JP7815815B2 - Laminate and packaging container - Google Patents

Description

This disclosure relates to a laminate and a packaging container.

Conventionally, resin films made of polyesters such as polyethylene terephthalate (hereinafter also referred to as "polyester films") have been used as base materials for packaging materials due to their excellent mechanical properties, chemical stability, heat resistance, and transparency, as well as their low cost (see, for example, Patent Document 1).

The polyester film is, for example, laminated with a polyethylene film that functions as a heat-seal layer. Packaging containers are produced using packaging materials made from the laminate thus obtained. However, packaging containers made from polyester film and polyethylene film are generally difficult to separate into the individual films. Therefore, such packaging containers are not suitable for recycling after use, and are not actively recycled at present.

In light of this current situation, efforts are being made to create mono-material packaging containers with the aim of improving the recyclability of packaging containers. For example, instead of polyester film, consideration is being given to packaging materials made from laminates that use stretched polyethylene film (hereinafter also referred to as "stretched polyethylene film") as the base material, and a polyethylene film made from the same resin material as the heat-sealable layer.

Japanese Patent Application Laid-Open No. 2005-053223

When using stretched polyethylene film as the base material of a packaging material instead of a heat-resistant film such as polyester film, it is desirable to perform heat sealing at a low temperature to prevent thermal degradation of the base material during heat sealing. Conventionally, polyethylene film has been used as a heat-sealing layer. However, conventional heat-sealing layers have not been able to achieve sufficient heat-sealing strength when heat-sealed at low temperatures. Furthermore, when improving heat resistance by using a multilayer polyethylene base material, the hand-tearability (tearability) of the resulting laminate has been reduced. Furthermore, when laminating the base material and heat-sealing layer via an adhesive, the drying process of the adhesive after application must also be performed at a low temperature or for a short time to prevent thermal degradation of the base material. In such cases, the solvent contained in the adhesive remains in the laminate, and a solvent odor can occur when packaging bags are made using the laminate.

The problem to be solved by this disclosure is to provide a laminate comprising a substrate made of polyethylene and a heat seal layer, which has good heat seal strength and tearability, and has a reduced solvent odor.

The laminate of the present disclosure is a laminate comprising a substrate and a heat seal layer,
the substrate is a polyethylene multilayer substrate that has been subjected to a stretching treatment;
The heat seal layer is
The film includes at least a first layer and a second layer,
the first layer contains an ethylene-α-olefin copolymer;
The melting point of the first layer is 112°C or less,
the second layer comprises polyethylene;
The melting point of the second layer is 114°C or higher;
The surface layer on one side of the laminate is a first layer of the heat seal layer,
The substrate and the heat seal layer are laminated via an adhesive layer,
The adhesive layer is made of a solventless adhesive.

This disclosure provides a laminate comprising a substrate and a heat seal layer made of polyethylene, which has excellent heat seal strength and tearability while using the same material (monomaterial) throughout the laminate, and has a reduced solvent odor.

FIG. 1 is a cross-sectional schematic view of one embodiment of a laminate of the present disclosure. FIG. 2 is a cross-sectional schematic view of one embodiment of a substrate constituting the laminate of the present disclosure. FIG. 3 is a cross-sectional schematic diagram of one embodiment of a heat seal layer that constitutes a laminate of the present disclosure. FIG. 4 is a cross-sectional schematic view of another embodiment of a heat seal layer. FIG. 5 is a cross-sectional schematic view of another embodiment of a heat seal layer. FIG. 6 is a cross-sectional schematic view of another embodiment of a heat seal layer. FIG. 7 is a cross-sectional schematic view of another embodiment of a heat seal layer. FIG. 8 is a perspective view of one embodiment of a stand-up pouch. FIG. 9 is a perspective view of another embodiment of a standing pouch. FIG. 10 is a top view of another embodiment of a standing pouch.

The following describes an embodiment of the present invention. In the drawings accompanying this specification, the scale and aspect ratios have been appropriately changed and exaggerated from those of the actual objects for the sake of ease of illustration and understanding.
As used in this specification, terms such as "orthogonal" and "identical" that specify shapes, geometric conditions, and their degrees, as well as values of lengths and angles, are not limited to their strict meanings but are interpreted to include a range within which similar functions can be expected.

The terms used in this disclosure are explained below.
"Polyethylene" refers to a polymer in which the content of ethylene-derived structural units is 50 mol% or more of all repeating structural units. In this polymer, the content of ethylene-derived structural units is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more. The content is measured by nuclear magnetic resonance (NMR) spectroscopy.

The density of the high density polyethylene is preferably greater than 0.945 g/cm ^3. The upper limit of the density of the high density polyethylene is, for example, 0.965 g/cm ³ .
The density of the medium density polyethylene is preferably greater than 0.925 g/cm ³ and not greater than 0.945 g/cm ³ .
The density of the low density polyethylene is preferably greater than 0.900 g/cm ³ and not greater than 0.925 g/cm ³ .
The density of the linear low-density polyethylene is preferably more than 0.900 g/cm ³ and not more than 0.925 g/cm ³ .
The density of the very low density polyethylene is preferably 0.900 g/cm ³ or less. The lower limit of the density of the very low density polyethylene is, for example, 0.860 g/cm ³ .
The density of polyethylene is measured in accordance with Method B (pycnometer method) or Method D (density gradient tube method) of JIS K7112 (1999). Method B or Method D is selected appropriately depending on the shape and mass of the test piece to be measured. In Method D, the measurement temperature (liquid temperature) is 23°C.

[Laminate]
The laminate of the present disclosure will be described with reference to the drawings.
1 shows one embodiment of a laminate of the present disclosure. The laminate 1 includes a substrate 10 and a heat seal layer 20. The substrate 10 and the heat seal layer 20 are laminated together via an adhesive layer 30. The laminate 1 may further include a printed layer (not shown) on the substrate 10 as needed. The printed layer is usually formed on the surface of the substrate 10 facing the heat seal layer 20.

In one embodiment, the substrate 10 constituting the laminate of the present disclosure is, as shown in FIG.
a first layer 11 containing medium density polyethylene and high density polyethylene;
a second layer 12 containing medium density polyethylene and linear low density polyethylene;
a third layer 13 containing linear low density polyethylene;
a fourth layer 14 containing medium density polyethylene and linear low density polyethylene;
The fifth layer 15 contains medium-density polyethylene and high-density polyethylene in this order in the thickness direction, and is stretched.
Hereinafter, the polyethylene multilayer substrate will also be simply referred to as "multilayer substrate."

In one embodiment, the surface layer on one side of the multilayer substrate 10 is the first layer 11, and the surface layer on the other side of the multilayer substrate 10 is the fifth layer 15. The multilayer substrate 10 may include other layers between the first to fifth layers, but in one embodiment, the multilayer substrate consists only of the first to fifth layers.

Furthermore, as shown in FIG. 3, the heat seal layer 20 constituting the laminate of the present disclosure comprises at least a first layer 21 and a second layer 22. The first layer 21 contains an ethylene-α-olefin copolymer and has a melting point of 112°C or less. The second layer 22 contains polyethylene and has a melting point of 114°C or more.

The heat seal layer may further include a third layer. The third layer contains polyethylene and is a layer that does not fall under the first or second layer.

The surface layer on one side of the laminate is the first layer 21 of the heat-seal layer 20. In one embodiment, when a packaging container is produced using a packaging material made of the laminate of the present disclosure, the first layer 21 of the heat-seal layer 20 is the layer that faces the contents to be placed in the packaging container.

In one embodiment of the laminate of the present disclosure, the substrate and the heat seal layer are made of the same resin material, polyethylene. That is, in one embodiment, the substrate is made of polyethylene, and the heat seal layer is made of the same resin material, polyethylene, as the resin material constituting the substrate. By using a laminate having such a configuration, for example, it is possible to produce a packaging container with excellent recyclability.

The polyethylene content of the entire laminate of the present disclosure is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more. Because such laminates use polyethylene, a homogeneous resin material, they can be classified as monomaterial materials and are suitable for use, for example, in the production of monomaterial packaging containers. Each layer constituting the laminate of the present disclosure is described below.

[Polyethylene multilayer base material]
In one embodiment, the polyethylene multilayer substrate comprises:
a first layer containing medium density polyethylene and high density polyethylene;
a second layer containing medium density polyethylene and linear low density polyethylene;
a third layer containing linear low density polyethylene;
a fourth layer containing medium density polyethylene and linear low density polyethylene;
and a fifth layer containing medium density polyethylene and high density polyethylene, in this order in the thickness direction.

<First Layer and Fifth Layer>
The first layer contains one or more medium density polyethylenes and one or more high density polyethylenes.
The fifth layer contains one or more medium density polyethylenes and one or more high density polyethylenes.
The layer containing medium-density polyethylene has the heat resistance required for printing and heat sealing, and also contributes to improving the stretchability of the laminate, which is the precursor of the multilayer substrate.

The medium-density polyethylene contained in the first layer and the medium-density polyethylene contained in the fifth layer may be the same or different, but from the viewpoint of facilitating the production of the multilayer base material, it is preferable that they are the same.
The high-density polyethylene contained in the first layer and the high-density polyethylene contained in the fifth layer may be the same or different, but from the viewpoint of facilitating the production of the multilayer base material, it is preferable that they are the same.

The first layer and the fifth layer may each independently contain, in addition to the medium-density polyethylene and the high-density polyethylene, a polyethylene other than these polyethylenes. Examples of polyethylene other than the medium-density polyethylene and the high-density polyethylene include low-density polyethylene (high-pressure low-density polyethylene), linear low-density polyethylene, and ultra-low-density polyethylene. From the viewpoint of further improving the ink adhesion and heat resistance of the multilayer substrate, it is preferable that the first layer contains only medium-density polyethylene and high-density polyethylene as the polyethylene. From the viewpoint of further improving the ink adhesion and heat resistance of the multilayer substrate, it is preferable that the fifth layer contains only medium-density polyethylene and high-density polyethylene as the polyethylene.

