Stacked body and packaging material

Abstract

The laminate of the present application comprises: a substrate; an intermediate layer; a heat-seal layer; a first adhesive layer provided between the substrate and the intermediate layer; and a second adhesive layer provided between the intermediate layer and the heat-seal layer. The substrate, the intermediate layer, and the heat-seal layer are composed of polyethylene. When the substrate is a stretched polyethylene film, the intermediate layer is an unstretched polyethylene film, and when the intermediate layer is a stretched polyethylene film, the substrate is an unstretched polyethylene film. The proportion of polyethylene in the laminate is 90 mass% or more.

Description

Technical Field

[0001] This invention relates to laminates, and more specifically to laminates with excellent recyclability. It also relates to packaging materials using this laminate.

[0002] This application claims priority based on Japanese Patent Application No. 2020-209293, filed on December 17, 2020, the contents of which are incorporated herein by reference. Background Technology

[0003] With increasing calls for building a circular society, there is a growing demand for packaging materials with high recyclability. Generally, packaging materials are considered highly recyclable when the main resin content is above 90% by mass. However, most existing packaging materials are composed of multiple resin materials and do not meet this standard, therefore they are not currently being recycled.

[0004] Regarding this issue, Patent Document 1 describes a laminate comprising a substrate, an adhesive layer, and a heat-sealing layer, wherein the substrate and the heat-sealing layer are made of polyethylene. By using the same material to construct the substrate and the heat-sealing layer, the aforementioned standard can be easily achieved.

[0005] Stretched polyethylene film is used as the substrate.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2020-55157 Summary of the Invention

[0009] The technical problem that the invention aims to solve

[0010] The inventors have found that when the laminate described in Patent Document 1 is applied to packaging materials, the strength is sometimes insufficient.

[0011] The inventors have solved this problem while maintaining high recyclability.

[0012] The purpose of this invention is to provide a laminate that has sufficient strength and is easy to recycle when used in packaging materials.

[0013] Means for solving technical problems

[0014] The first aspect of the present invention is a laminate comprising: a substrate; an intermediate layer; a heat-sealing layer; a first adhesive layer disposed between the substrate and the intermediate layer; and a second adhesive layer disposed between the intermediate layer and the heat-sealing layer.

[0015] The substrate, intermediate layer, and heat-sealing layer are composed of polyethylene.

[0016] When the substrate is a stretched polyethylene film, the intermediate layer is an unstretched polyethylene film; when the intermediate layer is a stretched polyethylene film, the substrate is an unstretched polyethylene film.

[0017] Polyethylene accounts for more than 90% by mass in the laminate.

[0018] The second aspect of the present invention is a packaging material formed by bonding heat-sealing layers using a laminate of the first aspect.

[0019] Invention Effects

[0020] The laminate of the present invention has sufficient strength when applied to packaging materials and is easy to recycle. Attached Figure Description

[0021] Figure 1 This is a schematic cross-sectional view of the laminated body according to the first embodiment of the present invention.

[0022] Figure 2 This is a schematic cross-sectional view of the laminated body according to the second embodiment of the present invention.

[0023] Figure 3 This is a schematic cross-sectional view of the laminated body in an embodiment. Detailed Implementation

[0024] The following is for reference Figure 1 as well as Figure 2 The first embodiment of the present invention will be described.

[0025] Figure 1 This is a schematic cross-sectional view of the laminate 1 according to this embodiment. The laminate 1 includes a substrate 10, an intermediate layer 20, and a heat-sealing layer 30. The substrate 10 and the intermediate layer 20 are bonded together by a first adhesive layer 40. The intermediate layer 20 and the heat-sealing layer 30 are bonded together by a second adhesive layer 50.

[0026] The substrate 10 is a stretch film made of polyethylene. It is the part that becomes the outer surface when the packaging material is formed using the laminate 1.

[0027] The substrate 10 can be a uniaxially stretched film or a biaxially stretched film. The stretch ratio in the machine direction (MD) of the stretched film is preferably 2 times or more and 10 times or less, more preferably 3 times or more and 7 times or less. By making the stretch ratio 2 times or more, the strength and heat resistance of the laminate 1 can be improved. There is no particular upper limit to the stretch ratio, but from the viewpoint of the tensile strength of the stretched film, it is preferably set to 10 times or less.

[0028] When the film is biaxially stretched, the stretch ratio in the direction orthogonal to the MD (Transverse Direction, TD) is preferably 2 times or more and 10 times or less, more preferably 3 times or more and 7 times or less. The stretch ratio in the MD and the stretch ratio in the TD may also be different, but they are preferably the same.

[0029] From the viewpoints of strength, heat resistance, and tensile suitability, high-density polyethylene (HDPE) and medium-density polyethylene (MDPE) are preferred as the polyethylene contained in the substrate 10, and MDPE is more preferred from the viewpoint of tensile suitability. A multilayer stretched polyethylene film obtained by co-extruding polyethylene of different densities can also be used as the substrate 10.

[0030] As HDPE, a density of 0.945 g / cm³ can be used. 3 The above-mentioned polyethylene, as MDPE, can be used with a density of 0.925 g / cm³. 3 Above and below 0.945 g / cm³ 3 Polyethylene.

[0031] The aforementioned polyethylenes with different densities or branching can be obtained by appropriately selecting polymerization methods. For example, it is preferable to use multi-site catalysts such as Ziegler-Natta catalysts or single-site catalysts such as metallocene catalysts as polymerization catalysts, and to carry out the polymerization in one or more stages using any one of the following methods: gas-phase polymerization, slurry polymerization, solution polymerization, and high-pressure ionic polymerization.

[0032] The aforementioned single-site catalyst refers to a catalyst capable of forming uniform active species, typically prepared by contacting a metallocene transition metal compound or a non-metallocene transition metal compound with an activation auxiliary catalyst. Compared to multi-site catalysts, single-site catalysts have a more uniform active site structure, enabling the polymerization of high-molecular-weight polymers with highly uniform structures, and are therefore preferred. Metallocene catalysts are particularly preferred as single-site catalysts. A metallocene catalyst is a catalyst comprising a Group IV transition metal compound containing a ligand with a cyclopentadiene skeleton, an auxiliary catalyst, an organometallic compound as needed, and a support.

[0033] In the aforementioned Group IV transition metal compounds containing ligands with a cyclopentadiene skeleton, the cyclopentadiene skeleton refers to cyclopentadienyl, substituted cyclopentadienyl, etc. A substituted cyclopentadienyl group is a group having at least one substituent selected from hydrocarbon groups having 1 to 30 carbon atoms, silyl, silyl-substituted alkyl, silyl-substituted aryl, cyano, cyanoalkyl, cyanoaryl, halogen, haloalkyl, halosilyl, etc. The substituted cyclopentadienyl group may have two or more substituents, and these substituents may bond with each other to form a ring, such as an indenyl ring, fluorenyl ring, azuleyl ring, or its hydride. The ring formed by the bonding of substituents may further have substituents on each other.

