JP7842964B2 - Laminates and packaging materials - Google Patents

Description

This disclosure relates to laminates and packaging materials.

Conventionally, packaging materials have been manufactured using resin films made from resin materials. Packaging materials, for example, comprise a base material and a heat-seal layer. For instance, resin films made from polyethylene are widely used as heat-seal layers in packaging materials because they possess flexibility, transparency, and excellent heat-sealability (see, for example, Patent Document 1).

On the other hand, polyethylene is a resin that softens at relatively low temperatures compared to other thermoplastic resins. Therefore, when used as a base material for packaging materials, it may deform or, in some cases, melt during heat-sealing. Furthermore, polyethylene film may have insufficient strength compared to other thermoplastic resin films. For this reason, it is common to use resin films with excellent strength and heat resistance, such as polyester film and nylon film, as base materials for packaging materials. For example, bags are manufactured by laminating a base material such as polyester film or nylon film with a polyethylene film, and then heat-sealing it so that the polyethylene film side is on the inside of the packaging bag (see, for example, the background art in Patent Document 2).

Incidentally, in recent years, with the growing demand for the creation of a circular economy, attempts have been made to recycle and reuse packaging materials. However, laminates obtained by bonding different types of resin films, as described above, are difficult to separate by resin type and are therefore not suitable for recycling.

Japanese Patent Publication No. 2009-202519 Japanese Patent Publication No. 2017-031233

Therefore, the present disclosers discovered that the strength and heat resistance of a resin film made of polyethylene can be improved by stretching, and considered using a polyethylene multilayer substrate, which comprises multiple polyethylene-containing layers and has been stretched, as the base material.

The substrate used in packaging materials, for example, is subjected to heat during heat sealing of the packaging material. However, the disclosers have found that laminates comprising the above-mentioned polyethylene multilayer substrate may exhibit significant thermal shrinkage due to heat application, resulting in insufficient heat resistance.

One of the objectives of this disclosure is to provide a laminate comprising a polyethylene multilayer substrate and a heat-seal layer containing polyethylene as the main component, thereby providing excellent heat resistance.

The laminate of this disclosure comprises a polyethylene multilayer substrate and a heat-seal layer containing polyethylene as the 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 formed by stretching. In one embodiment, the indentation modulus of the first polyethylene layer of the multilayer substrate is 1.0 GPa or higher, and the indentation modulus of the third polyethylene layer is 1.0 GPa or higher. In another embodiment, the indentation hardness of the first polyethylene layer of the multilayer substrate is 45 MPa or higher, and the indentation hardness of the third polyethylene layer is 45 MPa or higher.

According to this disclosure, a laminate comprising a polyethylene multilayer substrate and a heat-seal layer containing polyethylene as the main component can be provided, exhibiting excellent heat resistance.

This is a schematic cross-sectional view showing one embodiment of a polyethylene multilayer substrate. This is a schematic cross-sectional view showing one embodiment of the laminate of the present disclosure. This is a schematic cross-sectional view showing one embodiment of the laminate of the present disclosure. This is a schematic cross-sectional view showing one embodiment of the laminate of the present disclosure. This is a schematic cross-sectional view showing one embodiment of the laminate of the present disclosure. This is a schematic diagram illustrating a method for measuring the thermal shrinkage rate of a laminate.

[term]
The following definitions are used in this disclosure.
"Polyethylene" refers to a polymer in which the content of ethylene-derived constituent units is 50 mol% or more of the total repeating constituent units. In this polymer, the content of ethylene-derived constituent units is preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more. The above content is measured by nuclear magnetic resonance (NMR) spectroscopy.

The "polyethylene layer" refers to a layer containing polyethylene as its main component, that is, a layer containing polyethylene in a range of more than 50% by mass. The polyethylene content in the polyethylene layer is preferably 60% by mass or more, more preferably 70% by mass or more, even 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 limit of the density of high-density polyethylene is, for example, 0.965 g/ ^cm³ . The density of medium-density polyethylene is preferably greater than 0.925 g/ ^cm³ and ^less than or equal to 0.945 g/ ^cm³ . The density of low-density polyethylene is preferably greater than 0.900 g/ ^cm³ and less than or equal to 0.925 g/ ^cm³ . The density of linear low-density polyethylene is preferably greater than 0.900 g/ ^cm³ and less than or equal to 0.925 g/cm³. The density of ultra-low-density polyethylene is preferably 0.900 g/ ^cm³ or less. The lower limit of the density of ultra-low-density polyethylene is, for example, 0.860 g/ ^cm³ . The density of polyethylene is measured in accordance with JIS K7112, particularly Method D (density gradient pipe method, 23°C).

In this disclosure, polyethylene includes, for example, ethylene homopolymers and copolymers of ethylene with 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 copolymers mentioned above include copolymers of ethylene and α-olefins having 3 to 20 carbon atoms, copolymers of ethylene and at least one selected from vinyl acetate and (meth)acrylic acid esters, and copolymers of ethylene and α-olefins having 3 to 20 carbon atoms and at least one selected from vinyl acetate and (meth)acrylic acid esters.

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

A single-site catalyst is a catalyst capable of forming a uniform active species. It is typically prepared by contacting a metallocene transition metal compound or a non-metallocene transition metal compound with an activation co-catalyst. Single-site catalysts are preferred over multi-site catalysts because their active site structure is more uniform, allowing for the production of polymers with high molecular weight and high uniformity.

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

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

In transition metal compounds, the cyclopentadienyl skeleton refers to a cyclopentadienyl group or a substituted cyclopentadienyl group. A substituted cyclopentadienyl group has at least one substituent selected from, for example, a hydrocarbon group having 1 to 30 carbon atoms, a silyl group, a silyl-substituted alkyl group, a silyl-substituted aryl group, a cyano group, a cyanoalkyl group, a cyanoaryl group, a halogen group, a haloalkyl group, and a halosilyl group. A substituted cyclopentadienyl group may have one or more substituents, and these substituents may bond to each other to form a ring, forming an indenyl ring, a fluorenyl ring, an azlenyl ring, or a hydrogenated form thereof. The ring formed by the bonding of substituents may further contain substituents.

Transition metal compounds typically have two ligands having a cyclopentadienyl skeleton. Preferably, each ligand having a cyclopentadienyl skeleton is bonded to one another by a bridging group. Examples of bridging groups include alkylene groups with 1 to 4 carbon atoms, silylene groups, substituted silylene groups such as dialkylsilylene groups and diarylsilylene groups, and substituted germylene groups such as dialkylgermylene groups and diarylgermylene groups. Among these, substituted silylene groups are preferred.

A co-catalyst is a component that can effectively enable transition metal compounds of Group IV of the periodic table to function as polymerization catalysts, or a component that can balance the ionic charge in a catalytically activated state. Examples of co-catalysts include benzene-soluble aluminoxanes or benzene-insoluble organoaluminum oxy compounds, ion-exchangeable layered silicates, boron compounds, ionic compounds consisting of 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.

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

Transition metal compounds may be used supported on an inorganic or organic compound. Preferred supports are porous oxides of inorganic or organic compounds, specifically including ion-exchangeable layered silicates such as montmorillonite, _SiO₂ , _Al₂O₃ , _MgO , _ZrO₂ , TiO₂, _B₂O₃ , _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 manufactured using polyethylene multilayer substrates. Biomass-derived polyethylene can be produced, for example, by the method described in Japanese Patent Publication No. 2013-177531. Commercially available biomass-derived polyethylene (for example, Green PE, commercially available from Braschem) may also be used.

Recycled polyethylene obtained through mechanical recycling may be used. Mechanical recycling generally involves crushing collected polyethylene film, alkaline washing to remove dirt and foreign matter from the film surface, then drying it under high temperature and reduced pressure for a certain period to disperse contaminants remaining inside the film, decontaminating it, and returning the polyethylene film to its original polyethylene state.

In the following description, each component (for example, polyethylene such as high-density polyethylene, medium-density polyethylene, low-density polyethylene, and linear low-density polyethylene, additives, colorants, resin materials, and adhesives) may be used individually or in combination of two or more types.
The following describes the polyethylene multilayer substrate provided by the laminate of this disclosure, followed by a description of the laminate of this disclosure.

