JP2023111720A - Polyethylene multilayer substrate, printing substrate, laminate, and packaging material - Google Patents

Abstract

To provide a polyethylene multilayer substrate that has an excellent ink adhesion property and a heat resistance property.SOLUTION: A polyethylene multilayer substrate made through stretching includes, in the following order in a thickness direction: a first layer containing medium density polyethylene and high density polyethylene; a second layer containing medium density polyethylene and linear low density polyethylene; a third layer containing medium density polyethylene and linear low density polyethylene; a fourth layer containing medium density polyethylene and linear low density polyethylene: and a fifth layer containing a medium-density polyethylene and high-density polyethylene.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to polyethylene multilayer substrates, printed substrates, 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.

By the way, images such as letters and figures are usually printed with ink on substrates used for packaging materials and the like. However, according to further studies by the present disclosure persons, it has been found that the polyethylene multilayer substrate may not have sufficient ink adhesion. Moreover, the polyethylene multilayer base material is preferably excellent in heat resistance because heat may be applied during printing or the like.

One object of the present disclosure is to provide a polyethylene multilayer substrate having excellent ink adhesion and heat resistance.

The polyethylene multilayer substrate of the present disclosure includes a first layer containing medium density polyethylene and high density polyethylene, a second layer containing medium density polyethylene and linear low density polyethylene, medium density polyethylene and linear A third layer containing linear low density polyethylene, a fourth layer containing medium density polyethylene and linear low density polyethylene, and a fifth layer containing medium density polyethylene and high density polyethylene, It is prepared in this order in the vertical direction and is stretched.

According to the present disclosure, it is possible to provide a polyethylene multilayer base material that is excellent in ink adhesion and heat resistance.

1 is a cross-sectional schematic diagram illustrating one embodiment of a polyethylene multilayer substrate 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. 1 is a cross-sectional schematic diagram illustrating one embodiment of a laminate of the present disclosure; FIG.

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, and still more preferably 90 mol % or more. The content ratio is measured by a nuclear magnetic resonance method (NMR method).

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).

[Polyethylene multilayer substrate]
The polyethylene multilayer substrate 10 of the present disclosure, as shown in FIG.
a first layer 12 containing medium density polyethylene and high density polyethylene;
a second layer 18 containing medium density polyethylene and linear low density polyethylene;
a third layer 20 containing medium density polyethylene and linear low density polyethylene;
a fourth layer 22 containing medium density polyethylene and linear low density polyethylene;
A fifth layer 14 containing medium density polyethylene and high density polyethylene is provided in this order in the thickness direction and stretched.
Hereinafter, the polyethylene multilayer substrate is also simply referred to as "multilayer substrate".

In one embodiment, the surface layer on one side of the multilayer substrate is the first layer and the surface layer on the other side of the multilayer substrate is the fifth layer. Although the multilayer substrate may comprise other layers between the first through fifth layers, in one embodiment the multilayer substrate consists only of the first through fifth layers.

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. A 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 promoter, an organic metal compound if necessary, and a support if necessary.

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. A substituted cyclopentadienyl group is, 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 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 multi-layer 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 to remain 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.

The melt flow rate (MFR) of the polyethylene contained in the multilayer substrate of the present disclosure is preferably 0.1 g/10 min or more and 50 g/10 min or less, or more, from the viewpoint of film formability and processability of the multilayer substrate. It is preferably 0.3 g/10 minutes or more and 30 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.

Examples of polyethylene include high density polyethylene, medium density polyethylene, low density polyethylene (high pressure low density polyethylene), linear low density polyethylene and ultra low density polyethylene.
Each layer constituting the multilayer substrate will be described below.

<First Layer and Fifth Layer>
The first layer contains one or more medium density polyethylenes and one or more high density polyethylenes.
The fifth layer contains one or more medium density polyethylene and one or more high density polyethylene.

When printing an image on a base material, the base material is usually subjected to surface treatment such as corona discharge treatment as a pretreatment. A layer containing medium-density polyethylene tends to have higher durability to surface treatment than a layer containing only high-density polyethylene as polyethylene. Therefore, a layer containing medium density polyethylene has excellent ink adhesion during printing after surface treatment. Layers containing medium density polyethylene and high density polyethylene also have the necessary heat resistance during printing and heat sealing. In addition, the layer containing medium-density polyethylene contributes to improving the stretchability of the laminate, which is the precursor of the multilayer base material.

