Laminate and packaging material

Abstract

To provide a laminate which has sufficient strength when applied to a packaging material and is easy to recycle.SOLUTION: The laminate 1 includes a base material 10, an intermediate layer 20, a heat seal layer 30, a first adhesive layer 40 provided between the base material and the intermediate layer, and a second adhesive layer 50 provided between the intermediate layer and the heat seal layer. The base material, the intermediate layer, and the heat seal layer are configured to include polyethylene. The base material is a stretched polyethylene film, and the intermediate layer is a multilayer unstretched polyethylene film. The proportion of polyethylene in the laminate 1 is 90% by mass or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminate, more particularly to a laminate with excellent recyclability, and also to a packaging material using the laminate. [Background technology]

[0002] As calls for the creation of a recycling-oriented society grow, there is a demand for packaging materials with high recyclability. Generally, packaging materials are considered highly recyclable if they contain 90% or more of the main resin by mass. However, many conventional packaging materials are composed of multiple resin materials and do not meet this standard, so they are not currently recycled.

[0003] In relation to this problem, Patent Document 1 describes a laminate including a substrate, an adhesive layer, and a heat-sealing layer, in which the substrate and the heat-sealing layer are made of polyethylene. By making the substrate and the heat-sealing layer out of the same material, it becomes easier to meet the above criteria. The substrate is a stretched polyethylene film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-55157 Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors have found that when the laminate described in Patent Document 1 is applied to a packaging material, the strength may not be sufficient. The inventors have solved this problem while maintaining high recyclability.

[0006] An object of the present invention is to provide a laminate that has sufficient strength when applied to packaging materials and is easy to recycle. [Means for solving the problem]

[0007] A first aspect of the present invention is a laminate comprising 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 is a stretched polyethylene film, and the intermediate layer is a multi-layer unstretched polyethylene film. The proportion of polyethylene in the laminate is 90% by mass or more.

[0008] A second aspect of the present invention is a packaging material formed by using the laminate according to the first aspect and joining it by heat sealing or the like. [Effects of the Invention]

[0009] The laminate of the present invention has sufficient strength when applied to packaging materials and is easy to recycle. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view of a laminate according to a first embodiment of the present invention. [Figure 2] FIG. 3 is a schematic cross-sectional view of a laminate according to a second embodiment of the present invention. [Figure 3] FIG. 2 is a schematic cross-sectional view of a laminate according to an example. DETAILED DESCRIPTION OF THE INVENTION

[0011] A first embodiment of the present invention will be described below with reference to FIGS. 1 is a schematic cross-sectional view of a laminate 1 according to this embodiment. The laminate 1 includes a substrate 10, an intermediate layer 20, and a heat-seal 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-seal layer 30 are bonded together by a second adhesive layer 50.

[0012] The substrate 10 is a stretched film made of polyethylene, and is the portion that becomes the outer surface when the laminate 1 is used to form a packaging material. The substrate 10 may be a uniaxially stretched film or a biaxially stretched film. The stretching ratio in the machine direction (MD) of the stretched film is preferably 2 to 10 times, more preferably 3 to 7 times. By setting the stretching ratio to 2 times or more, the strength and heat resistance of the laminate 1 can be improved. There is no particular upper limit to the stretching ratio, but from the viewpoint of the breaking limit of the stretched film, it is preferably 10 times or less. In the case of a biaxially stretched film, the stretching ratio in the direction perpendicular to the MD (TD) is preferably 2 to 10, more preferably 3 to 7. The stretching ratio in the MD and the stretching ratio in the TD may be different, but are preferably the same.

[0013] From the viewpoints of strength, heat resistance, and stretchability, high-density polyethylene (HDPE) and medium-density polyethylene (MDPE) are preferred as the polyethylene contained in the substrate 10, and from the viewpoint of stretchability, MDPE is more preferred. It is also possible to use, as the substrate 10, a multilayer stretched polyethylene film obtained by coextruding polyethylenes of different densities. As HDPE, the density is 0.945g / cm 3 Polyethylene with a density of 0.925 g / cm or more can be used. 3 More than 0.945g / cm 3 Less than 100% polyethylene can be used.