The mass ratio of the medium-density polyethylene to the high-density polyethylene (medium-density polyethylene/high-density polyethylene) in the first layer and the fifth layer is preferably 1.1 or more and 5 or less, more preferably 1.5 or more and 3 or less, thereby further improving the balance between ink adhesion and heat resistance.
The total content of the medium-density polyethylene and the high-density polyethylene in the first layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, thereby further improving the ink adhesion and heat resistance of the multilayer substrate.
The total content of the medium-density polyethylene and the high-density polyethylene in the fifth layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, thereby further improving the ink adhesion and heat resistance of the multilayer substrate.

The thickness of each of the first layer and the fifth layer is preferably 0.5 μm or more and 10 μm or less, more preferably 1 μm or more and 8 μm or less, and even more preferably 1 μm or more and 5 μm or less. This further improves the ink adhesion and heat resistance of the multilayer substrate.

The thickness of each of the first layer and fifth layer is preferably smaller than the total thickness of the second layer, third layer, and fourth layer (hereinafter, the second to fourth layers will be collectively referred to as the "multilayer intermediate layer"). The ratio of the thickness of each of the first layer and fifth layer to the total thickness of the multilayer intermediate layer (first layer or fifth layer/multilayer intermediate layer) is preferably 0.05 or more and 0.8 or less, more preferably 0.1 or more and 0.7 or less, and even more preferably 0.1 or more and 0.4 or less. This further improves the rigidity, strength, and heat resistance of the multilayer substrate.

<Second Layer and Fourth Layer>
The second layer contains one or more medium density polyethylenes and one or more linear low density polyethylenes.
The fourth layer contains one or more medium density polyethylenes and one or more linear low density polyethylenes.
The second layer and the fourth layer each contribute to improving the stretchability of the laminate, which is the precursor of the multi-layer substrate.

The medium-density polyethylene contained in the second layer and the medium-density polyethylene contained in the fourth layer may be the same or different, but from the viewpoint of facilitating the production of the multilayer base material, it is preferable that they are the same.
The linear low-density polyethylene contained in the second layer and the linear low-density polyethylene contained in the fourth layer may be the same or different, and from the viewpoint of facilitating the production of the multilayer base material, it is preferable that they are the same.
The medium density polyethylene contained in the second layer and the fourth layer may be the same as or different from the medium density polyethylene contained in the first layer and the fifth layer.

The second layer and the fourth layer may each independently contain, in addition to the medium-density polyethylene and linear low-density polyethylene, a polyethylene other than these polyethylenes. Examples of polyethylene other than medium-density polyethylene and linear low-density polyethylene include high-density polyethylene, low-density polyethylene (high-pressure low-density polyethylene), and ultra-low-density polyethylene. From the viewpoint of further improving the stretchability of the laminate, which is the precursor to the multilayer substrate, it is preferable that the second layer contains only medium-density polyethylene and linear low-density polyethylene as the polyethylene. From the viewpoint of further improving the stretchability of the laminate, which is the precursor to the multilayer substrate, it is preferable that the fourth layer contains only medium-density polyethylene and linear low-density polyethylene as the polyethylene.

The mass ratio of the medium-density polyethylene to the linear low-density polyethylene in the second layer and the fourth layer (medium-density polyethylene/linear low-density polyethylene) is preferably 0.25 or more and 4 or less, more preferably 0.4 or more and 2.4 or less, respectively, thereby further improving the balance between heat resistance, rigidity, and stretchability.
The total content of the medium-density polyethylene and the linear low-density polyethylene in the second layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, thereby further improving the stretchability of the precursor laminate.
The total content of the medium-density polyethylene and the linear low-density polyethylene in the fourth layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, thereby further improving the stretchability of the precursor laminate.

The thickness of each of the second layer and the fourth layer is preferably 0.5 μm or more and 15 μm or less, more preferably 1 μm or more and 10 μm or less, and even more preferably 1 μm or more and 8 μm or less. This further improves the stretchability of the precursor laminate.

<Third Layer>
The third layer contains one or more linear low-density polyethylenes, and contributes to improving the stretchability of the laminate, which is a precursor to the multilayer substrate.

The linear low-density polyethylene contained in the third layer may be the same as or different from the linear low-density polyethylene contained in the second and fourth layers.

The third layer may further contain, in addition to the linear low-density polyethylene, another polyethylene other than linear low-density polyethylene. Examples of other polyethylenes other than linear low-density polyethylene include high-density polyethylene, medium-density polyethylene, low-density polyethylene (high-pressure low-density polyethylene), and ultra-low-density polyethylene. From the viewpoint of further improving the stretchability of the laminate, which is the precursor to the multilayer substrate, it is preferable that the third layer contain only linear low-density polyethylene as the polyethylene.

The content of linear low-density polyethylene in the third layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. This further improves the balance between heat resistance, rigidity, and extensibility.

The thickness of the third layer is preferably 1 μm or more and 50 μm or less, more preferably 2 μm or more and 40 μm or less, and even more preferably 5 μm or more and 30 μm or less. This allows for a better balance of heat resistance, rigidity, and extensibility.

The ratio of the total thickness of the second and fourth layers to the thickness of the third layer (total thickness of the second and fourth layers / thickness of the third layer) is preferably 0.1 to 10, more preferably 0.2 to 5, and even more preferably 0.5 to 2. This further improves the rigidity, strength, and heat resistance of the multilayer substrate.

The first to fifth layers constituting the multilayer substrate may each independently contain one or more additives. Examples of additives include crosslinkers, antioxidants, antiblocking agents, slip agents, UV absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, and modifying resins.

In one embodiment, in the multilayer substrate of the present disclosure, the density of the polyethylene in the second layer is lower than the density of the polyethylene in the first layer, the density of the polyethylene in the third layer is lower than the density of the polyethylene in the second layer, the density of the polyethylene in the fourth layer is higher than the density of the polyethylene in the third layer, and the density of the polyethylene in the fifth layer is higher than the density of the polyethylene in the fourth layer. A multilayer substrate having this configuration has an excellent balance of ink adhesion, heat resistance, and manufacturability (stretchability of the precursor laminate).

When one layer contains multiple types of polyethylene (n types; n is an integer of 2 or more) with different densities, the average density _Dav calculated according to the following formula (1) is taken as the density of the polyethylene constituting the layer.
D _av = ΣW _i ×D _i …(1)
In formula (1), Σ means taking the sum of W _i × D _i for i from 1 to n, where n is an integer of 2 or more, W _i represents the mass fraction of the i-th polyethylene, and D _i represents the density (g/cm ³ ) of the i-th polyethylene.

When any adjacent layers selected from the first to fifth layers in a multilayer substrate are referred to as layer (1) and layer (2), the absolute value of the difference between the density of the polyethylene constituting layer (1) and the density of the polyethylene constituting layer (2) is preferably 0.030 g/cm or less, more preferably ^0.025 g/cm ^or less, and even more preferably 0.020 g/cm ^or less. Hereinafter, this requirement is also referred to as the "density difference requirement." In other words, it is preferable that any pair of adjacent layers in the thickness direction selected from the first to fifth layers included in the multilayer substrate (e.g., the pair of the first layer and the second layer, the pair of the second layer and the third layer, the pair of the third layer and the fourth layer, and the pair of the fourth layer and the fifth layer) satisfy the density difference requirement.
In the following description, density differences always refer to absolute values of the differences.

A multilayer substrate that meets the above density difference requirements has a small density difference between the first through fifth layers, as described above. Therefore, a multilayer substrate that meets the above density difference requirements exhibits high interlayer strength.

The polyethylene multilayer substrate may be the substrate described above, or may be the substrate of the embodiments described below. Hereinafter, a layer containing 80% or more by weight of polyethylene will be referred to as a "polyethylene layer." For example, a layer containing 80% or more by weight of high-density polyethylene will be referred to as a "high-density polyethylene layer."

Examples of polyethylene include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, and very low-density polyethylene. From the viewpoint of the strength and heat resistance of the multilayer substrate, high-density polyethylene and medium-density polyethylene are preferred, and from the viewpoint of stretchability, medium-density polyethylene is preferred.

The multilayer substrate may contain one or more resin materials other than polyethylene. Examples of such resin materials include polyolefins such as polypropylene, (meth)acrylic resins, vinyl resins, cellulose resins, polyamides, polyesters, and ionomer resins. From the perspective of recyclability, it is particularly preferable that the multilayer substrate does not contain any resin materials other than polyethylene.

The multilayer substrate has a structure of two or more layers. In one embodiment, the number of layers in the multilayer substrate is from two to seven, for example, from three to seven, or from three to five. The number of layers in the multilayer substrate is preferably an odd number, for example, three, five, or seven. By having the substrate have a multilayer structure, the balance between rigidity, strength, heat resistance, printability, and stretchability can be improved. Each layer of the multilayer substrate is preferably composed of polyethylene.

The multilayer substrate of the first embodiment comprises a high-density polyethylene layer and a medium-density polyethylene layer in this order in the thickness direction. Having the surface resin layer of the substrate be a high-density polyethylene layer can improve, for example, the strength and heat resistance of the substrate. Having the substrate comprise a medium-density polyethylene layer can improve, for example, the stretchability of the pre-stretch laminate.

The multilayer substrate of the second embodiment comprises a high-density polyethylene layer, a medium-density polyethylene layer, and a high-density polyethylene layer, in that order in the thickness direction. This configuration can, for example, improve the strength and heat resistance of the substrate, suppress curling in the substrate, and improve the stretchability of the pre-stretch laminate.