[0034] In Group IV transition metal compounds containing ligands with a cyclopentadiene skeleton, examples of such transition metals include zirconium, titanium, and hafnium, with zirconium and hafnium being particularly preferred. Preferably, the transition metal compound contains two ligands with a cyclopentadiene skeleton, each ligand bonded to each other by a crosslinking group. Furthermore, examples of crosslinking groups include substituted methylene silanes, dialkylmethylene silanes, diarylmethylene silanes, dialkylgermanium silanes, and diarylgermanium silanes having 1 to 4 carbon atoms. Substituted methylene silanes are preferred. The aforementioned Group IV transition metal compounds containing ligands with a cyclopentadiene skeleton can be used as catalyst components in the form of one or a mixture of two or more.

[0035] As an auxiliary catalyst, it refers to a substance that can make the aforementioned transition metal compounds of Group IV in the periodic table effective as polymerization catalysts, or that can balance the ionic charges of catalytically activated states. Examples of auxiliary catalysts include benzene-soluble aluminoxanes or benzene-insoluble organoalumina compounds, ion-exchangeable layered silicates, boron compounds, ionic compounds formed by cations containing or without active hydrogen groups and noncoordinate anions, lanthanide salts such as lanthanum oxide, tin oxide, and fluorine-containing phenoxy compounds.

[0036] Group IV transition metal compounds containing ligands with a cyclopentadiene skeleton can also be used on supports of inorganic or organic compounds. Porous oxides of inorganic or organic compounds are preferred as supports, specifically ion-exchangeable layered silicates such as montmorillonite, SiO2, Al2O3, MgO, ZrO2, TiO2, B2O3, CaO, ZnO, BaO, ThO2, and mixtures thereof. Organometallic compounds used as needed include organoaluminum compounds, organomagnesium compounds, and organozinc compounds. Organoaluminum compounds are preferred.

[0037] Without impairing the characteristics of the present invention, copolymers of ethylene with other monomers may also be used. Examples of ethylene copolymers include copolymers formed from ethylene and α-olefins having 3 to 20 carbon atoms. 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. Furthermore, copolymers with vinyl acetate or acrylates may also be used, provided that the scope of the present invention is not impaired.

[0038] In this invention, ethylene derived from biomass can be used as a raw material for obtaining the aforementioned high-density polyethylene, etc., instead of ethylene obtained from fossil fuels. Since this biomass-derived polyethylene is a carbon-neutral material, it can be used to produce packaging materials with a lower environmental impact. This biomass-derived polyethylene can be manufactured, for example, using the method described in Japanese Patent Application Publication No. 2013-177531. Alternatively, commercially available biomass-derived polyethylene (e.g., Green PE, commercially available from Braskem Corporation) can also be used.

[0039] Polyethylene that has been recycled through mechanical recycling can also be used in the substrate layer 10. Here, mechanical recycling generally refers to the following method: after crushing the recycled polyethylene film and washing it with alkali to remove dirt and foreign matter from the film surface, drying it under high temperature and reduced pressure for a certain period of time to allow the pollutants remaining inside the film to diffuse and purify it, removing the dirt from the polyethylene film, melting and forming the film again, and turning it into a polyethylene film again.

[0040] In the substrate 10, an ink layer 11 is formed on the first surface 10a on the side that is bonded to the intermediate layer 20. The ink layer 11 imparts displays or various patterns related to the contents to the laminate. Since the ink layer 11 provided on the first surface 10a will not be exposed to the outer surface when it becomes packaging material, damage or deterioration of the display after manufacturing can be suppressed.

[0041] By using an ink layer 11 with light-blocking properties to form an ink layer 11 on the entire first surface 10a, the contents can be protected from light. This light-blocking ink layer can be made, for example, by repeatedly printing a colored ink containing white and black pigments, with the black pigments accounting for 3 to 5 wt% of the total pigments, onto one or more layers of white ink formed by full-surface printing, thereby forming a colored ink layer with a chroma of 1 to 4 according to the Munsell color system.

[0042] By combining a light-blocking ink layer with a printed layer (image printing layer) of patterns or text formed from non-light-blocking ink, the appearance of the ink layer 11 can be freely set while simultaneously imparting light-blocking properties. In this case, an image printing layer is first formed on the substrate 10, followed by the formation of the light-blocking ink layer, thereby improving the visibility of the image.

[0043] The ink layer 11 is preferably formed from biomass-derived ink. Therefore, packaging materials with a lower environmental impact can be produced using the laminate 1. The method of image formation is not particularly limited, and various conventionally known printing methods such as gravure printing, offset printing, and flexographic printing can be cited. From an environmental perspective, flexographic printing is preferred.

[0044] To improve the adhesion of the ink layer 11, surface treatments such as corona treatment or plasma treatment can be applied to the first surface 10a of the substrate 10.

[0045] Since the substrate 10 is a stretched film with excellent transparency, the display formed by the ink layer 11 disposed on the first surface 10a side can preferably be seen in the laminate 1. The transparency that makes the preferred visibility possible is 20% or less, and becomes even better when the haze value is 10% or less, as measured according to JIS K7105.

[0046] The thickness of the substrate 10 is preferably 10 μm or more and 50 μm or less, more preferably 12 μm or more and 35 μm or less. By making the thickness of the substrate 10 10 μm or more, the strength of the laminate 1 can be improved. By making the thickness of the substrate 10 50 μm or less, the processability of the laminate 1 can be improved.

[0047] The substrate layer 10 may contain additives without impairing the characteristics of the present invention. Examples of additives that may be used include crosslinking agents, antioxidants, anti-adhesion agents, lubricants, UV absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, and modified resins.

[0048] The thickness of the substrate 10 is preferably 10 μm or more and 50 μm or less, more preferably 12 μm or more and 35 μm or less. By making the thickness of the substrate 10 10 μm or more, the strength of the laminate 1 can be improved. In addition, by making the thickness of the substrate 10 50 μm or less, the processability of the laminate 1 can be improved.

[0049] The interlayer 20 is an unstretched film made of polyethylene. From the viewpoint of strength and heat resistance, HDPE and MDPE are preferred as the polyethylene contained in the interlayer 20. Like the substrate 10, the interlayer 20 can also be a multilayer film.

[0050] The thickness of the intermediate layer 20 is preferably 9 μm or more and 50 μm or less, more preferably 12 μm or more and 30 μm or less. By making the thickness of the intermediate layer 20 9 μm or more, the strength and heat resistance of the laminate 1 can be improved. By making the thickness of the intermediate layer 20 50 μm or less, the processability of the laminate 1 can be improved.

