JP7848835B2 - Laminate - Google Patents

Description

This disclosure relates to laminates and packaging bags.

In many fields, including food, beverages, pharmaceuticals, and chemicals, packaging materials are used that are appropriate for the contents. Packaging materials must have gas barrier properties to prevent the permeation of water vapor and other gases that can cause deterioration of the contents. Furthermore, depending on the contents, packaging materials may also require oil resistance to prevent oil from seeping out.

In recent years, growing environmental awareness, stemming from issues such as marine plastic waste, has led to a momentum for reducing plastic use. From the perspective of reducing the amount of plastic material used, the use of paper as a substitute for plastic materials is being considered in various fields. For example, Patent Document 1 below discloses a laminate in which a barrier layer is laminated onto paper.

Japanese Patent Publication No. 2020-69783

Paper possesses the characteristic of being easy to process due to its crease-holding ability (also known as dead-holding ability). However, our research has revealed that when using packaging bags with sharper creases (pillow packaging, three-side seal packaging, and gusset packaging), cracks can form in the barrier layer, reducing oil resistance, indicating that there is still room for improvement.

Furthermore, from the perspective of the Law for the Promotion of Effective Utilization of Resources, it is required to reduce the amount of plastic material used in laminates as well.

Therefore, this disclosure aims to provide a laminate made of paper that possesses sufficient oil resistance not only initially but also after being folded, and a packaging bag containing the same.

To solve the above problems, this disclosure provides the following laminates and packaging bags.
[1] A laminate having a structure in which at least a paper substrate, an anchor coat layer, an aluminum vapor deposition layer, and an overcoat layer are laminated in this order, wherein the aluminum vapor deposition layer has a full width at half maximum of 1.6° or more of the peak of the (111) crystal plane of aluminum in X-ray diffraction measurement.
[2] The laminate according to [1], wherein the anchor coat layer comprises a polyolefin or polyvinyl alcohol-based resin having polar groups.
[3] The laminate according to [1] or [2], wherein the overcoat layer comprises a polyolefin having polar groups.
[4] The laminate according to any one of [1] to [3], wherein the hardness of the anchor coat layer measured by nanoindentation in a cross-section in the thickness direction of the laminate is 0.3 GPa or less.
[5] The laminate according to any one of [1] to [4], wherein the hardness of the overcoat layer measured by nanoindentation in a cross-section in the thickness direction of the laminate is 0.3 GPa or less.
[6] The laminate according to any one of [1] to [5] above, wherein the thickness of the aluminum vapor deposition layer is 20 nm or more and 100 nm or less.
[7] The laminate according to any one of [1] to [6] above, wherein the aluminum vapor-deposited layer has a full width at half maximum of the peak of the (111) crystal plane of aluminum in X-ray diffraction measurement of 2.0° or more and 15.0° or less.
[8] The laminate according to [7], wherein the aluminum vapor-deposited layer is in contact with a resin layer containing an ionomer or a polyvinyl alcohol-based resin with a degree of saponification of 95% or more.
[9] A packaging bag containing the laminate described in any of [1] to [8] above.
[10] The packaging bag described in [9] above, having a folded portion.

According to this disclosure, it is possible to provide a laminate made of paper that possesses sufficient oil resistance not only initially but also after being folded, and a packaging bag containing the same. Because the laminate uses paper, it retains the crease-holding properties characteristic of paper, while also contributing to a reduction in the amount of plastic material used.

This is a schematic cross-sectional view showing a laminate according to one embodiment of the present disclosure. A perspective view showing a packaging bag according to one embodiment of this disclosure.

The embodiments of this disclosure will be described in detail below, with reference to the drawings as appropriate. However, this disclosure is not limited to the embodiments described below.

<Laminated structure>
The laminate according to this embodiment is a laminate having a structure in which at least a paper substrate, an anchor coat layer, an aluminum vapor-deposited layer, and an overcoat layer are laminated in this order, wherein the aluminum vapor-deposited layer is a laminate in which the full width at half maximum (FWHM) of the peak of the (111) crystal plane of aluminum in X-ray diffraction measurement is 1.6° or more. Here, the FWHM of the aluminum vapor-deposited layer in X-ray diffraction represents the degree of lattice strain in the crystal structure of aluminum. If the strain is large, the FWHM is large, and if the strain is small, the FWHM is small. Also, the smaller the strain, the denser the crystal structure of aluminum is considered to be. In the above laminate, by having the FWHM of the aluminum vapor-deposited layer be 1.6° or more, the density of the crystal structure of aluminum can be moderately reduced to a sparse state. As a result, the stress applied to the aluminum vapor-deposited layer when the laminate is bent is distributed throughout the entire layer, which suppresses the occurrence of cracks in the aluminum vapor-deposited layer when bent, and reduces the size of cracks that occur in the aluminum vapor-deposited layer. Therefore, with the above laminate, sufficient oil resistance can be obtained not only initially but also after bending. Furthermore, with the above laminate, by keeping the half-width of the aluminum vapor-deposited layer within the above range, sufficient water vapor barrier properties can be obtained not only initially but also after bending. Moreover, with the above laminate, if a material having oxygen barrier properties is used for the anchor coat layer, sufficient oxygen barrier properties can be obtained not only initially but also after bending by keeping the half-width of the aluminum vapor-deposited layer within the above range. The laminate according to this embodiment is useful as an oil-resistant laminate or a gas barrier laminate.