In the multilayer substrates of the first and second embodiments, the thickness of the high-density polyethylene layer is preferably equal to or less than the thickness of the medium-density polyethylene layer. The ratio of the thickness of the high-density polyethylene layer to the thickness of the medium-density polyethylene layer is preferably 0.1 or more and 1 or less, more preferably 0.2 or more and 0.5 or less.

The multilayer substrate of the third embodiment comprises, in this order in the thickness direction, a high-density polyethylene layer, a medium-density polyethylene layer, a low-density polyethylene layer, a linear low-density polyethylene layer or an ultra-low-density polyethylene layer (for simplicity, these three layers are collectively referred to as the "low-density polyethylene layer, etc."), a medium-density polyethylene layer, and a high-density polyethylene layer. This configuration can, for example, improve the stretchability of the pre-stretch laminate, improve the strength and heat resistance of the substrate, and suppress curling in the substrate.

In the multilayer substrate of the third embodiment, the thickness of the high-density polyethylene layer is preferably equal to or less than the thickness of the medium-density polyethylene layer. The ratio of the thickness of the high-density polyethylene layer to the thickness of the medium-density polyethylene layer is preferably 0.1 or more and 1 or less, more preferably 0.2 or more and 0.5 or less.

In the multilayer substrate of the third embodiment, the thickness of the high-density polyethylene layer is preferably equal to or greater than the thickness of the low-density polyethylene layer, etc. The ratio of the thickness of the high-density polyethylene layer to the thickness of the low-density polyethylene layer, etc. is preferably 1 or more and 4 or less, more preferably 1 or more and 2 or less.

Other embodiments of the multilayer substrate include a substrate comprising, in the thickness direction, a high-density polyethylene layer, a high-density polyethylene layer, a blend layer of medium-density polyethylene and high-density polyethylene, a high-density polyethylene layer, and a high-density polyethylene layer, in that order; and a substrate comprising, in the thickness direction, a medium-density polyethylene layer, a high-density polyethylene layer, a linear low-density polyethylene layer, a high-density polyethylene layer, and a medium-density polyethylene layer, in that order.

Another example is a substrate having, in the thickness direction, a high-density polyethylene layer, a blend layer of high-density polyethylene and medium-density polyethylene, a low-density polyethylene layer, a blend layer of high-density polyethylene and medium-density polyethylene, and a high-density polyethylene layer, in this order.

<Method of manufacturing stretched multilayer substrate>
The multilayer substrate of the present disclosure can be produced by, for example, forming a laminate from multiple polyethylene materials by an inflation method or a T-die method, and then stretching the resulting laminate. Stretching can improve the transparency, rigidity, strength, and heat resistance of the multilayer substrate, making it suitable for use as a base material for packaging materials, for example.

The multilayer substrate can be obtained, for example, by stretching a laminate (precursor) having, in the thickness direction, a layer containing medium-density polyethylene and high-density polyethylene, a layer containing medium-density polyethylene and linear low-density polyethylene, a layer containing linear low-density polyethylene, a layer containing medium-density polyethylene and linear low-density polyethylene, and a layer containing medium-density polyethylene and high-density polyethylene, in that order.

Specifically, a laminate can be produced by co-extruding from the outside a layer containing medium-density polyethylene and high-density polyethylene, a layer containing medium-density polyethylene and linear low-density polyethylene, a layer containing linear low-density polyethylene, a layer containing medium-density polyethylene and linear low-density polyethylene, and a layer containing medium-density polyethylene and high-density polyethylene into a tubular shape. Alternatively, a laminate can be produced by co-extruding from the outside a layer containing medium-density polyethylene and high-density polyethylene, a layer containing medium-density polyethylene and linear low-density polyethylene, and a layer containing linear low-density polyethylene into a tubular shape, and then pressing the opposing layers containing linear low-density polyethylene together using a rubber roll or the like. By producing a laminate using this method, the number of defective products can be significantly reduced and production efficiency can be improved.
The multilayer substrates of other embodiments can be produced in the same manner.

When producing a laminate using the T-die method, the melt flow rate (MFR) of the polyethylene constituting each layer is preferably 3 g/10 min or more and 20 g/10 min or less, from the viewpoints of film-forming properties and the processability of the multilayer substrate.

When producing a laminate using the inflation method, the MFR of the polyethylene constituting each layer is preferably 0.5 g/10 min or more and 5 g/10 min or less, from the viewpoints of film-forming properties and the processability of the multilayer substrate.

The multilayer substrate of the present disclosure can be obtained, for example, by stretching the laminate described above. Note that the laminate can also be stretched in an inflation film-making machine. This allows for the production of a multilayer substrate, further improving production efficiency.

The multilayer substrate of the present disclosure may be a uniaxially stretched film or a biaxially stretched film. In one embodiment, the multilayer substrate is a uniaxially stretched film, more specifically, a uniaxially stretched film that has been stretched in the machine direction (MD).

In one embodiment, the stretching ratio in the longitudinal direction (MD) of the multilayer substrate is preferably 2 to 10 times, and more preferably 3 to 7 times. In one embodiment, the stretching ratio in the transverse direction (TD) of the multilayer substrate is preferably 2 to 10 times, and more preferably 3 to 7 times.

When the stretching ratio is 2x or more, for example, the rigidity, strength, and heat resistance of the multilayer substrate can be improved, the ink adhesion to the multilayer substrate can be improved, and the transparency of the multilayer substrate can be improved. When the stretching ratio is 10x or less, the laminate can be stretched well.

The haze value of the multilayer substrate is preferably 25% or less, more preferably 15% or less, and even more preferably 10% or less. A smaller haze value is preferable, but in one embodiment, the lower limit may be 0.1% or 1%. The haze value of the multilayer substrate is measured in accordance with JIS K7136.

The polyethylene content in the multi-layer substrate is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. This improves the recyclability of the multi-layer substrate.

It is preferable that the multilayer substrate be surface-treated. This improves adhesion between the surface layer of the multilayer substrate and the layers laminated on the multilayer substrate. Surface treatment methods include, for example, physical treatments such as corona discharge treatment, ozone treatment, low-temperature plasma treatment using gases such as oxygen gas and nitrogen gas, and glow discharge treatment; and chemical treatments such as oxidation treatment using chemicals.

The total thickness of the multilayer substrate is preferably 10 μm or more and 60 μm or less, more preferably 15 μm or more and 50 μm or less. A thickness of 10 μm or more improves the rigidity and strength of the multilayer substrate. A thickness of 60 μm or less improves the processability of the multilayer substrate.

In this disclosure, polyethylene includes, for example, ethylene homopolymers and copolymers of ethylene with other monomers. Examples of other monomers include α-olefins having 3 to 20 carbon atoms, vinyl acetate, and (meth)acrylic acid esters. Examples of α-olefins having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 3-methyl-1-butene, 4-methyl-1-pentene, and 6-methyl-1-heptene. Examples of (meth)acrylic acid esters include alkyl (meth)acrylates such as methyl (meth)acrylate and ethyl (meth)acrylate.

Examples of the copolymer include a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms, a copolymer of ethylene and at least one selected from vinyl acetate and (meth)acrylic acid esters, and a copolymer of ethylene, an α-olefin having 3 to 20 carbon atoms, and at least one selected from vinyl acetate and (meth)acrylic acid esters.

Polyethylenes with different densities or branching can be obtained by appropriately selecting the polymerization method. For example, it is preferable to use a multi-site catalyst such as a Ziegler-Natta catalyst or a single-site catalyst such as a metallocene catalyst as the polymerization catalyst, and to carry out polymerization in one stage or two or more stages using any of gas phase polymerization, slurry polymerization, solution polymerization, and high-pressure ionic polymerization.

A single-site catalyst is a catalyst capable of forming a uniform active species, and is typically prepared by contacting a metallocene transition metal compound or a non-metallocene transition metal compound with an activating cocatalyst. Compared to multi-site catalysts, single-site catalysts have a uniform active site structure, making them preferable because they can produce polymers with high molecular weights and highly uniform structures.

A metallocene catalyst is preferred as a single-site catalyst. A metallocene catalyst is a catalyst containing a transition metal compound of Group IV of the periodic table that contains a ligand having a cyclopentadienyl skeleton, a cocatalyst, optionally an organometallic compound, and optionally a support.

Examples of transition metals in the transition metal compound include zirconium, titanium, and hafnium, with zirconium and hafnium being preferred.

The cyclopentadienyl skeleton in the transition metal compound is a cyclopentadienyl group or a substituted cyclopentadienyl group. The substituted cyclopentadienyl group has at least one substituent selected from, for example, a hydrocarbon group having 1 to 30 carbon atoms, a silyl group, a silyl-substituted alkyl group, a silyl-substituted aryl group, a cyano group, a cyanoalkyl group, a cyanoaryl group, a halogen group, a haloalkyl group, and a halosilyl group. The substituted cyclopentadienyl group has one or more substituents, and the substituents may be bonded to each other to form a ring, such as an indenyl ring, a fluorenyl ring, an azulenyl ring, or a hydrogenated version thereof. The ring formed by bonding the substituents to each other may further have a substituent.

Transition metal compounds typically have two ligands having a cyclopentadienyl skeleton. The ligands having each cyclopentadienyl skeleton are preferably bonded to each other via a bridging group. Examples of bridging groups include alkylene groups having 1 to 4 carbon atoms, silylene groups, substituted silylene groups such as dialkylsilylene groups and diarylsilylene groups, and substituted germylene groups such as dialkylgermylene groups and diarylgermylene groups. Among these, substituted silylene groups are preferred.