[0051] The intermediate layer 20 can be produced by forming a film of polyethylene using methods such as T-molding or blow molding.

[0052] When fabricating the intermediate layer 20 using the T-die method, the melt flow rate (MFR) of the polyethylene is preferably 3 g / 10 min or more and 20 g / 10 min or less. By setting the MFR to 3 g / 10 min or more, the processability of the laminate 1 can be improved. Furthermore, by setting the MFR to 20 g / 10 min or less, breakage of the fabricated substrate layer can be prevented.

[0053] When producing the intermediate layer 20 using the blow-blown method, it is preferable that the molecular weight filtration rate (MFR) of the polyethylene is 0.5 g / 10 min or more and 5 g / 10 min or less. By setting the MFR to 0.5 g / 10 min or more, the processability of the laminate 1 can be improved. In addition, by setting the MFR to 5 g / 10 min or less, the film-forming properties can be improved.

[0054] In addition to the above methods, the unstretched membrane that becomes the intermediate layer 20 can also be obtained from the membrane in circulation.

[0055] A gas barrier layer 21 is formed on one side of the intermediate layer 20. In this embodiment, the gas barrier layer 21 is formed on the first side 20a facing the substrate 10, but it may also be formed on the opposite side.

[0056] The gas barrier layer 21 imparts oxygen barrier and water vapor barrier properties to the laminate 1.

[0057] Examples of components for the gas barrier layer 21 include vapor-deposited layers formed of metal oxides such as aluminum oxide, silicon oxide, magnesium oxide, and tin oxide. From the viewpoint of transparency and barrier properties, aluminum oxide, silicon oxide, and magnesium oxide can be selected as the metal oxide. Furthermore, considering cost, aluminum oxide and silicon oxide can be selected. Furthermore, from the viewpoint of excellent stretchability during processing, a layer using silicon oxide is more preferred. By using a vapor-deposited layer formed of metal oxide in the barrier layer, high barrier properties can be obtained with an extremely thin layer that does not affect the recyclability of the laminate 1.

[0058] Vaporized layers formed from metal oxides have the following advantages over vaporized layers formed from metals due to their transparency: users holding packaging materials formed from laminates are less likely to mistake them for metal foil.

[0059] When alumina is selected as the vapor-deposited layer, the O / Al ratio is preferably 1.4 or higher. When the O / Al ratio is 1.4 or higher, it is easy to suppress the proportion of unbonded aluminum atoms and obtain good transparency. In addition, the O / Al ratio is preferably 1.7 or lower. When the O / Al ratio is 1.7 or lower, it is possible to prevent the crystallinity of AlO from increasing and the vapor-deposited layer from becoming too hard, and good tensile strength can be obtained. In packaging bags using the laminate 1, the substrate 10 may shrink due to the heat during boiling treatment. However, when the O / Al ratio of the gas barrier layer 21 is 1.7 or lower, it is easy to follow this shrinkage, and the reduction in barrier properties caused by cracks or the like in the gas barrier layer 21 can be suppressed. From the viewpoint of obtaining these effects more fully, it is preferable that the O / Al ratio of the vapor-deposited layer that becomes the gas barrier layer 21 is 1.4 or higher and 1.7 or lower, more preferably 1.5 or higher and 1.55 or lower.

[0060] When silicon oxide is selected as the vapor-deposited layer, the O / Si ratio is preferably 1.7 or higher. When the O / Si ratio is 1.7 or higher, it is easier to suppress the proportion of unbonded silicon atoms, thus obtaining good transparency. Furthermore, the O / Si ratio is preferably 2.0 or lower. When the O / Si ratio is 2.0 or lower, it is possible to prevent the increased crystallinity of SiO from causing the vapor-deposited layer to become too hard, thus obtaining good tensile strength. Additionally, since the O / Si ratio of the gas barrier layer 21 is 2.0 or lower, it is easier to follow the aforementioned shrinkage, thus suppressing the decrease in barrier properties. From the viewpoint of obtaining these effects more fully, the O / Si ratio of the vapor-deposited layer that becomes the gas barrier layer 21 is preferably 1.75 or higher and 1.9 or lower, more preferably 1.8 or higher and 1.85 or lower.

[0061] The thickness of the vapor-deposited layer formed from alumina is preferably 5 nm or more and 30 nm or less. When the film thickness is 5 nm or more, sufficient gas barrier properties can be obtained. Furthermore, when the film thickness is 30 nm or less, cracking caused by deformation due to internal stress of the film can be suppressed, and the reduction in gas barrier properties can be prevented. Moreover, when the film thickness exceeds 30 nm, the cost tends to increase due to the increased material usage and longer film formation time, making it less desirable from an economic point of view. From the same perspective, the film thickness of the vapor-deposited layer is more preferably 7 nm or more and 15 nm or less.

[0062] The thickness of the vapor-deposited layer formed from silicon oxide is preferably 10 nm or more and 50 nm or less. When the film thickness is 10 nm or more, sufficient gas barrier properties can be obtained. Furthermore, when the film thickness is 50 nm or less, cracking caused by deformation due to internal stress of the film can be suppressed, and the reduction in gas barrier properties can be prevented. Moreover, when the film thickness exceeds 50 nm, the cost tends to increase due to the increased material usage and longer film formation time, which is not preferred from an economic point of view. From the same perspective, the film thickness of the vapor-deposited layer is more preferably 20 nm or more and 40 nm or less.

[0063] Vacuum-deposited layers can be formed, for example, by vacuum deposition. Physical vapor deposition (PVD) or chemical vapor deposition (CVD) can be used in vacuum deposition. Examples of PVD include vacuum evaporation, sputtering, and ion plating, but are not limited to these. Examples of CVD include thermal CVD, plasma CVD, and photochemical CVD, but are not limited to these.

[0064] Among the aforementioned vacuum film deposition methods, resistance heating vacuum evaporation, EB (Electron Beam) heating vacuum evaporation, induction heating vacuum evaporation, sputtering, reactive sputtering, dual magnetron sputtering, and plasma chemical vapor deposition (PECVD) are particularly preferred. However, considering productivity, vacuum evaporation is currently the most superior method. As for the heating method in vacuum evaporation, electron beam heating, resistance heating, or induction heating are preferred.

[0065] When the intermediate layer 20 has a gas barrier layer 21 as in this embodiment, a known anchoring agent can be used to form an anchoring layer on the surface where the gas barrier layer is formed. This improves the adhesion of the gas barrier layer formed from the metal oxide. Examples of anchoring agents include polyester-based polyurethane resins and polyether-based polyurethane resins. From the viewpoint of heat resistance and interlayer adhesion strength, polyester-based polyurethane resins are preferred.

[0066] Furthermore, in order to improve the adhesion to the first adhesive layer 40, the second adhesive layer 50, the gas barrier layer 21, and the aforementioned anchor coating, surface treatments such as corona treatment or plasma treatment can be applied to the corresponding surfaces of the intermediate layer 20.

