Gas barrier laminate

Abstract

This invention provides a laminate that exhibits excellent gas (especially oxygen) barrier properties and prevents cracking even when molded into paper containers, etc., by forming a sealing layer on a paper substrate that is less prone to defects during layer formation and molding, and further improving the interfacial peel strength between the sealing layer and the gas barrier layer with an anchor layer. [Solution] A laminate comprising a paper substrate, a sealing layer, an anchor layer, and a gas barrier layer in that order, wherein the sealing layer is a dispersion of water with a glass transition temperature of 30°C or lower and a solid content concentration of 40% by mass, with a shear rate of 150 s. -1 The invention is characterized by containing at least one styrene-butadiene copolymer or acrylic resin having a viscosity of 20 mPa·s or less at 25°C, wherein the anchor layer contains at least a water-soluble amine resin, and the gas barrier layer contains at least cellulose nanocrystals.

Description

[Technical Field]

[0001] The present invention relates to a laminate comprising a sealing layer, an anchoring layer, and a gas barrier layer formed on a paper substrate, and more specifically, to a laminate that does not crack even when molded into a paper container or the like, and that exhibits excellent gas barrier properties. [Background technology]

[0002] Environmentally friendly paper substrates are widely used as materials for paper containers and other applications. Because paper substrates alone have poor liquid resistance and gas barrier properties, they are often used with a liquid-resistant resin layer or gas barrier layer laminated onto the substrate surface. However, since directly applying a gas barrier material to a liquid-resistant substrate does not result in a good gas barrier layer, a sealing layer made of liquid-resistant resin is sometimes used, with the gas barrier layer laminated on top. For example, Patent Document 1 below describes a base paper or processed paper having a resin solid content of 0.1 to 30 g / m² after drying on at least one side. 2 A sealant layer made of styrene-butadiene copolymer is formed by a coating method, such that the wettability of the surface of the sealant layer is 36 mN / m or more, and the Cobb water absorption is 10 g / m 2 The following conditions apply, and the resin solid content on the sealing agent layer after drying is 0.5 to 30 g / m². 2 A gas barrier paper material has been proposed, characterized in that a gas barrier layer made of polyvinyl alcohol-based resin is formed by a coating method. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 5869829 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In the above-mentioned Patent Document 1, the penetration of polyvinyl alcohol-based resin into paper is prevented by a sealing layer. However, the sealing layer formed on a porous paper substrate may have defects such as pinholes or cracks. Furthermore, while the gas barrier properties of the gas barrier paper material are evaluated after a bending test, only the adhesion between the sealing layer and the gas barrier layer is considered, and the possibility of cracks occurring in the sealing layer during molding, which could reduce the gas barrier properties, is not considered. Moreover, since the gas barrier layer made of polyvinyl alcohol-based resin is directly formed on the sealing layer, the interfacial peel strength between the sealing layer and the gas barrier layer, and the gas barrier properties of the gas barrier paper material, are not sufficiently satisfactory.

[0005] Therefore, the object of the present invention is to provide a laminate capable of exhibiting excellent gas barrier properties by forming a sealing layer on a paper substrate that is less prone to defects during layer formation and molding, and further improving the interfacial peel strength between the sealing layer and the gas barrier layer with an anchor layer. [Means for solving the problem]

[0006] According to the present invention, a laminate comprising a sealing layer, an anchor layer, and a gas barrier layer in that order on a paper substrate, wherein the sealing layer is a dispersion obtained by dispersing a dispersion in water such that the glass transition temperature is 30°C or lower and the solid content concentration is 40% by mass, and the shear rate is 150 s. -1 A laminate is provided which contains at least one of a styrene-butadiene copolymer or an acrylic resin having a viscosity of 20 mPa·s or less at 25°C, wherein the anchor layer contains at least a water-soluble amine resin, and the gas barrier layer contains at least cellulose nanocrystals.

[0007] In the present invention, it is preferable that a paper container is formed from the above-mentioned laminate. That is, according to the present invention, there is provided a paper container having a laminated structure including a blocking layer, an anchor layer, and a gas barrier layer in this order on a paper base material, wherein the blocking layer contains at least one of a styrene-butadiene copolymer or an acrylic resin having a glass transition temperature of 30°C or lower and a viscosity at a shear rate of 150 s -1 of 20 mPa·s or less at 25°C in a dispersion liquid dispersed in water so that the solid content concentration is 40% by mass, the anchor layer contains at least a water-soluble amine resin, and the gas barrier layer contains at least cellulose nanocrystal.

Advantages of the Invention

[0008] In the laminate of the present invention, as the blocking layer formed on a paper base material having poor surface smoothness, a styrene-butadiene copolymer or an acrylic resin having a viscosity at a shear rate of 150 s -1 of 20 mPa·s or less at 25°C in a dispersion liquid dispersed in water so that the glass transition temperature is 30°C or lower and the solid content concentration is 40% by mass is used, whereby defects such as cracks and pinholes can be prevented from occurring during the formation of the blocking layer. Further, the blocking layer made of the styrene-butadiene copolymer or acrylic resin does not crack even when a forming load is applied when the laminate is formed into a container or the like. Furthermore, since the gas barrier layer is formed via the anchor layer on the blocking layer, it is possible to improve the interlayer adhesion between the blocking layer and the gas barrier layer, and interfacial failure (interlayer peeling) is effectively prevented even when a forming load is applied. Therefore, the laminate of the present invention can exhibit excellent gas barrier properties (particularly oxygen barrier properties) even after being formed.

[0009] Furthermore, in the laminate of the present invention, since the anchor layer contains a water-soluble amine resin, as will be described later, the gas barrier layer is formed from a mixture of cellulose nanocrystal and a water-soluble amine resin. As a result, the self-organized structure by cellulose nanocrystal is strengthened by the water-soluble amine resin, so that gas barrier properties superior to those exhibited by only cellulose nanocrystal can be exhibited. Further, due to the presence of the water-soluble amine resin in the anchor layer, the adhesion strength at the interface between the blocking layer and the anchor layer and at the interface between the anchor layer and the gas barrier layer is improved, and interfacial failure (delamination) due to the molding load during molding into a container or the like is effectively prevented. Furthermore, since the gas barrier layer contains cellulose nanocrystals, it is excellent in heat resistance and bending resistance, and does not deteriorate even when subjected to heat sealing treatment or bending treatment during molding into a container or the like, and the excellent gas barrier property of the laminate can be maintained in the molded product.

Brief Description of the Drawings

[0010] [Figure 1] It is a cross-sectional view showing the basic structure of the laminate of the present invention.