Furthermore, conventional gas barrier laminates had room for improvement in that their water vapor barrier properties deteriorated when stored under high temperature and high humidity conditions. When a gas barrier laminate with deteriorated water vapor barrier properties was observed under a microscope using transmitted light after being stored under high temperature and high humidity conditions (40°C, 90% humidity), numerous minute bright spots were observed. This suggests that the deterioration of water vapor barrier properties was due to transmission defects occurring in the aluminum vapor-deposited layer. In contrast, the laminate according to this embodiment includes an aluminum vapor-deposited layer in which the full width at half maximum of the peak of the (111) crystal plane of aluminum in X-ray diffraction measurements is 1.6° or more. This suppresses the occurrence of transmission defects in the aluminum vapor-deposited layer even when stored under high temperature and high humidity conditions, thereby suppressing the deterioration of water vapor barrier properties. The inventors speculate on the reason for this effect as follows:

The formation of permeation defects in the aluminum vapor-deposited layer is due to pitting corrosion of aluminum by corrosive ions and expansion and contraction stress caused by dimensional changes due to moisture absorption and dehydration of the paper substrate. From the perspective of the crystallinity of the aluminum vapor-deposited layer, higher crystallinity is superior in terms of resistance to corrosive ions, but amorphous materials, which can easily follow expansion and contraction, are considered to be superior in terms of stress resistance. Here, the aluminum vapor-deposited layer is thought to have a structure in which amorphous regions fill the periphery of crystallites. Furthermore, the broadening of the X-ray diffraction linewidth of aluminum is due to the diameter of the crystallites and the distortion of the crystal. A narrow X-ray diffraction linewidth is thought to be a state in which the crystallites, which consist of an ideal crystal lattice, and the amorphous regions are clearly separated. Therefore, when the X-ray diffraction linewidth is narrow, it is presumed that pitting corrosion in the amorphous regions and fracture of the ideal crystal lattice or between crystal and amorphous regions due to expansion and contraction stress are more likely to occur. On the other hand, a broad X-ray diffraction linewidth is thought to be a state in which the crystal structure is distorted and the separation of crystalline and amorphous regions is ambiguous. Therefore, it is presumed that a wider X-ray diffraction linewidth suppresses pitting corrosion and fracture due to stretching stress, making transmission defects less likely to occur. For these reasons, it is believed that a full width at half maximum (FWHM) of 1.6° or higher in the X-ray diffraction of the aluminum vapor-deposited layer suppresses the occurrence of transmission defects in the aluminum vapor-deposited layer, even when the laminate is stored under high temperature and high humidity conditions, thereby suppressing the deterioration of the water vapor barrier properties. This effect is even more pronounced when the FWHM is 2.0° or higher.

Figure 1 is a schematic cross-sectional view showing a laminate according to one embodiment. The laminate 10 according to this embodiment comprises, in this order, a paper substrate 1, an anchor coat layer 2, an aluminum vapor-deposited layer 3, and an overcoat layer 4.

The thickness of the laminate 10 may be 20 to 100 μm, 30 to 80 μm, or 40 to 60 μm. When the thickness of the laminate 10 is within the above range, the laminate 10 can achieve better water vapor barrier properties and oil resistance not only initially but also after bending.

[Paper base material]
The paper substrate 1 may be paper whose main component is plant-derived pulp. Specific examples of the paper substrate 1 include fine paper, special fine paper, coated paper, art paper, cast coated paper, imitation paper, kraft paper, and glassine paper. The basis weight of the paper substrate 1 may be 20 to 500 g/ ^m² or 30 to 100 g/ ^m² .

The paper substrate 1 may have a coating layer on at least the side in contact with the anchor coat layer 2. If the paper substrate 1 has a coating layer, it may comprise at least a paper layer and a coating layer. The coating layer may be provided on both surfaces of the paper substrate 1. Providing a coating layer prevents the anchor coat layer 2 from seeping into the paper, and also acts as a sealer to fill in the irregularities of the paper, allowing for the uniform and defect-free formation of the anchor coat layer 2. The coating layer may include, for example, various copolymers such as styrene-butadiene, styrene-acrylic, and ethylene-vinyl acetate, polyvinyl alcohol resins, cellulose resins, and paraffin (wax) as binder resins, and may contain clay, kaolin, calcium carbonate, talc, mica, etc. as fillers. The coating layer may also be a clay coating layer containing at least clay as a filler.

If the paper substrate 1 has a coating layer, the thickness of the coating layer may be 1.5 μm or more and 15 μm or less. The thickness of the coating layer may also be 1.8 μm or more, 3 μm or more, 5 μm or more, or 6 μm or more. The thickness of the coating layer may also be 12 μm or less, or 10 μm or less. When the thickness of the coating layer is within the above range, the laminate 10 can obtain better water vapor barrier properties and oil resistance not only initially but also after folding.

The thickness of the paper substrate 1 may be 20 to 100 μm, 30 to 80 μm, or 40 to 60 μm. When the thickness of the paper substrate 1 is within the above range, the laminate 10 can achieve better water vapor barrier properties and oil resistance, not only initially but also after folding.

The ratio of the thickness of the coating layer to the thickness of the paper substrate 1 may be 3 to 25%, or 5 to 20%. When this ratio is within the above range, the laminate 10 can achieve better water vapor barrier properties and oil resistance, not only initially but also after being folded.

The weight of paper is preferably 50% or more by mass of the entire laminate, more preferably 70% or more by mass, and even more preferably 80% or more by mass. If the weight of paper is 50% or more by mass of the entire laminate, the amount of plastic material used can be sufficiently reduced, the entire laminate can be considered to be made of paper, and it has excellent recyclability.

[Anchor Coat Layer]
The anchor coat layer 2 is provided on the surface of the paper substrate 1 to improve adhesion between the paper substrate 1 and the aluminum vapor deposition layer 3 (described later), and to improve the gas barrier properties and oil resistance of the laminate. The anchor coat layer 2 may contain a polyolefin or polyvinyl alcohol-based resin having polar groups.

When the anchor coat layer 2 contains a polyolefin with polar groups, the anchor coat layer 2 exhibits excellent flexibility, suppressing cracking of the aluminum vapor-deposited layer 3 after bending (folding), and improving adhesion between the anchor coat layer 2 and the aluminum vapor-deposited layer 3. Furthermore, the inclusion of a polyolefin with polar groups enables the formation of a dense film due to the crystalline properties of the polyolefin, resulting in water vapor barrier properties and oil resistance. The crystalline properties of the polyolefin contribute to water vapor barrier properties and oil resistance, while the presence of polar groups ensures adhesion with the aluminum vapor-deposited layer 3.

A polyolefin having a polar group may have at least one selected from a carboxyl group, a salt of a carboxyl group, a carboxylic acid anhydride group, and a carboxylic acid ester.

