JP2023056928A - Laminate and packaging material - Google Patents

Abstract

To provide a laminate comprising a polyethylene multilayer substrate and a heat seal layer primarily composed of polyethylene, the laminate having excellent heat resistance.SOLUTION: A laminate comprises a polyethylene multilayer substrate and a heat seal layer primarily composed of polyethylene. The polyethylene multilayer substrate has been drawn and comprises a first polyethylene layer, a second polyethylene layer, and a third polyethylene layer in the stated order in a thickness direction, where the first polyethylene layer has an indentation elastic modulus of 1.0 GPa or more and the third polyethylene layer has an indentation elastic modulus of 1.0 GPa or more.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to laminates and packaging materials.

Conventionally, packaging materials and the like are manufactured using resin films made of resin materials. The packaging material comprises, for example, a substrate and a heat seal layer. For example, a resin film made of polyethylene is widely used as a heat-sealing layer in packaging materials because it has flexibility and transparency and excellent heat-sealing properties (see, for example, Patent Document 1).

On the other hand, polyethylene is a resin that softens at a relatively low temperature compared to other thermoplastic resins, so if it is used as a base material for packaging materials, it may deform or even melt during heat sheet processing. Sometimes. Moreover, polyethylene films sometimes have insufficient strength compared to other thermoplastic resin films. For this reason, resin films having excellent strength and heat resistance, such as polyester films and nylon films, are generally used as base materials for packaging materials. For example, a base material such as a polyester film or a nylon film is laminated with a polyethylene film, and heat-sealed so that the polyethylene film side faces the inside of the packaging bag to form a bag (see, for example, Patent Documents 2, Background Art).

By the way, in recent years, along with the increasing demand for building a recycling-oriented society, attempts have been made to recycle and use packaging materials. However, it is difficult to separate the laminated body obtained by laminating different types of resin films as described above according to the type of resin, and it is not suitable for recycling.

JP 2009-202519 A JP 2017-031233 A

Therefore, the present inventors have found that the strength and heat resistance of a resin film composed of polyethylene can be improved by stretching treatment, and have provided a plurality of layers containing polyethylene as a substrate, and a polyethylene multilayer substrate obtained by stretching treatment was considered to be used.

Heat is applied to substrates used in packaging materials and the like, for example, when the packaging materials are heat-sealed. However, the present inventors have found that laminates comprising the polyethylene multilayer base material may undergo a large amount of heat shrinkage due to the application of heat, and the heat resistance is not sufficient.

One object of the present disclosure is to provide a laminate having excellent heat resistance, comprising a polyethylene multilayer base material and a heat seal layer containing polyethylene as a main component.

A laminate of the present disclosure comprises a polyethylene multilayer substrate and a heat seal layer containing polyethylene as a main component. The polyethylene multilayer substrate comprises a first polyethylene layer, a second polyethylene layer, and a third polyethylene layer in this order in the thickness direction, and is stretched. In one embodiment of the multilayer base material, the first polyethylene layer has an indentation modulus of 1.0 GPa or more, and the third polyethylene layer has an indentation modulus of 1.0 GPa or more. In one embodiment of the multilayer substrate, the first polyethylene layer has an indentation hardness of 45 MPa or more, and the third polyethylene layer has an indentation hardness of 45 MPa or more.

According to the present disclosure, it is possible to provide a laminate having excellent heat resistance, comprising a polyethylene multilayer substrate and a heat seal layer containing polyethylene as a main component.

1 is a schematic cross-sectional view showing one embodiment of a polyethylene multilayer substrate; FIG. 1 is a cross-sectional schematic diagram illustrating one embodiment of a laminate of the present disclosure; FIG. 1 is a cross-sectional schematic diagram illustrating one embodiment of a laminate of the present disclosure; FIG. 1 is a cross-sectional schematic diagram illustrating one embodiment of a laminate of the present disclosure; FIG. 1 is a cross-sectional schematic diagram illustrating one embodiment of a laminate of the present disclosure; FIG. It is the schematic explaining the measuring method of the heat shrinkage rate of a laminated body.

[the term]
Terms used in the present 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 the polymer, the content of ethylene-derived structural units is preferably 70 mol % or more, more preferably 80 mol % or more, still more preferably 90 mol % or more, and particularly preferably 95 mol % or more. The content ratio is measured by a nuclear magnetic resonance method (NMR method).

A "polyethylene layer" is a layer containing polyethylene as a main component, that is, a layer containing polyethylene in an amount exceeding 50% by mass. The content of polyethylene in the polyethylene layer is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more, 85% by mass or more, 90% by mass or more, or 95% by mass or more.

The density of high density polyethylene is preferably greater than 0.945 g/ ^cm3 . The upper density limit of high-density polyethylene is, for example, 0.965 g/cm ³ . The density of medium density polyethylene is preferably greater than 0.925 g/cm ³ and less than or equal to 0.945 g/cm ³ . The density of the low density polyethylene is preferably greater than 0.900 g/cm ³ and less than or equal to 0.925 g/cm ³ . The density of the linear low-density polyethylene is preferably greater than 0.900 g/cm ³ and less than or equal to 0.925 g/cm ³ . The density of the ultra-low density polyethylene is preferably 0.900 g/cm ³ or less. The lower limit of the density of ultra-low density polyethylene is, for example, 0.860 g/cm ³ . The density of polyethylene is measured according to JIS K7112, particularly D method (density gradient tube method, 23°C).

In the present disclosure, polyethylene includes, for example, homopolymers of ethylene and copolymers of ethylene and other monomers. Other monomers include, for example, 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, and a copolymer of ethylene and at least one selected from vinyl acetate and (meth)acrylic acid ester. Polymers, and copolymers 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 branches can be obtained by appropriately selecting the polymerization method. For example, using a multi-site catalyst such as a Ziegler-Natta catalyst or a single-site catalyst such as a metallocene catalyst as a polymerization catalyst, one-stage polymerization is performed by any of gas phase polymerization, slurry polymerization, solution polymerization and high-pressure ion polymerization. Alternatively, it is preferable to carry out the polymerization in two or more stages.

A single-site catalyst is a catalyst capable of forming uniform active species, and is usually prepared by contacting a metallocene-based transition metal compound or a non-metallocene-based transition metal compound with an activating cocatalyst. A single-site catalyst has a more uniform structure of active sites than a multi-site catalyst, and is therefore preferable because a polymer having a high molecular weight and a highly uniform structure can be obtained.

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

Examples of transition metals in transition metal compounds 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. Substituted cyclopentadienyl groups include, for example, hydrocarbon groups having 1 to 30 carbon atoms, silyl groups, silyl-substituted alkyl groups, silyl-substituted aryl groups, cyano groups, cyanoalkyl groups, cyanoaryl groups, halogen groups, and haloalkyl groups. , and halosilyl groups. A substituted cyclopentadienyl group has one or more substituents, and the substituents are bonded to each other to form a ring, an indenyl ring, a fluorenyl ring, an azulenyl ring, or a hydrogenation product thereof. may be formed. A ring formed by combining substituents with each other may further have a substituent.

A transition metal compound usually has two ligands having a cyclopentadienyl skeleton. Each ligand having a cyclopentadienyl skeleton is preferably linked to each other by a bridging group. Examples of the cross-linking group include an alkylene group having 1 to 4 carbon atoms, a silylene group, a substituted silylene group such as a dialkylsilylene group and a diarylsilylene group, and a substituted germylene group such as a dialkylgermylene group and a diarylgermylene group. . Among these, substituted silylene groups are preferred.

A co-catalyst is a component that allows a transition metal compound of group IV of the periodic table to function effectively as a polymerization catalyst, or a component that balances ionic charges in a catalytically activated state. Examples of co-catalysts include benzene-soluble aluminoxanes, benzene-insoluble organoaluminumoxy compounds, ion-exchange layered silicates, boron compounds, and ions composed of cations containing or not containing active hydrogen groups and non-coordinating anions. lanthanide salts such as lanthanum oxide, tin oxide, and phenoxy compounds containing fluoro groups.

Optional organometallic compounds include, for example, organoaluminum compounds, organomagnesium compounds, and organozinc compounds. Among these, organoaluminum compounds are preferred.

The transition metal compound may be supported on an inorganic or organic compound carrier before use. As the carrier, porous oxides _of inorganic or organic compounds are preferred, and specific examples include ion-exchange layered silicates such as montmorillonite, _SiO2 , _Al2O3 , MgO, _ZrO2 , _TiO2 , and _B2O . ₃ , CaO, ZnO, BaO, _ThO2 , or mixtures thereof.

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

Polyethylene recycled by mechanical recycling may also be used. Mechanical recycling generally involves pulverizing collected polyethylene film, washing with alkali to remove dirt and foreign matter from the surface of the film, and then drying it for a certain period of time under high temperature and reduced pressure until it remains inside the film. In this method, the contaminants are diffused to decontaminate the polyethylene film, and then the dirt is removed from the polyethylene film, which is then returned to polyethylene.

In the following description, each component appearing (for example, polyethylene such as high-density polyethylene, medium-density polyethylene, low-density polyethylene and linear low-density polyethylene, additives, coloring agents, resin materials, and adhesives) is A seed may be used, or two or more may be used.
Hereinafter, the laminate of the present disclosure will be described after the polyethylene multilayer base material included in the laminate of the present disclosure is described.

[Polyethylene multilayer substrate]
The polyethylene multilayer base material is
a first polyethylene layer;
a second polyethylene layer;
A third polyethylene layer is provided in this order in the thickness direction and stretched.
Hereinafter, the polyethylene multilayer substrate is also simply referred to as "multilayer substrate".

