EP4656380A1

EP4656380A1 - Laminate and packaging bag

Info

Publication number: EP4656380A1
Application number: EP24780359.6A
Authority: EP
Inventors: Rika Ishii; Yoshiki Koshiyama; Yumiko Kojima; Junichi Kaminaga; Hiroyuki Wakabayashi
Original assignee: Toppan Holdings Inc
Current assignee: Toppan Holdings Inc
Priority date: 2023-03-30
Filing date: 2024-03-26
Publication date: 2025-12-03
Also published as: EP4656380A4; JPWO2024204251A1; US20260021948A1; WO2024204251A1

Abstract

A laminate including a base paper and a gas barrier resin layer provided directly on the base paper, in which a binder resin contained in the gas barrier resin layer includes at least one selected from the group consisting of polyolefin resins and polyvinyl alcohol-based resins, the gas barrier resin layer contains an inorganic pigment in a first region extending from a surface thereof on the base paper side to 50% of the total thickness of the gas barrier resin layer, and 80% by volume or more of the total amount of the inorganic pigment contained in the gas barrier resin layer is present in the first region.

Description

[Technical Field]

The present invention relates to a laminate and a packaging bag.

[Background Art]

In many fields such as food products, beverages, pharmaceutical products, and chemical products, packaging materials have been used according to the contents of the packaging materials. Packaging materials are required to have gas barrier properties that prevent the permeation of water vapor or the like that may cause deterioration of the contents.
In recent years, there has been a growing momentum to move away from plastic due to growing environmental awareness stemming from issues such as marine plastic waste. In order to reduce the amount of plastic materials used, the use of paper instead of plastic materials has been considered in various fields. For example, PTL 1 specified below discloses a laminate in which a clay coating layer, a resin layer, and a vapor-deposited layer are laminated on paper to impart barrier properties. The clay coating layer is provided to seal and smooth the paper.

[Citation List]

[Patent Literature]

[PTL 1] JP 2022-104487 A

[Summary of the Invention]

[Technical Problem]

Paper is easy to process due to its crease retention properties (also called dead-fold properties). However, the inventors conducted investigations and found that when packaging bags have sharper folds (pillow packaging, three-side-sealed packaging, and gusset packaging), cracks tend to occur in the laminate starting from the clay coating layer, which reduces the barrier performance.
An object of the present disclosure is to provide a laminate using paper that exhibits sufficient water vapor barrier performance not only initially but also after being folded, and a packaging bag including the laminate.

[Solution to Problem]

In order to solve the above problems, the present disclosure provides the following laminate and packaging bag.

[1] A laminate including a base paper and a gas barrier resin layer provided directly on the base paper, wherein a binder resin contained in the gas barrier resin layer includes at least one selected from the group consisting of polyolefin resins and polyvinyl alcohol-based resins, the gas barrier resin layer contains an inorganic pigment in a first region extending from a surface thereof on the base paper side to 50% of the total thickness of the gas barrier resin layer, and 80% by volume or more of the total amount of the inorganic pigment contained in the gas barrier resin layer is present in the first region.
[2] The laminate according to [1] above, further including a vapor-deposited inorganic layer on a surface of the gas barrier resin layer opposite to that facing the base paper.
[3] The laminate according to [2] above, further including an overcoat layer on a surface of the vapor-deposited inorganic layer opposite to that facing the gas barrier resin layer.
[4] The laminate according to [3] above, in which the overcoat layer contains a polyolefin resin.
[5] The laminate according to any one of [1] to [4] above, in which the content of the inorganic pigment in the gas barrier resin layer is 50 parts by volume or less relative to 100 parts by volume of the binder resin.
[6] The laminate according to any one of [1] to [5] above, in which the content of the inorganic pigment in the first region is 2 to 200 parts by volume relative to 100 parts by volume of the binder resin in the first region.
[7] The laminate according to any one of [1] to [6] above, in which the inorganic pigment has an aspect ratio of 1 to 200.
[8] The laminate according to any one of [1] to [7] above, in which 100% by volume of the inorganic pigment contained in the gas barrier resin layer is present in the first region.
[9] The laminate according to any one of [1] to [8] above, in which a surface of the gas barrier resin layer opposite to that facing the base paper has a surface roughness Ra of 1.0 µm or less.
[10] The laminate according to any one of [1] to [9] above, in which the gas barrier resin layer has a thickness of 1 to 20 µm.
[11] The laminate according to any one of [1] to [10] above, in which the gas barrier resin layer has a thickness of 3 to 5 µm.
[12] A packaging bag comprising the laminate according to any one of [1] to [11] above.

[Advantageous Effects of the Invention]

According to the present disclosure, a laminate using paper can be provided that exhibits sufficient water vapor barrier performance not only initially but also after being folded, and a packaging bag including the laminate. Since the laminate uses paper, it exhibits the crease retention properties characteristic to paper, and also contributes to a reduction in the amount of plastic materials used.

[Brief Description of the Drawings]

Fig. 1 is a schematic cross-sectional view showing a laminate according to an embodiment of the present disclosure.
Fig. 2 is a perspective view of a packaging bag according to an embodiment of the present disclosure.

[Description of the Embodiments]

An embodiment of the present disclosure will now be described in detail with reference to the drawings as necessary. Note that the present disclosure is not limited to the following embodiment.

