Laminates, packaging materials, and packaging bags

Abstract

To provide a laminate that has superior recycling suitability and superior heat sealability.SOLUTION: A laminate comprises a protective layer, a substrate layer, and a sealant layer, laminated in the stated order. The substrate layer and the sealant layer each comprise polyethylene. The protective layer is a heated and dried product of a composition that comprises at least one of a hydroxy group-containing polymer compound and a hydrolysate thereof, and at least one selected from the group consisting of a metalalkoxide, a silane coupling agent and hydrolysates thereof. In the laminate, the content of the polyethylene is 90 mass% or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to laminates, packaging materials and packaging bags using the same. More specifically, this invention relates to laminates with excellent recyclability and low environmental impact, packaging materials and packaging bags using the same. [Background technology]

[0002] Packaging bags are made from a variety of materials, depending on the nature and quantity of the contents being packaged, post-processing to prevent deterioration of the contents, the method of transporting the packaging bags, the method of opening the packaging bags, and the method of disposal.

[0003] For example, in flexible packaging bags that use laminated films, biaxially oriented films such as polypropylene or polyester are used to obtain the mechanical strength of the packaging bag, and polyethylene, polypropylene, or ethylene vinyl acetate copolymers are used as heat-sealing materials to seal the contents. In addition, to suppress the deterioration of the contents, aluminum foil or ethylene vinyl alcohol copolymers are laminated into the bags.

[0004] Laminates using the functionally separated materials described above are designed with an emphasis on suitability in each process, from packaging the contents to transportation, storage, and opening. However, with the growing awareness of environmental issues in recent years, emphasis has been placed on functions such as resource conservation and recyclability of various products, and similar functions are now required of laminates used in packaging bags. Generally, it is thought that packaging materials have high recyclability if the proportion of the main resin in the material is 90% by mass or more, but many conventional packaging materials are composed of multiple resin materials and, in some cases, paper and metal materials, and do not meet this standard, so they are not currently recycled.

[0005] Therefore, Patent Document 1 describes a laminate comprising a base material, an adhesive layer, and a heat-seal layer, wherein the base material and the heat-seal layer are made of polyethylene. By making the base material and the heat-seal layer from the same material, it becomes easier to meet the above-mentioned recyclability standards. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-55157 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, when the laminate described in Patent Document 1 is applied to a packaging bag, the bag-making process for forming the packaging bag involves a step in which the heat-seal layers (sealant layers) of the laminate are placed facing each other and heat-sealed by applying pressure from a high-temperature jig from the outer surface of the base material layer of the laminate. The jig of the heat-sealing machine becomes hot, and the outer surface of the base material layer that is in direct contact with the jig is exposed to high temperatures. As a result, with conventional laminates, problems such as the base material layer being affected by the heat and sticking to the jig, or wrinkles forming in the heat-sealed area, may occur, and the heat sealability was not sufficient. Therefore, the optimal conditions for bag-making temperature were narrow, resulting in poor productivity, and the strength of the packaging bag was sometimes insufficient.

[0008] Therefore, the present invention aims to provide a laminate that is excellent in recyclability and heat sealability, as well as a packaging material and a packaging bag using the same. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a laminate having a structure in which a protective layer, a base material layer, and a sealant layer are laminated in this order, wherein the base material layer and the sealant layer contain polyethylene, and the protective layer is a heat-dried product of a composition containing at least one of a hydroxyl group-containing polymer compound and its hydrolyzate, and at least one selected from the group consisting of metal alkoxides, silane coupling agents, and their hydrolyzates, and the proportion of polyethylene in the laminate is 90% by mass or more.

[0010] In the above laminate, the composition may contain a silane coupling agent, and the silane coupling agent may contain 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate.

[0011] In the above laminate, a vapor deposition layer may be provided between the base material layer and the sealant layer.

[0012] In the above laminate, the vapor deposition layer may contain a metal oxide.

[0013] In the above laminate, the thickness of the protective layer may be 0.4% or more and 2.0% or less of the total thickness of the laminate.

[0014] In the above laminate, the base material layer may contain high-density polyethylene or medium-density polyethylene.

[0015] In the above laminate, the sealant layer may contain low-density polyethylene.

[0016] In the above laminate, at least one of the base material layer and the sealant layer may be a layer made of an unstretched polyethylene film.

[0017] The above laminate includes an intermediate layer located between the base material layer and the sealant layer, and the intermediate layer may contain polyethylene.

[0018] In the laminate described above, the intermediate layer may contain high-density polyethylene or medium-density polyethylene.

[0019] In the laminate described above, the intermediate layer may be a layer made of unstretched polyethylene film.

[0020] The present invention also provides a packaging material comprising the laminate described above.