The multilayer substrate further comprises a polyethylene layer 2a between the first polyethylene layer and the second polyethylene layer and a polyethylene layer 2b between the second polyethylene layer and the third polyethylene layer. may The multilayer base material in this case comprises a first polyethylene layer, a second polyethylene layer, a second polyethylene layer, a second polyethylene layer, and a third polyethylene layer in this order in the thickness direction. Prepare. The 2a polyethylene layer, the 2nd polyethylene layer and the 2b polyethylene layer constitute an intermediate layer (multilayer intermediate layer) in the multilayer substrate.

In one embodiment, the surface layer on one side of the multilayer substrate is the first polyethylene layer and the surface layer on the other side of the multilayer substrate is the third polyethylene layer. The multilayer substrate may comprise other layers between at least one of the first polyethylene layer, the second polyethylene layer, the second polyethylene layer, the second polyethylene layer, the second polyethylene layer and the third polyethylene layer. In one embodiment, the multilayer substrate consists only of the first polyethylene layer, the second polyethylene layer, the second polyethylene layer, the second polyethylene layer, the second polyethylene layer and the third polyethylene layer.

Hereinafter, the polyethylene layer is also referred to as "PE layer".

Examples of polyethylene contained in the multilayer base material include high-density polyethylene, medium-density polyethylene, low-density polyethylene (high-pressure low-density polyethylene), linear low-density polyethylene, and ultra-low-density polyethylene.

The melt flow rate (MFR) of the polyethylene contained in the multilayer substrate is preferably 0.1 g/10 min or more and 50 g/10 min or less, more preferably 0, from the viewpoint of film formability and processability of the multilayer substrate. 2 g/10 min or more and 30 g/10 min or less, more preferably 0.2 g/10 min or more and 15 g/10 min or less, still more preferably 0.2 g/10 min or more and 10 g/10 min or less, particularly preferably 0.2 g/10 min or more and 10 g/10 min or less. It is 2 g/10 minutes or more and 5 g/10 minutes or less. In the present disclosure, MFR is measured according to ASTM D1238 under conditions of a temperature of 190° C. and a load of 2.16 kg.

FIG. 1 shows one embodiment of a multilayer substrate.
The multilayer substrate 10 of FIG.
a first PE layer 12;
a second a PE layer 18;
a second PE layer 20;
a second b PE layer 22;
A third PE layer 14 is provided in this order in the thickness direction. In the multilayer substrate 10 of FIG. 1, the 2a PE layer 18 and the 2b PE layer 22 may be omitted.

For example, a first PE layer may contain medium density polyethylene and high density polyethylene, and a third PE layer may contain medium density polyethylene and high density polyethylene. By adjusting the amount ratio of medium density polyethylene and high density polyethylene, for example, the indentation modulus and indentation hardness, which will be described later, can be adjusted. This can further improve the ink adhesion and heat resistance of the multilayer substrate.

The mass ratio of medium density polyethylene to high density polyethylene (medium density polyethylene/high density polyethylene) in the first PE layer and the third PE layer is independently preferably 1.1 or more and 5 or less, more preferably is 1.5 or more and 3 or less. This can further improve the balance between ink adhesion and heat resistance.

The total content of medium-density polyethylene and high-density polyethylene in the first PE layer and the third PE layer is each independently preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass. % or more. This can further improve the ink adhesion and heat resistance of the multilayer substrate.

For example, the second PE layer may contain linear low density polyethylene. With such a configuration, for example, the indentation elastic modulus and indentation hardness, which will be described later, tend to be adjusted to low ranges. Thereby, the stretchability of the laminate, which is the precursor of the multilayer base material, can be improved.

The content of the linear low-density polyethylene in the second PE layer is preferably more than 50% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, and 90% by mass or more. % by mass or more, or 95% by mass or more. This can further improve the balance between heat resistance, rigidity and stretchability.

The 2a PE layer and the 2b PE layer may each contain high density polyethylene in one embodiment. With such a configuration, for example, the indentation elastic modulus and indentation hardness, which will be described later, tend to be adjusted within a high range. These layers contribute to improving the heat resistance of the multilayer substrate. That is, by including high-density polyethylene in the 2a PE layer and the 2b PE layer in addition to the first PE layer and the third PE layer, the heat resistance of the multilayer substrate can be further improved.

The 2a PE layer and the 2b PE layer may each further comprise low density polyethylene in one embodiment. With such a configuration, for example, the indentation elastic modulus and indentation hardness, which will be described later, may be adjusted. Thereby, the balance of heat resistance, rigidity and workability of the multilayer base material can be further improved.

The mass ratio of high-density polyethylene to low-density polyethylene (high-density polyethylene/low-density polyethylene) in the PE layer 2a and the PE layer 2b is preferably 1 or more and 4 or less, more preferably 1 0.5 or more and 3 or less. Thereby, the balance of heat resistance, rigidity and workability of the multilayer base material can be further improved.

The content ratio of high-density polyethylene in the PE layer 2a and the PE layer 2b is preferably more than 50% by mass, more preferably 55% by mass or more, and still more preferably 60% by mass or more. Thereby, the heat resistance of the multilayer substrate can be further improved.

The total content of high-density polyethylene and low-density polyethylene in the PE layer 2a and the PE layer 2b is independently preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass. % or more. Thereby, the balance of heat resistance, rigidity and workability of the multilayer base material can be further improved.

In other embodiments, the 2a PE layer may contain medium density polyethylene and linear low density polyethylene, and the 2b PE layer comprises medium density polyethylene and linear low density polyethylene. may contain. By adjusting the ratio of medium density polyethylene and linear low density polyethylene, for example, the indentation modulus and indentation hardness, which will be described later, can be adjusted. These layers contribute to improving the stretchability of the laminate, which is the precursor of the multilayer base material.

The mass ratio of medium density polyethylene to linear low density polyethylene (medium density polyethylene/linear low density polyethylene) in the PE layer 2a and the PE layer 2b is independently preferably 0.25. 4 or less, more preferably 0.4 or more and 2.4 or less. This can further improve the balance between heat resistance, rigidity and stretchability.

The total content of medium density polyethylene and linear low density polyethylene in the PE layer 2a and the PE layer 2b is independently preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably is 95% by mass or more. Thereby, the stretchability of the laminate, which is the precursor, can be further improved.

The thickness of each of the first PE layer and the third PE layer is preferably 0.5 μm or more and 10 μm or less, more preferably 1 μm or more and 8 μm or less, still more preferably 1 μm or more and 5 μm or less. This can further improve the ink adhesion and heat resistance of the multilayer substrate.

The respective thicknesses of the first PE layer and the third PE layer are equal to the thicknesses of the 2a PE layer, the second PE layer and the 2b PE layer (hereinafter collectively the 2a, 2nd and 2b layers). (also referred to as a "multilayer intermediate layer"). The ratio of the thickness of each of the first PE layer and the third PE layer to the total thickness of the multilayer intermediate layer (first PE layer or third PE layer/multilayer intermediate layer) is preferably 0.05 0.8 or less, more preferably 0.1 or more and 0.7 or less, and still more preferably 0.1 or more and 0.4 or less. Thereby, the rigidity, strength and heat resistance of the multilayer substrate can be further improved.

The thickness of the second PE layer is preferably 1 μm or more and 50 μm or less, more preferably 2 μm or more and 40 μm or less, and still more preferably 5 μm or more and 30 μm or less. This can further improve the balance between heat resistance, rigidity and stretchability.

The thickness of each of the 2a PE layer and the 2b PE layer is independently preferably 0.5 μm or more and 15 μm or less, more preferably 1 μm or more and 10 μm or less, still more preferably 1 μm or more and 8 μm or less. This can further improve the heat resistance of the multilayer substrate or the stretchability of the precursor laminate.

The ratio of the total thickness of the 2a PE layer and the 2b PE layer to the thickness of the 2nd PE layer (the total thickness of the 2a PE layer and the 2b PE layer / the thickness of the second PE layer is preferably 0.1 or more and 10 or less, more preferably 0.2 or more and 5 or less, and still more preferably 0.5 or more and 2 or less. Thereby, the rigidity, strength and heat resistance of the multilayer substrate can be further improved.
The thickness of each layer described above is the thickness after stretching.

Each layer constituting the multilayer base material may contain an additive independently. Examples of additives include cross-linking agents, antioxidants, anti-blocking agents, slip agents, UV absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments and modifying resins. be done.

At least one layer selected from the first PE layer, the second PE layer, and the third PE layer in the multilayer substrate, specifically, the first PE layer, the second PE layer, the second At least one layer selected from the PE layer, the 2b PE layer, and the third PE layer may contain a slip agent. Thereby, for example, the workability of the multilayer base material can be improved. For example, the second PE layer may contain the slip agent and all of the layers may contain the slip agent.

Slip agents include, for example, amide lubricants, fatty acid esters such as glycerin fatty acid esters, hydrocarbon waxes, higher fatty acid waxes, metallic soaps, hydrophilic silicones, silicone-modified (meth)acrylic resins, silicone-modified epoxy resins, and silicones. modified polyethers, silicone-modified polyesters, block-type silicone (meth)acrylic copolymers, polyglycerol-modified silicones and paraffins.

Among lubricants, amide-based lubricants are preferred. Examples of amide lubricants include saturated fatty acid amides, unsaturated fatty acid amides, substituted amides, methylolamides, saturated fatty acid bisamides, unsaturated fatty acid bisamides, fatty acid ester amides and aromatic bisamides.