The medium-density polyethylene contained in the first layer and the medium-density polyethylene contained in the fifth layer may be the same or different, and are the same from the viewpoint that the multilayer base material can be easily manufactured. is preferred.
The high-density polyethylene contained in the first layer and the high-density polyethylene contained in the fifth layer may be the same or different, and are the same from the viewpoint that the multilayer substrate can be easily manufactured. is preferred.

Each of the first layer and the fifth layer may independently contain medium-density polyethylene and high-density polyethylene, as well as polyethylene other than these polyethylenes. Examples of polyethylene other than medium-density polyethylene and high-density polyethylene include low-density polyethylene (high-pressure low-density polyethylene), linear low-density polyethylene, and ultra-low-density polyethylene. The first layer may contain only medium-density polyethylene and high-density polyethylene as polyethylene from the viewpoint that the ink adhesion and heat resistance of the multilayer substrate can be further improved. The fifth layer may contain only medium-density polyethylene and high-density polyethylene as polyethylene from the viewpoint of further improving 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 layer and the fifth layer is preferably 1.1 or more and 5 or less, more preferably 1. 0.5 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 layer is 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.

The total content of medium density polyethylene and high density polyethylene in the fifth layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. This can further improve the ink adhesion and heat resistance of the multilayer substrate.

The thickness of each of the first layer and the fifth layer is preferably 0.5 μm or more and 10 μm or less, more preferably 1 μm or more and 8 μm or less, and 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 thickness of each of the first layer and the fifth layer is the same as that of the second layer, the third layer and the fourth layer (hereinafter, the second to fourth layers are also collectively referred to as a "multilayer intermediate layer"). ) is preferably smaller than the total thickness of The ratio of the thickness of each of the first layer and the fifth layer to the total thickness of the multilayer intermediate layer (first layer or fifth layer/multilayer intermediate layer) is preferably 0.05 or more and 0.8 Below, it is 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.

<Second Layer and Fourth Layer>
The second layer contains one or more medium density polyethylene and one or more linear low density polyethylene.
The fourth layer contains one or more medium density polyethylene and one or more linear low density polyethylene.

The second layer and the fourth layer each contribute to improving the interlaminar strength of the multilayer substrate. Specifically, a second layer containing medium density polyethylene and linear low density polyethylene is provided between the third layer and the first layer containing medium density polyethylene and high density polyethylene, By providing a fourth layer containing medium density polyethylene and linear low density polyethylene between the third layer and the fifth layer containing medium density polyethylene and high density polyethylene, the inter-layer density can reduce the difference. Thereby, the interlayer strength can be improved, and the occurrence of delamination can be suppressed.

The medium density polyethylene contained in the second layer and the medium density polyethylene contained in the fourth layer may be the same or different, and are the same from the viewpoint of facilitating the production of the multilayer base material. is preferred.

The linear low density polyethylene contained in the second layer and the linear low density polyethylene contained in the fourth layer may be the same or different, and it is said that the multilayer substrate can be easily produced. From the point of view, they are preferably the same.

The medium density polyethylene contained in the second layer and the fourth layer and the medium density polyethylene contained in the first layer, the third layer and the fifth layer may be the same or different. The linear low-density polyethylene contained in the second and fourth layers and the linear low-density polyethylene contained in the third layer may be the same or different.

Each of the second layer and the fourth layer may independently contain medium density polyethylene and linear low density polyethylene, as well as polyethylene other than these polyethylenes. Other polyethylenes than medium density polyethylene and linear low density polyethylene include, for example, high density polyethylene, low density polyethylene and ultra-low density polyethylene. The second layer may contain only medium-density polyethylene and linear low-density polyethylene as polyethylene from the viewpoint that the interlaminar strength of the multilayer base material can be further improved. The fourth layer may contain only medium-density polyethylene and linear low-density polyethylene as polyethylene, from the viewpoint of further improving the interlaminar strength of the multilayer substrate.