Embodiments for Carrying Out the Invention

[0011] As shown in FIG. 1, the laminate of the present invention is a laminate having a blocking layer 2, an anchor layer 3, and a gas barrier layer 4 in this order on a paper base material 1, wherein the blocking layer has a glass transition temperature of 30 ° C. or lower and a solid content concentration of 40% by mass. It contains at least one of a styrene-butadiene copolymer or an acrylic resin such that the viscosity at a shear rate of 150 s -1 at 25 ° C. is 20 mPa·s or less. It is an important feature that the anchor layer contains at least a water-soluble amine resin, and the gas barrier layer contains at least cellulose nanocrystals. In the blocking layer of the laminate of the present invention, by containing a specific styrene-butadiene copolymer or acrylic resin, it is possible to form a blocking layer that does not cause defects such as cracks and pinholes during layer formation and does not cause cracks during molding. In the anchor layer of the laminate of the present invention, since the anchor layer contains a water-soluble amine resin, the adhesion between the blocking layer and the gas barrier layer can be improved by the anchor effect. Further, as will be described later, the water-soluble amine resin in the anchor layer migrates to the gas barrier layer, and the gas barrier layer is formed as a layer composed of a mixture of cellulose nanocrystals and a water-soluble amine resin. As a result, the self-assembled structure formed by the cellulose nanocrystals is strengthened by the water-soluble amine resin, so that a gas barrier property superior to that exhibited by only the cellulose nanocrystals can be exhibited.

[0012] (Paper base material) Examples of the paper base material that is the base material of the laminate of the present invention include, but are not limited to, for example, fine paper, imitation paper, art paper, coated paper, pure white roll paper, kraft paper, label paper with enhanced water resistance, cup base paper, cardboard, ivory paper, paperboard such as manila board, milk carton base paper, cup base paper, synthetic paper, clay coated paper, water-resistant paper, acid-resistant paper, and other known paper base materials. The thickness of the paper base material is preferably in the range of 50 to 450 μm, and when forming a cup-shaped container, it is preferably in the range of 150 to 400 μm. The basis weight of the paper base material is 2 , particularly preferably in the range of 150 to 350 g / m 2 .

[0013] (Blocking layer) In the laminate of the present invention, the blocking layer formed to impart water resistance to the paper base material contains at least one of a styrene-butadiene copolymer or an acrylic resin such that the glass transition temperature and the viscosity of the dispersion liquid are within a specific numerical range. Thereby, it is possible to prevent defects such as cracks and pinholes from occurring during layer formation, and it is also possible to prevent cracks from occurring during molding. Further, in combination with the presence of the anchor layer described later, the adhesion between the paper base material and the gas barrier layer can be improved.

[0014] The styrene-butadiene copolymer and acrylic resin used in the sealing layer of the present invention have a glass transition temperature of 30°C or lower and are dispersed in water to a solid content concentration of 40% by mass. The dispersion is subjected to a shear rate of 150 s. -1 The viscosity at which it is determined is 20 mPa·s or less at 25°C. The sealing layer of the present invention is preferably formed solely from the styrene-butadiene copolymer or acrylic resin. The sealing layer of the present invention is formed by dispersing a compound with a glass transition temperature higher than 30°C in water to a solid content concentration of 40% by mass, and subjecting the dispersion to a shear rate of 150 s. -1 It does not contain any compounds whose viscosity at 25°C is higher than 20 mPa·s.

[0015] The glass transition temperatures of the styrene-butadiene copolymer and acrylic resin in the present invention are values ​​measured with a differential scanning calorimeter, and are preferably -70 to 30°C, more preferably -70 to 0°C, and even more preferably -30 to 0°C. If the glass transition temperature is higher than the range mentioned above, the processability of the resulting sealing layer may be reduced compared to when it is within the range mentioned above, and cracks may occur during the molding process. The viscosity of the styrene-butadiene copolymer and acrylic resin in this invention is the shear viscosity measured using a rheometer on a dispersion at 25°C, obtained by dispersing the styrene-butadiene copolymer and acrylic resin in water to a solid content concentration of 40% by mass, with a cone plate measurement of 2.5s. -1 Shear rate of 150s when accelerating or decelerating at / s -1 This is the value at [location]. A viscosity of 0.1 to 20 mPa·s is preferable, and 10 to 20 mPa·s is more preferable. If the shear viscosity is higher than the range mentioned above, the coating properties will be inferior to those within the range mentioned above, and the leveling properties of the resulting sealant layer may decrease.

[0016] [Styrene-butadiene copolymer] The styrene-butadiene copolymer can be water-insoluble, and those having anionic functional groups such as sulfate groups, sulfo groups, carboxyl groups, and phosphate groups are preferred. Examples of styrene-butadiene copolymers include emulsion polymerized styrene-butadiene copolymers, solution polymerized styrene-butadiene copolymers, and modified styrene-butadiene copolymers in which the terminals and / or main chain are modified. The amount of styrene groups in the styrene-butadiene copolymer is preferably 5 to 40% by mass, and more preferably 20 to 30% by mass. The amount of vinyl groups in the styrene-butadiene copolymer is preferably 5 to 40% by mass, and more preferably 10 to 30% by mass. The particle size of the styrene-butadiene copolymer is not particularly limited, but for example, the average particle size (D50) is 60 to 500 nm, and 80 to 230 nm is preferred.

[0017] [Acrylic resin] The acrylic resin may be a copolymer of (meth)acrylic acid or a homopolymer or copolymer of alkyl (meth)acrylate esters, and should be water-insoluble. It may also be internally crosslinked fine particles, or it may form an emulsion when added to water. Examples of acrylic resins include vinyl acetate-(meth)acrylic acid copolymer, vinyl acetate-(meth)acrylate alkyl ester copolymer, acrylonitrile-(meth)acrylic acid copolymer, acrylonitrile-(meth)acrylate alkyl ester copolymer, (meth)acrylic acid-(meth)acrylate alkyl ester-(meth)acrylamide copolymer, (meth)acrylic acid-(meth)acrylamide-styrene copolymer, (meth)acrylate alkyl ester-fumaric acid copolymer, (meth)acrylate alkyl ester-(meth)acrylate alkyl-maleic anhydride copolymer, (meth)acrylate alkyl ester-styrene-maleic anhydride copolymer, (meth)acrylate alkyl ester-itaconic acid copolymer, and metal salts or modified products thereof. The above acrylic resins can be used individually or in combination of two or more. The particle size of the fine particles or emulsion made of acrylic resin is not particularly limited, but for example, fine particles with an average particle size (D50) of 60 to 500 nm, preferably 100 to 200 nm, can be used.

