Polyethylene multilayer substrates, printing substrates, laminates and packaging materials

Abstract

To provide a polyethylene multilayer base material excellent in ink adhesion and heat resistance.SOLUTION: A polyethylene multilayer base material includes: a first layer containing high-density polyethylene and medium-density polyethylene; a second layer containing medium-density polyethylene; a third layer containing linear low-density polyethylene and medium-density polyethylene; a fourth layer containing medium-density polyethylene; and a fifth layer containing high-density polyethylene and medium-density polyethylene, in this order in a thickness direction. The polyethylene multilayer base material is processed with a drawing treatment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to polyethylene multilayer substrates, printed substrates, laminates and packaging materials. [Background technology]

[0002] Conventionally, packaging materials and the like have been produced using resin films made of resin materials. The packaging materials include, for example, a base material and a heat-sealing layer. For example, resin films made of polyethylene are widely used as heat-sealing layers in packaging materials because they are flexible, transparent, and have excellent heat-sealing properties (see, for example, Patent Document 1).

[0003] On the other hand, polyethylene is a resin that softens at a relatively low temperature compared to other thermoplastic resins, and therefore, when used as a base material for packaging materials, it may deform or even melt during heat sheet processing. Furthermore, polyethylene film may lack strength compared to other thermoplastic resin films. For this reason, resin films with excellent strength and heat resistance, such as polyester film and nylon film, are generally used as base materials for packaging materials. For example, bags are made by laminating a base material such as polyester film or nylon film with a polyethylene film, and then heat-sealing the polyethylene film side so that it is on the inside of the packaging bag (see, for example, the background art of Patent Document 2).

[0004] In recent years, along with the growing demand for the creation of a recycling-oriented society, attempts have been made to recycle and reuse packaging materials. However, laminates obtained by laminating different types of resin films as described above are difficult to separate by type of resin, and are therefore not suitable for recycling. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-202519 [Patent Document 2] Japanese Patent Application Publication No. 2017-031233 Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, the present inventors 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 as the substrate, which has multiple layers containing polyethylene and has been stretched. Incidentally, images such as letters and figures are usually printed with ink on substrates used for packaging materials, etc. However, further investigation by the present inventors has revealed that polyethylene multilayer substrates may have insufficient ink adhesion.

[0007] Furthermore, since the polyethylene multilayer substrate may be subjected to heat during printing, etc., it is preferable that the substrate has excellent heat resistance.

[0008] One object of the present disclosure is to provide a polyethylene multilayer substrate that has excellent ink adhesion and heat resistance. [Means for solving the problem]

[0009] The polyethylene multilayer substrate of the present disclosure comprises: a first layer containing high density polyethylene and medium density polyethylene; a second layer containing medium density polyethylene; a third layer containing linear low density polyethylene and medium density polyethylene; a fourth layer containing medium density polyethylene; and a fifth layer containing high density polyethylene and medium density polyethylene; are provided in this order in the thickness direction and are subjected to a stretching treatment. [Effects of the Invention]

[0010] According to the present disclosure, a polyethylene multilayer substrate having excellent ink adhesion and heat resistance can be provided. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a cross-sectional schematic diagram illustrating one embodiment of a polyethylene multilayer substrate of the present disclosure. [Figure 2] 1 is a cross-sectional schematic diagram illustrating one embodiment of a laminate of the present disclosure. [Figure 3] 1 is a cross-sectional schematic diagram illustrating one embodiment of a laminate of the present disclosure. [Figure 4] 1 is a cross-sectional schematic diagram illustrating one embodiment of a laminate of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] The terms used in this disclosure are explained below. "Polyethylene" refers to a polymer in which the content of ethylene-derived structural units is 50 mol% or more of all repeating structural units. In such a polymer, the content of ethylene-derived structural units is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more. The content is measured by nuclear magnetic resonance (NMR) spectroscopy.

[0013] The density of the high density polyethylene is preferably 0.945 g / cm 3 The upper limit of the density of high density polyethylene is, for example, 0.965 g / cm 3 is. The density of the medium density polyethylene is preferably 0.925 g / cm 3 Exceeds 0.945g / cm 3 The following is the result. The density of the low density polyethylene is preferably 0.900 g / cm 3 Exceeds 0.925g / cm 3 The following is the result. The density of the linear low density polyethylene is preferably 0.900 g / cm 3 Exceeds 0.925g / cm 3 The following is the result. The density of the ultra-low density polyethylene is preferably 0.900 g / cm 3 The lower limit of the density of the ultra-low density polyethylene is, for example, 0.860 g / cm 3 is. The density of polyethylene is measured in accordance with JIS K7112 (1999).

[0014] [Polyethylene multi-layer base material] As shown in FIG. 1, the polyethylene multilayer substrate 10 of the present disclosure has: a first layer 12 containing high density polyethylene and medium density polyethylene; a second layer 18 containing medium density polyethylene; a third layer 20 containing linear low density polyethylene and medium density polyethylene; a fourth layer 22 containing medium density polyethylene; a fifth layer 14 containing high density polyethylene and medium density polyethylene; are provided in this order in the thickness direction and are subjected to a stretching treatment. Hereinafter, the polyethylene multilayer substrate will also be simply referred to as "multilayer substrate."

[0015] 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. The multilayer substrate may have other layers between the first to fifth layers, but in one embodiment, the multilayer substrate consists only of the first to fifth layers.

[0016] In the present disclosure, examples of polyethylene include ethylene homopolymers and copolymers of ethylene with other monomers. Examples of other monomers include α-olefins having 3 to 20 carbon atoms, vinyl acetate, and (meth)acrylic acid esters. Examples of α-olefins having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 3-methyl-1-butene, 4-methyl-1-pentene, and 6-methyl-1-heptene. Examples of (meth)acrylic acid esters include alkyl (meth)acrylates such as methyl (meth)acrylate and ethyl (meth)acrylate.

[0017] Examples of the copolymer include a copolymer of ethylene and an α-olefin having 3 to 20 carbon atoms, a copolymer of ethylene and at least one selected from vinyl acetate and (meth)acrylic acid esters, and a copolymer of ethylene, an α-olefin having 3 to 20 carbon atoms, and at least one selected from vinyl acetate and (meth)acrylic acid esters.

[0018] Polyethylenes with different densities or branches 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 as a polymerization catalyst and carry out polymerization in one or more stages by any of gas phase polymerization, slurry polymerization, solution polymerization, and high-pressure ionic polymerization.