Saturated fatty acid amides include, for example, lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide and hydroxystearic acid amide. Unsaturated fatty acid amides include, for example, oleic acid amide and erucic acid amide. Substituted amides include, for example, N-oleyl palmitic acid amide, N-stearyl stearic acid amide, N-stearyl oleic acid amide, N-oleyl stearic acid amide and N-stearyl erucic acid amide. Methylolamides include, for example, methylol stearamide. Examples of saturated fatty acid bisamides include methylenebisstearic acid amide, ethylenebiscapric acid amide, ethylenebislauric acid amide, ethylenebisstearic acid amide, ethylenebishydroxystearic acid amide, ethylenebisbehenic acid amide, and hexamethylenebisstearic acid. amides, hexamethylenebisbehenamide, hexamethylenehydroxystearateamide, N,N'-distearyladipamide and N,N'-distearylsebacamide. Examples of unsaturated fatty acid bisamides include ethylenebisoleic acid amide, ethylenebiserucic acid amide, hexamethylenebisoleic acid amide, N,N'-dioleyladipic acid amide and N,N'-dioleylsebacic acid amide. mentioned. Fatty acid ester amides include, for example, stearamide ethyl stearate. Examples of aromatic bisamides include m-xylylenebisstearic acid amide, m-xylylenebishydroxystearic acid amide and N,N'-distearylisophthalic acid amide.
Among slip agents, erucamide is preferred.

In order to increase the dispersibility of the slip agent in the resin composition forming each layer, a masterbatch containing the slip agent and polyethylene may be used. The content of the slip agent in the masterbatch is preferably from 1% by mass to 30% by mass, more preferably from 2% by mass to 20% by mass, and even more preferably from 3% by mass to 10% by mass. Specific examples of polyethylene include those mentioned above. The preferred physical properties (density, MFR, etc.) that polyethylene satisfies are also as described above.

In the multilayer base material, the content of the slip agent in the layer containing the slip agent may be, for example, 0.01% by mass or more and 3% by mass or less, or may be 0.03% by mass or more and 1% by mass or less. Thereby, the workability of the multilayer base material can be further improved.

When multiple types of polyethylene with different densities (n types; n is an integer of 2 or more) are contained in one layer, the density of polyethylene constituting the layer may be measured in accordance with the above JIS K7112. , the average density D _av calculated according to the following formula (1) may be used as the density of the polyethylene constituting the layer.

D _av =ΣW _i ×D _i (1)
In formula (1), Σ means the sum of W _i ×D _i from 1 to n for i, n is an integer of 2 or more, and W _i is the mass fraction of the i-th polyethylene and D _i indicates the density (g/cm ³ ) of the i-th polyethylene.

The multi-layer base material is stretched and has unique physical properties, so that it is superior in rigidity, strength, heat resistance, and ink adhesion to conventional polyethylene films. Therefore, the polyethylene multilayer substrate can be used, for example, as a substrate for packaging materials, and a clear image can be formed on the surface of the multilayer substrate.

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

The polyethylene content in the multilayer base material is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more. Thereby, the recyclability of the multilayer base material can be improved.

Specific embodiments of the polyethylene multilayer substrate are described below.
The polyethylene multilayer substrate of the first embodiment comprises a first PE layer, a second PE layer, a second PE layer, a second b PE layer, and a third PE layer, each having a thickness of Prepared in this order in the direction and stretched,
the first PE layer contains medium density polyethylene and high density polyethylene;
the PE layer of 2a contains high density polyethylene and optionally low density polyethylene;
the second PE layer contains linear low density polyethylene;
the 2b PE layer contains high density polyethylene and optionally low density polyethylene;
A third PE layer contains medium density polyethylene and high density polyethylene.

The polyethylene multilayer substrate of the second embodiment comprises a first PE layer, a second PE layer, a second PE layer, a second b PE layer, and a third PE layer, each having a thickness of Prepared in this order in the direction and stretched,
the first PE layer contains medium density polyethylene and high density polyethylene;
the PE layer of 2a contains medium density polyethylene and linear low density polyethylene;
the second PE layer contains linear low density polyethylene;
the 2b PE layer contains medium density polyethylene and linear low density polyethylene;
A third PE layer contains medium density polyethylene and high density polyethylene.

The medium density polyethylene contained in the first PE layer and the medium density polyethylene contained in the third PE layer may be the same or different. is preferably
The high-density polyethylene contained in the first PE layer and the high-density polyethylene contained in the third PE layer may be the same or different. is preferably

In the first embodiment, the high-density polyethylene contained in the PE layer 2a and the high-density polyethylene contained in the PE layer 2b may be the same or different to facilitate the formation of a multilayer substrate. From the standpoint of manufacturability, they are preferably the same.

In the second embodiment, the linear low density polyethylene contained in the second PE layer and the linear low density polyethylene contained in the 2a PE layer and the 2b PE layer are the same may also be different.
In a second embodiment, the medium density polyethylene contained in the PE layer 2a and the medium density polyethylene contained in the PE layer 2b may be the same or different, facilitating the multi-layer substrate. From the standpoint of manufacturability, they are preferably the same.
In the second embodiment, the linear low density polyethylene contained in the 2a PE layer and the linear low density polyethylene contained in the 2b PE layer may be the same or different, It is preferable that they are the same from the viewpoint that the multilayer base material can be easily manufactured.
In the second embodiment, the medium density polyethylene contained in the 2a PE layer and the 2b PE layer and the medium density polyethylene contained in the first PE layer and the third PE layer are the same. may also be different.

<Method for producing polyethylene multilayer substrate>
The polyethylene multilayer substrate can be produced by, for example, film-forming a plurality of polyethylene materials by an inflation method or a T-die method to form a laminate, and stretching the obtained laminate. The stretching treatment can improve the transparency, rigidity, strength and heat resistance of the multilayer base material, and the multilayer base material can be suitably used as a base material for packaging materials, for example.

The polyethylene multilayer substrate of the first embodiment includes, for example, a layer containing medium density polyethylene and high density polyethylene, a layer containing high density polyethylene, a layer containing linear low density polyethylene, and a layer containing high density polyethylene. It is obtained by stretching a laminate (precursor) having a layer containing polyethylene and a layer containing medium-density polyethylene and high-density polyethylene in this order in the thickness direction.

Specifically, from the outside, a layer containing medium density polyethylene and high density polyethylene, a layer containing high density polyethylene, a layer containing linear low density polyethylene, and a layer containing high density polyethylene. , a layer containing medium density polyethylene and high density polyethylene can be co-extruded into a tube to form a laminate. Alternatively, a layer containing medium-density polyethylene and high-density polyethylene, a layer containing high-density polyethylene, and a layer containing linear low-density polyethylene are coextruded from the outside into a tubular shape, and then facing straight A laminate can be produced by pressing layers containing linear low-density polyethylene together with a rubber roll or the like. By manufacturing a laminate by such a method, the number of defective products can be significantly reduced, and production efficiency can be improved.

The polyethylene multilayer substrate of the second embodiment and other polyethylene multilayer substrates can also be produced, for example, by the method described above.

When a laminate is produced by the T-die method, the melt flow rate (MFR) of polyethylene constituting each layer is preferably 3 g/10 min or more and 20 g/10 from the viewpoint of film formability and processability of the multilayer base material. minutes or less.

When a laminate is produced by the inflation method, the MFR of polyethylene constituting each layer is preferably 0.2 g/10 min or more and 5 g/10 min or less from the viewpoint of film formability and processability of the multilayer substrate. .

A multilayer base material is obtained, for example, by stretching the laminate described above. In addition, in the inflation film forming machine, the laminate can also be stretched. As a result, a multilayer base material can be produced, and production efficiency can be further improved.

The multilayer substrate may be a uniaxially stretched film or a biaxially stretched film. The multilayer substrate, in one embodiment, 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 times or more and 10 times or less, more preferably 3 times or more and 7 times or less. In one embodiment, the stretch ratio in the transverse direction (TD) of the multilayer base material is preferably 2 times or more and 10 times or less, more preferably 3 times or more and 7 times or less.

When the draw ratio is 2 times 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 draw ratio is 10 times or less, the laminate can be satisfactorily drawn.

The laminate or multilayer substrate is preferably surface-treated. This can improve the adhesion between the surface layer of the multilayer substrate and the layers laminated on the multilayer substrate. Examples of surface treatment methods include physical treatments such as corona discharge treatment, ozone treatment, low-temperature plasma treatment using gases such as oxygen gas and nitrogen gas, glow discharge treatment; and oxidation treatment using chemicals. Chemical treatment can be mentioned.

A conventionally known anchor coating agent may be used to form an anchor coat layer on the surface of the laminate or multilayer substrate.

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. When the thickness of the multilayer substrate is 10 µm or more, the rigidity and strength of the multilayer substrate can be improved. When the thickness of the multilayer base material is 60 µm or less, the processability of the multilayer base material can be improved. In the range in which the above effects can be obtained, it is preferable from the viewpoint of cost reduction, for example, that the thickness of the multilayer base material is small.

[Laminate]
The laminate of the present disclosure is
the polyethylene multilayer substrate described above;
and a heat seal layer containing polyethylene as a main component.

In the present disclosure, the indentation elastic moduli of the first PE layer, the 2a PE layer, the second PE layer, the 2b PE layer and the third PE layer are respectively defined as an indentation modulus 1 and an indentation modulus 2a. , indentation modulus 2, indentation modulus 2b, and indentation modulus 3. The ratio of the indentation modulus of the first PE layer to the indentation modulus of the second PE layer is also described as the ratio (modulus 1/modulus 2). The same applies to other cases.

In the present disclosure, the indentation hardness of the first PE layer, the 2a PE layer, the second PE layer, the 2b PE layer and the third PE layer are respectively defined as an indentation hardness of 1, an indentation hardness of 2a, an indentation hardness of 2. Also referred to as indentation hardness 2b and indentation hardness 3. The ratio of the indentation hardness of the first PE layer to the indentation hardness of the second PE layer is also described as the ratio (hardness 1/hardness 2). The same applies to other cases.