A laminate according to the present embodiment includes a base paper and a gas barrier resin layer provided directly on the base paper, in which a binder resin contained in the gas barrier resin layer includes at least one selected from the group consisting of polyolefin resins and polyvinyl alcohol-based resins, the gas barrier resin layer contains an inorganic pigment in a first region extending from a surface thereof on the base paper side to 50% of the total thickness of the gas barrier resin layer, and 80% by volume or more of the total amount of the inorganic pigment contained in the gas barrier resin layer is present in the first region. The laminate according to the present embodiment may further include a vapor-deposited inorganic layer on a surface of the gas barrier resin layer opposite to that facing the base paper, and may further include an overcoat layer on a surface of the vapor-deposited inorganic layer opposite to that facing the gas barrier resin layer.
According to the above laminate, a gas barrier resin layer is provided directly on the base paper with no intermediate clay coating layer, and the binder resin contained in the gas barrier resin layer includes the specific resin described above, thereby achieving high flexibility. This suppresses the occurrence of cracks in the gas barrier resin layer when folded, and sufficient water vapor barrier performance can be achieved not only initially but also after being folded. Furthermore, since the inorganic pigment is concentrated in the first region on the base paper side of the gas barrier resin layer, it is possible to prevent the binder resin from permeating excessively into the base paper, and the inorganic pigment can serve to seal the asperities on the paper, thereby achieving a smooth gas barrier resin layer with fewer defects and asperities. This provides stable water vapor barrier performance. In addition, when the vapor-deposited inorganic layer is formed on a smooth gas barrier resin layer, a uniform vapor-deposited inorganic layer can be formed, and the water vapor barrier performance can be further improved.
Fig. 1 is a schematic cross-sectional view showing a laminate according to one embodiment. A laminate 10 according to one embodiment includes a base paper 1, a gas barrier resin layer 2, a vapor-deposited inorganic layer 3, and an overcoat layer 4, in this order. Each layer will now be described.

[Base Paper 1]

The base paper is paper that does not have a coating layer such as a clay coating layer. The base paper may be paper whose main component is plant pulp. Specific examples of the base paper include high-quality paper, special high-quality paper, imitation paper, kraft paper, and glassine paper.
The basis weight of the base paper may be 20 to 500 g/m², or 30 to 100 g/m². The thickness of the base paper may be 20 to 100 µm, 30 to 80 µm, or 40 to 60 µm. When the basis weight or thickness of the base paper is within the above range, the laminate can exhibit better water vapor barrier performance not only initially but also after being folded.
The mass ratio of the base paper to the total mass of the laminate is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. When the mass ratio of the base paper is 50% by mass or more, it is possible to sufficiently reduce the amount of plastic materials used. This allows the laminate as a whole to be labelled as made of paper and also improves recyclability.

[Gas Barrier Resin Layer 2]

