Polyethylene multilayer substrate, printing substrate, laminate, and packaging material

Abstract

To provide a polyethylene multilayer substrate excellent in ink adhesion and interlaminar strength.SOLUTION: A polyethylene multilayer substrate is provided with a layer (A) containing medium-density polyethylene, two or more multilayer medium layers (B) each containing polyethylene, and a layer (C) containing medium density polyethylene in this order in a thickness direction, wherein the multilayer substrate is subjected to drawing treatment, and an absolute value of a difference between a density of polyethylene constituting a layer (1) and a density of polyethylene constituting a layer (2) is 0.030 g / cm3 or less when arbitrary polyethylene-containing layers adjacent to each other in the thickness direction in the multilayer substrate are described as the layer (1) and the layer (2).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a polyethylene multilayer substrate, a printed substrate, a laminate, and a packaging material.

Background Art

[0002] Conventionally, packaging materials and the like have been manufactured using resin films made of resin materials. The packaging material includes, for example, a substrate and a heat-sealing layer. For example, a resin film made of polyethylene has flexibility and transparency and is excellent in heat-sealing properties, and thus is widely used as a heat-sealing layer in packaging materials (see, for example, Patent Document 1).

[0003] On the other hand, since polyethylene is a resin that softens at a relatively low temperature compared to other thermoplastic resins, it may deform or melt in some cases during heat-sealing when used as a substrate for packaging materials. In addition, a polyethylene film may have insufficient strength compared to other thermoplastic resin films. For this reason, it is common to use resin films having excellent strength and heat resistance, such as polyester films and nylon films, as the substrate for packaging materials. For example, a substrate such as a polyester film and a nylon film is laminated with a polyethylene film, and a bag is formed by heat-sealing so that the polyethylene film side is on the inner side of the packaging bag (see, for example, the background art of Patent Document 2).

[0004] By the way, in recent years, with the increasing demand for building a recycling-based society, attempts have been made to recycle and use packaging materials. However, in a laminate obtained by laminating different resin films as described above, it is difficult to separate each type of resin, and it is not suitable for recycling.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[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 substrate having a plurality of layers containing polyethylene as a base material and being stretched. 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 a polyethylene multilayer substrate may not have sufficient ink adhesion and may not have sufficient interlayer strength. One problem of the present disclosure is to provide a polyethylene multilayer substrate having excellent ink adhesion and interlayer strength. [Means for Solving the Problems]

[0007] The polyethylene multilayer substrate of the present disclosure is a polyethylene multilayer substrate including a layer (A) containing medium-density polyethylene, two or more multilayer intermediate layers (B) each containing polyethylene, and a layer (C) containing medium-density polyethylene, in this order in the thickness direction. The multilayer substrate is stretched. When any two adjacent polyethylene-containing layers in the thickness direction of the multilayer substrate are described 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 or less. [Effects of the Invention]

[0008] According to the present disclosure, a polyethylene multilayer substrate having excellent ink adhesion and interlayer strength can be provided. [Brief Description of the Drawings]

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Mode for Carrying Out the Invention

[0010] Hereinafter, the terms used in the present disclosure will be explained. "Polyethylene" refers to a polymer in which the content ratio of the constitutional unit derived from ethylene is 50 mol% or more in all the repeating constitutional units. In the polymer, the content ratio of the constitutional unit derived from ethylene 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).

[0011] 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 The density of medium-density polyethylene preferably exceeds 0.925 g / cm 3 and is less than 0.945 g / cm 3 The density of low-density polyethylene preferably exceeds 0.900 g / cm 3 and is less than 0.925 g / cm 3 The density of linear low-density polyethylene preferably exceeds 0.900 g / cm 3 and is less than 0.925 g / cm 3 ​​​​The density of the ultra-low density polyethylene is preferably 0.900 g / cm 3 or less. The lower limit of the density of the ultra-low density polyethylene is, for example, 0.860 g / cm 3 . The density of the polyethylene is measured in accordance with JIS K7112 (1999).

[0012] [Polyethylene multi-layer substrate] As shown in FIG. 1, the polyethylene multi-layer substrate 10 of the present disclosure comprises a layer (A) 12 containing medium density polyethylene, two or more multi-layer intermediate layers (B) 16 each containing polyethylene, and a layer (C) 14 containing medium density polyethylene in this order in the thickness direction. The polyethylene multi-layer substrate of the present disclosure is stretched. Hereinafter, the above polyethylene multi-layer substrate is also simply referred to as "multi-layer substrate".

[0013] When printing an image on a substrate, surface treatment such as corona discharge treatment is usually performed on the substrate as a pretreatment. The layer containing medium density polyethylene tends to have higher durability against surface treatment than a layer containing only high density polyethylene as polyethylene. For this reason, the layer containing medium density polyethylene is excellent in ink adhesion during printing after surface treatment. Further, the layer containing medium density polyethylene also has the heat resistance required during printing and heat sealing. Further, the layer containing medium density polyethylene contributes to the improvement of the stretchability of the laminate which is a precursor of the multi-layer substrate.

[0014] In one embodiment, the surface layer on one side of the multi-layer substrate is layer (A), and the surface layer on the other side of the multi-layer substrate is layer (C).

[0015] When arbitrarily adjacent polyethylene-containing layers in the multi-layer substrate in the thickness direction are described 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 / cm3 is as follows, preferably 0.025 g / cm 3 or less, more preferably 0.020 g / cm 3 or less. Hereinafter, this requirement is also referred to as the "density difference requirement". That is, any combination of adjacent polyethylene-containing layers in the thickness direction included in the multilayer substrate satisfies the above density difference requirement. In addition, when describing the density difference hereinafter, it always means the absolute value of the difference.

[0016] For example, a laminate including, in this order in the thickness direction, a first layer containing medium density polyethylene (a), a second layer containing high density polyethylene (b), a third layer containing medium density polyethylene (c) and high density polyethylene (d), a fourth layer containing high density polyethylene (e), and a fifth layer containing medium density polyethylene (f) will be described. For convenience, symbols are added to each polyethylene.

[0017] The above density difference requirement is the density difference between medium density polyethylene (a) and high density polyethylene (b), the difference between the density of high density polyethylene (b) and the average density of medium density polyethylene (c) and high density polyethylene (d), the difference between the average density of medium density polyethylene (c) and high density polyethylene (d) and the density of high density polyethylene (e), and the density difference between high density polyethylene (e) and medium density polyethylene (f) all mean that they are 0.030 g / cm 3 or less.