[0018] (Anchor layer) In the laminate of the present invention, the anchor layer contains at least a water-soluble amine resin. The water-soluble amine resin is a water-soluble or water-dispersible resin having a cationic functional group. As described above, since the anchor layer in the present invention contains a water-soluble amine resin, the adhesion between the sealing layer and the gas barrier layer can be improved by the anchoring effect of the water-soluble amine resin. In the laminate of the present invention, it is preferable that the anchor layer further contains a metal carbonate and / or a hydroxyl group-containing polymer. By incorporating a metal carbonate into the anchor layer, the cellulose nanocrystals that have migrated from the gas barrier layer-forming dispersion (described later) to the anchor layer and the metal ions derived from the metal carbonate form ionic crosslinks, further strengthening the self-assembled structure of the cellulose nanocrystals. Furthermore, by incorporating a hydroxyl group-containing polymer into the anchor layer, it is expected that the shedding of the metal carbonate from the anchor layer will be suppressed and the adhesion between the anchor layer and the gas barrier layer will be improved.

[0019] [Water-soluble amine resin] Examples of water-soluble amine resins include polyethyleneimine, polyallylamine, polyamine polyamide epichlorohydrin, and polyamine epichlorohydrin. Polyethyleneimine can be suitably used, and branched polyethyleneimine or dendritic polyethyleneimine can be more suitably used. In this specification, water solubility means that 1 g of solute can dissolve in 1 L of water at 25°C. The above water-soluble amine resins can be used individually or in combination of two or more. The number-average molecular weight of the water-soluble amine resin is not particularly limited, but is usually 100 to 200,000, with 1,000 to 180,000 being preferred, 10,000 to 150,000 being more preferred, and 80,000 to 120,000 being even more preferred. The number-average molecular weights used herein are values ​​obtained by measuring by gel permeation chromatography (GPC) and expressed as polystyrene-based molecular weights. The amine value of the water-soluble amine resin is not particularly limited, but is usually 0.1 to 100 mmol / g solid, with 10 to 40 mmol / g solid being preferred and 15 to 25 mmol / g solid being more preferred. The amine value used herein is measured by dissolving the water-soluble amine resin and acetic acid in methanol, setting this solution in an automatic titrator, and performing a non-aqueous titration with 0.5 N p-toluenesulfonic acid / acetic acid titrant. The amine ratio of water-soluble amine resins is not particularly limited, but in the case of branched structures, it is usually 25-45% primary amines, 35-50% secondary amines, and 20-30% tertiary amines. 13 This can be confirmed by measuring 1C-NMR.

[0020] [Metal carbonates] Examples of metal carbonates include carbonates of 1- to 3-valent metals such as alkaline earth metals (magnesium, calcium, strontium, barium, etc.), Group 8 metals of the periodic table (iron, ruthenium, etc.), Group 11 metals of the periodic table (copper, etc.), Group 12 metals of the periodic table (zinc, etc.), and Group 13 metals of the periodic table (aluminum, etc.). However, carbonates of 2- to 3-valent metals are particularly preferred, and more preferably, carbonates of divalent metals such as calcium, magnesium, and zinc can be used. Furthermore, one or more of the above metal ions can be used. In the present invention, calcium carbonate is particularly suitable. The content of the metal carbonate is preferably 10 to 500 parts by mass, and more preferably 100 to 300 parts by mass, per 100 parts by mass of the water-soluble amine resin.

[0021] [Hydroxyl group-containing polymer] Examples of hydroxyl group-containing polymers in the anchor layer of the present invention include polyvinyl alcohol, vinyl acetate alcohol copolymer, ethylene vinyl alcohol copolymer, polyacrylic acid, polymethacrylic acid, carboxymethylcellulose, and starch, but polyvinyl alcohol can be preferably used. The polyvinyl alcohol is preferably fully saponified and has a degree of polymerization of 100 to 10,000. The content of the hydroxyl group-containing polymer is preferably 0.1 to 20 parts by mass per 100 parts by mass of the water-soluble amine resin.

[0022] (Gas barrier layer) In the laminate of the present invention, the gas (particularly oxygen) barrier layer contains at least cellulose nanocrystals. In the laminate of the present invention, it is preferable that the gas barrier layer further contains a layered inorganic compound, a hydroxyl group-containing polymer, and / or a reactive crosslinking agent. By incorporating these components into the gas barrier layer, the laminate can exhibit excellent gas barrier properties even when exposed to high humidity (e.g., 80% RH).

[0023] In the laminate of the present invention, it is preferable that the gas barrier layer consists of a mixed layer of cellulose nanocrystals and a water-soluble amine resin, either partially or entirely. That is, by forming the gas barrier layer on an anchor layer containing a water-soluble amine resin, a mixed layer having a mixture state capable of exhibiting adhesion to the anchor layer is formed in the gas barrier layer. It should be noted that such a mixed gas barrier layer cannot be formed from a pre-mixed liquid of cellulose nanocrystals and water-soluble amine resin. Rather, as described later, it can be formed by coating a gas barrier layer-forming dispersion containing cellulose nanocrystals onto an anchor layer containing water-soluble amine resin. In other words, although it is difficult to qualitatively or quantitatively describe the mixed state of the gas barrier layer in the laminate of the present invention, it is formed only when the water-soluble amine resin and cellulose nanocrystals are mixed while the self-organizing structure of the cellulose nanocrystals is maintained.

[0024] [Cellulose nanocrystals] The cellulose nanocrystals in this invention are nanocellulose materials as defined in ISO / TS20477:2017, and are particles with an aspect ratio of 5 to 50. Because cellulose nanocrystals have fewer anionic functional groups compared to cellulose nanofibers, they have less repulsion with anionic styrene-butadiene copolymers and acrylic resins, resulting in less impact on defects such as cracks and pinholes, and also reducing the risk of yellowing due to thermal degradation.

[0025] The cellulose nanocrystals in the present invention preferably have anionic functional groups such as sulfate groups and / or sulfo groups, carboxyl groups, and phosphate groups, an average fiber diameter of 50 nm or less, particularly in the range of 2 to 50 nm, an average fiber length in the range of 100 to 500 nm, and a crystallinity of 60% or more, particularly in the range of 70% or more. The total amount of anionic functional groups in cellulose nanocrystals is preferably in the range of more than 0.1 mmol / g and less than or equal to 4.0 mmol / g. If the total amount of anionic functional groups is greater than 0.1 mmol / g, the charge repulsion of the cellulose nanocrystals increases, improving dispersibility. On the other hand, if the total amount of anionic functional groups is 4.0 mmol / g or less, the crystal structure of the cellulose nanocrystals is easier to maintain, and the excellent properties such as crystallinity, strength, and gas barrier properties inherent in cellulose nanocrystals can be expressed. A more preferable range for the total amount of anionic functional groups is 0.50 to 2.00 mmol / g, and a particularly preferable range is 1.20 to 1.60 mmol / g. From the viewpoint of gas barrier properties, it is preferable for the anionic functional groups of cellulose nanocrystals to have sulfate groups and / or sulfo groups, and more preferably to have only sulfate groups and / or sulfo groups. When the anionic functional group consists only of a sulfate group and / or a sulfo group, the more preferred range is 0.10 to 1.80 mmol / g, and the particularly preferred range is 0.20 to 0.45 mmol / g. In this specification, the term sulfate group also includes sulfate ester groups, and the term phosphate group also includes phosphate ester groups.

