Polyethylene multilayer substrates, printing substrates, laminates, and packaging materials

Abstract

To provide a polyethylene multilayer substrate that is excellent in ink adhesion and heat resistance.SOLUTION: A polyethylene multilayer substrate is formed by stretching, having a first layer containing middle-density polyethylene and high-density polyethylene, a second layer containing high-density polyethylene, a third layer containing linear low-density polyethylene, a fourth layer containing high-density polyethylene, and a fifth layer containing middle-density polyethylene and high-density polyethylene, in a thickness direction in this order.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to polyethylene multilayer substrates, printing substrates, laminates, and packaging materials. [Background technology]

[0002] Conventionally, packaging materials have been manufactured using resin films made from resin materials. Packaging materials, for example, comprise a base material and a heat-seal layer. For instance, resin films made from polyethylene are widely used as heat-seal layers in packaging materials because they possess flexibility, transparency, and excellent heat-sealability (see, for example, Patent Document 1).

[0003] On the other hand, polyethylene is a resin that softens at relatively low temperatures compared to other thermoplastic resins, so when used as a base material for packaging materials, it may deform or, in some cases, melt during heat sheeting. Also, polyethylene film may have insufficient strength compared to other thermoplastic resin films. For this reason, it is common to use resin films with excellent strength and heat resistance, such as polyester film and nylon film, as base materials for packaging materials. For example, bags are made by laminating a base material such as polyester film or nylon film with polyethylene film and heat sealing with the polyethylene film side facing the inside of the packaging bag (see, for example, background art in Patent Document 2).

[0004] Incidentally, in recent years, with the growing demand for the creation of a circular economy, attempts have been made to recycle and reuse packaging materials. However, laminates obtained by bonding different types of resin films together, as described above, are difficult to separate by resin type 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 Laid-Open No. 2017-031233 [Summary of the Invention] [Problems to be Solved by the Invention]

[0006] Therefore, the present inventors have found that the strength and heat resistance of a resin film made of polyethylene can be improved by stretching treatment, and have considered using a polyethylene multilayer base material having a plurality of layers containing polyethylene and being stretched as a base material.

[0007] By the way, images such as characters and figures are usually printed on a base material used for packaging materials and the like using ink. However, according to further studies by the present inventors, it has been found that the polyethylene multilayer base material may not have sufficient ink adhesion. In addition, since heat may be applied to the polyethylene multilayer base material during printing or the like, it is preferable that it has excellent heat resistance.

[0008] One problem of the present disclosure is to provide a polyethylene multilayer base material having excellent ink adhesion and heat resistance. [Means for Solving the Problems]

[0009] The polyethylene multilayer base material of the present disclosure includes, in this order in the thickness direction, a first layer containing medium-density polyethylene and high-density polyethylene, a second layer containing high-density polyethylene, a third layer containing linear low-density polyethylene, a fourth layer containing high-density polyethylene, and a fifth layer containing medium-density polyethylene and high-density polyethylene, and is stretched. [Effects of the Invention]

[0010] According to the present disclosure, a polyethylene multilayer base material having excellent ink adhesion and heat resistance can be provided. [Brief Description of the Drawings]

[0011] [Figure 1] It is a schematic cross-sectional view showing an embodiment of the polyethylene multilayer substrate of the present disclosure. [Figure 2] It is a schematic cross-sectional view showing an embodiment of the laminate of the present disclosure. [Figure 3] It is a schematic cross-sectional view showing an embodiment of the laminate of the present disclosure. [Figure 4] It is a schematic cross-sectional view showing an embodiment of the laminate of the present disclosure. [Figure 5] It is a schematic cross-sectional view showing an embodiment of the laminate of the present disclosure.

Mode for Carrying Out the Invention

[0012] Hereinafter, the terms used in the present disclosure will be described. "Polyethylene" refers to a polymer in which the content ratio of ethylene-derived constitutional units is 50 mol% or more in all repeating constitutional units. In the polymer, the content ratio of ethylene-derived constitutional units is preferably 70 mol% or more, more preferably 80 mol% or more, and still more preferably 90 mol% or more. The above content ratio is measured by nuclear magnetic resonance method (NMR method).

[0013] The density of high-density polyethylene preferably exceeds 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 medium-density polyethylene preferably exceeds 0.925 g / cm 3 and is 0.945 g / cm or less. 3 The density of low-density polyethylene preferably exceeds 0.900 g / cm 3 and is 0.925 g / cm or less. 3 The density of linear low-density polyethylene preferably exceeds 0.900 g / cm 3 and is 0.925 g / cm or less. 3 The density of ultra-low density polyethylene preferably exceeds 0.900 g / cm 3 ​​​The following applies: The lower limit of the density of ultra-low density polyethylene is, for example, 0.860 g / cm³. 3 That is the case. The density of polyethylene is measured in accordance with JIS K7112, particularly Method D (density gradient pipe method, 23°C).

[0014] [Polyethylene multilayer substrate] As shown in Figure 1, the polyethylene multilayer substrate 10 of this disclosure is A first layer 12 containing medium-density polyethylene and high-density polyethylene, A second layer 18 containing high-density polyethylene, A third layer 20 containing linear low-density polyethylene, A fourth layer 22 containing high-density polyethylene, A fifth layer 14 containing medium-density polyethylene and high-density polyethylene These are arranged in this order in the thickness direction and then stretched. Hereinafter, the polyethylene multilayer substrate described above will also simply be referred to as the "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 this disclosure, polyethylene includes, for example, ethylene homopolymers and copolymers of ethylene with other monomers. Other monomers include, for example, α-olefins having 3 to 20 carbon atoms, vinyl acetate, and (meth)acrylic acid esters. Examples of α-olefins having 3 to 20 carbon atoms include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene, 1-octadecene, 1-eicosene, 3-methyl-1-butene, 4-methyl-1-pentene, and 6-methyl-1-heptene. Examples of (meth)acrylic acid esters include alkyl (meth)acrylates such as methyl (meth)acrylate and ethyl (meth)acrylate.

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

[0018] Polyethylenes with different densities or branching can be obtained by appropriately selecting a polymerization method. For example, it is preferable to use a multi-site catalyst such as a Ziegler-Natta catalyst or a single-site catalyst such as a metallocene catalyst as the polymerization catalyst, and to carry out polymerization in one or more stages using one of the following methods: gas-phase polymerization, slurry polymerization, solution polymerization, or high-pressure ionic polymerization.

[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 activation co-catalyst. Compared to multi-site catalysts, single-site catalysts are preferred because they have a more uniform active site structure, allowing for the production of polymers with high molecular weight and high uniformity.

[0020] As a single-site catalyst, a metallocene catalyst is preferred. The metallocene catalyst is a catalyst comprising a transition metal compound of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton, a co-catalyst, an organometallic compound if necessary, and a support if necessary.