[Polyethylene multilayer substrate]
Polyethylene multilayer substrate is
The first polyethylene layer,
A second polyethylene layer,
The third polyethylene layer is arranged in this order in the thickness direction and has been stretched.
Hereinafter, the polyethylene multilayer substrate described above will also simply be referred to as the "multilayer substrate."

The multilayer substrate may further include a second polyethylene layer (2a) between the first polyethylene layer and the second polyethylene layer, and a second polyethylene layer (2b) between the second polyethylene layer and the third polyethylene layer. In this case, the multilayer substrate comprises the first polyethylene layer, the second polyethylene layer (2a), the second polyethylene layer, the second polyethylene layer (2b), and the third polyethylene layer in this order in the thickness direction. The second polyethylene layer (2a), the second polyethylene layer, and the second polyethylene layer (2b) 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 a first polyethylene layer, and the surface layer on the other side of the multilayer substrate is a third polyethylene layer. The multilayer substrate may have other layers between at least one of the first polyethylene layer, the seconda polyethylene layer, the second polyethylene layer, the secondb polyethylene layer, and the third polyethylene layer. In one embodiment, the multilayer substrate consists only of the first polyethylene layer, the seconda polyethylene layer, the second polyethylene layer, the secondb polyethylene layer, and the third polyethylene layer.

Hereafter, the polyethylene layer will also be referred to as the "PE layer."

Examples of polyethylene included in multilayer substrates 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 polyethylene contained in the multilayer substrate is preferably 0.1 g/10 min to 50 g/10 min, more preferably 0.2 g/10 min to 30 g/10 min, even more preferably 0.2 g/10 min to 15 g/10 min, even more preferably 0.2 g/10 min to 10 g/10 min, and particularly preferably 0.2 g/10 min to 5 g/10 min, from the viewpoint of film-forming properties and the processability of the multilayer substrate. In this disclosure, the MFR is measured in accordance with ASTM D1238 under conditions of a temperature of 190°C and a load of 2.16 kg.

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

For example, the first PE layer may contain medium-density polyethylene and high-density polyethylene, and the third PE layer may also contain medium-density polyethylene and high-density polyethylene. By adjusting the ratio of medium-density polyethylene and high-density polyethylene, the magnitude of the indentation modulus and indentation hardness, for example, as described later, can be adjusted. This further improves 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 preferably 1.1 to 5, more preferably 1.5 to 3, independently of each other. This further improves 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 preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, respectively. This further improves the ink adhesion and heat resistance of the multilayer substrate.

For example, the second PE layer may contain linear low-density polyethylene. Such a configuration tends to allow for adjustment of the indentation modulus and indentation hardness to a lower range, as described later. This improves the stretchability of the laminate, which is a precursor to the multilayer substrate.

The content of 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, and even more preferably 80% by mass or more, 90% by mass or more, or 95% by mass or more. This allows for a further improvement in the balance of heat resistance, rigidity, and stretchability.

In one embodiment, the PE layer 2a and the PE layer 2b may each contain high-density polyethylene. This configuration tends to allow for adjustment of the indentation modulus and indentation hardness, for example, to a higher range. These layers contribute to improving the heat resistance of the multilayer substrate. Specifically, by incorporating high-density polyethylene into the PE layer 2a and the PE layer 2b, in addition to the first and third PE layers, the heat resistance of the multilayer substrate can be further improved.

In one embodiment, the PE layer 2a and the PE layer 2b may each further contain low-density polyethylene. This configuration allows for adjustment of, for example, the indentation modulus and indentation hardness, as described later. This further improves the balance of heat resistance, rigidity, and processability of the multilayer substrate.

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 to 4, more preferably 1.5 to 3, independently of each other. This further improves the balance of heat resistance, rigidity, and processability of the multilayer substrate.

The content 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 even more preferably 60% by mass or more, independently of each other. This further improves the heat resistance of the multilayer substrate.

The total content of high-density polyethylene and low-density polyethylene in the PE layer 2a and the PE layer 2b is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, respectively. This allows for a further improvement in the balance of heat resistance, rigidity, and processability of the multilayer substrate.

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

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 preferably 0.25 to 4, and more preferably 0.4 to 2.4, independently of each other. This allows for a further improvement in the balance of 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 preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, respectively. This further improves the stretchability of the precursor laminate.

The thickness of the first PE layer and the third PE layer are, independently of each other, preferably 0.5 μm to 10 μm, more preferably 1 μm to 8 μm, and even more preferably 1 μm to 5 μm. This further improves the ink adhesion and heat resistance of the multilayer substrate.

The thickness of the first PE layer and the third PE layer are preferably smaller than the total thickness of the second a PE layer, the second PE layer, and the second b PE layer (hereinafter, the second a, second, and second b layers are collectively referred to as the "multilayer intermediate layer"). The ratio of the thickness 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 to 0.8, more preferably 0.1 to 0.7, and even more preferably 0.1 to 0.4. This further improves the rigidity, strength, and heat resistance of the multilayer substrate.

The thickness of the second PE layer is preferably 1 μm to 50 μm, more preferably 2 μm to 40 μm, and even more preferably 5 μm to 30 μm. This allows for a further improvement in the balance of heat resistance, rigidity, and stretchability.

The thickness of the PE layer 2a and the PE layer 2b are, independently of each other, preferably 0.5 μm to 15 μm, more preferably 1 μm to 10 μm, and even more preferably 1 μm to 8 μm. This further improves the heat resistance of the multilayer substrate or the stretchability of the precursor laminate.

The ratio of the total thickness of the PE layer 2a and the PE layer 2b to the thickness of the second PE layer (total thickness of the PE layer 2a and the PE layer 2b / thickness of the second PE layer) is preferably 0.1 to 10, more preferably 0.2 to 5, and even more preferably 0.5 to 2. This further improves the rigidity, strength, and heat resistance of the multilayer substrate.
The thicknesses of each layer mentioned above are all after the stretching process.

Each layer constituting the multilayer substrate may independently contain additives. Examples of additives include crosslinking agents, antioxidants, antiblocking agents, lubricants, UV absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, and modifying resins.

At least one layer selected from the first PE layer, the second PE layer, and the third PE layer in the multilayer substrate—specifically, at least one layer selected from the first PE layer, the seconda PE layer, the second PE layer, the secondb PE layer, and the third PE layer—may contain a slip agent. This can, for example, improve the processability of the multilayer substrate. For instance, the second PE layer may contain a slip agent, or all of the above layers may contain a slip agent.

Examples of slip agents include amide lubricants, fatty acid esters such as glycerin fatty acid esters, hydrocarbon waxes, higher fatty acid waxes, metal soaps, hydrophilic silicones, silicone-modified (meth)acrylic resins, silicone-modified epoxy resins, silicone-modified polyethers, silicone-modified polyesters, block-type silicone (meth)acrylic copolymers, polyglycerol-modified silicones, and paraffin.

Among lubricants, amide-based lubricants are preferred. Examples of amide-based 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.

Examples of saturated fatty acid amides include lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, and hydroxystearic acid amide. Examples of unsaturated fatty acid amides include oleic acid amide and erucic acid amide. Examples of substituted amides include N-oleyl palmitic acid amide, N-stearyl stearate amide, N-stearyl oleic acid amide, N-oleyl stearate amide, and N-stearyl erucic acid amide. An example of a methylolamide is methylol stearate amide. Examples of saturated fatty acid bisamides include methylenebisstearate, ethylenebiscaprate, ethylenebislaurate, ethylenebisstearate, ethylenebishydroxystearate, ethylenebisbehenamide, hexamethylenebisstearate, hexamethylenebisbehenamide, hexamethylenehydroxystearate, N,N'-distearyladipamide, and N,N'-distearylsebacinamide. Examples of unsaturated fatty acid bisamides include ethylenebisoleamide, ethylenebiserucamide, hexamethylenebisoleamide, N,N'-dioleyladipamide, and N,N'-dioleylsebacinamide. Examples of fatty acid ester amides include stearamidoethyl stearate. Examples of aromatic bisamides include m-xylylenebisstearate, m-xylylenebishydroxystearate, and N,N'-distearyl isophthalamide.
Among slip agents, erucic acid amide is preferred.

To improve 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 slip agent content in the masterbatch is preferably 1% to 30% by mass, more preferably 2% to 20% by mass, and even more preferably 3% to 10% by mass. Examples of polyethylene include those described above. The preferred physical properties (density, MFR, etc.) of the polyethylene are also as described above.