[0014] The polyethylenes having different densities and branching levels can be obtained by appropriately selecting a polymerization method. For example, it is preferable to use a multi-site catalyst such as a Ziegler-Natta catalyst or a single-site catalyst such as a metallocene catalyst as the polymerization catalyst, and to carry out the polymerization in one or more stages by any of gas phase polymerization, slurry polymerization, solution polymerization, and high-pressure ionic polymerization. The single-site catalyst is a catalyst capable of forming a uniform active species, and is usually prepared by contacting a metallocene transition metal compound or a non-metallocene transition metal compound with an activating co-catalyst. Single-site catalysts are preferred because they have a more uniform active site structure than multi-site catalysts and can polymerize polymers with high molecular weights and highly uniform structures. As the single-site catalyst, it is particularly preferable to use a metallocene catalyst. The metallocene catalyst is a catalyst containing the following catalytic components: a transition metal compound of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton, a co-catalyst, and optionally an organometallic compound and a support. In the above-mentioned transition metal compound of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton, the cyclopentadienyl skeleton may be a cyclopentadienyl group, a substituted cyclopentadienyl group, or the like. The substituted cyclopentadienyl group has 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 may have two or more substituents, and the substituents may be bonded to each other to form a ring, such as an indenyl ring, a fluorenyl ring, an azulenyl ring, or a hydrogenated product thereof. The rings formed by bonding the substituents to each other may further have substituents. In the transition metal compound of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton, the transition metal can be zirconium, titanium, hafnium, etc., with zirconium and hafnium being particularly preferred. The transition metal compound typically contains two ligands having a cyclopentadienyl skeleton, and the cyclopentadienyl ligands are preferably bonded to each other via a bridging group. Examples of the bridging group include alkylene groups having 1 to 4 carbon atoms, silylene groups, substituted silylene groups such as dialkylsilylene groups and diarylsilylene groups, and substituted germylene groups such as dialkylgermylene groups and diarylgermylene groups. Substituted silylene groups are preferred. The above-mentioned transition metal compounds of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton can be used as a catalyst component, either singly or in combination. The co-catalyst refers to a catalyst that can effectively use the above-mentioned transition metal compound of Group IV of the periodic table as a polymerization catalyst or that can balance the ionic charge in a catalytically activated state. Examples of the co-catalyst include benzene-soluble aluminoxanes of organoaluminum oxy compounds and benzene-insoluble organoaluminum oxy compounds, ion-exchangeable layered silicates, boron compounds, ionic compounds consisting of a cation with or without an active hydrogen group and a non-coordinating anion, lanthanoid salts such as lanthanum oxide, tin oxide, and phenoxy compounds containing a fluoro group. The transition metal compound of Group IV of the periodic table containing a ligand having a cyclopentadienyl skeleton may be used by being supported on an inorganic or organic carrier, preferably an inorganic or organic porous oxide, such as montmorillonite or other ion-exchange layered silicates, SiO2, Al2O3, MgO, ZrO2, TiO2, BO3, CaO, ZnO, BaO, or ThO. 2、 and mixtures thereof. Organometallic compounds that may be used as needed include organoaluminum compounds, organomagnesium compounds, and organozinc compounds. Of these, organoaluminum compounds are preferred.

[0015] Copolymers of ethylene and other monomers can also be used as long as they do not impair the properties of the present invention. Examples of ethylene copolymers include copolymers of ethylene and an α-olefin 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 acrylic esters may also be used as long as they do not impair the objectives of the present invention. In the present invention, biomass-derived ethylene may be used as a raw material for obtaining the above-mentioned high-density polyethylene, instead of ethylene obtained from fossil fuels. Such biomass-derived polyethylene is a carbon-neutral material, and therefore can be used as a packaging material with even less environmental impact. Such biomass-derived polyethylene can be produced, for example, by a method such as that described in JP 2013-177531 A. Alternatively, commercially available biomass-derived polyethylene (e.g., Green PE commercially available from Braskem) may be used. Polyethylene recycled by mechanical recycling can also be used for the substrate 10. Here, mechanical recycling generally refers to a method in which recovered polyethylene film or the like is crushed and washed with an alkali to remove dirt and foreign matter from the film surface, and then dried at high temperature and reduced pressure for a certain period of time to diffuse contaminants remaining inside the film for decontamination, and the dirt is removed from the polyethylene film, which is then melted and formed into a film to return it to a polyethylene film.

[0016] An ink layer 11 is formed on a first surface 10a of the substrate 10, which is the side to be bonded to the intermediate layer 20. The ink layer 11 provides the laminate with indications regarding the contents, various designs, etc. The ink layer 11 provided on the first surface 10a is not exposed to the outer surface when the laminate is made into a packaging material, thereby suppressing damage and deterioration of the indications after production. The contents can be protected from light by forming an ink layer 11 over the entire first surface 10a using a light-blocking ink. Such a light-blocking ink layer can be produced, for example, by overprinting, by solid printing, a chromatic ink containing a white pigment and a black pigment, with the proportion of the black pigment in the total pigment being 3 to 5 wt %, on one or more white ink layers formed by full-surface printing (solid printing), to form a chromatic ink layer with a chroma of 1 to 4 on the Munsell color system. By combining a light-blocking ink layer with a printed layer (image printed layer) of a picture, character, or the like made of ink that does not have light-blocking properties, it is possible to impart light-blocking properties while freely setting the appearance of the ink layer 11. In this case, by first forming the image printed layer on the substrate 10 and then forming the light-blocking ink layer, it is possible to improve the visibility of the image. The ink layer 11 is preferably formed using a biomass-derived ink. This allows the laminate 1 to be used to produce a packaging material with a lower environmental impact. The method for forming the image is not particularly limited, and examples include various conventionally known printing methods such as gravure printing, offset printing, and flexographic printing. Of these, flexographic printing is preferred from the perspective of environmental impact. The first surface 10a of the substrate 10 may be subjected to a surface treatment such as a corona treatment or a plasma treatment in order to improve the adhesion of the ink layer 11.

[0017] Since the substrate 10 is a stretched film and has excellent transparency, the display made by the ink layer 11 provided on the first surface 10a side of the laminate 1 can be easily viewed. The transparency that allows easy viewing is 20% or less in terms of haze value measured in accordance with JIS K 7105, and is even better when it is 10% or less.

[0018] The thickness of the substrate 10 is preferably 10 μm or more and 50 μm or less, and 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.

[0019] The substrate 10 may contain additives to the extent that the properties of the present invention are not impaired. Examples of additives include crosslinking agents, antioxidants, antiblocking agents, slip agents, UV absorbers, light stabilizers, fillers, reinforcing agents, antistatic agents, pigments, and modifying resins. The thickness of the substrate 10 is preferably 10 μm or more and 50 μm or less, and 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. Furthermore, by making the thickness of the substrate 10 50 μm or less, the processability of the laminate 1 can be improved.

[0020] The intermediate layer 20 is an unstretched film made of polyethylene. From the viewpoints of strength and heat resistance, HDPE and MDPE are preferred as the polyethylene contained in the intermediate layer 20. Like the substrate 10, the intermediate layer 20 may be a multilayer film. The thickness of the intermediate layer 20 is preferably 9 μm or more and 50 μm or less, and 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.