[0019] A single-site catalyst is a catalyst capable of forming a uniform active species, and is usually prepared by contacting a metallocene transition metal compound or a non-metallocene transition metal compound with an activating cocatalyst. Single-site catalysts are preferred because they have a more uniform structure of the active site than multi-site catalysts, making it possible to obtain polymers with high molecular weights and highly uniform structures.

[0020] The single-site catalyst is preferably a metallocene catalyst, which comprises a transition metal compound of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton, a cocatalyst, an organometallic compound as needed, and a support as needed.

[0021] Examples of the transition metal in the transition metal compound include zirconium, titanium, and hafnium, with zirconium and hafnium being preferred.

[0022] The cyclopentadienyl skeleton in the transition metal compound is a cyclopentadienyl group or a substituted cyclopentadienyl group. The substituted cyclopentadienyl group has at least one substituent selected from, for example, a hydrocarbon group having 1 to 30 carbon atoms, a silyl group, a silyl-substituted alkyl group, a silyl-substituted aryl group, a cyano group, a cyanoalkyl group, a cyanoaryl group, a halogen group, a haloalkyl group, and a halosilyl group. The substituted cyclopentadienyl group has one or more substituents, and the substituents may be bonded to each other to form a ring, such as an indenyl ring, a fluorenyl ring, an azulenyl ring, or a hydrogenated version thereof. The ring formed by bonding the substituents to each other may further have a substituent.

[0023] A transition metal compound usually has two ligands having a cyclopentadienyl skeleton. The ligands having each cyclopentadienyl skeleton are preferably bonded to each other via a bridging group. Examples of the bridging group include alkylene groups having 1 to 4 carbon atoms, silylene groups, substituted silylene groups such as dialkylsilylene groups and diarylsilylene groups, and substituted germylene groups such as dialkylgermylene groups and diarylgermylene groups. Among these, substituted silylene groups are preferred.

[0024] The co-catalyst refers to a component that enables a transition metal compound of Group IV of the periodic table to function effectively as a polymerization catalyst or a component that balances the ionic charge in a catalytically activated state. Examples of the co-catalyst include benzene-soluble aluminoxanes or benzene-insoluble organoaluminum oxy-compounds, ion-exchangeable layered silicates, boron compounds, ionic compounds consisting of a cation with or without an active hydrogen group and a non-coordinating anion, lanthanoid salts such as lanthanum oxide, tin oxide, and phenoxy compounds containing a fluoro group.

[0025] Examples of organometallic compounds that may be used as needed include organoaluminum compounds, organomagnesium compounds, and organozinc compounds. Of these, organoaluminum compounds are preferred.

[0026] The transition metal compound may be used by being supported on an inorganic or organic carrier, preferably a porous oxide of an inorganic or organic compound, such as montmorillonite or other ion-exchangeable layered silicates, SiO2, Al2O3, MgO, ZrO2, TiO2, BO3, CaO, ZnO, BaO, ThO2, or mixtures thereof.

[0027] Biomass-derived ethylene may be used as a raw material for obtaining polyethylene instead of ethylene obtained from fossil fuels. Biomass-derived polyethylene is a carbon-neutral material, and therefore can reduce the environmental impact of packaging materials produced using multilayer substrates. Biomass-derived polyethylene can be produced, for example, by the method described in JP 2013-177531 A. Commercially available biomass-derived polyethylene (e.g., Green PE available from Braskem) may also be used.

[0028] You can also use polyethylene recycled through mechanical recycling. Mechanical recycling generally involves crushing collected polyethylene film, washing it with alkali to remove dirt and foreign matter from the film surface, and then drying it at high temperature and reduced pressure for a certain period of time to diffuse any contaminants remaining inside the film, thereby decontaminating it and removing the dirt from the polyethylene film and returning it to polyethylene. The melt flow rate (MFR) of the polyethylene contained in the multilayer substrate of the present disclosure is preferably 0.1 g / 10 min or more and 50 g / 10 min or less, more preferably 0.3 g / 10 min or more and 30 g / 10 min or less, from the viewpoints of film-forming ability and processability of the multilayer substrate. In the present disclosure, the MFR is measured in accordance with ASTM D1238 at a temperature of 190°C and a load of 2.16 kg.

[0029] Examples of polyethylene include high-density polyethylene, medium-density polyethylene, low-density polyethylene (high-pressure low-density polyethylene), linear low-density polyethylene, and very low-density polyethylene. Each layer constituting the multilayer substrate will now be described.

[0030] <First layer and fifth layer> The first layer contains one or more high density polyethylenes and one or more medium density polyethylenes. The fifth layer contains one or more high density polyethylenes and one or more medium density polyethylenes. When printing an image on a substrate, the substrate is usually subjected to a surface treatment such as corona discharge treatment as a pretreatment. A layer containing medium-density polyethylene tends to have higher durability against the surface treatment than a layer containing only high-density polyethylene as the polyethylene. Therefore, the layer containing medium-density polyethylene has excellent ink adhesion during printing after the surface treatment. In addition, the layer containing medium-density polyethylene also has the heat resistance required during printing and heat sealing. In addition, the layer containing medium-density polyethylene contributes to improving the stretchability of the laminate, which is a precursor to the multilayer substrate.

[0031] The high-density polyethylene contained in the first layer and the high-density polyethylene contained in the fifth layer may be the same or different, but from the viewpoint of facilitating the production of the multilayer base material, it is preferable that they are the same. The medium-density polyethylene contained in the first layer and the medium-density polyethylene contained in the fifth layer may be the same or different, but from the viewpoint of facilitating the production of the multilayer base material, it is preferable that they are the same.

[0032] The first layer and the fifth layer may each independently contain, in addition to the high-density polyethylene and the medium-density polyethylene, a polyethylene other than these polyethylenes. Examples of the polyethylene other than the high-density polyethylene and the medium-density polyethylene include low-density polyethylene (high-pressure low-density polyethylene), linear low-density polyethylene, and very low-density polyethylene. From the viewpoint of further improving the ink adhesion and heat resistance of the multilayer substrate, the first layer preferably contains only high-density polyethylene and medium-density polyethylene as the polyethylene. From the viewpoint of further improving the ink adhesion and heat resistance of the multilayer substrate, the fifth layer preferably contains only high-density polyethylene and medium-density polyethylene as the polyethylene.