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

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

[0023] Transition metal compounds typically have two ligands having a cyclopentadienyl skeleton. Preferably, each ligand having a cyclopentadienyl skeleton is bonded to one another by a bridging group. Examples of bridging groups include alkylene groups 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] A co-catalyst is a component that can effectively enable transition metal compounds of Group IV of the periodic table to function as polymerization catalysts, or a component that can balance the ionic charge in a catalytically activated state. Examples of co-catalysts include benzene-soluble aluminoxanes or benzene-insoluble organoaluminum oxy compounds, ion-exchangeable layered silicates, boron compounds, ionic compounds consisting of cations containing or not containing active hydrogen groups and non-coordinating anions, lanthanide salts such as lanthanum oxide, tin oxide, and phenoxy compounds containing fluoro groups.

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

[0026] Transition metal compounds may be used supported on an inorganic or organic compound. Preferred supports are porous oxides of inorganic or organic compounds, specifically ion-exchangeable layered silicates such as montmorillonite, SiO2, Al2O3, MgO, ZrO2, TiO2, B2O3, CaO, ZnO, BaO, ThO2, or mixtures thereof.

[0027] As a raw material for obtaining polyethylene, biomass-derived ethylene may be used instead of ethylene obtained from fossil fuels. Since biomass-derived polyethylene is a carbon-neutral material, it can reduce the environmental impact of packaging materials manufactured using multilayer substrates. Biomass-derived polyethylene can be produced, for example, by the method described in Japanese Patent Application Publication No. 2013-177531. Commercially available biomass-derived polyethylene (for example, Green PE, commercially available from Braschem) may also be used.

[0028] Recycled polyethylene obtained through mechanical recycling may be used. Mechanical recycling generally involves crushing collected polyethylene film, washing it with alkali to remove dirt and foreign matter from the film surface, drying it at high temperature and reduced pressure for a certain period of time to disperse contaminants remaining inside the film, decontamination, and removing dirt from the polyethylene film, thus returning it to polyethylene.

[0029] The melt flow rate (MFR) of polyethylene contained in the multilayer substrate of this disclosure is preferably 0.1 g / 10 min to 50 g / 10 min, and more preferably 0.3 g / 10 min to 30 g / 10 min, from the viewpoint of film-forming properties and processability of the multilayer substrate. In this disclosure, the MFR is measured in accordance with ASTM D1238 under conditions of a temperature of 190°C and a load of 2.16 kg.

[0030] 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. The following describes each layer that makes up the multilayer substrate.

[0031] <Layer 1 and Layer 5> The first layer contains one or more types of medium-density polyethylene and one or more types of high-density polyethylene. The fifth layer contains one or more types of medium-density polyethylene and one or more types of high-density polyethylene.

[0032] When printing images onto a substrate, surface treatments such as corona discharge are typically performed on the substrate as a pretreatment. Layers containing medium-density polyethylene tend to have higher durability to surface treatments compared to layers containing only high-density polyethylene. Therefore, layers containing medium-density polyethylene have excellent ink adhesion during printing after surface treatment. Furthermore, layers containing both medium-density and high-density polyethylene also possess the heat resistance required during printing and heat sealing. In addition, layers containing medium-density polyethylene contribute to improving the stretchability of laminates, which are precursors to multilayer substrates.

[0033] 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 easily manufacturing a multilayer substrate, it is preferable that they be the same. The high-density polyethylene contained in the first layer and the high-density polyethylene contained in the fifth layer may be the same or different, but it is preferable that they be the same from the viewpoint of easily manufacturing a multilayer substrate.

[0034] The first and fifth layers may each independently contain, along with medium-density polyethylene and high-density polyethylene, other polyethylenes other than these. Examples of other polyethylenes 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 of further improving the ink adhesion and heat resistance of the multilayer substrate. 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.

[0035] The mass ratio of medium-density polyethylene to high-density polyethylene (medium-density polyethylene / high-density polyethylene) in the first and fifth layers is preferably 1.1 to 5, and more preferably 1.5 to 3, independently of each other. This further improves the balance between ink adhesion and heat resistance.

[0036] 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 even more preferably 95% by mass or more. This further improves the ink adhesion and heat resistance of the multilayer substrate.

[0037] 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 further improves the ink adhesion and heat resistance of the multilayer substrate.

[0038] The thickness of the first layer and the fifth layer are, independently, preferably 0.5 μm to 10 μm, more preferably 1 μm to 8 μm, and even more preferably 1 μm to 5 μm. This further improves the ink adhesion and heat resistance of the multilayer substrate.

[0039] The thickness of the first layer and the fifth layer is preferably smaller than the total thickness of the second, third, and fourth layers (hereinafter, the second to fourth layers are collectively referred to as the "multilayer intermediate layer"). The ratio of the thickness 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 or less, more preferably 0.1 or more and 0.7 or less, and even more preferably 0.1 or more and 0.4 or less. This further improves the rigidity, strength, and heat resistance of the multilayer substrate.

[0040] <The second and fourth layers> The second layer contains one or more types of high-density polyethylene. The fourth layer contains one or more types of high-density polyethylene. The second and fourth layers each contribute to improving the heat resistance of the multilayer substrate. Specifically, by incorporating high-density polyethylene into the second and fourth layers, in addition to the first and fifth layers, the heat resistance of the multilayer substrate can be further improved.

[0041] The high-density polyethylene contained in the second layer and the high-density polyethylene contained in the fourth layer may be the same or different, but it is preferable that they be the same from the viewpoint of easily manufacturing a multilayer substrate.

[0042] The second layer may further contain one or more types of low-density polyethylene. The fourth layer may further contain one or more types of low-density polyethylene. This allows for a further improvement in the balance between heat resistance, rigidity, and processability of the multilayer substrate. The low-density polyethylene contained in the second layer and the low-density polyethylene contained in the fourth layer may be the same or different, but from the viewpoint of easily manufacturing a multilayer substrate, it is preferable that they be the same.

[0043] The second and fourth layers may each independently further contain high-density polyethylene and low-density polyethylene, along with other polyethylenes other than these. Examples of other polyethylenes other than high-density polyethylene and low-density polyethylene include medium-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene. The second layer may contain only high-density polyethylene and low-density polyethylene as polyethylene, from the viewpoint of further improving the heat resistance of the multilayer substrate. The fourth layer may contain only high-density polyethylene and low-density polyethylene as polyethylene, from the viewpoint of further improving the heat resistance of the multilayer substrate.

[0044] The mass ratio of high-density polyethylene to low-density polyethylene (high-density polyethylene / low-density polyethylene) in the second and fourth layers is preferably 1 to 4, and more preferably 1.5 to 3, independently of each other. This further improves the balance of heat resistance, rigidity, and processability of the multilayer substrate.

[0045] The content of high-density polyethylene in the second layer is preferably more than 50% by mass, more preferably 55% by mass or more, and even more preferably 60% by mass or more. This further improves the heat resistance of the multilayer substrate.