The laminate of the first aspect of the present disclosure is characterized in that the first PE layer has an indentation modulus of elasticity of 1.0 GPa or more, and the third PE layer has an indentation modulus of elasticity of 1.0 GPa or more. and Thereby, the heat resistance of the laminate can be improved, and for example, thermal shrinkage of the laminate when heat is applied such as heat sealing can be suppressed.

The indentation elastic modulus 1 and indentation elastic modulus 3 in the laminate of the first aspect are each independently 1.0 GPa or more, preferably 1.05 GPa or more, more preferably 1.1 GPa or more, and still more preferably 1.1 GPa or more. 15 GPa or more, particularly preferably 1.3 GPa or more; It is 5 GPa or less, 2.0 GPa or less, or 1.8 GPa or less. This tends to further suppress thermal shrinkage of the laminate during heat sealing, for example. The ranges of the indentation modulus 1 and the indentation modulus 3 may independently be any combination of the above lower limit and upper limit, for example, 1.0 GPa or more and 4.5 GPa or less.

The indentation modulus 2 of the laminate of the first aspect is preferably 0.03 GPa or more, more preferably 0.05 GPa or more, still more preferably 0.1 GPa or more, still more preferably 0.13 GPa or more, and particularly preferably 0 preferably 0.7 GPa or less, more preferably 0.6 GPa or less, even more preferably 0.5 GPa or less, even more preferably 0.4 GPa or less, and particularly preferably 0.3 GPa or less. With such a design, for example, the stretchability of the laminate before stretching tends to be more excellent. The range of the indentation modulus 2 may be any combination of the above lower limit and upper limit, for example, 0.03 GPa or more and 0.7 GPa or less.

The indentation elastic modulus 2a and the indentation elastic modulus 2b in the laminate of the first aspect are each independently preferably 0.3 GPa or more, more preferably 0.4 GPa or more, still more preferably 0.5 GPa or more, and even more preferably 0.6 GPa or more; preferably 3.5 GPa or less, more preferably 3.0 GPa or less, still more preferably 2.5 GPa or less, even more preferably 2.0 GPa or less, and particularly preferably 1.5 GPa or less. This tends to further suppress thermal shrinkage of the laminate during heat sealing, for example. The ranges of the indentation elastic modulus 2a and the indentation elastic modulus 2b may be independently any combination of the above lower limit and upper limit, for example, 0.3 GPa or more and 3.5 GPa or less.

In the laminate of the first aspect, the magnitude of the indentation elastic modulus of each PE layer preferably satisfies the relationship of indentation elastic modulus 1>indentation elastic modulus 2a>indentation elastic modulus 2, and indentation elastic modulus 3>indentation elasticity. It is preferable to satisfy the relationship of modulus 2b>indentation modulus 2. This tends to further improve the balance between heat resistance and stretchability (workability, productivity) of the multilayer base material, for example.

In the laminate of the first aspect, the indentation modulus of the first PE layer is preferably at least 3.5 times the indentation modulus of the second PE layer, and the indentation modulus of the third PE layer is preferably at least 3.5 times the indentation modulus of the second PE layer. As a result, the heat resistance of the laminate can be improved, and for example, thermal shrinkage of the laminate can be further suppressed when heat is applied such as during heat sealing.

The ratio (elastic modulus 1/elastic modulus 2) and ratio (elastic modulus 3/elastic modulus 2) in the laminate of the first aspect are each independently preferably 3.5 or more, more preferably 4.0 or more, More preferably 4.5 or more, still more preferably 5.0 or more, particularly preferably 5.5 or more; preferably 16.0 or less, more preferably 14.0 or less, still more preferably 12.0 or less, More preferably 10.0 or less, particularly preferably 9.0 or less. The range of the ratio (elastic modulus 1/elastic modulus 2) and the range of the ratio (elastic modulus 3/elastic modulus 2) may each independently be any combination of the above lower and upper limits, such as 3.5. 16.0 or less may be sufficient.

In the laminate of the first aspect, the indentation modulus of the PE layer 2a is preferably at least 2.0 times the indentation modulus of the second PE layer, and the indentation modulus of elasticity of the PE layer 2b is preferably at least 2.0 times the indentation modulus of the second PE layer. This tends to further suppress thermal shrinkage of the laminate during heat sealing, for example.

The ratio (elastic modulus 2a/elastic modulus 2) and ratio (elastic modulus 2b/elastic modulus 2) in the laminate of the first aspect are each independently preferably 2.0 or more, more preferably 2.5 or more, More preferably 3.0 or more; preferably 14.0 or less, more preferably 12.0 or less, still more preferably 10.0 or less, still more preferably 9.0 or less, particularly preferably 8.5 or less be. The range of the ratio (elastic modulus 2a/elastic modulus 2) and the range of the ratio (elastic modulus 2b/elastic modulus 2) may each independently be any combination of the above lower and upper limits, such as 2.0. It may be above 14.0 or below.

In the laminate of the first aspect, the ratio (elastic modulus 1/elastic modulus 3) is preferably 0.6 or more and 1.7 or less, more preferably 0.7 or more and 1.4 or less, further preferably 0.8 It is more than or equal to 1.2 or less, more preferably 0.9 or more and 1.1 or less. As a result, for example, the symmetry of the layer structure of the multilayer base material can be improved, so curling of the multilayer base material can be suppressed, and workability such as printing and lamination tends to be improved.

In the laminate of the first aspect, the ratio (elastic modulus 2a/elastic modulus 2b) is preferably 0.6 or more and 1.7 or less, more preferably 0.7 or more and 1.4 or less, further preferably 0.8 It is more than or equal to 1.2 or less, more preferably 0.9 or more and 1.1 or less. As a result, for example, the symmetry of the layer structure of the multilayer base material can be improved, so curling of the multilayer base material can be suppressed, and workability such as printing and lamination tends to be improved.

The laminate of the second aspect of the present disclosure is characterized in that the first PE layer has an indentation hardness of 45 MPa or more, and the third PE layer has an indentation hardness of 45 MPa or more. Thereby, the heat resistance of the laminate can be improved, and for example, thermal shrinkage of the laminate when heat is applied such as heat sealing can be suppressed.

Indentation hardness 1 and indentation hardness 3 in the laminate of the second aspect are each independently 45 MPa or more, preferably 48 MPa or more, more preferably 50 MPa or more, and still more preferably 52 MPa or more; preferably 110 MPa or less, It is more preferably 90 MPa or less, still more preferably 80 MPa or less, even more preferably 75 MPa or less, and particularly preferably 70 MPa or less. This tends to further suppress thermal shrinkage of the laminate during heat sealing, for example. The range of indentation hardness 1 and indentation hardness 3 may be each independently any combination of the above lower limit and upper limit, for example, 45 MPa or more and 110 MPa or less. The laminate of the first aspect may further satisfy the above-described requirements for an indentation hardness of 1 and an indentation hardness of 3.

The indentation hardness 2 of the laminate of the second aspect is preferably 1 MPa or more, more preferably 3 MPa or more, still more preferably 7 MPa or more, still more preferably 10 MPa or more, and particularly preferably 15 MPa or more; preferably 40 MPa or less, It is more preferably 35 MPa or less, still more preferably 30 MPa or less, even more preferably 26 MPa or less, and particularly preferably 23 MPa or less. With such a design, for example, the stretchability of the laminate before stretching tends to be more excellent. The range of indentation hardness 2 may be any combination of the above lower limit and upper limit, for example, 1 MPa or more and 40 MPa or less. The laminate of the first aspect may further satisfy the above-described requirements for an indentation hardness of 2.

The indentation hardness 2a and the indentation hardness 2b in the laminate of the second aspect are each independently preferably 20 MPa or higher, more preferably 30 MPa or higher, still more preferably 35 MPa or higher, and even more preferably 37 MPa or higher; preferably 100 MPa. Below, it is more preferably 80 MPa or less, still more preferably 70 MPa or less, still more preferably 65 MPa or less, and particularly preferably 60 MPa or less. This tends to further suppress thermal shrinkage of the laminate during heat sealing, for example. The ranges of the indentation hardness 2a and the indentation hardness 2b may independently be any combination of the above lower limit and upper limit, for example, 20 MPa or more and 100 MPa or less. The laminate of the first aspect may further satisfy the above-described requirements for indentation hardness 2a and indentation hardness 2b.

In the laminate of the second aspect, the indentation hardness of each PE layer preferably satisfies the relationship of indentation hardness 1>indentation hardness 2a>indentation hardness 2, and indentation hardness 3>indentation hardness 2b>indentation hardness 2. It is preferable to satisfy the relationship of This tends to further improve the balance between heat resistance and stretchability (workability, productivity) of the multilayer base material, for example.

In the laminate of the second aspect, the indentation hardness of the first PE layer is preferably at least 2.0 times the indentation hardness of the second PE layer, and the indentation hardness of the third PE layer is It is preferably at least 2.0 times the indentation hardness of the PE layer No. 2. As a result, the heat resistance of the laminate can be improved, and for example, thermal shrinkage of the laminate can be further suppressed when heat is applied such as during heat sealing.

The ratio (hardness 1/hardness 2) and ratio (hardness 3/hardness 2) in the laminate of the second aspect are each independently preferably 2.0 or more, more preferably 2.2 or more, and still more preferably 2 preferably 6.0 or less, more preferably 5.5 or less, even more preferably 5.0 or less, still more preferably It is 4.5 or less, particularly preferably 4.0 or less or 3.5 or less. The range of the ratio (hardness 1/hardness 2) and the range of the ratio (hardness 3/hardness 2) may each independently be any combination of the above lower and upper limits, for example, 2.0 to 6.0. It can be below. The laminate of the first aspect may further satisfy the above requirements relating to the ratio (hardness 1/hardness 2) and ratio (hardness 3/hardness 2).