In a multilayer substrate, the slip agent content in the layer containing the slip agent may be, for example, 0.01% to 3% by mass, or 0.03% to 1% by mass. This further improves the processability of the multilayer substrate.

If a single layer contains multiple types of polyethylene with different densities (n types; n is an integer of 2 or more), the density of the polyethylene constituting the layer may be measured in accordance with JIS K7112, or 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 equation (1), Σ means taking the sum of _Wi × _Di for i from 1 to n, where n is an integer greater than or equal to 2, _Wi represents the mass fraction of the i-th polyethylene, and _Di represents the density (g/ ^cm³ ) of the i-th polyethylene.

The multilayer substrate, having undergone stretching treatment and possessing unique physical properties, exhibits superior rigidity, strength, and heat resistance compared to conventional polyethylene films, as well as superior ink adhesion. Therefore, the polyethylene multilayer substrate can be used, for example, as a base material for packaging materials, and a clear image can be formed on its surface.

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

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

The following describes specific embodiments of polyethylene multilayer substrates.
The polyethylene multilayer substrate of the first embodiment comprises a first PE layer, a seconda PE layer, a second PE layer, a secondb PE layer, and a third PE layer in this order in the thickness direction, and is subjected to a stretching process.
The first PE layer contains medium-density polyethylene and high-density polyethylene.
The PE layer of the second a contains high-density polyethylene and optionally low-density polyethylene.
The second PE layer contains linear low-density polyethylene.
The PE layer of the second b contains high-density polyethylene and optionally low-density polyethylene.
The 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 seconda PE layer, a second PE layer, a secondb PE layer, and a third PE layer in this order in the thickness direction, and is subjected to a stretching process.
The first PE layer contains medium-density polyethylene and high-density polyethylene.
The PE layer of the second a contains medium-density polyethylene and linear low-density polyethylene.
The second PE layer contains linear low-density polyethylene.
The PE layer of the second b contains medium-density polyethylene and linear low-density polyethylene.
The 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, but from the viewpoint of easily manufacturing a multilayer substrate, it is preferable that they be the same.
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, but from the viewpoint of easily manufacturing a multilayer substrate, it is preferable that they be the same.

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, but from the viewpoint of easily manufacturing a multilayer substrate, it is preferable that they be 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 PE layer 2a and the PE layer 2b may be the same or different.
In the 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, but it is preferable that they be the same from the viewpoint of easily manufacturing a multilayer substrate.
In the second embodiment, the linear low-density polyethylene contained in the PE layer of 2a and the linear low-density polyethylene contained in the PE layer of 2b may be the same or different, but it is preferable that they be the same from the viewpoint of easily manufacturing a multilayer substrate.
In the second embodiment, the medium-density polyethylene contained in the PE layer 2a and the PE layer 2b may be the same as or different from the medium-density polyethylene contained in the first PE layer and the third PE layer.

<Manufacturing method for polyethylene multilayer substrate>
Polyethylene multilayer substrates can be manufactured, for example, by forming a laminate by creating films of multiple polyethylene materials using an inflation method or a T-die method, and then stretching the resulting laminate. The stretching process improves the transparency, rigidity, strength, and heat resistance of the multilayer substrate, making it suitable for use as a base material for packaging materials, for example.

The polyethylene multilayer substrate of the first embodiment is obtained by stretching a laminate (precursor) which comprises, 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, a layer containing high-density polyethylene, and a layer containing medium-density polyethylene and high-density polyethylene, in this order in the thickness direction.

Specifically, a laminate can be manufactured by co-extruding layers containing medium-density polyethylene and high-density polyethylene, a high-density polyethylene layer, a linear low-density polyethylene layer, a high-density polyethylene layer, and a medium-density polyethylene and high-density polyethylene layer into a tubular shape. Alternatively, a laminate can be manufactured by co-extruding layers containing medium-density polyethylene and high-density polyethylene, a high-density polyethylene layer, and a linear low-density polyethylene layer into a tubular shape, and then pressing opposing linear low-density polyethylene layers together using rubber rolls or the like. By manufacturing laminates using these methods, 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 manufactured, for example, by the method described above.

When manufacturing laminates using the T-die method, the melt flow rate (MFR) of the polyethylene constituting each layer is preferably 3 g/10 min to 20 g/10 min, from the viewpoint of film-forming properties and the processability of the multilayer substrate.

When manufacturing laminates by the inflation method, the MFR of the polyethylene constituting each layer is preferably 0.2 g/10 min to 5 g/10 min, from the viewpoint of film-forming properties and processability of the multilayer substrate.

Multilayer substrates can be obtained, for example, by stretching the laminates described above. Furthermore, the stretching of the laminates can be performed simultaneously in an inflation film deposition machine. This allows for the production of multilayer substrates, thereby improving production efficiency.

The multilayer substrate may be a uniaxially oriented film or a biaxially oriented film. In one embodiment, the multilayer substrate is a uniaxially oriented film, and more specifically, a uniaxially oriented film stretched in the longitudinal direction (MD).

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

When the stretching ratio is 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 stretching ratio is 10 times or less, the laminate can be stretched well.

It is preferable that the laminate or multilayer substrate be surface-treated. This improves the adhesion between the surface layer of the multilayer substrate and the layers laminated onto 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 and nitrogen, and glow discharge treatment; and chemical treatments such as oxidation treatment using chemicals.

An anchor coat layer may be formed on the surface of the laminate or multilayer substrate using a conventionally known anchor coat agent.

The total thickness of the multilayer substrate is preferably 10 μm to 60 μm, more preferably 15 μm to 50 μm. A thickness of 10 μm or more improves the rigidity and strength of the multilayer substrate. A thickness of 60 μm or less improves the processability of the multilayer substrate. Within the range where the above effects are obtained, a smaller thickness of the multilayer substrate is preferable, for example, from the viewpoint of cost reduction.

[Laminate]
The laminates disclosed herein are
The polyethylene multilayer substrate described above,
It comprises a heat-seal layer containing polyethylene as the main component.

In this disclosure, the indentation modulus of the first PE layer, the seconda PE layer, the second PE layer, the secondb PE layer, and the third PE layer are also referred to as indentation modulus 1, indentation modulus 2a, indentation modulus 2, indentation modulus 2b, and indentation modulus 3, respectively. The ratio of the indentation modulus of the first PE layer to the indentation modulus of the second PE layer is also referred to as the ratio (modulus 1 / modulus 2). The same applies to other cases.

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

The laminate according to the first aspect of this disclosure is characterized in that the indentation modulus of the first PE layer is 1.0 GPa or higher, and the indentation modulus of the third PE layer is 1.0 GPa or higher. This improves the heat resistance of the laminate and suppresses thermal shrinkage of the laminate during heat application, such as during heat sealing.

In the laminate of the first embodiment, the indentation modulus 1 and indentation modulus 3 are each independently 1.0 GPa or higher, preferably 1.05 GPa or higher, more preferably 1.1 GPa or higher, even more preferably 1.15 GPa or higher, and particularly preferably 1.3 GPa or higher; preferably 4.5 GPa or lower, more preferably 4.0 GPa or lower, even more preferably 3.5 GPa or lower, even more preferably 3.0 GPa or lower, particularly preferably 2.5 GPa or lower, 2.0 GPa or lower, or 1.8 GPa or lower. This tends to further suppress thermal shrinkage of the laminate during heat sealing, for example. The ranges of indentation modulus 1 and indentation modulus 3 may be any combination of the above lower and upper limits, for example, 1.0 GPa or higher and 4.5 GPa or lower.

The indentation modulus 2 in the laminate of the first embodiment is preferably 0.03 GPa or higher, more preferably 0.05 GPa or higher, even more preferably 0.1 GPa or higher, even more preferably 0.13 GPa or higher, and particularly preferably 0.15 GPa or higher; preferably 0.7 GPa or lower, more preferably 0.6 GPa or lower, even more preferably 0.5 GPa or lower, even more preferably 0.4 GPa or lower, and particularly preferably 0.3 GPa or lower. Such a design tends to result in, for example, better stretchability of the pre-stretched laminate. The range of the indentation modulus 2 may be any combination of the above lower and upper limits, for example, 0.03 GPa or higher and 0.7 GPa or lower.