As polyolefins having polar groups, copolymers of ethylene or propylene with unsaturated carboxylic acids (unsaturated compounds having carboxyl groups, such as acrylic acid, methacrylic acid, and maleic anhydride), unsaturated carboxylic acid esters, and salts obtained by neutralizing carboxylic acids with basic compounds may be used. Other copolymers, such as those with vinyl acetate, epoxy compounds, chlorine compounds, urethane compounds, and polyamide compounds, may also be used.

Examples of polyolefins having polar groups include copolymers of acrylic acid esters and maleic anhydride, ethylene-vinyl acetate copolymers, and ethylene-glycidyl methacrylate copolymers.

On the other hand, when the anchor coat layer 2 contains a polyvinyl alcohol-based resin, the polyvinyl alcohol-based resin has polar groups (hydroxyl groups), and these polar groups readily bond with metals such as aluminum in the aluminum vapor-deposited layer 3. Therefore, the adhesion between the aluminum vapor-deposited layer 3 and the anchor coat layer 2 can be easily improved. Furthermore, such an anchor coat layer 2 has excellent flexibility, which can suppress cracking of the aluminum vapor-deposited layer 3 after bending (folding). In addition, the inclusion of a polyvinyl alcohol-based resin in the anchor coat layer 2 can improve the oxygen barrier properties of the laminate.

Polyvinyl alcohol-based resins are resins that contain vinyl alcohol as a constituent unit. Examples of polyvinyl alcohol-based resins include fully saponified polyvinyl alcohol resins, partially saponified polyvinyl alcohol resins, modified polyvinyl alcohol resins, and ethylene-vinyl alcohol copolymer resins. From the viewpoint of oxygen barrier properties, a higher degree of saponification of the polyvinyl alcohol resin is preferable, which may be 95% or higher, and may also be 98% or higher.

The anchor coat layer 2 may contain both a polyolefin having polar groups and a polyvinyl alcohol-based resin.

The anchor coat layer 2 may contain other components in addition to the polyolefin and polyvinyl alcohol-based resin having the polar groups mentioned above. Examples of other components include polyolefins other than those having the polar groups mentioned above, silane coupling agents, organic titanates, polyacrylics, polyesters, polyurethanes, polycarbonates, polyureas, polyamides, polyimides, melamines, phenols, and the like.

The content of the polyolefin or polyvinyl alcohol-based resin having the polar group in the anchor coat layer 2 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 anchor coat layer 2 may be, for example, 0.5 μm or more, 1 μm or more, 2 μm or more, 20 μm or less, 10 μm or less, or 5 μm or less. If the thickness of the anchor coat layer 2 is 0.5 μm or more, the irregularities of the paper substrate described above can be efficiently filled, and the aluminum vapor-deposited layer described later can be uniformly laminated. Furthermore, if the thickness of the anchor coat layer 2 is 20 μm or less, the aluminum vapor-deposited layer can be uniformly laminated while keeping costs down.

The anchor coat layer 2 may have a hardness of 0.3 GPa or less, as measured by nanoindentation in a cross-section in the thickness direction of the laminate 10. Such an anchor coat layer 2 exhibits excellent flexibility, suppressing cracking of the aluminum vapor-deposited layer 3 (described later) after bending (folding), and improving adhesion between the anchor coat layer 2 and the aluminum vapor-deposited layer 3.

Examples of solvents included in the coating solution for the anchor coat layer 2 include water, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, n-pentyl alcohol, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, toluene, hexane, heptane, cyclohexane, acetone, methyl ethyl ketone, diethyl ether, dioxane, tetrahydrofuran, ethyl acetate, and butyl acetate. These solvents may be used individually or in combination of two or more. Among these, methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, ethyl acetate, methyl ethyl ketone, and water are preferred from a properties standpoint. Furthermore, methyl alcohol, ethyl alcohol, isopropyl alcohol, and water are preferred from an environmental standpoint.

The anchor coat layer 2 can be obtained by applying a coating solution containing the aforementioned polar group-containing polyolefin or polyvinyl alcohol-based resin and solvent onto a paper substrate and then drying it.

[Aluminum vapor-deposited layer]
The aluminum vapor-deposited layer 3 is a layer on which aluminum or an aluminum compound has been deposited. The aluminum vapor-deposited layer may be obtained by depositing aluminum, or it may contain aluminum oxide ( _AlOx ), silicon oxide ( _SiOx ), etc.

The thickness of the aluminum vapor-deposited layer 3 can be set appropriately depending on the application, but is preferably 10 to 300 nm, more preferably 20 to 100 nm, and even more preferably 30 to 100 nm. A thickness of 10 nm or more in the aluminum vapor-deposited layer 3 makes it easier to ensure sufficient continuity, while a thickness of 300 nm or less sufficiently suppresses the occurrence of curling and cracking, making it easier to achieve sufficient gas barrier performance, oil resistance, and flexibility. Furthermore, a thickness of 20 nm to 100 nm in the aluminum vapor-deposited layer makes it more resistant to cracking, allowing for sufficient water vapor barrier and oil resistance even after bending. From the viewpoint of further suppressing the deterioration of the water vapor barrier performance of the laminate 10 when stored under high temperature and high humidity, the thickness of the aluminum vapor-deposited layer 3 may be 50 to 300 nm, 60 to 150 nm, or 60 to 100 nm.

The aluminum vapor-deposited layer 3 is preferably deposited by a vacuum deposition method from the viewpoint of water vapor and oxygen gas barrier performance, oil resistance, and film uniformity. While there are known deposition methods such as vacuum deposition, sputtering, and chemical vapor deposition (CVD), vacuum deposition is preferred due to its high deposition rate and productivity. Among vacuum deposition methods, electron beam heating is particularly effective because the deposition rate can be easily controlled by the irradiation area and electron beam current, and the heating and cooling of the deposition material can be performed in a short time.