[0046] The content of high-density polyethylene in the fourth layer is preferably more than 50% by mass, more preferably 55% by mass or more, and even more preferably 60% by mass or more. This further improves the heat resistance of the multilayer substrate.

[0047] The total content of high-density polyethylene and low-density polyethylene in the second layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. This further improves the balance of heat resistance, rigidity, and processability of the multilayer substrate.

[0048] The total content of high-density polyethylene and low-density polyethylene in the fourth layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. This further improves the balance of heat resistance, rigidity, and processability of the multilayer substrate.

[0049] The thickness of the second and fourth layers is preferably 0.5 μm to 15 μm, more preferably 1 μm to 10 μm, and even more preferably 1 μm to 8 μm, respectively. This further improves the heat resistance of the multilayer substrate.

[0050] <Third Layer> The third layer contains one or more types of linear low-density polyethylene. The third layer contributes to improving the stretchability of the laminate, which is a precursor to the multilayer substrate.

[0051] The third layer may further contain other polyethylenes besides linear low-density polyethylene, along with linear low-density polyethylene. Examples of other polyethylenes besides linear low-density polyethylene include high-density polyethylene, medium-density polyethylene, low-density polyethylene (high-pressure low-density polyethylene), and ultra-low-density polyethylene.

[0052] The third layer may further contain one or more types of low-density polyethylene.

[0053] The content of linear low-density polyethylene in the third layer is preferably more than 50% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, and even more preferably 80% by mass or more, 90% by mass or more, or 95% by mass or more. This allows for a further improvement in the balance of heat resistance, rigidity, and stretchability.

[0054] When the third layer contains low-density polyethylene, the content of low-density polyethylene is preferably less than 50% by mass, more preferably 5% to 40% by mass, and even more preferably 10% to 30% by mass.

[0055] The thickness of the third layer is preferably 1 μm to 50 μm, more preferably 2 μm to 40 μm, and even more preferably 5 μm to 30 μm. This allows for a further improvement in the balance of heat resistance, rigidity, and stretchability.

[0056] The ratio of the total thickness of the second and fourth layers to the thickness of the third layer (total thickness of the second and fourth layers / thickness of the third layer) is preferably 0.1 to 10, more preferably 0.2 to 5, and even more preferably 0.5 to 2. This further improves the rigidity, strength, and heat resistance of the multilayer substrate.

[0057] <Additives> Each of the first to fifth layers constituting the multilayer substrate may independently contain one or more additives. Examples of additives include crosslinking agents, antioxidants, antiblocking agents, lubricants, ultraviolet absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, and modifying resins.

[0058] At least one layer selected from the first, second, third, fourth, and fifth layers of the multilayer substrate of this disclosure may contain a slip agent. This can improve, for example, the processability of the multilayer substrate. For example, the third layer may contain a slip agent, or all of the first to fifth layers may contain a slip agent.

[0059] Examples of slip agents include amide lubricants, fatty acid esters such as glycerin fatty acid esters, hydrocarbon waxes, higher fatty acid waxes, metal soaps, hydrophilic silicones, silicone-modified (meth)acrylic resins, silicone-modified epoxy resins, silicone-modified polyethers, silicone-modified polyesters, block-type silicone (meth)acrylic copolymers, polyglycerol-modified silicones, and paraffins.

[0060] Among lubricants, amide 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.

[0061] Examples of saturated fatty acid amides include lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, and hydroxystearic acid amide. Examples of unsaturated fatty acid amides include oleic acid amide and erucic acid amide. Examples of substituted amides include N-oleyl palmitic acid amide, N-stearyl stearate amide, N-stearyl oleic acid amide, N-oleyl stearate amide, and N-stearyl erucic acid amide. An example of a methylolamide is methylol stearate amide. Examples of saturated fatty acid bisamides include methylenebisstearate, ethylenebiscaprate, ethylenebislaurate, ethylenebisstearate, ethylenebishydroxystearate, ethylenebisbehenamide, hexamethylenebisstearate, hexamethylenebisbehenamide, hexamethylenehydroxystearate, N,N'-distearyladipamide, and N,N'-distearylsebacinamide. Examples of unsaturated fatty acid bisamides include ethylenebisoleamide, ethylenebiserucamide, hexamethylenebisoleamide, N,N'-dioleyladipamide, and N,N'-dioleylsebacinamide. Examples of fatty acid ester amides include stearamidoethyl stearate. Examples of aromatic bisamides include m-xylylenebisstearate, m-xylylenebishydroxystearate, and N,N'-distearyl isophthalamide. Among slip agents, erucic acid amide is preferred. One or more types of slip agents can be used.

[0062] To improve the dispersibility of the slip agent in the resin composition forming each layer, a masterbatch containing the slip agent and polyethylene may be used. The slip agent content in the masterbatch is preferably 1% by mass or more and 30% by mass or less, more preferably 2% by mass or more and 20% by mass or less, and even more preferably 3% by mass or more and 10% by mass or less. Specific examples of polyethylene can be found as described above. The preferred physical properties (density, MFR, etc.) of the polyethylene are also as described above.

[0063] In a multilayer substrate, the slip agent content in the layer containing the slip agent may be, for example, 0.01% by mass or more and 3% by mass or less, or 0.03% by mass or more and 1% by mass or less. This can further improve the processability of the multilayer substrate.

[0064] In one embodiment, in the multilayer substrate of the present disclosure, the density of polyethylene in the first layer is approximately the same as the density of polyethylene in the second layer, 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 fourth layer is higher than the density of polyethylene in the third layer, and the density of polyethylene in the fourth layer is approximately the same as the density of polyethylene in the fifth layer. A multilayer substrate having such a configuration is superior in balance between ink adhesion, 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 is, for example, 0.020 g / cm³. 3 The following is also acceptable: 0.010 g / cm³ 3 The following is also acceptable: The absolute value of the difference between the density of polyethylene in the fourth layer and the density of polyethylene in the fifth layer is, for example, 0.020 g / cm³. 3 The following is also acceptable: 0.010 g / cm³ 3 The following is also acceptable.

[0065] If a single layer contains multiple types of polyethylene with different densities (n types; n is an integer of 2 or more), the density of the polyethylene constituting that layer may be measured in accordance with JIS K7112, and the average density D calculated according to the following formula (1) may be used. av This may be the density of the polyethylene constituting the layer.

[0066] D av = ΣW i ×D i …(1) In equation (1), Σ represents W from 1 to n for i. i ×D i This means taking the sum of n, where n is an integer greater than or equal to 2, and W i This indicates the mass fraction of the i-th polyethylene, and D i The density of the i-th polyethylene (g / cm³) 3 ) indicates.

[0067] <Method for manufacturing multilayer substrates> The multilayer substrate of this disclosure can be manufactured, for example, by forming a laminate by depositing multiple polyethylene materials using an inflation method or a T-die method, and then stretching the resulting laminate. The stretching process 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.