[0021] The intermediate layer 20 can be produced by forming a polyethylene film by a T-die method, an inflation method, or the like. When the intermediate layer 20 is produced by 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, the produced substrate can be prevented from breaking. When the intermediate layer 20 is produced by an inflation method, the MFR of the polyethylene is preferably 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. Furthermore, by setting the MFR to 5 g / 10 min or less, the film-forming properties can be improved. The unstretched film to be the intermediate layer 20 may be produced by the method described above, or may be obtained from a commercially available source.

[0022] A gas barrier layer 21 is formed on one surface of the intermediate layer 20. In this embodiment, the gas barrier layer 21 is formed on the first surface 20a facing the substrate 10, but may be formed on the opposite surface. The gas barrier layer 21 imparts oxygen barrier properties and water vapor barrier properties to the laminate 1. The gas barrier layer 21 may be configured as, for example, a vapor-deposited layer made of a metal oxide such as aluminum oxide, silicon oxide, magnesium oxide, or tin oxide. From the viewpoints of transparency and barrier properties, the metal oxide may be selected from the group consisting of aluminum oxide, silicon oxide, and magnesium oxide. Furthermore, from the viewpoint of cost, it is selected from aluminum oxide and silicon oxide. Furthermore, from the viewpoint of excellent tensile elongation during processing, a layer using silicon oxide is more preferable. By using a vapor-deposited layer made of a metal oxide as the barrier layer, high barrier properties can be obtained with an extremely thin layer that does not affect the recyclability of the laminate 1. A vapor-deposited layer made of a metal oxide has transparency, and therefore has the advantage that, compared to a vapor-deposited layer made of a metal, it is less likely to cause a user who holds a packaging material made of the laminate to mistakenly believe that a metal foil is used.

[0023] When aluminum oxide is selected for the vapor-deposited layer, the O / Al ratio is preferably 1.4 or higher. An O / Al ratio of 1.4 or higher reduces the proportion of dangling bonds in aluminum atoms, making it easier to achieve good transparency. Furthermore, the O / Al ratio is preferably 1.7 or lower. An O / Al ratio of 1.7 or lower increases the crystallinity of AlO, preventing the vapor-deposited layer from becoming too hard and providing good tensile strength. In packaging bags using the laminate 1, the substrate 10 may shrink due to the heat generated during the boiling treatment. However, if the O / Al ratio of the gas barrier layer 21 is 1.7 or lower, the gas barrier layer 21 can easily accommodate this shrinkage and prevent degradation of the barrier properties due to cracks or the like in the gas barrier layer 21. To fully achieve these effects, the O / Al ratio of the vapor-deposited layer that becomes the gas barrier layer 21 is preferably 1.4 or higher and 1.7 or lower, more preferably 1.5 or higher and 1.55 or lower.

[0024] When silicon oxide is selected for the vapor-deposited layer, the O / Si ratio is desirably 1.7 or higher. An O / Si ratio of 1.7 or higher reduces the proportion of dangling bonds in silicon atoms, making it easier to achieve good transparency. Furthermore, the O / Si ratio is preferably 2.0 or lower. An O / Si ratio of 2.0 or lower increases the crystallinity of SiO, preventing the vapor-deposited layer from becoming too hard and providing good tensile strength. Furthermore, an O / Si ratio of 2.0 or lower in the gas barrier layer 21 makes it easier to accommodate the shrinkage described above and prevents a decrease in barrier properties. To fully achieve these effects, 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, and more preferably 1.8 or higher and 1.85 or lower.

[0025] The thickness of the vapor-deposited layer made of aluminum oxide is preferably 5 nm or more and 30 nm or less. A thickness of 5 nm or more can provide sufficient gas barrier properties. Furthermore, a thickness of 30 nm or less can prevent cracks from occurring due to deformation caused by internal stress in the thin film, thereby preventing a decrease in gas barrier properties. Note that a thickness exceeding 30 nm is undesirable from an economic standpoint, as it increases costs due to an increase in the amount of material used and a longer film formation time. From the same viewpoint as above, the thickness of the vapor-deposited layer is more preferably 7 nm or more and 15 nm or less. The thickness of the vapor-deposited layer made of silicon oxide is preferably 10 nm or more and 50 nm or less. A thickness of 10 nm or more can provide sufficient gas barrier properties. Furthermore, a thickness of 50 nm or less can prevent cracks from occurring due to deformation caused by internal stress in the thin film, thereby preventing a decrease in gas barrier properties. Note that a thickness exceeding 50 nm is undesirable from an economic standpoint, as it increases costs due to an increase in the amount of material used and a longer film formation time. From the same viewpoint as above, the thickness of the vapor-deposited layer is more preferably 20 nm or more and 40 nm or less.

[0026] The deposition layer can be formed by, for example, vacuum film formation. In vacuum film formation, physical vapor deposition or chemical vapor deposition can be used. Examples of physical vapor deposition include, but are not limited to, vacuum deposition, sputtering, and ion plating. Examples of chemical vapor deposition include, but are not limited to, thermal CVD, plasma CVD, and photo CVD. In the vacuum film formation, resistance heating vacuum evaporation, EB (Electron Beam) heating vacuum evaporation, induction heating vacuum evaporation, sputtering, reactive sputtering, dual magnetron sputtering, plasma enhanced chemical vapor deposition (PECVD), and the like are particularly preferably used. However, in terms of productivity, vacuum evaporation is currently the most superior. As a heating means for vacuum evaporation, it is preferable to use any of the electron beam heating method, resistance heating method, and induction heating method.