The aluminum vapor-deposited layer 3 is a layer in which the full width at half maximum (FWHM) of the peak of the (111) crystal plane of aluminum in X-ray diffraction measurements is 1.6° or more. The above FWHM may be 1.8° or more, 2.0° or more, or 2.1° or more. When the FWHM is 1.6° or more, it is possible to suppress the occurrence of cracks in the aluminum vapor-deposited layer 3 when the laminate 10 is bent, and to suppress the decrease in gas barrier properties and oil resistance after bending. This effect is more pronounced when the above FWHM is 2.0° or more. Furthermore, when the above FWHM is 1.6° or more, even when the laminate 10 is stored under high temperature and high humidity conditions (for example, under a 40°C 90% environment), it is possible to suppress the occurrence of permeation defects in the aluminum vapor-deposited layer 3, and to suppress the deterioration of the water vapor barrier properties of the laminate 10. This effect is also more pronounced when the above FWHM is 2.0° or more. The upper limit of the above-mentioned full width at half maximum (FWHM) may be, for example, 15.0° or less, or 10.0° or less, from the viewpoint of the density of the aluminum crystal structure. If the resin layer in contact with the aluminum vapor-deposited layer contains an ionomer or a polyvinyl alcohol-based resin with a saponification degree of 95% or higher, the aluminum vapor-deposited layer is susceptible to corrosion. This problem is more likely to occur if the crystallinity of the aluminum vapor-deposited layer is low. If the above-mentioned FWHM is 15.0° or less, corrosion of the aluminum vapor-deposited layer becomes less likely, even if the resin layer in contact with the aluminum vapor-deposited layer contains an ionomer or a polyvinyl alcohol-based resin with a high saponification degree. This effect is even more pronounced when the above-mentioned FWHM is 10.0° or less. To achieve the above effects, the above half-width is preferably between 1.6° and 15.0°, 1.6° and 10.0°, 1.6° and 7.0°, 1.6° and 5.0°, 2.0° and 15.0°, 2.0° and 10.0°, 2.0° and 7.0°, or 2.0° and 5.0°.

The full width at half maximum (2θ) of the peak of the (111) crystal plane of aluminum in the aluminum vapor-deposited layer 3 is measured using an X-ray diffractometer. For example, an ATX-G (product name) manufactured by Rigaku Electric Co., Ltd. can be used as the X-ray diffractometer. The measurement can be performed on the overcoat layer 4 with the laminate as the sample, fixed on a glass slide. For the X-ray diffraction of aluminum, the full width at half maximum of the peak at 2θ = 38.5° corresponding to the (111) plane (d = 2.34) is measured. The measurement conditions are as follows.
Light source: CuKα ray tube Voltage: 50kV
Tube current: 300mA
Optical system: Parallel beam optical system; Scanning method: 2θ/θ method; Measurement range: 30° to 50°
Sampling step: 0.02°
Scan speed: 2°/min
Slit S1: 10.0 mm x 1.0 mm
S2: 10.0mm x 0.5mm
Solar (res): 0.4mm

The above-mentioned full width at half maximum (FWHM) can be controlled by adjusting the conditions during the deposition of the aluminum vapor-deposited layer 3. For example, the FWHM can be controlled by adjusting the pressure inside the deposition chamber during the deposition of the aluminum vapor-deposited layer 3. Here, increasing the pressure inside the deposition chamber increases the FWHM, while decreasing the pressure inside the deposition chamber decreases it. The pressure inside the deposition chamber during the deposition of the aluminum vapor-deposited layer 3 may be 0.05 Pa or higher, 0.10 Pa or higher, or 0.20 Pa or higher, as this makes it easier to adjust the FWHM to 1.6° or higher. The upper limit of the pressure is not particularly limited as long as the deposition of the aluminum vapor-deposited layer 3 is possible, but for example, it may be 0.50 Pa or lower, or 0.40 Pa or lower.

[Overcoat layer]
The overcoat layer 4 is provided on the surface of the aluminum vapor-deposited layer 3, in contact with the aluminum vapor-deposited layer 3. The overcoat layer may contain a polyolefin having polar groups.

A polyolefin having a polar group may have at least one selected from a carboxyl group, a salt of a carboxyl group, a carboxylic acid anhydride group, and a carboxylic acid ester.

As polyolefins having polar groups, copolymers of ethylene or propylene with unsaturated carboxylic acids (unsaturated compounds having carboxyl groups, such as acrylic acid and methacrylic acid), unsaturated carboxylic acid esters, and salts obtained by neutralizing carboxylic acids with basic compounds may be used. Other copolymers with vinyl acetate, epoxy compounds, chlorine compounds, urethane compounds, polyamide compounds, etc., may also be used.

Examples of polyolefins having polar groups include copolymers of acrylic acid esters and maleic anhydride, ethylene-vinyl acetate copolymers, and ethylene-glycidyl methacrylate copolymers.

By containing a polyolefin with polar groups, the overcoat layer 4 exhibits excellent flexibility, suppressing cracking of the aluminum vapor-deposited layer after bending (folding), and providing excellent adhesion to the aluminum vapor-deposited layer. Furthermore, the inclusion of the aforementioned polyolefin with polar groups enables the formation of a dense film due to the crystalline properties of the polyolefin, resulting in water vapor barrier and oil resistance. The presence of polar groups also contributes to adhesion to the aluminum vapor-deposited layer. Additionally, because the overcoat layer 4 contains the aforementioned polyolefin with polar groups, it can also function as a heat-seal layer, eliminating the need for a separate heat-seal layer.

The overcoat layer 4 may contain other components in addition to the polyolefin having the polar group described above. Examples of other components include silane coupling agents, organic titanates, polyacrylics, polyesters, polyurethanes, polycarbonates, polyureas, polyamides, polyolefin emulsions, polyimides, melamines, and phenols.

The content of the polyolefin having polar groups in the overcoat layer 4 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 4 may be, for example, 0.05 μm or more, 0.5 μm or more, 1 μm or more, 2 μm or more, 20 μm or less, 10 μm or less, or 5 μm or less. If the thickness of the overcoat layer 4 is 0.05 μm or more, it can fully perform its role as a heat seal layer as described above. Furthermore, if the thickness of the overcoat layer 4 is 20 μm or less, it can sufficiently exhibit adhesion and barrier properties with the aluminum vapor-deposited layer while keeping costs down. Also, by setting the thickness of the overcoat layer 4 to 2 μm or more and 10 μm or less, the aluminum vapor-deposited layer becomes more resistant to cracking, and sufficient water vapor barrier and oil resistance can be obtained even after bending.