A co-catalyst is a component that enables a transition metal compound of Group IV of the periodic table to function effectively as a polymerization catalyst, or a component that balances the ionic charge in a catalytically activated state. Examples of co-catalysts include benzene-soluble aluminoxanes or benzene-insoluble organoaluminum oxy-compounds, ion-exchangeable layered silicates, boron compounds, ionic compounds consisting of a cation with or without an active hydrogen group and a non-coordinating anion, lanthanoid salts such as lanthanum oxide, tin oxide, and phenoxy compounds containing a fluoro group.

Examples of organometallic compounds that may be used as needed include organoaluminum compounds, organomagnesium compounds, and organozinc compounds. Of these, organoaluminum compounds are preferred.

The transition metal compound may be used by being supported on an inorganic or organic carrier. The carrier is preferably an inorganic or organic porous oxide, and specific examples thereof include ion-exchange layered silicates such as montmorillonite, SiO ₂ , Al ₂ O ₃ , MgO, ZrO ₂ , TiO ₂ , B ₂ O ₃ , CaO, ZnO, BaO, ThO ₂ , and mixtures thereof.

Instead of ethylene obtained from fossil fuels, biomass-derived ethylene may be used as a raw material for obtaining polyethylene. Because biomass-derived polyethylene is a carbon-neutral material, it can reduce the environmental impact of packaging materials produced using multilayer substrates. Biomass-derived polyethylene can be produced, for example, by the method described in JP 2013-177531 A. Commercially available biomass-derived polyethylene (for example, Green PE, available from Braskem) may also be used.

Polyethylene recycled by mechanical recycling may also be used. Mechanical recycling is a method in which collected polyethylene film is generally crushed, washed with alkali to remove dirt and foreign matter from the film surface, and then dried at high temperature and reduced pressure for a certain period of time to diffuse contaminants remaining inside the film, thereby decontaminating it and removing the dirt from the polyethylene film and returning it to polyethylene.
The melt flow rate (MFR) of the polyethylene contained in the multilayer substrate of the present disclosure is preferably 0.1 g/10 min or more and 50 g/10 min or less, more preferably 0.3 g/10 min or more and 30 g/10 min or less, from the viewpoints of film-forming ability and processability of the multilayer substrate. In the present disclosure, MFR is measured in accordance with ASTM D1238 at a temperature of 190°C and a load of 2.16 kg.

[Heat seal layer]
The heat seal layer constituting the laminate of the present disclosure comprises the first layer and the second layer as described above, and the first layer contains an ethylene-α-olefin copolymer as a main component and has a melting point of 112°C or less. The second layer contains polyethylene as a main component and has a melting point of 114°C or more. By providing at least such a first layer and second layer, low-temperature sealability and hand tearability can be improved. The reasons for this are believed to be as follows.

The multilayer substrate described above is made of polyethylene, which has a lower melting point than conventional resin films such as polyester and nylon, so the heat-sealing temperature cannot be set too high when manufacturing packaging bags using the laminate. With the laminate disclosed herein, the first layer of the heat-sealable layer can be heat-sealed at a lower temperature than the second layer, so the sealing properties of the packaging bag can be maintained even when combined with a multilayer substrate made of polyethylene.

In addition, because multilayer substrates made of polyethylene have higher tear strength than resin films such as polyester or nylon, when the laminate is processed into a form such as a packaging bag, the hand tearability (tearability) when opening the bag is reduced. According to the present disclosure, combining a multilayer substrate with a two-layer heat seal layer as described above improves the tearability of the laminate. While the reason for this is unclear, it can be assumed that the heat seal layer contains polyethylene with a melting point of 114°C or higher, which improves toughness and thus the tearability of the laminate.

In this specification, the melting point is a value determined using a differential scanning calorimeter in accordance with JIS K7121:2012. Specifically, a sample is taken from each layer of the heat-sealable layer. Approximately 10 mg of the sample is then placed in an aluminum cell and heated in a nitrogen atmosphere at a heating rate of 10°C/min from 20°C to a temperature sufficiently higher than the melting point (e.g., 200°C). The temperature is then maintained at this temperature for 10 minutes, and then cooled to 20°C at a cooling rate of 10°C/min. This heating, maintenance, and cooling process is repeated once more, and the melting peak temperature of the maximum endothermic peak observed during the second heating is determined and taken as the melting point. The differential scanning calorimeter may be, for example, a thermal analyzer TA7000 series manufactured by Hitachi High-Tech Science Corporation.

<First layer>
The first layer in the heat-sealable layer contains an ethylene-α-olefin copolymer and has a melting point of 112°C or less. This improves the low-temperature sealability of the heat-sealable layer, as described above. The first layer is one of the surface layers in the heat-sealable layer and also one of the surface layers of the laminate.

The α-olefin used as the comonomer in the copolymer is an α-olefin having 3 to 20 carbon atoms, such as propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-nonene, or 4-methylpentene. The higher the carbon number, the better the tearability tends to be. Considering low-temperature sealing and tearability, 1-hexene and 1-octene are preferred α-olefins.

From the viewpoint of the low-temperature sealing properties of the heat-sealable layer, the melting point of the first layer is preferably 110°C or lower, more preferably 105°C or lower, and even more preferably 100°C or lower. The melting point of the first layer is, for example, 80°C or higher, and may be 90°C or higher.

From the viewpoint of the balance between the low-temperature sealability and rigidity of the heat-sealable layer, the difference between the melting point of the second layer and the melting point of the first layer is preferably 4°C or more, more preferably 15°C or more, even more preferably 20°C or more, and is preferably 50°C or less, more preferably 48°C or less, even more preferably 46°C or less, and may be, for example, 40°C or less.

The density of the first layer is preferably 0.915 g/cm ^or less, more preferably 0.912 g/cm ^or less, and even more preferably 0.908 g/cm ^or less. The density of the first layer is, for example, 0.890 g/cm ^or more, and may be 0.900 g/cm or ^more .

By setting the density of the first layer to 0.915 g/cm ^or less, the low-temperature sealability of the heat seal layer can be improved. By setting the density of the first layer to 0.890 g/cm ^or more, the blocking resistance of the laminate can be improved.

The content of ethylene-α-olefin copolymer in the first layer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

In one embodiment, the first layer contains an ethylene-α-olefin copolymer having a density of preferably 0.912 g/cm ^or less, more preferably 0.908 g/cm ^or less, and even more preferably 0.905 g/cm or ^less . The density of the ethylene-α-olefin copolymer is preferably 0.890 g/cm ^or more, and more preferably 0.895 g/cm or ^more .

The first layer contains an ethylene-α-olefin copolymer having a density of 0.912 g/cm ^or less, thereby improving the low-temperature sealability of the heat-sealable layer. The ethylene-α-olefin copolymer having a density of 0.890 g/cm ^or more improves the blocking resistance of the laminate.

The thickness of the first layer is, for example, 5 μm or more, and may be 15 μm or more. The thickness of the first layer is, for example, 50 μm or less, and may be 30 μm or less. The first layer may be a single layer or a multilayer structure in which each layer has the same composition. If the first layer is a multilayer structure, the thickness of the first layer is the total thickness of each layer.

The ratio of the thickness of the first layer to the thickness of the heat seal layer is preferably 3% or more, more preferably 5% or more, even more preferably 10% or more, and particularly preferably 15% or more, and is preferably 40% or less, more preferably 35% or less, even more preferably 30% or less, and particularly preferably 25% or less. This further improves the balance between the low-temperature sealability and rigidity of the heat seal layer.

In one embodiment, the first layer is preferably in contact with the second layer or the third layer, and more preferably in contact with the second layer. That is, in one embodiment, the first layer is preferably in contact with the second layer or the third layer without an adhesive layer therebetween.
In one embodiment, the first layer is an unstretched resin layer.

The first layer may contain one or more additives. Examples of additives include plasticizers, UV stabilizers, color inhibitors, matting agents, deodorizers, flame retardants, weather resistance agents, antistatic agents, friction reducers, slip agents, antiblocking agents, antioxidants, ion exchange agents, and color pigments. The first layer preferably contains a slip agent and/or an antiblocking agent.

<Second layer>
The second layer in the heat seal layer contains polyethylene and has a melting point of 114° C. or higher, which can improve the rigidity of the heat seal layer as described above.
From the viewpoint of the rigidity of the heat seal layer, the melting point of the second layer is preferably 117° C. or higher, more preferably 120° C. or higher. The melting point of the second layer is, for example, 150° C. or lower, and may be 135° C. or lower.

The density of the second layer is preferably 0.916 g/cm or ^more , more preferably 0.920 g/cm ^or more, and even more preferably 0.930 g/cm or ^more . The density of the second layer is, for example, 0.950 g/cm ^or less, and may be 0.945 g/cm or ^less .
By setting the density of the second layer to 0.916 g/cm ^or more, the rigidity and tearability of the heat seal layer can be improved. By setting the density of the second layer to 0.950 g/cm ^or less, the impact resistance of the heat seal layer can be improved.

The polyethylene content in the second layer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and particularly preferably 95% by mass or more.

In one embodiment, the second layer contains polyethylene having a density of preferably 0.915 g/cm ^or more, more preferably 0.935 g/cm or ^more . The density of the polyethylene is preferably 0.970 g/cm ^or less, more preferably 0.960 g/cm ^or less.

The second layer contains polyethylene having a density of 0.915 g/cm ^or more, thereby improving the rigidity and tearability of the heat seal layer. The density of the polyethylene is 0.970 g/cm ^or less, thereby improving the impact resistance of the heat seal layer.
The second layer may contain an ethylene-α-olefin copolymer as the polyethylene. The content of the ethylene-α-olefin copolymer in the second layer is preferably 50% by mass or more, more preferably 70% by mass or more, based on the entire second layer. The content of the ethylene-α-olefin copolymer in the second layer is preferably 90% by mass or less, more preferably 80% by mass or less.