[0033] The mass ratio of the high-density polyethylene to the medium-density polyethylene (high-density polyethylene / medium-density polyethylene) in the first layer and the fifth layer is preferably 1.1 or more and 5 or less, more preferably 1.5 or more and 3 or less, thereby further improving the balance between ink adhesion and heat resistance. The total content of high-density polyethylene and medium-density polyethylene in the first layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, thereby further improving the ink adhesion and heat resistance of the multilayer substrate. The total content of high-density polyethylene and medium-density polyethylene in the fifth layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, thereby further improving the ink adhesion and heat resistance of the multilayer substrate.

[0034] The thickness of each of the first layer and the fifth layer is independently preferably from 0.5 μm to 10 μm, more preferably from 1 μm to 8 μm, and even more preferably from 1 μm to 5 μm, thereby further improving the ink adhesion and heat resistance of the multilayer substrate.

[0035] The thickness of each of the first layer and the fifth layer is preferably smaller than the total thickness of the second layer, the third layer, and the fourth layer (hereinafter, the second to fourth layers are collectively referred to as the "multilayer intermediate layer"). 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 to 0.8, more preferably 0.1 to 0.7, and even more preferably 0.1 to 0.4. This can further improve the rigidity, strength, and heat resistance of the multilayer substrate.

[0036] <Second and fourth layers> The second layer contains one or more medium density polyethylenes. The fourth layer contains one or more medium density polyethylenes. The second layer and the fourth layer each contribute to improving the stretchability of the laminate, which is the precursor of the multilayer substrate.

[0037] The medium-density polyethylene contained in the second layer and the medium-density polyethylene contained in the fourth layer may be the same or different, but from the viewpoint of facilitating the production of the multilayer base material, it is preferable that they are the same. The medium-density polyethylene contained in the second and fourth layers may be the same as or different from the medium-density polyethylene contained in the first and fifth layers.

[0038] The second layer and the fourth layer may each independently contain, in addition to the medium-density polyethylene, a polyethylene other than the medium-density polyethylene. Examples of the polyethylene other than the medium-density polyethylene include high-density polyethylene, low-density polyethylene (high-pressure low-density polyethylene), linear low-density polyethylene, and ultra-low-density polyethylene. From the viewpoint of further improving the stretchability of the laminate, which is the precursor of the multilayer substrate, it is preferable that the second layer contains only medium-density polyethylene as the polyethylene. From the viewpoint of further improving the stretchability of the laminate, which is the precursor of the multilayer substrate, it is preferable that the fourth layer contains only medium-density polyethylene as the polyethylene.

[0039] The content of medium-density polyethylene in the second layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, which can further improve the stretchability of the precursor laminate. The content of medium-density polyethylene in the fourth layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, which can further improve the stretchability of the precursor laminate.

[0040] The thickness of each of the second layer and the fourth layer is independently preferably 0.5 μm to 15 μm, more preferably 1 μm to 10 μm, and even more preferably 1 μm to 8 μm, which can further improve the stretchability of the precursor laminate.

[0041] <Third Layer> The third layer contains one or more linear low-density polyethylenes and one or more medium-density polyethylenes, and contributes to improving the stretchability of the laminate, which is a precursor to the multilayer substrate.

[0042] The medium-density polyethylene contained in the third layer may be the same as or different from the medium-density polyethylene contained in the first, second, fourth and fifth layers.

[0043] The third layer may contain, in addition to the linear low-density polyethylene and medium-density polyethylene, other polyethylenes. Examples of polyethylenes other than the linear low-density polyethylene and medium-density polyethylene include high-density polyethylene, low-density polyethylene (high-pressure low-density polyethylene), and very low-density polyethylene. From the viewpoint of further improving the stretchability of the laminate, which is the precursor of the multilayer substrate, it is preferable that the third layer contains only linear low-density polyethylene and medium-density polyethylene as the polyethylene.

[0044] The mass ratio of the linear low-density polyethylene to the medium-density polyethylene in the third layer (linear low-density polyethylene / medium-density polyethylene) is preferably 0.25 to 4, more preferably 0.4 to 2.4, thereby further improving the balance between heat resistance, rigidity, and stretchability. The total content of the linear low-density polyethylene and the medium-density polyethylene in the third layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, thereby further improving the stretchability of the precursor laminate.

[0045] The thickness of the third layer is preferably from 1 μm to 50 μm, more preferably from 2 μm to 40 μm, and even more preferably from 5 μm to 30 μm, which can further improve the balance between heat resistance, rigidity, and stretchability.

[0046] 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 to 10, more preferably 0.2 to 5, and even more preferably 0.5 to 2. This can further improve the rigidity, strength, and heat resistance of the multilayer substrate.

[0047] The first to fifth layers constituting the multilayer substrate may each independently contain one or more additives, such as crosslinkers, antioxidants, antiblocking agents, slip agents, UV absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, and modifying resins.

[0048] In one embodiment, in a multilayer substrate of the present disclosure, the density of the polyethylene in the second layer is lower than the density of the polyethylene in the first layer, the density of the polyethylene in the third layer is lower than the density of the polyethylene in the second layer, the density of the polyethylene in the fourth layer is higher than the density of the polyethylene in the third layer, and the density of the polyethylene in the fifth layer is higher than the density of the polyethylene in the fourth layer. A multilayer substrate having such a configuration has an excellent balance of ink adhesion, heat resistance, and manufacturability (stretchability of the precursor laminate).

[0049] When multiple types of polyethylene with different densities (n types; n is an integer of 2 or more) are contained in one layer, the average density D calculated according to the following formula (1) av is the density of the polyethylene constituting the layer.

[0050] D av = ΣW i ×D i …(1) In equation (1), Σ is W for i from 1 to n. i ×D i where n is an integer greater than or equal to 2, and W i denotes the mass fraction of the i-th polyethylene, and D i is the density of the i-th polyethylene (g / cm 3 ) is shown.