[0067] The heat-sealing layer 30 is made of polyethylene and is bonded by heat-melting adhesion (heat sealing) when packaging materials such as packaging bags are formed using the laminate 1. From the viewpoint of heat-sealing performance, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and ultra-low-density polyethylene (VLDPE) are preferred as the polyethylene constituting the heat-sealing layer 30. Furthermore, from the viewpoint of environmental impact, it is preferable to use biomass-derived polyethylene or recycled polyethylene in the heat-sealing layer 30.

[0068] As a low-density polyethylene, a density of 0.900 g / cm³ can be used. 3 Above and below 0.925 g / cm³ 3 Polyethylene. As a linear low-density polyethylene, a density of 0.900 g / cm³ can be used. 3 Above and below 0.925 g / cm³ 3 Polyethylene. As ultra-low density polyethylene, it can be used with a density of less than 0.900 g / cm³. 3 Polyethylene.

[0069] Without compromising the properties of laminate 1, copolymers of ethylene with other monomers may be used in heat-sealing layer 30.

[0070] The heat-sealing layer 30 can be a single layer or a multi-layer structure. When it has a multi-layer structure, it can include at least one of MDPE and HDPE.

[0071] For example, it can be made into a three-layer structure consisting of a layer containing at least one of LDPE, LLDPE, and VLDPE, a layer containing at least one of MDPE and HDPE, and a layer containing at least one of LDPE, LLDPE, and VLDPE. By making such a structure, the bag-making suitability and strength of the laminate 1 can be further improved while maintaining heat-sealing properties.

[0072] The thickness of the heat-sealing layer 30 can be appropriately varied depending on the weight of the contents filled in the packaging material. For example, when manufacturing a packaging bag filled with 1g or more but less than 200g of contents, it is preferable that the thickness of the heat-sealing layer 30 is 20μm or more but less than 60μm. By making the thickness 20μm or more, leakage of the filled contents due to damage to the heat-sealing layer 30 can be prevented. By making the thickness 60μm or less, the processability of the laminate 1 can be improved.

[0073] As another example, when manufacturing stand-up pouches filled with 50g or more but less than 2000g of contents, the thickness of the heat-sealing layer 30 is preferably 50μm or more but less than 200μm. By making the thickness 50μm or more, leakage of the filled contents due to damage to the heat-sealing layer 30 can be prevented. In addition, by making the thickness 200μm or less, the processing suitability of the laminate 1 can be improved.

[0074] The first adhesive layer 40 is a layer containing at least one adhesive, disposed between the substrate 10 and the intermediate layer 20, bonding the substrate 10 and the intermediate layer 20. The second adhesive layer 50 is a layer containing at least one adhesive, disposed between the intermediate layer 20 and the heat-sealing layer 30, bonding the intermediate layer 20 and the heat-sealing layer 30.

[0075] Any type of adhesive, such as a one-component curing type or a two-component curing type urethane adhesive, can also be used in the first adhesive layer 40 and the second adhesive layer 50.

[0076] To further enhance barrier properties, these adhesives may also contain layered inorganic compounds.

[0077] The first adhesive layer 40 or the second adhesive layer 50 can also be formed using an adhesive that exhibits gas barrier properties after curing. In particular, when the first adhesive layer 40, which contacts the gas barrier layer, is formed using an adhesive that exhibits gas barrier properties, the reduction in gas barrier properties caused by cracking of the gas barrier layer 21 can be further suppressed. This further improves the gas barrier performance of the laminate 1. Examples of such gas barrier adhesives include epoxy adhesives and polyester-polyurethane adhesives. Specific examples include "Maxive" manufactured by Mitsubishi GAS Chemical Co., Ltd., and "Paslim" manufactured by DIC Corporation.

[0078] The thickness of the first adhesive layer 40 and the second adhesive layer 50 is preferably 0.5 μm or more and 6 μm or less, more preferably 0.8 μm or more and 5 μm or less, and even more preferably 1 μm or more and 4.5 μm or less. By making the thickness of the first adhesive layer 40 and the second adhesive layer 50 0.5 μm or more, the adhesiveness of the first adhesive layer 40 and the second adhesive layer 50 can be improved. By making the thickness of the first adhesive layer 40 and the second adhesive layer 50 6 μm or less, the processability of the laminate 1 can be improved.

[0079] The first adhesive layer 40 and the second adhesive layer 50 can be formed, for example, by various known methods such as direct gravure roller coating, gravure roller coating, coincidence coating, reverse roller coating, ink fountain roller coating, and transfer roller coating.

[0080] By using polyethylene to form the substrate 10, the intermediate layer 20, and the heat-sealing layer 30, the proportion of polyethylene in the laminate 1 of this embodiment, as described above, is 90% by mass (wt%) or more. Therefore, the laminate 1 has high recyclability.

[0081] The percentage (%) of polyethylene in laminate 1 can be calculated by the following formula (1).

[0082] (mass of substrate 10 + mass of intermediate layer 20 + mass of heat seal layer 30) / total mass of laminate 1 × 100 (1)

[0083] When one laminate 1 is bent with the heat-sealing layers 30 facing each other, or when two laminates 1 are overlapped with the heat-sealing layers 30 facing each other, a packaging bag composed of laminates 1 can be formed when the filling portion of the residual contents is joined with the heat-sealing layers 30 of the periphery by heat sealing.

[0084] By clamping the bent bottom film while performing the aforementioned joining, a stand-up pouch can be formed.

[0085] Thus, laminate 1 can be applied to various packaging materials.

[0086] The aforementioned packaging bags or stand-up pouches can contain various contents, including solids, liquids, and gases.

[0087] The inventors discovered that packaging materials using the laminate described in Patent Document 1, which includes a stretched high-density polyethylene film layer, are sometimes prone to tearing due to impact upon drop. They believe that the orientation of the crystalline molecular chains in the stretched high-density polyethylene film, which serves as the base layer, is a significant contributing factor.

[0088] Details will also be shown in the embodiments, but the inventors have successfully improved strength while maintaining high recyclability by forming a structure in which an intermediate layer 20 formed of an unstretched film is incorporated into a substrate 10 formed of a stretched film.

[0089] Unstretched polyethylene film has a molecular structure in which spherulites are linked by binding molecules that are non-crystalline. It is believed that when subjected to an impact from a falling object, the folded molecular chains in the spherulites extend and absorb the impact. As a result, it is thought that this can improve the overall strength of the laminate 1.