In the laminate of the first embodiment, the indentation modulus 2a and indentation modulus 2b are, independently, preferably 0.3 GPa or higher, more preferably 0.4 GPa or higher, even more preferably 0.5 GPa or higher, and even more preferably 0.6 GPa or higher; preferably 3.5 GPa or lower, more preferably 3.0 GPa or lower, even more preferably 2.5 GPa or lower, even more preferably 2.0 GPa or lower, and particularly preferably 1.5 GPa or lower. This tends to further suppress thermal shrinkage of the laminate during heat sealing, for example. The range of the indentation modulus 2a and indentation modulus 2b may be any combination of the above lower and upper limits, for example, 0.3 GPa or higher and 3.5 GPa or lower.

In the laminate of the first embodiment, it is preferable that the magnitude of the indentation modulus of each PE layer satisfies the relationship: indentation modulus 1 > indentation modulus 2a > indentation modulus 2, and more preferably, indentation modulus 3 > indentation modulus 2b > indentation modulus 2. This tends to further improve the balance between the heat resistance and stretchability (processability, productivity) of the multilayer substrate.

In the laminate according to the first embodiment, the indentation modulus of the first PE layer is preferably 3.5 times or more that of the second PE layer, and the indentation modulus of the third PE layer is preferably 3.5 times or more that of the second PE layer. This improves the heat resistance of the laminate and further suppresses thermal shrinkage of the laminate during heat application, such as during heat sealing.

In the laminate of the first embodiment, the ratio (elastic modulus 1/elastic modulus 2) and the ratio (elastic modulus 3/elastic modulus 2) are, independently, preferably 3.5 or higher, more preferably 4.0 or higher, even more preferably 4.5 or higher, even more preferably 5.0 or higher, and particularly preferably 5.5 or higher; preferably 16.0 or lower, more preferably 14.0 or lower, even more preferably 12.0 or lower, even more preferably 10.0 or lower, and particularly preferably 9.0 or lower. The range of the ratio (elastic modulus 1/elastic modulus 2) and the range of the ratio (elastic modulus 3/elastic modulus 2) may independently be any combination of the above lower and upper limits, for example, 3.5 or higher and 16.0 or lower.

In the laminate according to the first embodiment, the indentation modulus of the PE layer 2a is preferably 2.0 times or more than that of the second PE layer, and the indentation modulus of the PE layer 2b is preferably 2.0 times or more than that of the second PE layer. This tends to further suppress thermal shrinkage of the laminate during, for example, heat sealing.

In the laminate of the first embodiment, the ratio (elastic modulus 2a/elastic modulus 2) and the ratio (elastic modulus 2b/elastic modulus 2) are, independently, preferably 2.0 or higher, more preferably 2.5 or higher, and even more preferably 3.0 or higher; preferably 14.0 or lower, more preferably 12.0 or lower, even more preferably 10.0 or lower, even more preferably 9.0 or lower, and particularly preferably 8.5 or lower. The range of the ratio (elastic modulus 2a/elastic modulus 2) and the range of the ratio (elastic modulus 2b/elastic modulus 2) may independently be any combination of the above lower and upper limits, for example, 2.0 or higher and 14.0 or lower.

In the laminate of the first embodiment, the ratio (elastic modulus 1/elastic modulus 3) is preferably 0.6 to 1.7, more preferably 0.7 to 1.4, even more preferably 0.8 to 1.2, and even more preferably 0.9 to 1.1. This, for example, improves the symmetry of the layer structure of the multilayer substrate, and therefore tends to suppress curling of the multilayer substrate, thereby improving processability such as printing and lamination.

In the laminate of the first embodiment, the ratio (elastic modulus 2a/elastic modulus 2b) is preferably 0.6 to 1.7, more preferably 0.7 to 1.4, even more preferably 0.8 to 1.2, and even more preferably 0.9 to 1.1. This, for example, improves the symmetry of the layer structure of the multilayer substrate, and therefore tends to suppress curling of the multilayer substrate, thereby improving processability such as printing and lamination.

The laminate according to the second aspect of this disclosure is characterized in that the indentation hardness of the first PE layer is 45 MPa or higher, and the indentation hardness of the third PE layer is 45 MPa or higher. This improves the heat resistance of the laminate and suppresses thermal shrinkage of the laminate during heat application, such as during heat sealing.

In the laminate of the second embodiment, the indentation hardness 1 and indentation hardness 3 are each independently 45 MPa or higher, preferably 48 MPa or higher, more preferably 50 MPa or higher, and even more preferably 52 MPa or higher; preferably 110 MPa or lower, more preferably 90 MPa or lower, even more preferably 80 MPa or lower, even more preferably 75 MPa or lower, and particularly preferably 70 MPa or lower. 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 any combination of the above lower and upper limits, for example, 45 MPa or higher and 110 MPa or lower. The laminate of the first embodiment may further satisfy the above requirements for indentation hardness 1 and indentation hardness 3.

The indentation hardness 2 in the laminate of the second embodiment is preferably 1 MPa or more, more preferably 3 MPa or more, even more preferably 7 MPa or more, even more preferably 10 MPa or more, and particularly preferably 15 MPa or more; preferably 40 MPa or less, more preferably 35 MPa or less, even more preferably 30 MPa or less, even more preferably 26 MPa or less, and particularly preferably 23 MPa or less. Such a design tends to result in, for example, better stretchability of the pre-stretched laminate. The range of indentation hardness 2 may be any combination of the above lower and upper limits, for example, 1 MPa or more and 40 MPa or less. The laminate of the first embodiment may further satisfy the above requirements related to indentation hardness 2.

In the laminate of the second embodiment, the indentation hardness 2a and indentation hardness 2b are, independently, preferably 20 MPa or more, more preferably 30 MPa or more, even more preferably 35 MPa or more, and even more preferably 37 MPa or more; preferably 100 MPa or less, more preferably 80 MPa or less, even more preferably 70 MPa or less, even 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 range of indentation hardness 2a and indentation hardness 2b may be any combination of the above lower and upper limits, for example, 20 MPa or more and 100 MPa or less. The laminate of the first embodiment may further satisfy the above requirements related to indentation hardness 2a and indentation hardness 2b.

In the laminate of the second embodiment, it is preferable that the indentation hardness of each PE layer satisfies the relationship: indentation hardness 1 > indentation hardness 2a > indentation hardness 2, and more preferably, indentation hardness 3 > indentation hardness 2b > indentation hardness 2. This tends to further improve the balance between the heat resistance and stretchability (processability, productivity) of the multilayer substrate.

In the laminate of the second embodiment, the indentation hardness of the first PE layer is preferably 2.0 times or more the indentation hardness of the second PE layer, and the indentation hardness of the third PE layer is preferably 2.0 times or more the indentation hardness of the second PE layer. This improves the heat resistance of the laminate and further suppresses thermal shrinkage of the laminate during heat application, such as during heat sealing.

In the laminate of the second embodiment, the ratio (hardness 1/hardness 2) and the ratio (hardness 3/hardness 2) are, independently, preferably 2.0 or higher, more preferably 2.2 or higher, even more preferably 2.4 or higher, even more preferably 2.6 or higher, and particularly preferably 2.8 or higher; preferably 6.0 or lower, more preferably 5.5 or lower, even more preferably 5.0 or lower, even more preferably 4.5 or lower, and particularly preferably 4.0 or lower or 3.5 or lower. The range of the ratio (hardness 1/hardness 2) and the range of the ratio (hardness 3/hardness 2) may independently be any combination of the above lower and upper limits, for example, 2.0 or higher and 6.0 or lower. The laminate of the first embodiment may further satisfy the above requirements regarding the ratio (hardness 1/hardness 2) and the ratio (hardness 3/hardness 2).

In the laminate of the second embodiment, the indentation hardness of the PE layer 2a is preferably 1.5 times or more the indentation hardness of the second PE layer, and the indentation hardness of the PE layer 2b is preferably 1.5 times or more the indentation hardness of the second PE layer. This tends to further suppress thermal shrinkage of the laminate during, for example, heat sealing.