By setting the content of the ethylene-α-olefin copolymer to 50% by mass or more, the impact resistance of the heat seal layer can be improved, and by setting the content of the ethylene-α-olefin copolymer to 90% by mass or less, the tearability of the heat seal layer can be improved.
The second layer may contain an ethylene homopolymer as the polyethylene. The content of the ethylene homopolymer in the second layer is preferably 10% by mass or more, more preferably 15% by mass or more, based on the total mass of the second layer. The content of the ethylene homopolymer in the second layer is preferably 50% by mass or less, more preferably 25% by mass or less.

By setting the content of the ethylene homopolymer to 10% by mass or more, the tearability of the heat-sealable layer can be improved, and by setting the content of the ethylene homopolymer to 50% by mass or less, the impact resistance of the heat-sealable layer can be improved.
In one embodiment, when the heat-sealing layer is composed of two layers, the second layer is the surface layer on the substrate side of the heat-sealing layer. In one embodiment, when the heat-sealing layer is composed of three or more layers, the second layer is the surface layer on the substrate side of the heat-sealing layer and/or the intermediate layer. In this case, it is preferable that the first layer and the intermediate layer are made of different materials from the viewpoint of the balance between low-temperature sealability and rigidity.

The intermediate layer refers to a layer located between one surface layer and the other surface layer of the heat seal layer. The intermediate layer may be a single layer or multiple layers. If the intermediate layer is multiple layers, the composition of each intermediate layer may be the same or different.

For example, when the heat seal layer comprises a first layer, an intermediate layer, and a surface layer on the substrate side, it is preferable that the melting point of the intermediate layer be higher than that of the surface layer on the substrate side. It is also preferable that the melting point of the intermediate layer be higher than that of the first layer. It is also preferable that the melting point of the surface layer on the substrate side be higher than that of the first layer. This configuration can further improve, for example, the low-temperature sealability, rigidity, and impact resistance of the heat seal layer.

For example, the difference between the melting point of the intermediate layer and the melting point of the surface layer on the substrate side may be 0°C or higher and 30°C or lower, 1°C or higher, 2°C or higher, 25°C or lower, 20°C or lower, 15°C or lower, or 10°C or lower. For example, the difference between the melting point of the intermediate layer and the melting point of the first layer may be 2°C or higher and 50°C or lower, 4°C or higher, 15°C or higher, 40°C or lower, or 35°C or lower. For example, the difference between the melting point of the surface layer on the substrate side and the melting point of the first layer may be 2°C or higher and 40°C or lower, 4°C or higher, 15°C or higher, 35°C or lower, or 30°C or lower.

In a heat seal layer comprising a first layer, an intermediate layer, and a surface layer on the substrate side, the ratio of the thickness of the first layer to the thickness of the heat seal layer and the ratio of the thickness of the surface layer on the substrate side are each independently preferably 3% or more, more preferably 5% or more, even more preferably 10% or more, and particularly preferably 15% or more, and preferably 40% or less, more preferably 35% or less, even more preferably 30% or less, and particularly preferably 25% or less.

In a heat seal layer comprising a first layer, an intermediate layer, and a surface layer on the substrate side, the ratio of the thickness of the intermediate layer to the thickness of the heat seal layer is preferably 20% or more, more preferably 30% or more, even more preferably 40% or more, particularly preferably 50% or more, and is preferably 94% or less, more preferably 90% or less, even more preferably 80% or less, particularly preferably 70% or less.
A plurality of second layers may be present in the heat seal layer as long as they contain polyethylene and have a melting point of 114° C. or higher. For example, both the surface layer and the intermediate layer on the substrate side may be second layers.

The thickness of the second layer is, for example, 10 μm or more, and may be 45 μm or more. The thickness of the second layer is, for example, 250 μm or less, and may be 170 μm or less. When the second layer is multi-layered, the thickness of the second layer is the total thickness of each layer.
From the viewpoint of the rigidity of the heat-sealable layer, the ratio of the thickness TB of the second layer to the thickness TA of the heat-sealable layer (thickness TB/thickness TA) is preferably 1/5 or more, more preferably 1/2 or more, and even more preferably 2/3 or more. The ratio TB/TA is, for example, 19/20 or less, and may be 9/10.
In one embodiment, the second layer is an unstretched resin layer.

The second layer may contain one or more additives. Examples of additives include plasticizers, UV stabilizers, color inhibitors, matting agents, deodorizers, flame retardants, weather resistance agents, antistatic agents, friction reducers, slip agents, antiblocking agents, antioxidants, ion exchange agents, and color pigments. The second layer preferably contains a slip agent and/or an antiblocking agent.

According to other embodiments of the laminate of the present disclosure, the heat seal layer 20 may include a first layer 21A, a second layer 22, and a first layer 21B in this order in the thickness direction, as shown in FIG. 4, or may include a first layer 21, a second layer 22A, and a second layer 22B in this order in the thickness direction, as shown in FIG. 5. Also, as shown in FIG. 6, the heat seal layer 20 may include a first layer 21, a second layer 22, and a third layer 23 in this order in the thickness direction, or as shown in FIG. 7, the heat seal layer 20 may include a first layer 21, a third layer 23, and a second layer 22 in this order in the thickness direction.

<Third Layer>
The heat seal layer may further include a third layer in addition to the first and second layers. The third layer is a layer containing polyethylene as a main component.
In one embodiment, the third layer is a surface layer (laminate layer) on the substrate side and/or an intermediate layer. A plurality of third layers may be present in the heat seal layer.
In one embodiment, the third layer is an unstretched resin layer.
The third layer may contain one or more additives. Preferably, the third layer does not contain an antistatic agent. Examples of additives contained in the third layer include an antiblocking agent, a plasticizer, a UV stabilizer, a color inhibitor, a matting agent, a deodorizer, a flame retardant, a weather resistance agent, a thread friction reducer, a slip agent, an antioxidant, an ion exchange agent, and a color pigment.

The heat-sealable layer, which includes the first and second layers described above and an optional third layer, can be produced by a conventionally known method. Specifically, it can be produced by a known method such as an inflation method or a T-die method, in the same manner as the multilayer substrate described above. In one embodiment, the heat-sealable layer is an unstretched film that has not been subjected to a stretching treatment.

The thickness of the heat seal layer is preferably 20 μm or more, more preferably 70 μm or more, and even more preferably 100 μm or more. On the other hand, the thickness of the heat seal layer is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less.

The ethylene-α-olefin copolymer content in the heat seal layer is preferably 50% by mass or more, and more preferably 70% by mass or more, based on the entire heat seal layer. The ethylene-α-olefin copolymer content in the heat seal layer is preferably 90% by mass or less, and more preferably 80% by mass or less.

By making the ethylene-α-olefin copolymer content 50% by mass or more, the impact resistance of the heat seal layer can be improved. By making the ethylene-α-olefin copolymer content 90% by mass or less, the tear resistance of the heat seal layer can be improved.

By using an ethylene-α-olefin copolymer produced using a metallocene catalyst in the first layer, it is possible to achieve, for example, improved low-temperature sealability compared to when an ethylene-α-olefin copolymer produced using a Ziegler-Natta catalyst is used. By using an ethylene-α-olefin copolymer produced using a metallocene catalyst in the second or third layer, it is possible to achieve, for example, improved impact resistance compared to when an ethylene-α-olefin copolymer produced using a Ziegler-Natta catalyst is used.

The surface of the heat seal layer opposite the first layer may be surface treated. This can improve adhesion to adjacent layers. The surface treatment method is not particularly limited, and examples include physical treatments such as corona treatment, flame treatment, ozone treatment, low-temperature plasma treatment using oxygen gas and/or nitrogen gas, and glow discharge treatment, as well as chemical treatments such as oxidation treatment using chemicals.

The heat-seal layer is typically an unstretched layer. For example, a film comprising the heat-seal layer described above can be laminated onto a multilayer substrate, optionally with an adhesive layer interposed between them, or the heat-seal layer can be formed by melt-extruding a resin material containing polyethylene onto a multilayer substrate, etc.

In one embodiment, the heat seal layer does not have an adhesive layer between each layer selected from the first layer, the second layer, and optionally the third layer that make up the heat seal layer. For example, the heat seal layer is a coextruded film.

[Adhesive layer]
1 , the adhesive layer 30 provided between the substrate 10 and the heat seal layer 20 can improve the adhesion between the substrate 10 and the heat seal layer 20 by laminating the two layers. The adhesive layer 30 can be formed by applying, for example, a one-component curing adhesive, a two-component curing adhesive, or a non-curing adhesive to the surface of either or both of the substrate 10 and the heat seal layer 20.

In the laminate of the present disclosure, a solvent-free adhesive is used as the adhesive. Because the multilayer substrate made of polyethylene as described above is used as the substrate, it is necessary to lower the drying temperature or shorten the drying time after applying the adhesive compared to when conventional polyester or nylon substrates are used. Therefore, when a solvent-based adhesive is used, the solvent contained in the adhesive, specifically the organic solvent, is not sufficiently removed (volatilized) during the drying process after adhesive application, which can result in a solvent odor when used as a packaging bag. By using a solvent-free adhesive, it is possible to create a packaging bag that does not have a solvent odor, even when a multilayer substrate made of polyethylene is used as the substrate.

Examples of the organic solvent include hydrocarbon solvents such as toluene, xylene, n-hexane, and methylcyclohexane; ester solvents such as ethyl acetate, n-propyl acetate, n-butyl acetate, and isobutyl acetate; alcohol solvents such as methanol, ethanol, isopropyl alcohol, n-butyl alcohol, and isobutyl alcohol; and ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone.