[0021] The present invention further provides a packaging bag which is a bag made from the above-mentioned packaging material. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a laminate that is excellent in recyclability and heat sealability, as well as a packaging material and a packaging bag using the same. [Brief explanation of the drawing]

[0023] [Figure 1] This is a schematic cross-sectional view of a laminate according to one embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view of a laminate according to another example of one embodiment of the present invention. [Modes for carrying out the invention]

[0024] The embodiments of the present invention will be described in detail below, with reference to the drawings as appropriate. However, the present invention is not limited to the following embodiments.

[0025] Figure 1 is a schematic cross-sectional view showing one embodiment of the laminate of the present invention. The laminate 1 shown in Figure 1 comprises a base layer 10, a first adhesive layer 40, an intermediate layer 20, a second adhesive layer 50, and a sealant layer 30. The base layer 10 has a protective layer 11 on its outer surface 10a, and the intermediate layer 20 has a vapor-deposited layer 14 on one side. The laminate 1 also has a printed layer 12 on its inner surface 10b, and a gas barrier coating layer 15 on the side of the vapor-deposited layer 14 opposite to the intermediate layer 20. Each layer will be described below.

[0026] The base layer 10 is a layer containing polyethylene, and may be, for example, an unstretched film made of polyethylene. The base layer 10 is the outer surface when forming a packaging material using the laminate 1. However, in the laminate 1 of this embodiment, the outer surface of the base layer 10 is protected by the protective layer 11.

[0027] The base layer 10 is made of high-density polyethylene (density 0.94 g / cm³). 3 (The above), or medium-density polyethylene (density 0.925~0.945 g / cm³) 3 A film made of the following materials can be used. These materials may be derived from petroleum, plants, or mixtures thereof. The surface of the base layer 10 can be treated with an easy-adhesion treatment by a dry surface treatment such as corona treatment or atmospheric pressure plasma treatment. It is also possible to use a multilayer unoriented polyethylene film, which is extruded by co-extrusion of polyethylenes with different densities, as the base layer 10.

[0028] The thickness of the base layer 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 base layer 10 10 μm or more, the strength of the laminate 1 can be improved. By making the thickness of the base layer 10 50 μm or less, the processability of the laminate 1 can be improved.

[0029] The base layer 10 can be manufactured by forming a film of polyethylene using a T-die method or an inflation method. When manufacturing the base layer 10 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 can be improved. Furthermore, by setting the MFR to 20 g / 10 min or less, it is possible to prevent the manufactured base layer 10 from rupturing.

[0030] When the base layer 10 is produced by the inflation method, the polyethylene MFR 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 can be improved. Furthermore, by setting the MFR to 5 g / 10 min or less, the film-forming properties can be improved.

[0031] The melting points of the high-density polyethylene and medium-density polyethylene used as the base layer 10 are generally between 120°C and 140°C. On the other hand, the melting point of the low-density polyethylene used as the sealant layer 30, which will be described later, is generally between 90°C and 120°C. In order to heat-seal the laminate of these base layer 10 and sealant layer 30, the heat seal bar, which is a jig of the heat sealing machine, is heated to about 130°C to 140°C, and heat is transferred to the sealant layer 30 through the base layer 10 and the intermediate layer 20, which will be described later, and heat welding occurs. Because the melting point of the polyethylene forming the base layer 10 and the temperature of the heat seal bar are almost the same, if the base layer 10 is used as the outermost layer, there is a possibility of cosmetic defects such as wrinkles and adhesion (detachment) of the base layer 10 to the heat seal bar due to heat welding.

[0032] The protective layer 11 is provided to prevent problems during heat sealing when making bags or filling and sealing, and to ensure suitability for heat sealing. For this purpose, the protective layer 11 may be provided as the outermost layer of the laminate.

[0033] The thickness of the laminate is changed according to the weight of the contents being packaged. When packaging lightweight contents, it is common to make it thinner to consider cost, and when filling with heavy contents, it is common to make it thicker to consider strength. As the thickness of the laminate increases, the amount of heat required for the heat-seal surface of the sealant layer to melt increases. For this reason, it is preferable to change the thickness of the protective layer 11 in proportion to the total thickness of the laminate. The ratio of the thickness of the protective layer 11 to the total thickness of the laminate is preferably 0.4% or more and 2.0% or less. If this ratio is 0.4% or more, the desired heat resistance can be easily obtained and better heat sealability can be obtained, and if it is 2.0% or less, the waste of material of the protective layer 11 can be suppressed and the increase in the amount of heat required for heat sealing can be suppressed.

[0034] The thickness of the protective layer 11 is adjusted according to the total thickness of the laminate as described above, but from the viewpoint of improving heat resistance and reducing the amount of heat required for heat sealing, it may be, for example, 0.1 to 5.0 μm, 0.2 to 4.0 μm, 0.3 to 2.0 μm, or 0.5 to 2.0 μm.