[0027] When the intermediate layer 20 has a gas barrier layer 21 as in this embodiment, an anchor coating layer may be formed on the surface on which the gas barrier layer is to be formed using a known anchor coating agent. This can improve the adhesion of the gas barrier layer made of metal oxide. Examples of anchor coating agents include polyester-based polyurethane resins and polyether-based polyurethane resins. From the viewpoints of heat resistance and interlayer adhesive strength, polyester-based polyurethane resins are preferred.

[0028] Furthermore, in order to improve adhesion between the first adhesive layer 40 and the second adhesive layer 50, the gas barrier layer 21, and the above-mentioned anchor coat layer, the corresponding surfaces of the intermediate layer 20 may be subjected to surface treatment such as corona treatment or plasma treatment.

[0029] The heat seal layer 30 is made of polyethylene and is bonded by heat fusion (heat sealing) when the laminate 1 is used to form a packaging material such as a packaging bag. From the viewpoint of heat sealing properties, the polyethylene constituting the heat seal layer 30 is preferably low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), or very low-density polyethylene (VLDPE). From the viewpoint of environmental impact, it is also preferable to use biomass-derived polyethylene or recycled polyethylene for the heat seal layer 30. Low density polyethylene has a density of 0.900 g / cm 3 More than 0.925g / cm 3 As the linear low density polyethylene, polyethylene having a density of 0.900 g / cm3 or less can be used. 3 More than 0.925g / cm 3 Ultra-low density polyethylene can be used with a density of 0.900 g / cm. 3 Less than 100% polyethylene can be used. The heat seal layer 30 may contain a copolymer of ethylene and other monomers as long as the properties of the laminate 1 are not impaired.

[0030] The heat seal layer 30 may be a single layer or may have a multi-layer structure. When it has a multi-layer structure, it may have a layer containing at least one of MDPE and HDPE. For example, a three-layer structure may be used, 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. This structure can further improve the bag-making suitability and strength of the laminate 1 while maintaining heat-sealability.

[0031] The thickness of the heat seal layer 30 can be changed as appropriate depending on the weight of the contents to be filled into the packaging material to be produced. For example, when producing a packaging bag to be filled with contents of 1 g or more and 200 g or less, the thickness of the heat seal layer 30 is preferably 20 μm or more and 60 μm or less. By making the thickness 20 μm or more, it is possible to prevent the filled contents from leaking due to damage to the heat seal layer 30. By making the thickness 60 μm or less, it is possible to improve the processability of the laminate 1. As another example, when producing a standing pouch to be filled with contents of 50 g or more and 2000 g or less, the thickness of the heat seal layer 30 is preferably 50 μm or more and 200 μm or less. By making the thickness 50 μm or more, it is possible to prevent the filled contents from leaking due to damage to the heat seal layer 30. Furthermore, by making the thickness 200 μm or less, it is possible to improve the processability of the laminate 1.

[0032] The first adhesive layer 40 is a layer containing at least one type of adhesive and is provided between the substrate 10 and the intermediate layer 20 to bond them together. The second adhesive layer 50 is a layer containing at least one type of adhesive and is provided between the intermediate layer 20 and the heat seal layer 30 to bond them together. Any adhesive such as a one-component curing type or two-component curing type urethane adhesive can be used for the first adhesive layer 40 and the second adhesive layer 50 . These adhesives may contain layered inorganic compounds to further enhance the barrier properties.

[0033] The first adhesive layer 40 and the second adhesive layer 50 can also be formed using an adhesive that exhibits gas barrier properties after curing. In particular, forming the first adhesive layer 40, which contacts the gas barrier layer, using an adhesive that exhibits gas barrier properties can further suppress deterioration of the gas barrier properties due to cracking of the gas barrier layer 21. This can further improve the gas barrier performance of the laminate 1. Examples of such gas barrier adhesives include epoxy-based adhesives and polyester-polyurethane-based adhesives. Specific examples include "Maxieve" manufactured by Mitsubishi Gas Chemical Company, Inc. and "Paslim" manufactured by DIC Corporation.

[0034] 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. The first adhesive layer 40 and the second adhesive layer 50 can be formed by various known methods such as direct gravure roll coating, gravure roll coating, kiss coating, reverse roll coating, Fontaine method, and transfer roll coating.

[0035] In the laminate 1 of this embodiment configured as described above, the base material 10, the intermediate layer 20, and the heat seal layer 30 are made of polyethylene, so that the proportion of polyethylene in the laminate 1 is 90% by mass (wt%) or more, which makes the laminate 1 highly recyclable. The proportion (%) of polyethylene in the laminate 1 can be calculated by the following formula (1). (mass of the substrate 10 + mass of the intermediate layer 20 + mass of the heat seal layer 30) / mass of the entire laminate 1 × 100... (1)

[0036] A packaging bag made of the laminate 1 can be formed by folding one laminate 1 with the heat seal layers 30 facing each other, or by stacking two laminates 1 with the heat seal layers 30 facing each other, and then joining the heat seal layers 30 at the peripheral edges by heat sealing, leaving the filling area for the contents. By carrying out the above-described joining while sandwiching the folded bottom film, a standing pouch can be formed. In this way, the laminate 1 can be applied to various packaging materials.

[0037] The above-mentioned packaging bags and stand-up pouches can contain various contents, such as solids, liquids, and gases. The inventors have found that packaging materials using the laminate described in Patent Document 1, which includes a stretched high-density polyethylene film layer, can easily break when dropped. The inventors believe that the main reason for this is that the crystalline molecular chains in the stretched high-density polyethylene film, which is the base material, are oriented in a certain direction.