[0051] When any adjacent layers selected from the first to fifth layers in the multilayer substrate are referred to as layer (1) and layer (2), the absolute value of the difference between the density of the polyethylene constituting layer (1) and the density of the polyethylene constituting layer (2) is preferably 0.030 g / cm 3or less, more preferably 0.025 g / cm 3 or less, more preferably 0.020 g / cm 3 The following is the requirement. Hereinafter, this requirement will also be referred to as the "density difference requirement." In other words, it is preferable that any pair of adjacent layers in the thickness direction selected from the first to fifth layers included in the multilayer base material (for example, the pair of the first layer and the second layer, the pair of the second layer and the third layer, the pair of the third layer and the fourth layer, or the pair of the fourth layer and the fifth layer) satisfy the density difference requirement. In the following description, density differences always refer to absolute values ​​of the differences.

[0052] A multilayer substrate that satisfies the density difference requirement has a small difference in density between the first to fifth layers, as described above, and therefore exhibits high interlayer strength.

[0053] <Method of manufacturing multilayer substrate> The multilayer substrate of the present disclosure can be produced by forming a laminate from multiple polyethylene materials using, for example, an inflation method or a T-die method, and then stretching the resulting laminate. Stretching can improve the transparency, rigidity, strength, and heat resistance of the multilayer substrate, making it suitable for use as a base material for packaging materials, for example.

[0054] The multilayer substrate can be obtained, for example, by stretching a laminate (precursor) having, in the thickness direction, a layer containing high-density polyethylene and medium-density polyethylene, a layer containing medium-density polyethylene, a layer containing linear low-density polyethylene and medium-density polyethylene, a layer containing medium-density polyethylene, and a layer containing high-density polyethylene and medium-density polyethylene, in this order.

[0055] Specifically, a laminate can be produced by co-extruding from the outside a layer containing high-density polyethylene and medium-density polyethylene, a layer containing medium-density polyethylene, a layer containing linear low-density polyethylene and medium-density polyethylene, a layer containing medium-density polyethylene, and a layer containing high-density polyethylene and medium-density polyethylene into a tubular shape. Alternatively, a laminate can be produced by co-extruding from the outside a layer containing high-density polyethylene and medium-density polyethylene, a layer containing medium-density polyethylene, and a layer containing linear low-density polyethylene and medium-density polyethylene into a tubular shape, and then pressing the opposing layers containing linear low-density polyethylene and medium-density polyethylene together using a rubber roll or the like. By producing a laminate using this method, the number of defective products can be significantly reduced and production efficiency can be improved.

[0056] When a laminate is produced by the T-die method, the melt flow rate (MFR) of the polyethylene constituting each layer is preferably 3 g / 10 min or more and 20 g / 10 min or less from the viewpoint of film-forming properties and processability of the multilayer substrate.

[0057] When a laminate is produced by inflation extrusion, the MFR of the polyethylene constituting each layer is preferably 0.5 g / 10 min or more and 5 g / 10 min or less from the viewpoint of film formability and processability of the multilayer substrate.

[0058] The multilayer substrate of the present disclosure can be obtained, for example, by stretching the above-described laminate. Note that the stretching of the laminate can also be performed in an inflation film-forming machine. This allows the multilayer substrate to be produced, thereby further improving production efficiency.

[0059] The multilayer substrate of the present disclosure may be a uniaxially stretched film or a biaxially stretched film. In one embodiment, the multilayer substrate is a uniaxially stretched film, more specifically, a uniaxially stretched film that has been stretched in the machine direction (MD).

[0060] In one embodiment, the stretching ratio in the machine direction (MD) of the multilayer substrate is preferably 2 to 10, more preferably 3 to 7. In one embodiment, the stretching ratio in the transverse direction (TD) of the multilayer substrate is preferably 2 to 10, more preferably 3 to 7.

[0061] A stretching ratio of 2 or more can improve, for example, the rigidity, strength, and heat resistance of the multilayer substrate, improve the ink adhesion to the multilayer substrate, and improve the transparency of the multilayer substrate.A stretching ratio of 10 or less can ensure good stretching of the laminate.

[0062] The haze value of the multilayer substrate is preferably 25% or less, more preferably 15% or less, and even more preferably 10% or less. The smaller the haze value, the better, 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.

[0063] The content of polyethylene 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, which can improve the recyclability of the multilayer substrate.

[0064] The laminate or multilayer substrate is preferably subjected to a surface treatment. This can improve the adhesion between the surface layer of the multilayer substrate and the layer 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, and glow discharge treatment; and chemical treatments such as oxidation treatment using chemicals.

[0065] An anchor coating layer may be formed on the surface of the laminate or multilayer substrate using a conventionally known anchor coating agent.

[0066] 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 substrate is 60 μm or less, the processability of the multilayer substrate can be improved.

[0067] [Printing base material] The printing substrate of the present disclosure comprises the polyethylene multilayer substrate of the present disclosure and a printing layer formed on the multilayer substrate. The printing layer is formed, for example, on the first layer or the fifth layer of the multilayer substrate. The multilayer substrate has excellent ink adhesion, allowing for the formation of a good image.

[0068] The printed layer includes, for example, an image. Examples of images include letters, figures, symbols, and combinations thereof. Examples of methods for forming the printed layer include 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 a biomass-derived ink.

[0069] [Laminate] 2, a laminate 30 of the present disclosure includes a polyethylene multilayer substrate 10 of the present disclosure and a heat seal layer 32. In the multilayer substrate 10, the second layer 18, the third layer 20, and the fourth layer 22 are collectively referred to as a multilayer intermediate layer 16.

[0070] In one embodiment, the laminate 30 further includes a printed layer (not shown) on the multilayer substrate 10. The printed layer is usually formed on a surface layer of the multilayer substrate on which a heat seal layer is provided, for example, on the first layer described above.

[0071] In one embodiment, as shown in FIG. 3, the laminate 30 includes a barrier layer 34 and an adhesive layer 36 between the multi-layer substrate 10 and the heat seal layer 32 . In one embodiment, as shown in FIG. 4, the laminate 30 includes an adhesive layer 36 between the multi-layer substrate 10 and the heat seal layer 32 .

[0072] In the laminate of the present 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 contents of the resin materials in each layer constituting the laminate.

[0073] <Heat seal layer> The heat seal layer is preferably made of polyethylene, which provides a laminate for packaging materials having sufficient rigidity, strength, and heat resistance, as well as excellent recyclability.