The gas barrier resin layer is provided directly on a surface of the base paper. The gas barrier resin layer is provided to improve the gas barrier performance of the laminate. The gas barrier resin layer also serves to improve the adhesion between the base paper and the vapor-deposited inorganic layer described later.
The binder resin of the gas barrier resin layer includes at least one selected from the group consisting of polyolefin resin and polyvinyl alcohol-based resin. These binder resins allow the gas barrier resin layer to have good water vapor barrier performance and high flexibility, so that the occurrence of cracks in the gas barrier resin layer when folded can be suppressed, and sufficient water vapor barrier performance can be achieved not only initially but also after being folded. Furthermore, when a polyvinyl alcohol-based resin is used as the binder resin, good oxygen barrier performance can also be obtained both initially and after being folded.
Examples of the polyolefin resin include low density polyethylenes, medium density polyethylenes, high density polyethylenes, ethylene-α-olefin copolymers, homopolypropylenes, block polypropylenes, random polypropylenes, and propylene-α-olefin copolymers.
The polyolefin resin may be a polyolefin resin having a polar group. When a polyolefin resin having a polar group is used, the polar group can further improve the adhesion between the gas barrier resin layer and the vapor-deposited inorganic layer.
The polyolefin having a polar group may have at least one selected from a carboxyl group, a salt of a carboxyl group, a carboxylic anhydride group, and carboxylic ester.
Examples of the polyolefin having a polar group include copolymers of ethylene or propylene with unsaturated carboxylic acids (unsaturated compounds having a carboxyl group, such as acrylic acid, methacrylic acid, and maleic anhydride) or unsaturated carboxylic acid esters, and salts of carboxylic acids neutralized with basic compounds. Further examples include copolymers of ethylene or propylene with vinyl acetate, epoxy compounds, chlorine compounds, urethane compounds, and polyamide compounds.
Specific examples of the polyolefin having a polar group include copolymers of acrylic acid ester and maleic anhydride, ethylene-vinyl acetate copolymers, and ethylene-glycidyl methacrylate copolymers.
The polyvinyl alcohol-based resin is a resin that includes vinyl alcohol as a constituent unit. The polyvinyl alcohol-based resin can be any resin having vinyl alcohol units obtained by saponifying vinyl ester units, and examples thereof include polyvinyl alcohol (PVA) resins and ethylene-vinyl alcohol copolymers (EVOH).
When the gas barrier resin layer contains a polyvinyl alcohol-based resin, the polar groups (hydroxyl groups) of the polyvinyl alcohol-based resin facilitate its binding to the vapor-deposited inorganic layer, thereby improving the adhesion between the gas barrier resin layer and the vapor-deposited inorganic layer. A gas barrier resin layer containing a polyvinyl alcohol-based resin also has high flexibility, so that the occurrence of cracks in the gas barrier resin layer when folded can be suppressed, and sufficient water vapor barrier performance can be achieved not only initially but also after being folded. Furthermore, when the gas barrier resin layer contains a polyvinyl alcohol-based resin, the oxygen barrier performance of the laminate can be improved.
Examples of PVA include resins obtained by polymerizing a vinyl ester alone, such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, or vinyl versatate, and then saponifying the polymerized product. The PVA may also be a modified PVA obtained by copolymerization modification or post-modification. The modified PVA may be obtained by, for example, copolymerizing a vinyl ester and an unsaturated monomer copolymerizable with the vinyl ester, and then saponifying the polymerized product. Examples of unsaturated monomers copolymerizable with vinyl ester include: olefins such as ethylene, propylene, isobutylene, α-octene, α-dodecene, and α-octadecene; hydroxy group-containing α-olefins such as 3-buten-1-ol, 4-pentyn-1-ol, and 5-hexen-1-ol; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, maleic anhydride, itaconic acid, and undecylenic acid; nitriles such as acrylonitrile and methacrylonitrile; amides such as diacetone acrylamide, acrylamide, and methacrylamide; olefin sulfonic acids such as ethylene sulfonic acid, allyl sulfonic acid, and methallyl sulfonic acid; vinyl compounds such as alkyl vinyl ether, dimethyl allyl vinyl ketone, N-vinylpyrrolidone, vinyl chloride, vinyl ethylene carbonate, 2,2-dialkyl-4-vinyl-1,3-dioxolane, glycerin monoallyl ether, and 3,4-diacetoxy-1-butene; vinylidene chloride, 1,4-diacetoxy-2-butene, and vinylene carbonate.
The degree of polymerization of the PVA may be 300 to 3,000. When the degree of polymerization is 300 or more, the barrier performance is likely to be improved, and when it is 3,000 or less, the decrease in coating suitability due to an increase in viscosity is likely to be suppressed. From the perspective of barrier performance, the degree of saponification of the PVA may be 50 mol% or more, 80 mol% or more, 90 mol% or more, 95 mol% or more, or 99 mol% or more. The degree of saponification of the PVA may be 100 mol% or less, or 99.9 mol% or less. The degree of polymerization and degree of saponification of the PVA can be determined according to the method described in JIS K 6726 (1994).
In general, EVOH is obtained by saponifying a copolymer of ethylene and an acid vinyl ester such as vinyl acetate, vinyl formate, vinyl propionate, vinyl valerate, vinyl caprate, vinyl laurate, vinyl stearate, vinyl pivalate, or vinyl versatate.
The degree of polymerization of EVOH is preferably 300 to 3,000. When the degree of polymerization is less than 300, the barrier performance tends to decrease, and when it is more than 3,000, coating suitability tends to decrease due to the viscosity being too high. From the perspective of barrier performance, the degree of saponification of the vinyl ester component of the EVOH may be 50 mol% or more, 80 mol% or more, 90 mol% or more, 95 mol% or more, or 99 mol% or more. The degree of saponification of the EVOH may be 100 mol% or less. The degree of saponification of the EVOH is determined from the peak area of hydrogen atoms in the vinyl ester structure and the peak area of hydrogen atoms in the vinyl alcohol structure by performing nuclear magnetic resonance (1H-NMR) measurement.
The content of ethylene units in the EVOH may be 10 mol% or more, 15 mol% or more, 20 mol% or more, or 25 mol% or more. The content of ethylene units in the EVOH may be 65 mol% or less, 55 mol% or less, or 50 mol% or less. When the content of ethylene units is 10 mol% or more, good gas barrier performance or dimensional stability can be maintained under high humidity. On the other hand, when the content of ethylene units is 65 mol% or less, the gas barrier performance can be improved. The content of ethylene units in the EVOH can be calculated by an NMR method.
A binder resin contained in the gas barrier resin layer may include one or more resins other than polyolefin resins and polyvinyl alcohol-based resins. Examples of the other resins include polyacrylic resins, polyester resins, polyurethane resins, polycarbonate resins, polyurea resins, polyamide resins, polyimide resins, melamine resins, and phenolic resins.
The binder resin composition may be the same throughout the entire gas barrier resin layer. This allows the entire gas barrier resin layer to be highly flexible, prevents the occurrence of cracks in the gas barrier resin layer due to differences in resin composition, and more adequately suppresses the deterioration of the water vapor barrier performance after being folded.
The total content of the polyolefin resin and the polyvinyl alcohol-based resin relative to the total mass of the binder resin in the gas barrier resin layer may be 50% by mass or more, 70% by mass or more, 90% by mass or more, or 100% by mass. When the total content of the polyolefin resin and the polyvinyl alcohol-based resin is within this range, the gas barrier resin layer can exhibit high water vapor barrier performance and high flexibility, and can exhibit good water vapor barrier performance both initially and after being folded.