[0035] The protective layer 11 provided on the outer surface of the base layer 10 needs to have heat resistance so that it does not soften, melt, or decompose even when heated to, for example, 140°C during heat sealing. For this reason, the protective layer 11 is a heat-dried product of a composition containing at least one of a hydroxyl group-containing polymer compound and its hydrolysate, and at least one selected from the group consisting of metal alkoxides, silane coupling agents, and their hydrolysates.

[0036] When hydroxyl group-containing polymer compounds and their hydrolysates undergo a dehydration condensation polymerization reaction with metal alkoxides, silane coupling agents, and their hydrolysates, they become insoluble in water and organic solvents (resulting in the protective layer 11 having excellent water resistance), and sufficient heat resistance is obtained to provide heat sealability. Furthermore, when a packaging bag made of a packaging material using a laminate provided with the protective layer according to the present invention is filled with contents, sealed by heat sealing, and subjected to a boiling treatment in which it is immersed in hot water for heat sterilization, the protective layer 11 does not peel off and maintains a good appearance.

[0037] As a means of forming the protective layer 11, for example, it can be formed using a composition (hereinafter referred to as a coating agent) obtained by adding a hydroxyl group-containing polymer compound and a metal alkoxide and / or silane coupling agent to water or a water / alcohol mixture. The coating agent can be prepared, for example, by mixing a solution obtained by dissolving a water-soluble polymer, such as a hydroxyl group-containing polymer compound, in an aqueous solvent (water or a water / alcohol mixture) with a metal alkoxide and / or silane coupling agent, either directly or after being treated by hydrolysis or other means.

[0038] Examples of hydroxyl group-containing polymer compounds include polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinylpyrrolidone, starch, methylcellulose, carboxymethylcellulose, and sodium alginate. Among these, polyvinyl alcohol (PVA) is preferred when used as a coating agent for the protective layer because it exhibits particularly excellent heat-sealing properties.

[0039] Examples of metal alkoxides include compounds represented by the following general formula (I). M(OR 1 ) m (R 2 ) n-m …(I) In the above general formula (I), R 1 and R 2Each is independently a monovalent organic group having 1 to 8 carbon atoms, and is 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 of 1 to n. Incidentally, R 1 or R 2 When there are a plurality of them, R 1 each other or R 2 each other may be the same or different.

[0040] Specific examples of the metal alkoxide include tetraethoxysilane [Si(OC2H5)4], triisopropoxyaluminum [Al(O-2’-C3H7)3], and the like. Tetraethoxysilane and triisopropoxyaluminum are preferable because they are relatively stable in an aqueous solvent after hydrolysis.

[0041] Examples of the silane coupling agent include compounds 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 11 represents an alkyl group such as a methyl group or an ethyl group, R 12 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, and R 13 represents a monovalent organic functional group, and p represents an integer of 1 to 3. Incidentally, R 11 or R 12 When there are a plurality of them, R 11 each other or R 12 each other may be the same or different. Examples of the monovalent organic functional group represented by R 13 include a glycidyloxy group, an epoxy group, a mercapto group, a hydroxyl group, an amino group, an alkyl group substituted with a halogen atom, or a monovalent organic functional group containing an isocyanate group.

[0042] Examples of silane coupling agents include vinyltrimethoxysilane, γ-chloropropylmethyldimethoxysilane, γ-chloropropyltrimethoxysilane, glycidooxypropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropylmethyldimethoxysilane.

[0043] Furthermore, the silane coupling agent may be a polymer of the compound represented by the above general formula (II). A trimer is preferred as the polymer, and more preferably 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate. This is a condensed polymer of 3-isocyanate alkylalkoxysilane. It is known that in 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate, the isocyanate portion loses its chemical reactivity, but the reactivity is ensured by the polarity of the nulate portion. Generally, it is added to adhesives and the like, similar to 3-isocyanate alkylalkoxylane, and is known as an adhesion improver. Therefore, by adding 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate to a hydroxyl group-containing polymer compound, the water resistance of the protective layer 11 can be improved by hydrogen bonding. While 3-isocyanate alkylalkoxylanes are highly reactive and have low liquid stability, 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate, although its nurate portion is not water-soluble due to its polarity, disperses easily in aqueous solutions and can maintain stable liquid viscosity. Furthermore, the water resistance performance of 3-isocyanate alkylalkoxylanes and 1,3,5-tris(3-trialkoxysilylalkyl)isocyanurate is equivalent.

[0044] 1,3,5-Tris(3-trialkoxysilylalkyl)isocyanurate can also be produced by thermal condensation of 3-isocyanatetopropylalkoxysilane, and may contain the raw material 3-isocyanatetopropylalkoxysilane, but this does not pose a particular problem. More preferably, it is 1,3,5-tris(3-trialkoxysilylpropyl)isocyanurate, and even more preferably, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate. Since the methoxy group hydrolyzes quickly and those containing the propyl group are relatively inexpensive to obtain, 1,3,5-tris(3-trimethoxysilylpropyl)isocyanurate is practically advantageous.