[0026] Cellulose nanocrystals are obtained by hydrolyzing cellulose raw materials with a strong acid. Specific examples of cellulose nanocrystals are not limited to those listed below, but the following (1) to (3) are examples. (1) Sulfate group and / or sulfo group-containing cellulose nanocrystals obtained by treating cellulose raw material with sulfuric acid hydrolysis. (2) Cellulose nanocrystals containing sulfate groups and / or sulfo groups, or cellulose nanocrystals containing sulfate groups and / or sulfo groups and phosphate groups or carboxyl groups, obtained by hydrophilizing the sulfate group and / or sulfo group-containing cellulose nanocrystals of (1) above using any of the following: water-soluble carbodiimide, sulfuric acid, sulfur trioxide-pyridine complex, phosphate-urea, TEMPO catalyst, or oxidizing agent. Alternatively, cellulose nanocrystals containing sulfate groups and / or sulfo groups, or cellulose nanocrystals containing sulfate groups and / or sulfo groups and phosphate groups and / or carboxyl groups, obtained by Never Dry treatment or by combining Never Dry treatment with the above hydrophilization treatment. (3) A phosphate-containing cellulose nanocrystal obtained by treating a cellulose raw material with a phosphate-containing compound and then performing a defibrillation treatment.

[0027] The cellulose nanocrystals described in (1) above are rod-shaped cellulose crystalline fibers obtained by acid hydrolysis treatment of cellulose fibers with sulfuric acid. Sulfuric acid hydrolysis treatment yields cellulose nanocrystals having sulfate groups and / or sulfo groups that can contribute to the formation of a self-assembled structure. Cellulose nanocrystals obtained by sulfuric acid hydrolysis treatment generally contain sulfate groups and / or sulfo groups in an amount of 0.01 to 0.5 mmol / g.

[0028] The cellulose nanocrystals of (2) described above are obtained by adjusting the amount of sulfate groups and / or sulfo groups in the cellulose nanocrystals of (1) described above by treatment with a water-soluble carbodiimide, sulfuric acid, or sulfur trioxide-pyridine complex. This treatment further refines the cellulose nanocrystals into finer fibers. Additionally, anionic functional groups such as phosphate groups and carboxyl groups are introduced by treatment with a phosphate-urea, TEMPO catalyst, or oxidizing agent. Alternatively, by NeverDry treatment, or a combination of NeverDry treatment and the above hydrophilization treatment, anionic functional groups such as phosphate groups and carboxyl groups are introduced along with the adjustment of the amount of sulfate groups and / or sulfo groups. Furthermore, for hydrophilization treatment, any one of the treatments is sufficient as long as the total amount of anionic functional groups such as sulfate groups, sulfo groups, carboxyl groups, and phosphate groups is within the above range, but the same treatment may be performed multiple times, or multiple times in combination with other treatments.

[0029] <Hydrophilic treatment using NeverDry treatment> Cellulose nanocrystals undergo drying processes such as spray drying, heating, and reduced pressure to solidify into powders, but during solidification by drying, some of the anionic functional groups of the cellulose nanocrystals are removed, reducing their hydrophilicity. In other words, a never-dry treatment that does not involve solidification into powders, etc., for cellulose nanocrystals containing anionic functional groups can be considered a hydrophilization treatment. Examples of anionic functional groups include sulfate groups and / or sulfo groups.

[0030] <Hydrophilic treatment using carbodiimide> In the treatment using carbodiimide, cellulose nanocrystals and carbodiimide are stirred in a solvent such as dimethylformamide, sulfuric acid is added, and the mixture is reacted at a temperature of 0 to 80°C for 5 to 300 minutes to produce a sulfuric acid ester. It is preferable to use carbodiimide and sulfuric acid in amounts of 5 to 30 mmol per 1 g (solid content) of cellulose nanocrystals. Next, it is preferable to add an alkaline compound such as sodium hydroxide to convert the sulfate and / or sulfo groups introduced into the cellulose nanocrystals from the H type to the Na type in order to improve the yield. Subsequently, the sulfate and / or sulfo group-containing cellulose nanocrystals are prepared by removing impurities by filtration using a dialysis membrane or the like. The sulfate and / or sulfo group-containing cellulose nanocrystals produced by this process contain sulfate and / or sulfo groups in an amount of 0.3 to 1.3 mmol / g. Examples of carbodiimides include 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide, which is a water-soluble compound having a carbodiimide group (-N=C=N-) in its molecule. Alternatively, dicyclohexylcarbodiimide, which is soluble in organic solvents, can also be used.

[0031] <Hydrophilic treatment using sulfuric acid> The cellulose nanocrystals used in this invention are preferably obtained by hydrolyzing cellulose fibers with sulfuric acid, but these cellulose nanocrystals are further hydrophilized using sulfuric acid. The sulfuric acid is preferably used in an amount of 40 to 65 parts by mass per 1 g (solid content) of cellulose nanocrystals. The reaction is carried out at a temperature of 40 to 60°C for 5 to 300 minutes, and then impurities are removed by filtration using a dialysis membrane or the like, thereby adjusting the amount of sulfate groups and / or sulfo groups in the cellulose nanocrystals.

[0032] <Hydrophilic treatment using sulfur trioxide-pyridine complex> In the treatment using the sulfur trioxide-pyridine complex, cellulose nanocrystals and the sulfur trioxide-pyridine complex are reacted in dimethyl sulfoxide at a temperature of 0 to 60°C for 5 to 240 minutes. This reaction introduces sulfate groups and / or sulfo groups to the hydroxyl groups at position 6 of the cellulose glucose units, thereby preparing sulfate and / or sulfo group-containing cellulose nanocrystals. The sulfate and / or sulfo group-containing cellulose nanocrystals produced by this treatment contain sulfate and / or sulfo groups in an amount of 0.3 to 1.3 mmol / g. The sulfur trioxide-pyridine complex is preferably blended in an amount of 0.5 to 4 g by mass per 1 g (solid content) of cellulose nanocrystals. After the above reaction is complete, it is preferable to add an alkaline compound such as sodium hydroxide to convert the sulfate and / or sulfo groups introduced into the cellulose nanocrystals from the H type to the Na type in order to improve the yield. Subsequently, dimethylformamide or isopropyl alcohol is added, and after washing by centrifugation or the like, impurities are removed by filtration using a dialysis membrane or the like to prepare sulfate and / or sulfo group-modified cellulose nanocrystals.