In the laminate of the second aspect, the indentation hardness of the 2a PE layer is preferably at least 1.5 times the indentation hardness of the second PE layer, and the indentation hardness of the 2b PE layer is It is preferably at least 1.5 times the indentation hardness of the PE layer of No. 2. This tends to further suppress thermal shrinkage of the laminate during heat sealing, for example.

The ratio (hardness 2a/hardness 2) and ratio (hardness 2b/hardness 2) in the laminate of the second aspect are each independently preferably 1.5 or more, more preferably 1.7 or more, and still more preferably 1 preferably 6.0 or less, more preferably 5.5 or less, even more preferably 5.0 or less, still more preferably 4.5 or less, particularly preferably 4.0 or less or 3.5 or less is. This tends to further suppress thermal shrinkage of the laminate during heat sealing, for example. The range of the ratio (hardness 2a/hardness 2) and the range of the ratio (hardness 2b/hardness 2) may each independently be any combination of the above lower and upper limits, for example, 1.5 to 6.0. It can be below. The laminate of the first aspect may further satisfy the above requirements for the ratio (hardness 2a/hardness 2) and ratio (hardness 2b/hardness 2).

In the laminate of the second aspect, the ratio (hardness 1/hardness 3) is preferably 0.6 or more and 1.7 or less, more preferably 0.7 or more and 1.4 or less, still more preferably 0.8 or more and 1 0.2 or less, more preferably 0.9 or more and 1.1 or less. As a result, for example, the symmetry of the layer structure of the multilayer base material can be improved, so curling of the multilayer base material can be suppressed, and workability such as printing and lamination tends to be improved.

In the laminate of the second aspect, the ratio (hardness 2a/hardness 2b) is preferably 0.6 or more and 1.7 or less, more preferably 0.7 or more and 1.4 or less, still more preferably 0.8 or more and 1 0.2 or less, more preferably 0.9 or more and 1.1 or less. As a result, for example, the symmetry of the layer structure of the multilayer base material can be improved, so curling of the multilayer base material can be suppressed, and workability such as printing and lamination tends to be improved.

In the present disclosure, the indentation modulus and indentation hardness of each PE layer can be adjusted, for example, by appropriately selecting polyethylene contained in each PE layer. In the PE layer, the indentation elastic modulus and indentation hardness tend to be increased by increasing the content of high-density polyethylene such as high-density polyethylene. In the PE layer, the indentation modulus and indentation hardness tend to decrease by increasing the content of low-density polyethylene such as low-density polyethylene and linear low-density polyethylene. The indentation modulus and indentation hardness of each PE layer can also be adjusted by the draw ratio. For example, when the draw ratio is increased, the indentation modulus and indentation hardness of each PE layer tend to increase. For example, when the draw ratio is decreased, the indentation modulus and indentation hardness of each PE layer tend to decrease.

In the present disclosure, the indentation modulus and indentation hardness of each PE layer are measured by the nanoindentation method. Specifically, the indentation elastic modulus and the indentation hardness of the laminate are measured using a nanoindenter using a cross section parallel to the TD direction of each PE layer of the polyethylene multilayer substrate as a measurement surface. The measurement conditions are as follows. A Berkovich indenter (triangular pyramid indenter) is used as an indenter for the nanoindenter. Over 10 seconds, the indenter was pushed into the PE layer from a cross section parallel to the TD direction of the laminate to a depth of 200 nm, held in that state for 5 seconds, and then unloaded over 10 seconds. Obtain the projected contact area A with depth and the load-displacement curve. The elastic modulus and hardness values are calculated from the obtained load-displacement curve. The measurement is carried out in a room temperature (25°C) environment. The measurement is performed at 5 points on the same cross section, and the average value of the elastic moduli is defined as the indentation elastic modulus, and the average value of the hardness is defined as the indentation hardness. Details of the measurement conditions are described in Examples.

A laminate 30 of the present disclosure comprises a polyethylene multilayer substrate 10 and a heat seal layer 32, as shown in FIG. In the multilayer substrate 10 , an intermediate layer including the second polyethylene layer and optionally the 2a and 2b polyethylene layers was described as an intermediate layer 16 .

In one embodiment, laminate 30 further comprises a printed layer (not shown) on multilayer substrate 10 . The printed layer is usually formed on the surface layer of the multilayer substrate provided with the heat seal layer, for example, on the first polyethylene layer described above.

In one embodiment, laminate 30 comprises barrier layer 34 and adhesive layer 36 between multilayer substrate 10 and heat seal layer 32, as shown in FIG. In this embodiment, barrier layer 34 is formed on the surface of multilayer substrate 10 .
In one embodiment, the laminate 30 comprises an adhesive layer 36 and a barrier layer 34 between the multilayer substrate 10 and the heat seal layer 32, as shown in FIG. In this embodiment, barrier layer 34 is formed on the surface of heat seal layer 32 .
In one embodiment, laminate 30 comprises an adhesive layer 36 between multilayer substrate 10 and heat seal layer 32, as shown in FIG.

In the laminate of the present disclosure, the polyethylene content is preferably 90% by mass or more. Thereby, the recyclability of the laminate can be improved. The content ratio of polyethylene in the laminate means the ratio of the content of polyethylene to the sum of the content of the resin material in each layer constituting the laminate.

The laminate of the present disclosure exhibits the following thermal shrinkage in one embodiment. MD refers to the longitudinal or machine direction of the laminate and TD refers to the direction perpendicular to the MD.

The MD thermal shrinkage (MD) of the laminate is, for example, 15% or less, preferably 13% or less, more preferably 11% or less, even more preferably 10% or less, even more preferably 8% or less, and particularly preferably is 7% or less. The lower limit of the heat shrinkage (MD) is preferably as low as possible, but may be, for example, 0.5%, 1%, 2% or 3%. A laminate having such a low heat shrinkage (MD) is excellent in, for example, printability and bag-making aptitude when a packaging bag is produced by heat-sealing.

The thermal shrinkage (TD) of the TD of the laminate is, for example, 15% or less, preferably 13% or less, more preferably 11% or less, even more preferably 10% or less, even more preferably 8% or less, and particularly preferably is 7% or less. The lower limit of the heat shrinkage (MD) is preferably as low as possible, but may be, for example, 0.5%, 1%, 2% or 3%. A laminate having such a low thermal shrinkage (TD) is excellent in, for example, printability and bag-making aptitude when a packaging bag is produced by heat sealing.

The ratio (MD/TD) between the thermal shrinkage (MD) and the thermal shrinkage (TD) of the laminate is preferably 0.5 or more and 2.0 or less, more preferably 0.7 or more and 1.4 or less, and further It is preferably 0.8 or more and 1.2 or less, particularly preferably 0.9 or more and 1.1 or less. If the ratio (MD/TD) is in such a range, the laminate shrinks relatively uniformly in the MD and TD even when subjected to heat treatment, so that, for example, image distortion in the printed layer of the laminate can be suppressed. .

The thermal shrinkage of the laminate is measured as follows. The laminate is cut to 10 cm x 10 cm to produce 3 sample pieces each. Each sample piece was folded in half parallel to MD or TD so that the heat seal layer side of each sample was on the inside, and using a heat seal tester, the temperature was 120° C., the pressure was 1 kgf/cm ² , and the time was 1 second. A 10 cm area is heat sealed (see Figure 6). In FIG. 6, hatched portions indicate heat-sealed portions. After heat-sealing, the seal width of the sample is measured, and the MD shrinkage rate (see FIG. 6(a)) and the TD shrinkage rate (see FIG. 6(b)) are calculated. Let the average value of three sample pieces be each heat shrinkage rate.

Each thermal contraction rate is calculated by the following formula.
Thermal shrinkage (MD) (%) = {(length in the MD direction of the heat-sealable portion of the laminate (1.5 cm) - length in the MD direction of the heat-sealed portion of the laminate after heat sealing) / lamination Length in the MD direction of the part to be heat-sealed of the body (1.5 cm)} x 100
Thermal shrinkage (TD) (%) = {(length in the TD direction of the heat-sealable portion of the laminate (1.5 cm) - length in the TD direction of the heat-sealed portion of the laminate after heat sealing) / lamination Length in the TD direction of the part to be heat-sealed of the body (1.5 cm)} x 100

For example, when the laminate is sealed with a 1.5 cm heat seal bar and the sample seal width is 1.4 cm, the heat shrinkage rate is (1.5-1.4)/ 1.5×100=6.7%.

<Heat seal layer>
The heat seal layer is a layer containing polyethylene as a main component, that is, a layer containing polyethylene in an amount exceeding 50% by mass. The content of polyethylene in the heat seal layer is preferably 60% by mass or more, more preferably 70% by mass or more, and still more preferably 80% by mass or more, 85% by mass or more, 90% by mass or more, or 95% by mass or more. . With such a configuration, a laminate for packaging material having sufficient rigidity, strength and heat resistance and excellent recyclability can be obtained.

The laminate of the present disclosure includes a polyethylene multilayer substrate and a heat-sealable layer containing polyethylene as a main component (hereinafter also referred to as a "heat-sealable polyethylene layer"). In one embodiment, a printed layer (image) is formed on at least one side of the multilayer substrate. It is preferable that the printed layer is formed on the side of the multilayer base material on which the heat-sealable polyethylene layer is provided, since this prevents deterioration of the image over time.

In one embodiment, the first polyethylene layer or the third polyethylene layer constitutes the surface layer on one side of the laminate and the heat seal layer constitutes the surface layer on the other side of the laminate.

In the laminate comprising a polyethylene multilayer substrate and a heat-sealable polyethylene layer, the resin layers contained in the laminate are all polyethylene layers in one embodiment, and the laminate is a polyester film, a nylon film, or the like. different kinds of resin films. In addition, the polyethylene multilayer base material satisfies the rigidity, strength and heat resistance required as the outer layer film of the packaging material, and the heat-sealable polyethylene layer enables packaging. Therefore, the laminate is suitable as a material constituting a packaging material that requires recyclability.