In the laminate of the second embodiment, the ratio (hardness 2a/hardness 2) and the ratio (hardness 2b/hardness 2) are, independently, preferably 1.5 or higher, more preferably 1.7 or higher, and even more preferably 1.9 or higher; preferably 6.0 or lower, more preferably 5.5 or lower, even more preferably 5.0 or lower, even more preferably 4.5 or lower, and particularly preferably 4.0 or lower or 3.5 or lower. 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 independently be any combination of the above lower and upper limits, for example, 1.5 or higher and 6.0 or lower. The laminate of the first embodiment may further satisfy the above requirements regarding the ratio (hardness 2a/hardness 2) and the ratio (hardness 2b/hardness 2).

In the laminate of the second embodiment, the ratio (hardness 1/hardness 3) is preferably 0.6 to 1.7, more preferably 0.7 to 1.4, even more preferably 0.8 to 1.2, and even more preferably 0.9 to 1.1. This, for example, improves the symmetry of the layer structure of the multilayer substrate, and therefore tends to suppress curling of the multilayer substrate, thereby improving processability such as printing and lamination.

In the laminate of the second embodiment, the ratio (hardness 2a/hardness 2b) is preferably 0.6 to 1.7, more preferably 0.7 to 1.4, even more preferably 0.8 to 1.2, and even more preferably 0.9 to 1.1. This, for example, improves the symmetry of the layer structure of the multilayer substrate, and therefore tends to suppress curling of the multilayer substrate, thereby improving processability such as printing and lamination.

In this disclosure, the indentation modulus and indentation hardness of each PE layer can be adjusted, for example, by appropriately selecting the polyethylene contained in each PE layer. In the PE layer, increasing the proportion of high-density polyethylene, such as high-density polyethylene, tends to increase the indentation modulus and indentation hardness. In the PE layer, increasing the proportion of low-density polyethylene, such as low-density polyethylene and linear low-density polyethylene, tends to decrease the indentation modulus and indentation hardness. The indentation modulus and indentation hardness of each PE layer can also be adjusted by the stretch ratio. For example, increasing the stretch ratio tends to increase the indentation modulus and indentation hardness of each PE layer, while decreasing the stretch ratio tends to decrease the indentation modulus and indentation hardness of each PE layer.

In this disclosure, the indentation modulus and indentation hardness of each PE layer are measured by nanoindentation. Specifically, for the laminate, the indentation modulus and indentation hardness are measured using a nanoindenter, with the measurement surface being a cross section parallel to the TD direction of each PE layer of the polyethylene multilayer substrate. The measurement conditions are as follows: A Berkovich indenter (triangular pyramidal indenter) is used as the indenter for the nanoindenter. The indenter is pressed into the PE layer from a cross section parallel to the TD direction of the laminate to an indentation depth of 200 nm over 10 seconds, held in that position for 5 seconds, and then unloaded over 10 seconds to obtain the maximum load Pmax, the contact projected area A at the maximum depth, and the load-displacement curve. The values of modulus and hardness are calculated from the obtained load-displacement curve. The measurement is performed in a room temperature (25°C) environment. The measurement is performed at five locations on the same cross section, and the average value of the modulus is taken as the indentation modulus, and the average value of the hardness is taken as the indentation hardness. Details of the measurement conditions are described in the Examples section.

As shown in Figure 2, the laminate 30 of this disclosure comprises a polyethylene multilayer substrate 10 and a heat-seal layer 32. In the multilayer substrate 10, an intermediate layer including a second polyethylene layer and, optionally, seconda and secondb polyethylene layers, is referred to as the intermediate layer 16.

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

In one embodiment, as shown in Figure 3, the laminate 30 includes a barrier layer 34 and an adhesive layer 36 between the multilayer substrate 10 and the heat seal layer 32. In this embodiment, the barrier layer 34 is formed on the surface of the multilayer substrate 10.
In one embodiment, as shown in Figure 4, the laminate 30 includes an adhesive layer 36 and a barrier layer 34 between the multilayer substrate 10 and the heat seal layer 32. In this embodiment, the barrier layer 34 is formed on the surface of the heat seal layer 32.
In one embodiment, as shown in Figure 5, the laminate 30 includes an adhesive layer 36 between the multilayer substrate 10 and the heat seal layer 32.

In the laminate according to this disclosure, the polyethylene content is preferably 90% by mass or more. This improves the recyclability of the laminate. The polyethylene content in the laminate refers to the ratio of the polyethylene content to the sum of the resin material content in each layer constituting the laminate.

In one embodiment, the laminate of this disclosure exhibits the following thermal shrinkage rates. MD refers to the longitudinal direction or flow direction of the laminate, and TD refers to the direction perpendicular to MD.

The thermal shrinkage coefficient (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 7% or less. A lower lower limit for the thermal shrinkage coefficient (MD) is preferable, but it may be, for example, 0.5%, 1%, 2%, or 3%. Laminates with such a low thermal shrinkage coefficient (MD) have excellent properties, for example, printability and suitability for bag making when producing packaging bags by heat sealing.

The thermal shrinkage coefficient (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 7% or less. A lower lower limit for the thermal shrinkage coefficient (MD) is preferable, but it may be, for example, 0.5%, 1%, 2%, or 3%. Laminates with such low thermal shrinkage coefficients (TD) exhibit excellent properties, for example, printability and suitability for bag making when producing packaging bags by heat sealing.

The ratio of the thermal shrinkage rate (MD) to the thermal shrinkage rate (TD) of the laminate (MD/TD) is preferably 0.5 to 2.0, more preferably 0.7 to 1.4, even more preferably 0.8 to 1.2, and particularly preferably 0.9 to 1.1. When the ratio (MD/TD) is within this range, the laminate shrinks relatively uniformly in terms of MD and TD even after heat treatment, thus suppressing, for example, image distortion in the printed layer of the laminate.

The thermal shrinkage rate of the laminate is measured as follows: Cut the laminate into 10 cm x 10 cm sections to create three sample pieces. Fold each sample piece in half parallel to the medium diameter (MD) or medium diameter (TD) so that the heat-seal layer side is facing inward. Using a heat seal tester, heat seal a 1.5 cm x 10 cm area at a temperature of 120°C, a pressure of 1 kgf/ ^cm² , and for 1 second (see Figure 6). In Figure 6, the shaded area indicates the heat-sealed area. After heat sealing, measure the seal width of the sample and calculate the MD shrinkage rate (see Figure 6(a)) and the TD shrinkage rate (see Figure 6(b)). The average value of the three sample pieces is taken as the thermal shrinkage rate.

Each thermal shrinkage rate is calculated using the following formula.
Thermal shrinkage ratio (MD) (%) = {(Length in the MD direction of the heat-sealed portion of the laminate (1.5 cm) - Length in the MD direction of the heat-sealed portion of the laminate after heat sealing) / Length in the MD direction of the heat-sealed portion of the laminate (1.5 cm)} × 100
Thermal shrinkage rate (TD) (%) = {(Length in the TD direction of the area to be heat-sealed in the laminate (1.5 cm) - Length in the TD direction of the heat-sealed area of the laminate after heat-sealing) / Length in the TD direction of the area to be heat-sealed in the laminate (1.5 cm)} × 100

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

<Heat seal layer>
The heat seal layer is a layer containing polyethylene as its main component, that is, a layer containing polyethylene in a range of more than 50% by mass. The polyethylene content in the heat seal layer is preferably 60% by mass or more, more preferably 70% by mass or more, even 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 can be obtained that has sufficient rigidity, strength and heat resistance, and is also highly recyclable.

The laminate of this disclosure comprises a polyethylene multilayer substrate and a heat-sealable layer (hereinafter also referred to as the "heat-sealable polyethylene layer") containing polyethylene as the main component. In one embodiment, a printed layer (image) is formed on at least one surface of the multilayer substrate. It is preferable that the printed layer be formed on the side of the multilayer substrate where the heat-sealable polyethylene layer is provided, as 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 above-described laminate comprising a polyethylene multilayer substrate and a heat-sealable polyethylene layer, in one embodiment, all resin layers included in the laminate are polyethylene layers, and the laminate does not contain dissimilar resin films such as polyester film and nylon film. Furthermore, the polyethylene multilayer substrate satisfies the rigidity, strength, and heat resistance required for an outer layer film of a packaging material, and the heat-sealable polyethylene layer enables packaging. Therefore, the above-described laminate is suitable as a material for packaging materials where recyclability is required.

In one embodiment, the laminate of the present disclosure consists only of a polyethylene multilayer substrate on which a printed layer is formed as needed, and a heat-sealable polyethylene layer. As a result, since each resin layer of the laminate of the present disclosure is composed of polyethylene, which is the same material, recyclability can be particularly improved.