[0074] The recyclability will be described below. Compared with other thermoplastic resin films, polyethylene film has poorer heat resistance, and therefore, when used as a base material for packaging materials, it can deform during heat sealing. Furthermore, polyethylene film has poor rigidity, making it less suitable for printing, and it is not possible to form clear images on its surface. Furthermore, polyethylene film does not have high strength and does not meet the durability required for the outer layer of packaging materials. Therefore, packaging materials are produced by laminating a resin film (base material) that has excellent rigidity, strength, and heat resistance, such as polyester film or nylon film, with a polyethylene film (heat seal layer) to obtain a laminate, and then heat-sealing the edges of the laminate so that the polyethylene film side of the laminate is on the inside.

[0075] In recent years, with the growing demand for the creation of a recycling-oriented society, attempts have been made to recycle and reuse packaging materials. 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. For this reason, such a laminate is not suitable for recycling.

[0076] In contrast, the polyethylene multilayer substrate of the present disclosure has been stretched as described above and has a unique layer structure, and therefore is superior in rigidity, strength, heat resistance, and ink adhesion compared to conventional polyethylene films. 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.

[0077] In one embodiment, the laminate of the present disclosure comprises 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 surface of the multilayer substrate. Since this can prevent deterioration of the image over time, it is preferable that the printed layer is formed on the side of the multilayer substrate where the heat-sealable polyethylene layer is provided.

[0078] In one embodiment of the laminate comprising the polyethylene multilayer substrate and the heat-sealable polyethylene layer of the present disclosure, the resin layers included in the laminate are all polyethylene layers, and the laminate does not include a different type of resin film, such as a polyester film or a nylon film. Furthermore, the polyethylene multilayer substrate meets 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 laminate is suitable as a material for constituting packaging materials that require recyclability.

[0079] In one embodiment, the laminate of the present disclosure comprises only the multilayer substrate on which a printing layer is optionally formed and a heat seal layer made of polyethylene, whereby each resin layer of the laminate of the present disclosure is made of the same material, polyethylene, thereby improving recyclability.

[0080] The heat-seal layer is usually a non-stretched layer. For example, the heat-seal layer can be formed by laminating an unstretched polyethylene film onto a multilayer substrate or the like, optionally via an adhesive layer, or by melt-extruding a polyethylene-containing resin material onto a multilayer substrate or the like. Examples of the adhesive layer include the adhesive layer described below.

[0081] Examples of polyethylene constituting the heat seal layer include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, and very low-density polyethylene. From the viewpoint of heat sealability, low-density polyethylene, linear low-density polyethylene, and very low-density polyethylene are preferred. From the viewpoint of reducing the environmental load, biomass-derived polyethylene or recycled polyethylene may also be used.

[0082] The content of polyethylene 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, which can improve the recyclability of the laminate. The heat seal layer may contain one or more of the above additives.

[0083] 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 or more and 300 μm or less. From the viewpoint of the strength of the heat seal layer and the processability of the laminate, it is preferable to change the thickness of the heat seal layer appropriately depending on the mass of the contents to be filled into, for example, a packaging material produced using the laminate of the present disclosure.

[0084] For example, when the packaging material is a pouch, the thickness of the heat seal layer is preferably 20 μm or more and 60 μm or less, so that the pouch can be well filled with contents of, for example, 1 g or more and 200 g or less. For example, when 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, so that the stand-up pouch can be well filled with contents of, for example, 50 g or more and 2000 g or less.

[0085] <Barrier layer> In one embodiment, the laminate of the present disclosure includes a barrier layer between the multilayer substrate and the heat-sealing 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-sealing layer. Alternatively, the barrier layer may be provided between the multilayer substrate and the heat-sealing layer via an adhesive or the like.

[0086] In one embodiment, the barrier layer is a vapor-deposited layer. Vapor-deposited layers are made of, for example, metals such as aluminum, or 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.

[0087] 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 even more preferably 10 nm or more and 40 nm or less. By making the thickness of the barrier layer 1 nm or more, the oxygen barrier property and water vapor barrier property of the laminate can be further improved. By making the thickness of the barrier layer 150 nm or less, the occurrence of cracks in the barrier layer can be suppressed and the recyclability of the laminate can be improved.

[0088] Examples of methods for forming the barrier layer include physical vapor deposition (PVD) methods such as vacuum deposition, sputtering, and ion plating; and chemical vapor deposition (CVD) methods such as plasma-enhanced chemical vapor deposition, thermal chemical vapor deposition, and photochemical vapor deposition. The barrier layer may be a composite film containing two or more barrier layers made of different inorganic oxides, formed by combining physical vapor deposition and chemical vapor deposition.

[0089] The vacuum level in the deposition chamber was 10 -2 ~10 -8 After oxygen is introduced, the pressure is preferably about 10 -1 ~10 -6 A pressure of about mbar is preferred. The amount of oxygen introduced varies depending on the size of the deposition machine. An inert gas such as argon gas, helium gas, or nitrogen gas may be used as a carrier gas for the introduced oxygen, provided that no problems occur. The conveying speed of the multilayer substrate is, for example, about 10 to 800 m / min.

[0090] The surface of the barrier layer is preferably subjected to the above-mentioned surface treatment, which can improve the adhesion between the barrier layer and the adjacent layer.

[0091] When the vapor-deposited layer is made of an inorganic oxide such as aluminum oxide or silicon oxide, a barrier coat layer may be provided on the surface of the vapor-deposited layer to form a barrier layer comprising the vapor-deposited layer and the barrier coat layer.

[0092] In one embodiment, the barrier coat layer is made of a gas barrier resin, such as ethylene-vinyl alcohol copolymer (EVOH), polyvinyl alcohol, polyacrylonitrile, polyamide resins such as nylon 6, nylon 6,6, and polymetaxylylene adipamide (MXD6), polyester resins, polyurethane resins, and (meth)acrylic resins.

[0093] 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 making the thickness of the barrier coat layer 0.01 μm or more, the gas barrier property can be further improved. By making the thickness of the barrier coat layer 10 μm or less, the processability of the laminate can be improved. Furthermore, the laminate can be suitably used for producing mono-material packaging containers.

[0094] The barrier coat layer can be formed, for example, by dissolving or dispersing a material such as a gas barrier resin in water or an appropriate organic solvent, applying the resulting coating liquid, and drying it.

[0095] In another embodiment, the barrier coat layer is a gas barrier coating film formed from a composition containing a hydrolyzate of a metal alkoxide or a hydrolyzed condensate of a metal alkoxide 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, etc. By providing such a barrier coating layer on the vapor deposition layer, it is possible to effectively prevent cracks from occurring in the vapor deposition layer.