[0090] Furthermore, in this invention, "unstretched polyethylene film" refers to a polyethylene film having a structure in which spherical crystals (spherulites) of approximately 10–100 μm, composed of randomly folded polyethylene molecular chains, are linked by non-crystalline molecules. "Stretched polyethylene film" refers to a polyethylene film having a structure in which the molecular chains are oriented by stretching the unstretched polyethylene film above its glass transition temperature and below its melting point, thereby breaking down the spherical crystals (spherulites). These structures can be confirmed by observation using scanning electron microscopy (SEM) or X-ray diffraction.

[0091] Reference Figure 2 The second embodiment of the present invention will be described below. In the following description, configurations identical to those already described will be marked with the same reference numerals and repeated descriptions will be omitted.

[0092] Figure 2 This refers to the laminate 2 of this embodiment. The laminate 2 includes a substrate 110 instead of the substrate 10, and an intermediate layer 120 instead of the intermediate layer 20. A gas barrier layer 21 is formed on the first surface 110a of the substrate 110.

[0093] The substrate 110 is made of an unstretched polyethylene film. The same film as the intermediate layer 20 in the first embodiment can be used as the unstretched polyethylene film.

[0094] The intermediate layer 120 is made of stretched polyethylene film. The same film as the substrate 10 in the first embodiment can be used as the stretched polyethylene film.

[0095] That is, the laminate 2 in this embodiment can be understood as a configuration in which the intermediate layer and the substrate are interchanged in the first embodiment.

[0096] In this embodiment, the laminate 2 is also composed of a stretched polyethylene film and an unstretched polyethylene film, similar to the first embodiment. Therefore, it can achieve both improved strength and high recyclability of the laminate as a whole.

[0097] Figure 2 An example is described in which a gas barrier layer 21 is formed on the substrate 110, but it can also be formed on the intermediate layer 120 in the same way as in the first embodiment.

[0098] in addition, Figure 2 The diagram shows a configuration without an ink layer, but an ink layer can be included in the same manner as in the first embodiment. In this case, the ink layer can be formed on the surface of the gas barrier layer 21 on the side of the first adhesive layer 40.

[0099] In either the first or second embodiment, a capping layer covering the gas barrier layer may be provided. The capping layer protects the gas barrier layer while independently providing barrier properties. When the capping layer is provided, an ink layer may also be formed on the capping layer.

[0100] The overcoat can be formed using a gas barrier coating forming composition (hereinafter also referred to as a coating agent) comprising at least one of a hydroxyl-containing polymer, a metal alkoxide, a silane coupling agent, and their hydrolysates, or a water / alcohol mixture as the main agent.

[0101] From the viewpoint of more adequately maintaining gas barrier properties after hot water treatment such as high-temperature cooking, the coating agent preferably contains at least a silane coupling agent or its hydrolysate, more preferably at least one selected from hydroxyl-containing polymers, metal alkoxides and their hydrolysates, and a silane coupling agent or its hydrolysate, and even more preferably contains a hydroxyl-containing polymer or its hydrolysate, a metal alkoxide or its hydrolysate, and a silane coupling agent or its hydrolysate. The coating agent can be prepared, for example, by directly mixing a metal alkoxide and a silane coupling agent, or by mixing a product pre-treated by hydrolysis of the metal alkoxide and the silane coupling agent, in a solution containing a water-soluble hydroxyl-containing polymer in an aqueous (water or water / alcohol mixture) solvent.

[0102] The components contained in the above-mentioned coating agent are described in detail. Examples of hydroxyl-containing polymers used in the coating agent include polyvinyl alcohol (PVA), polyvinylpyrrolidone, starch, methylcellulose, carboxymethylcellulose, and sodium alginate. When PVA is used in the coating agent, it is preferred because the gas barrier properties of the overcoat layer are particularly excellent.

[0103] From the viewpoint of obtaining excellent gas barrier properties, the capping coating is preferably formed from a composition comprising at least one of the metal alkoxides and their hydrolysates represented by the following general formula (I).

[0104] M(OR1)m(R2)nm(I)

[0105] Furthermore, in the above general formula (I), R1 and R2 are each independently a monovalent organic group with 1 to 8 carbon atoms, preferably an alkyl group such as methyl or ethyl. M represents an n-valent metal atom such as Si, Ti, Al, or Zr. m is an integer from 1 to n. When there are multiple R1 or R2, R1 or R2 can be the same or different from each other.

[0106] Examples of metal alkoxides include tetraethoxysilane [Si(OC2H5)4] and triisopropoxyaluminum [Al(O-2'-C3H7)3]. Tetraethoxysilane and triisopropoxyaluminum are preferred because they are relatively stable in aqueous solvents after hydrolysis.

[0107] Compounds represented by the following general formula (II) can be cited as silane coupling agents.

[0108] Si(OR11)p(R12)3-pR13(II)

[0109] Furthermore, in the above general formula (II), R11 represents alkyl groups such as methyl and ethyl. R12 represents monovalent organic groups such as alkyl, aralkyl, aryl, alkenyl, alkyl substituted with acryloyloxy, or alkyl substituted with methacryloyloxy. R13 represents a monovalent organic functional group. p represents an integer from 1 to 3. When multiple R11 or R12 are present, R11 or R12 may be the same or different from each other. Examples of monovalent organic functional groups represented by R13 include glycidoxy, epoxy, mercapto, hydroxyl, amino, alkyl substituted with halogen atoms, or monovalent organic functional groups containing isocyanate groups.

[0110] Specific examples of silane coupling agents include vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, γ-methacryloyloxypropyltrimethoxysilane, and γ-methacryloyloxypropylmethyldimethoxysilane.

[0111] The silane coupling agent can also be a polymer formed by polymerizing the compound shown in general formula (II) above. As a polymer, a trimer is preferred, and more preferably 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate. This is a condensation polymer of 3-isocyanate alkylalkoxysilane. It is known that the 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate loses its chemical reactivity at the isocyanate group, but the reactivity is ensured by utilizing the polarity of the ureate group. Generally, it is known to be added to adhesives and the like as an adhesiveness improver, similar to 3-isocyanate alkylalkoxysilane. Therefore, by adding 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate to a hydroxyl-containing polymer, the water resistance of the gas barrier coating can be improved through hydrogen bonding. 3-Isocyanate alkylalkoxysilanes exhibit high reactivity and low liquid stability, while the ureate portion of 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate, although insoluble in water due to its polarity, is easily dispersed in aqueous solutions and can stably maintain liquid viscosity. Furthermore, both 3-isocyanate alkylalkoxysilanes and 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate have equivalent water resistance.

[0112] 1,3,5-Tris(3-trialkoxysilylpropyl)isocyanurate is produced by the thermal condensation of 3-isocyanatepropylalkoxysilane, sometimes containing the 3-isocyanatepropylalkoxysilane of the starting material, but this is not a particular problem. Further preferred is 1,3,5-tris(3-trialkoxysilylpropyl)isocyanurate, and even more preferred is 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate. The methoxy group is hydrolyzed rapidly, and the propyl group is readily available at a lower cost; therefore, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate is practically advantageous.