The amount of residual solvent in the laminate of the present disclosure is preferably 6 mg/ ^m2 or less, more preferably 5 mg/ ^m2 or less, and even more preferably 3 mg/ ^m2 or less. The lower limit of the residual solvent amount is preferably as small as possible, and may be, for example, 0.1 mg/ ^m2 or 0.2 mg/ ^m2 .

Examples of solvent-free adhesives include polyether adhesives, polyester adhesives, silicone adhesives, epoxy adhesives, and urethane adhesives. Of these, two-component curing urethane adhesives are preferred. Examples of solvent-based adhesives include rubber adhesives, vinyl adhesives, silicone adhesives, epoxy adhesives, phenolic adhesives, and olefin adhesives. Of these, two-component curing urethane adhesives containing polyester polyol and an isocyanate compound are particularly suitable. Two-component curing urethane adhesives undergo a curing reaction even at low temperatures and exhibit high hardness after curing. This not only eliminates the solvent odor but also improves the tearability (hand tearability) of the laminate.

In one embodiment, the solventless adhesive is a two-component curing adhesive containing a base agent and a curing agent. From the standpoint of coatability, the weight-average molecular weight (Mw) of the polymer component contained in the base agent is preferably 800 to 10,000, more preferably 1,200 to 4,000. The polydispersity index (Mw/Mn) of the polymer component contained in the base agent is preferably 2.8 or less, more preferably 1.2 to 2.7, even more preferably 1.5 to 2.6, and particularly preferably 2.0 to 2.5. Here, Mn is the number-average molecular weight of the polymer component contained in the base agent. Each average molecular weight is measured by gel permeation chromatography (GPC) in accordance with JIS K7252-1 (2008) and is expressed in polystyrene equivalents.

In one embodiment, by using a solvent-free adhesive, for example, the adhesive layer can be made thinner than when a solvent-based adhesive is used. This allows the polyethylene content in the entire laminate to be further increased. Such a laminate is suitable for producing mono-material packaging containers.

In one embodiment, the use of a solvent-free adhesive can improve the tearability of the laminate compared to when a solvent-based adhesive is used.

A solventless, two-component curing urethane adhesive will now be described. The urethane adhesive is preferably an adhesive having a base agent containing a polyol compound such as polyester polyol and a curing agent containing an isocyanate compound.
Examples of the polyol compound include polyester polyol, polyether polyol, polycarbonate polyol, and (meth)acrylic polyol. Among these, polyester polyol is preferred.

Polyester polyols have two or more hydroxyl groups per molecule. They have, for example, a polyester structure or a polyester polyurethane structure as their main backbone. Polyester polyols can be obtained, for example, by a dehydration condensation reaction, transesterification, or ring-opening reaction between a polyhydric alcohol component and a polycarboxylic acid component.

Examples of polyhydric alcohol components include diols such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, and cyclohexanedimethanol; and tri- or higher functional polyols such as glycerin, triethylolpropane, trimethylolpropane, pentaerythritol, and sorbitol.

Examples of polycarboxylic acid components include aliphatic polycarboxylic acids, alicyclic polycarboxylic acids, and aromatic polycarboxylic acids, as well as their ester derivatives and acid anhydrides. Examples of aliphatic polycarboxylic acids include aliphatic dicarboxylic acids such as succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedicarboxylic acid, maleic acid, fumaric acid, and dimer acid. Examples of alicyclic polycarboxylic acids include 1,3-cyclopentanedicarboxylic acid and 1,4-cyclohexanedicarboxylic acid. Examples of aromatic polycarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, pyromellitic acid, naphthalenedicarboxylic acid, naphthalic acid, biphenyldicarboxylic acid, and 1,2-bis(phenoxy)ethane-p,p'-dicarboxylic acid.

If necessary, the polyester polyol can be pre-chain-lengthened with a polyisocyanate. Examples of polyisocyanates include diisocyanates such as 1,6-hexamethylene diisocyanate, isophorone diisocyanate, norbornene diisocyanate, m-xylylene diisocyanate, α,α,α'α'-tetramethyl-m-xylylene diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, and diphenylmethane diisocyanate; as well as biuret, nurate, or trimethylolpropane adducts of diisocyanates.

From the viewpoint of coatability, the weight-average molecular weight (Mw) of polyol compounds such as polyester polyols is preferably 800 to 10,000, more preferably 1,200 to 4,000. The polydispersity (Mw/Mn) of polyol compounds such as polyester polyols is preferably 2.8 or less, more preferably 1.2 to 2.7, even more preferably 1.5 to 2.6, and particularly preferably 2.0 to 2.5. Here, Mn is the number-average molecular weight of the polyol compound. Each average molecular weight is measured by gel permeation chromatography (GPC) in accordance with JIS K7252-1 (2008) and is expressed in terms of polystyrene.

The isocyanate compound has two or more isocyanate groups in one molecule.
Examples of the isocyanate compound include aromatic isocyanates and aliphatic isocyanates. The isocyanate compound may be a blocked isocyanate compound obtained by addition reaction using a known isocyanate blocking agent by a known, conventional, appropriate method.

Examples of isocyanate compounds include diisocyanates such as tetramethylene diisocyanate, hexamethylene diisocyanate, norbornene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, hydrogenated diphenylmethane diisocyanate, m-xylylene diisocyanate, hydrogenated xylylene diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, and α,α,α'α'-tetramethyl-m-xylylene diisocyanate; trimers of these diisocyanates; and adducts, biuret compounds, and allophanate compounds obtained by reacting these diisocyanate compounds with low-molecular-weight active hydrogen compounds or their alkylene oxide adducts, or high-molecular-weight active hydrogen compounds.

Examples of low-molecular-weight active hydrogen compounds include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, 1,4-butanediol, neopentyl glycol, 1,6-hexamethylene glycol, 1,8-octamethylene glycol, 1,4-cyclohexanedimethanol, meta-xylylene alcohol, 1,3-bishydroxyethylbenzene, 1,4-bishydroxyethylbenzene, trimethylolethane, trimethylolpropane, glycerol, pentaerythritol, erythritol, sorbitol, ethylenediamine, monoethanolamine, diethanolamine, triethanolamine, and meta-xylylenediamine. Examples of high-molecular-weight active hydrogen compounds include polyesters, polyether polyols, and polyamides.

From the viewpoint of the adhesive strength of the adhesive layer and the processability of the laminate, the thickness of the adhesive layer is preferably 0.5 μm to 6 μm, more preferably 0.8 μm to 5 μm, and even more preferably 1 μm to 4.5 μm. By using a solvent-free adhesive, the thickness of the adhesive layer can be reduced to, for example, 2 μm or less, and in one embodiment, it is 0.5 μm to 2 μm.

The adhesive can be applied to the surface of the substrate 10 or the like by applying and drying the adhesive using methods such as direct gravure roll coating, gravure roll coating, kiss coating, reverse roll coating, Fountain coating, and transfer roll coating.

[Printing layer]
In one embodiment, the laminate of the present disclosure may further include a printing layer on the above-described substrate 10. The printing layer is formed, for example, on the first layer or fifth layer of the multilayer substrate 10. When printing an image on a substrate, the substrate is usually subjected to a surface treatment such as a corona discharge treatment as a pretreatment. In one embodiment of the present disclosure, since the first layer or fifth layer of the multilayer substrate 10 contains medium-density polyethylene as described above, it tends to have higher durability against the surface treatment than a layer containing only high-density polyethylene. Therefore, the layer containing medium-density polyethylene has excellent ink adhesion during printing after the surface treatment. In addition, the layer containing medium-density polyethylene also has the heat resistance required during printing and heat sealing.

In one embodiment, the laminate of the present disclosure preferably has a printed layer on the surface of the substrate 10 facing the heat seal layer 20, as this can prevent deterioration of the image over time.

The printed layer includes, for example, an image. Examples of images include letters, figures, symbols, and combinations thereof. Methods for forming the printed layer include, for example, gravure printing, offset printing, and flexographic printing. In one embodiment, from the perspective of reducing the environmental impact, flexographic printing is preferred. Furthermore, from the perspective of reducing the environmental impact, the printed layer may be formed on the surface of the substrate using ink derived from biomass.

[Uses of the laminate]
The laminate of the present disclosure can be suitably used for packaging material applications.
The packaging material is used to produce a packaging container. The packaging container includes the laminate of the present disclosure. The packaging container can be produced by using the laminate of the present disclosure in part or in whole. By using the laminate of the present disclosure, a packaging container with excellent low-temperature sealing properties and tearability can be produced.

In one embodiment, the laminate of the present disclosure consists solely of the above-mentioned multilayer substrate, on which a printed layer is formed as needed, and a heat seal layer made of polyethylene. As a result, packaging containers using the laminate of the present disclosure have particularly improved recyclability, as each resin layer is made of the same material, polyethylene.

FIG. 8 is a schematic diagram showing an embodiment of a stand-up pouch, which is an example of a packaging container according to the present disclosure. As shown in FIG. 8 , the stand-up pouch 40 includes a body 41 and a bottom 42. The body 41 is composed of two side sheets 43, and the bottom 42 is composed of a bottom sheet 44. In the stand-up pouch 40, the side sheets 43 are made of the laminate 1 according to the present disclosure. Therefore, the stand-up pouch 40 is manufactured so that the first layer 21 of the heat-seal layer 20 of the laminate 1 constituting the side sheets 43 is the innermost layer. The side sheets 43 and the bottom sheet 44 of the stand-up pouch 40 may be made of the same material or different materials. In the present disclosure, when the laminate according to the present disclosure is used for both the side sheets 43 and the bottom sheet 44, it is preferable that the laminate used for the side sheets 43 be thinner than the laminate used for the bottom sheet 44, considering tearability.
In Fig. 8, the hatched areas indicate the heat-sealed areas. The bottom sheet maintains the shape of the side sheets, giving the pouch self-supporting properties and enabling it to be a standing pouch. A storage space for storing contents is formed within the area surrounded by the side sheets and the bottom sheet.