[0096] In one embodiment, the metal alkoxide is represented by the following general formula: R 1 n M(OR 2 ) m In the above formula, R 1 and R 2 each independently represents 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.

[0097] R 1 and R 2 Examples of the organic group represented by the formula (I) include alkyl groups such as a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, and an i-butyl group. Examples of the metal atom M include silicon, zirconium, titanium, and aluminum.

[0098] 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).

[0099] It is preferable to use a silane coupling agent together with the metal alkoxide, and as the silane coupling agent, a known organoalkoxysilane containing an organic reactive group can be used.

[0100] As the water-soluble polymer, polyvinyl alcohol and ethylene-vinyl alcohol copolymer are preferred, and from the viewpoints of oxygen barrier property, water vapor barrier property, water resistance and weather resistance, it is preferred to use these in combination.

[0101] As the catalyst for the sol-gel method, an acid or amine compound is suitable.

[0102] The composition may further contain an acid. The acid is used as a catalyst for the hydrolysis of sol-gel process catalysts, mainly metal alkoxides and silane coupling agents. Examples of the acid include mineral acids such as sulfuric acid, hydrochloric acid, and nitric acid, and organic acids such as acetic acid and tartaric acid.

[0103] The composition may contain an organic solvent, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, and n-butanol.

[0104] 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. This further improves the gas barrier properties. By making the thickness of the gas barrier coating film 0.01 μm or more, the oxygen barrier properties and water vapor barrier properties of the laminate can be improved, and the occurrence of cracks in the vapor deposition layer can be prevented. By making the thickness of the gas barrier coating film 100 μm or less, the laminate can be made suitable for use in producing mono-material packaging containers.

[0105] The gas barrier coating film can be formed by applying a composition containing the above-mentioned materials by a conventionally known means such as roll coating using a gravure roll coater or the like, spray coating, spin coating, dipping, brush coating, bar coating, or applicator, and then polycondensing the composition by a sol-gel method.

[0106] An embodiment of the 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 catalyst, water, an organic solvent, and optionally a silane coupling agent, etc. A polycondensation reaction gradually proceeds in the composition.

[0107] Next, the composition is applied onto the vapor-deposited layer by the conventionally known means and dried. This drying further promotes the polycondensation reaction of the metal alkoxide and the water-soluble polymer (and the silane coupling agent, if the composition contains one) to form a composite polymer layer. Finally, heating is performed to form a gas barrier coating film.

[0108] <Adhesive layer> In one embodiment, the laminate of the present disclosure includes an adhesive layer between any of the layers (for example, 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), which can improve the adhesion between the layers included in the laminate.

[0109] The adhesive layer contains one or more types of adhesives, such as one-component curing adhesives, two-component curing adhesives, and non-curing adhesives.

[0110] The adhesive may be a solvent-free adhesive or a solvent-based adhesive, with solvent-free adhesives being preferred from the viewpoint of environmental impact. Examples of solvent-free adhesives include polyether adhesives, polyester adhesives, silicone adhesives, epoxy adhesives, and urethane adhesives. Among these, two-component curing urethane adhesives are preferred. Examples of solvent-based adhesives include rubber adhesives, vinyl adhesives, silicone adhesives, epoxy adhesives, phenol adhesives, and olefin adhesives.

[0111] In the case of an adhesive layer adjacent to a barrier layer such as an aluminum vapor-deposited layer, the adhesive layer is preferably formed from a cured product of a resin composition containing a polyester polyol, an isocyanate compound, and a phosphoric acid-modified compound. By forming the adhesive layer in this manner, the oxygen barrier property and water vapor barrier property of the laminate of the present disclosure can be further improved.

[0112] From the viewpoint of the adhesiveness of the adhesive layer and the processability of the laminate, 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 even more preferably 1 μm or more and 4.5 μm or less.

[0113] The adhesive layer can be formed by applying an adhesive to a multilayer substrate or the like by a method such as direct gravure roll coating, gravure roll coating, kiss coating, reverse roll coating, Fontaine coating, or transfer roll coating, and then drying the adhesive.

[0114] [Application] The polyethylene multilayer substrate, printed substrate, and laminate of the present disclosure can be suitably used for packaging material applications such as packaging bags, etc. The packaging material of the present disclosure comprises the polyethylene multilayer substrate, printed substrate, or laminate of the present disclosure.

[0115] For example, a packaging material can be produced by folding the laminate in half and overlapping it so that the multilayer base material is on the outside and the heat seal layer is on the inside, and then heat-sealing the edges, etc. Alternatively, a packaging material can be produced by overlapping multiple laminates so that the heat seal layers face each other and heat-sealing the edges, etc. The entire packaging material may be composed of the laminate, or only a part of the packaging material may be composed of the laminate.

[0116] Examples of heat-sealing methods for packaging materials include side seals, two-sided seals, three-sided seals, four-sided seals, envelope seals, palm seals (pillow seals), pleated seals, flat-bottom seals, square-bottom seals, and gusset seals. Self-standing packaging bags (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.

[0117] For example, a stand-up pouch having a body and a bottom can be manufactured as follows: First, one or more of the above laminates are formed into a cylindrical shape with the heat-sealable layer facing inward, and the body is formed by heat-sealing. Next, another of the above laminates is folded into a V shape with the heat-sealable layer facing outward. The V-shaped laminate is sandwiched into one end of the body and heat-sealed to form the bottom.

[0118] In the stand-up pouch, only the body may be formed from the laminate, only the bottom may be formed from the laminate, or both the body and the bottom may be formed from the laminate.

[0119] The contents to be filled into the packaging material include, for example, liquids, powders, and gels, and may be food or non-food. After the contents are filled into the packaging material, the opening of the packaging material is heat-sealed to obtain a package.