[0113] In the coating agent, isocyanate compounds, or known additives such as dispersants, stabilizers, viscosity modifiers, and colorants may be added as needed, within a range that does not impair gas barrier properties.

[0114] The thickness of the capping coating is preferably 50 to 1000 nm, more preferably 100 to 500 nm. When the thickness of the capping coating is 50 nm or more, it tends to achieve more adequate gas barrier properties, while when it is 1000 nm or less, it tends to maintain sufficient flexibility.

[0115] The coating liquid used to form the capping coating can be applied using methods such as dip coating, roller coating, gravure coating, reverse gravure coating, air knife coating, comma roller coating, mold coating, screen printing, spraying, and gravure offset printing. The coating film formed by applying the coating liquid can be dried using methods such as hot air drying, hot roller drying, high-frequency irradiation, infrared irradiation, UV irradiation, or combinations thereof.

[0116] The temperature at which the coating is dried can be, for example, 50–150°C, preferably 70–100°C. By keeping the drying temperature within the above range, cracks in the inorganic oxide layer (evaporated layer) or gas barrier coating can be further suppressed, resulting in excellent barrier properties.

[0117] The overcoat layer can also be formed using a coating agent containing polyvinyl alcohol-based resins and silane compounds. Acid catalysts, base catalysts, photopolymerization initiators, etc., can also be added to this coating agent as needed.

[0118] Polyvinyl alcohol-based resins can use the above-mentioned resins. Examples of silane compounds include silane coupling agents, polysilazanes, and siloxanes; specifically, examples include tetramethoxysilane, tetraethoxysilane, glycidoxypropyltrimethoxysilane, acryloyloxypropyltrimethoxysilane, and hexamethyldisilazane.

[0119] The laminated body of this embodiment will be further described using examples and comparative examples. The present invention is not limited in any way by the specific content of the examples and comparative examples.

[0120] (Preparation of anchoring agent)

[0121] Acrylic polyol and toluene diisocyanate were mixed in equal amounts relative to the number of OH groups in the acrylic polyol and the number of NCO groups in the toluene diisocyanate. The mixture was diluted with ethyl acetate to achieve a total solids content (total amount of acrylic polyol and toluene diisocyanate) of 5% by mass. β-(3,4-epoxycyclohexyl)trimethoxysilane was further added to the diluted mixture to achieve a total solids content of 5% by mass relative to 100 parts by mass of the total acrylic polyol and toluene diisocyanate. The mixture was then combined to prepare the anchoring agent.

[0122] (Preparation of the covering agent)

[0123] Mix the following liquids A, B, and C in a mass ratio of 70 / 20 / 10 to prepare a cover coat.

[0124] Solution A: A hydrolyzed solution with a solid content of 5% by mass (SiO2 conversion) is obtained by adding 72.1g of 0.1N hydrochloric acid to 17.9g of tetraethoxysilane (Si(OC2H5)4) and 10g of methanol and stirring for 30 minutes.

[0125] Solution B: A 5% by mass water / methanol solution of polyvinyl alcohol (water:methanol mass ratio is 95:5).

[0126] Solution C: 1,3,5-tris(3-trialkoxysilylpropyl)isocyanurate was diluted to a hydrolysis solution with a solid content of 5% by mass using a mixture of water and isopropanol (water:isopropanol mass ratio of 1:1).

[0127] (Making the intermediate layer A)

[0128] The anchoring agent described above was applied to a 25 μm thick unstretched polyethylene film (composed of three layers of HDPE / MDPE / HDPE) that had undergone corona treatment on both sides using a gravure coating method, and then dried to form an anchoring layer with a thickness of 0.1 μm. Next, a transparent gas barrier layer (silica vapor-deposited film) with a thickness of 30 nm was formed using a vacuum evaporation apparatus with electron beam heating. The O / Si ratio of the silica vapor-deposited film was adjusted to 1.8 by adjusting the types of vapor-deposited materials. The cover agent described above was then applied to the gas barrier layer using a gravure coating method and dried to form a cover layer with a thickness of 0.3 μm that provides gas barrier function.

[0129] The above results in an intermediate layer A having a gas barrier layer composed of silicon dioxide.

[0130] (Making the intermediate layer B)

[0131] An anchoring agent was applied to an unstretched polyethylene film, identical to the intermediate layer A, using gravure coating and then dried to form an anchoring layer with a thickness of 0.1 μm. Next, a transparent gas barrier layer (alumina vapor-deposited film) of 10 nm thickness was formed using a vacuum evaporation apparatus with electron beam heating. The O / Al ratio of the alumina vapor-deposited film was adjusted to 1.5 by adjusting the types of vapor-deposited materials. A cover coating agent was then applied to the gas barrier layer using gravure coating and dried to form a cover coating layer with a thickness of 0.3 μm that provides gas barrier functionality.

[0132] The above results in an intermediate layer B with a gas barrier layer composed of aluminum oxide.

[0133] (Creating the intermediate layer C)

[0134] An anchoring agent was applied to an unstretched polyethylene film, identical to the intermediate layer A, using a gravure coating method and then dried to form an anchoring layer with a thickness of 0.1 μm. Next, a transparent gas barrier layer (silicon dioxide vapor-deposited film) with a thickness of 30 nm was formed using a vacuum evaporation apparatus employing electron beam heating. The O / Si ratio of the silicon dioxide vapor-deposited film was adjusted to 1.8.

[0135] The above results in an intermediate layer C with a gas barrier layer made of silicon dioxide and no overcoat layer.

[0136] (The creation of the intermediate layer D)

[0137] An anchoring agent was applied to a 25 μm thick biaxially stretched polyethylene film (comprising three layers of HDPE / MDPE / HDPE) that had undergone corona treatment on both sides using a gravure coating method, and then dried to form an anchoring layer with a thickness of 0.1 μm. Next, a transparent gas barrier layer (silica vapor-deposited film) with a thickness of 30 nm was formed using a vacuum evaporation apparatus with electron beam heating. The O / Si ratio of the silica vapor-deposited film was adjusted to 1.8 by adjusting the types of vapor-deposited materials. A cover coating agent was then applied to the gas barrier layer using a gravure coating method and dried to form a cover coating layer with a thickness of 0.3 μm that provides gas barrier functionality.

[0138] The above results in an intermediate layer D with a gas barrier layer composed of silicon dioxide.

[0139] (The creation of the intermediate layer E)

[0140] An anchoring agent was applied to an unstretched polyethylene film, identical to the intermediate layer A, using a gravure coating method and then dried to create an anchoring layer with a thickness of 0.1 μm. Next, a transparent gas barrier layer (alumina vapor-deposited film) with a thickness of 10 nm was formed using a vacuum evaporation apparatus employing electron beam heating. The O / Al ratio of the alumina vapor-deposited film was adjusted to 1.5 by controlling the types of materials used in the evaporation process.