[0045] When the coating agent contains a silane coupling agent, the molecular chains formed by the dehydration condensation polymerization reaction between the hydroxyl group-containing polymer compound and its hydrolysate and the metal alkoxide and its hydrolysate form an even higher-dimensional network structure, thereby improving the thermal water resistance of the laminate 1. When the silane coupling agent contains 1,3,5-tris(3-trialkoxysilylalkyl) isocyanurate, the silane coupling agent in the coating agent possesses flexibility derived from the nurate skeleton along with coupling performance, thus preventing peeling due to bending, crushing, etc. that occur during boiling, further improving the thermal water resistance of the laminate 1. When the silane coupling agent contains 1,3,5-tris(3-trimethoxysilylpropyl) isocyanurate, the thermal water resistance is further improved.

[0046] The amount of metal alkoxide in the coating agent can be 1 to 4 parts by mass, and may be 2 to 3 parts by mass, per 1 part by mass of the hydroxyl group-containing polymer compound, from the viewpoint of adhesion to the substrate layer 10. Similarly, the amount of silane coupling agent can be 0.01 to 1 part by mass, and may be 0.1 to 0.5 parts by mass, per 1 part by mass of the hydroxyl group-containing polymer compound. When a silane compound (alkoxysilane) is used as the metal alkoxide, the amount of silane compound (metal alkoxide and silane coupling agent) in the coating agent can be 1 to 4 parts by mass, and may be 2 to 3 parts by mass, per 1 part by mass of the hydroxyl group-containing polymer compound.

[0047] The coating agent may also contain isocyanate compounds or known additives such as dispersants, stabilizers, viscosity modifiers, and colorants, as needed, to the extent that they do not impair the heat water resistance and water resistance. Heat water resistance refers to practical applicability to boiling sterilization treatment, meaning that when laminate 1 or a packaging bag made using laminate 1 is immersed in 80°C hot water and subjected to boiling sterilization treatment for 30 minutes, no significant peeling, lifting, or roughening occurs in the protective layer.

[0048] The coating agent can be applied by methods such as dipping, roll coating, gravure coating, reverse gravure coating, air knife coating, comma coating, die coating, screen printing, spray coating, and gravure offset. The coating film obtained by applying the coating agent can be dried by methods such as hot air drying, hot roll drying, high-frequency irradiation, infrared irradiation, UV irradiation, or a combination thereof.

[0049] The temperature at which the above coating film is dried can be, for example, 50 to 150°C, and preferably 70 to 100°C. By keeping the drying temperature within this range, thermal shrinkage of the substrate layer 10 can be prevented.

[0050] The protective layer 11 may be formed using a coating agent containing a hydroxyl group-containing polymer compound (e.g., polyvinyl alcohol-based resin) and a silane compound. Acid catalysts, alkali catalysts, photoinitiators, etc., may be added to the coating agent as needed.

[0051] Examples of silane compounds include silane coupling agents, polysilazanes, and siloxanes. Specifically, examples include tetramethoxysilane, tetraethoxysilane, glycidoxypropyltrimethoxysilane, acryloxypropyltrimethoxysilane, and hexamethyldisilazane.

[0052] Since the protective layer 11 is a heat-dried product of the above coating agent, the protective layer 11 contains carbon atoms and silicon atoms. The molar ratio of silicon atoms to carbon atoms (Si / C) on the surface of the protective layer 11 may be 0.1 or more and 1 or less, 0.2 or more and 0.9 or less, 0.4 or more and 0.8 or less, or 0.4 or more and 0.6 or less. When the Si / C on the surface of the protective layer 11 is 0.1 or more, the water resistance of the protective layer 11 is further improved, and the water resistance tends to improve further as the Si / C increases. When the Si / C on the surface of the protective layer 11 is 1 or less, the brittleness of the surface of the protective layer 11 can be reduced, and the brittleness of the protective layer 11 tends to be further reduced as the Si / C decreases. When the protective layer becomes brittle, the surface of the protective layer may powderize and detach, which can lead to deterioration of the appearance of the laminate or damage. If the Si / C ratio on the surface of the protective layer 11 is within the above range, then, for example, when a packaging bag is formed using a laminate 1 having the protective layer 11 as the outermost layer, deterioration of the appearance and damage to the packaging bag can be suppressed. The Si / C ratio on the surface of the protective layer 11 can be measured by the method described in the examples below.

[0053] To improve the adhesion between the base material layer 10 and the protective layer 11, an adhesion-enhancing layer may be provided on the base material layer 10, to the extent that it does not impair recyclability.