[0038] As will be shown in more detail later in the examples, the inventors have succeeded in improving strength while maintaining high recyclability by combining a substrate 10 made of a stretched film with an intermediate layer 20 made of an unstretched film. Unstretched polyethylene film has a molecular structure in which spherulites are connected to each other by tie molecules, which are amorphous molecules, and it is thought that when it is dropped, the folded molecular chains in the spherulites stretch, absorbing the impact of the drop. As a result, it is thought that the strength of the laminate 1 as a whole can be improved.

[0039] In the present invention, "unstretched polyethylene film" refers to a polyethylene film having a structure in which spherical crystals (spherulites) of about 10 to 100 μm, composed of randomly folded polyethylene molecular chains, are connected by amorphous molecules. "Stretched polyethylene film" refers to a polyethylene film having a structure in which unstretched polyethylene film is stretched at a temperature above the glass transition temperature and below the melting point, thereby destroying the spherical crystals (spherulites) and orienting the molecular chains. These structures can be confirmed by observation with a scanning electron microscope (SEM) or X-ray diffraction.

[0040] A second embodiment of the present invention will be described with reference to Fig. 2. In the following description, components common to those already described will be assigned the same reference numerals and redundant description will be omitted. 2 shows a laminate 2 according to 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. The gas barrier layer 21 is formed on a first surface 110a of the substrate 110.

[0041] The substrate 110 is made of an unstretched polyethylene film. As the unstretched polyethylene film, the same film as that used for the intermediate layer 20 in the first embodiment can be used. The intermediate layer 120 is made of a stretched polyethylene film. As the stretched polyethylene film, the same one as that used for the intermediate layer 20 in the first embodiment can be used. That is, the laminate 2 of this embodiment can be understood to have a configuration in which the intermediate layer and the substrate in the first embodiment are interchanged.

[0042] As in the first embodiment, the laminate 2 of this embodiment is constructed by combining a stretched polyethylene film and an unstretched polyethylene film, which allows for both improved strength of the entire laminate and high recyclability.

[0043] Although an example in which the gas barrier layer 21 is formed on the substrate 110 has been described in FIG. 2, it may also be formed on the intermediate layer 120, as in the first embodiment. 2 shows a configuration without an ink layer, an ink layer may be provided as in the first embodiment. In this case, the ink layer may be formed on the surface of the gas barrier layer 21 on the side of the first adhesive layer 40.

[0044] In both the first and second embodiments, an overcoat layer may be provided to cover the gas barrier layer. The overcoat layer protects the gas barrier layer and exhibits barrier properties independently of the gas barrier layer. When an overcoat layer is provided, an ink layer may be formed on the overcoat layer.

[0045] The overcoat layer can be formed using a composition for forming a gas barrier coating layer (hereinafter also referred to as a coating agent) whose main component is an aqueous solution or a water / alcohol mixed solution containing at least one selected from the group consisting of hydroxyl group-containing polymer compounds, metal alkoxides, silane coupling agents, and their hydrolysates. From the viewpoint of more adequately maintaining gas barrier properties after hot water treatment such as retort treatment, the coating agent preferably contains at least a silane coupling agent or a hydrolyzate thereof, more preferably contains at least one selected from the group consisting of a hydroxyl group-containing polymer compound, a metal alkoxide, and their hydrolyzates, and a silane coupling agent or a hydrolyzate thereof, and even more preferably contains a hydroxyl group-containing polymer compound or a hydrolyzate thereof, a metal alkoxide or a hydrolyzate thereof, and a silane coupling agent or a hydrolyzate thereof. The coating agent can be prepared, for example, by mixing a metal alkoxide and a silane coupling agent directly, or after having been previously treated by hydrolysis, with a solution obtained by dissolving a hydroxyl group-containing polymer compound, which is a water-soluble polymer, in an aqueous solvent (water or a water / alcohol mixture).

[0046] Each component contained in the coating agent described above will be described in detail. Examples of hydroxyl group-containing polymer compounds used in the coating agent include polyvinyl alcohol (PVA), polyvinylpyrrolidone, starch, methyl cellulose, carboxymethyl cellulose, and sodium alginate. The use of PVA in the coating agent is preferred because it provides an overcoat layer with particularly excellent gas barrier properties.

[0047] From the viewpoint of obtaining excellent gas barrier properties, the overcoat layer is preferably formed from a composition containing at least one selected from the group consisting of metal alkoxides represented by the following general formula (I) and hydrolysates thereof. M(OR 1 ) m (R 2 ) n-m …(I) In the above general formula (I), R 1 and R 2 are each independently a monovalent organic group having 1 to 8 carbon atoms, and are preferably an alkyl group such as a methyl group or an ethyl group. M represents an n-valent metal atom such as Si, Ti, Al, or Zr. m is an integer from 1 to n. R 1 or R 2 If there are multiple 1 Comrades or R 2 They may be the same or different. Specific examples of metal alkoxides include tetraethoxysilane [Si(OC2H5)4], triisopropoxyaluminum [Al(O-2'-C3H7)3], etc. Tetraethoxysilane and triisopropoxyaluminum are preferred because they are relatively stable in aqueous solvents after hydrolysis.

[0048] The silane coupling agent includes a compound represented by the following general formula (II). Si(OR 11 ) p (R 12 ) 3-p R 13 …(II) In the above general formula (II), R 11R indicates an alkyl group such as a methyl group or an ethyl group. 12 R represents a monovalent organic group such as an alkyl group, an aralkyl group, an aryl group, an alkenyl group, an alkyl group substituted with an acryloxy group, or an alkyl group substituted with a methacryloxy group. 13 represents a monovalent organic functional group. p represents an integer of 1 to 3. R 11 or R 12 If there are multiple 11 Comrades or R 12 R may be the same or different. 13 Examples of the monovalent organic functional group represented by the formula (I) include a monovalent organic functional group containing a glycidyloxy group, an epoxy group, a mercapto group, a hydroxyl group, an amino group, an alkyl group substituted with a halogen atom, or an isocyanate group. Specific examples of the silane coupling agent include vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, glycidoxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropylmethyldimethoxysilane.

[0049] The silane coupling agent may be a polymer formed by polymerization of the compound represented by the general formula (II). The polymer is preferably a trimer, more preferably 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate. This is a condensation polymer of 3-isocyanatoalkylalkoxysilane. It is known that 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate has no chemical reactivity in the isocyanate moiety, but the reactivity is ensured by the polarity of the nurate moiety. It is generally added to adhesives, similar to 3-isocyanatoalkylalkoxysilane, and is known as an adhesion improver. Therefore, adding 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate to a hydroxyl group-containing polymer compound can improve the water resistance of a gas barrier coating layer through hydrogen bonding. While 3-isocyanate alkyl alkoxysilanes are highly reactive and have low liquid stability, 1,3,5-tris(3-trialkoxysilylalkyl) isocyanurates are not water-soluble due to the polarity of the nurate moiety, but they are easily dispersed in aqueous solutions and can maintain stable liquid viscosity. Furthermore, the water resistance of 3-isocyanate alkyl alkoxysilanes and 1,3,5-tris(3-trialkoxysilylalkyl) isocyanurates is equivalent. Some 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurates are produced by thermal condensation of 3-isocyanatepropylalkoxysilane, and although the raw material 3-isocyanatepropylalkoxysilane may be contained, this does not pose any particular problems. 1,3,5-tris(3-trialkoxysilylpropyl)isocyanurate is more preferred, and 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate is even more preferred. Because the methoxy group hydrolyzes quickly and those containing the propyl group are relatively inexpensive, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate is practically advantageous.

[0050] If necessary, known additives such as an isocyanate compound, a dispersant, a stabilizer, a viscosity adjuster, a colorant, etc. may be added to the coating agent within a range that does not impair the gas barrier properties.

[0051] The thickness of the overcoat layer is preferably 50 to 1000 nm, and more preferably 100 to 500 nm. When the thickness of the overcoat layer is 50 nm or more, more sufficient gas barrier properties tend to be obtained, and when it is 1000 nm or less, sufficient flexibility tends to be maintained. The coating liquid for forming the overcoat layer can be applied by, for example, dipping, roll coating, gravure coating, reverse gravure coating, air knife coating, comma coating, die coating, screen printing, spray coating, gravure offset, etc. The coating film obtained by applying this coating liquid can be dried by, for example, hot air drying, hot roll drying, high frequency irradiation, infrared irradiation, UV irradiation, or a combination thereof. The temperature at which the coating film is dried can be, for example, 50 to 150° C., and preferably 70 to 100° C. By keeping the drying temperature within the above range, the occurrence of cracks in the inorganic oxide layer and the gas barrier coating layer can be further suppressed, and excellent barrier properties can be achieved.

[0052] The overcoat layer may be formed using a coating agent containing a polyvinyl alcohol resin and a silane compound, to which an acid catalyst, an alkali catalyst, a photopolymerization initiator, etc. may be added as needed. The polyvinyl alcohol resin may be any of those described above. Examples of the silane compound include a silane coupling agent, polysilazane, and siloxane, and specific examples thereof include tetramethoxysilane, tetraethoxysilane, glycidoxypropyltrimethoxysilane, acryloxypropyltrimethoxysilane, and hexamethyldisilazane.

[0053] The laminate of this embodiment will be further described using examples and comparative examples, but the present invention is not limited to the specific contents of the examples and comparative examples.

[0054] (Preparation of anchor coating agent) Acrylic polyol and tolylene diisocyanate were mixed so that the number of NCO groups in the tolylene diisocyanate was equal to the number of OH groups in the acrylic polyol, and the mixture was diluted with ethyl acetate to a total solids content (total amount of acrylic polyol and tolylene diisocyanate) of 5% by mass. β-(3,4-epoxycyclohexyl)trimethoxysilane was added to the diluted mixture in an amount of 5 parts by mass per 100 parts by mass of the total amount of acrylic polyol and tolylene diisocyanate, and the mixture was mixed to prepare an anchor coating agent.

[0055] (Preparation of Overcoat Agent) An overcoat agent was prepared by mixing the following liquids A, B, and C in a mass ratio of 70 / 20 / 10, respectively. Solution A: A hydrolysis solution with a solid content of 5% by mass (SiO2 equivalent) obtained by adding 72.1 g of 0.1N hydrochloric acid to 17.9 g of tetraethoxysilane (Si(OC2H5)4) and 10 g of methanol and stirring for 30 minutes. Solution B: 5% by mass of polyvinyl alcohol in water / methanol (water:methanol mass ratio 95:5). Liquid C: A hydrolysis solution in which 1,3,5-tris(3-trialkoxysilylpropyl) isocyanurate was diluted with a mixture of water and isopropyl alcohol (water:isopropyl alcohol mass ratio 1:1) to a solid content of 5 mass%.