The heat-seal layer is typically an unstretched layer. For example, a heat-seal layer can be formed by laminating an unstretched polyethylene film onto a multilayer substrate via an adhesive layer as needed, or by melt-extruding a polyethylene-containing resin material onto a multilayer substrate. Examples of adhesive layers include those described later.

Examples of polyethylene materials that constitute the heat seal layer include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene. From the viewpoint of heat sealability, low-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene are preferred. From the viewpoint of reducing environmental impact, biomass-derived polyethylene or recycled polyethylene may be used.

The polyethylene content in the heat seal layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. This improves the recyclability of the laminate.
The heat seal layer may contain the above-mentioned additives.

The heat seal layer may be one layer or two or more layers. In one embodiment, the number of heat seal layers is one to three.
The thickness of the heat seal layer is, for example, 10 μm to 300 μm.
The thickness of the heat seal layer is preferably adjusted as appropriate according to the mass of the contents to be filled into the packaging material manufactured, for example, by the laminate of this disclosure, from the viewpoint of the strength of the heat seal layer and the processability of the laminate.

For example, if the packaging material is a small bag, the thickness of the heat-seal layer is preferably 20 μm or more and 60 μm or less. In this case, for example, 1 g or more and 200 g of contents can be well filled into the small bag.
For example, if the packaging material is a stand-up pouch, the thickness of the heat-seal layer is preferably 50 μm or more and 200 μm or less. In this case, for example, contents weighing 50 g to 2000 g can be well filled into the stand-up pouch.

<Barrier layer>
In one embodiment, the laminate of the present disclosure includes a barrier layer between the multilayer substrate and the heat-seal layer. This improves the gas barrier properties of the laminate, specifically the oxygen barrier properties and water vapor barrier properties. The barrier layer may be formed on the surface of the multilayer substrate or on the surface of the heat-seal layer. Alternatively, the 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 vapor-deposited layer. The vapor-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 vapor-deposited layer is preferred.

The thickness of the barrier layer is preferably 1 nm to 150 nm, more preferably 5 nm to 60 nm, and even more preferably 10 nm to 40 nm. A barrier layer thickness of 1 nm or more can further improve the oxygen barrier and water vapor barrier properties of the laminate. A barrier layer thickness of 150 nm or less can suppress crack formation in the barrier layer and improve the recyclability of the laminate.

Methods for forming the barrier layer include, for example, physical vapor deposition (PVD) methods such as vacuum deposition, sputtering, and ion plating; and chemical vapor deposition (CVD) methods such as plasma chemical vapor deposition, thermochemical vapor deposition, and photochemical vapor deposition. The barrier layer may be a composite film containing two or more barrier layers of different inorganic oxides, formed by combining both physical vapor deposition and chemical vapor deposition methods.

The vacuum level of the deposition chamber is preferably about ^10⁻² to ^10⁻⁸ mbar before oxygen introduction and about ^10⁻¹ to ^10⁻⁶ mbar after oxygen introduction. The amount of oxygen introduced will vary depending on the size of the deposition machine. For the oxygen introduced, inert gases such as argon, helium, and nitrogen may be used as carrier gases within a range that does not cause problems. The transport speed of the multilayer substrate is, for example, about 10 to 800 m/min.

It is preferable that the surface of the barrier layer be subjected to the surface treatment described above. This improves the adhesion between the barrier layer and the adjacent layer.

If the vapor-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 vapor-deposited layer to form a barrier layer comprising both the vapor-deposited layer and the barrier coat layer.

In one embodiment, the barrier coating 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, and (meth)acrylic resins.

The thickness of the barrier coat layer is preferably 0.01 μm to 10 μm, more preferably 0.1 μm to 5 μm. A barrier coat layer thickness of 0.01 μm or more can further improve gas barrier properties. A barrier coat layer thickness of 10 μm or less can improve the processability of the laminate. Furthermore, it allows for the creation of a laminate suitable for use in the manufacture of monomaterial packaging containers.

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

In other embodiments, the barrier coating layer is a gas barrier coating film formed from a composition containing a hydrolyzed metal alkoxide or a hydrolyzed condensate of a metal alkoxide, obtained by polycondensation of 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, and an organic solvent.
By providing such a barrier coating layer on the vapor-deposited layer, the occurrence of cracks in the vapor-deposited layer can be effectively prevented.

In one embodiment, the metal alkoxide is represented by the following general formula.
R ¹ _n M (OR ² ) _m
In the above formula, ^R1 and ^R2 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, m represents an integer of 1 or more, and n+m represents the valence of M.

Examples of organic groups represented by ^R1 and ^R2 include alkyl groups such as methyl, ethyl, n-propyl, isopropyl, n-butyl, and isobutyl groups. Examples of metal atoms M include silicon, zirconium, titanium, and aluminum.

Examples of metal alkoxides that satisfy the above general formula include tetramethoxysilane (Si( _OCH3 ) ₄ ), tetraethoxysilane (Si( _OC2H5 ) _{4 ) ,} tetrapropoxysilane (Si( _OC3H7 ) ₄ ), and tetrabutoxysilane (Si( _OC4H9 ) _{4 )} .

It is preferable to use a silane coupling agent together with the above-mentioned metal alkoxide. Known organic reactive group-containing organoalkoxysilanes can be used as the silane coupling agent.

As the water-soluble polymer, polyvinyl alcohol and ethylene-vinyl alcohol copolymers are preferred. Depending on the desired physical properties such as oxygen barrier properties, water vapor barrier properties, water resistance, and weather resistance, either polyvinyl alcohol or ethylene-vinyl alcohol copolymer may be used, or both may be used in combination. Furthermore, a gas barrier coating film obtained using polyvinyl alcohol and a gas barrier coating film obtained using ethylene-vinyl alcohol copolymer may be laminated.

Acid or amine compounds are preferred as catalysts for the sol-gel process.

The above composition may further contain an acid. The acid is used as a catalyst for hydrolysis, primarily for sol-gel catalysts, metal alkoxides, and silane coupling agents. Examples of acids include mineral acids such as sulfuric acid, hydrochloric acid, and nitric acid, as well as organic acids such as acetic acid and tartaric acid.

The above composition may contain an organic solvent. Examples of organic solvents include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, and n-butanol.

The thickness of the gas barrier coating is preferably 0.01 μm to 100 μm, more preferably 0.1 μm to 50 μm. This further improves the gas barrier properties. By setting the thickness of the gas barrier coating to 0.01 μm or more, the oxygen barrier and water vapor barrier properties of the laminate can be improved, and crack formation in the vapor-deposited layer can be prevented. By setting the thickness of the gas barrier coating to 100 μm or less, a laminate suitable for use in the manufacture of monomaterial packaging containers can be obtained.

A gas barrier coating film can be formed by applying a composition containing the above-mentioned material using conventionally known methods such as roll coating (including gravure roll coaters), spray coating, spin coating, dipping, brushing, bar coating, and applicators, and then polycondensing the composition by a sol-gel method.

The following describes one embodiment of a method for forming a gas barrier coating film.
First, a composition is prepared by mixing a metal alkoxide, a water-soluble polymer, a sol-gel catalyst, water, an organic solvent, and optionally a silane coupling agent. A polycondensation reaction gradually proceeds within the composition. Next, the composition is applied to a vapor-deposited layer and dried using the conventionally known method described above. This drying further promotes the polycondensation reaction between the metal alkoxide and the water-soluble polymer (and the silane coupling agent if the composition contains one), forming 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 an adhesive layer between any of the layers (for example, between a multilayer substrate and a barrier layer, between a barrier layer and a heat seal layer, or between a multilayer substrate and a heat seal layer). This improves the adhesion between the layers contained in the laminate.

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 either a solvent-free or solvent-based adhesive; however, from an environmental perspective, a solvent-free adhesive is preferred. Examples of solvent-free adhesives include 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-component curing type urethane-based adhesive is preferred.

In the case of an adhesive layer adjacent to a barrier layer such as an aluminum vapor-deposited layer, it is preferable to constitute the adhesive layer with a cured product of a resin composition containing a polyester polyol, an isocyanate compound, and a phosphate-modified compound. By using such a configuration for the adhesive layer, the oxygen barrier and water vapor barrier properties of the laminate of this disclosure can be further improved.