[0033] <Hydrophilic treatment using urea phosphate> Hydrophilization treatment using phosphate-urea can be carried out in the same manner as conventionally known treatments for introducing phosphate groups using phosphate-urea. Specifically, by reacting cellulose nanocrystals and a phosphate group-containing compound with a urea-containing compound at a temperature of 135-180°C for 5-120 minutes in the presence of a urea-containing compound, phosphate groups are introduced to the hydroxyl groups of cellulose glucose units, and cellulose nanocrystals containing sulfate groups and / or sulfo groups and phosphate groups are prepared. The cellulose nanocrystals containing sulfate groups and / or sulfo groups and phosphate groups obtained by this treatment contain a total amount of sulfate groups and / or sulfo groups and phosphate groups of 0.01-4.0 mmol / g. Examples of phosphate-containing compounds include phosphoric acid, lithium phosphate salts, sodium phosphate salts, potassium phosphate salts, and ammonium phosphate salts. Among these, sodium dihydrogen phosphate, ammonium dihydrogen phosphate, and phosphoric acid can be used particularly well. It is preferable to add the phosphate-containing compound in an amount of 10 to 100 mmol per 10 g (solid content) of cellulose nanocrystal. Examples of urea-containing compounds include urea, thiourea, biuret, phenylurea, benzylurea, and dimethylurea. Among these, urea is particularly suitable. The urea-containing compound is preferably used in an amount of 150 to 200 mmol per 10 g (solid content) of cellulose nanocrystal.

[0034] <Hydrophilic treatment using TEMPO catalyst> The hydrophilic treatment using TEMPO catalyst (2,2,6,6 - tetramethylpiperidine - 1 - oxyl) can be carried out in the same manner as the conventionally known oxidation method using TEMPO catalyst. Specifically, cellulose nanocrystal having a sulfate group and / or a sulfo group is subjected to a hydrophilic reaction that oxidizes the hydroxyl group at the 6 - position of the cellulose glucose unit to a carboxyl group under the conditions of an aqueous system, normal temperature, and normal pressure via TEMPO catalyst (2,2,6,6 - tetramethylpiperidine - 1 - oxyl). The cellulose nanocrystal containing sulfate group and / or sulfo group obtained by this treatment contains the sulfate group and / or sulfo group and the carboxyl group in a total amount of 0.01 - 4.0 mmol / g. As the TEMPO catalyst, in addition to the above - mentioned 2,2,6,6 - tetramethylpiperidine - 1 - oxyl, derivatives of TEMPO such as 4 - acetamido - TEMPO, 4 - carboxy - TEMPO, 4 - phosphonoxy - TEMPO, etc. can also be used. The amount of the TEMPO catalyst used is 0.01 - 100 mmol, preferably 0.01 - 5 mmol, per 1 g (solid content) of cellulose nanocrystal. Also, during the hydrophilic oxidation treatment, it is preferable to use a co - oxidant such as an oxidizing agent, bromide, or iodide alone or in combination with the TEMPO catalyst, and these can be added according to the conventionally known formulations.

[0035] The cellulose nanocrystal in (3) above is a phosphate - group - containing cellulose nanocrystal obtained by treating a cellulose - based raw material with a phosphate - group - containing compound, introducing a phosphate group to the hydroxyl group at the 6 - position of the cellulose glucose unit, and then performing fibrillation treatment. By this treatment, the phosphate - group - containing cellulose nanocrystal contains the phosphate group in an amount of 0.01 - 4.0 mmol / g. Treatment using a phosphate group-containing compound can be carried out in the same manner as the treatment using phosphate-urea described above. Furthermore, the defibration treatment performed after such treatment can be carried out by conventionally known methods, and specifically, it can be finely milled using an ultra-high pressure homogenizer, ultrasonic homogenizer, grinder, high-speed blender, bead mill, ball mill, jet mill, disintegrator, beater, twin-screw extruder, etc. The defibration treatment can be carried out either dry or wet, but since the subsequent crosslinking treatment is preferably carried out in a slurry state, it is preferable to finely mill it using an ultra-high pressure homogenizer or the like with water or the like as a dispersion medium.

[0036] [Layered inorganic compounds] The layered inorganic compounds can be natural or synthetic, or conventionally known compounds that exhibit hydrophilicity or hydrophobicity and swell to cleave when exposed to a solvent. Examples of layered inorganic compounds include kaolinite, dickite, nacrite, halloysite, antigolite, chrysotile, pyrophyllite, montmorillonite, hectorite, mica, tetrasilicic mica, sodium teniolite, muscovite, margalite, talc, vermiculite, phlogopite, xanthophyllite, chlorite, etc. Synthetic mica (hydrophilic swelling mica) can be suitably used. The content of the layered inorganic compound is preferably 1 to 50 parts by mass per 100 parts by mass of cellulose nanocrystal.

[0037] [Hydroxyl group-containing polymer] Examples of hydroxyl group-containing polymers in the gas barrier layer of the present invention include polyvinyl alcohol, vinyl acetate alcohol copolymer, ethylene vinyl alcohol copolymer, polyacrylic acid, polymethacrylic acid, carboxymethylcellulose, and starch, but polyvinyl alcohol can be preferably used. The polyvinyl alcohol is preferably fully saponified and has a degree of polymerization of 100 to 10,000. The content of the hydroxyl group-containing polymer is preferably 1 to 50 parts by mass per 100 parts by mass of cellulose nanocrystal.

[0038] [Reactive crosslinking agent] The reactive crosslinking agent can be used without limitation as long as it is capable of forming a crosslinked structure between cellulose nanocrystals. Since the cellulose nanocrystals used in this invention can be stably dispersed without aggregation even under acidic conditions, it is preferable to use a polycarboxylic acid or its anhydride, which has good reaction efficiency, as the reactive crosslinking agent. Examples of polycarboxylic acids include alkyl dicarboxylic acids such as citric acid, oxalic acid, and malonic acid, aromatic dicarboxylic acids such as terephthalic acid, maleic acid, or their anhydrides, with anhydride citric acid being particularly suitable. The amount of reactive crosslinking agent varies depending on the type, but when using anhydrous citric acid, it is preferably 1 to 50 parts by mass per 100 parts by mass of cellulose nanocrystals.