[0018] When a plurality of types (n types; n is an integer of 2 or more) of polyethylene having different densities are included in one layer, the average density D calculated according to the following formula (1) av is taken as the density of the polyethylene constituting the layer.

[0019] D av = ΣW i × D i …(1) In formula (1), Σ means taking the sum of W i ×D i from 1 to n for i, n is an integer of 2 or more, W i represents the mass fraction of the i-th polyethylene, and D i represents the density (g / cm 3 ) of the i-th polyethylene.

[0020] In the multilayer substrate of the present disclosure, the density difference between the polyethylene-containing layers is as small as described above. Therefore, the multilayer substrate of the present disclosure exhibits high interfacial strength. Further, the multilayer substrate of the present disclosure has excellent ink adhesion as described above, has heat resistance and transparency, and also has sufficient rigidity, strength and stiffness as a multilayer substrate used for manufacturing packaging materials and the like. Therefore, the multilayer substrate of the present disclosure is useful as a substrate on which a printing layer is formed.

[0021] In the present disclosure, examples of the polyethylene include a homopolymer of ethylene and a copolymer of ethylene and another monomer. Examples of the other monomer include α-olefins having 3 to 20 carbon atoms, vinyl acetate, and (meth)acrylic acid esters. Examples of the 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 the (meth)acrylic acid ester include (meth)acrylic acid alkyl such as (meth)acrylic acid methyl and (meth)acrylic acid ethyl.

[0022] 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 and an α-olefin having 3 to 20 carbon atoms and at least one selected from vinyl acetate and (meth)acrylic acid esters.

[0023] Polyethylenes with different densities or degrees of branching can be obtained by appropriately selecting the polymerization method. For example, as the polymerization catalyst, a multi-site catalyst such as a Ziegler-Natta catalyst or a single-site catalyst such as a metallocene catalyst is used, and polymerization is preferably carried out in one or more than two stages by any of the methods of gas-phase polymerization, slurry polymerization, solution polymerization, and high-pressure ionic polymerization.

[0024] A single-site catalyst is a catalyst that can form a uniform active species, and is usually prepared by contacting a metallocene-based transition metal compound or a non-metallocene-based transition metal compound with an activating cocatalyst. Since the structure of the active sites of a single-site catalyst is more uniform than that of a multi-site catalyst, it is preferable because a polymer having a high molecular weight and a high degree of uniformity can be obtained.

[0025] A metallocene catalyst is preferred as the single-site catalyst. A 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 cocatalyst, an organometallic compound if necessary, and a carrier if necessary.

[0026] Examples of the transition metal in the transition metal compound include zirconium, titanium, and hafnium, with zirconium and hafnium being preferred.

[0027] The cyclopentadienyl skeleton in a transition metal compound is a cyclopentadienyl group or a substituted cyclopentadienyl group. The substituted cyclopentadienyl group has, for example, at least one substituent selected from hydrocarbon groups having 1 to 30 carbon atoms, silyl groups, silyl-substituted alkyl groups, silyl-substituted aryl groups, cyano groups, cyanoalkyl groups, cyanoaryl groups, halogen groups, haloalkyl groups, and halosilyl groups. The substituted cyclopentadienyl group has one or more substituents, and the substituents may be bonded to each other to form a ring, which may form an indenyl ring, a fluorenyl ring, an azulene ring, or a hydrogenated product thereof. The ring formed by bonding the substituents to each other may further have a substituent.

[0028] The transition metal compound usually has two ligands having a cyclopentadienyl skeleton. It is preferable that the ligands having each cyclopentadienyl skeleton are bonded to each other by a bridging group. Examples of the bridging group include substituted silylene groups such as alkylene groups having 1 to 4 carbon atoms, silylene groups, dialkylsilylene groups, and diarylsilylene groups, and substituted germylene groups such as dialkylgermylene groups and diarylgermylene groups. Among these, substituted silylene groups are preferable.

[0029] The cocatalyst refers to a component that can effectively function as a polymerization catalyst for a transition metal compound of Group IV of the periodic table, or a component that can balance the ionic charges in a catalytically activated state. Examples of the cocatalyst include benzene-soluble aluminoxane or benzene-insoluble organoaluminum oxy compound, ion-exchangeable layered silicate, boron compound, ionic compound composed of a cation with or without an active hydrogen group and a non-coordinating anion, lanthanoid salts such as lanthanum oxide, tin oxide, and a phenoxy compound containing a fluoro group.

[0030] Examples of the organometallic compound that may be used as necessary include organoaluminum compounds, organomagnesium compounds, and organozinc compounds. Among these, organoaluminum compounds are preferable.

[0031] The transition metal compound may be used by being supported on a carrier of an inorganic or organic compound. As the carrier, a porous oxide of an inorganic or organic compound is preferable, and specifically, an ion-exchangeable layered silicate such as montmorillonite, SiO2, Al2O3, MgO, ZrO2, TiO2, B2O3, CaO, ZnO, BaO, ThO2, or a mixture thereof can be mentioned.

[0032] As a raw material for obtaining polyethylene, ethylene derived from biomass may be used instead of ethylene obtained from fossil fuels. Since polyethylene derived from biomass is a carbon-neutral material, it is possible to reduce the environmental load of packaging materials manufactured using a multilayer substrate. Polyethylene derived from biomass can be produced, for example, by the method described in JP-A-2013-177531. Commercially available polyethylene derived from biomass (for example, Green PE commercially available from Braskem) may be used.

[0033] Polyethylene recycled by mechanical recycling may be used. Mechanical recycling generally refers to a method in which a recovered polyethylene film or the like is pulverized, alkali-washed to remove dirt and foreign substances on the film surface, and then dried under high temperature and reduced pressure for a certain period of time to diffuse and remove contaminants remaining inside the film, remove the dirt of the film made of polyethylene, and return it to polyethylene again. From the viewpoints of film-forming properties and processability of the multilayer substrate, 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. In the present disclosure, MFR is measured in accordance with ASTM D1238 under the conditions of a temperature of 190°C and a load of 2.16 kg.

[0034] <Layer (A) and Layer (C)> Layer (A) contains one or more medium-density polyethylenes. Layer (C) contains one or more medium-density polyethylenes.

[0035] The medium-density polyethylene contained in layer (A) and the medium-density polyethylene contained in layer (C) may be the same or different, and are preferably the same from the viewpoint of enabling easy production of the multilayer base material.