[0054] The printed layer 12 can be formed on the outer surface 10a of the substrate layer 10, which is the side on which the protective layer 11 is formed, or on the inner surface 10b, which is the side on which it is laminated with the intermediate layer 20. The method of forming the image is not particularly limited and can be done by conventional gravure printing or flexographic printing, using inks appropriate for each. As for the inks, there are solvent-based inks and water-based inks, but it is preferable to use water-based inks from an environmental standpoint. In addition, the outer surface 10a or inner surface 10b of the substrate layer 10 may be subjected to surface treatments such as corona treatment or plasma treatment to improve the adhesion of the printed layer 12.

[0055] The intermediate layer 20 is a layer containing polyethylene, and may be, for example, an unoriented film made of polyethylene. From the viewpoint of strength and heat resistance, high-density polyethylene and medium-density polyethylene are preferred as the polyethylene contained in the intermediate layer 20. These materials may be derived from petroleum, plants, or mixtures thereof. As with the base layer 10, it is also possible to use an unoriented polyethylene film with a multilayer structure obtained by co-extrusion of polyethylenes of different densities as the intermediate layer 20. Furthermore, the surface of the intermediate layer 20 can be treated with an easy-adhesion treatment by dry surface treatment such as corona treatment or atmospheric pressure plasma treatment.

[0056] Here, unoriented polyethylene film refers to a polyethylene film in which no stretching treatment is performed during film formation, and the film is composed of spherical crystals (spherulites) of about 10 to 100 μm in size, made up of randomly folded polyethylene molecular chains, which are linked together by amorphous molecules. Unoriented polyethylene film has the property that when subjected to a strong impact, the spherulites break, and the molecular chains orient and stretch, preventing the film itself from tearing. Therefore, a package made from a laminate in which unoriented polyethylene film is laminated as a base layer 10, an intermediate layer 20, and a sealant layer 30 (a package bag made, filled with contents and sealed) has the characteristic of having excellent drop strength.

[0057] 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 can be improved. By making the thickness of the intermediate layer 20 50 μm or less, the processability of the laminate can be improved.

[0058] The intermediate layer 20 can be produced by forming a film of polyethylene using a T-die method or an inflation method. When producing 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 can be improved. Furthermore, by setting the MFR to 20 g / 10 min or less, it is possible to prevent the produced film from rupturing.

[0059] When the intermediate layer 20 is produced by the inflation method, the polyethylene MFR 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 can be improved. Furthermore, by setting the MFR to 5 g / 10 min or less, the film-forming ability can be improved.

[0060] In the laminate 1, a vapor-deposited layer 14 is formed on at least one surface of the intermediate layer 20. In this embodiment, the vapor-deposited layer 14 is formed on the surface of the intermediate layer 20 facing the second adhesive layer 50, but it may also be formed on the opposite surface. The vapor-deposited layer 14 imparts oxygen barrier properties and water vapor barrier properties to the laminate 1.

[0061] The structure of the vapor-deposited layer 14 can be, for example, a vapor-deposited layer made of a metal oxide such as aluminum oxide, silicon oxide, magnesium oxide, or tin oxide. From the viewpoint of transparency and barrier properties, the metal oxide may be selected from the group consisting of aluminum oxide, silicon oxide, and magnesium oxide. Furthermore, considering cost, it is selected from aluminum oxide and silicon oxide. Furthermore, from the viewpoint of excellent tensile stretchability during processing, it is more preferable to use a layer made of silicon oxide. By making the vapor-deposited layer 14 a barrier film made of a metal oxide, high barrier properties can be obtained with a very thin layer that does not affect the recyclability of the laminate 1.

[0062] Because a vapor-deposited layer made of metal oxide is transparent, it has the advantage of being less likely to cause users to mistakenly believe that metal foil is used when handling the laminated packaging material, compared to a vapor-deposited layer made of metal.

[0063] The thickness of the vapor-deposited layer made of aluminum oxide is preferably between 5 nm and 30 nm. A thickness of 5 nm or more provides sufficient gas barrier properties. Furthermore, a thickness of 30 nm or less suppresses the occurrence of cracks due to deformation caused by internal stress in the thin film, thereby suppressing a decrease in gas barrier properties. However, a thickness exceeding 30 nm is undesirable from an economic standpoint because it tends to increase costs due to increased material usage and longer film formation times. From the same viewpoint as above, a thickness of 7 nm or more and 15 nm is more preferable.

[0064] The thickness of the silicon dioxide deposition layer is preferably between 10 nm and 50 nm. A thickness of 10 nm or more provides sufficient gas barrier properties. A thickness of 50 nm or less suppresses crack formation due to deformation caused by internal stress in the thin film, thereby suppressing a decrease in gas barrier properties. However, a thickness exceeding 50 nm is undesirable from an economic standpoint because it tends to increase costs due to increased material usage and longer film formation times. From the same viewpoint as above, a thickness of 20 nm or more and 40 nm is more preferable.