In the laminate 10, when the overcoat layer 4 contains a polyolefin having polar groups, the thickness of the overcoat layer 4 is 2 μm to 10 μm, and the thickness of the aluminum vapor-deposited layer 3 is 20 nm to 100 nm, the aluminum vapor-deposited layer 3 becomes less prone to cracking, and a particularly significant effect is achieved in that sufficient water vapor barrier properties and oil resistance can be obtained even after bending.

The overcoat layer 4 may have a hardness of 0.3 GPa or less, as measured by nanoindentation in a cross-section in the thickness direction of the laminate 10. Such an overcoat layer 4 exhibits excellent flexibility, suppressing cracking of the aluminum vapor-deposited layer 3 after bending (folding), and preventing a decrease in gas barrier properties and oil resistance.

Examples of solvents included in the coating solution for the overcoat layer 4 include water, methyl alcohol, ethyl alcohol, isopropyl alcohol, n-propyl alcohol, n-butyl alcohol, n-pentyl alcohol, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, toluene, hexane, heptane, cyclohexane, acetone, methyl ethyl ketone, diethyl ether, dioxane, tetrahydrofuran, ethyl acetate, and butyl acetate. These solvents may be used individually or in combination of two or more. Among these, methyl alcohol, ethyl alcohol, isopropyl alcohol, toluene, ethyl acetate, methyl ethyl ketone, and water are preferred from a properties standpoint. Furthermore, methyl alcohol, ethyl alcohol, isopropyl alcohol, and water are preferred from an environmental standpoint.

The overcoat layer 4 can be obtained by applying a coating solution containing the aforementioned polyolefin having polar groups and a solvent onto the aluminum vapor-deposited layer and drying it. The melting point of the polyolefin having polar groups in the coating solution is preferably 70 to 160°C, and more preferably 80 to 120°C. A lower melting point of the polyolefin having polar groups has the advantage of lowering the heat-sealing start-up temperature. However, a lower melting point increases the risk of blocking in high-temperature environments. Furthermore, from the viewpoint of preventing blocking, a larger particle size is preferable to reduce the contact area. While not particularly limited, the particle size may be 1 nm or larger, 0.1 μm or larger, 1 μm or less, 0.7 μm or less, or 0.5 μm or less.

(Method for preparing cross-sections of measurement samples using nanoindentation)
Measurement by nanoindentation involves measuring the anchor coat layer 2 and the overcoat layer 4 from the cross-section of the laminate 10. The laminate sample, including the anchor coat layer 2 and the overcoat layer 4, is cut with a razor blade into a strip or wedge shape and embedded in resin. A photocurable resin (for example, D-800 from Toagosei Co., Ltd.) is used as the embedding resin, and it is cured by light irradiation after embedding. The cured sample embedding resin is fixed with an AFM sample holder insert, and trimming and cross-sectional cutting of the laminate are performed with a glass knife at room temperature (25°C). Cross-sectional cutting is then performed with a diamond knife at a cutting speed of 1.0 mm/s and a cutting film thickness of 200 nm until a mirror finish is achieved. The cross-sectional sample is then used for measurement by nanoindentation while fixed with an AFM sample holder insert. For example, a Leica EMUC7 ultramicrotome can be used as the cross-sectional cutting device. The cutting direction should be parallel to the layer interface.

(Measurement method using nanoindentation)
The hardness and composite modulus of the anchor coat layer and overcoat layer are expressed as those calculated by the nanoindentation method. The nanoindentation method is a measurement method that obtains the mechanical properties of a sample by performing a quasi-static indentation test on the target object to be measured. For the measuring device, for example, the Hystron TI-Premier (product name) manufactured by Bruker Japan Co., Ltd. can be used. For the indenter, a Berkovich-type diamond indenter manufactured by Bruker Japan Co., Ltd. can be used. In the nanoindentation method, first, a shape image of the sample is obtained by scanning the cross-section of the sample with the diamond indenter, and the measurement position of the desired layer is specified. Then, at room temperature (25°C) in displacement control mode, the sample is indented to a depth of 80 nm at an indentation speed of 80 nm/second, held at the maximum depth for 1 second, and then unloaded at a speed of 80 nm/second. The method for calculating the hardness and composite modulus involves pre-testing a standard sample of fused silica and calibrating the relationship between the contact depth and contact projected area between the indenter and the sample. Subsequently, the unloading curve in the 60-95% range relative to the maximum load at unloading is analyzed using the Oliver-Pharr method to calculate the hardness and composite modulus.

The hardness of the anchor coat layer 2 and the overcoat layer 4, measured by nanoindentation in the thickness-direction cross-section of the laminate 10, may be 0.3 GPa or less. This mitigates the direct transmission of deformation stress from the paper substrate caused by bending the laminate to the aluminum vapor-deposited layer, preventing defects from occurring in the aluminum vapor-deposited layer. Therefore, the deterioration of gas barrier properties and oil resistance after bending can be suppressed. From this viewpoint, the hardness of the anchor coat layer 2 and the overcoat layer 4 may be 0.25 GPa or less, or 0.2 GPa or less. While the lower limit of hardness is not particularly limited, it can be set to 0.05 MPa or higher from the viewpoint of obtaining sufficient strength to maintain gas barrier properties and oil resistance.

To form a flexible anchor coat layer 2 and overcoat layer 4 with a hardness of 0.3 GPa or less, as measured by nanoindentation in the thickness-direction cross-section of the laminate 10, it is preferable to use a resin material whose elongation at the break point, measured in accordance with JIS K7161 at 20°C and 65% RH, is preferably 150% or more, more preferably 200% or more, when forming the anchor coat layer 2 and overcoat layer 4.

<Packaging bag>
Figure 2 is a perspective view showing a gusset bag 20 made of a laminate 10. The packaging bag is manufactured by sealing the opening at the top of the gusset bag 20. The gusset bag 20 has folded sections (folded sections B1 and B2) where the laminate 10 is folded. Folded section B1 is where the laminate 10 is valley-folded when viewed from the innermost layer side, while folded section B2 is where the laminate 10 is mountain-folded when viewed from the innermost layer side.