The gas barrier resin layer contains an inorganic pigment. As shown in Fig. 1, an inorganic pigment 5 is contained in a first region A1 extending from the surface of the gas barrier resin layer 2 on the base paper 1 side to 50% of the total thickness D of the gas barrier resin layer (D/2). In addition, 80% by volume or more of the total amount of the inorganic pigment 5 in the gas barrier resin layer 2 is present in the first region A1.
When the gas barrier resin layer contains an inorganic pigment so as to satisfy the above conditions, it is possible to prevent the binder resin from permeating excessively into the base paper, and the inorganic pigment can serve to seal the asperities on the paper, thereby achieving a smooth gas barrier resin layer with fewer defects and asperities. This provides stable water vapor barrier performance. In addition, when the vapor-deposited inorganic layer is formed on a smooth gas barrier resin layer, a uniform vapor-deposited inorganic layer can be formed, and the water vapor barrier performance can be further improved.
Examples of the inorganic pigment include clay, kaolin, calcium carbonate, talc, and mica. These may be used singly or in combination of two or more.
In order to achieve good coating suitability, more adequately suppress the occurrence of cracks in the gas barrier resin layer originating from the inorganic pigment during folding, and further smooth the surface of the gas barrier resin layer, the average particle size of the inorganic pigment may be 0.1 to 10 µm, or 0.1 to 5 µm. The average particle size is a volume-based median diameter (d50) obtained from laser diffraction/scattering particle size distribution measurements.
In order to achieve good coating suitability, more adequately suppress the occurrence of cracks in the gas barrier resin layer originating from the inorganic pigment during folding, and further smooth the surface of the gas barrier resin layer, the aspect ratio of the inorganic pigment may be 1 to 200, or 5 to 200. The aspect ratio can be measured, for example, by observation using an electron microscope or X-ray diffraction measurement.
The content of the inorganic pigment in the gas barrier resin layer may be 50 parts by volume or less, 1 to 45 parts by volume, 3 to 40 parts by volume, or 5 to 35 parts by volume, relative to 100 parts by volume of the binder resin. When the content is 50 parts by volume or less, the occurrence of cracks in the gas barrier resin layer when folded tends to be more adequately prevented. When it is 1 part by volume or more, the binder resin can be more reliably prevented from permeating excessively into the base paper, and the inorganic pigment can more adequately serve to seal the asperities on the paper, which contribute to a smooth gas barrier resin layer with even fewer defects and asperities.
The content of the inorganic pigment in the first region of the gas barrier resin layer may be 2 to 200 parts by volume, 5 to 150 parts by volume, or 10 to 125 parts by volume, relative to 100 parts by volume of the binder resin in the first region. When the content is 200 parts by volume or less, the occurrence of cracks in the gas barrier resin layer when folded tends to be more adequately prevented, and when it is 2 parts by volume or more, the binder resin can be more reliably prevented from permeating excessively into the base paper, and the inorganic pigment can more adequately serve to seal the asperities on the paper, which contribute to a smooth gas barrier resin layer with even fewer defects and asperities.
In the gas barrier resin layer, 80% by volume or more of the total amount of the inorganic pigment is present in the first region, but 90% by volume or more, 95% by volume or more, 99% by volume or more, or 100% by volume of the total amount of the inorganic pigment may be present in the first region. When all or most of the inorganic pigment is present in the first region as described above, it is possible to prevent the binder resin from permeating excessively into the base paper, and the inorganic pigment can serve to seal the asperities on the paper, thereby achieving a smooth gas barrier resin layer with fewer defects and asperities. Furthermore, since the region other than the first region, in other words, the region on the vapor-deposited inorganic layer side of the gas barrier resin layer, has a low content of the inorganic pigment or is free of it, it is possible to more adequately achieve the effects of further improving the smoothness of the surface on the vapor-deposited inorganic layer side of the gas barrier resin layer, further improving the adhesion between the gas barrier resin layer and the vapor-deposited inorganic layer, and suppressing the deterioration of the barrier performance due to the occurrence of cracks in the gas barrier resin layer or the vapor-deposited inorganic layer when folded. Whether 80% by volume or more of the total amount of the inorganic pigment in the gas barrier resin layer is present in the first region can be determined, for example, by observing a cross-section of the gas barrier resin layer with an electron microscope, or based on the method used to form the gas barrier resin layer and the composition of the coating solution used.
When the inorganic pigment is present only in a partial region of the gas barrier resin layer, the thickness of the region where the inorganic pigment is present may be 0.1 to 50%, 1 to 40%, or 10 to 40% of the total thickness of the gas barrier resin layer. When the thickness ratio is greater than or equal to the lower limit, the sealing effect tends to be enhanced.
The thickness of the gas barrier resin layer may be, for example, 1 to 20 µm, 2 to 10 µm, 3 to 8 µm, 3 to 5 µm, or 3 to 4 µm. When the thickness of the gas barrier resin layer is 1 µm or more, the asperities on the surface of the base paper can be sealed more efficiently, allowing the vapor-deposited inorganic layer described below to be laminated more smoothly and uniformly, resulting in better barrier performance. When the thickness of the gas barrier resin layer is 20 µm or less, it is possible to not only obtain good coating suitability but also reduce the proportion of resin, which is also preferable in terms of recycling.
The gas barrier resin layer may contain one or more other components in addition to the binder resin and inorganic pigment mentioned above. Examples of the other components include silane coupling agents and organic titanates.
The gas barrier resin layer may be provided by applying a coating solution containing the binder resin and the inorganic pigment onto the base paper, and then applying a coating solution containing the binder resin but not the inorganic pigment thereon. By applying two types of coating solutions, one with an inorganic pigment and one without an inorganic pigment, it is possible to form a state in which the base paper side of the gas barrier resin layer contains the inorganic pigment, whereas the vapor-deposited inorganic layer side does not. The gas barrier resin layer may be formed in this manner so that it has a two-layer structure including a layer containing an inorganic pigment and a layer not containing an inorganic pigment.
Examples of the solvent used in the coating solution include water, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, n-pentyl alcohol, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, toluene, hexane, heptane, cyclohexane, acetone, methyl ethyl ketone, diethyl ether, dioxane, tetrahydrofuran, ethyl acetate, and butyl acetate. These solvents may be used singly or in combination of two or more. Of these solvents, based on their properties, the solvent is preferably methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, ethyl acetate, methyl ethyl ketone, or water. From an environmental viewpoint, the solvent is preferably methyl alcohol, ethyl alcohol, isopropyl alcohol, or water.
The coating method is not particularly limited, but examples thereof include direct gravure coating, reverse coating, air knife coating, and blade coating.
After the two types of coating solutions are applied, a smoothing treatment such as calendaring may be performed to smooth the surface of the gas barrier resin layer.
A surface roughness Ra of the gas barrier resin layer on the side opposite to that facing the base paper (the vapor-deposited inorganic layer side) may be 1.0 µm or less. When the surface roughness Ra is 1.0 µm or less, the vapor-deposited inorganic layer can be formed more uniformly on the gas barrier resin layer, and better water vapor barrier performance can be obtained both initially and after being folded. The surface roughness Ra of the gas barrier resin layer can be measured using a surface roughness measuring device.