[0068] A multilayer substrate can be obtained, for example, by stretching a laminate (precursor) which comprises, in the thickness direction, a layer containing medium-density polyethylene and high-density polyethylene, a layer containing high-density polyethylene, a layer containing linear low-density polyethylene, a layer containing high-density polyethylene, and a layer containing medium-density polyethylene and high-density polyethylene, in this order.

[0069] Specifically, a laminate can be manufactured by co-extruding layers containing medium-density polyethylene and high-density polyethylene, a layer containing high-density polyethylene, a layer containing linear low-density polyethylene, a layer containing high-density polyethylene, and a layer containing medium-density polyethylene and high-density polyethylene into a tubular shape. Alternatively, a laminate can be manufactured by co-extruding layers containing medium-density polyethylene and high-density polyethylene, a layer containing high-density polyethylene, and a layer containing linear low-density polyethylene into a tubular shape, and then pressing opposing linear low-density polyethylene layers together using rubber rolls or the like. By manufacturing laminates in this way, the number of defective products can be significantly reduced and production efficiency can be improved.

[0070] When manufacturing laminates using the T-die method, the melt flow rate (MFR) of the polyethylene constituting each layer is preferably 3 g / 10 min or more and 20 g / 10 min or less, from the viewpoint of film-forming properties and processability of the multilayer substrate.

[0071] When manufacturing laminates by the inflation method, the MFR of the polyethylene constituting each layer is preferably 0.2 g / 10 min to 5 g / 10 min, from the viewpoint of film-forming properties and processability of the multilayer substrate.

[0072] The multilayer substrate of this disclosure can be obtained, for example, by stretching the laminate described above. Furthermore, the stretching of the laminate can also be performed in an inflation film deposition machine. This allows for the production of multilayer substrates, thereby improving production efficiency.

[0073] The multilayer substrate of this disclosure may be a uniaxially oriented film or a biaxially oriented film. In one embodiment, the multilayer substrate is a uniaxially oriented film, more specifically, a uniaxially oriented film that has been stretched in the longitudinal direction (MD).

[0074] In one embodiment, the stretching ratio in the longitudinal direction (MD) of the multilayer substrate is preferably 2 to 10 times, and more preferably 3 to 7 times. In one embodiment, the stretching ratio in the transverse direction (TD) of the multilayer substrate is preferably 2 to 10 times, and more preferably 3 to 7 times.

[0075] When the stretching ratio is 2 times or more, for example, the rigidity, strength, and heat resistance of the multilayer substrate can be improved, the ink adhesion to the multilayer substrate can be improved, and the transparency of the multilayer substrate can be improved. When the stretching ratio is 10 times or less, the laminate can be stretched well.

[0076] The haze value of the multilayer substrate is preferably 25% or less, more preferably 15% or less, and even more preferably 10% or less. A smaller haze value is preferable, but in one embodiment, the lower limit may be 0.1% or 1%. The haze value of the multilayer substrate is measured in accordance with JIS K7136.

[0077] The polyethylene content in the multilayer substrate is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. This improves the recyclability of the multilayer substrate.

[0078] It is preferable that the laminate or multilayer substrate is surface-treated. This improves 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 and nitrogen gas, and glow discharge treatment; and chemical treatments such as oxidation treatment using chemicals.

[0079] An anchor coat layer may be formed on the surface of the laminate or multilayer substrate using a conventionally known anchor coat agent.

[0080] The total thickness of the multilayer substrate is preferably 10 μm to 60 μm, more preferably 15 μm to 50 μm. A thickness of 10 μm or more improves the rigidity and strength of the multilayer substrate. A thickness of 60 μm or less improves the processability of the multilayer substrate. Within the range where the above effects are obtained, a smaller thickness of the multilayer substrate is preferable, for example, from the viewpoint of cost reduction.

[0081] [Printing base material] The printing substrate of this disclosure comprises a polyethylene multilayer substrate of this disclosure and a printing layer formed on the multilayer substrate. The printing layer is formed, for example, on a first or fifth layer of the multilayer substrate. Since the multilayer substrate has excellent ink adhesion, a good image can be formed.

[0082] The printed layer includes, for example, an image. Examples of images include characters, 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. Also, from the viewpoint of reducing environmental impact, the printed layer may be formed on the surface of the multilayer substrate using biomass-derived ink.

[0083] [Laminated structure] As shown in Figure 2, the laminate 30 of this disclosure comprises the polyethylene multilayer substrate 10 of this 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 the multilayer intermediate layer 16.

[0084] In one embodiment, the laminate 30 further comprises a printed layer (not shown) on the multilayer substrate 10. The printed layer is typically formed on a surface layer of the multilayer substrate where a heat-seal layer is provided, for example, on the first layer described above.

[0085] In one embodiment, as shown in Figure 3, the laminate 30 includes a barrier layer 34 and an adhesive layer 36 between the multilayer substrate 10 and the heat seal layer 32. In this embodiment, the barrier layer 34 is formed on the surface of the multilayer substrate 10. In one embodiment, as shown in Figure 4, the laminate 30 includes an adhesive layer 36 and a barrier layer 34 between the multilayer substrate 10 and the heat seal layer 32. In this embodiment, the barrier layer 34 is formed on the surface of the heat seal layer 32. In one embodiment, as shown in Figure 5, the laminate 30 includes an adhesive layer 36 between the multilayer substrate 10 and the heat seal layer 32.

[0086] In the laminate of this disclosure, the polyethylene content is preferably 90% by mass or more. This improves the recyclability of the laminate. The polyethylene content in the laminate refers to the ratio of the polyethylene content to the sum of the resin material content in each layer constituting the laminate.

[0087] <Heat seal layer> The heat-seal layer is preferably made of polyethylene. This configuration provides a laminate for packaging materials that has sufficient rigidity, strength, and heat resistance, as well as excellent recyclability.

[0088] The following explains the recyclability mentioned above. Compared to other thermoplastic resin films, polyethylene film has poor heat resistance, which can cause deformation during heat sealing when used as a base material for packaging. Furthermore, polyethylene film has poor rigidity, resulting in poor printability and the inability to form clear images on its surface. Additionally, polyethylene film lacks high strength and cannot meet the durability requirements for an outer layer of packaging material. Therefore, packaging materials are manufactured by laminating a polyethylene film (heat-seal layer) with a resin film (base material) that has excellent rigidity, strength, and heat resistance, such as polyester film or nylon film. The laminate is then heat-sealed at the edges of the laminate so that the polyethylene film side faces inward.

[0089] In recent years, with the growing demand for a circular economy, attempts have been made to recycle and reuse packaging materials. However, when laminates are manufactured by bonding different types of resin films together, it is difficult to separate the resin films from each other. For this reason, such laminates are not suitable for recycling.