The packaging bag may be formed by folding a single laminate in half so that the overcoat layers 4 face each other, then folding it appropriately to the desired shape and heat-sealing it, or by stacking two laminates so that the overcoat layers 4 face each other and then heat-sealing them to form a bag.

In the packaging bag according to this embodiment, the heat seal strength may be 2N or higher, and may be 4N or higher. While there is no particular upper limit to the heat seal strength, it may be, for example, 10N or lower.

The packaging bag can contain contents such as food and pharmaceuticals. It is particularly suitable for containing confectionery and similar items. The packaging bag according to this embodiment maintains high gas barrier and oil resistance even when it has a folded portion.

In this embodiment, a gusseted bag was given as an example of a packaging bag. However, the laminate according to this embodiment may also be used to produce, for example, pillow bags, three-sided sealed bags, or standing pouches.

The present disclosure will be further described below with reference to examples, but the disclosure is not limited to these examples.

<Fabrication of laminates>
(Example 1)
A paper substrate having a 5 μm thick clay coat layer (total thickness including the clay coat layer: 55 μm) was coated onto the clay coat layer side surface using a bar coater with an aqueous dispersion of polyolefin containing a carboxyl group salt (manufactured by Sumitomo Seika Co., Ltd., trade name: Zychsen AC, particle size: less than 0.2 μm, solvent: water/IPA = 1/1 (mass ratio), solid content concentration: 22.5% by mass), and dried in an oven to form a 3 μm thick anchor coat layer.

Next, Al deposition was performed on the anchor coat layer using a vacuum deposition method to form a 50 nm thick Al deposition layer (aluminum deposition layer). The pressure inside the deposition chamber during aluminum deposition was adjusted to the values shown in Table 1.

Next, an aqueous dispersion of polyolefin containing a carboxyl group salt (manufactured by Mitsui Chemicals, Inc., product name: Chemipearl S100, particle size: less than 0.1 μm, solvent: water/IPA = 1/1 (mass ratio), solid content concentration: 20.0% by mass) was coated onto the Al vapor-deposited layer using a bar coater and dried in an oven to form a 3 μm thick overcoat layer. This obtained a laminate.

(Example 2)
A laminate was obtained in the same manner as in Example 1, except that the pressure inside the deposition chamber when forming the Al deposition layer was changed to the value shown in Table 1.

(Example 3)
A laminate was obtained in the same manner as in Example 1, except that the paper substrate was changed to a paper substrate having a clay coat layer with a thickness of 5 μm (thickness including the clay coat layer: 50 μm).

(Example 4)
A laminate was obtained in the same manner as in Example 1, except that the anchor coat layer was formed by the following method. Specifically, an aqueous dispersion of polyolefin containing a carboxyl group salt (manufactured by Mitsui Chemicals, Inc., trade name: Chemipearl S100, particle size: less than 0.1 μm, solvent: water/IPA = 1/1 (mass ratio), solid content concentration: 20.0 mass%) was applied to the clay coat layer side surface of a paper substrate (thickness including the clay coat layer: 55 μm) using a bar coater, and dried in an oven to form an anchor coat layer with a thickness of 3 μm.

(Example 5)
A laminate was obtained in the same manner as in Example 1, except that the overcoat layer was formed by the following method. Specifically, an aqueous dispersion of polyolefin containing a carboxyl group salt (manufactured by Mitsui Chemicals, Inc., trade name: Chemipearl S500, particle size: 0.7 μm, solvent: water/IPA = 1/1 (mass ratio), solid content concentration: 20.0 mass%) was coated onto the Al vapor-deposited layer with a bar coater and dried in an oven to form an overcoat layer with a thickness of 3 μm.

(Examples 6-7)
A laminate was obtained in the same manner as in Example 1, except that the pressure inside the deposition chamber when forming the Al deposition layer was changed to the value shown in Table 1, and the thickness of the Al deposition layer was changed to the value shown in Table 1.

(Example 8)
A laminate was obtained in the same manner as in Example 1, except that the anchor coat layer was formed by the following method. Specifically, a solution of polyvinyl alcohol (PVA) resin with a degree of saponification of 98% and a degree of polymerization of 500 dissolved in a solvent of water/IPA = 8/2 (mass ratio) at a solid content concentration of 10% by mass was applied to the surface on the clay coat side of a paper substrate (thickness including the clay coat layer: 55 μm) using a bar coater, and dried in an oven to form an anchor coat layer with a thickness of 3 μm.

(Example 9)
A laminate was obtained in the same manner as in Example 8, except that the pressure inside the deposition chamber when forming the Al deposition layer was changed to the value shown in Table 2.

(Comparative Examples 1-2)
A laminate was obtained in the same manner as in Example 1, except that the pressure inside the deposition chamber when forming the Al deposition layer was changed to the value shown in Table 2.

(Comparative Example 3)
A laminate was obtained in the same manner as in Example 8, except that the pressure inside the deposition chamber when forming the Al deposition layer was changed to the value shown in Table 2.

<Preparation of paper substrate>
The following clay-coated papers 1-3 and uncoated paper 4 were prepared as paper substrates.
Clay coated paper 1: When changing from a temperature of 40°C and relative humidity of 20% RH to a temperature of 40°C and relative humidity of 90% RH, the dimensional change rates are CD = 0.75%, MD = 0.13%, and basis weight: 60 g/ ^m².
Clay coated paper 2: When changing from a temperature of 40°C and relative humidity of 20% RH to a temperature of 40°C and relative humidity of 90% RH, the dimensional change rates were CD = 0.55%, MD = 0.07%, and basis weight: 60 g/ ^m².
Clay coated paper 3: When changing from a temperature of 40°C and relative humidity of 20% RH to a temperature of 40°C and relative humidity of 90% RH, the dimensional change rates were CD = 0.35%, MD = 0.15%, and basis weight: 60 g/ ^m².
Uncoated paper 4: When changing from a temperature of 40°C and relative humidity of 20% RH to a temperature of 40°C and relative humidity of 90% RH, the dimensional change rates were CD = 1.34%, MD = 0.03%, and basis weight: 62 g/ ^m².