[Vapor-deposited Inorganic Layer 3]

Examples of the material forming the vapor-deposited inorganic layer include metals such as aluminum, and inorganic oxides such as aluminum oxide, silicon oxide, magnesium oxide, and tin oxide. From the perspectives of transparency and barrier performance, the inorganic oxide may be selected from the group consisting of aluminum oxide, silicon oxide, and magnesium oxide. The vapor-deposited inorganic layer may be a layer formed using aluminum or silicon oxide due to their good stretchability during processing. By using a vapor-deposited inorganic layer, high barrier performance can be obtained with a very thin layer that does not affect the recyclability of the laminate.
The thickness of the vapor-deposited inorganic layer may be appropriately determined according to usage, but it is preferably 10 to 300 nm, more preferably 20 to 100 nm, and even more preferably 30 to 100 nm. The vapor-deposited inorganic layer, when having a thickness of 10 nm or more, may be made adequately continuous with ease. When the thickness is 300 nm or less, the occurrence of curling or cracking can be adequately prevented, and thus adequate barrier performance and flexibility can be easily achieved. When the thickness of the vapor-deposited inorganic layer is 20 nm or more and 100 nm or less, it is less likely to crack, and sufficient water vapor barrier performance can be exhibited even after being folded.
From the perspectives of water vapor barrier performance and film uniformity, the vapor-deposited inorganic layer is preferably formed using a vacuum film forming method. The film forming method may be a known method such as vacuum vapor deposition, sputtering, or chemical vapor deposition (CVD). Due to its high film forming speed and high productivity, vacuum vapor deposition is preferable. Of the vacuum vapor deposition methods, in particular, a film forming method using electron beam heating is effective. This is because the film forming speed can be easily controlled by an irradiation area, an electron beam current, or the like and because a temperature of a vapor deposition material can be increased or decreased in a short time.

[Overcoat Layer 4]

The overcoat layer is provided on the surface of the vapor-deposited inorganic layer so as to be in contact with the vapor-deposited inorganic layer. The overcoat layer may contain a polyolefin having a polar group.
The polyolefin having a polar group may have at least one selected from a carboxyl group, a salt of a carboxyl group, a carboxylic anhydride group, and carboxylic ester.
Examples of the polyolefin having a polar group include copolymers of ethylene or propylene with unsaturated carboxylic acids (unsaturated compounds having a carboxyl group, such as acrylic acid and methacrylic acid) or unsaturated carboxylic acid esters, and salts of carboxylic acids neutralized with basic compounds. Further examples include copolymers of ethylene or propylene with vinyl acetate, epoxy compounds, chlorine compounds, urethane compounds, and polyamide compounds.
Specific examples of the polyolefin having a polar group include copolymers of acrylic acid ester and maleic anhydride, ethylene-vinyl acetate copolymers, and ethylene-glycidyl methacrylate copolymers.
Since the overcoat layer contains a polyolefin having a polar group, it can be highly flexible, can prevent the vapor-deposited inorganic layer from cracking after being bent (folded), and can improve its adhesion with the vapor-deposited inorganic layer. The inclusion of the above polyolefin having a polar group also enables the formation of a dense film that provides water vapor barrier properties due to the crystallinity of the polyolefin. In addition, the polar group provides tight adhesion to the vapor-deposited inorganic layer. Furthermore, since the overcoat layer contains the polyolefin having a polar group, it can also function as a heat seal layer, which eliminates the need to provide a separate heat seal layer.
The overcoat layer may contain one or more other components in addition to the polyolefin having a polar group. Examples of the other components include silane coupling agents, organic titanates, polyacrylic materials, polyesters, polyurethanes, polycarbonates, polyureas, polyamides, polyolefin emulsions, polyimides, melamines, and phenols.
The content of the polyolefin having a polar group in the overcoat layer may be, for example, 50% by mass or more, 70% by mass or more, 90% by mass or more, or 100% by mass.
The thickness of the overcoat layer may be, for example, 0.05 µm or more, 0.5 µm or more, 1 µm or more, 2 µm or more, and 20 µm or less, 10 µm or less, or 5 µm or less. When the thickness of the overcoat layer is 0.05 µm or more, it can sufficiently fulfill the role of the heat seal layer described above. When the thickness of the overcoat layer is 20 µm or less, it can exhibit sufficient adhesion to the vapor-deposited inorganic layer and sufficient barrier performance while keeping the cost down. When the thickness of the overcoat layer is 2 µm or more and 10 µm or less, the vapor-deposited inorganic layer is less likely to crack, and sufficient water vapor barrier performance can be exhibited even after being folded.
In the laminate, when the overcoat layer contains a polyolefin having a polar group, the thickness of the overcoat layer is 2 µm or more and 10 µm or less, and the thickness of the vapor-deposited inorganic layer is 20 nm or more and 100 nm or less, the vapor-deposited inorganic layer is less likely to crack, and the effect of exhibiting sufficient water vapor barrier performance even after being folded is particularly notable.
Examples of the solvent contained in a coating solution of the overcoat layer include water, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, n-pentyl alcohol, dimethyl sulfoxide, dimethyl formamide, dimethyl acetamide, toluene, hexane, heptane, cyclohexane, acetone, methyl ethyl ketone, diethyl ether, dioxane, tetrahydrofuran, ethyl acetate, and butyl acetate. These solvents may be used singly or in combination of two or more. Of these solvents, based on their properties, the solvent is preferably methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, ethyl acetate, methyl ethyl ketone, or water. From an environmental viewpoint, the solvent is preferably methyl alcohol, ethyl alcohol, isopropyl alcohol, or water.
The overcoat layer can be provided by applying a coating solution containing the above polyolefin having a polar group, the solvent, and the like onto the vapor-deposited inorganic layer and then drying the applied solution. The melting point of the polyolefin having a polar group in the coating solution is preferably 70 to 160°C, more preferably 80 to 120°C. When the polyolefin having a polar group has a low melting point, the advantage of reducing the onset temperature during heat sealing can be achieved. When the polyolefin having a polar group has a high melting point, the risk of blocking in a high-temperature environment increases. From the perspective of preventing blocking, it is preferable that the particle size is large in order to reduce the contact area. Although not particularly limited, the particle size may specifically be 1 nm or more, 0.1 µm or more, and may be 1 µm or less, 0.7 µm or less, or 0.5 µm or less.
The thickness of the laminate including the above layers may be 20 to 150 µm, 30 to 100 µm, or 40 to 90 µm. When the thickness of the laminate is within this range, it can exhibit better water vapor barrier performance not only initially but also after being folded.

