of 23°C and 0% RH (dry conditions).
Measurements were taken on the sheet sample as is (no creases) and on a sheet sample that had been folded with the barrier layer side facing outward, with a rubber roller weighing approximately 400 g rolling it back and forth five times to create a cross crease (creased).The folded sample was measured so that the cross was positioned in the center of the jig.The measured values are shown in Table 1.

Adhesion evaluation An adhesive tape (Cellotape (registered trademark) manufactured by Nichiban Co., Ltd., 12 mm wide) was attached to the surface of a sheet sample (the side on which the water vapor barrier layer and gas barrier layer were present), and an approximately 2,300 g rubber roller was rolled over the tape five times. The Cellotape (registered trademark) was then forcefully peeled off in a direction perpendicular to the surface of the sheet sample, and the manner in which each barrier layer peeled off (the state of peeling) was observed and evaluated as follows. The results are shown in Table 1.
○: The coating film at the adhesive tape affixed portion peeled off together with part (or all) of the paper substrate (suitable for practical use)
×: Only the coating film peeled off from the area where the adhesive tape was attached (unsuitable for practical use)

[Example 1]
(Preparation of paper substrate)
A hardwood bleached kraft pulp (LBKP) having a Canadian standard freeness (CSF) of 500 ml and a softwood bleached kraft pulp (NBKP) having a CSF of 530 ml were blended in a weight ratio of 80/20 to prepare a raw material pulp.
To the raw pulp, 0.1% by weight of the bone-dry pulp of polyacrylamide (PAM) with a molecular weight of 2.5 million was added as a dry strength agent, 0.35% by weight of the bone-dry pulp of alkyl ketene dimer (AKD) as a sizing agent, 0.15% by weight of the bone-dry pulp of polyamide epichlorohydrin (PAEH) resin as a wet strength agent, and 0.08% by weight of the bone-dry pulp of polyacrylamide (PAM) with a molecular weight of 10 million was added as a retention agent. The mixture was then made at a speed of 300 m/min on a Duoformer FM papermaking machine to obtain paper with a basis weight of 59 g/ ^m² .
Next, polyvinyl alcohol (PVA117, manufactured by Kuraray Co., Ltd.) adjusted to a solids concentration of 2% was coated on both sides of the obtained paper using a rod metering size press in an amount of 1.0 g/ ^m2 in total, and the paper was dried to obtain a base paper with a basis weight of 60 g/ ^m2 . The obtained base paper was smoothed using a chilled calender at a speed of 300 m/min, a linear pressure of 50 kgf/cm, and one pass to obtain a paper substrate.

(Preparation of Coating Solution 1 for Water Vapor Barrier Layer)
Sodium polyacrylate was added as a dispersant (0.2% relative to the pigment) to engineered kaolin (Imerys, Barrisurf HX, average particle size 90 μm, aspect ratio 80-100), and the mixture was dispersed in a Serie mixer to prepare a kaolin slurry with a solids concentration of 55%. 25 parts (solids) of a styrene-acrylic copolymer emulsion (Tg 23°C) and 20 parts (solids) of an ethylene-acrylic copolymer emulsion (Tg 25°C) were blended into the resulting kaolin slurry as water vapor barrier resins per 100 parts (solids) of pigment, yielding Coating Solution 1 for water vapor barrier layer with a solids concentration of 48.5%.

(Preparation of Coating Solution 1 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 and used as coating solution 1 for gas barrier layer.

(Preparation of paper barrier packaging materials)
Coating Solution 1 for water vapor barrier layer was coated on one side of the obtained paper substrate to give a coating amount of 12.0 g/ ^m2 in dry weight, and after drying, Coating Solution 1 for gas barrier layer was coated on top of that on one side to give a coating amount of 3.0 g/ ^m2 in dry weight, to obtain paper barrier packaging material 1.

"Example 2"
(Preparation of Coating Solution 2 for Gas Barrier Layer)
Sodium polyacrylate was added as a dispersant to engineered kaolin (Imerys, Barisurf HX, average particle size 90 μm, aspect ratio 80-100) (0.2% relative to the pigment), and the mixture was dispersed in a Serie mixer to prepare a kaolin slurry with a solids concentration of 55%.
Coating Solution 1 for gas barrier layer and kaolin slurry were mixed so that the solid content ratio of PVA:pigment was 100:10, to obtain Coating Solution 2 for gas barrier layer with a solid content concentration of 12.9%.
(Preparation of paper barrier packaging materials)
A paper barrier packaging material 2 was obtained in the same manner as in Example 1, except that this gas barrier layer coating solution 2 was applied to one side so that the dry weight was 3.5 g/ ^m2 .