From the viewpoint of adhesive properties of the adhesive layer and processability of the laminate, the thickness of the adhesive layer is preferably 0.5 μm to 6 μm, more preferably 0.8 μm to 5 μm, and even more preferably 1 μm to 4.5 μm.

The adhesive layer can be formed by applying and drying an adhesive onto a multilayer substrate, for example, using methods such as the direct gravure roll coating method, gravure roll coating method, kiss coating method, reverse roll coating method, fontein method, and transfer roll coating method.

<Print layer>
The laminate of this disclosure may comprise a printed layer formed on a polyethylene multilayer substrate. The printed layer is formed, for example, on a first PE layer or a third PE layer in the multilayer substrate. Since the multilayer substrate has excellent ink adhesion, a good image can be formed. Since the multilayer substrate has excellent heat resistance, such as heat shrinkage resistance, it is suitable for printing applications.

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

In one embodiment, the printed layer contains a colorant. Examples of colorants include pigments such as inorganic and organic pigments; and dyes such as acid dyes, direct dyes, disperse dyes, oil-soluble dyes, metal-containing oil-soluble dyes, and sublimable dyes. Fluorescent materials, such as ultraviolet-emitting materials that emit fluorescence upon absorbing ultraviolet light, and infrared-emitting materials that emit fluorescence upon absorbing infrared light, are also examples of colorants.

In one embodiment, the printed layer may contain a resin material. Examples of resin materials include cellulose resin, (meth)acrylic resin, urethane resin, alkyd resin, polyester, polycarbonate, polyolefin, polystyrene, norbornene-based resin, polyvinyl chloride, polyvinyl acetate, and vinyl chloride-vinyl acetate copolymer.

[Application]
The laminate of this disclosure can be suitably used for packaging material applications such as packaging bags. The packaging material of this disclosure comprises the laminate of this disclosure.

For example, the above laminate can be folded in half so that the multilayer substrate is on the outside and the heat-seal layer is on the inside, and the edges can be heat-sealed to produce a packaging material. Alternatively, multiple of the above laminates can be stacked so that the heat-seal layers face each other, and the edges can be heat-sealed to produce a packaging material. The entire packaging material may be composed of the above laminate, or only a portion of the packaging material may be composed of the above laminate.

Examples of heat sealing forms for packaging materials include side seals, two-side seals, three-side seals, four-side seals, envelope seals, gusset seals (pillow seals), pleated seals, flat-bottom seals, square-bottom seals, and gusset seals. Stand-up pouches are also possible. Examples of heat sealing methods include bar seals, rotary roll seals, belt seals, impulse seals, high-frequency seals, and ultrasonic seals.

For example, a stand-up pouch having a body and a bottom can be manufactured as follows: First, one or more of the laminated materials are formed into a cylindrical shape with the heat-seal layer facing inward and then heat-sealed to form the body. Next, another laminated material is folded into a V-shape with the heat-seal layer facing outward. The V-shaped laminated material is then sandwiched at one end of the body and heat-sealed to form the bottom.

In a stand-up pouch, the body may be formed solely from the laminate, the bottom may be formed solely from the laminate, or both the body and bottom may be formed from the laminate.

Examples of contents to be filled into the packaging material include liquids, powders, and gels, and may be food or non-food items. After filling the packaging material with contents, the opening of the packaging material is heat-sealed to obtain the package.

This disclosure relates, for example, to the following [1] to [13].
[1] A laminate comprising a polyethylene multilayer substrate and a heat-seal layer mainly composed of polyethylene, wherein 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, the indentation modulus of the first polyethylene layer is 1.0 GPa or more, and the indentation modulus of the third polyethylene layer is 1.0 GPa or more.
[2] The laminate according to [1] above, wherein the indentation modulus of the first polyethylene layer is 4.5 GPa or less, and the indentation modulus of the third polyethylene layer is 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 laminate according to any one of [1] to [3] above, wherein the polyethylene multilayer substrate further comprises a second polyethylene layer a between the first polyethylene layer and the second polyethylene layer, and a second polyethylene layer b between the second polyethylene layer and the third polyethylene layer, and the indentation modulus of the second polyethylene layer and the indentation modulus of the second polyethylene layer and the indentation modulus of the second polyethylene layer b are each independently 0.3 GPa or more and 3.5 GPa or less.
[5] A laminate comprising a polyethylene multilayer substrate and a heat-seal layer mainly composed of polyethylene, wherein 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, the indentation hardness of the first polyethylene layer is 45 MPa or more, and the indentation hardness of the third polyethylene layer is 45 MPa or more.
[6] The laminate according to [5] above, wherein the indentation hardness of the first polyethylene layer is 110 MPa or less, and the indentation hardness of the third polyethylene layer is 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 laminate according to any one of [5] to [7] above, wherein the polyethylene multilayer substrate further comprises a second polyethylene layer a between the first polyethylene layer and the second polyethylene layer, and a second polyethylene layer b between the second polyethylene layer and the third polyethylene layer, and the indentation hardness of the second polyethylene layer and the indentation hardness of the second polyethylene layer b are independently 20 MPa or more and 100 MPa or less.
[9] The laminate according to any one of [1] to [8] above, wherein the thermal shrinkage rate in the longitudinal direction (MD) of the laminate is 15% or less, and the thermal shrinkage rate in the direction perpendicular to the MD (TD) of the laminate is 15% or less.
[10] The laminate according to any one of [1] to [9] above, further comprising a printed layer on a polyethylene multilayer substrate.
[11] The laminate according to any one of [1] to [10], further comprising a barrier layer formed on the surface of a polyethylene multilayer substrate or on the surface of a 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 described in any of [1] to [12] above.

The laminates of this disclosure will be described in more detail based on examples, but the laminates of this disclosure are not limited to the examples. Hereinafter, "mass portion" will simply be referred to as "portion."

The polyethylene used in the following examples and comparative examples is described below.
Medium-density polyethylene (hereinafter referred to as "MDPE"):
Product name Enable4002MC
Density: 0.940 g/ ^cm³ , Melting point: 128°C, MFR: 0.25 g/10 min
ExxonMobil High-Density Polyethylene (1) (hereinafter referred to as "HDPE (1)"):
Product name: Elite5960G
Density: 0.960 g/ ^cm³ , Melting point: 134°C, MFR: 0.8 g/10 min
Dowchemical High-Density Polyethylene (2) (hereinafter referred to as "HDPE (2)"):
Product name H619F
Density: 0.965 g/ ^cm³ , Melting point: 135°C, MFR: 0.7 g/10 min
SCG-manufactured linear low-density polyethylene (hereinafter referred to as "LLDPE"):
Product name: Exceed XP8656ML
Density: 0.916 g/ ^cm³ , Melting point: 121°C, MFR: 0.5 g/10 min
Low-density polyethylene (LDPE) manufactured by ExxonMobil:
Product name LD2420F
Density: 0.922 g/ ^cm³ , Melting point: 112°C, MFR: 0.75 g/10 min
PTT Corporation's slip-resistant MB:
Product name SLIP61 10061-K
Density: 0.910g/cm ³ , MFR: 10g/10min,
Polyethylene base, containing 5% by mass of erucic acid amide slip agent.
Ampace Corporation

[Preparation of blended polyethylene]
Blended polyethylene A1
70 parts of MDPE and 30 parts of HDPE(1) were mixed to obtain blended polyethylene A1 (hereinafter referred to as "blended PE(A1)") with an average density of 0.948 g/ ^cm³ .
Blended polyethylene B1
70 parts HDPE(2) and 30 parts LDPE were mixed to obtain blended polyethylene B1 (hereinafter referred to as "blended PE(B1)") with an average density of 0.950 g/ ^cm³ .
Blended polyethylene B2
Fifty parts of MDPE and fifty parts of LLDPE were mixed to obtain blended polyethylene B2 (hereinafter referred to as "blended PE (B2)") with an average density of 0.929 g/ ^cm³ .
Blended polyethylene C1
98 parts of LLDPE and 2 parts of slip agent-containing MB were mixed to obtain blended polyethylene C1 (hereinafter referred to as "blended PE (C1)") ^with an average density of 0.916 g/cm³.