In one embodiment, the side sheet 43 can be formed by preparing two sheets of the laminate 1 of the present disclosure, overlapping them with their heat-sealable layers 20 facing each other, and heat-sealing both side edges to form a bag.

In another embodiment, the side sheets can be formed by preparing two laminates of the present disclosure, overlapping them with their heat-sealable layers facing each other, and inserting two V-folded laminates with their heat-sealable layers facing outward between the laminates at the side edges on both sides of the overlapped laminates, and then heat-sealing the resulting laminates. This manufacturing method results in a standing pouch 40 having a body 41 with side gussets 41a, as shown in Figure 9.

In another embodiment of the standing pouch, when the contents are liquid, viscous material, or powder, the standing pouch may be equipped with a dispensing nozzle 45, as shown in FIG. 10. From the perspective of ease of opening, the standing pouch 40 may also be equipped with a curved portion 46 that curves inward, as shown in FIG. 10. Furthermore, it may also be equipped with a cutout portion 47 formed by a laser beam or the like.

Although a stand-up pouch has been described as an example of a packaging container using the laminate of the present disclosure, the packaging container may be a packaging bag other than a stand-up pouch, and examples of packaging bags include side-sealed, two-sided sealed, three-sided sealed, four-sided sealed, envelope-sealed, palm-sealed (pillow-sealed), pleated sealed, flat-bottom sealed, square-bottom sealed, and gusseted.

The present disclosure relates to, for example, the following [1] to [15].
[1] A laminate comprising a substrate and a heat-sealing layer, wherein the substrate is a stretched polyethylene multilayer substrate, the heat-sealing layer comprises at least a first layer and a second layer, the first layer contains an ethylene-α-olefin copolymer and has a melting point of 112°C or less, the second layer contains polyethylene and has a melting point of 114°C or more, the surface layer on one side of the laminate is the first layer of the heat-sealing layer, and the substrate and the heat-sealing layer are laminated via an adhesive layer, and the adhesive layer is made of a solventless adhesive.
[2] The laminate according to the above [1], wherein the density of the first layer of the heat seal layer is 0.915 g/cm ³ or less.
[3] The laminate according to the above [1] or [2], wherein the density of the second layer of the heat seal layer is 0.917 g/cm ³ or more.
[4] The laminate according to any one of the above [1] to [3], wherein the content of the ethylene-α-olefin copolymer is 50% by mass or more and 90% by mass or less based on the entire heat seal layer.
[5] The laminate according to any one of [1] to [4] above, wherein the polyethylene multilayer substrate comprises, in the thickness direction, a first layer containing medium-density polyethylene and high-density polyethylene, a second layer containing medium-density polyethylene and linear low-density polyethylene, a third layer containing linear low-density polyethylene, a fourth layer containing medium-density polyethylene and linear low-density polyethylene, and a fifth layer containing medium-density polyethylene and high-density polyethylene, in this order.
[6] The laminate according to the above [5], wherein the mass ratio of the medium-density polyethylene to the high-density polyethylene (medium-density polyethylene/high-density polyethylene) in the first layer and the fifth layer of the substrate is independently 1.1 or more and 5 or less, and the mass ratio of the medium-density polyethylene to the linear low-density polyethylene (medium-density polyethylene/linear low-density polyethylene) in the second layer and the fourth layer of the substrate is independently 0.25 or more and 4 or less.
[7] The laminate according to [5] or [6] above, wherein the total content of medium-density polyethylene and high-density polyethylene in the first layer of the substrate is 80% by mass or more, the total content of medium-density polyethylene and linear low-density polyethylene in the second layer of the substrate is 80% by mass or more, the total content of linear low-density polyethylene in the third layer of the substrate is 80% by mass or more, the total content of medium-density polyethylene and linear low-density polyethylene in the fourth layer of the substrate is 80% by mass or more, and the total content of medium-density polyethylene and high-density polyethylene in the fifth layer of the substrate is 80% by mass or more.
[8] The laminate according to any one of the above [5] to [7], wherein, when any adjacent layers selected from the first to fifth layers in the substrate are referred to as layer (1) and layer (2), the absolute value of the difference between the density of the polyethylene constituting layer (1) and the density of the polyethylene constituting layer (2) is 0.030 g/ ^cm3 or less.
[9] A laminate according to any one of the above [1] to [8], which has a printed layer on at least one surface of the substrate, and the surface of the substrate on the printed layer side is laminated to the surface of the heat seal layer on the second layer side via an adhesive layer.
[10] The laminate according to any one of the above [1] to [9], wherein the amount of residual solvent in the laminate is 6 mg/ ^m2 or less.
[11] The laminate according to any one of the above [1] to [10], wherein the solventless adhesive is a two-component curing adhesive having a base agent and a curing agent, and the weight average molecular weight (Mw) of the polymer component contained in the base agent is 800 or more and 10,000 or less.
[12] The laminate according to any one of the above [1] to [11], wherein the solventless adhesive is a two-component curing adhesive having a base agent and a curing agent, and the polydispersity (Mw/Mn) of the polymer component contained in the base agent is 2.8 or less.
[13] The laminate according to any one of the above [1] to [12], wherein the thickness of the adhesive layer is 0.5 μm or more and 2 μm or less.
[14] A packaging container comprising the laminate according to any one of [1] to [13] above.
[15] The packaging container according to [14] above, which is a standing pouch.

The laminate of the present disclosure will be explained in more detail using examples, but the laminate of the present disclosure is not limited to these examples. Hereinafter, "parts by mass" will simply be referred to as "parts."

[Example 1]
<Preparation of stretched multilayer substrate>
The following polyethylenes were used:
Medium density polyethylene (hereinafter referred to as "MDPE"):
Product name: Elite 5538G
Density: 0.941 g/cm ³ , melting point: 129°C, MFR: 1.3 g/10 min,
High-density polyethylene (hereinafter referred to as "HDPE") manufactured by Dow Chemical:
Product name: Elite 5960G
Density: 0.960 g/cm ³ , melting point: 134°C, MFR: 0.8 g/10 min,
Dow Chemical Linear Low Density Polyethylene (hereinafter referred to as "LLDPE"):
Product name: Elite 5400G
Density: 0.916 g/cm ³ , melting point: 123°C, MFR: 1.3 g/10 min,
Dow Chemical Blended Polyethylene A
70 parts of MDPE and 30 parts of LLDPE were mixed to obtain a blended polyethylene A (hereinafter referred to as "blended polyethylene (A)") having an average density of 0.934 g/ ^cm3 .
70 parts of MDPE and 30 parts of HDPE were mixed to obtain a blended polyethylene B (hereinafter referred to as "blended PE (B)") having an average density of 0.947 g/cm ³ .

LLDPE, blend PE (A), and blend PE (B) were coextruded into a five-layer tube using an inflation molding method with a layer thickness ratio of blend PE (B) layer (15 μm)/blend PE (A) layer (22.5 μm)/LLDPE layer (50 μm)/blend PE (A) layer (22.5 μm)/blend PE (B) layer (15 μm). A polyethylene film with a total thickness of 125 μm was obtained, and the tubular film was folded at a nip to form two layers. The numbers in parentheses indicate the layer thicknesses.
The polyethylene film prepared above was stretched in the longitudinal direction (MD) at a stretching ratio of 5 times, and the blend PE (C) layer (surface layer) on one side was subjected to a corona discharge treatment. The end was then slit and divided into two pieces to obtain a stretched multilayer base material with a thickness of 25 μm.

<Preparation of film for heat seal layer>
The following polyethylenes were used:
Ethylene-α-olefin copolymer (hereinafter referred to as “Copolymer A”):
Copolymer of ethylene and C8 olefin, density: 0.902 g/cm ³ , MFR: 1.0 g/10 min, polymerization catalyst: metallocene catalyst/ethylene-α-olefin copolymer (hereinafter referred to as “Copolymer B”):
Copolymer of ethylene and C8 olefin, density: 0.918 g/cm ³ , MFR: 0.8 g/10 min, polymerization catalyst: metallocene catalyst/ethylene-α-olefin copolymer (hereinafter referred to as “copolymer C”):
Copolymer of ethylene and C8 olefin, density: 0.941 g/cm ³ , MFR: 1.3 g/10 min, polymerization catalyst: metallocene catalyst/high-pressure low-density polyethylene (hereinafter referred to as “LDPE”):
Density: 0.919g/cm ³ , MFR: 2.0g/10min
Slip agent masterbatch (hereinafter referred to as "slip agent MB"):
Base material: polyethylene, slip agent: erucic acid amide, slip agent content: 2.0 mass %, density: 0.921 g/cm ³ , MFR: 5.4 g/10 min
Antiblocking agent masterbatch (hereinafter referred to as "AB agent MB"):
Base material: polyethylene, antiblocking agent: acrylic resin, content of antiblocking agent: 30.0 mass %, density: 0.959 g/cm ³ , MFR: 2.5 g/10 min

A 130 μm-thick heat seal film was obtained by three-layer extrusion film formation, with the first layer (sealing layer) being a mixture of 93 parts by weight of copolymer A, 1 part by weight of slip agent MB, and 6 parts by weight of AB agent MB. The second layer (intermediate layer) was a mixture of 69 parts by weight of copolymer C, 30 parts by weight of LDPE, and 1 part by weight of slip agent MB. The second layer (laminating layer) was a mixture of 89 parts by weight of copolymer B, 10 parts by weight of LDPE, and 1 part by weight of slip agent MB. The thickness ratio of the first layer (sealing layer):second layer (intermediate layer):second layer (laminating layer) was 1:3:1.