In one embodiment, the laminate of the present disclosure consists only of a polyethylene multilayer substrate optionally formed with a printed layer, and a heat-sealable polyethylene layer. Thereby, in the laminate of the present disclosure, each resin layer is made of polyethylene, which is the same material, so that the recyclability can be particularly improved.

The heat seal layer is typically a non-stretched layer. For example, by laminating an unstretched polyethylene film on a multilayer substrate or the like via an adhesive layer as necessary, or by melt extruding a resin material containing polyethylene onto a multilayer substrate or the like, a heat seal layer is formed. can be formed. Examples of the adhesive layer include an adhesive layer to be described later.

Examples of polyethylene constituting the heat-seal layer include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene. Linear low density polyethylene and ultra low density polyethylene are preferred. From the viewpoint of reducing environmental load, biomass-derived polyethylene or recycled polyethylene may be used.

The content of polyethylene in the heat seal layer is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more. Thereby, the recyclability of the laminate can be improved.
The heat seal layer may contain the above additives.

The heat seal layer may be one layer or two or more layers. In one embodiment, the number of layers of the heat seal layer is one to three.
The thickness of the heat seal layer is, for example, 10 μm or more and 300 μm or less.
The thickness of the heat-sealing layer can be appropriately changed from the viewpoint of the strength of the heat-sealing layer and the processability of the laminate, depending on the mass of the contents filled in the packaging material produced, for example, by the laminate of the present disclosure. preferable.

For example, when the packaging material is a sachet, the thickness of the heat seal layer is preferably 20 μm or more and 60 μm or less. In this case, for example, the contents of 1 g or more and 200 g or less are satisfactorily filled in the pouch.
For example, when the packaging material is a stand pouch, the thickness of the heat seal layer is preferably 50 µm or more and 200 µm or less. In this case, for example, the contents of 50 g or more and 2000 g or less can be satisfactorily filled in the stand pouch.

<Barrier layer>
In one embodiment, the laminate of the present disclosure comprises a barrier layer between the multilayer substrate and the heat seal layer. Thereby, the gas barrier property of the laminate, specifically, the oxygen barrier property and the water vapor barrier property can be improved. The barrier layer may be formed on the surface of the multilayer base material, or may be formed on the surface of the heat seal layer. Also, a barrier layer may be provided between the multilayer substrate and the heat seal layer via an adhesive or the like.

In one embodiment, the barrier layer is a deposited layer. The deposited layer is composed of, for example, metals such as aluminum and inorganic oxides such as aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, zirconium oxide, titanium oxide, boron oxide, hafnium oxide and barium oxide. Among these, an aluminum deposition layer is preferable.

The thickness of the barrier layer is preferably 1 nm or more and 150 nm or less, more preferably 5 nm or more and 60 nm or less, and still more preferably 10 nm or more and 40 nm or less. By setting the thickness of the barrier layer to 1 nm or more, the oxygen barrier property and water vapor barrier property of the laminate can be further improved. By setting the thickness of the barrier layer to 150 nm or less, the occurrence of cracks in the barrier layer can be suppressed and the recyclability of the laminate can be improved.

Examples of methods for forming the barrier layer include physical vapor deposition (PVD) methods such as vacuum deposition, sputtering and ion plating; A chemical vapor deposition method (CVD method) such as a phase growth method can be used. The barrier layer may be a composite film including two or more barrier layers of different inorganic oxides, which is formed using both physical vapor deposition and chemical vapor deposition.

The degree of vacuum in the vapor deposition chamber is preferably about 10 ^-2 to 10 ^-8 mbar before introducing oxygen, and about 10 ^-1 to 10 ^-6 mbar after introducing oxygen. The amount of oxygen to be introduced varies depending on the size of the vapor deposition machine. Inert gases such as argon gas, helium gas and nitrogen gas may be used as a carrier gas for oxygen to be introduced as long as there is no problem. The conveying speed of the multilayer base material is, for example, about 10 to 800 m/min.

The surface of the barrier layer is preferably subjected to the surface treatment described above. Thereby, the adhesion between the barrier layer and the adjacent layer can be improved.

When the deposited layer is composed of inorganic oxides such as aluminum oxide and silicon oxide, a barrier coat layer may be provided on the surface of the deposited layer to form a barrier layer comprising the deposited layer and the barrier coat layer.

In one embodiment, the barrier coat layer is composed of a gas barrier resin. Examples of gas barrier resins include polyamide resins such as ethylene-vinyl alcohol copolymer (EVOH), polyvinyl alcohol, polyacrylonitrile, nylon 6, nylon 6,6 and polymetaxylylene adipamide (MXD6), polyester resins, Polyurethane resins as well as (meth)acrylic resins can be mentioned.

The thickness of the barrier coat layer is preferably 0.01 μm or more and 10 μm or less, more preferably 0.1 μm or more and 5 μm or less. By setting the thickness of the barrier coat layer to 0.01 μm or more, the gas barrier property can be further improved. By setting the thickness of the barrier coat layer to 10 μm or less, the workability of the laminate can be improved. In addition, it can be a laminate that can be suitably used for manufacturing a mono-material packaging container.

The barrier coat layer can be formed by, for example, dissolving or dispersing a material such as a gas barrier resin in water or a suitable organic solvent, applying the obtained coating liquid, and drying.

In another embodiment, the barrier coat layer is obtained by polycondensing a mixture of a metal alkoxide and a water-soluble polymer by a sol-gel method in the presence of a sol-gel catalyst, water, an organic solvent, and the like. It is a gas barrier coating film formed from a composition containing a decomposition product or a hydrolytic condensate of a metal alkoxide.
By providing such a barrier coat layer on the vapor deposition layer, the generation of cracks in the vapor deposition layer can be effectively prevented.

In one embodiment, the metal alkoxide is represented by the following general formula.
^R1nM ₍ ^OR2 ) _m
In the above formula, R ¹ and R ² each independently represent an organic group having 1 to 8 carbon atoms, M represents a metal atom, n represents an integer of 0 or more, and m represents an integer of 1 or more. , n+m represents the valence of M.

Examples of organic groups represented by R ¹ and R ² include alkyl groups such as methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group and isobutyl group. Metal atoms M include, for example, silicon, zirconium, titanium and aluminum.

Metal alkoxides satisfying the general formula include, for example, tetramethoxysilane (Si( _OCH3 ) ₄ ), tetraethoxysilane ₍ Si _{( OC2H5} ) ₄ ), tetrapropoxysilane (Si( _OC3H7 ) ₄ ), and tetrabutoxysilane (Si(OC ₄ H ₉ ) ₄ ).

It is preferable to use a silane coupling agent together with the metal alkoxide. A known organic reactive group-containing organoalkoxysilane can be used as the silane coupling agent.

Polyvinyl alcohol and ethylene-vinyl alcohol copolymers are preferred as the water-soluble polymer. Either one of polyvinyl alcohol and ethylene-vinyl alcohol copolymer may be used, or both may be used in combination, depending on desired physical properties such as oxygen barrier properties, water vapor barrier properties, water resistance, and weather resistance. Alternatively, a gas barrier coating film obtained using polyvinyl alcohol and a gas barrier coating film obtained using an ethylene-vinyl alcohol copolymer may be laminated.

As the sol-gel process catalyst, an acid or amine compound is suitable.

The composition may further contain an acid. Acids are used as catalysts for hydrolysis of sol-gel process catalysts, mainly metal alkoxides and silane coupling agents. Acids include, for example, mineral acids such as sulfuric acid, hydrochloric acid and nitric acid, and organic acids such as acetic acid and tartaric acid.

The composition may contain an organic solvent. Organic solvents include, for example, methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol and n-butanol.

The thickness of the gas barrier coating film is preferably 0.01 μm or more and 100 μm or less, more preferably 0.1 μm or more and 50 μm or less. Thereby, gas barrier property can be improved more. By setting the thickness of the gas barrier coating film to 0.01 μm or more, the oxygen barrier property and water vapor barrier property of the laminate can be improved, and the occurrence of cracks in the deposited layer can be prevented. By setting the thickness of the gas-barrier coating film to 100 μm or less, it is possible to obtain a laminate that can be suitably used for manufacturing a mono-material packaging container.

The gas barrier coating film is formed by applying a composition containing the above materials by conventionally known means such as roll coating such as gravure roll coater, spray coating, spin coating, dipping, brush, bar coating, and applicator. The composition can be formed by polycondensation by a sol-gel method.

An embodiment of a method for forming a gas barrier coating film will be described below.
First, a composition is prepared by mixing a metal alkoxide, a water-soluble polymer, a sol-gel process catalyst, water, an organic solvent, and optionally a silane coupling agent. A polycondensation reaction proceeds gradually in the composition. Next, the above composition is applied onto the deposited layer by the above-described conventionally known means and dried. By this drying, the polycondensation reaction of the metal alkoxide and the water-soluble polymer (and the silane coupling agent when the composition contains a silane coupling agent) further proceeds to form a composite polymer layer. Finally, a gas barrier coating film can be formed by heating.

<Adhesive layer>
In one embodiment, the laminate of the present disclosure includes any interlayer (e.g., between the multilayer substrate and the barrier layer, between the barrier layer and the heat seal layer, or between the multilayer substrate and the heat seal layer). is provided with an adhesive layer. Thereby, the adhesion between the layers included in the laminate can be improved.

The adhesive layer contains an adhesive. Examples of adhesives include one-component curing adhesives, two-component curing adhesives, and non-curing adhesives.