[0141] The above results in an intermediate layer E with a gas barrier layer made of silicon dioxide and no overcoat layer.

[0142] (Fabrication of substrate layer A)

[0143] The aforementioned anchoring agent was applied using a gravure coating method onto a 25 μm thick unstretched polyethylene film (composed of three layers: HDPE / MDPE / HDPE) that had undergone corona treatment on one side, and then dried to form an anchoring coating layer with a thickness of 0.1 μm. Next, a 30 nm thick transparent gas barrier layer (silicon dioxide vapor-deposited film) was formed from silicon dioxide using a vacuum evaporation apparatus with electron beam heating. The O / Si ratio of the silicon dioxide vapor-deposited film was adjusted to 1.8 by adjusting the types of vapor-deposited materials.

[0144] The above results in a substrate layer A having a gas barrier layer made of silicon dioxide.

[0145] (Fabrication of substrate layer B)

[0146] The aforementioned anchoring agent was applied using a gravure coating method onto a 25 μm thick biaxially stretched polyethylene film (composed of three layers: HDPE / MDPE / HDPE) that had undergone corona treatment on one side, and then dried to form an anchoring coating layer with a thickness of 0.1 μm. Next, a 30 nm thick transparent gas barrier layer (silica vapor-deposited film) was formed using a vacuum evaporation apparatus with electron beam heating. The O / Si ratio of the silica vapor-deposited film was adjusted to 1.8.

[0147] The substrate layer B, which has a gas barrier layer made of silicon dioxide, is obtained from the above.

[0148] (Example 1)

[0149] As a substrate, a 25 μm thick uniaxially stretched polyethylene film (HDPE / MDPE / HDPE 3-layer composition, haze value: 5%) with one side corona treated was prepared. An image was formed on the corona-treated surface of the substrate using gravure printing with urethane-based ink. Then, white urethane ink (non-opaque) was printed over the entire surface of the formed image using gravure printing. This process resulted in the formation of an ink layer consisting of multiple inks on the substrate.

[0150] Next, using a dry lamination method with a urethane adhesive, the surface of the substrate with the ink layer is bonded to the surface of the intermediate layer A with the gas barrier layer using the first adhesive layer.

[0151] Furthermore, an unstretched polyethylene film (a single layer of LLDPE) with a thickness of 40 μm is prepared as the heat-sealing layer, and the intermediate layer is bonded to the heat-sealing layer using a dry lamination method employing a urethane-based adhesive.

[0152] The laminate of Example 1 is obtained from the above.

[0153] (Example 2)

[0154] Except for a 25 μm thick biaxially stretched polyethylene film (HDPE / MDPE / HDPE 3-layer composition, haze value: 4.5%) with one side corona treated as the substrate, the laminate of Example 2 was obtained using the same sequence as in Example 1.

[0155] (Example 3)

[0156] In addition to forming a light-shielding ink layer on the substrate layer by gravure printing a light-shielding brown ink on a white urethane ink, the laminate of Example 3 was obtained using the same sequence as in Example 2.

[0157] (Example 4)

[0158] Except that intermediate layer B is used instead of intermediate layer A, the laminate of Example 4 is obtained using the same sequence as in Example 3.

[0159] (Example 5)

[0160] Prepare the same heat-sealing layer as in Example 1, and laminate the heat-sealing layer on the gas barrier layer side of the intermediate layer C using a dry lamination method with a gas barrier adhesive.

[0161] As the gas barrier adhesive constituting the second adhesive layer, an epoxy-based adhesive was used, obtained by mixing 16 parts by mass of Maxive C93T (manufactured by Mitsubishi GAS Chemical Co., Ltd.) and 5 parts by mass of Maxive M-100 (manufactured by Mitsubishi GAS Chemical Co., Ltd.) in 23 parts by mass of a solvent containing ethyl acetate and methanol in a 1:1 mass ratio. The thickness of the gas barrier adhesive was 3 μm.

[0162] As a substrate, a 25 μm thick biaxially stretched polyethylene film (HDPE / MDPE / HDPE 3-layer composition, haze value: 5%) with one side corona treated was prepared. An image was formed on the corona-treated surface of the substrate using gravure printing with urethane-based inks. Then, white urethane ink (non-opaque) was printed over the entire surface of the formed image using gravure printing. This process formed an ink layer consisting of multiple inks on the substrate.

[0163] Furthermore, by using a dry lamination method with a urethane adhesive, the ink layer side of the substrate, the intermediate layer C, and the intermediate layer side of the heat-sealing layer laminate are bonded together.

[0164] The laminate of Example 5 is obtained from the above. The second adhesive layer of this example is formed by a gas barrier adhesive.

[0165] The layer structure of Example 5 is shown below. Figure 3 In Example 5, the gas barrier layer 21 is located on the side of the heat seal layer 30.

[0166] (Example 6)

[0167] Except that intermediate layer E is used instead of intermediate layer C, the laminate of Example 6 is obtained using the same sequence as in Example 5.

[0168] (Example 7)

[0169] Except for the use of a 25 μm thick unstretched polyethylene film (composed of three layers of HDPE / MDPE / HDPE) that has undergone corona treatment on both sides as an intermediate layer, the laminate of Example 7 was obtained using the same sequence as in Example 1. Example 6 is an example without a gas barrier layer.

[0170] (Example 8)

[0171] A 25 μm thick unstretched polyethylene film (HDPE / MDPE / HDPE 3-layer composition, haze value: 5%) with one side corona treated was prepared as the substrate. At this time, no image was formed on the corona-treated surface of the substrate.

[0172] Next, using a dry lamination method with a urethane adhesive, the substrate is bonded to the surface of the intermediate layer D where the gas barrier layer is formed using the first adhesive layer. Apart from the above, the laminate of Example 8 is obtained using the same sequence as in Example 1.

[0173] (Example 9)

[0174] As the intermediate layer, a 25μm thick biaxially stretched polyethylene film (HDPE / MDPE / HDPE 3-layer composition, haze value: 5%) with double-sided corona treatment was prepared.

[0175] Next, by using a dry lamination method with an epoxy adhesive, the corona-treated surface of the intermediate layer is bonded to the surface of the substrate layer A with a gas barrier layer by using the first adhesive layer.

[0176] Furthermore, an unstretched polyethylene film (a single layer of LLDPE) with a thickness of 40 μm is prepared as the heat-sealing layer, and the intermediate layer is bonded to the heat-sealing layer by dry lamination using a urethane adhesive.

[0177] The laminate of Example 9 is obtained from the above.

[0178] (Example 10)

[0179] Except that substrate layer B is used instead of substrate layer A, the laminate of Example 10 is obtained using the same sequence as in Example 9.