[0036] Layers (A) and (C) may each independently contain only medium-density polyethylene as the polyethylene. Layers (A) and (C) may each independently further contain, together with the medium-density polyethylene, another polyethylene other than the medium-density polyethylene. Examples of the other polyethylene other than the medium-density polyethylene include high-density polyethylene, low-density polyethylene (low-pressure process low-density polyethylene), linear low-density polyethylene, and ultra-low-density polyethylene. Among these, high-density polyethylene is preferable from the viewpoint of further improving heat resistance and abrasion resistance. That is, in one embodiment, layers (A) and (C) each independently contain medium-density polyethylene and high-density polyethylene.

[0037] In this case, the mass ratio (medium-density polyethylene / other polyethylene) of the medium-density polyethylene and the other polyethylene such as high-density polyethylene in layers (A) and (C) is each independently preferably 0.25 or more and 4 or less, more preferably 0.4 or more and 2.4 or less. Thereby, the ink adhesion, durability against surface treatment, and heat resistance of the multilayer base material can be further improved.

[0038] The density of the polyethylene constituting layers (A) and (C) is each independently preferably more than 0.925 g / cm 3 and 0.960 g / cm 3 or less, more preferably more than 0.925 g / cm 3 and 0.955 g / cm 3 or less, still more preferably more than 0.925 g / cm 3 and 0.945 g / cm 3The following applies. When two or more types of polyethylene are contained in the same layer, the density of polyethylene means the average density described above. As a result, the ink adhesion, durability against surface treatment, and heat resistance of the multilayer substrate can be further improved.

[0039] The content ratio of polyethylene in layer (A) and layer (C) is, independently of each other, preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more.

[0040] Layer (A) and layer (C) may each independently contain one or more additives. Examples of the additives include crosslinking agents, antioxidants, antiblocking agents, slip agents, ultraviolet absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, and modifying resins.

[0041] The thickness of each of layer (A) and layer (C) in the multilayer substrate is, independently of each other, preferably 0.5 μm or more and 10 μm or less, more preferably 1 μm or more and 8 μm or less, and still more preferably 1 μm or more and 5 μm or less. As a result, the ink adhesion and heat resistance of the multilayer substrate can be further improved.

[0042] The thickness of each of layer (A) and layer (C) is preferably smaller than the total thickness of the multilayer intermediate layer (B). The ratio of the thickness of each of layer (A) or layer (C) to the total thickness of the multilayer intermediate layer (B) (layer (A) or layer (C) / multilayer intermediate layer (B)) is preferably 0.05 or more and 0.8 or less, more preferably 0.1 or more and 0.7 or less, and still more preferably 0.1 or more and 0.4 or less. As a result, the rigidity, strength, and heat resistance of the multilayer substrate can be further improved.

[0043] <Multilayer intermediate layer (B)> The multilayer intermediate layer (B) includes two or more layers containing one or more types of polyethylene.

[0044] Examples of the polyethylene include high density polyethylene, medium density polyethylene, low density polyethylene (low density polyethylene by high pressure method), linear low density polyethylene, and ultra low density polyethylene.

[0045] For example, when layers (A) and (C) do not contain high density polyethylene, the multilayer intermediate layer (B) preferably includes a layer containing high density polyethylene. Thereby, the heat resistance and rigidity of the multilayer substrate can be improved.

[0046] For example, when layers (A) and (C) contain high density polyethylene, the multilayer intermediate layer (B) preferably includes a layer containing medium density polyethylene and linear low density polyethylene. Thereby, the balance between the heat resistance and stretchability of the multilayer substrate can be improved.

[0047] The content ratio of polyethylene in each layer constituting the multilayer intermediate layer (B) is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more, independently of each other.

[0048] Each layer constituting the multilayer intermediate layer (B) may independently contain one or more additives. Examples of the additives include crosslinking agents, antioxidants, antiblocking agents, slip agents, ultraviolet absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, and modifying resins.

[0049] The total thickness of the multilayer intermediate layer (B) is preferably 1 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, and still more preferably 10 μm or more and 30 μm or less. Thereby, the heat resistance of the multilayer substrate can be further improved.

[0050] The number of layers of the multilayer intermediate layer (B) is 2 or more, preferably 3 or more, and more preferably 3 or more and 5 or less, from the viewpoints of the rigidity, strength, and manufacturability of the multilayer substrate.

[0051] Hereinafter, as specific examples of the multilayer intermediate layer (B), the first to fourth embodiments will be described. The multilayer intermediate layer of the first embodiment comprises a layer containing high-density polyethylene, a layer containing medium-density polyethylene and high-density polyethylene, and a layer containing high-density polyethylene in this order in the thickness direction. In the layer containing medium-density polyethylene and high-density polyethylene, the mass ratio of medium-density polyethylene to high-density polyethylene (medium-density polyethylene / high-density polyethylene) is preferably 0.25 or more and 4 or less, more preferably 0.4 or more and 2.4 or less.

[0052] As shown in FIG. 2, the multilayer substrate 10 including the multilayer intermediate layer of the first embodiment comprises a first layer 12 (layer (A)) containing medium-density polyethylene, a second layer 18 containing high-density polyethylene, a third layer 20 containing medium-density polyethylene and high-density polyethylene, a fourth layer 22 containing high-density polyethylene, and a fifth layer 14 (layer (C)) containing medium-density polyethylene in this order in the thickness direction and is stretched.

[0053] The multilayer intermediate layer of the second embodiment comprises a layer containing medium-density polyethylene, a layer containing medium-density polyethylene and linear low-density polyethylene, and a layer containing medium-density polyethylene in this order in the thickness direction. In the layer containing medium-density polyethylene and linear low-density polyethylene, the mass ratio of medium-density polyethylene to linear low-density polyethylene (medium-density polyethylene / linear low-density polyethylene) is preferably 0.25 or more and 4 or less, more preferably 0.4 or more and 2.4 or less.

[0054] The multilayer substrate including the multilayer intermediate layer of the second embodiment is, for example, A first layer (layer (A)) containing medium-density polyethylene, a second layer containing medium-density polyethylene, a third layer containing medium-density polyethylene and linear low-density polyethylene, a fourth layer containing medium-density polyethylene, a fifth layer (layer (C)) containing medium-density polyethylene are provided in this order in the thickness direction and are stretch-processed.

[0055] The multilayer intermediate layer of the third embodiment is a layer containing medium-density polyethylene and linear low-density polyethylene, a layer containing linear low-density polyethylene, a layer containing medium-density polyethylene and linear low-density polyethylene are provided in this order in the thickness direction. In the layer containing medium-density polyethylene and linear low-density polyethylene, the mass ratio of medium-density polyethylene to linear low-density polyethylene (medium-density polyethylene: linear low-density polyethylene) is preferably 0.25 or more and 4 or less, more preferably 0.4 or more and 2.4 or less.