[0039] (Other layers) In the laminate of the present invention, in addition to the paper substrate, sealing layer, anchor layer, and gas barrier layer described above, other layers may be formed as needed. For example, conventionally known layers such as a layer made of a hydrophobic thermoplastic resin to improve water resistance, a heat-sealable resin layer, or a foamed resin layer can be formed on the surface of the gas barrier layer and / or paper substrate as needed. As hydrophobic thermoplastic resins capable of providing water resistance, olefin polymers, olefin copolymers, aromatic polyesters, aliphatic polyesters, polyamides, styrene copolymers, vinyl chloride copolymers, acrylic copolymers, polycarbonates, etc., can be used. However, olefin polymers, olefin copolymers, and polyester resins are particularly suitable from the viewpoint of water resistance and heat sealability. Furthermore, a printed layer can be provided in each layer as needed.

[0040] (Method of manufacturing a laminate) In manufacturing the laminate of the present invention, first, a sealing layer is formed on the surface of the paper substrate. From the viewpoint of coating properties and film-forming properties, the dispersion for forming the sealing layer preferably contains 30 to 60% by mass of styrene-butadiene copolymer and / or acrylic resin on a solid content basis. As the solvent used in the dispersion for forming the sealing layer, water alone is preferable from the viewpoint of coating properties and film-forming properties, but a mixed solvent of water and a water-miscible organic solvent (containing 70% or more water by volume based on the volume of the solvent) may also be used. The water-miscible organic solvent is not particularly limited as long as it is miscible with water, and examples include ketone solvents such as acetone and methyl ethyl ketone; amide solvents such as N,N'-dimethylformamide and dimethylacetamide; alcohol solvents such as methanol, ethanol and isopropanol; ether solvents such as ethylene glycol monobutyl ether and ethylene glycol monohexyl ether; and pyrrolidone solvents such as 1-methyl-2-pyrrolidone and 1-ethyl-2-pyrrolidone. One of these water-miscible organic solvents may be mixed with water, or two or more may be mixed with water.

[0041] The dispersion for forming the sealing layer contains a total solid content of styrene-butadiene copolymer and / or acrylic resin of 1 m³. 2 It is preferable to coat the material in an amount of 5 to 25 g per unit. Coating methods include, for example, spray painting, dipping, or application using a bar coater, roll coater, gravure coater, etc. Drying methods for the coating include oven drying, infrared heating, and high-frequency heating. Drying conditions can be, for example, heating and drying at 5-200°C for 0.1 seconds to 24 hours.

[0042] Next, an anchor layer is formed by applying an anchor layer-forming solution to the surface of the sealing layer. The anchor layer forming solution preferably contains 0.1 to 10% by mass, particularly 0.2 to 2% by mass, of water-soluble amine resin on a solid content basis. If the amount of water-soluble amine resin is 0.1% by mass or more, better gas barrier properties and interfacial peel strength can be achieved. On the other hand, if the amount is 10% by mass or less, excellent gas barrier properties and interfacial peel strength can be achieved, as well as excellent coating properties and film-forming properties. Solvents used in the anchor layer formation solution include water, water-miscible organic solvents, mixed solvents of water and water-miscible organic solvents, or aromatic solvents such as toluene. The water-miscible organic solvent is not particularly limited as long as it is miscible with water, and examples include the ketone solvents, amide solvents, alcohol solvents, ether solvents, and pyrrolidone solvents mentioned above.

[0043] The amount of anchor layer forming solution to be applied is determined by the concentration of water-soluble amine resin in the anchor layer forming solution, based on the amount of cellulose nanocrystals (solid content) in the gas barrier layer. In other words, as mentioned above, if the amount of cellulose nanocrystals (solid content) is 1 m 2 When contained in an amount of 1.0g per unit, the water-soluble amine resin is 1m 2 It is preferable to coat the material in an amount of 0.01 to 2.0 g per unit. 2 If the amount is 0.01g or more per unit, the interfacial peel strength between the sealing layer and the anchor layer can be improved. On the other hand, the amount of water-soluble amine resin is 1m 2 If the amount per unit is 2.0g or less, the gas barrier properties of the laminate will improve. Coating methods include, for example, spray painting, dipping, or application using a bar coater, roll coater, gravure coater, etc. Drying methods for the coating include oven drying, infrared heating, and high-frequency heating. Drying conditions can be, for example, heating and drying at 5-200°C for 0.1 seconds to 24 hours.

[0044] Next, a gas barrier layer is formed by applying a dispersion liquid for forming a gas barrier layer to the surface of the anchor layer. The dispersion for forming a gas barrier layer preferably contains cellulose nanocrystals in an amount of 0.01 to 10% by mass, particularly 0.5 to 5.0% by mass, based on solid content. If the amount of cellulose nanocrystals is 0.01% by mass or more, the gas barrier properties are improved. On the other hand, if the amount is 10% by mass or less, the coating properties and film-forming properties are excellent. Solvents used in dispersions for gas barrier layer formation include water, water-miscible organic solvents, mixed solvents of water and water-miscible organic solvents, or aromatic solvents such as toluene. The water-miscible organic solvent is not particularly limited as long as it is miscible with water, and examples include the ketone solvents, amide solvents, alcohol solvents, ether solvents, and pyrrolidone solvents mentioned above.

[0045] The dispersion for forming the gas barrier layer contains cellulose nanocrystals (solid content) in a 1m³ 2 It is preferable to coat the material in an amount of 0.1 to 3.0 g per unit. The coating method, drying method, and drying conditions for the dispersion liquid for forming the gas barrier layer may be the same as those for the solution for forming the anchor layer.

[0046] The anchor layer forming solution or the gas barrier layer forming dispersion may contain, as needed, known additives such as fillers, colorants, UV absorbers, antistatic agents, water-resistant agents, clay minerals, crosslinking agents, metal salts, fine particles, colloidal silica, alumina sol, and titanium dioxide. These additives may also be included in the sealing layer forming solution, but the sealing layer forming dispersion preferably contains only a specific styrene-butadiene copolymer or acrylic resin.

[0047] (Applications of laminates) The laminate of the present invention exhibits excellent gas barrier properties and interlayer adhesion even after molding. Therefore, it is preferable to mold paper containers such as cups and trays from a laminate using a paper substrate. The molding method for paper containers and the like is not particularly limited, and can be molded by conventionally known methods depending on the shape of the molded product.