The melting point of each layer in the obtained heat seal film was determined using a differential scanning calorimeter in accordance with JIS K7121: 2012. As the differential scanning calorimeter, a thermal analyzer TA7000 series manufactured by Hitachi High-Tech Science Corporation was used.
Specifically, a sample of each layer was taken from the sealant film. Approximately 10 mg of the sample was placed in an aluminum cell and heated in a nitrogen atmosphere from 20°C to a temperature (e.g., 200°C) sufficiently higher than the melting point at a heating rate of 10°C/min. The temperature was then maintained at that temperature for 10 minutes, and the sample was then cooled to 20°C at a cooling rate of 10°C/min. This heating, maintaining, and cooling process was repeated once more, and the melting peak temperature of the maximum endothermic peak observed during the second heating was determined and defined as the melting point.
As a result, the melting point of the first layer was 99°C, the melting point of the second layer (intermediate layer) was 122°C, and the melting point of the second layer (laminate layer) was 117°C.

<Preparation of Laminate>
The blend PE (B) layer (surface layer) on one side of the stretched multilayer substrate obtained as described above was subjected to a corona discharge treatment. Then, a print layer was formed on the corona discharge-treated surface of the stretched multilayer substrate by gravure printing using oil-based gravure ink (manufactured by DIC Graphics Corporation, trade name: Finart). The print layer had a thickness of 1 μm.
The surface of the second layer of the heat seal layer was subjected to corona discharge treatment. Next, the printed layer surface of the stretched multilayer substrate and the surface of the second layer of the heat seal layer were laminated via a two-component curing urethane-based solventless adhesive (RN-920/HN-920, manufactured by Rock Paint Co., Ltd.) so that they faced each other, thereby obtaining a laminate. The thickness of the adhesive layer was 1 μm. The weight-average molecular weight (Mw) of the polymer component contained in the base material of the two-component curing urethane-based solventless adhesive was in the range of 2,000 to 2,500, and the polydispersity (Mw/Mn) of the polymer component contained in the base material was in the range of 2.0 to 2.5.

<Making packaging bags>
Two sheets of the obtained laminate were prepared, and the laminates were overlapped with each other so that the first layers of the heat-sealing layers faced each other, and two sides were heat-sealed to form a body. Next, another laminate was folded into a V shape so that the heat-sealing layer was on the outside, and one end of the body was sandwiched between them and heat-sealed to form a bottom, thereby producing a standing pouch. The heat-sealing conditions were a temperature of 140°C, a pressure of 1 kgf/ ^cm2 , and a time of 1 second.

[Comparative Example 1]
A laminate was prepared in the same manner as in Example 1, and a packaging bag was obtained, except that a single-layer heat-sealing film (thickness: 130 μm) was used as the heat-sealing film, which was formed using a mixture of 93 parts by mass of linear low-density polyethylene ( ^SP1520 , manufactured by Prime Polymer Co., Ltd., density: 0.913 g/cm 3 , melting point: 116°C), 1 part by mass of slip agent MB, and 6 parts by mass of AB agent MB.

[Comparative Example 2]
A laminate was produced in the same manner as in Example 1, except that the stretched multilayer substrate and the heat seal layer were dry laminated using a two-component curing urethane solvent-based adhesive (Ru-77T/H-7, manufactured by Rock Paint Co., Ltd.), and a packaging bag was obtained.

[Comparative Example 3]
A laminate was produced in the same manner as in Comparative Example 1, except that the stretched multilayer substrate and the heat seal layer were dry laminated using a two-component curing urethane solvent-based adhesive (Ru-77T/H-7, manufactured by Rock Paint Co., Ltd.), and a packaging bag was obtained.

<Heat seal strength>
The peel strength of the heat-sealed portion of the resulting packaging bag was measured in accordance with JIS-Z-1707. A Tensilon universal material testing machine RTC-1530 was used as the measuring machine, and the peel strength of a 15 mm width was measured at 300 mm/min. Measurements were made on five test pieces, and the average value was taken as the heat-seal strength.

<Tear strength>
Test pieces were prepared by laminating 16 sheets of each of the laminates used in the Examples and Comparative Examples, and the tear strength was measured in accordance with the Elmendorf tear method of JIS K7128-2: 1998. The measuring instrument used was an Elmendorf tear tester IM-701 manufactured by Tester Sangyo Co., Ltd. Measurement was carried out on five test pieces, and the average value was taken as the tear strength.

<Checking for residual solvent>
The total amount (mg/ ^m ) of toluene, ethyl acetate, isopropyl alcohol, methanol, and methyl ethyl ketone contained in the laminate was measured by gas chromatography. Specifically, the amount of residual solvent was measured by a calibration curve method using a 10 cm square sample cut out of the laminate and a gas chromatograph GC-2014 manufactured by Shimadzu Corporation.

<Drop test>
Each standing pouch was filled with 400 g of water and dropped horizontally five times and vertically five times from a height of 1 m to check for any breakage of the pouch.

<Pressure test>
400 g of water was placed in each standing pouch, and a load of 100 kgf was applied for 1 minute to check for breakage of the pouch.

<Piercing strength>
The puncture strength was measured in accordance with "2. Test Methods for Strength, etc." in "Standards and Criteria for Foods, Food Additives, etc., Part 3: Apparatus and Containers/Packaging" (Ministry of Health and Welfare Notification No. 20, 1982) under the Food Sanitation Act. A needle with a diameter of 1.0 mm and a radius of 0.5 mm was pierced into the laminate at a puncture speed of 50 mm/min, and the strength at which the needle penetrated the laminate was measured. The measured value was divided by the thickness of the laminate to calculate the puncture strength [N/μm] per μm of thickness. Two types of puncture were performed: from the stretched multilayer substrate side and from the heat seal layer side. Five measurements were taken for each type, and the average value was calculated.

1: Laminate 10: Substrate 20: Heat seal layer 30: Adhesive layer 40: Packaging container (standing pouch)
41: Body (side sheet)
42: Bottom (bottom sheet)
41a: Side gusset

Claims (14)

A laminate comprising a substrate and a heat seal layer,
the substrate is a polyethylene multilayer substrate that has been subjected to a stretching treatment,
The polyethylene multilayer substrate is
a first layer containing medium density polyethylene and high density polyethylene;
a second layer containing medium density polyethylene and linear low density polyethylene;
a third layer containing linear low density polyethylene;
a fourth layer containing medium density polyethylene and linear low density polyethylene;
a fifth layer containing medium density polyethylene and high density polyethylene;
in this order in the thickness direction,
The heat seal layer is
The film includes at least a first layer and a second layer,
the first layer contains an ethylene-α-olefin copolymer;
the melting point of the first layer is 112°C or less;
the second layer comprises polyethylene;
The melting point of the second layer is 114°C or higher,
a surface layer on one side of the laminate is a first layer of the heat seal layer;
the substrate and the heat seal layer are laminated via an adhesive layer,
The adhesive layer is made of a solventless adhesive.
Laminate. The laminate according to claim 1 , wherein the density of the first layer of the heat seal layer is 0.915 g/cm ³ or less. The laminate according to claim 1 or 2, wherein the density of the second layer of the heat seal layer is 0.917 g/cm ³ or more. The laminate according to any one of claims 1 to 3, wherein the content of the ethylene-α-olefin copolymer is 50% by mass or more and 90% by mass or less of the entire heat seal layer. the mass ratio of the medium-density polyethylene to the high-density polyethylene (medium-density polyethylene/high-density polyethylene) in the first layer and the fifth layer of the substrate is independently 1.1 or more and 5 or less;
the mass ratio of the medium-density polyethylene to the linear low-density polyethylene (medium-density polyethylene/linear low-density polyethylene) in the second layer and the fourth layer of the substrate is independently 0.25 or more and 4 or less;
The laminate according to any one of claims 1 to 4 . the total content of medium-density polyethylene and high-density polyethylene in the first layer of the substrate is 80% by mass or more,
the total content of the medium-density polyethylene and the linear low-density polyethylene in the second layer of the substrate is 80% by mass or more,
the content of linear low-density polyethylene in the third layer of the substrate is 80% by mass or more,
the total content of the medium-density polyethylene and the linear low-density polyethylene in the fourth layer of the substrate is 80% by mass or more,
the total content of the medium-density polyethylene and the high-density polyethylene in the fifth layer of the substrate is 80% by mass or more;
The laminate according to any one of claims 1 to 5 . 7. The laminate according to claim 1, wherein, when any adjacent layers selected from the first to fifth layers in the substrate are referred to as layer (1) and layer (2), the absolute value of the difference between the density of the polyethylene constituting layer (1) and the density of the polyethylene constituting layer ( 2 ) is 0.030 g/ ^cm3 or less. The laminate according to any one of claims 1 to 7, wherein a printed layer is provided on at least one surface of the substrate, and the surface of the substrate on the printed layer side is laminated to the surface of the heat seal layer on the second layer side via an adhesive layer. The laminate according to any one of claims 1 to 8 , wherein the amount of residual solvent in the laminate is 6 mg/ ^m2 or less. The laminate according to any one of claims 1 to 9, wherein the solventless adhesive is a two-component curing adhesive having a base agent and a curing agent, and the weight average molecular weight (Mw) of a polymer component contained in the base agent is 800 or more and 10,000 or less. The laminate according to any one of claims 1 to 10, wherein the solventless adhesive is a two-component curing adhesive having a base agent and a curing agent, and the polydispersity (Mw/Mn) of a polymer component contained in the base agent is 2.8 or less. The laminate according to any one of claims 1 to 11 , wherein the adhesive layer has a thickness of 0.5 µm or more and 2 µm or less. A packaging container comprising the laminate according to any one of claims 1 to 12 . The packaging container according to claim 13 , which is a stand-up pouch.