<Fabrication of laminates>
(Example 10)
Clay-coated paper 1 was prepared as the paper substrate. An aqueous dispersion of polyolefin containing a carboxyl group salt (manufactured by Sumitomo Seika Co., Ltd., product name: Zychsen AC, particle size: less than 0.2 μm, solvent: water/IPA = 1/1 (mass ratio), solid content concentration: 22.5% by mass) was applied to the clay-coated surface of the paper substrate using a gravure coater, and dried in an oven to form an anchor coat layer with a thickness of 3 μm.

Next, an Al deposition layer was formed on the anchor coat layer using a roll-to-roll induction heating vacuum deposition apparatus. The pressure inside the deposition chamber and the thickness of the Al deposition layer were adjusted to the values shown in Table 3.

Next, an aqueous dispersion of polyolefin containing a carboxyl group salt (Mitsui Chemicals, Inc., product name: Chemipearl S100, particle size: less than 0.1 μm, solvent: water/IPA = 1/1 (mass ratio), solid content concentration: 20.0% by mass) was coated onto the Al vapor-deposited layer using a gravure coater and dried in an oven to form a 3 μm thick overcoat layer. This obtained a laminate.

(Example 11)
A laminate was obtained in the same manner as in Example 10, except that the paper substrate was changed to clay-coated paper 2, and the pressure inside the deposition chamber and the thickness of the Al deposition layer when forming the Al deposition layer were changed to the values shown in Table 3.

(Example 12)
A laminate was obtained in the same manner as in Example 10, except that the Al vapor deposition layer was formed by the following method. Specifically, the Al vapor deposition layer was formed on the anchor coat layer using a roll-to-roll EB heating type vacuum deposition apparatus. The pressure inside the deposition chamber and the thickness of the Al vapor deposition layer during Al deposition were adjusted to the values shown in Table 3.

(Example 13)
A laminate was obtained in the same manner as in Example 12, except that the paper substrate was changed to clay-coated paper 2.

(Example 14)
A laminate was obtained in the same manner as in Example 12, except that the paper substrate was changed to clay-coated paper 3.

(Example 15)
Clay-coated paper 2 was prepared as the paper substrate. A solution of polyvinyl alcohol (Kuraray Co., Ltd., product name: Poval 5-98) with a degree of saponification of 98% and a degree of polymerization of 500, dissolved in a water/IPA = 8/2 (mass ratio) solvent at a solid content concentration of 10% by mass, was applied to the surface of the clay-coated layer of the paper substrate using a gravure coater, and dried in an oven to form an anchor coat layer with a thickness of 4 μm.

Next, an Al deposition layer was formed on the anchor coat layer using a roll-to-roll EB heating type vacuum deposition apparatus. The pressure inside the deposition chamber and the thickness of the Al deposition layer were adjusted to the values shown in Table 3.

Next, an aqueous dispersion of polyolefin containing a carboxyl group salt (Mitsui Chemicals, Inc., product name: Chemipearl S500, particle size: 0.7 μm, solvent: water/IPA = 1/1 (mass ratio), solid content concentration: 20.0% by mass) was coated onto the Al vapor-deposited layer using a gravure coater and dried in an oven to form a 3 μm thick overcoat layer. This yielded a laminate.

(Example 16)
A laminate was obtained in the same manner as in Example 15, except that the paper substrate was changed to clay-coated paper 1, and the pressure inside the deposition chamber and the thickness of the Al deposition layer when forming the Al deposition layer were changed to the values shown in Table 3.

(Example 17)
Uncoated paper 4 was prepared as the paper substrate. A solution of polyvinyl alcohol (Kuraray Co., Ltd., product name: Poval 5-98) with a degree of saponification of 98% and a degree of polymerization of 500, dissolved in a water/IPA = 8/2 (mass ratio) solvent at a solid content concentration of 10% by mass, was applied to one surface of the paper substrate using a gravure coater and dried in an oven to form an anchor coat layer with a thickness of 3 μm.

Next, an Al deposition layer was formed on the anchor coat layer using a roll-to-roll EB heating type vacuum deposition apparatus. The pressure inside the deposition chamber and the thickness of the Al deposition layer were adjusted to the values shown in Table 4.

Next, an aqueous dispersion of ethylene-acrylic acid copolymer resin (MICHELMAN, product name: MC9100, solid content concentration: 20% by mass) was applied to the Al vapor-deposited layer using a gravure coater and dried in an oven to form a 3 μm thick overcoat layer. This yielded a laminate.

(Comparative Examples 4-6)
A laminate was obtained in the same manner as in Example 10, except that the pressure inside the deposition chamber and the thickness of the Al deposition layer were changed to the values shown in Table 4.

(Comparative Example 7)
A laminate was obtained in the same manner as in Example 12, except that the pressure inside the deposition chamber and the thickness of the Al deposition layer were changed to the values shown in Table 4.

(Comparative Example 8)
A laminate was obtained in the same manner as in Example 15, except that the pressure inside the deposition chamber and the thickness of the Al deposition layer were changed to the values shown in Table 4.

<Measurement of aluminum vapor deposition layer thickness>
The laminate was embedded in UV-curing resin, and a cross-sectional sample was prepared by cutting the cross-section using a cryomicrotome. The cross-section of this sample was observed with an electron microscope at a magnification of 50,000x, and SEM images were acquired. The thickness of the Al vapor deposition layer was measured from the obtained SEM images. The results are shown in Tables 1 to 4.

<X-ray diffraction measurement>
The full width at half maximum (FWHM) of the peak of the (111) crystal plane of aluminum in the Al-deposited layer was measured using the following procedure. An X-ray diffractometer (product name: ATX-G) manufactured by Rigaku Electric Co., Ltd. was used for the FWHM measurement. CuKα rays were used as the light source, the tube voltage was 50 kV, the tube current was 300 mA, the optical system was a parallel beam optical system, the scanning method was the 2θ/θ method, the measurement range was 30° to 50°, and the scanning speed was 2°/min. The sampling step was 0.02°, and the slits were S1: 10.0 mm × 1.0 mm, S2: 10.0 mm × 0.5 mm, and Solar (res): 0.4 mm. The laminates obtained in the examples and comparative examples were used as samples, and the paper substrate side was attached to a glass slide with double-sided tape for X-ray diffraction measurement. For the X-ray diffraction of aluminum, the FWHM of the peak at 2θ = 38.5° corresponding to the (111) plane (d = 2.34) was measured. The results are shown in Tables 1 to 4.