The adhesive may be a non-solvent type adhesive or a solvent type adhesive, and a non-solvent type adhesive is preferable from the viewpoint of environmental load. Solvent-free adhesives include, for example, polyether-based adhesives, polyester-based adhesives, silicone-based adhesives, epoxy-based adhesives, and urethane-based adhesives. Examples of solvent-based adhesives include rubber-based adhesives, vinyl-based adhesives, silicone-based adhesives, epoxy-based adhesives, phenol-based adhesives, olefin-based adhesives, and urethane-based adhesives. Among these, a two-liquid curing type urethane adhesive is preferable.

In the case of an adhesive layer adjacent to a barrier layer such as an aluminum deposition layer, the adhesive layer is preferably composed of a cured resin composition containing a polyester polyol, an isocyanate compound and a phosphoric acid-modified compound. Such a configuration of the adhesive layer can further improve the oxygen barrier properties and water vapor barrier properties of the laminate of the present disclosure.

The thickness of the adhesive layer is preferably 0.5 μm or more and 6 μm or less, more preferably 0.8 μm or more and 5 μm or less, and still more preferably 1 μm or more and 4.5 μm or less, from the viewpoint of adhesiveness of the adhesive layer and processability of the laminate. is.

The adhesive layer is formed by applying and drying an adhesive on a multilayer substrate or the like by a method such as a direct gravure roll coating method, a gravure roll coating method, a kiss coating method, a reverse roll coating method, a fonten method or a transfer roll coating method. can be formed by

<Print layer>
Laminates of the present disclosure may comprise printed layers formed on a polyethylene multilayer substrate. The printed layer is formed, for example, on the first PE layer or the third PE layer in the multilayer substrate. Since the multilayer base material has excellent ink adhesion, it can form good images. Multilayer substrates are suitable for printing applications because they are excellent in heat resistance such as heat shrinkage resistance.

The print layer contains, for example, an image. Images include, for example, characters, graphics, symbols, and combinations thereof. Examples of methods for forming the printed layer include gravure printing, offset printing, and flexographic printing. In one embodiment, the flexographic printing method is preferred from the viewpoint of reducing environmental load. Moreover, from the viewpoint of reducing the environmental burden, a printed layer may be formed on the surface of the multilayer substrate using ink derived from biomass.

The print layer contains a colorant in one embodiment. Examples of coloring agents include pigments such as inorganic pigments and organic pigments; dyes such as acid dyes, direct dyes, disperse dyes, oil-soluble dyes, metal-containing oil-soluble dyes, and sublimation dyes. Examples of the coloring agent include fluorescent light-emitting materials such as ultraviolet light-emitting materials that emit fluorescence by absorbing ultraviolet rays and infrared light-emitting materials that emit fluorescence by absorbing infrared rays.

The print layer may contain a resin material in one embodiment. Examples of resin materials include cellulose resins, (meth)acrylic resins, urethane resins, alkyd resins, polyesters, polycarbonates, polyolefins, polystyrenes, norbornene resins, polyvinyl chlorides, polyvinyl acetates, and vinyl chloride-vinyl acetate copolymers. are mentioned.

[Use]
The laminate of the present disclosure can be suitably used for packaging materials such as packaging bags. A packaging material of the present disclosure comprises a laminate of the present disclosure.

For example, a packaging material can be produced by folding the laminate into two so that the multilayer base material is positioned outside and the heat-seal layer is positioned inside, and then heat-sealing the ends and the like. Moreover, a packaging material can be produced by stacking a plurality of the laminates so that the heat-seal layers face each other and heat-sealing the edges and the like. The entire packaging material may be composed of the laminate, or part of the packaging material may be composed of the laminate.

The forms of heat sealing in packaging materials include, for example, a side seal type, a two-side seal type, a three-side seal type, a four-side seal type, an envelope pasting seal type, a joining hands pasting seal type (pillow seal type), a pleated seal type, and a flat bottom. Examples include seal type, square bottom seal type, and gusset type. Self-supporting packaging bags (stand pouches) are also possible. Methods of heat sealing include, for example, bar sealing, rotary roll sealing, belt sealing, impulse sealing, high frequency sealing, and ultrasonic sealing.

For example, a standing pouch with a body and bottom can be manufactured as follows. First, one or more of the laminates are heat-sealed into a cylindrical shape with the heat-seal layer on the inside to form the body. Then, the further laminate is V-shaped so that the heat seal layer is on the outside. A bottom portion is formed by sandwiching the V-shaped laminate at one end of the trunk portion and heat-sealing.

In the stand pouch, only the body may be formed of the laminate, only the bottom may be formed of the laminate, or both the body and the bottom may be formed of the laminate. good.

Contents filled in packaging materials include, for example, liquids, powders, and gels, and may be foods or non-foods. After filling the contents in the packaging material, the opening of the packaging material is heat-sealed to obtain the package.

The present disclosure relates to, for example, the following [1] to [13].
[1] A laminate comprising a polyethylene multilayer substrate and a heat seal layer containing polyethylene as a main component, wherein the polyethylene multilayer substrate includes a first polyethylene layer, a second polyethylene layer, and a third polyethylene layer. are provided in this order in the thickness direction and stretched, the first polyethylene layer has an indentation modulus of 1.0 GPa or more, and the third polyethylene layer has an indentation modulus of 1.0 GPa or more. A laminate of 0 GPa or more.
[2] The laminate according to [1] above, wherein the first polyethylene layer has an indentation modulus of elasticity of 4.5 GPa or less, and the third polyethylene layer has an indentation modulus of elasticity of 4.5 GPa or less.
[3] The laminate according to [1] or [2] above, wherein the indentation modulus of the second polyethylene layer is 0.03 GPa or more and 0.7 GPa or less.
[4] The polyethylene multilayer substrate has a polyethylene layer 2a between the first polyethylene layer and the second polyethylene layer and a polyethylene layer 2b between the second polyethylene layer and the third polyethylene layer. , wherein the indentation elastic modulus of the 2a polyethylene layer and the indentation elastic modulus of the 2b polyethylene layer are each independently 0.3 GPa or more and 3.5 GPa or less, above [1] to [3] The laminate according to any one of .
[5] A laminate comprising a polyethylene multilayer substrate and a heat seal layer containing polyethylene as a main component, wherein the polyethylene multilayer substrate includes a first polyethylene layer, a second polyethylene layer, and a third polyethylene layer. and a polyethylene layer in this order in the thickness direction and stretched, the first polyethylene layer has an indentation hardness of 45 MPa or more, and the third polyethylene layer has an indentation hardness of 45 MPa or more. body.
[6] The laminate according to [5] above, wherein the first polyethylene layer has an indentation hardness of 110 MPa or less, and the third polyethylene layer has an indentation hardness of 110 MPa or less.
[7] The laminate according to [5] or [6] above, wherein the indentation hardness of the second polyethylene layer is 1 MPa or more and 40 MPa or less.
[8] The polyethylene multilayer substrate has a polyethylene layer 2a between the first polyethylene layer and the second polyethylene layer and a polyethylene layer 2b between the second polyethylene layer and the third polyethylene layer. , and the indentation hardness of the polyethylene layer 2a and the indentation hardness of the polyethylene layer 2b are each independently 20 MPa or more and 100 MPa or less, according to any one of [5] to [7] above. laminate.
[9] The above [1] to [8], wherein the laminate has a heat shrinkage rate of 15% or less in the longitudinal direction (MD) and a heat shrinkage rate of 15% or less in the direction perpendicular to the MD (TD) of the laminate. ] The laminated body in any one of ].
[10] The laminate according to any one of [1] to [9] above, further comprising a print layer on the polyethylene multilayer substrate.
[11] The laminate according to any one of [1] to [10] above, further comprising a barrier layer formed on the surface of the polyethylene multilayer substrate or the surface of the heat seal layer.
[12] The laminate according to any one of [1] to [11] above, further comprising an adhesive layer between the polyethylene multilayer substrate and the heat seal layer.
[13] A packaging material comprising the laminate according to any one of [1] to [12] above.

The laminate of the present disclosure will be described in more detail based on examples, but the laminate of the present disclosure is not limited by the examples. Hereinafter, "mass part" is simply described as "part".

The polyethylene used in the following examples and comparative examples will be described.
-Medium density polyethylene (hereinafter referred to as "MDPE"):
Product name Enable4002MC
Density: 0.940 g/cm ³ Melting point: 128°C MFR: 0.25 g/10 minutes
High-density polyethylene (1) manufactured by ExxonMobil (hereinafter referred to as "HDPE (1)"):
Product name Elite5960G
Density: 0.960 g/cm ³ Melting point: 134°C MFR: 0.8 g/10 minutes
Dowchemical high-density polyethylene (2) (hereinafter referred to as “HDPE (2)”):
Product name H619F
Density: 0.965 g/cm ³ Melting point: 135°C MFR: 0.7 g/10 minutes
Linear low-density polyethylene manufactured by SCG (hereinafter referred to as “LLDPE”):
Product name Exceed XP8656ML
Density: 0.916 g/cm ³ Melting point: 121°C MFR: 0.5 g/10 minutes
Low-density polyethylene manufactured by ExxonMobil (hereinafter referred to as "LDPE"):
Product name LD2420F
Density: 0.922 g/cm ³ Melting point: 112°C MFR: 0.75 g/10 minutes
MB containing slip agent manufactured by PTT:
Product name SLIP61 10061-K
Density: 0.910 g/cm ³ , MFR: 10 g/10 minutes,
Polyethylene base, containing 5% by mass of erucamide-based slip agent,
Made by Ampacet

[Production of blended polyethylene]
・Blended polyethylene A1
70 parts of MDPE and 30 parts of HDPE (1) were mixed to obtain a blended polyethylene A1 (hereinafter referred to as "blended PE (A1)") having an average density of 0.948 g/cm ³ .
・Blended polyethylene B1
70 parts of HDPE (2) and 30 parts of LDPE were mixed to obtain a blended polyethylene B1 (hereinafter referred to as "blended PE (B1)") having an average density of 0.950 g/cm ³ .
・Blended polyethylene B2
50 parts of MDPE and 50 parts of LLDPE were mixed to obtain a blended polyethylene B2 (hereinafter referred to as “blended PE (B2)”) having an average density of 0.929 g/cm ³ .
・Blend polyethylene C1
98 parts of LLDPE and 2 parts of slip agent-containing MB were mixed to obtain a blended polyethylene C1 (hereinafter referred to as “blended PE (C1)”) having an average density of 0.916 g/cm ³ .