The mass ratio of medium density polyethylene to linear low density polyethylene (medium density polyethylene/linear low density polyethylene) in the second layer and the fourth layer is preferably 1.1 or more. Below, more preferably 1.5 or more and 3 or less. Thereby, the balance between interlayer strength, heat resistance, rigidity and workability of the multilayer base material can be further improved.

The total content of medium density polyethylene and linear low density polyethylene in the second 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 balance between interlayer strength, heat resistance, rigidity and workability of the multilayer base material can be further improved.

The total content of medium density polyethylene and linear low density polyethylene in the fourth 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 balance between interlayer strength, heat resistance, rigidity and workability of the multilayer base material can be further improved.

The thickness of each of the second layer and the fourth layer is preferably 0.5 μm or more and 15 μm or less, more preferably 1 μm or more and 10 μm or less, and still more preferably 1 μm or more and 8 μm or less. Thereby, the interlaminar strength of the multilayer substrate can be further improved.

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

The third layer may further contain polyethylene other than these polyethylenes along with medium density polyethylene and linear low density polyethylene. Examples of polyethylene other than medium-density polyethylene and linear low-density polyethylene include high-density polyethylene, low-density polyethylene (high-pressure low-density polyethylene), and ultra-low-density polyethylene.

The mass ratio of medium density polyethylene to linear low density polyethylene (medium density polyethylene/linear low density polyethylene) in the third layer is preferably 0.25 or more and 4 or less, more preferably 0.4 or more. 2.4 or less. This can further improve the balance between ink adhesion and heat resistance.

The mass ratio (medium density polyethylene/linear low density polyethylene) in the second layer is preferably greater than the mass ratio (medium density polyethylene/linear low density polyethylene) in the third layer. It is more preferably 1.3 times or more and 3.5 times or less, and even more preferably 1.7 times or more and 3.0 times or less, the above mass ratio in the layer No. 3. This can further improve the balance between interlayer strength and heat resistance.

The mass ratio (medium density polyethylene/linear low density polyethylene) in the fourth layer is preferably greater than the mass ratio (medium density polyethylene/linear low density polyethylene) in the third layer. It is more preferably 1.3 times or more and 3.5 times or less, and even more preferably 1.7 times or more and 3.0 times or less, the above mass ratio in the layer No. 3. This can further improve the balance between interlayer strength and heat resistance.

The total content of medium density polyethylene and linear low density polyethylene in the third layer is 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 balance between heat resistance, rigidity and stretchability.

The thickness of the third layer is preferably 1 μm or more and 50 μm or less, more preferably 2 μm or more and 40 μm or less, and 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 ratio of the total thickness of the second layer and the fourth layer to the thickness of the third layer (total thickness of the second layer and the fourth layer/thickness of the third 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.

<Additive>
Each of the first to fifth layers constituting the multilayer substrate may independently contain one or more additives. 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 layer, the second layer, the third layer, the fourth layer and the fifth layer in the multilayer substrate of the present disclosure may contain a slip agent. Thereby, for example, the workability of the multilayer base material can be improved. For example, the third layer may contain the slip agent and all of the first to fifth 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.
One or two or more slip agents can be used.

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.

In one embodiment, in the multilayer substrate of the present disclosure, the density of polyethylene in the second layer is lower than the density of polyethylene in the first layer, and the density of polyethylene in the third layer is lower than the density of polyethylene in the second layer. The density of polyethylene in the layer is lower than the density of polyethylene in the third layer, the density of polyethylene in the fourth layer is higher than the density of polyethylene in the third layer, and the density of polyethylene in the fifth layer is higher than the density of polyethylene in the fourth layer is higher. A multilayer base material having such a structure is excellent in the balance among ink adhesion, interlayer strength, heat resistance, and manufacturability (stretchability of the precursor laminate). The absolute value of the difference between the density of polyethylene in the first layer and the density of polyethylene in the second layer may be, for example, 0.020 g/cm ³ or less. The absolute value of the difference between the density of polyethylene in the second layer and the density of polyethylene in the third layer may be, for example, 0.020 g/cm ³ or less, or 0.010 g/cm ³ or less. The absolute value of the difference between the density of polyethylene in the third layer and the density of polyethylene in the fourth layer may be, for example, 0.020 g/cm ³ or less, or 0.010 g/cm ³ or less. The absolute value of the difference between the density of polyethylene in the fourth layer and the density of polyethylene in the fifth layer may be, for example, 0.020 g/cm ³ or less.