"Example 3"
(Preparation of Coating Solution 3 for Gas Barrier Layer)
Coating Solution 3 for gas barrier layer with a solids concentration of 14.6% was prepared in the same manner as Coating Solution 2 for gas barrier layer, except that the solids ratio was PVA:pigment=100:30.
(Preparation of paper barrier packaging materials)
A paper barrier packaging material 3 was obtained in the same manner as in Example 1, except that this gas barrier layer coating solution 3 was applied to one side so that the dry weight was 3.5 g/ ^m2 .
"Example 4"
(Preparation of Coating Solution 4 for Gas Barrier Layer)
Coating Solution 4 for gas barrier layer with a solids concentration of 17.0% was prepared in the same manner as Coating Solution 2 for gas barrier layer, except that the solids ratio was PVA:pigment=100:60.
(Preparation of paper barrier packaging materials)
A paper barrier packaging material 4 was obtained in the same manner as in Example 1, except that this gas barrier layer coating solution 4 was applied to one side so that the dry weight was 3.5 g/ ^m2 .

"Example 5"
(Preparation of Coating Solution 5 for Gas Barrier Layer)
An aqueous solution of ethylene copolymerized polyvinyl alcohol (RS-4104, manufactured by Kuraray Co., Ltd.) with a solids concentration of 13% was prepared and used as Coating Solution 5 for gas barrier layer.
(Preparation of paper barrier packaging materials)
A paper barrier packaging material 5 was obtained in the same manner as in Example 1, except that this gas barrier layer coating solution 5 was applied to one side so that the dry weight was 3.0 g/ ^m2 .

"Example 6"
(Preparation of Coating Solution 6 for Gas Barrier Layer)
A polyethyleneimine-based adhesive aid was blended into Coating Solution 1 for gas barrier layer so that the amount was 10 parts (solid content) per 100 parts of polyvinyl alcohol to give Coating Solution 6 for gas barrier layer with a solid content concentration of 12%.
(Preparation of paper barrier packaging materials)
A paper barrier packaging material 6 was obtained in the same manner as in Example 1, except that this gas barrier layer coating solution 6 was applied to one side so that the dry weight was 3.3 g/ ^m2 .

"Example 7"
(Preparation of Coating Solution 7 for Gas Barrier Layer)
Sodium polyacrylate was added as a dispersant to engineered kaolin (Imerys, Barisurf HX, average particle size 90 μm, aspect ratio 80-100) (0.2% relative to the pigment), and the mixture was dispersed in a Serie mixer to prepare a kaolin slurry with a solids concentration of 55%.
Coating Solution 6 for gas barrier layer and kaolin slurry were mixed so that the solids concentration was 12.9% (PVA:pigment = 100:30 in solids content), to obtain Coating Solution 7 for gas barrier layer.
(Preparation of paper barrier packaging materials)
Paper barrier packaging material 7 was obtained in the same manner as in Example 1, except that this gas barrier layer coating solution 7 was applied to one side so that the dry weight was 3.5 g/ ^m2 .

"Example 8"
(Preparation of Coating Solution 8 for Gas Barrier Layer)
A plasticizer (glycerin) was blended with 100 parts of polyvinyl alcohol and 10 parts (solid content) of polyvinyl alcohol in Coating Solution 1 for gas barrier layer to prepare a PVA solution.
Sodium polyacrylate was added as a dispersant to engineered kaolin (Imerys, Barisurf HX, average particle size 90 μm, aspect ratio 80-100) (0.2% relative to the pigment), and the mixture was dispersed in a Serie mixer to prepare a kaolin slurry with a solids concentration of 55%.
The PVA solution and kaolin slurry were mixed so that the solid content ratio of PVA to pigment was 100:60, to obtain Coating Solution 8 for gas barrier layer with a solid content concentration of 17.1%.
(Preparation of paper barrier packaging materials)
A paper barrier packaging material 8 was obtained in the same manner as in Example 1, except that this gas barrier layer coating solution 8 was applied to one side so that the dry weight was 3.5 g/ ^m2 .