Fig. 2 is a perspective view illustrating a gusset bag 20 made of the laminate 10. The upper opening of the gusset bag 20 is sealed to produce a packaging bag. The gusset bag 20 has portions where the laminate 10 is folded (folded portions B1 and B2). The folded portion B1 is a portion where the laminate 10 is valley-folded as viewed from the innermost layer side, while the folded portion B2 is a portion where the laminate 10 is mountain-folded as viewed from the innermost layer side.
The packaging bag may be produced by folding a sheet of the laminate in two such that portions of the overcoat layer face each other, further folding the laminate as appropriate so as to obtain a desired shape, and then performing heat sealing such that a bag is formed. It is also possible to stack two sheets of the laminate so that their overcoat layers face each other, and then performing heat sealing such that the sheets form a bag.
In the packaging bag according to this embodiment, the heat seal strength may be 2N or more, or 4N or more. The upper limit of the heat seal strength is not particularly limited, but may be, for example, 10 N or less.
The packaging bag may contain food, pharmaceuticals, or the like. In particular, among foods, it is suitable for containing sweets and the like. The packaging bag according to the present embodiment can maintain good gas barrier performance even when it has a shape with a folded portion.
In this embodiment, a gusset bag is given as an example of a packaging bag; however, the laminate according to this embodiment may be used to produce, for example, a pillow bag, a three-side-sealed bag, or a standing pouch.

Examples

The present disclosure will be described in more detail with reference to the following examples; however, the present disclosure is not limited to these examples.

[Example 1]

A first coating solution was prepared by adding 50 parts by volume of kaolin to 100 parts by volume (solids volume) of a fully saponified polyvinyl alcohol resin having a degree of polymerization of 500 (solids concentration: 10% by mass, solvent: water) and mixing them.

A fully saponified polyvinyl alcohol resin having a degree of polymerization of 500 (solids concentration: 10% by mass, solvent: water) was prepared as a second coating solution.

A base paper made of kraft paper having a basis weight of 50 g/m² was coated with the first coating solution using a bar coater so that the thickness of the coating would be 1 µm after the calendaring described below, and the coating was dried in an oven to form a first layer. Then, the second coating solution was applied onto the first layer using a bar coater so that the thickness of the coating would be 3 µm after the calendaring described below, and the coating was dried in an oven to form a second layer. Calendaring was performed to press the first and second layers and smooth the surface of the second layer, thereby obtaining a gas barrier resin layer made up of the first and second layers, having a total thickness of 4 µm. The content of the inorganic pigment in the entire gas barrier resin layer was 9.1 parts by volume per 100 parts by volume of the resin. The proportion of the inorganic pigment present in the first region to the total amount of the inorganic pigment in the gas barrier resin layer was 100% by volume.
Aluminum was vapor-deposited on the gas barrier resin layer by vacuum deposition to form a vapor-deposited aluminum layer having a thickness of 50 nm. Furthermore, an aqueous dispersion of a polyolefin resin containing a salt of a carboxyl group (Chemipearl S500 manufactured by Mitsui Chemicals, Inc., solids concentration: 20% by mass, solvent: a mixed solvent of water/IPA = 8/2 (mass ratio)) was applied onto the vapor-deposited aluminum layer using a bar coater, and then dried in an oven to form an overcoat layer with a thickness of 3 µm. Thus, a laminate was obtained.

[Example 2]

A first coating solution was prepared by adding 200 parts by volume of kaolin to 100 parts by volume (solids volume) of a fully saponified polyvinyl alcohol resin having a degree of polymerization of 500 (solids concentration: 10% by mass, solvent: water) and mixing them.

A base paper made of kraft paper having a basis weight of 50 g/m² was coated with the first coating solution using a bar coater so that the thickness of the coating would be 1.5 µm after the calendaring described below, and the coating was dried in an oven to form a first layer. Then, the second coating solution was applied onto the first layer using a bar coater so that the thickness of the coating would be 2.5 µm after the calendaring described below, and the coating was dried in an oven to form a second layer. Calendaring was performed to press the first and second layers and smooth the surface of the second layer, thereby obtaining a gas barrier resin layer made up of the first and second layers, having a total thickness of 4 µm. The content of the inorganic pigment in the entire gas barrier resin layer was 33.3 parts by volume per 100 parts by volume of the resin. The proportion of the inorganic pigment present in the first region to the total amount of the inorganic pigment in the gas barrier resin layer was 100% by volume. Subsequently, a vapor-deposited aluminum layer and an overcoat layer were formed on the gas barrier resin layer in the same manner as in Example 1 to obtain a laminate.

[Example 3]

A first coating solution was prepared by adding 50 parts by volume of kaolin to 100 parts by volume (solids volume) of an ethylene-vinyl alcohol copolymer resin having an ethylene content of 29 mol% (solids concentration: 10% by mass, solvent: a mixed solvent of water/IPA = 1/1 (mass ratio)) and mixing them.

An ethylene-vinyl alcohol copolymer resin having an ethylene content of 29 mol% (solids concentration: 10% by mass, solvent: a mixed solvent of water/IPA = 1/1 (mass ratio)) was prepared as a second coating solution.

A laminate was produced in the same manner as in Example 1, except that the above first and second coating solutions were used.

[Example 4]

A first coating solution was prepared by adding 50 parts by volume of kaolin to 100 parts by volume (solids volume) of a polyvinyl alcohol resin having a degree of polymerization of 500 and a degree of saponification of 85 mol% (solids concentration: 10% by mass, solvent: water) and mixing them.

A polyvinyl alcohol resin having a degree of polymerization of 500 and a degree of saponification of 85 mol% (solids concentration: 10% by mass, solvent: water) was prepared as a second coating solution.

[Example 5]

A first coating solution was prepared by adding 50 parts by volume of kaolin to 100 parts by volume (solids volume) of an aqueous dispersion of a polyolefin resin containing a salt of a carboxyl group (Chemipearl S500 manufactured by Mitsui Chemicals, Inc., solids concentration: 20% by mass, solvent: a mixed solvent of water/IPA = 8/2 (mass ratio)), and mixing them.