[0090] In contrast, the polyethylene multilayer substrate of this disclosure is stretched as described above and has a unique layer structure, and therefore has superior rigidity, strength, and heat resistance, as well as superior ink adhesion, compared to conventional polyethylene films. Accordingly, the polyethylene multilayer substrate of this disclosure can be used as a substrate for packaging materials, for example, and a clear image can be formed on the surface of the multilayer substrate.

[0091] Furthermore, in one embodiment, the laminate of the present disclosure comprises a polyethylene multilayer substrate of the present disclosure and a heat-sealable layer containing polyethylene (hereinafter also referred to as the "heat-sealable polyethylene layer"). In one embodiment, a printed layer (image) is formed on at least one surface of the multilayer substrate. It is preferable that the printed layer be formed on the side of the multilayer substrate where the heat-sealable polyethylene layer is provided, in order to prevent deterioration of the image over time.

[0092] In the laminate comprising the polyethylene multilayer substrate and a heat-sealable polyethylene layer according to this disclosure, in one embodiment, the resin layers included in the laminate are all polyethylene layers, and the laminate does not contain dissimilar resin films such as polyester film and nylon film. Furthermore, the polyethylene multilayer substrate satisfies the rigidity, strength, and heat resistance required as an outer layer film for packaging materials, and the heat-sealable polyethylene layer enables packaging. For this reason, the laminate is suitable as a material constituting a packaging material where recyclability is required.

[0093] In one embodiment, the laminate of the present disclosure consists only of the multilayer substrate on which a printed layer is formed as needed, and a heat-seal layer made of polyethylene. As a result, since each resin layer of the laminate of the present disclosure is made of polyethylene, which is the same material, the recyclability can be particularly improved.

[0094] The heat-seal layer is typically an unstretched layer. For example, a heat-seal layer can be formed by laminating an unstretched polyethylene film onto a multilayer substrate via an adhesive layer as needed, or by melt-extruding a polyethylene-containing resin material onto a multilayer substrate. Examples of adhesive layers include those described later.

[0095] Examples of polyethylene that can be used to constitute the heat seal layer include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene. From the viewpoint of heat sealability, low-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene are preferred. From the viewpoint of reducing environmental impact, biomass-derived polyethylene or recycled polyethylene may be used.

[0096] The polyethylene content in the heat seal layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. This improves the recyclability of the laminate. The heat seal layer may contain one or more of the above-mentioned additives.

[0097] 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, between 10 μm and 300 μm. The thickness of the heat seal layer is preferably adjusted as appropriate according to the mass of the contents to be filled into the packaging material manufactured, for example, by the laminate of this disclosure, from the viewpoint of the strength of the heat seal layer and the processability of the laminate.

[0098] For example, if the packaging material is a small bag, the thickness of the heat-seal layer is preferably 20 μm to 60 μm. In this case, for example, contents weighing 1 g to 200 g can be well filled into the small bag. For example, if the packaging material is a stand-up pouch, the thickness of the heat-seal layer is preferably 50 μm to 200 μm. In this case, for example, contents weighing 50 g to 2000 g can be well filled into the stand-up pouch.

[0099] <Barrier layer> In one embodiment, the laminate of the present disclosure includes a barrier layer between the multilayer substrate and the heat-seal layer. This improves the gas barrier properties of the laminate, specifically the oxygen barrier properties and water vapor barrier properties. The barrier layer may be formed on the surface of the multilayer substrate or on the surface of the heat-seal layer. Alternatively, the barrier layer may be provided between the multilayer substrate and the heat-seal layer via an adhesive or the like.

[0100] In one embodiment, the barrier layer is a vapor-deposited layer. The vapor-deposited layer is composed of, for example, a metal such as aluminum, and inorganic oxides such as aluminum oxide, silicon oxide, magnesium oxide, calcium oxide, zirconium oxide, titanium oxide, boron oxide, hafnium oxide, and barium oxide. Among these, an aluminum vapor-deposited layer is preferred.

[0101] The thickness of the barrier layer is preferably 1 nm to 150 nm, more preferably 5 nm to 60 nm, and even more preferably 10 nm to 40 nm. By making the barrier layer thickness 1 nm or more, the oxygen barrier and water vapor barrier properties of the laminate can be further improved. By making the barrier layer thickness 150 nm or less, the occurrence of cracks in the barrier layer can be suppressed, and the recyclability of the laminate can be improved.

[0102] 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 chemical vapor deposition, thermochemical vapor deposition, and photochemical vapor deposition. The barrier layer may be a composite film containing two or more barrier layers of different inorganic oxides, formed by using both physical vapor deposition and chemical vapor deposition methods in combination.

[0103] The vacuum level of the deposition chamber before oxygen introduction was 10 -2 ~10 -8 A bar of approximately mbar is preferred, and after oxygen introduction, 10 -1 ~10 -6 A pressure of approximately mbar is preferred. The amount of oxygen introduced will vary depending on the size of the deposition machine. Inert gases such as argon, helium, and nitrogen may be used as carrier gases for the oxygen introduced, within reasonable limits. The transport speed of the multilayer substrate is, for example, about 10 to 800 m / min.

[0104] It is preferable that the surface of the barrier layer is subjected to the surface treatment described above. This improves the adhesion between the barrier layer and the adjacent layer.

[0105] If the vapor-deposited layer is composed of inorganic oxides such as aluminum oxide and silicon oxide, a barrier coat layer may be provided on the surface of the vapor-deposited layer to form a barrier layer comprising the vapor-deposited layer and the barrier coat layer.

[0106] In one embodiment, the barrier coating layer is composed of a gas barrier resin. Examples of gas barrier resins include polyamide resins such as ethylene-vinyl alcohol copolymer (EVOH), polyvinyl alcohol, polyacrylonitrile, nylon 6, nylon 6,6 and polymethoxyylene adipamide (MXD6), polyester resins, polyurethane resins, and (meth)acrylic resins.

[0107] The thickness of the barrier coat layer is preferably 0.01 μm to 10 μm, more preferably 0.1 μm to 5 μm. A barrier coat layer thickness of 0.01 μm or more can further improve gas barrier properties. A barrier coat layer thickness of 10 μm or less can improve the processability of the laminate. Furthermore, it allows for the creation of a laminate suitable for use in the manufacture of monomaterial packaging containers.

[0108] A barrier coating layer can be formed, for example, by dissolving or dispersing a material such as a gas barrier resin in water or a suitable organic solvent, and then applying and drying the resulting coating solution.

[0109] In other embodiments, the barrier coating layer is a gas barrier coating film formed from a composition containing a hydrolyzed metal alkoxide or a hydrolyzed condensate of a metal alkoxide, obtained by polycondensation of a mixture of a metal alkoxide and a water-soluble polymer by a sol-gel method in the presence of a sol-gel catalyst, water, and an organic solvent. By providing such a barrier coating layer on the vapor-deposited layer, the occurrence of cracks in the vapor-deposited layer can be effectively prevented.