[0120] The present disclosure relates to, for example, the following [1] to

[14] . [1] A polyethylene multilayer substrate comprising, in the thickness direction, a first layer containing high-density polyethylene and medium-density polyethylene, a second layer containing medium-density polyethylene, a third layer containing linear low-density polyethylene and medium-density polyethylene, a fourth layer containing medium-density polyethylene, and a fifth layer containing high-density polyethylene and medium-density polyethylene, in that order, and which has been subjected to a stretching treatment. [2] The polyethylene multilayer substrate according to [1] above, wherein the mass ratio of high-density polyethylene to medium-density polyethylene (high-density polyethylene / medium-density polyethylene) in the first layer and the fifth layer is independently 1.1 or more and 5 or less, and the mass ratio of linear low-density polyethylene to medium-density polyethylene (linear low-density polyethylene / medium-density polyethylene) in the third layer is 0.25 or more and 4 or less. [3] The polyethylene multilayer substrate according to [1] or [2] above, wherein the first layer contains 80% or more of high-density polyethylene and medium-density polyethylene in total, the second layer contains 80% or more of medium-density polyethylene in total, the third layer contains 80% or more of linear low-density polyethylene and medium-density polyethylene in total, the fourth layer contains 80% or more of medium-density polyethylene in total, and the fifth layer contains 80% or more of high-density polyethylene and medium-density polyethylene in total. [4] In the multilayer substrate, when any adjacent layers selected from the first to fifth layers are referred to as layer (1) and layer (2), the absolute value of the difference between the density of the polyethylene constituting layer (1) and the density of the polyethylene constituting layer (2) is 0.030 g / cm 3 The polyethylene multilayer substrate according to any one of the above [1] to [3], which is: [5] A printing substrate comprising the polyethylene multilayer substrate according to any one of [1] to [4] above and a printing layer formed on the multilayer substrate. [6] A laminate comprising the polyethylene multilayer substrate according to any one of the above [1] to [4] and a heat seal layer. [7] The laminate according to [6] above, wherein the heat seal layer contains polyethylene. [8] The laminate according to [6] or [7] above, further comprising a printed layer on the multilayer substrate. [9] The laminate according to any one of the above [6] to [8], further comprising a barrier layer between the multilayer substrate and the heat seal layer.

[10] The laminate according to [9] above, wherein the barrier layer is a vapor-deposited layer.

[11] The laminate according to [9] or

[10] above, further comprising an adhesive layer between the multilayer substrate and the barrier layer.

[12] The laminate according to any one of the above [6] to [8], further comprising an adhesive layer between the multilayer substrate and the heat seal layer.

[13] The laminate according to any one of the above [6] to

[12] , which is used for packaging material applications.

[14] A packaging material comprising the polyethylene multilayer substrate described in any one of [1] to [4] above, the printing substrate described in [5] above, or the laminate described in any one of [6] to

[13] above. [Example]

[0121] The multilayer substrate of the present disclosure will be described in more detail based on examples, but the multilayer substrate of the present disclosure is not limited to these examples. Hereinafter, "parts by mass" will be simply referred to as "parts".

[0122] The polyethylene used in the following examples and comparative examples will be described. Medium-density polyethylene (hereinafter referred to as "MDPE"): Product name: Elite5538G Density: 0.941g / cm 3 Melting point: 129°C, MFR: 1.3g / 10min, manufactured by Dow Chemical High-density polyethylene (hereinafter referred to as "HDPE"): Product name: Elite5960G Density: 0.960g / cm 3 Melting point: 134°C, MFR: 0.8g / 10min, manufactured by Dow Chemical Linear low-density polyethylene (hereinafter referred to as "LLDPE"): Product name: Elite5400G Density: 0.916g / cm 3 Melting point: 123°C, MFR: 1.3g / 10min, manufactured by Dow Chemical Blended polyethylene A 50 parts MDPE and 50 parts HDPE were mixed to give an average density of 0.951 g / cm 3 A blended polyethylene A (hereinafter referred to as "blended PE(A)") was obtained. Blended polyethylene B 50 parts MDPE and 50 parts LLDPE were mixed to give an average density of 0.929 g / cm 3 Blend polyethylene B (hereinafter referred to as "blend PE(B)") was obtained. Blend polyethylene D A mixture of 30 parts MDPE and 70 parts HDPE gave an average density of 0.954 g / cm 3 A blended polyethylene D (hereinafter referred to as "blended PE(D)") was obtained.

[0123] [Reference Example 1 and Example 1]

[0124] MDPE, blend PE (B), and blend PE (D) were coextruded into a five-layer tube using an inflation molding method with a layer thickness ratio of blend PE (D) layer (15 μm) / MDPE layer (22.5 μm) / blend PE (B) layer (50 μm) / MDPE layer (22.5 μm) / blend PE (D) layer (15 μm). A polyethylene film with a total thickness of 125 μm was obtained, and the tubular film was folded at the nip to form two layers. The numbers in parentheses indicate the layer thicknesses. The polyethylene film prepared above was stretched in the machine direction (MD) at a stretch ratio of 5 times, and the blend PE (D) layer (surface layer) on one side was subjected to a corona discharge treatment. The edge was then slit and divided into two pieces to obtain a 25 μm-thick stretched multilayer substrate (Example 1). The blend PE (D) layer (surface layer) on one side of the polyethylene film prepared above was also subjected to a corona discharge treatment (Reference Example 1).

[0125] [Comparative Example 1] A polyethylene film and a stretched multilayer base material were obtained in the same manner as in Example 1, except that the layer structure was changed as shown in Table 1.

[0126] [Extensibility evaluation] The stretchability was evaluated according to the following criteria. AA: The substrate (polyethylene film) did not break during stretching, and stable stretching was possible. BB: The substrate (polyethylene film) breaks during stretching. It was not possible to extend it stably.

[0127] [Ink adhesion evaluation] Images were formed by gravure printing on the corona discharge treated surface of the stretched multilayer substrates obtained in the Examples and Comparative Examples and the polyethylene film obtained in the Reference Example using oil-based gravure ink (manufactured by DIC Graphics Corporation, trade name: Finart). The images formed on the stretched multilayer substrates and polyethylene films were visually observed and evaluated based on the following evaluation criteria.

[0128] (Evaluation criteria) AA: When Cellotape (registered trademark) was applied to the image-forming side of the stretched multilayer substrate or polyethylene film and then peeled off, the ink adhered well to the stretched multilayer substrate or polyethylene film and no ink peeling off from the Cellotape (registered trademark) occurred. BB: When Cellotape (registered trademark) was applied to the image-forming side of the stretched multilayer substrate or polyethylene film and then peeled off, the ink did not adhere well to the stretched multilayer substrate or polyethylene film, and the ink peeled off from the Cellotape (registered trademark).