<Method for processing the cross-section of a sample>
Samples for measuring the hardness and composite modulus of the anchor coat layer and overcoat layer were prepared from the cross-sections of the laminates obtained in the examples and comparative examples using the following procedure. First, the laminate, including the anchor coat layer and overcoat layer, was cut with a razor blade so that it was in the shape of a strip or wedge, and the resulting sample was embedded in resin. D-800 photocurable resin manufactured by Toagosei Co., Ltd. was used as the embedding resin, and after embedding, it was cured by light irradiation. The cured sample embedding resin was fixed with an AFM sample holder insert, and trimming and cross-sectional cutting of the film were performed with a glass knife at room temperature (25°C). Cross-sectional cutting was then performed with a diamond knife at a cutting speed of 1.0 mm/second and a cutting film thickness of 200 nm until a mirror finish was achieved. The cross-sectional samples were used for measurement by nanoindentation while fixed with an AFM sample holder insert. A Leica EMUC7 ultramicrotome was used as the cross-sectional cutting device. The cutting direction was parallel to the layer interface.

<Measurement of hardness and composite modulus>
The hardness and composite modulus of the anchor coat layer and overcoat layer are expressed as those calculated using the nanoindentation method. The nanoindentation method is a measurement method that obtains the mechanical properties of a sample by performing a quasi-static indentation test on the target object. The measuring instrument used was the Hystron TI-Premier (product name) manufactured by Bruker Japan Co., Ltd. The indenter used was a Berkovich-type diamond indenter manufactured by Bruker Japan Co., Ltd. For the nanoindentation measurement, first, a shape image of the sample was obtained by scanning the cross-section of the sample with the diamond indenter, and the measurement position of the desired layer was specified. Then, at room temperature (25°C) in displacement control mode, the sample was indented to a depth of 80 nm at an indentation speed of 80 nm/second, held at the maximum depth for 1 second, and then unloaded at a speed of 80 nm/second. For the calculation method of hardness and composite modulus, a standard sample of fused silica was tested in advance, and the relationship between the contact depth and contact projected area between the indenter and the sample was calibrated. Subsequently, the unloading curve in the 60-95% range relative to the maximum load at unloading was analyzed using the Oliver-Pharr method, and the hardness and composite modulus were calculated. The results are shown in Tables 1 to 4.

<Measurement of elongation at the breaking point>
The elongation at the breaking point of the anchor coat layer and overcoat layer was measured by applying the coating liquid that forms the anchor coat layer and overcoat layer to the support substrate, drying it, peeling it off the support substrate, punching it into a 1A-type dumbbell shape to form a test specimen, and measuring it according to the method described in JIS K7161. An autograph testing machine AGS-X (manufactured by Shimadzu Corporation) was used as the apparatus, and the tensile test speed was set to 50 mm/min, and the measurements were taken in an environment of 20°C and 65% humidity. The results are shown in Tables 1 to 4.

<Measurement of KIT value>
The oil resistance (KIT value) of the surface on the overcoat layer side of the laminates obtained in the examples and comparative examples was measured using the TAPPI UM-557 method (KIT method). In addition, a fold parallel to the MD direction was made in the laminate by rolling a 1500g roller at a speed of 300mm/min so that the laminate was valley-folded when viewed from the paper substrate side (so that the overcoat layer was on the outside), and the oil resistance (KIT value) of the folded portion of the laminate after unfolding was measured in the same way. The KIT value is shown on a scale from 0 to 12, with higher numbers indicating higher oil resistance. The highest oil resistance score given by the KIT test solution that did not show penetration was used as the evaluation result. A KIT value of 6 or higher is preferable; if it is lower than 6, it may not satisfy the oil resistance requirements for food packaging. The results are shown in Tables 1 to 4.

<Measurement of water vapor transmission rate>
The water vapor transmission rate (g/ ^m² /day) of the laminates obtained in the examples and comparative examples was measured using the MOCON method in accordance with JIS K7129-2, under an atmosphere of 40°C and 90% RH. A water vapor transmission rate analyzer (MOCON Corporation, product name: PERMATRAN-W3/34G) was used for the measurement. Furthermore, the laminates were stored in a constant temperature and humidity chamber at 40°C and 90% RH for one week, and the same measurement was performed. The initial and post-storage water vapor transmission rates are shown in Tables 1 to 4.

As shown in Tables 1 to 4, the laminates of the examples exhibited good oil resistance (KIT value) not only initially but also after bending. Furthermore, as shown in Tables 1 to 4, the laminates of the examples maintained a water vapor transmission rate of 6 g/ ^m² /d or less even after storage at 40°C and 90% RH for one week, confirming that they could maintain good water vapor barrier properties.

1…Paper substrate, 2…Anchor coat layer, 3…Aluminum vapor-deposited layer, 4…Overcoat layer, 10…Laminate, 20…Gusseted bag, B1, B2…Folded section.

Claims (5)

A laminate having a structure in which at least a paper substrate, an anchor coat layer, and an aluminum vapor deposition layer are laminated in this order,
The aluminum vapor-deposited layer has a heat-sealable layer on its surface,
The aluminum vapor-deposited layer has a full width at half maximum of the peak of the (111) crystal plane of aluminum in X-ray diffraction measurements of 1.6° or more and 15.0° or less.
A laminate in which the anchor coat layer contains a polyolefin or polyvinyl alcohol-based resin having polar groups. The laminate according to claim 1, wherein the hardness of the anchor coat layer, as measured by nanoindentation in a cross-section in the thickness direction of the laminate, is 0.3 GPa or less. The laminate according to claim 1, wherein the thickness of the aluminum vapor-deposited layer is 20 nm or more and 100 nm or less. The laminate according to claim 1, wherein the thickness of the paper substrate is 20 μm or more and 100 μm or less. The laminate according to claim 1, wherein the aluminum vapor-deposited layer is in contact with a resin layer containing an ionomer or a polyvinyl alcohol-based resin with a saponification degree of 95% or more.