"Comparative Example 1"
(Preparation of Coating Solution 9 for Gas Barrier Layer)
Sodium polyacrylate was added as a dispersant to engineered kaolin (Imerys, Barisurf HX, average particle size 90 μm, aspect ratio 80-100) (0.2% relative to the pigment), and the mixture was dispersed in a Serie mixer to prepare a kaolin slurry with a solids concentration of 55%.
Coating Solution 1 for gas barrier layer and kaolin slurry were mixed so that the solid content ratio of PVA:pigment was 100:125, to obtain Coating Solution 9 for gas barrier layer with a solid content concentration of 21.2%.
(Preparation of paper barrier packaging materials)
A paper barrier packaging material 9 was obtained in the same manner as in Example 1, except that this gas barrier layer coating solution 9 was applied to one side so that the dry weight was 4.0 g/ ^m2 .

"Comparative Example 2"
(Preparation of Coating Solution 10 for Water Vapor Barrier Layer)
Sodium polyacrylate was added as a dispersant (0.2% relative to the pigment) to engineered kaolin (Imerys Corporation, Barrisurf HX, average particle size 90 μm, aspect ratio 80-100), and the mixture was dispersed in a Serie mixer to prepare a kaolin slurry with a solids concentration of 55%. 30 parts (solids) of an acrylic copolymer emulsion (Tg -9°C) and 10 parts (solids) of a wax emulsion (Seiko PMC Corporation, WR3932) were blended into the resulting kaolin slurry as water vapor barrier resins per 100 parts (solids) of pigment, yielding Coating Solution 10 for water vapor barrier layer with a solids concentration of 48.0%.
(Preparation of paper barrier packaging materials)
This water vapor barrier layer Coating Solution 10 was coated on one side to a dry coating amount of 13.0 g/ ^m2 and dried, after which the gas barrier layer Coating Solution 1 was coated on top of it on one side to a dry coating amount of 4.0 g/ ^m2 , thereby obtaining a paper barrier packaging material 10.

"Example 9"
A paper barrier packaging material 11 was obtained in the same manner as in Example 1, except that a styrene-acrylic copolymer emulsion with a Tg of 9°C was used instead of the styrene-acrylic copolymer emulsion with a Tg of 23°C.

The paper barrier packaging materials obtained in Examples 1 to 9 of the present invention were able to maintain high gas barrier properties even after being folded. As the amount of pigment added increased, there was a tendency for flex resistance to decrease and adhesion to improve, but it was confirmed that flex resistance could be maintained by adding an adhesion aid and plasticizer.

Claims (7)

A paper substrate having a water vapor barrier layer and a gas barrier layer,
the water vapor barrier layer contains a water vapor barrier resin and a pigment,
the water vapor barrier resin contains a styrene-based resin having a glass transition temperature of −20 to 95° C. and an ethylene-based resin having a glass transition temperature of −20 to 95° C. in a weight ratio (dry weight) of 99/1 to 1/99;
1. A paper barrier packaging material characterized in that the gas barrier layer contains a gas barrier resin, and the pigment content per 100 parts by weight of the gas barrier resin is 0 parts by weight or more and 90 parts by weight or less. The paper barrier packaging material according to claim 1, characterized in that it has the water vapor barrier layer and the gas barrier layer in this order on the paper substrate. The paper barrier packaging material according to claim 1 or 2, characterized in that the pigment content of the gas barrier layer is, on a dry weight basis, 5 to 80 parts by weight per 100 parts by weight of the gas barrier resin. The paper barrier packaging material according to any one of claims 1 to 3, characterized in that the water vapor barrier layer contains a pigment with an average particle size of 5 μm or more and an aspect ratio of 10 or more. The paper barrier packaging material according to any one of claims 1 to 4, characterized in that the gas barrier resin contains a polyvinyl alcohol-based resin. The paper barrier packaging material according to any one of claims 1 to 5, characterized in that the gas barrier layer contains a plasticizer. The paper barrier packaging material according to any one of claims 1 to 6, characterized in that the gas barrier layer contains an adhesive aid.