[Manufacturing Example 1]
Blended PE (A1), blended PE (B1), and blended PE (C1) were co-extruded in five layers by inflation molding with the layer thickness ratio of blended PE (A1) layer (15 μm) / blended PE (B1) layer (22.5 μm) / blended PE (C1) layer (50 μm) / blended PE (B1) layer (22.5 μm) / blended PE (A1) layer (15 μm) to form a tubular film with a total thickness of 125 μm. The tubular film was folded at the nip and doubled up. The numbers in parentheses indicate the layer thickness.

The polyethylene film prepared above was stretched in the longitudinal direction (MD) at a stretching ratio of 5 times. Furthermore, the blended PE (A1) layer (surface layer) on one side was subjected to corona discharge treatment. The ends were then slit, dividing the film into two layers to obtain a 25 μm thick polyethylene multilayer substrate (stretched multilayer substrate).

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

[Examples and Comparative Examples: Fabrication of Laminates]
A first linear low-density polyethylene (SP2520, manufactured by Prime Polymer Co., Ltd., density: 0.925 g/ ^cm³ , melting point: 122°C) and a second linear low-density polyethylene (SP0510, manufactured by Prime Polymer Co., Ltd., density: 0.903 g/ ^cm³ , melting point: 98°C) were multilayer extruded by inflation molding to produce an unstretched polyethylene film comprising a 20 μm thick first linear low-density polyethylene layer and a 20 μm thick second linear low-density polyethylene layer. 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-sealed layer) prepared above and the corona-discharge treated side of the stretched multilayer substrate obtained in the manufacturing example were dry-laminated using a two-component curing urethane adhesive (Rock Paint Co., Ltd., Ru-77T/H-7) 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 substrate obtained in the manufacturing example using gravure printing with oil-based gravure ink (manufactured by DIC Graphics Co., Ltd., product name: Finart). The image formed on the stretched multilayer substrate was observed visually and evaluated based on the following evaluation criteria.

(Evaluation criteria)
AA: When cellophane tape (registered trademark) was applied to the image-forming surface of a stretched multilayer substrate and then peeled off, the ink adhered well to the stretched multilayer substrate, and no ink peeling occurred on the cellophane tape (registered trademark).
BB: When cellophane tape (registered trademark) was applied to the image-forming surface of a stretched multilayer substrate and then peeled off, the ink adhesion to the stretched multilayer substrate was weak, resulting in ink peeling from the cellophane tape (registered trademark).

[Contraction evaluation]
The laminate prepared as described above was cut into 10 cm x 10 cm sections to create three sample pieces. Each sample piece was folded in half with the heat-seal layer facing inward, and a 1.5 cm x 10 cm area was heat-sealed using a heat seal tester at a temperature of 120°C, a pressure of 1 kgf/ ^cm² , and for 1 second. After heat sealing, the seal width of the sample was measured, and the shrinkage rates of the medium diameter (MD) and total diameter (TD) were calculated. The average values of the three sample pieces were used as the respective heat shrinkage rates.

[Heat resistance evaluation]
Heat resistance was evaluated according to the following criteria.
AA: During printing, dry lamination, and heat sealing of the laminated material produced above, there was no significant shrinkage of the stretched multilayer substrate, and the desired product was manufactured cleanly.
BB: Significant shrinkage occurred in the stretched multilayer substrate during printing, dry lamination, and heat sealing of the laminated material produced above, making it impossible to manufacture the desired product cleanly.

[Hayes's rating]
The haze value of the stretched multilayer substrate obtained in the manufacturing example was measured in accordance with JIS K7136.

[Stiffness evaluation]
The stretched multilayer substrate obtained in the manufacturing example was cut into 10 mm wide test pieces, and the stiffness of the test pieces was measured using a loop stiffness tester (manufactured by Toyo Seiki Seisakusho, product name: Loop Stiffness Tester). The loop length was set to 60 mm.

[Strength assessment]
A 10 mm wide dumbbell-shaped test specimen was cut from the stretched multilayer substrate obtained in the manufacturing example. The tensile strength of the above test specimen in the MD direction was measured using a tensile testing machine (Orientec Co., Ltd., RTC-1310A). The distance between the chucks was 10 mm, and the tensile speed was 300 mm/min.

[Indentation modulus and indentation hardness evaluation]
For the laminates obtained in the examples and comparative examples, the indentation modulus and hardness were determined by using a nanoindenter ("TI950 TriboIndenter" manufactured by HYSITRON) to measure the elastic modulus and hardness obtained at five locations on the same cross-section of each polyethylene layer of the stretched multilayer substrate, with the measurement surface being a cross-section parallel to the TD direction. The indentation modulus and hardness were then averaged. A Berkovich indenter (triangular pyramidal indenter) was used as the indenter for the nanoindenter.

The measurement conditions were as follows: The indenter was pressed into the polyethylene layer of the laminate from a cross section parallel to the TD direction to a depth of 200 nm over 10 seconds, and held in that position for 5 seconds. Then, the load was removed over 10 seconds. This allowed us to obtain the maximum load Pmax, the contact projected area A at the maximum depth, and the load-displacement curve. From the obtained load-displacement curve, the values of elastic modulus and hardness were calculated. The measurements were performed at room temperature (25°C). Cross-sections were prepared by cutting the laminate parallel to the TD direction using a cryo-ultramicrotome at a -100°C environment. Finishing was performed with a diamond knife. The thickness of each layer could also be measured by observing the above cross-section.

The evaluation results are shown in Tables 1 to 3.

10: Polyethylene multilayer substrate 12: First polyethylene layer 14: Third polyethylene layer 16: Intermediate layer including the second polyethylene layer 18: 2a polyethylene layer 20: Second polyethylene layer 22: 2b polyethylene layer 30: Laminate 32: Heat seal layer 34: Barrier layer 36: Adhesive layer

Claims (8)

Polyethylene multilayer substrate and
A laminate comprising a heat-seal layer containing polyethylene as the main component,
The polyethylene multilayer substrate is
A first polyethylene layer containing at least medium-density polyethylene and high-density polyethylene,
A polyethylene layer 2a containing at least linear low-density polyethylene,
A second polyethylene layer containing at least linear low-density polyethylene,
A second polyethylene layer b containing at least linear low-density polyethylene,
It has a five-layer structure comprising, in this order in the thickness direction, a third polyethylene layer containing at least medium-density polyethylene and high-density polyethylene,
Of the five polyethylene layers, at least one layer is composed of a blend of at least two types of polyethylene with different densities .
In the first polyethylene layer, the mass ratio of medium-density polyethylene to high-density polyethylene (medium-density polyethylene/high-density polyethylene) is 1.1 or more and 5 or less.
In the third polyethylene layer, the mass ratio of medium-density polyethylene to high-density polyethylene (medium-density polyethylene/high-density polyethylene) is 1.1 or more and 5 or less.
The total content of medium-density polyethylene and high-density polyethylene in the first polyethylene layer is 80% by mass or more.
The total content of medium-density polyethylene and high-density polyethylene in the third polyethylene layer is 80% by mass or more.
The content of linear low-density polyethylene in the second polyethylene layer is more than 50% by mass.
The polyethylene multilayer substrate is stretched to a ratio of 2 to 10 times in the longitudinal direction (MD) and/or transverse direction (TD), respectively.
The indentation modulus of the first polyethylene layer is 1.0 GPa or more and 4.5 GPa or less.
The indentation modulus of the third polyethylene layer is 1.0 GPa or more and 4.5 GPa or less.
Laminated structure. The laminate according to claim 1, wherein the indentation modulus of the second polyethylene layer is 0.03 GPa or more and 0.7 GPa or less. The indentation modulus of the polyethylene layer 2a and the indentation modulus of the polyethylene layer 2b are each independently 0.3 GPa or more and 3.5 GPa or less.
The laminate according to claim 1 or 2. The thermal shrinkage rate in the longitudinal direction (MD) of the laminate is 15% or less.
The thermal shrinkage coefficient of the laminate in the direction perpendicular to the medium (TD) is 15% or less.
The laminate according to any one of claims 1 to 3. The laminate according to any one of claims 1 to 4, further comprising a printed layer on the polyethylene multilayer substrate. The laminate according to any one of claims 1 to 5, 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 6, further comprising an adhesive layer between the polyethylene multilayer substrate and the heat-seal layer. A packaging material comprising a laminate according to any one of claims 1 to 7.