An aqueous dispersion of a polyolefin resin containing a salt of a carboxyl group (Chemipearl S500 manufactured by Mitsui Chemicals, Inc., solids concentration: 20% by mass, solvent: a mixed solvent of water/IPA = 8/2 (mass ratio)) was prepared as a second coating solution.

[Example 6]

A first coating solution was prepared by adding 50 parts by volume of talc to 100 parts by volume (solids volume) of a fully saponified polyvinyl alcohol resin having a degree of polymerization of 500 (solids concentration: 10% by mass, solvent: water) and mixing them.

[Comparative Example 1]

An aqueous dispersion of a polyurethane resin (Takelac XWPB-LJ4 manufactured by Mitsui Chemicals, Inc., solids concentration: 20% by mass, solvent: a mixed solvent of /IPA = 8/2 (mass ratio)) was applied onto the clay coating layer (thickness: 5 µm) of a clay-coated paper with a basis weight of 60 g/m², in which the clay coating layer is provided on a base paper, using a bar coater to form a coating with a thickness of 3 µm after drying, and then dried in an oven to form a gas barrier resin layer. Subsequently, a vapor-deposited aluminum layer and an overcoat layer were formed on the gas barrier resin layer in the same manner as in Example 1 to obtain a laminate.

[Comparative Example 2]

A base paper made of kraft paper having a basis weight of 50 g/m² was coated with the first coating solution using a bar coater so that the thickness of the coating would be 3 µm after the calendaring described below, and the coating was dried in an oven to form a first layer. Then, the second coating solution was applied onto the first layer using a bar coater so that the thickness of the coating would be 1 µm after the calendaring described below, and the coating was dried in an oven to form a second layer. Calendaring was performed to press the first and second layers and smooth the surface of the second layer, thereby obtaining a gas barrier resin layer made up of the first and second layers, having a total thickness of 4 µm. The content of the inorganic pigment in the entire gas barrier resin layer was 100 parts by volume per 100 parts by volume of the resin. The proportion of the inorganic pigment present in the first region to the total amount of the inorganic pigment in the gas barrier resin layer was 67% by volume. Subsequently, a vapor-deposited aluminum layer and an overcoat layer were formed on the gas barrier resin layer in the same manner as in Example 1 to obtain a laminate.

[Comparative Example 3]

A fully saponified polyvinyl alcohol resin having a degree of polymerization of 500 (solids concentration: 10% by mass, solvent: water) was applied onto a base paper made of glassine paper having a basis weight of 60 g/m² using a bar coater so that the thickness of the coating would be 3 µm after drying, and then dried in an oven to form a gas barrier resin layer. Subsequently, a vapor-deposited aluminum layer and an overcoat layer were formed on the gas barrier resin layer in the same manner as in Example 1 to obtain a laminate.

[Comparative Example 4]

A base paper made of kraft paper having a basis weight of 50 g/m² was coated with the first coating solution using a bar coater so that the thickness of the coating would be 4 µm after drying, and the coating was dried in an oven to form a gas barrier resin layer. The content of the inorganic pigment in the entire gas barrier resin layer was 50 parts by volume per 100 parts by volume of the resin. The proportion of the inorganic pigment present in the first region to the total amount of the inorganic pigment in the gas barrier resin layer was 50% by volume. Subsequently, a vapor-deposited aluminum layer and an overcoat layer were formed on the gas barrier resin layer in the same manner as in Example 1 to obtain a laminate.

[Comparative Example 5]

A fully saponified polyvinyl alcohol resin having a degree of polymerization of 500 (solids concentration: 10% by mass, solvent: water) was applied onto a base paper made of kraft paper having a basis weight of 50 g/m² using a bar coater so that the thickness of the coating would be 4 µm after drying, and then dried in an oven to form a gas barrier resin layer. Subsequently, a vapor-deposited aluminum layer and an overcoat layer were formed on the gas barrier resin layer in the same manner as in Example 1 to obtain a laminate.

[Comparative Example 6]

A first coating solution was prepared by adding 50 parts by volume of kaolin to 100 parts by volume (solids volume) of an aqueous dispersion of a polyurethane resin (Takelac XWPB-LJ4 manufactured by Mitsui Chemicals, Inc., solids concentration: 20% by mass, solvent: a mixed solvent of /IPA = 8/2 (mass ratio)), and mixing them.

An aqueous dispersion of a polyurethane resin (Takelac XWPB-LJ4 manufactured by Mitsui Chemicals, Inc., solids concentration: 20% by mass, solvent: a mixed solvent of /IPA = 8/2 (mass ratio)) was prepared as a second coating solution.

[Measurement of Surface Roughness Ra]

For each of the gas barrier resin layers obtained in the Examples and Comparative Examples, the surface roughness (Ra) on the side opposite to that facing the base paper was measured using a surface roughness measuring device (Surfcom 130A manufactured by TOKYO SEIMITSU CO., LTD.). The measurement conditions were as follows. The results are shown in Tables 1 and 2.

(Measurement conditions)

Evaluation length: 40 mm
Measurement range: ±400 µm
Measurement speed: 0.3 mm/s
Tilt correction: Linear
Cutoff value: 0.8 mm
Cutoff ratio: 300
Filter type: Gaussian

[Measurement of Water Vapor Transmission Rate (WVTR)]

For each of the laminates obtained in the Examples and Comparative Examples, the water vapor transmission rate (unit: g/m²·day) was measured using the Mocon method under conditions of 40°C and 90% RH, in accordance with JIS K 7129-2. The measurement was carried out three times to obtain an average value. The results are shown in Tables 1 and 2.

[Measurement of Oxygen Transmission Rate (OTR)]

For each of the laminates obtained in the Examples and Comparative Examples, the oxygen transmission rate (unit: cc/m²·day·atm) was measured using the Mocon method under conditions of 30°C and 70% RH. The measurement was carried out three times to obtain an average value. The results are shown in Tables 1 and 2.