[0110] 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 2Each of these independently represents an organic group with 1 to 8 carbon atoms, M represents a metal atom, n represents a non-negative integer, m represents a non-negative integer, and n+m represents the valence of M.

[0111] R 1 and R 2 Examples of organic groups represented by include alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, and i-butyl groups. Examples of metal atoms M include silicon, zirconium, titanium, and aluminum.

[0112] 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).

[0113] It is preferable to use a silane coupling agent together with the above-mentioned metal alkoxide. Known organic reactive group-containing organoalkoxysilanes can be used as the silane coupling agent.

[0114] Preferred water-soluble polymers are polyvinyl alcohol and ethylene-vinyl alcohol copolymer. Depending on the desired physical properties such as oxygen barrier properties, water vapor barrier properties, water resistance, and weather resistance, either polyvinyl alcohol or ethylene-vinyl alcohol copolymer may be used, or both may be used in combination. Alternatively, a gas barrier coating film obtained using polyvinyl alcohol and a gas barrier coating film obtained using ethylene-vinyl alcohol copolymer may be laminated.

[0115] Acid or amine compounds are preferred as catalysts for the sol-gel process.

[0116] The above composition may further contain an acid. The acid is used as a catalyst for hydrolysis, mainly for sol-gel catalysts, metal alkoxides, and silane coupling agents. Examples of acids include mineral acids such as sulfuric acid, hydrochloric acid, and nitric acid, as well as organic acids such as acetic acid and tartaric acid.

[0117] The above composition may contain an organic solvent. Examples of organic solvents include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, and n-butanol.

[0118] The thickness of the gas barrier coating is preferably 0.01 μm to 100 μm, more preferably 0.1 μm to 50 μm. This further improves the gas barrier properties. By setting the thickness of the gas barrier coating to 0.01 μm or more, the oxygen barrier and water vapor barrier properties of the laminate can be improved, and the occurrence of cracks in the vapor-deposited layer can be prevented. By setting the thickness of the gas barrier coating to 100 μm or less, a laminate suitable for use in the manufacture of monomaterial packaging containers can be obtained.

[0119] A gas barrier coating film can be formed by applying a composition containing the above-mentioned material using conventionally known means such as roll coating (including gravure roll coaters), spray coating, spin coating, dipping, brushing, bar coating, and applicators, and then polycondensing the composition by a sol-gel method.

[0120] The following describes one embodiment of a method for forming a gas barrier coating film. First, a composition is prepared by mixing a metal alkoxide, a water-soluble polymer, a sol-gel catalyst, water, an organic solvent, and, if necessary, a silane coupling agent. A polycondensation reaction gradually proceeds within this composition.

[0121] Next, the composition is applied to the vapor-deposited layer by the conventionally known means described above and dried. This drying further promotes the polycondensation reaction between the metal alkoxide and the water-soluble polymer (and the silane coupling agent if the composition contains one), forming a composite polymer layer. Finally, heating allows for the formation of a gas barrier coating film.

[0122] <Adhesive layer> In one embodiment, the laminate of the present disclosure includes an adhesive layer between any of the layers (for example, between a multilayer substrate and a barrier layer, between a barrier layer and a heat seal layer, or between a multilayer substrate and a heat seal layer). This improves the adhesion between the layers contained in the laminate.

[0123] The adhesive layer contains one or more types of adhesives. Examples of adhesives include one-component curing adhesives, two-component curing adhesives, and non-curing adhesives.

[0124] The adhesive may be either a solvent-free adhesive or a solvent-based adhesive, but from the viewpoint of environmental impact, a solvent-free adhesive is preferred. Examples of solvent-free adhesives include polyether-based adhesives, polyester-based adhesives, silicone-based adhesives, epoxy-based adhesives, and urethane-based adhesives. Examples of solvent-based adhesives include rubber-based adhesives, vinyl-based adhesives, silicone-based adhesives, epoxy-based adhesives, phenol-based adhesives, olefin-based adhesives, and urethane-based adhesives. Among these, a two-component curing type urethane-based adhesive is preferred.

[0125] In the case of an adhesive layer adjacent to a barrier layer such as an aluminum vapor-deposited layer, it is preferable to constitute the adhesive layer with a cured product of a resin composition containing a polyester polyol, an isocyanate compound, and a phosphate-modified compound. By configuring the adhesive layer in this way, the oxygen barrier properties and water vapor barrier properties of the laminate of this disclosure can be further improved.

[0126] From the viewpoint of the adhesive properties of the adhesive layer and the processability of the laminate, the thickness of the adhesive layer is preferably 0.5 μm to 6 μm, more preferably 0.8 μm to 5 μm, and even more preferably 1 μm to 4.5 μm.

[0127] The adhesive layer can be formed by applying and drying an adhesive onto a multilayer substrate, for example, using methods such as the direct gravure roll coating method, gravure roll coating method, kiss coating method, reverse roll coating method, fontein method, and transfer roll coating method.

[0128] [Application] The polyethylene multilayer substrates, printing substrates, and laminates of this disclosure can be suitably used for packaging material applications such as packaging bags. The packaging material of this disclosure comprises the polyethylene multilayer substrates, printing substrates, or laminates of this disclosure.

[0129] For example, packaging material can be manufactured by folding the above laminate in half so that the multilayer substrate is on the outside and the heat-seal layer is on the inside, overlapping the layers, and then heat-sealing the edges. Alternatively, packaging material can be manufactured by overlapping multiple above laminates so that the heat-seal layers face each other, and then heat-sealing the edges. The entire packaging material may be made up of the above laminate, or only a part of the packaging material may be made up of the above laminate.

[0130] Examples of heat sealing forms for packaging materials include side seals, two-side seals, three-side seals, four-side seals, envelope seals, gusset seals (pillow seals), pleated seals, flat-bottom seals, square-bottom seals, and gusset seals. Stand-up pouches are also possible. Examples of heat sealing methods include bar seals, rotary roll seals, belt seals, impulse seals, high-frequency seals, and ultrasonic seals.

[0131] For example, a stand-up pouch having a body and a bottom can be manufactured as follows: First, one or more of the laminates are formed into a cylindrical shape with the heat-seal layer facing inward and then heat-sealed to form the body. Next, another laminate is folded into a V-shape with the heat-seal layer facing outward. The V-shaped laminate is sandwiched at one end of the body and heat-sealed to form the bottom.

[0132] In a stand pouch, the body may be formed only from the laminate, the bottom may be formed only from the laminate, or both the body and the bottom may be formed from the laminate.

[0133] Examples of contents to be filled into the packaging material include liquids, powders, and gels, and may be food or non-food items. After filling the packaging material with contents, the package is obtained by heat-sealing the opening of the packaging material.