[0129] [Delamination evaluation] First, linear low-density polyethylene (Prime Polymer Co., Ltd., SP2520, density: 0.925 g / cm 3 , melting point: 122°C) and a second linear low-density polyethylene (Prime Polymer Co., Ltd., SP1520, density: 0.913 g / cm 3A multilayer extrusion film was formed from a first linear low-density polyethylene layer having a thickness of 20 μm and a second linear low-density polyethylene layer having a thickness of 20 μm by inflation molding. This unstretched polyethylene film was used as a heat-sealing layer as described below.

[0130] The first linear low-density polyethylene layer side of the unstretched polyethylene film (heat seal layer) prepared above was dry laminated with the stretched multilayer substrate obtained in the Examples and Comparative Examples, or the polyethylene film obtained in the Reference Examples, via a two-component curing urethane adhesive (Ru-77T / H-7, manufactured by Rock Paint Co., Ltd.) to obtain a laminate.

[0131] The laminate prepared above was cut into 10 cm x 10 cm pieces to prepare three sample pieces. Each sample piece was folded in half with the heat seal layer side facing inward, and tested at a temperature of 140°C and a pressure of 1 kgf / cm using a heat seal tester. 2 An area of ​​1 cm x 10 cm was heat-sealed under the conditions of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 69, 70

[0132] The heat-sealed sample pieces were cut into 15 mm wide strips, and both ends that were not heat-sealed were clamped in a tensile tester. A tensile test was carried out at a speed of 300 mm / min and a load range of 50 N to check for the occurrence of delamination of the stretched multilayer substrate or polyethylene film. AA: During the tensile test, delamination of the stretched multilayer substrate or polyethylene film occurs. It did not occur. BB: Delamination occurred between layers of the stretched multilayer substrate or polyethylene film during the tensile test.

[0133] [Heat resistance evaluation] The heat resistance was evaluated according to the following criteria. AA: There was no shrinkage of the substrate (stretched multilayer substrate or polyethylene film) during printing, dry lamination, and heat sealing of the laminate produced above, and the target product was produced cleanly. BB: During printing, dry lamination, and heat sealing of the laminate produced above, shrinkage of the substrate (stretched multilayer substrate or polyethylene film) occurred, and the target product could not be produced cleanly.

[0134] [Haze Rating] The haze values ​​of the stretched multilayer substrates obtained in the Examples and Comparative Examples and the polyethylene films obtained in the Reference Examples were measured in accordance with JIS K7136.

[0135] [Rigidity evaluation] The stretched multilayer substrates obtained in the Examples and Comparative Examples and the polyethylene films obtained in the Reference Examples were 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 60 mm.

[0136] [Strength evaluation] Dumbbell-shaped test pieces with a width of 10 mm were cut out from the stretched multilayer substrates obtained in the Examples and Comparative Examples, and the polyethylene film obtained in the Reference Example. The tensile strength of the test pieces in the MD direction was measured using a tensile tester (Orientec Co., Ltd., RTC-1310A). The chuck distance was 10 mm, and the pulling speed was 300 mm / min. The evaluation results are shown in Table 1.

[0137] [Table 1] [Explanation of symbols]

[0138] 10: Polyethylene multilayer base material 12: First layer containing high density polyethylene and medium density polyethylene 14: A fifth layer containing high density polyethylene and medium density polyethylene 16: Multi-layer intermediate layer consisting of a second layer, a third layer, and a fourth layer 18: A second layer containing medium density polyethylene 20: A third layer containing linear low density polyethylene and medium density polyethylene 22: A fourth layer containing medium density polyethylene 30: Laminate 32: Heat seal layer 34: Barrier layer 36: Adhesive layer

Claims

1. a first layer containing high density polyethylene and medium density polyethylene; a second layer containing medium density polyethylene; a third layer containing linear low density polyethylene and medium density polyethylene; a fourth layer containing medium density polyethylene; and a fifth layer containing high density polyethylene and medium density polyethylene; A polyethylene multilayer substrate having the above in this order in the thickness direction and subjected to a stretching treatment.

2. a mass ratio of the high-density polyethylene to the medium-density polyethylene (high-density polyethylene / medium-density polyethylene) in the first layer and the fifth layer is independently 1.1 or more and 5 or less; a mass ratio of the linear low-density polyethylene to the medium-density polyethylene in the third layer (linear low-density polyethylene / medium-density polyethylene) is 0.25 or more and 4 or less; The polyethylene multi-layer substrate of claim 1.

3. the total content of the high-density polyethylene and the medium-density polyethylene in the first layer is 80% by mass or more, the content of the medium-density polyethylene in the second layer is 80% by mass or more, the content ratio of the linear low-density polyethylene and the medium-density polyethylene in the third layer is 80% by mass or more, the content of the medium-density polyethylene in the fourth layer is 80% by mass or more, the total content of the high-density polyethylene and the medium-density polyethylene in the fifth layer is 80% by mass or more; The polyethylene multilayer substrate according to claim 1 or 2.

4. When any adjacent layers selected from the first to fifth layers in the multilayer base material are referred to as layer (1) and layer (2), the absolute value of the difference between the density of the polyethylene constituting layer (1) and the density of the polyethylene constituting layer (2) is 0.030 g / cm ３ Below is the The polyethylene multilayer substrate according to any one of claims 1 to 3.

5. The polyethylene multilayer substrate according to any one of claims 1 to 4, a printing layer formed on the multilayer substrate; A printing substrate comprising:

6. The polyethylene multilayer substrate according to any one of claims 1 to 4, Heat seal layer and A laminate comprising:

7. The laminate of claim 6 wherein the heat seal layer comprises polyethylene.

8. The laminate according to claim 6 or 7, further comprising a printed layer on the multilayer substrate.

9. The laminate according to any one of claims 6 to 8, further comprising a barrier layer between the multilayer substrate and the heat seal layer.

10. The laminate of claim 9 , wherein the barrier layer is a vapor-deposited layer.

11. The laminate according to claim 9 or 10, further comprising an adhesive layer between the multilayer substrate and the barrier layer.

12. The laminate according to any one of claims 6 to 8, further comprising an adhesive layer between the multilayer substrate and the heat seal layer.

13. The laminate according to any one of claims 6 to 12, which is used for packaging material applications.

14. A packaging material comprising the polyethylene multilayer substrate according to any one of claims 1 to 4, the printing substrate according to claim 5, or the laminate according to any one of claims 6 to 13.

Images