[Production Example 1]
Blend PE (A1), blend PE (B1) and blend PE (C1) were formed into blend PE (A1) layer (15 μm)/blend PE (B1) layer (22.5 μm)/blend PE (C1) by inflation molding method. ) layer (50 μm)/blend PE (B1) layer (22.5 μm)/blend PE (A1) layer (15 μm) layer thickness ratio of 5 layers co-extruded to form a tubular film with a total thickness of 125 μm A polyethylene film was obtained, and the tubular film was folded at the nip to form a double layer. Numbers in parentheses indicate layer thicknesses.

The polyethylene film prepared above was stretched in the longitudinal direction (MD) at a draw ratio of 5 times, and the blended PE (A1) layer (surface layer) on one side was subjected to corona discharge treatment, and then the ends were stretched. It was slit and divided into two pieces to obtain a polyethylene multilayer substrate (stretched multilayer substrate) having a thickness of 25 μm.

[Production Examples 2 and 3]
A polyethylene film and a stretched multilayer substrate were obtained in the same manner as in Production Example 1, except that the layer structure was changed as shown in Table 3.

[Examples and Comparative Examples: Production of laminates]
A first linear low-density polyethylene (SP2520, manufactured by Prime Polymer Co., density: 0.925 g/cm ³ , melting point: 122° C.) and a second linear low-density polyethylene (SP0510, manufactured by Prime Polymer Co., Ltd., Density: 0.903 g/cm ³ , Melting point: 98° C.) is formed into a multilayer extrusion film by an inflation molding method, and a first linear low-density polyethylene layer with a thickness of 20 μm and a second linear low-density polyethylene layer with a thickness of 20 μm and a linear low density polyethylene layer of . This unstretched polyethylene film was used as a heat seal layer as described below.

The first linear low-density polyethylene layer side of the unstretched polyethylene film (heat seal layer) prepared above and the corona discharge-treated surface side of the stretched multi-layer base material obtained in Production Example were combined into a two-component curing type. Dry lamination was performed via a urethane-based adhesive (Ru-77T/H-7 manufactured by Rock Paint Co., Ltd.) to obtain a laminate. The thickness of the adhesive layer was 3.0 μm.

[Ink adhesion evaluation]
An image was formed on the corona discharge-treated side of the stretched multilayer base material obtained in Production Example by gravure printing using an oil-based gravure ink (manufactured by DIC Graphics, trade name: Finart). Images formed on the stretched multilayer substrate were visually observed and evaluated based on the following evaluation criteria.

(Evaluation criteria)
AA: When Sellotape (registered trademark) was attached to the image forming surface side of the stretched multilayer base material and peeled off, the ink adhered to the stretched multilayer base material was good, and the ink did not peel off from the Cellotape (registered trademark). rice field.
BB: When Cellotape (registered trademark) was attached to the image forming surface side of the stretched multilayer substrate and then peeled off, the adhesion of the ink to the stretched multilayer substrate was weak, and the ink peeled off from the Cellotape (registered trademark).

[Shrinkage evaluation]
The laminate produced above was cut into 10 cm×10 cm to produce three sample pieces each. Each sample piece was folded in half with the heat seal layer side facing inward, and a heat seal tester was used to heat seal a 1.5 cm x 10 cm area at a temperature of 120°C and a pressure of 1 kgf/cm ² for 1 second. bottom. After heat-sealing, the seal width of the sample was measured, and the MD and TD shrinkage ratios were calculated. The average value of three sample pieces was taken as each thermal shrinkage rate.

[Heat resistance evaluation]
Heat resistance was evaluated according to the following criteria.
AA: There was no significant shrinkage of the stretched multilayer base material during printing, during dry lamination, and during heat sealing of the laminate prepared above, and the intended product was produced neatly.
BB: During printing, during dry lamination, and during heat sealing of the laminate prepared above, large shrinkage of the stretched multilayer base material occurred, and the desired object could not be produced neatly.

[Haze evaluation]
The haze value of the stretched multilayer substrate obtained in Production Examples was measured according to JIS K7136.

[Rigidity evaluation]
The stretched multilayer base material obtained in Production Example was cut into a test piece having a width of 10 mm, and the rigidity of the test piece was measured using a loop stiffness measuring tester (manufactured by Toyo Seiki Seisakusho, trade name: Loop Stiffness Tester). The loop length was 60 mm.

[Strength evaluation]
A dumbbell-shaped test piece with a width of 10 mm was cut out from the stretched multilayer base material obtained in the production example. The tensile strength of the test piece in the MD direction was measured with a tensile tester (RTC-1310A manufactured by Orientec Co., Ltd.). The chuck-to-chuck distance was 10 mm, and the tensile speed was 300 mm/min.

[Evaluation of indentation elastic modulus and indentation hardness]
For the laminates obtained in Examples and Comparative Examples, a nanoindenter ("TI950 TriboIndenter" manufactured by HYSITRON) was used to examine a cross section parallel to the TD direction of each polyethylene layer of the stretched multilayer substrate. As the measurement surface, the indentation elastic modulus and indentation hardness were obtained by averaging the values of the elastic modulus and the hardness obtained by measuring at five points on the same cross section. A Berkovich indenter (triangular pyramid indenter) was used as an indenter for the nanoindenter.

Measurement conditions are as follows. Over 10 seconds, the indenter was pressed into the polyethylene layer from a cross section parallel to the TD direction of the laminate to a depth of 200 nm, and this state was held for 5 seconds. It was then unloaded for 10 seconds. As a result, the maximum load Pmax, the contact projected area A at the maximum depth, and the load-displacement curve could be obtained, and the elastic modulus and hardness values were calculated from the obtained load-displacement curve. The measurement was performed in a room temperature (25°C) environment. The cross section was prepared by cutting the laminate parallel to the TD direction in an environment of −100° C. using a cryo-ultramicrotome. Finishing was performed with a diamond knife. The thickness of each layer can also be measured by observing the cross section.

Tables 1 to 3 show the above evaluation results.

10: polyethylene multilayer substrate 12: first polyethylene layer 14: third polyethylene layer 16: middle layer including second polyethylene layer 18: second a polyethylene layer 20: second polyethylene layer 22: second b Polyethylene layer 30: laminate 32: heat seal layer 34: barrier layer 36: adhesive layer

Claims (13)

a polyethylene multilayer substrate;
A laminate comprising a heat seal layer containing polyethylene as a main component,
The polyethylene multilayer substrate is
a first polyethylene layer;
a second polyethylene layer;
A third polyethylene layer is provided in this order in the thickness direction and stretched,
The indentation modulus of the first polyethylene layer is 1.0 GPa or more,
The third polyethylene layer has an indentation modulus of 1.0 GPa or more.
laminate. The indentation modulus of the first polyethylene layer is 4.5 GPa or less,
The indentation modulus of the third polyethylene layer is 4.5 GPa or less,
The laminate according to claim 1. The laminate according to claim 1 or 2, wherein the indentation elastic modulus of the second polyethylene layer is 0.03 GPa or more and 0.7 GPa or less. The polyethylene multilayer substrate comprises a polyethylene layer 2a between the first polyethylene layer and the second polyethylene layer and a polyethylene layer 2b between the second polyethylene layer and the third polyethylene layer. further comprising a layer and
The indentation elastic modulus of the polyethylene layer 2a and the indentation elastic modulus of the polyethylene layer 2b are each independently 0.3 GPa or more and 3.5 GPa or less.
The laminate according to any one of claims 1-3. a polyethylene multilayer substrate;
A laminate comprising a heat seal layer containing polyethylene as a main component,
The polyethylene multilayer substrate is
a first polyethylene layer;
a second polyethylene layer;
A third polyethylene layer is provided in this order in the thickness direction and stretched,
The indentation hardness of the first polyethylene layer is 45 MPa or more,
The indentation hardness of the third polyethylene layer is 45 MPa or more,
laminate. The indentation hardness of the first polyethylene layer is 110 MPa or less,
The indentation hardness of the third polyethylene layer is 110 MPa or less,
The laminate according to claim 5. The laminate according to claim 5 or 6, wherein the indentation hardness of the second polyethylene layer is 1 MPa or more and 40 MPa or less. The polyethylene multilayer substrate comprises a polyethylene layer 2a between the first polyethylene layer and the second polyethylene layer and a polyethylene layer 2b between the second polyethylene layer and the third polyethylene layer. further comprising a layer and
The indentation hardness of the polyethylene layer 2a and the indentation hardness of the polyethylene layer 2b are each independently 20 MPa or more and 100 MPa or less.
The laminate according to any one of claims 5-7. The laminate has a heat shrinkage rate of 15% or less in the longitudinal direction (MD),
The laminate has a heat shrinkage rate of 15% or less in a direction perpendicular to the MD (TD).
The laminate according to any one of claims 1-8. The laminate according to any one of claims 1 to 9, further comprising a printed layer on said polyethylene multilayer substrate. The laminate according to any one of claims 1 to 10, further comprising a barrier layer formed on the surface of the polyethylene multilayer substrate or the surface of the heat seal layer. The laminate according to any one of claims 1 to 11, further comprising an adhesive layer between the polyethylene multilayer substrate and the heat seal layer. A packaging material comprising the laminate according to any one of claims 1-12.

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