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 taking 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.

<Method for producing multilayer substrate>
The multilayer base material of the present disclosure can be produced, for example, by film-forming a plurality of polyethylene materials to form a laminate by an inflation method or a T-die method, 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 multilayer substrate includes, for example, a layer containing medium density polyethylene and high density polyethylene, a layer containing medium density polyethylene and linear low density polyethylene, and a layer containing medium density polyethylene and linear low density polyethylene. , a layer containing medium density polyethylene and linear low density polyethylene, and a layer containing medium density polyethylene and high density polyethylene in this order in the thickness direction. obtained by

Specifically, from the outside, a layer containing medium density polyethylene and high density polyethylene, a layer containing medium density polyethylene and linear low density polyethylene, and a medium density polyethylene and linear low density polyethylene. A layer, a layer containing medium-density polyethylene and linear low-density polyethylene, and a layer containing medium-density polyethylene and high-density polyethylene can be co-extruded into a tube to form a laminate to produce a laminate. Alternatively, from the outside, a layer containing medium density polyethylene and high density polyethylene, a layer containing medium density polyethylene and linear low density polyethylene, and a layer containing medium density polyethylene and linear low density polyethylene A laminate can be produced by co-extrusion into a tubular shape, and then pressing the opposing layers containing medium density polyethylene and 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.

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. .

The multilayer base material of the present disclosure 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 substrates of the present disclosure may be uniaxially stretched films or biaxially stretched films. 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 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 substrate 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.

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. In terms of heat resistance and rigidity, for example, it is preferable that the thickness of the multilayer base material is large within the range in which the effects described above can be obtained.

[Print substrate]
A printed substrate of the present disclosure comprises a polyethylene multilayer substrate of the present disclosure and a printed layer formed on the multilayer substrate. The printed layer is formed, for example, on the first layer or the fifth layer in the multilayer substrate. Since the multilayer base material has excellent ink adhesion, it can form good images.

The print layer includes, 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 colorants 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. is mentioned.

[Laminate]
The laminate 30 of the present disclosure comprises the polyethylene multilayer substrate 10 of the present disclosure and a heat seal layer 32, as shown in FIG. In multilayer substrate 10 , second layer 18 , third layer 20 and fourth layer 22 are collectively described as multilayer intermediate layer 16 . In this embodiment, the heat seal layer 32 is provided on the first layer 12 . The heat seal layer 32 may be provided on the fifth layer 14 instead of the first layer 12 .

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 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.

<Heat seal layer>
The heat seal layer is preferably made of polyethylene. With such a structure, a laminate for packaging material having sufficient rigidity, strength and heat resistance and excellent recyclability can be obtained.

The recyclability will be described below.
Compared with other thermoplastic resin films, the polyethylene film is inferior in heat resistance, so that when it is used as a base material for packaging materials, it may be deformed during heat sheeting. In addition, the polyethylene film is poor in rigidity, and thus has low printability, so that a clear image cannot be formed on its surface. Moreover, the polyethylene film does not have high strength and cannot satisfy the durability required as the outer layer of the packaging material. Therefore, a laminate is obtained by laminating a resin film (base material) having excellent rigidity, strength and heat resistance such as a polyester film and a nylon film and a polyethylene film (heat seal layer), and the polyethylene film of the laminate is obtained. The packaging material has been produced by heat sealing the laminate ends so that the side is on the inside.

In recent years, attempts have been made to recycle and use packaging materials, along with growing calls for building a recycling-oriented society. However, when a laminate is produced by laminating different types of resin films as described above, it is difficult to separate the resin films from each other. Therefore, such laminates are not suitable for recycling.