[0056] The multilayer base material provided with the multilayer intermediate layer of the third embodiment is, for example, a first layer (layer (A)) containing medium-density polyethylene and high-density polyethylene, a second layer containing medium-density polyethylene and linear low-density polyethylene, a third layer containing linear low-density polyethylene, a fourth layer containing medium-density polyethylene and linear low-density polyethylene, a fifth layer (layer (C)) containing medium-density polyethylene and high-density polyethylene are provided in this order in the thickness direction and are stretch-processed.

[0057] The multilayer intermediate layer of the fourth embodiment is a layer containing medium-density polyethylene, A layer containing linear low density polyethylene and medium density polyethylene, a layer containing medium density polyethylene, are provided in this order in the thickness direction. In the layer containing linear low density polyethylene and medium density polyethylene, the mass ratio of linear low density polyethylene to medium density polyethylene (linear low density polyethylene / medium density polyethylene) is preferably 0.25 or more and 4 or less, more preferably 0.4 or more and 2.4 or less.

[0058] The multilayer base material provided with the multilayer intermediate layer of the fourth embodiment is, for example, a first layer (layer (A)) 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, a fifth layer (layer (C)) containing high density polyethylene and medium density polyethylene are provided in this order in the thickness direction and are stretched.

[0059] In the multilayer intermediate layer of the first to fourth embodiments, the ratio of the total thickness of the outer two layers to the thickness of the central layer (total thickness of the outer two layers / thickness of the central layer) is preferably 0.1 or more and 10 or less, more preferably 0.2 or more and 5 or less, still more preferably 0.5 or more and 2 or less. Thereby, the rigidity, strength, and heat resistance of the multilayer base material can be further improved. For example, in the case of the first embodiment, the outer two layers in the multilayer intermediate layer refer to the layer containing high density polyethylene, and the central layer refers to the layer containing medium density polyethylene and high density polyethylene.

[0060] <Method for manufacturing a multilayer base material> The multilayer base material of the present disclosure can be produced, for example, by forming a laminate by forming films of a plurality of polyethylene materials by an inflation method or a T-die method and stretching the obtained laminate. By the stretching treatment, the transparency, rigidity, strength, and heat resistance of the multilayer base material can be improved, and the multilayer base material can be suitably used, for example, as a base material for packaging materials.

[0061] The multilayer base material is obtained, for example, by stretching a laminate (precursor) including, in this order in the thickness direction, a layer containing medium-density polyethylene, two or more multilayer intermediate layers each containing polyethylene, and a layer containing medium-density polyethylene.

[0062] Specifically, from the outside, a layer containing medium-density polyethylene, two or more multilayer intermediate layers each containing polyethylene, and a layer containing medium-density polyethylene are co-extruded into a film in a tubular shape to produce a laminate. Alternatively, from the outside, a layer containing medium-density polyethylene and a layer containing polyethylene are co-extruded into a tube, and then the layers containing polyethylene facing each other are crimped by a rubber roll or the like to produce a laminate. By producing a laminate by such a method, the number of defective products can be significantly reduced, and the production efficiency can be improved.

[0063] When producing a laminate 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 viewpoints of film formability and processability of the multilayer base material.

[0064] When producing a laminate by the inflation method, 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 viewpoints of film formability and processability of the multilayer base material.

[0065] The multilayer base material of the present disclosure is obtained, for example, by stretching the above-described laminate. In an inflation film forming machine, stretching of the laminate can also be performed. Thereby, since the multilayer base material can be produced, the production efficiency can be further improved.

[0066] The multilayer base material of the present disclosure may be a uniaxially stretched film or a biaxially stretched film. In one embodiment, the multilayer base material is a uniaxially stretched film, and more specifically, a uniaxially stretched film stretched in the machine direction (MD).

[0067] In one embodiment, the stretching ratio in the machine direction (MD) of the multilayer base material is preferably 2 times or more and 10 times or less, and more preferably 3 times or more and 7 times or less. In one embodiment, the stretching ratio in the transverse direction (TD) of the multilayer base material is preferably 2 times or more and 10 times or less, and more preferably 3 times or more and 7 times or less.

[0068] When the stretching ratio is 2 times or more, for example, the rigidity, strength, and heat resistance of the multilayer base material can be improved, the ink adhesion to the multilayer base material can be improved, and the transparency of the multilayer base material can be improved. When the stretching ratio is 10 times or less, the laminate can be stretched well.

[0069] The haze value of the multilayer base material is preferably 25% or less, more preferably 15% or less, and even more preferably 10% or less. Although a smaller haze value is more preferable, in one embodiment, the lower limit value may be 0.1% or 1%. The haze value of the multilayer base material is measured in accordance with JIS K7136.

[0070] The content ratio of polyethylene in the multilayer base material is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. Thereby, the recyclability of the multilayer base material can be improved.

[0071] It is preferable that the laminate or the multilayer base material is subjected to a surface treatment. Thereby, the adhesion between the surface layer of the multilayer base material and the layer laminated on the multilayer base material can be improved. Examples of the surface treatment method 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.

[0072] An anchor coat layer may be formed on the surface of the laminate or the multi-layer substrate using a conventionally known anchor coating agent.

[0073] The total thickness of the multi-layer 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 multi-layer substrate is 10 μm or more, the rigidity and strength of the multi-layer substrate can be improved. When the thickness of the multi-layer substrate is 60 μm or less, the processability of the multi-layer substrate can be improved.

[0074] [Printing Substrate] The printing substrate of the present disclosure includes the polyethylene multi-layer substrate of the present disclosure and a printing layer formed on the multi-layer substrate. The printing layer is formed, for example, on layer (A) or layer (C) in the multi-layer substrate. Since the multi-layer substrate has excellent ink adhesion, a good image can be formed.

[0075] The printing layer includes, for example, an image. Examples of the image include characters, figures, symbols, and combinations thereof. Examples of the method for forming the printing layer include a gravure printing method, an offset printing method, and a flexographic printing method. In one embodiment, from the perspective of reducing environmental impact, the flexographic printing method is preferred. Also, from the perspective of reducing environmental impact, a printing layer may be formed on the surface of the multi-layer substrate using biomass-derived ink.