[0065] The deposited layer 14 can be formed, for example, by vacuum deposition. For vacuum deposition, physical vapor deposition or chemical vapor deposition can be used. Examples of physical vapor deposition include vacuum deposition, sputtering, and ion plating, but are not limited to these. Examples of chemical vapor deposition include thermal CVD, plasma CVD, and photoCVD, but are not limited to these.

[0066] In the vacuum deposition methods described above, resistance heating vacuum deposition, EB (Electron Beam) heating vacuum deposition, induction heating vacuum deposition, sputtering, reactive sputtering, dual magnetron sputtering, and plasma chemical vapor deposition (PECVD) are particularly preferred. However, considering productivity, vacuum deposition is currently the most superior method. For the heating means in vacuum deposition, it is preferable to use one of the following methods: electron beam heating, resistance heating, or induction heating.

[0067] An anchor coat layer may be formed on the side of the intermediate layer 20 where the vapor-deposited layer 14 is formed, using a known anchor coat agent. This improves the adhesion of the vapor-deposited layer made of metal oxide. Examples of anchor coat 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.

[0068] Furthermore, in order to improve adhesion with the first adhesive layer 40, the second adhesive layer 50, the vapor-deposited layer 14, and the aforementioned anchor coat layer, a surface treatment such as corona treatment or plasma treatment may be applied to the corresponding surface of the intermediate layer 20.

[0069] A polyvinyl alcohol-based resin may be used as the anchor coating agent. The polyvinyl alcohol-based resin can be any resin having vinyl alcohol units formed by saponification of vinyl ester units, such as polyvinyl alcohol (PVA) and ethylene-vinyl alcohol copolymer (EVOH).

[0070] When using a polyvinyl alcohol-based resin as an anchor coating agent, methods for forming the anchor coating layer include coating with a polyvinyl alcohol-based resin solution and multilayer extrusion. In the case of multilayer extrusion, lamination may be carried out via an adhesive resin such as maleic anhydride-grafted polyethylene.

[0071] For the purpose of improving gas barrier properties and protecting the vapor-deposited layer 14, a gas barrier coating layer 15 may be provided on the vapor-deposited layer 14. The gas barrier coating layer 15 may contain a hydroxyl group-containing polymer compound, and more specifically, it may be a heat-dried product of a composition containing at least one of a hydroxyl group-containing polymer compound and its hydrolysate, and at least one selected from the group consisting of metal alkoxides, silane coupling agents, and their hydrolysates. The gas barrier coating layer 15 may be a layer consisting of the same components as the protective layer 11.

[0072] The gas barrier coating layer 15 can be formed, for example, using a composition (hereinafter referred to as "overcoat agent") obtained by adding a hydroxyl group-containing polymer compound and a metal alkoxide and / or silane coupling agent to water or a water / alcohol mixture. The overcoat agent can be prepared, for example, by mixing a solution obtained by dissolving a water-soluble polymer, such as a hydroxyl group-containing polymer compound, in an aqueous solvent (water or a water / alcohol mixture) with a metal alkoxide and / or silane coupling agent, either directly or after prior treatment such as hydrolysis of these agents.

[0073] The same explanation as for hydroxyl group-containing polymer compounds used in the preparation of coating agents may apply to hydroxyl group-containing polymer compounds used in the preparation of coating agents.

[0074] The same explanation as for metal alkoxides used in the preparation of coating agents may apply to metal alkoxides used in the preparation of coating agents.

[0075] The same explanation as for silane coupling agents used in the preparation of coating agents may apply to silane coupling agents used in the preparation of overcoat agents.

[0076] The amount of metal alkoxide in the overcoat agent can be 1 to 4 parts by mass, and may be 2 to 3 parts by mass, per 1 part by mass of the hydroxyl group-containing polymer compound, from the viewpoint of maintaining adhesion to the vapor-deposited layer and gas barrier properties. Similarly, the amount of silane coupling agent can be 0.01 to 1 part by mass, and may be 0.1 to 0.5 parts by mass, per 1 part by mass of the hydroxyl group-containing polymer compound. When a silane compound (alkoxysilane) is used as the metal alkoxide, the amount of silane compound (metal alkoxide and silane coupling agent) in the overcoat agent can be 1 to 4 parts by mass, and may be 2 to 3 parts by mass, per 1 part by mass of the hydroxyl group-containing polymer compound.

[0077] The overcoat agent may also contain isocyanate compounds or known additives such as dispersants, stabilizers, viscosity modifiers, and colorants, as needed, provided that they do not impair the gas barrier properties.

[0078] The overcoat agent can be applied in the same manner as the coating agent. The coating film formed by applying the overcoat agent can be dried in the same manner as the coating film formed by applying the coating agent.