[0048] (Paper container) The paper container of the present invention is formed from the laminate of the present invention described above. As described above, the laminate of the present invention effectively prevents defects such as cracks and pinholes from occurring in the sealing layer even after molding, and also has excellent interlayer adhesion. Therefore, the paper container of the present invention formed using this laminate has excellent gas (oxygen) barrier properties. The form of the paper container of the present invention is not particularly limited, but since no defects such as cracks occur even when subjected to molding processes such as bending and stretching, it is preferable to use paper containers such as trays and cups. Furthermore, in the paper container of the present invention, depending on the application, it is preferable to further include a layer made of the hydrophobic thermoplastic resin described above to provide water resistance to the container, or a foamed resin layer to provide heat insulation. Furthermore, the hydrophobic thermoplastic resin layer formed on the surface of the gas barrier layer described above acts as a protective layer against processing loads such as rubbing and friction when forming the curled portion of the paper container, particularly the paper cup, and effectively prevents defects such as cracks and pinholes from occurring in the gas barrier layer. [Examples]

[0049] The following describes embodiments of the present invention. Note that the following embodiments are examples of the present invention, and the present invention is not limited to these embodiments. The measurement method for each item is as follows.

[0050] <Amount of anionic functional groups in cellulose nanocrystals> A dispersion of anionic functional group-containing cellulose nanocrystals was weighed and ion-exchanged water was added to prepare a volume of 100 mL. 0.1 g of cation exchange resin was added to this dispersion and stirred. The mixture was then filtered to separate the cation exchange resin from the anionic functional group-containing cellulose nanocrystal dispersion. A 0.05 mol / L sodium hydroxide solution was added dropwise to the cation-exchanged dispersion using a potentiometric automatic titrator (Kyoto Electronics Corporation), and the change in electrical conductivity of the anionic functional group-containing cellulose nanocrystal dispersion was measured. From the obtained conductivity curve, the amount of sodium hydroxide titrated for neutralization of the anionic functional group was determined, and the amount of anionic functional group (mmol / g) was calculated using the following formula (1). Amount of anionic functional groups (mmol / g) = Amount of sodium hydroxide titrated for neutralization of anionic functional groups (mL) × Concentration of sodium hydroxide (mmol / mL) ÷ Solid mass of cellulose nanocrystals containing anionic functional groups (g) ... (1)

[0051] <Glass transition temperature> A dispersion containing styrene-butadiene copolymer or acrylic resin was collected, and the solvent was evaporated at room temperature. Using a differential scanning calorimeter (DSC2500, TA Instruments), nitrogen gas was used as the ambient gas to raise the temperature from -70°C to 250°C at a heating rate of 10°C / min, and then cooled to -70°C at a cooling rate of 10°C / min. The glass transition temperature was calculated from the DSC curve when the temperature was raised again to 250°C at a heating rate of 10°C / min.

[0052] <Method for measuring shear viscosity> This measurement was conducted in reference to the description in "JIS K 5600-2-3:1999 General test methods for paints - Part 2: Cleanliness and stability of paints - Section 3: Viscosity (cone-plate viscometer method)". A rotary viscoelasticity measuring device (ARES-G2, manufactured by TA Instruments) was used for the measurement. Details are shown below. A dispersion containing styrene-butadiene copolymer or acrylic resin was diluted to a solid content concentration of 40 parts by mass. Next, a cone-plate viscometer was prepared, with the measuring section set to 25°C, and the dispersion, also heated to 25°C, was placed in the measuring section. After placement, the sample was allowed to stand for at least 15 minutes. The cone plate was rotated with the gap between the cone portion and the measuring section filled with the dispersion, and its shear acceleration was measured at 2.5 s⁻¹. -1 The system was accelerated or decelerated in seconds. Depending on the viscosity of the dispersion, one of the following cone plates (1) or (2) was used. Cone plate (1): Diameter 25mm, cone angle 0.02rad, tip gap 0.05mm Cone plate (2): Diameter 50mm, cone angle 0.02rad, tip gap 0.05mm Turn the cone plate 2.5s -1 Shear rate of 150s when accelerating or decelerating at / s -1 The viscosity was measured. Note: 2.5s -1 150s when accelerating at / s -1 Viscosity in 2.5s -1 150s when decelerating at / s -1 The viscosity was approximately the same.

[0053] <Pinhole prevention during sealing layer formation> Base paper (acid-resistant paper, Cobb water absorption 25g / m²) 2 , Oken type smoothness 38 seconds, basis weight 300g / m 2 ) On top of that, a dispersion liquid for forming a sealing layer is applied, with a concentration of styrene-butadiene copolymer or acrylic resin of 18 g / m². 2 The material was coated using a bar coater and dried with hot air at 150°C to form a sealing layer. Dilute iodine tincture (manufactured by Ken-ei Pharmaceutical Co., Ltd.) was applied to the sealing layer, and the presence or absence of pinholes was visually checked. <Rating> A: No pinholes were formed in the sealing layer. B: Pinholes formed in the sealing layer.

[0054] <Pinhole prevention during molding process> Base paper (acid-resistant paper, Cobb water absorption 25g / m²) 2 , Oken type smoothness 38 seconds, basis weight 300g / m 2 ) On top of that, a dispersion liquid for forming a sealing layer is applied, with a concentration of styrene-butadiene copolymer or acrylic resin of 18 g / m². 2 A laminate was used as a sample, which was coated using a bar coater and then dried with hot air at 150°C to form a sealing layer. The laminate was stretched in the CD direction using a strograph (Strograph EL, manufactured by Toyo Seiki Seisakusho Co., Ltd.) under the conditions of a tensile speed of 20 mm / min, a test width of 15 mm, and a chuck distance of 180 mm. Dilute iodine tincture (manufactured by Kenei Pharmaceutical Co., Ltd.) was applied to the sealing layer, and the presence or absence of pinholes was checked. <Rating> A: At an elongation of 6.0%, no pinholes were observed in the sealing layer. B: At an elongation of 3.0%, no pinholes were formed in the sealing layer. At an elongation of 6.0%, pinholes were observed in the sealing layer. C: At an elongation of 3.0%, pinholes were formed in the sealing layer.

[0055] <Oxygen permeability> Base paper (acid-resistant paper, Cobb water absorption 25g / m²) 2 , Oken type smoothness 38 seconds, basis weight 300g / m 2 ) On top of that, a dispersion liquid for forming a sealing layer is applied, with a concentration of styrene-butadiene copolymer or acrylic resin of 18 g / m². 2 The material was coated using a bar coater and then dried with hot air at 150°C to form a sealing layer. Furthermore, the anchor layer forming solution on the sealing layer contains a water-soluble amine resin in an amount of 0.3 g / m². 2 The material was coated using a bar coater and then dried with hot air at 150°C to form an anchor layer. Next, the dispersion for forming the gas barrier layer contains cellulose nanocrystals in an amount of 0.8 g / m². 2A laminate was used as a sample, which was coated using a bar coater to form a gas barrier layer and then dried with hot air at 150°C. Using an oxygen permeability measuring device (OX-TRAN2 / 22, manufactured by Mokon Corporation), the oxygen permeability (cc / m³) of the above laminate was measured under conditions of 23°C and 50% RH. 2 We measured (day·atm).