[0076] [Laminate] As shown in FIG. 3, the laminate 30 of the present disclosure includes the polyethylene multi-layer substrate 10 of the present disclosure and a heat seal layer 32. In one embodiment, the laminate 30 further includes a printing layer (not shown) on the multi-layer substrate 10. The printing layer is usually formed on the surface layer where the heat seal layer is provided in the multi-layer substrate, for example, on layer (A) described above.

[0077] In one embodiment, as shown in FIG. 4, 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. 5, the laminate 30 includes an adhesive layer 36 between the multilayer substrate 10 and the heat-seal layer 32.

[0078] In the laminate of the present disclosure, the content ratio of polyethylene is preferably 90% by mass or more. Thereby, the recyclability of the laminate can be improved. The content ratio of polyethylene in the laminate means the ratio of the content of polyethylene to the sum of the contents of the resin materials in each layer constituting the laminate.

[0079] <Heat-seal layer> The heat-seal layer is preferably made of polyethylene. By adopting such a configuration, a laminate for packaging materials can be obtained which has sufficient rigidity, strength and heat resistance and is excellent in recyclability.

[0080] Hereinafter, the above-mentioned recyclability will be described. Compared with other thermoplastic resin films, the polyethylene film has inferior heat resistance, so it may be deformed during heat-sealing when used as a substrate for packaging materials. In addition, since the polyethylene film has inferior rigidity, its printability is low and a clear image cannot be formed on its surface. Further, the polyethylene film does not have high strength and cannot satisfy the durability required for the outer layer of the packaging material. Therefore, a laminate is obtained by laminating a resin film (substrate) excellent in rigidity, strength and heat resistance such as a polyester film and a nylon film with a polyethylene film (heat-seal layer), and the laminate end is heat-sealed so that the polyethylene film side of the laminate is on the inside, thereby manufacturing a packaging material.

[0081] In recent years, with the increasing demand for building a recycling-oriented society, attempts have been made to recycle and use packaging materials. However, when a laminate is manufactured by laminating different 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.

[0082] On the other hand, since the polyethylene multilayer base material of the present disclosure is stretched as described above, it is excellent in rigidity, strength, heat resistance, and ink adhesion compared to conventional polyethylene films. Therefore, the polyethylene multilayer base material of the present disclosure can be used, for example, as a base material for packaging materials, and a clear image can be formed on the surface of the multilayer base material.

[0083] Further, in one embodiment, the laminate of the present disclosure includes the polyethylene multilayer base material of the present disclosure and a heat-sealing layer containing polyethylene (hereinafter also referred to as a "heat-sealable polyethylene layer"). In one embodiment, a printing layer (image) is formed on at least one surface of the multilayer base material. Since deterioration of the image over time can be prevented, it is preferable that the printing layer is formed on the side where the heat-sealable polyethylene layer in the multilayer base material is provided.

[0084] In the above laminate including the polyethylene multilayer base material of the present disclosure and the heat-sealable polyethylene layer, in one embodiment, all the resin layers included in the laminate are polyethylene layers, and the laminate does not include different resin films such as polyester films and nylon films. Further, the polyethylene multilayer base material satisfies the rigidity, strength, and heat resistance required for the outer layer film of the packaging material, and the heat-sealable polyethylene layer enables packaging. Therefore, the above laminate is suitable as a material constituting a packaging material that requires recyclability.

[0085] In one embodiment, the laminate of the present disclosure consists only of the above multilayer base material with a printing layer formed thereon as needed and a heat-sealing layer made of polyethylene. Thereby, 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.

[0086] The heat-sealing layer is usually an un-stretched layer. For example, an unstretched polyethylene film can be laminated onto a multi-layer substrate or the like via an adhesive layer as needed, or a resin material containing polyethylene can be melt-extruded onto a multi-layer substrate or the like to form the heat-sealing layer. Examples of the adhesive layer include the adhesive layers described below.

[0087] Examples of the polyethylene constituting the heat-sealing layer include high-density polyethylene, medium-density polyethylene, low-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene. From the perspective of heat-sealing properties, low-density polyethylene, linear low-density polyethylene, and ultra-low-density polyethylene are preferred. From the perspective of reducing environmental impact, polyethylene derived from biomass or recycled polyethylene may be used.

[0088] The content ratio of polyethylene in the heat-sealing layer is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more. Thereby, the recyclability of the laminate can be improved. The heat-sealing layer may contain one or more of the above additives.

[0089] The heat-sealing layer may be one layer or two or more layers. In one embodiment, the number of layers of the heat-sealing layer is 1 or more and 3 or less. The thickness of the heat-sealing layer is, for example, 10 μm or more and 300 μm or less. From the perspectives of the strength of the heat-sealing layer and the processability of the laminate, the thickness of the heat-sealing layer is preferably appropriately changed according to the mass of the content filled in the packaging material, for example, manufactured by the laminate of the present disclosure.

[0090] For example, when the packaging material is a pouch, the thickness of the heat-sealing layer is preferably 20 μm or more and 60 μm or less. In this case, for example, a content of 1 g or more and 200 g or less can be well filled in the pouch. For example, when the packaging material is a stand-up pouch, the thickness of the heat-sealing layer is preferably 50 μm or more and 200 μm or less. In this case, for example, contents of 50 g or more and 2000 g or less can be satisfactorily filled into the stand-up pouch.

[0091] <Barrier layer> In one embodiment, the laminate of the present disclosure includes a barrier layer between the multilayer base material and the heat-sealing layer. Thereby, the gas barrier property of the laminate, specifically, the oxygen barrier property and the water vapor barrier property can be improved. The barrier layer may be formed on the surface of the multilayer base material or on the surface of the heat-sealing layer. Further, the barrier layer may be provided between the multilayer base material and the heat-sealing layer via an adhesive or the like.

[0092] In one embodiment, the barrier layer is a vapor deposition layer. The vapor deposition 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 deposition layer is preferable.

[0093] The thickness of the barrier layer is preferably 1 nm or more and 150 nm or less, more preferably 5 nm or more and 60 nm or less, and still more preferably 10 nm or more and 40 nm or less. By setting the thickness of the barrier layer to 1 nm or more, the oxygen barrier property and the water vapor barrier property of the laminate can be further improved. By setting the thickness of the barrier layer to 150 nm or less, the generation of cracks in the barrier layer can be suppressed and the recyclability of the laminate can be improved.