[0180] (Comparative Example 1)

[0181] Except for preparing an unstretched polyethylene film (HDPE / MDPE / HDPE 3-layer composition, haze value: 30%) with a thickness of 25 μm that has undergone corona treatment on one side as a substrate, the laminate of Comparative Example 1 was obtained using the same sequence as in Example 1.

[0182] (Comparative Example 2)

[0183] Except that intermediate layer D is used instead of intermediate layer A, the laminate of Comparative Example 2 is obtained using the same sequence as in Example 1.

[0184] (Comparative Example 3)

[0185] Except for preparing an unstretched polyethylene film (HDPE / MDPE / HDPE 3-layer composition, haze value: 30%) with a thickness of 25 μm that has undergone corona treatment on one side as a substrate, the laminate of Comparative Example 3 was obtained using the same sequence as in Example 5.

[0186] The following evaluation is performed on the laminates of each embodiment and comparative example.

[0187] (Recyclability)

[0188] Based on the above formula (1), the wt% of polyethylene in each example laminate is calculated. It is evaluated into the following two levels.

[0189] 〇 (Good): Contains more than 90 wt% polyethylene.

[0190] × (Defective): Polyethylene content is less than 90 wt%.

[0191] (Image visibility)

[0192] For each example of the laminate, a sensory evaluation was performed by visually observing the image over the substrate from the side opposite to where the ink layer is formed. The evaluation was graded into two levels.

[0193] 〇 (Good): The image is clearly visible.

[0194] × (Poor): The image appears blurry.

[0195] (Puncture strength)

[0196] Puncture strength was determined according to JIS Z 1707:2019. Each laminate was hung flat on a fabric stretching machine, and a 1.0 mm diameter, hemispherical needle with a 0.5 mm radius tip was inserted from the substrate side at a rate of 50 mm / min. The force (Newtons: N) at puncture was measured.

[0197] (Impact resistance)

[0198] Using the laminated bodies of each example, make 10 packaging bags of 100mm × 150mm each, with the perimeter heat-sealed.

[0199] Fill the packaging bag with 200g of distilled water and seal it with heat, then store it at 5°C for 1 day.

[0200] After storage, each bag was dropped 50 times from a height of 1.5m, and the number of bags that broke was recorded.

[0201] (Light blocking properties)

[0202] The light-blocking property was determined using a measuring instrument based on JIS K 7361-1:1997.

[0203] Light was irradiated onto each example laminate from the substrate side, and the total light transmittance was measured.

[0204] (Oxygen permeability: OTR)

[0205] The measurements were performed using the MOCON method at 30°C and 70% RH (relative humidity).

[0206] (Water vapor transmission rate: WVTR)

[0207] The determination was performed using the MOCON method at 40°C and 90% RH.

[0208] (Oxidation inhibition due to light shading)

[0209] Using the laminated bodies of each example, a 180mm × 250mm packaging bag was made by heat-sealing the perimeter. 60g of potato chips were filled into this packaging bag as the contents, and it was sealed using heat sealing. The bag was then stored for 2 weeks at 40°C / 75% RH while being illuminated by a white fluorescent lamp (1000Lx illuminance).

[0210] After the storage period, the packaging bag was opened and the contents were removed and pulverized. The oil was extracted from the pulverized contents using ethyl ether, and the peroxide value (POV) was determined.

[0211] The results are shown in Table 1.

[0212]

[0213] As shown in Table 1, both the Examples and Comparative Examples exhibit high recyclability. However, the laminate of Comparative Example 1, where both the substrate and the intermediate layer are made of unstretched polyethylene film, has insufficient image visibility and puncture strength. On the other hand, the laminate of Comparative Example 2, where both the substrate and the intermediate layer are made of stretched polyethylene film, has insufficient impact resistance.

[0214] Since the laminates in each embodiment are made of stretched polyethylene film as the substrate and unstretched polyethylene film as the intermediate layer, they have high recyclability, as well as excellent puncture strength and impact resistance.

[0215] In addition, the same effect was achieved even when the middle layer was a stretched polyethylene film and the substrate was made of an unstretched polyethylene film.

[0216] Furthermore, by using a stretched polyethylene film as the substrate, the image formed by the ink layer also exhibits good visibility.

[0217] In embodiments incorporating a gas barrier layer and a capping coating, good OTR and WVTR were observed. In embodiments where the ink layer has light-blocking properties, oxidation of the contents due to light is preferably suppressed.

[0218] The various embodiments and examples of the present invention have been described above, but the specific configuration is not limited to these embodiments, and also includes changes and combinations of configurations that do not depart from the spirit and scope of the present invention.

[0219] For example, in the laminate of the present invention, the gas barrier layer may also be disposed on either the substrate side of the intermediate layer or the heat-sealing layer side.

[0220] Furthermore, the gas barrier layer is not essential in the laminate of the present invention. That is, when used in packaging materials where the contents do not require barrier properties, the gas barrier layer can be omitted.

[0221] Industrial availability

[0222] The laminate of the present invention has sufficient strength and is easy to recycle when applied to packaging materials.

[0223] Symbol Explanation

[0224] 1 and 2 layers

[0225] 10, 110 substrate

[0226] 10a, 110a First Page

[0227] 11 Ink Layer

[0228] 20, 120 intermediate layer

[0229] 21 Gas Barrier Layer

[0230] 30 heat seal layer

[0231] 40 First adhesive layer

[0232] 50 Second adhesive layer

Claims

1. A laminated body, comprising: Substrate; Intermediate layer; Heat seal layer; A first adhesive layer disposed between the substrate and the intermediate layer; and A second adhesive layer containing a urethane-based or epoxy-based adhesive is disposed between the intermediate layer and the heat-sealing layer. in, The substrate, the intermediate layer, and the heat-sealing layer are composed of polyethylene. The substrate is a stretched polyethylene film, and the intermediate layer is an unstretched polyethylene film. Polyethylene accounts for more than 90% by mass in the laminate.

2. The laminated body according to claim 1, wherein, The substrate and either the intermediate layer have a gas barrier layer.

3. The laminated body according to claim 2, wherein, The gas barrier layer includes an evaporated layer.

4. The laminated body according to claim 3, wherein, The vapor-deposited layer is formed of metal oxide.

5. The laminate according to claim 1 or 2, wherein, The substrate has an ink layer on a first surface facing the intermediate layer.

6. The laminate according to claim 5, wherein, The ink layer has light-shielding properties.

7. The laminate according to claim 1, wherein, At least one of the first adhesive layer and the second adhesive layer is a layer formed by curing a gas barrier adhesive, wherein the gas barrier adhesive is the epoxy adhesive.

8. A packaging material formed by joining the heat-sealing layers using a laminate according to any one of claims 1 to 7.

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