[0134] This disclosure relates, for example, to the following [1] to

[14] . [1] A polyethylene multilayer substrate comprising a first layer containing medium-density polyethylene and high-density polyethylene, a second layer containing high-density polyethylene, a third layer containing linear low-density polyethylene, a fourth layer containing high-density polyethylene, and a fifth layer containing medium-density polyethylene and high-density polyethylene, in this order in the thickness direction, and subjected to a stretching treatment. [2] The polyethylene multilayer substrate according to [1] above, wherein 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. [3] The polyethylene multilayer substrate according to [1] or [2] above, wherein the total content of medium-density polyethylene and high-density polyethylene in the first layer is 80% by mass or more, the content of high-density polyethylene in the second layer is more than 50% by mass, the content of linear low-density polyethylene in the third layer is more than 50% by mass, the content of high-density polyethylene in the fourth layer is more than 50% by mass, and the total content of medium-density polyethylene and high-density polyethylene in the fifth layer is 80% by mass or more. [4] A polyethylene multilayer substrate according to any one of [1] to [3] above, wherein at least one layer selected from the first, second, third, fourth, and fifth layers contains a slip agent. [5] A printing substrate comprising a polyethylene multilayer substrate as described in any of [1] to [4] above, and a printing layer formed on the multilayer substrate. [6] A laminate comprising a polyethylene multilayer substrate as described in any of [1] to [4] above 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 a multilayer substrate. [9] The laminate according to any one of [6] to [8] above, 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] , wherein the barrier layer is formed on the surface of the multilayer substrate or on the surface of the heat seal layer.

[12] The laminate according to any one of [6] to

[11] above, further comprising an adhesive layer between the multilayer substrate and the heat seal layer.

[13] A laminate according to any of the above [6] to

[12] , used for packaging material applications.

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

[13] above. [Examples]

[0135] The multilayer substrates of this disclosure will be described in more detail based on the examples, but the multilayer substrates of this disclosure are not limited to the examples. Hereinafter, "parts by mass" will be simply referred to as "parts".

[0136] The polyethylene used in the following examples and comparative examples is described below. • Medium-density polyethylene (hereinafter referred to as "MDPE"): Product name Enable4002MC Density: 0.940g / cm 3 Melting point: 128℃, MFR: 0.25g / 10min ExxonMobil Corporation • High-density polyethylene (1) (hereinafter referred to as "HDPE(1)"): Product name: Elite5960G Density: 0.960g / cm 3 Melting point: 134℃, MFR: 0.8g / 10min Manufactured by Dowchemical Corporation • High-density polyethylene (2) (hereinafter referred to as "HDPE(2)"): Product name H619F Density: 0.965g / cm 3 Melting point: 135℃, MFR: 0.7g / 10min SCG Corporation • Linear low-density polyethylene (hereinafter referred to as "LLDPE"): Product name: Exceed XP8656ML Density: 0.916g / cm 3 Melting point: 121℃, MFR: 0.5g / 10min ExxonMobil Corporation • Low-density polyethylene (hereinafter referred to as "LDPE"): Product name LD2420F Density: 0.922g / cm 3 Melting point: 112℃, MFR: 0.75g / 10min Made by PTT • Contains slip-resistant MB: Product name SLIP61 10061-K Density: 0.910g / cm 3 , MFR:10g / 10min, Polyethylene-based, containing 5% by mass of erucic acid amide-based slip agent. Manufactured by Ampacet

[0137] [Production of blended polyethylene] • Blended polyethylene A1 A mixture of 70 parts MDPE and 30 parts HDPE(1) was produced, resulting in an average density of 0.948 g / cm³. 3 Blended polyethylene A1 (hereinafter referred to as "Blended PE(A1)") was obtained. • Blended polyethylene B1 Mixing 70 parts HDPE(2) and 30 parts LDPE results in an average density of 0.950 g / cm³. 3 Blended polyethylene B1 (hereinafter referred to as "Blended PE (B1)") was obtained. • Blended polyethylene C1 98 parts LLDPE and 2 parts slip agent-containing MB were mixed to achieve an average density of 0.916 g / cm³. 3 A blended polyethylene C1 (hereinafter referred to as "Blended PE(C1)") was obtained.

[0138] • Blended polyethylene A2 Mixing 69 parts MDPE, 30 parts HDPE(1), and 1 part slip agent-containing MB results in an average density of 0.948 g / cm³. 3 A blended polyethylene A2 (hereinafter referred to as "Blended PE(A2)") was obtained. • Blended polyethylene B2 Mixing 69 parts HDPE(2), 30 parts LDPE, and 1 part slip agent-containing MB results in an average density of 0.949 g / cm³. 3 Blended polyethylene B2 (hereinafter referred to as "Blended PE (B2)") was obtained. • Blended polyethylene C2 99 parts LLDPE and 1 part slip agent-containing MB were mixed to achieve an average density of 0.916 g / cm³. 3 A blended polyethylene C2 (hereinafter referred to as "Blended PE(C2)") was obtained.

[0139] • Blended polyethylene C3 Mixing 68 parts LLDPE, 30 parts LDPE, and 2 parts slip agent-containing MB results in an average density of 0.918 g / cm³. 3 A blended polyethylene C3 (hereinafter referred to as "Blended PE(C3)") was obtained.

[0140] [Example 1] Blended PE(A1), Blended PE(B1), and Blended PE(C1) were co-extruded in five layers by inflation molding with the layer thickness ratio of Blended PE(A1) layer (15 μm) / Blended PE(B1) layer (22.5 μm) / Blended PE(C1) layer (50 μm) / Blended PE(B1) layer (22.5 μm) / Blended PE(A1) layer (15 μm) to form a tubular film with a total thickness of 125 μm. The tubular film was folded at the nip and doubled up. The numbers in parentheses indicate the layer thickness.

[0141] The polyethylene film prepared as described above was stretched in the longitudinal direction (MD) at a stretching ratio of 5 times. Furthermore, the blended PE(A1) layer (surface layer) on one side was subjected to corona discharge treatment, and then the ends were slit to divide it into two pieces, obtaining a stretched multilayer substrate with a thickness of 25 μm.

[0142] [Examples 2 and 3, 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, slip agent-containing MB is simply referred to as "MB".

[0143] [Example 4] Blended PE(A1), Blended PE(B1), and Blended PE(C1) were co-extruded in five layers by inflation molding with the layer thickness ratio of Blended PE(A1) layer (12 μm) / Blended PE(B1) layer (18 μm) / Blended PE(C1) layer (40 μm) / Blended PE(B1) layer (18 μm) / Blended PE(A1) layer (12 μm) to form a tubular film with a total thickness of 100 μm. The tubular film was folded at the nip and doubled up. The numbers in parentheses indicate the layer thickness.