[0094] Examples of the method for forming the barrier layer include physical vapor deposition methods (PVD methods) such as vacuum vapor deposition, sputtering, and ion plating; and chemical vapor deposition methods (CVD methods) such as plasma chemical vapor deposition, thermal chemical vapor deposition, and photo chemical vapor deposition. The barrier layer may be a composite film including two or more layers of barrier layers of different inorganic oxides formed by using both physical vapor deposition methods and chemical vapor deposition methods in combination.

[0095] As for the degree of vacuum in the vapor deposition chamber, before introducing oxygen, it is preferably about 10 -2 ~10 -8 mbar, and after introducing oxygen, it is preferably about 10 -1 ~10 -6 mbar. The amount of oxygen introduced etc. varies depending on the size of the vapor deposition machine etc. As the oxygen to be introduced, inert gases such as argon gas, helium gas and nitrogen gas may be used as carrier gases within a non-obstructive range. The conveyance speed of the multilayer substrate is, for example, about 10 to 800 m / min.

[0096] It is preferable that the above-described surface treatment is performed on the surface of the barrier layer. Thereby, the adhesiveness between the barrier layer and the adjacent layer can be improved.

[0097] When the vapor deposition 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 deposition layer, and a barrier layer including the vapor deposition layer and the barrier coat layer may be used.

[0098] In one embodiment, the barrier coat layer is composed of a gas barrier resin. Examples of the gas barrier resin include ethylene-vinyl alcohol copolymer (EVOH), polyvinyl alcohol, polyacrylonitrile, nylon 6, nylon 6,6 and polyamide resins such as polymetaxylylene adipamide (MXD6), polyester resins, polyurethane resins, and (meth)acrylic resins.

[0099] The thickness of the barrier coat layer is preferably 0.01 μm or more and 10 μm or less, more preferably 0.1 μm or more and 5 μm or less. By setting the thickness of the barrier coat layer to 0.01 μm or more, the gas barrier property can be further improved. By setting the thickness of the barrier coat layer to 10 μm or less, the processability of the laminate can be improved. Also, it can be made into a laminate suitably usable for producing a single-material packaging container.

[0100] The barrier coat 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, applying the resulting coating solution, and drying it.

[0101] In other embodiments, the barrier coat layer is a gas barrier coating film formed from a composition containing a hydrolyzate of a metal alkoxide or a hydrolytic 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 method catalyst, water, an organic solvent, and the like. By providing such a barrier coat layer on the vapor deposition layer, the occurrence of cracks in the vapor deposition layer can be effectively prevented.

[0102] 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 represent an organic group having 1 to 8 carbon atoms, M represents a metal atom, n represents an integer of 0 or more, m represents an integer of 1 or more, and n + m represents the valence of M.

[0103] R 1 and R 2 Examples of the organic group represented by include alkyl groups such as methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group and i-butyl group. Examples of the metal atom M include silicon, zirconium, titanium and aluminum.

[0104] Examples of the metal alkoxide satisfying the above general formula include tetramethoxysilane (Si(OCH3)4), tetraethoxysilane (Si(OC2H5)4), tetrapropoxysilane (Si(OC3H7)4), and tetrabutoxysilane (Si(OC4H9)4).

[0105] It is preferable to use a silane coupling agent together with the above metal alkoxide. As the silane coupling agent, a known organoalkoxysilane containing an organic reactive group can be used.

[0106] As the water-soluble polymer, polyvinyl alcohol and ethylene-vinyl alcohol copolymer are preferable, and from the viewpoints of oxygen barrier property, water vapor barrier property, water resistance and weather resistance, it is preferable to use them in combination.

[0107] As the sol-gel method catalyst, an acid or an amine-based compound is suitable.

[0108] The above composition may further contain an acid. The acid is used as a catalyst for hydrolysis of the sol-gel method catalyst, mainly metal alkoxide and silane coupling agent, etc. 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.

[0109] The above composition may contain an organic solvent. Examples of the organic solvent include methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol and n-butanol.

[0110] The thickness of the gas barrier coating film is preferably 0.01 μm or more and 100 μm or less, more preferably 0.1 μm or more and 50 μm or less. Thereby, the gas barrier property can be further improved. By setting the thickness of the gas barrier coating film to 0.01 μm or more, the oxygen barrier property and water vapor barrier property of the laminate can be improved, and the generation of cracks in the vapor deposition layer can be prevented. By setting the thickness of the gas barrier coating film to 100 μm or less, a laminate that can be suitably used for producing a monomaterial packaging container can be obtained.

[0111] The gas barrier coating film can be formed by applying a composition containing the above materials by means known in the art such as roll coating using a gravure roll coater, spray coating, spin coating, dipping, brushing, bar coating, and applicator, and subjecting the composition to polycondensation by the sol-gel method.

[0112] Hereinafter, an embodiment of a method for forming a gas barrier coating film will be described below. First, a metal alkoxide, a water-soluble polymer, a sol-gel catalyst, water, an organic solvent, and, if necessary, a silane coupling agent, etc. are mixed to prepare a composition. In the composition, the polycondensation reaction gradually proceeds.

[0113] Next, the composition is applied and dried on the vapor deposition layer by the above-mentioned conventionally known means. By this drying, the polycondensation reaction of the metal alkoxide and the water-soluble polymer (and also the silane coupling agent if the composition contains a silane coupling agent) further proceeds, and a layer of a composite polymer is formed. Finally, a gas barrier coating film can be formed by heating.

[0114] <Adhesive layer> In one embodiment, the laminate of the present disclosure includes an adhesive layer between any layers (for example, between a multilayer substrate and a barrier layer, between a barrier layer and a heat-sealing layer, or between a multilayer substrate and a heat-sealing layer). Thereby, the adhesion between the layers included in the laminate can be improved.

[0115] The adhesive layer contains one or more kinds of adhesives. Examples of the adhesive include a one-component curable adhesive, a two-component curable adhesive, and a non-curable adhesive.

[0116] The adhesive may be a solventless adhesive or a solvent-based adhesive. From the perspective of environmental impact, a solventless adhesive is preferred. Examples of solventless adhesives include polyether-based adhesives, polyester-based adhesives, silicone-based adhesives, epoxy-based adhesives, and urethane-based adhesives. Among these, a two-component curable urethane-based adhesive is preferred. Examples of solvent-based adhesives include rubber-based adhesives, vinyl-based adhesives, silicone-based adhesives, epoxy-based adhesives, phenol-based adhesives, and olefin-based adhesives.