[0056] (Preparation of intermediate layer A) The anchor coating agent described above was gravure coated onto a 25 μm-thick unstretched polyethylene film (HDPE / MDPE / HDPE trilayer structure) that had been corona-treated on both sides, followed by drying to form a 0.1 μm-thick anchor coating layer. Next, a 30 nm-thick transparent gas barrier layer (silica vapor deposition film) made of silicon oxide was formed using an electron beam heating vacuum deposition device. The O / Si ratio of the silica vapor deposition film was adjusted to 1.8 by adjusting the type of vapor deposition material. The overcoat agent described above was gravure coated onto the gas barrier layer and dried to form a 0.3 μm-thick overcoat layer with gas barrier properties. In this way, an intermediate layer A having a gas barrier layer made of silica formed thereon was obtained.

[0057] (Preparation of intermediate layer B) An anchor coating agent was applied to the same unstretched polyethylene film as used for intermediate layer A by gravure coating and dried to form a 0.1 μm-thick anchor coating layer. Next, a 10 nm-thick transparent gas barrier layer (alumina vapor deposition film) made of aluminum oxide was formed using an electron beam heating vacuum deposition device. The O / Al ratio of the alumina vapor deposition film was set to 1.5 by adjusting the type of vapor deposition material. An overcoat agent was applied to the gas barrier layer by gravure coating and dried to form a 0.3 μm-thick overcoat layer with gas barrier properties. In this way, an intermediate layer B having a gas barrier layer made of alumina formed thereon was obtained.

[0058] (Preparation of intermediate layer C) An anchor coating agent was applied to the same unstretched polyethylene film as used for intermediate layer A by gravure coating and dried to form a 0.1 μm thick anchor coating layer. Next, a 30 nm thick transparent gas barrier layer (silica vapor deposition film) made of silicon oxide was formed using a vacuum deposition device with electron beam heating. The O / Si ratio of the silica vapor deposition film was set to 1.8 by adjusting the type of vapor deposition material. In this way, an intermediate layer C was obtained in which a gas barrier layer made of silica was formed and which did not include an overcoat layer.

[0059] (Preparation of intermediate layer D) An anchor coating agent was applied by gravure coating to a 25 μm-thick biaxially oriented polyethylene film (three-layer structure: HDPE / MDPE / HDPE) that had been corona-treated on both sides, and dried to form a 0.1 μm-thick anchor coating layer. Next, a 30 nm-thick transparent gas barrier layer (silica vapor deposition film) made of silicon oxide was formed using a vacuum deposition device with electron beam heating. The O / Si ratio of the silica vapor deposition film was adjusted to 1.8 by adjusting the type of vapor deposition material. The above-mentioned overcoat agent was applied by gravure coating on top of the gas barrier layer and dried to form a 0.3 μm-thick overcoat layer with gas barrier properties. In this way, an intermediate layer D having a gas barrier layer made of silica formed thereon was obtained.

[0060] Example 1 A 25 μm thick uniaxially oriented polyethylene film (three-layer structure of HDPE / MDPE / HDPE, haze value: 5%) with one side corona-treated was prepared as the substrate. An image was formed on the corona-treated surface of the substrate by gravure printing using a urethane ink. Then, a white urethane ink (without light-blocking properties) was printed all over the formed image by gravure printing. In this way, an ink layer consisting of multiple inks was formed on the substrate. Next, the surface of the substrate on which the ink layer was formed and the surface of the intermediate layer A on which the gas barrier layer was formed were bonded together with a first adhesive layer by dry lamination using a urethane adhesive. Furthermore, a 40 μm thick unstretched polyethylene film (single layer of LLDPE) was prepared as a heat seal layer, and the intermediate layer and the heat seal layer were bonded together by dry lamination using a urethane adhesive. In this way, a laminate according to Example 1 was obtained.

[0061] Example 2 A laminate according to Example 2 was obtained in the same manner as in Example 1, except that a biaxially oriented polyethylene film (HDPE / MDPE / HDPE three-layer structure, haze value: 4.5%) having a thickness of 25 μm and one side of which was corona-treated was used as the substrate.

[0062] Example 3 A laminate according to Example 3 was obtained in the same manner as in Example 2, except that a light-blocking sepia ink was printed over the entire surface of the white urethane ink by gravure printing to form a light-blocking ink layer on the base layer.

[0063] Example 4 A laminate according to Example 4 was obtained in the same manner as in Example 3, except that intermediate layer B was used instead of intermediate layer A.

[0064] Example 5 The same heat seal layer as in Example 1 was prepared, and the heat seal layer was laminated on the gas barrier layer side of the intermediate layer C by dry lamination using a gas barrier adhesive. The gas barrier adhesive constituting the second adhesive layer was an epoxy adhesive prepared by mixing 23 parts by mass of a solvent made by mixing ethyl acetate and methanol at a mass ratio of 1:1 with 16 parts by mass of Maxieve C93T manufactured by Mitsubishi Gas Chemical Company, Inc. and 5 parts by mass of Maxieve M-100 manufactured by Mitsubishi Gas Chemical Company, Inc. The thickness of the gas barrier adhesive was 3 μm. A 25 μm-thick biaxially oriented polyethylene film (three-layer structure of HDPE / MDPE / HDPE, haze value: 5%) with one side corona-treated was prepared as the substrate. An image was formed on the corona-treated surface of the substrate by gravure printing using a urethane ink. Then, a white urethane ink (without light-blocking properties) was printed all over the formed image by gravure printing. In this way, an ink layer consisting of multiple inks was formed on the substrate. Furthermore, the ink layer side of the substrate and the intermediate layer side of the laminate of the intermediate layer C and the heat seal layer were joined by a dry lamination method using a urethane adhesive. In this way, a laminate according to Example 5 was obtained. In this example, the second adhesive layer was formed from a gas barrier adhesive. The layer structure of Example 5 is shown in Fig. 3. In Example 5, the gas barrier layer 21 is located on the heat seal layer 30 side.