[0144] The polyethylene film prepared as described above was stretched in the longitudinal direction (MD) at a stretching ratio of 5 times. Furthermore, the blended PE(A1) layer (surface layer) on one side was subjected to corona discharge treatment, and then the ends were slit to divide it into two sheets, obtaining a stretched multilayer substrate with a thickness of 20 μm.

[0145] [Examples 5 and 6] A polyethylene film and a stretched multilayer substrate were obtained in the same manner as in Example 4, except that the layer structure was changed as shown in Table 2. In Table 2, the slip agent-containing MB is simply referred to as "MB".

[0146] [Ink adhesion evaluation] Images were formed on the corona discharge treated side of the stretched multilayer substrates obtained in the examples and comparative examples using gravure printing with oil-based gravure ink (manufactured by DIC Graphics Co., Ltd., product name: Finart). The images formed on the stretched multilayer substrates were observed visually and evaluated based on the following evaluation criteria.

[0147] (Evaluation Criteria) AA: When cellophane tape (registered trademark) was applied to the image-forming surface of a stretched multilayer substrate and then peeled off, the ink adhered well to the stretched multilayer substrate, and no ink peeling occurred on the cellophane tape (registered trademark). BB: When cellophane tape (registered trademark) was applied to the image-forming surface of a stretched multilayer substrate and then peeled off, the ink adhesion to the stretched multilayer substrate was weak, resulting in ink peeling from the cellophane tape (registered trademark).

[0148] [Fabrication of laminates] First linear low-density polyethylene (Prime Polymer Co., Ltd., SP2520, density: 0.925 g / cm³) 3 (melting point: 122°C) and a second linear low-density polyethylene (Prime Polymer Co., Ltd., SP1520, density: 0.913 g / cm³). 3 A multilayer extruded film was prepared using an inflation molding method with a first linear low-density polyethylene layer of 20 μm thickness and a second linear low-density polyethylene layer of 20 μm thickness to create an unstretched polyethylene film. This unstretched polyethylene film was used as a heat seal layer as described below.

[0149] The first linear low-density polyethylene layer side of the unstretched polyethylene film (heat-seal layer) prepared as described above and the stretched multilayer substrate obtained in the examples and comparative examples were dry-laminated using a two-component curing urethane adhesive (Rock Paint Co., Ltd., Ru-77T / H-7) to obtain a laminate.

[0150] The laminate prepared above was cut into 10cm x 10cm sections to create three sample pieces. Each sample piece was folded in half with the heat-sealed layer facing inward, and a heat seal tester was used at a temperature of 140°C and a pressure of 1 kgf / cm². 2 A 1cm x 10cm area was heat-sealed under a 1-second condition.

[0151] [Heat resistance evaluation] Heat resistance was evaluated according to the following criteria. AA: During printing, dry lamination, and heat sealing of the laminated material produced above, there was no shrinkage of the stretched multilayer substrate, and the desired product was manufactured cleanly. BB: Shrinkage occurred in the stretched multilayer substrate during printing, dry lamination, and heat sealing of the laminated material produced above, making it impossible to manufacture the desired product cleanly.

[0152] [Hayes's rating] The haze values ​​of the stretched multilayer substrates obtained in the examples and comparative examples were measured in accordance with JIS K7136.

[0153] [Rigidity evaluation] The stretched multilayer substrates obtained in the examples and comparative 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.

[0154] [Strength assessment] Dumbbell-shaped test specimens with a width of 10 mm were cut from the stretched multilayer substrates obtained in the examples and comparative examples. The tensile strength in the MD direction of the above test specimens was measured using a tensile testing machine (Orientec Co., Ltd., RTC-1310A). The distance between the chucks was 10 mm, and the tensile speed was 300 mm / min. The evaluation results are shown in Tables 1 and 2.

[0155] [Table 1]

[0156] [Table 2] [Explanation of Symbols]

[0157] 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: Multilayer intermediate layer consisting of the second, third, and fourth layers 18: Second layer containing high-density polyethylene 20: Third layer containing linear low-density polyethylene 22: Fourth layer containing high-density polyethylene 30: Laminate 32: Heat seal layer 34: Barrier layer 36: Adhesive layer

Claims

1. A first layer containing medium-density polyethylene and high-density polyethylene, A second layer containing high-density polyethylene, A third layer containing linear low-density polyethylene, A fourth layer containing high-density polyethylene, A fifth layer containing medium-density polyethylene and high-density polyethylene A polyethylene multilayer substrate having these elements arranged in this order in the thickness direction and having been stretched, In the first layer, the mass ratio of medium-density polyethylene to high-density polyethylene (medium-density polyethylene / high-density polyethylene) is 1.1 or more and 5 or less. In the fifth layer, the mass ratio of medium-density polyethylene to high-density polyethylene (medium-density polyethylene / high-density polyethylene) is 1.1 or more and 5 or less. The total content ratio of the medium-density polyethylene and the high-density polyethylene in the first layer is 80% by mass or more. The content of the high-density polyethylene in the second layer is more than 50% by mass, The content of the linear low-density polyethylene in the third layer is more than 50% by mass, The content ratio of the high-density polyethylene in the fourth layer is more than 50% by mass, The total content ratio of the medium-density polyethylene and the high-density polyethylene in the fifth layer is 80% by mass or more. At least one of the first layer or the fifth layer constitutes the surface layer of the polyethylene multilayer substrate. The surface layer is subjected to one or more surface treatments selected from the group consisting of corona discharge treatment, ozone treatment, low-temperature plasma treatment, glow discharge treatment, and oxidation treatment using chemicals. Polyethylene multilayer substrate.

2. The polyethylene multilayer substrate according to claim 1, wherein at least one layer selected from the first, second, third, fourth, and fifth layers contains a slip agent.

3. A polyethylene multilayer substrate according to claim 1 or 2, A printed layer formed on the surface layer of the polyethylene multilayer substrate and A printing substrate equipped with the following features.

4. A polyethylene multilayer substrate according to claim 1 or 2, Heat seal layer and A laminate comprising the following features.

5. The laminate according to claim 4, wherein the heat-seal layer contains polyethylene.

6. The laminate according to claim 4 or 5, further comprising a printed layer on the surface layer of the polyethylene multilayer substrate.

7. The laminate according to any one of claims 4 to 6, further comprising a barrier layer between the polyethylene multilayer substrate and the heat seal layer.

8. The laminate according to claim 7, wherein the barrier layer is a vapor-deposited layer.

9. The laminate according to claim 7 or 8, wherein the barrier layer is formed on the surface of the polyethylene multilayer substrate or on the surface of the heat seal layer.

10. The laminate according to any one of claims 4 to 9, further comprising an adhesive layer between the polyethylene multilayer substrate and the heat seal layer.

11. A laminate according to any one of claims 4 to 10, used for packaging material applications.

12. A packaging material comprising a polyethylene multilayer substrate according to claim 1 or 2, a printing substrate according to claim 3, or a laminate according to any one of claims 4 to 11.

Images