[0117] In the case of the adhesive layer adjacent to the barrier layer such as the aluminum vapor deposition layer, it is preferably composed of a cured product of a resin composition containing a polyester polyol, an isocyanate compound, and a phosphoric acid-modified compound. By configuring the adhesive layer in this way, the oxygen barrier property and water vapor barrier property of the laminate of the present disclosure can be further improved.

[0118] From the viewpoints 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 still more preferably 1 μm or more and 4.5 μm or less.

[0119] The adhesive layer can be formed, for example, by applying and drying an adhesive on a multilayer substrate or the like by methods such as the direct gravure roll coating method, the gravure roll coating method, the kiss coating method, the reverse roll coating method, the fountain method, and the transfer roll coating method.

[0120] [Use] The polyethylene multilayer substrate, the printed substrate, and the laminate of the present disclosure can be suitably used for packaging material applications such as packaging bags. The packaging material of the present disclosure includes the polyethylene multilayer substrate, the printed substrate, or the laminate of the present disclosure.

[0121] For example, the laminate can be folded in half so that the multi-layer substrate is on the outside and the heat-sealing layer is on the inside, and the ends and the like are heat-sealed to produce a packaging material. Also, a plurality of the laminates can be stacked so that the heat-sealing layers face each other, and the ends and the like are heat-sealed to produce a packaging material. All of the packaging material may be composed of the laminate, or a part of the packaging material may be composed of the laminate.

[0122] Examples of the heat-sealing form in the packaging material include, for example, side-sealing type, two-side sealing type, three-side sealing type, four-side sealing type, envelope pasting seal type, clasp pasting seal type (pillow seal type), pleat attachment seal type, flat bottom seal type, corner bottom seal type, and gusset type. Also, a stand-up pouch for self-supporting packaging is possible. Examples of the heat-sealing method include bar sealing, rotary roll sealing, belt sealing, impulse sealing, high-frequency sealing, and ultrasonic sealing.

[0123] For example, a stand-up pouch having a body portion and a bottom portion can be manufactured as follows. First, one or more of the laminates are formed into a cylindrical shape with the heat-sealing layer on the inside and heat-sealed to form the body portion. Next, a further laminate is folded into a V shape with the heat-sealing layer on the outside. The V-shaped laminate is sandwiched between one end of the body portion and heat-sealed to form the bottom portion.

[0124] In the stand-up pouch, only the body portion may be formed of the laminate, only the bottom portion may be formed of the laminate, or both the body portion and the bottom portion may be formed of the laminate.

[0125] Examples of the contents filled in the packaging material include, for example, liquids, powders, and gels, and may be food or non-food. After filling the contents into the packaging material, the opening of the packaging material is heat-sealed to obtain a package.

[0126] The present disclosure relates to, for example, the following [1] to

[14] . [1] A polyethylene multilayer substrate comprising, in this order in the thickness direction, a layer (A) containing medium-density polyethylene, two or more multilayer intermediate layers (B) each containing polyethylene, and a layer (C) containing medium-density polyethylene. The multilayer substrate has been subjected to a stretching treatment. When any two adjacent polyethylene-containing layers in the thickness direction of the multilayer substrate are described 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 following polyethylene multilayer substrate. [2] The absolute value of the above difference is 0.025 g / cm 3 The polyethylene multilayer substrate according to [1] above. [3] The polyethylene multilayer substrate according to [1] or [2] above, wherein the number of layers of the multilayer intermediate layer (B) is 3 or more and 5 or less. [4] The polyethylene multilayer substrate according to any one of [1] to [3] above, wherein the content ratio of polyethylene in the multilayer substrate is 80% by mass or more. [5] A printed substrate comprising the polyethylene multilayer substrate according to any one of [1] to [4] above and a printed layer formed on the multilayer substrate. [6] A laminate comprising the polyethylene multilayer substrate according to any one of [1] to [4] above and a heat-sealing layer. [7] The laminate according to [6] above, wherein the heat-sealing 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 [6] to [8] above, further comprising a barrier layer between the multilayer substrate and the heat-sealing layer.

[10] The laminate according to [9] above, wherein the barrier layer is a vapor deposition 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 [6] to [8] above, further comprising an adhesive layer between the multilayer substrate and the heat-sealing layer.

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

[12] above, which is used for packaging materials.

[14] A packaging material comprising the polyethylene multilayer base material according to any one of [1] to [4] above, the printed base material according to [5] above, or the laminate according to any one of [6] to

[13] above.

Examples

[0127] The multilayer base material of the present disclosure will be further specifically described based on examples, but the multilayer base material of the present disclosure is not limited by the examples. Hereinafter, "parts by mass" will be simply described as "parts".

[0128] 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: 0.941 g / cm 3 , Melting point: 129 °C, MFR: 1.3 g / 10 min, Manufactured by Dowchemical · High-density polyethylene (hereinafter referred to as "HDPE"): Product name: Elite5960G Density: 0.960 g / cm 3 , Melting point: 134 °C, MFR: 0.8 g / 10 min, Manufactured by Dowchemical · Linear low-density polyethylene (hereinafter referred to as "LLDPE"): Product name: Elite5400G Density: 0.916 g / cm 3 , Melting point: 123 °C, MFR: 1.3 g / 10 min, Manufactured by Dowchemical · Blend polyethylene A 50 parts of MDPE and 50 parts of HDPE were mixed to obtain blend polyethylene A (hereinafter referred to as "blend PE(A)") with an average density of 0.951 g / cm 3 . · Blend polyethylene B 50 parts of MDPE and 50 parts of LLDPE were mixed to obtain a blended polyethylene B with an average density of 0.929 g / cm 3 (hereinafter referred to as "blended PE (B)"). · Blended polyethylene C 70 parts of MDPE and 30 parts of HDPE were mixed to obtain a blended polyethylene C with an average density of 0.947 g / cm 3 (hereinafter referred to as "blended PE (C)"). · Blended polyethylene D 30 parts of MDPE and 70 parts of HDPE were mixed to obtain a blended polyethylene D with an average density of 0.954 g / cm 3 (hereinafter referred to as "blended PE (D)").

[0129] [Example 1]

[0130] MDPE, HDPE and blended PE (A) were co-extruded in five layers by an inflation molding method with a layer thickness ratio of MDPE layer (15 μm) / HDPE layer (22.5 μm) / blended PE (A) layer (50 μm) / HDPE layer (22.5 μm) / MDPE layer (15 μm) to form a tubular film, and a polyethylene film with a total thickness of 125 μm was obtained. The tubular film was folded at the nip portion and made into a double layer. The numerical values in parentheses indicate the layer thicknesses. The polyethylene film prepared above was stretched in the longitudinal direction (MD) at a stretching ratio of 5 times, and further, after corona discharge treatment was performed on the MDPE layer (surface layer) on one side, the ends were slit and divided into two to obtain a stretched multilayer substrate with a thickness of 25 μm.