[Barrier Performance after Bending]

Each of the laminates obtained in the Examples and Comparative Examples was folded 180° without creating a crease, with the overcoat layer side surface facing outward, and was then creased by rolling a 1 kg roller across it once in one direction. Then, the laminate was unfolded, and the water vapor and oxygen transmission rates in a region centered around the fold were measured in the same manner as above. The results are shown in Tables 1 and 2.

[Table 1]

			Ex. 1	Ex. 2	Ex. 3	Ex. 4	Ex. 5	Ex. 6
Base paper	Type		Kraft paper	Kraft paper	Kraft paper	Kraft paper	Kraft paper	Kraft paper
	Basis weight [g/m²]		50	50	50	50	50	50
	Clay coating layer		No	No	No	No	No	No
Gas barrier resin layer	First layer	Material	PVA + kaolin	PVA + kaolin	EVOH + kaolin	PVA (partially saponified) + kaolin	Polyolefin + kaolin	PVA + talc
	First layer	Thickness [µm]	1	1.5	1	1	1	1
	Second layer	Material	PVA	PVA	EVOH	PVA (partially saponified)	Polyolefin	PVA
	Second layer	Thickness [µm]	3	2.5	3	3	3	3
	Inorganic pigment content [parts by volume/100 parts by volume of resin]		9.1	33.3	9.1	9.1	9.1	9.1
	Proportion of thickness of region containing inorganic pigment [%]		25	37.5	25	25	25	25
	Proportion of inorganic pigment present in first region to total amount of inorganic pigment [% by volume]		100	100	100	100	100	100
	Surface roughness Ra [µm]		0.56	0.45	0.52	0.51	0.36	0.48
Initial barrier performance	WVTR [g/m²·day]		0.8	0.6	0.6	0.8	0.6	0.9
Initial barrier performance	OTR [cc/m²·day·atm]		0.5	0.6	0.6	0.5	> 100	0.5
Barrier performance after bending	WVTR [g/m²·day]		2.8	2.9	2.9	2.8	1.8	2.4
Barrier performance after bending	OTR [cc/m²·day·atm]		1.1	2.2	2.2	1.1	> 100	1.2

[Table 2]

			Comp. Ex. 1	Comp. Ex. 2	Comp. Ex. 3	Comp. Ex. 4	Comp. Ex. 5	Comp. Ex. 6
Base paper	Type		Clay-coated paper	Kraft paper	Glassine Paper	Kraft paper	Kraft paper	Kraft paper
	Basis weight [g/m²]		60	50	60	50	50	50
	Clay coating layer		Yes	No	No	No	No	No
Gas barrier resin layer	First layer	Material	Polyurethane	PVA + kaolin	PVA	PVA + kaolin	PVA	Polyurethane + kaolin
	First layer	Thickness [µm]	3	3	3	4	4	1
	Second layer	Material	-	PVA	-	-	-	Polyurethane
	Second layer	Thickness [µm]	-	1	-	-	-	3
	Inorganic pigment content [parts by volume/100 parts by volume of resin]		-	100	-	50	-	9.1
	Proportion of thickness of region containing inorganic pigment [%]		-	75	-	100	-	25
	Proportion of inorganic pigment present in first region to total amount of inorganic pigment [% by volume]		-	67	-	50	-	100
	Surface roughness Ra [µm]		0.36	0.78	1.08	1.04	1.12	0.51
Initial barrier performance	WVTR [g/m²·day]		1.0	2.1	5.0	1.3	5.5	0.8
Initial barrier performance	OTR [cc/m²·day·atm]		0.8	2.0	15.0	2.0	11.0	0.5
Barrier performance after bending	WVTR [g/m²·day]		20.0	16.0	20.0	16.0	22.3	35.1
Barrier performance after bending	OTR [cc/m²·day·atm]		> 100	> 100	> 100	> 100	> 100	> 100

[Reference Signs List]

1 ... Base paper
2 ... Gas barrier resin layer
3 ... Vapor-deposited inorganic layer
4 ... Overcoat layer
5 ... Inorganic pigment
10 ... Laminate
20 ... Gusset bag
B1, B2 ... Folded portion

Claims

A laminate comprising a base paper and a gas barrier resin layer provided directly on the base paper,
wherein a binder resin contained in the gas barrier resin layer includes at least one selected from the group consisting of polyolefin resins and polyvinyl alcohol-based resins,

the gas barrier resin layer contains an inorganic pigment in a first region extending from a surface thereof on the base paper side to 50% of the total thickness of the gas barrier resin layer, and

80% by volume or more of the total amount of the inorganic pigment contained in the gas barrier resin layer is present in the first region.
The laminate according to claim 1, further comprising a vapor-deposited inorganic layer on a surface of the gas barrier resin layer opposite to that facing the base paper.
The laminate according to claim 2, further comprising an overcoat layer on a surface of the vapor-deposited inorganic layer opposite to that facing the gas barrier resin layer.
The laminate according to claim 3, wherein the overcoat layer contains a polyolefin resin.
The laminate according to claim 1, wherein the content of the inorganic pigment in the gas barrier resin layer is 50 parts by volume or less relative to 100 parts by volume of the binder resin.
The laminate according to claim 1, wherein the content of the inorganic pigment in the first region is 2 to 200 parts by volume relative to 100 parts by volume of the binder resin in the first region.
The laminate according to claim 1, wherein the inorganic pigment has an aspect ratio of 1 to 200.
The laminate according to claim 1, wherein 100% by volume of the inorganic pigment contained in the gas barrier resin layer is present in the first region.
The laminate according to claim 1, wherein a surface of the gas barrier resin layer opposite to that facing the base paper has a surface roughness Ra of 1.0 µm or less.
The laminate according to claim 1, wherein the gas barrier resin layer has a thickness of 1 to 20 µm.
The laminate according to claim 1, wherein the gas barrier resin layer has a thickness of 3 to 5 µm.
A packaging bag comprising the laminate according to any one of claims 1 to 11.