[0065] Example 6 A laminate according to Example 6 was obtained in the same manner as in Example 1, except that a 25 μm-thick unstretched polyethylene film (with a three-layer structure of HDPE / MDPE / HDPE) that had been corona-treated on both sides was used as the intermediate layer. Example 6 is an example that does not include a gas barrier layer.

[0066] (Comparative Example 1) A laminate according to Comparative Example 1 was obtained in the same manner as in Example 1, except that a 25 μm-thick unstretched polyethylene film (three-layer structure of HDPE / MDPE / HDPE, haze value: 30%) with one side corona-treated was used as the substrate.

[0067] (Comparative Example 2) A laminate according to Comparative Example 2 was obtained in the same manner as in Example 1, except that intermediate layer D was used instead of intermediate layer A.

[0068] The laminates according to the examples and comparative examples were evaluated as follows. (Recyclability) The wt% of polyethylene in the laminate of each example was calculated based on the above formula (1), and the evaluation was based on the following two levels. 〇 (good): Contains 90wt% or more polyethylene. × (bad): The polyethylene content is less than 90 wt%. (Image visibility) For each example of the laminate, the image was visually observed through the substrate from the side opposite to the side on which the ink layer was formed, and a sensory evaluation was performed. The evaluation was rated on the following two levels. ◯ (good): The image is clearly visible. ×(bad): The image appears cloudy.

[0069] (Puncture strength) The puncture strength was measured in accordance with JIS Z 1707: 2019. The laminate according to each example was held flat under tension, and a hemispherical needle with a diameter of 1.0 mm and a tip radius of 0.5 mm was pressed against it from the substrate side at a rate of 50 mm / min, and the force (Newton: N) at the time of puncture was measured. (shock resistance) Using the laminate according to each example, ten packaging bags measuring 100 mm x 150 mm were produced, the peripheral edges of which were heat-sealed. The packaging bag was filled with 200 g of distilled water, heat-sealed, and stored at 5°C for one day. After storage, each packaging bag was dropped 50 times from a height of 1.5 m, and the number of packaging bags that broke was recorded.

[0070] (Light blocking property) The light-blocking property was measured using a measuring instrument in accordance with JIS K 7361-1: 1997. The laminate according to each example was irradiated with light from the substrate side to measure the total light transmittance. (Oxygen Transmission Rate: OTR) Measurement was carried out using the Mocon method under conditions of 30° and 70% RH (relative humidity). (Water vapor transmission rate: WVTR) Measurement was carried out using the Mocon method under conditions of 40° and 90% RH. (Oxidation suppression by shading) Using the laminates of each example, 180mm x 250mm packaging bags with heat-sealed edges were prepared. 60g of potato chips were filled into the packaging bags, which were then heat-sealed and stored for two weeks under the light of a white fluorescent lamp (illumination intensity 1000Lx) at 40℃ and 75%RH. After the storage period, the packaging bag was opened, the contents were removed, and crushed. The oils and fats were extracted from the crushed contents using ethyl ether, and the peroxide value (POV) was measured. The results are shown in Table 1.

[0071] [Table 1]

[0072] As shown in Table 1, all of the Examples and Comparative Examples had high recyclability, but the laminate of Comparative Example 1, in which both the substrate and intermediate layer were made of unstretched polyethylene films, was insufficient in image visibility and puncture strength. On the other hand, the laminate of Comparative Example 2, in which both the substrate and intermediate layer were made of stretched polyethylene films, was insufficient in impact resistance.

[0073] In the laminates of each example, one of the substrate and intermediate layer was made of a stretched polyethylene film, and the other was made of an unstretched polyethylene film, so that the laminates had high recyclability and also excellent puncture strength and impact resistance. Furthermore, by using a stretched polyethylene film as the substrate, the visibility of the image formed by the ink layer was also good.

[0074] Examples with a gas barrier layer and an overcoat layer showed good OTR and WVTR. Examples with an ink layer having light-blocking properties were able to effectively suppress oxidation of the contents caused by light.

[0075] The above describes each embodiment and example of the present invention, but the specific configuration is not limited to these embodiments, and includes modifications and combinations of configurations within the scope that does not deviate from the gist of the present invention.

[0076] For example, in the laminate of the present invention, the gas barrier layer may be provided on either the substrate side or the heat seal layer side of the intermediate layer. Furthermore, the gas barrier layer is not essential for the laminate of the present invention, i.e., when the laminate is used in a packaging material in which the contents do not require barrier properties, the gas barrier layer may be omitted. [Explanation of symbols]

[0077] 1, 2 laminate 10, 110 base material 10a, 110a front page 11 Ink layer 20, 120 middle class 21 Gas barrier layer 30 Heat seal layer 40 First adhesive layer 50 Second adhesive layer

Claims

1. A substrate; The middle class and a heat seal layer; a first adhesive layer provided between the substrate and the intermediate layer; a second adhesive layer disposed between the intermediate layer and the heat seal layer; A laminate comprising: the substrate, the intermediate layer, and the heat seal layer are each composed of polyethylene; the substrate is a stretched polyethylene film, the intermediate layer is a multilayer unstretched polyethylene film, The proportion of polyethylene in the laminate is 90% by mass or more. Laminate.

2. Either the substrate or the intermediate layer has a gas barrier layer. The laminate according to claim 1 .

3. The gas barrier layer includes a vapor deposition layer. The laminate according to claim 2 .

4. The vapor-deposited layer is made of a metal oxide. The laminate according to claim 3 .

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

6. The ink layer has a light-blocking property. The laminate according to claim 5 .

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

8. A laminate formed by joining the heat seal layer using the laminate according to any one of claims 1 to 7. packaging materials.

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