[0079] When applying the overcoat agent, 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 vapor-deposited layer and the gas barrier coating layer can be further suppressed, and excellent barrier properties can be achieved.

[0080] The gas barrier coating layer may be formed using an overcoat agent containing a hydroxyl group-containing polymer compound (e.g., polyvinyl alcohol-based resin) and the silane compound described above. Acid catalysts, alkali catalysts, photoinitiators, etc., may be added to the overcoat agent as needed.

[0081] The thickness of the gas barrier coating layer is preferably 50 to 1000 nm, and more preferably 100 to 500 nm. When the thickness of the gas barrier coating layer is 50 nm or more, sufficient gas barrier properties tend to be obtained, and when it is 1000 nm or less, sufficient flexibility tends to be maintained.

[0082] The sealant layer 30 is made of polyethylene and is joined by heat sealing when forming packaging materials such as packaging bags using the laminate 1. From the viewpoint of heat sealability, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and very low-density polyethylene (VLDPE) are preferred for the polyethylene constituting the sealant layer 30. Furthermore, from the viewpoint of environmental impact, it is preferable that biomass-derived polyethylene or recycled polyethylene is used for the sealant layer 30. The sealant layer 30 may be made of an unoriented polyethylene film.

[0083] As a low-density polyethylene, its density is 0.900 g / cm³. 3 More than 0.925g / cm 3 Polyethylene with a density of less than 0.900 g / cm³ can be used. For linear low-density polyethylene, a density of 0.900 g / cm³ is acceptable. 3 More than 0.925g / cm 3 Polyethylene with a density of less than 0.900 g / cm³ can be used. Ultra-low density polyethylene has a density of 0.900 g / cm³. 3 Polyethylene of less than 150

[0084] The thickness of the sealant layer 30 can be appropriately changed according to the weight of the contents to be filled into the packaging material being manufactured. For example, when manufacturing a packaging bag to be filled with contents weighing 1 g or more and 200 g or less, the thickness of the sealant layer 30 is preferably 20 μm or more and 60 μm or less. By setting the thickness to 20 μm or more, it is possible to prevent the filled contents from leaking due to damage to the sealant layer 30. By setting the thickness to 60 μm or less, the processability of the laminate 1 can be improved.

[0085] As another example, when manufacturing a standing pouch filled with contents of 50g or more and 2000g or less, the thickness of the sealant layer 30 is preferably 50μm or more and 200μm or less. By making the thickness 50μm or more, it is possible to prevent the filled contents from leaking due to damage to the sealant layer 30. Furthermore, by making the thickness 200μm or less, the processability of the laminate 1 can be improved, and it is even more preferable to make it 150μm.

[0086] The polyethylene used in the base layer 10, the intermediate layer 20, and the sealant layer 30 may contain additives such as antioxidants, antistatic agents, nucleating agents, and ultraviolet absorbers.

[0087] The first adhesive layer 40 is a layer containing at least one type of adhesive and is provided between the base layer 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 sealant layer 30 to bond them together. Any adhesive, such as a one-component curing type or a two-component curing type urethane adhesive, can be used for the first adhesive layer 40 and the second adhesive layer 50. These adhesives may also contain layered inorganic compounds to further enhance their barrier properties.

[0088] 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 an adhesive layer in contact with the vapor-deposited layer using an adhesive that exhibits gas barrier properties can further suppress the decrease in gas barrier properties due to crack formation in the vapor-deposited layer. 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" from Mitsubishi Gas Chemical Company and "Paslim" from DIC Corporation.

[0089] 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 1.0 μm or more and 4.5 μm or less. By setting the thickness of the first adhesive layer 40 and the second adhesive layer 50 to 0.5 μm or more, the adhesion between the first adhesive layer 40 and the second adhesive layer 50 can be improved. By setting the thickness of the first adhesive layer 40 and the second adhesive layer 50 to 6 μm or less, the processability of the laminate 1 can be improved.

[0090] The first adhesive layer 40 and the second adhesive layer 50 can be formed by various known methods, such as the direct gravure roll coating method, gravure roll coating method, kiss coating method, reverse roll coating method, fontein method, and transfer roll coating method.

[0091] As described above, the laminate 1 of this embodiment has a base layer 10, an intermediate layer 20, and a sealant layer 30 made of polyethylene, so that the proportion of polyethylene in the laminate 1 is 90% by mass or more. As a result, the laminate 1 has high recyclability. When the base layer 10, the intermediate layer 20, and the sealant layer 30 are all made of polyethylene only, the proportion of polyethylene (by mass) in the laminate 1 can be calculated by the following formula (1). (Mass of base layer 10 + Mass of intermediate layer 20 + Mass of sealant layer 30) / Total mass of laminate 1 × 100 …(1)

[0092] By folding one laminate 1 with the sealant layers 30 facing each other, or by stacking two laminates 1 with the sealant layers 30 facing each other, and then joining the sealant layers 30 at the periphery while leaving the content filling area intact, a packaging bag made of laminate 1 can be formed. By performing the above joining while sandwiching a folded bottom film, a standing pouch can be formed. In addition, it can be used as various packaging bags such as pillow packaging, four-sided seals, three-sided seals, and gusset bags. Thus, laminate 1 can be applied to various packaging bags.