[0131] [Examples 2 to 4 and Comparative Examples 1 to 2] A polyethylene film and a stretched multilayer substrate were obtained in the same manner as in Example 1 except that the layer configuration was changed as described in Table 1.

[0132] [Ink Adhesion Evaluation] On the corona discharge-treated surface side of the drawn multilayer base material obtained in the examples and comparative examples, an image was formed by the gravure printing method using an oil-based gravure ink (manufactured by DIC Graphics Co., Ltd., trade name: Finart). The image formed on the drawn multilayer base material was visually observed and evaluated based on the following evaluation criteria.

[0133] (Evaluation Criteria) AA: When a cellophane tape (registered trademark) was attached to and peeled off from the image-forming surface side of the drawn multilayer base material, the ink adhesion to the drawn multilayer base material was good, and no ink peeling occurred on the cellophane tape (registered trademark). BB: When a cellophane tape (registered trademark) was attached to and peeled off from the image-forming surface side of the drawn multilayer base material, the ink adhesion to the drawn multilayer base material was weak, and ink peeling occurred on the cellophane tape (registered trademark).

[0134] [Interlayer Separation Evaluation] A first linear low-density polyethylene (manufactured by Prime Polymer Co., Ltd., SP2520, density: 0.925 g / cm 3 , melting point: 122 °C) and a second linear low-density polyethylene (manufactured by Prime Polymer Co., Ltd., SP1520, density: 0.913 g / cm 3 , melting point: 116 °C) were multilayer extruded into a film by the inflation molding method to produce an undrawn polyethylene film having a 20-μm-thick first linear low-density polyethylene layer and a 20-μm-thick second linear low-density polyethylene layer. This undrawn polyethylene film was used as a heat-sealing layer as described below.

[0135] The first linear low-density polyethylene layer side of the undrawn polyethylene film (heat-sealing layer) produced above and the drawn multilayer base material obtained in the examples and comparative examples were dry laminated via a two-component curable urethane-based adhesive (manufactured by Rock Paint Co., Ltd., Ru-77T / H-7) to obtain a laminate.

[0136] The laminate produced above was cut into 10 cm × 10 cm, and three sample pieces were prepared for each. Each sample piece was folded in half with the heat-sealing layer side on the inside, and using a heat-sealing tester, a 1 cm × 10 cm area was heat-sealed under the conditions of a temperature of 140°C, a pressure of 1 kgf / cm 2 , and a time of 1 second.

[0137] The sample pieces after heat-sealing were cut into strips with a width of 15 mm. Both ends that were not heat-sealed were gripped by a tensile testing machine, and a tensile test was carried out under the conditions of a speed of 300 mm / min and a load range of 50 N to confirm the presence or absence of delamination between the layers of the stretched multi-layer base material. AA: No delamination occurred between the layers of the stretched multi-layer base material during the tensile test. BB: Delamination occurred between the layers of the stretched multi-layer base material during the tensile test.

[0138] [Haze Evaluation] The haze values of the stretched multi-layer base materials obtained in the examples and comparative examples were measured in accordance with JIS K7136.

[0139] [Rigidity Evaluation] The stretched multi-layer base materials obtained in the examples and comparative examples were cut into test pieces with a width of 10 mm, and the rigidity of the test pieces was measured using a loop stiffness measuring tester (manufactured by Toyo Seiki Seisakusho, product name: Loop Stiffness Tester). The length of the loop was 60 mm.

[0140] [Strength Evaluation] Dumbbell-shaped test pieces with a width of 10 mm were cut out from the stretched multi-layer base materials obtained in the examples and comparative examples. The tensile strength in the MD direction of the above test pieces was measured using a tensile testing machine (manufactured by Orientec, RTC-1310A). The distance between the chucks was 10 mm, and the tensile speed was 300 mm / min. The above evaluation results are shown in Table 1.

[0141] [Table 1] [Explanation of Signs]

[0142] 10: Polyethylene multilayer substrate 12: Layer (A) 14: Layer (C) 16: Multilayer intermediate layer (B) 18: Layer containing high-density polyethylene 20: Layer containing medium-density polyethylene and high-density polyethylene 22: Layer containing high-density polyethylene 30: Laminate 32: Heat-sealing layer 34: Barrier layer 36: Adhesive layer

Claims

1. A layer (A) containing medium-density polyethylene, Two or more multi-layer intermediate layers (B) each containing polyethylene, A layer (C) containing medium-density polyethylene And a polyethylene multi-layer base material provided in this order in the thickness direction, The multi-layer base material has been subjected to a stretching treatment, When the arbitrarily adjacent polyethylene-containing layers in the multilayer substrate in the thickness direction are described 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 as follows: A polyethylene multi-layer base material.

2. The absolute value of the difference is 0.025 g / cm ３ The polyethylene multilayer substrate according to claim 1, wherein the absolute value is 0.025 g / cm or less.

3. The polyethylene multi-layer base material according to claim 1 or 2, wherein the number of layers of the multi-layer intermediate layer (B) is 3 or more and 5 or less.

4. The polyethylene multi-layer base material according to any one of claims 1 to 3, wherein the content ratio of polyethylene in the multi-layer base material is 80% by mass or more.

5. A printed base material comprising the polyethylene multi-layer base material according to any one of claims 1 to 4, And a printed layer formed on the multi-layer base material.

6. A laminate comprising the polyethylene multi-layer base material according to any one of claims 1 to 4, And a heat-sealing layer.

7. The laminate according to claim 6, wherein the heat-sealing layer contains polyethylene.

8. The laminate according to claim 6 or 7, further comprising a printed layer on the multi-layer base material.

9. The laminate according to any one of claims 6 to 8, further comprising a barrier layer between the multi-layer base material and the heat-sealing layer.

10. The laminate according to claim 9, wherein the barrier layer is a vapor deposition layer.

11. The laminate according to claim 9 or 10, further comprising an adhesive layer between the multi-layer base material and the barrier layer.

12. The laminate according to any one of claims 6 to 8, further comprising an adhesive layer between the multi-layer base material and the heat-sealing layer.

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

14. A packaging material comprising the polyethylene multi-layer base material according to any one of claims 1 to 4, the printed base material according to claim 5, or the laminate according to any one of claims 6 to 13.

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