On the other hand, the polyethylene multilayer substrate of the present disclosure is stretched as described above and has a unique layer structure, so it has higher rigidity, strength and heat resistance than conventional polyethylene films. Excellent ink adhesion. Therefore, the polyethylene multilayer substrate of the present disclosure 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.

In one embodiment, the laminate of the present disclosure includes the polyethylene multilayer substrate of the present disclosure and a heat-sealable layer containing polyethylene (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 the above laminate comprising a polyethylene multilayer substrate of the present disclosure and a heat-sealable polyethylene layer, in one embodiment, the resin layers contained in the laminate are all polyethylene layers, and the laminate is a polyester film And it does not have a different kind of resin film such as a nylon film. 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 the multi-layer base material optionally formed with a printed layer, and a heat seal layer made of polyethylene. 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 one or more of 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, metal such as aluminum and inorganic oxide 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, 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 one or more adhesives. 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-based 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. It can be formed by

[Use]
The polyethylene multilayer base material, printed base material and 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 polyethylene multilayer substrate, printed substrate or 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 pasted seal type, a palm pasted 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 [16].
[1] A first layer containing medium density polyethylene and high density polyethylene, a second layer containing medium density polyethylene and linear low density polyethylene, and medium density polyethylene and linear low density polyethylene A third layer, a fourth layer containing medium density polyethylene and linear low density polyethylene, and a fifth layer containing medium density polyethylene and high density polyethylene are provided in this order in the thickness direction. , a polyethylene multilayer substrate obtained by stretching.
[2] The mass ratio of medium density polyethylene to high density polyethylene (medium density polyethylene/high density polyethylene) in the first layer and the fifth layer is independently 1.1 or more and 5 or less. The polyethylene multilayer substrate according to [1].
[3] The mass ratio of medium density polyethylene to linear low density polyethylene (medium density polyethylene/linear low density polyethylene) in the second layer and the fourth layer is independently 1.1 or more. 5 or less, the polyethylene multilayer substrate according to the above [1] or [2].
[4] The above [1], wherein the mass ratio of medium density polyethylene to linear low density polyethylene (medium density polyethylene/linear low density polyethylene) in the third layer is 0.25 or more and 4 or less. The polyethylene multilayer substrate according to any one of to [3].
[5] The total content of medium density polyethylene and high density polyethylene in the first layer is 80% by mass or more, and the total content of medium density polyethylene and linear low density polyethylene in the second layer is 80. % by mass or more, the total content of medium density polyethylene and linear low density polyethylene in the third layer is 80% by mass or more, and the content of medium density polyethylene and linear low density polyethylene in the fourth layer Any one of the above [1] to [4], wherein the total content is 80% by mass or more, and the total content of medium density polyethylene and high density polyethylene in the fifth layer is 80% by mass or more. polyethylene multilayer substrate.
[6] The above [1] to [5], wherein at least one layer selected from the first layer, the second layer, the third layer, the fourth layer and the fifth layer contains a slip agent. The polyethylene multilayer substrate according to any one of Claims 1 to 3.
[7] A printing substrate comprising the polyethylene multilayer substrate according to any one of [1] to [6] above, and a printing layer formed on the multilayer substrate.
[8] A laminate comprising the polyethylene multilayer substrate according to any one of [1] to [6] above and a heat seal layer.
[9] The laminate according to [8] above, wherein the heat seal layer contains polyethylene.
[10] The laminate according to [8] or [9] above, further comprising a printed layer on the multilayer substrate.
[11] The laminate according to any one of [8] to [10] above, further comprising a barrier layer between the multilayer substrate and the heat seal layer.
[12] The laminate according to [11] above, wherein the barrier layer is a deposited layer.
[13] The laminate according to [11] or [12] above, wherein the barrier layer is formed on the surface of the multilayer base material or on the surface of the heat seal layer.
[14] The laminate according to any one of [8] to [13] above, further comprising an adhesive layer between the multilayer substrate and the heat seal layer.
[15] The laminate according to any one of [8] to [14] above, which is used as a packaging material.
[16] The polyethylene multilayer substrate according to any one of [1] to [6] above, the printing substrate according to [7] above, or the laminate according to any one of [8] to [15] above. A packaging material comprising:

The multilayer substrate of the present disclosure will be specifically described based on examples, but the multilayer substrate 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
MB manufactured by ExxonMobil containing a slip agent:
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 MDPE and 30 parts of LLDPE were mixed to obtain a blended polyethylene B1 (hereinafter referred to as "blended PE (B1)") having an average density of 0.933 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 .
・Blended polyethylene C2
49 parts of MDPE, 49 parts of LLDPE, and 2 parts of MB containing a slip agent were mixed to obtain a blended polyethylene C2 having an average density of 0.928 g/cm ³ (hereinafter referred to as "blended PE (C2)") got

[Example 1]
Blend PE (A1), blend PE (B1) and blend PE (C2) were formed into blend PE (A1) layer (15 μm)/blend PE (B1) layer (20 μm)/blend PE (C2) layer by inflation molding method. (55 μm)/blended PE (B1) layer (20 μm)/blended PE (A1) layer (15 μm) layer thickness ratio of 5 layers co-extruded to form a tubular film to form a polyethylene film with a total thickness of 125 μm. Then, the tubular film was folded at the nip to form a two-ply film. 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 of the surface layer on the corona treatment side shown in Table 1 was subjected to corona discharge treatment. , the end portion was slit and divided into two sheets to obtain a stretched multilayer substrate having a thickness of 25 μm.

[Comparative Examples 1 and 2]
A polyethylene film and a stretched multilayer substrate were obtained in the same manner as in Example 1, except that the layer structure was changed as shown in Table 1. In Table 1, the slip agent-containing MB is simply indicated as "MB".

[Example 2]
Blend PE (A1), blend PE (B1) and blend PE (C2) were formed into blend PE (A1) layer (12 μm)/blend PE (B1) layer (16 μm)/blend PE (C2) layer by inflation molding. (44 μm)/blended PE (B1) layer (16 μm)/blended PE (A1) layer (12 μm) layer thickness ratio of 5 layers co-extruded to form a tubular film to form a polyethylene film with a total thickness of 100 μm. Then, the tubular film was folded at the nip to form a two-ply film. 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 of the surface layer on the corona treatment side shown in Table 1 was subjected to corona discharge treatment. , the end portion was slit and divided into two sheets to obtain a stretched multilayer substrate having a thickness of 20 μm.

[Example 3]
Blend PE (A1), blend PE (B1) and blend PE (C2) were formed into a blend PE (A1) layer (24 μm)/blend PE (B1) layer (32 μm)/blend PE (C2) layer by an inflation molding method. (88 μm)/blended PE (B1) layer (32 μm)/blended PE (A1) layer (24 μm) layer thickness ratio of 5 layers co-extruded to form a tubular film to form a polyethylene film with a total thickness of 200 μm. Then, the tubular film was folded at the nip to form a two-ply film. 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 of the surface layer on the corona treatment side shown in Table 1 was subjected to corona discharge treatment. , the end portion was slit and divided into two sheets to obtain a stretched multilayer substrate having a thickness of 40 μm.

[Ink adhesion evaluation]
An image is formed by gravure printing using an oil-based gravure ink (manufactured by DIC Graphics Co., Ltd., trade name: Finart) on the corona discharge-treated surface side of the stretched multilayer substrates obtained in Examples and Comparative Examples. did. 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). Ta.
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).

[Preparation of laminate]
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 (SP1520, manufactured by Prime Polymer Co., Ltd.; Density: 0.913 g/cm ³ , Melting point: 116° 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 are formed. 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 substrates obtained in Examples and Comparative Examples were separated into two layers. Dry lamination was performed via a liquid-curing urethane adhesive (Ru-77T/H-7 manufactured by Rock Paint Co., Ltd.) to obtain a laminate.

The laminate produced above was cut into 10 cm×10 cm to produce three sample pieces each. Each sample piece was folded in half so that the heat seal layer side faced inside, and a 1 cm×10 cm area was heat sealed using a heat seal tester under the conditions of 140° C., 1 kgf/cm ² pressure, and 1 second.

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

[Haze evaluation]
The haze values of the stretched multilayer substrates obtained in Examples and Comparative Examples were measured according to JIS K7136.