[0056] <Example 1> [Preparation of dispersion for forming a sealing layer] A dispersion for forming a sealing layer with a solid content of 50% by mass was prepared by dispersing 50 parts by mass of styrene-butadiene copolymer emulsion (hereinafter sometimes referred to as "SBR"; manufactured by DIC Corporation, Luxstar 5275B) in water.

[0057] [Preparation of anchor layer formation solution] Polyethyleneimine (hereinafter sometimes referred to as "PEI") with a number-average molecular weight of 100,000 and an amine ratio of primary:secondary:tertiary = 30:40:30 was diluted and dispersed with water and ethanol. Light calcium carbonate (primary particle size 0.1-0.5 μm) and polyvinyl alcohol resin (hereinafter sometimes referred to as "PVA") were then added and dispersed to prepare an anchor layer forming solution with a solid content of 3.5% by mass, containing 0.5 parts by mass of PEI, 1.0 part by mass of calcium carbonate, and 2.0 parts by mass of PVA, with a solvent mixture ratio of 50 parts by mass of water to 50 parts by mass of ethanol.

[0058] [Preparation of Cellulose Nanocrystal-Containing Dispersion (Dispersion for Gas Barrier Layer Formation)] Cellulose nanocrystals having only sulfate groups as anionic functional groups were dispersed in water to obtain an aqueous dispersion of cellulose nanocrystals. These cellulose nanocrystals had a sulfate group content of 0.28 mmol / g, an average particle size of 150-200 nm obtained by dynamic light scattering, and an aspect ratio of 5-25. To the aforementioned cellulose nanocrystal dispersion, polyvinyl alcohol (fully saponified), synthetic mica (hydrophilic swelling mica), anhydrous citric acid, and sulfuric acid were added and stirred. Further ammonia was added and stirred until the pH reached 7. Finally, a predetermined amount of isopropanol was added and stirred to prepare a cellulose nanocrystal-containing dispersion with a solid content of 1.0 part by mass of cellulose nanocrystals, and with polyvinyl alcohol (fully saponified), synthetic mica (hydrophilic swelling mica), anhydrous citric acid, and sulfuric acid in parts of 30, 10, 10, and 2 parts by mass respectively per 100 parts by mass of cellulose nanocrystals, and a solvent mixture ratio of 90 parts by mass of water to 10 parts by mass of isopropanol, resulting in a solid content concentration of 1.52% by mass.

[0059] [Fabrication of laminates] Base paper (acid-resistant paper, Cobb water absorption 25g / m²) 2 , Oken type smoothness 38 seconds, basis weight 300g / m 2 ) On top of that, a dispersion liquid for forming a sealing layer with a solid content of 18 g / m² Dry coating amount 2 The coating was applied using a bar coater and dried with hot air at 150°C to form a sealing layer. Furthermore, the anchor layer forming solution was applied to the sealing layer using a bar coater and dried with hot air at 150°C, resulting in a dry coating amount of 0.3 g / m² of water-soluble amine resin. 2 An anchor layer was formed. Furthermore, the cellulose nanocrystal-containing dispersion was coated onto the anchor layer using a bar coater and dried with hot air at 150°C, resulting in a dry coating amount of 0.8 g / m². 2 A laminate was fabricated in which a gas barrier layer was formed. The oxygen permeability of the aforementioned laminate is 22.44 cc / m³. 2 It was a day ATM.

[0060] <Example 2> A laminate was prepared in the same manner as in Example 1, except that the styrene-butadiene copolymer in the dispersion liquid for forming the sealing layer was changed to Luxstar 3290N (manufactured by DIC Corporation) and the solid content concentration was changed to 51% by mass. The oxygen permeability of the aforementioned laminate is 63.75 cc / m³ 2 It was a day ATM.

[0061] <Example 3> A laminate was prepared in the same manner as in Example 1, except that the styrene-butadiene copolymer in the dispersion liquid for forming the sealing layer was changed to Boncoat R-3380-E (manufactured by DIC Corporation), which is an acrylic resin, and the solid content concentration was changed to 40% by mass.

[0062] <Comparative Example 1> A laminate was prepared in the same manner as in Example 1, except that the styrene-butadiene copolymer in the dispersion liquid for forming the sealing layer was changed to Luxstar DS-407H (manufactured by DIC Corporation) and the solid content concentration was changed to 51% by mass.

[0063] <Comparative Example 2> A laminate was prepared in the same manner as in Example 1, except that the styrene-butadiene copolymer in the dispersion liquid for forming the sealing layer was changed to Seikot TE-2316 (manufactured by Seikoh PMC Co., Ltd.), an acrylic resin, and the solid content concentration was changed to 40% by mass.

[0064] <Comparative Example 3> A laminate was prepared in the same manner as in Example 1, except that the styrene-butadiene copolymer in the dispersion for forming the sealing layer was changed to ChemiPearl S500 (manufactured by Mitsui Chemicals, Inc.), which is an ethylene-methacrylic resin, and the solid content concentration was changed to 40% by mass.

[0065] [Table 1] [Industrial applicability]

[0066] The laminate of the present invention forms a sealing layer that is less prone to defects during layer formation and molding, and further improves the interfacial peel strength between the sealing layer and the gas barrier layer with an anchor layer, thereby exhibiting excellent gas barrier properties, making it suitable for use in paper containers such as cups and trays.

Claims

1. A laminate comprising a paper substrate, a sealing layer, an anchoring layer, and a gas barrier layer in that order, The aforementioned sealing layer is a dispersion of water with a glass transition temperature of 30°C or lower and a solid content concentration of 40% by mass, subjected to a shear rate of 150 s. －１ It contains at least one styrene-butadiene copolymer or acrylic resin having a viscosity of 20 mPa·s or less at 25°C, and contains at least one styrene-butadiene copolymer or acrylic resin, The anchor layer contains at least a water-soluble amine resin, A laminate characterized in that the gas barrier layer contains at least cellulose nanocrystals.

2. A paper container having a laminated structure comprising a sealing layer, an anchoring layer, and a gas barrier layer in that order on a paper substrate, The aforementioned sealing layer is a dispersion of water with a glass transition temperature of 30°C or lower and a solid content concentration of 40% by mass, subjected to a shear rate of 150 s. －１ It contains at least one of a styrene-butadiene copolymer or an acrylic resin, having a viscosity of 20 mPa·s or less at 25°C. The anchor layer contains at least a water-soluble amine resin, A paper container characterized in that the gas barrier layer contains at least cellulose nanocrystals.

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