[Rigidity evaluation]
The stretched multilayer substrates obtained in Examples and Comparative Examples were cut into test pieces with a width of 10 mm, and the rigidity of the test pieces was measured using a loop stiffness measuring tester (manufactured by Toyo Seiki Seisakusho, trade name: Loop Stiffness Tester). did. The loop length was 60 mm.

[Strength evaluation]
Dumbbell-shaped specimens with a width of 10 mm were cut out from the stretched multilayer substrates obtained in Examples and Comparative Examples. 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.
Table 1 shows the above evaluation results.

10: Polyethylene multilayer substrate 12: First layer containing medium density polyethylene and high density polyethylene 14: Fifth layer containing medium density polyethylene and high density polyethylene 16: Second layer, third layer and Multilayer middle layer 18 consisting of a fourth layer: Second layer 20 containing medium density polyethylene and linear low density polyethylene: Third layer 22 containing medium density polyethylene and linear low density polyethylene: medium Fourth Layer Containing Density Polyethylene and Linear Low Density Polyethylene 30: Laminate 32: Heat Seal Layer 34: Barrier Layer 36: Adhesive Layer

Claims (16)

a first layer containing medium density polyethylene and high density polyethylene;
a second layer containing medium density polyethylene and linear low density polyethylene;
a third layer containing medium density polyethylene and linear low density polyethylene;
a fourth layer containing medium density polyethylene and linear low density polyethylene;
A polyethylene multilayer base material comprising medium-density polyethylene and a fifth layer containing high-density polyethylene in this order in the thickness direction and subjected to stretching. The mass ratio of the medium density polyethylene to the high density polyethylene (medium density polyethylene/high density polyethylene) in the first layer and the fifth layer is independently 1.1 or more and 5 or less. The polyethylene multilayer substrate according to claim 1. The mass ratio of the medium density polyethylene to the linear low density polyethylene (medium density polyethylene/linear low density polyethylene) in the second layer and the fourth layer is independently 1.1. 3. The polyethylene multilayer substrate according to claim 1 or 2, which is 5 or less. Claims 1 to 4, wherein the mass ratio of the medium density polyethylene to the linear low density polyethylene (medium density polyethylene/linear low density polyethylene) in the third layer is 0.25 or more and 4 or less. 4. The polyethylene multilayer substrate according to any one of 3. The total content of the medium density polyethylene and the high density polyethylene in the first layer is 80% by mass or more,
The total content of the medium density polyethylene and the linear low density polyethylene in the second layer is 80% by mass or more,
The total content of the medium density polyethylene and the linear low density polyethylene in the third layer is 80% by mass or more,
The total content of the medium density polyethylene and the linear low density polyethylene in the fourth layer is 80% by mass or more,
The total content of the medium density polyethylene and the high density polyethylene in the fifth layer is 80% by mass or more,
The polyethylene multilayer substrate according to any one of claims 1-4. 6. The method according to any one of claims 1 to 5, wherein at least one layer selected from the first layer, second layer, third layer, fourth layer and fifth layer contains a slip agent. 10. The polyethylene multilayer substrate according to Item 1. The polyethylene multilayer substrate according to any one of claims 1 to 6,
and a printing layer formed on the multilayer substrate. The polyethylene multilayer substrate according to any one of claims 1 to 6,
A laminate comprising a heat seal layer. 9. The laminate of Claim 8, wherein the heat seal layer comprises polyethylene. 10. The laminate according to claim 8 or 9, further comprising a printed layer on said multilayer substrate. The laminate according to any one of claims 8 to 10, further comprising a barrier layer between said multilayer substrate and said heat seal layer. 12. Laminate according to claim 11, wherein the barrier layer is a deposited layer. The laminate according to claim 11 or 12, wherein the barrier layer is formed on the surface of the multilayer substrate or the surface of the heat seal layer. The laminate according to any one of claims 8 to 13, further comprising an adhesive layer between the multilayer substrate and the heat seal layer. The laminate according to any one of claims 8 to 14, which is used for packaging materials. A packaging material comprising a polyethylene multilayer substrate according to any one of claims 1-6, a printed substrate according to claim 7, or a laminate according to any one of claims 8-15.