[0093] The laminate of the present invention enhances the heat resistance of the heat-sealed portion by providing a protective layer 11 as the outermost layer on the outer surface of the polyethylene-containing base layer 10, enabling bag manufacturing under appropriate conditions and improving the strength and appearance required for packaging bags. Furthermore, by combining it with an intermediate layer 20 made of an unoriented film with a vapor-deposited layer 14, the packaging bag will not easily rupture when dropped, even if filled with liquid, thus increasing the strength of the packaging bag.

[0094] Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments. For example, the laminate may not include one or more of the printed layer, intermediate layer, vapor-deposited layer, and gas barrier coating layer. If the laminate does not include an intermediate layer, the first adhesive layer is unnecessary, and the vapor-deposited layer may be provided on the substrate layer. Also, if the laminate does not include a gas barrier coating layer, the laminate may be as shown in Figure 2.

[0095] The laminate 2 shown in Figure 2 is obtained by removing the gas barrier coating layer 15 from the laminate 1. Instead of removing the gas barrier coating layer 15, the laminate 2 includes a second adhesive layer 60 formed using an adhesive that can exhibit gas barrier properties after curing (the gas barrier adhesive described above). This makes it possible to suppress the decrease in gas barrier properties due to crack formation in the vapor-deposited layer 14. The thickness and formation method of the second adhesive layer 60 may be the same as those of the second adhesive layer 50.

[0096] The laminated body 1 described above can be suitably used to form a packaging bag for packaging its contents. Examples of contents include liquids such as liquid seasonings, toiletries, soups, and liquid detergents; solids such as boiled dishes; and solid-liquid mixtures of liquids and solids such as curry.

[0097] Examples of packaging bags include flat pouch-shaped packaging bags and pillow packaging bags.

[0098] A flat pouch-shaped packaging bag may be formed by folding a single laminate 1 in half so that the sealant films face each other, and then heat-sealing three sides, or by stacking two laminates 1 so that the sealant films face each other, and then heat-sealing all four sides.

[0099] The pillow packaging bag formed from the laminate 1 may comprise a cylindrical body portion and a flange portion that extends along the axial direction of the body portion and protrudes from the body portion. The pillow packaging bag can be formed, for example, by using a known pillow packaging filling machine.

[0100] Laminates, packaging materials, and packaging bags relating to one aspect of the present invention are described, for example, in [1] to

[14] below, and these have been described in detail based on the above embodiments. [1] A laminate having a structure in which a protective layer, a base material layer, and a sealant layer are laminated in this order, The base layer and the sealant layer contain polyethylene. The protective layer comprises at least one of a hydroxyl group-containing polymer compound and its hydrolysate, A heat-dried product of a composition containing at least one selected from the group consisting of metal alkoxides, silane coupling agents, and their hydrolysates, A laminate in which the proportion of polyethylene in the laminate is 90% by mass or more. [2] The laminate according to [1], wherein the composition contains a silane coupling agent. [3] The laminate according to [2], comprising 1,3,5-tris(3-trialkoxysilylalkyl) isocyanurate as the silane coupling agent. [4] A laminate according to any one of [1] to [3], comprising a vapor-deposited layer located between the substrate layer and the sealant layer. [5] The laminate according to [4], wherein the vapor-deposited layer comprises a metal oxide. [6] The laminate according to any one of [1] to [5], wherein the thickness of the protective layer is 0.4% or more and 2.0% or less of the total thickness of the laminate. [7] The laminate according to any one of [1] to [6], wherein the base material layer comprises high-density polyethylene or medium-density polyethylene. [8] The laminate according to any one of [1] to [7], wherein the sealant layer comprises low-density polyethylene. [9] The laminate according to any one of [1] to [8], wherein at least one of the base material layer and the sealant layer is a layer made of unstretched polyethylene film.

[10] A laminate according to any one of [1] to [9], comprising an intermediate layer located between the base material layer and the sealant layer, wherein the intermediate layer contains polyethylene.

[11] The laminate according to

[10] , wherein the intermediate layer comprises high-density polyethylene or medium-density polyethylene.

[12] The laminate according to

[10] or [1], wherein the intermediate layer is a layer made of an unstretched polyethylene film. Packaging material comprising a laminate as described in any of

[13] [1] to

[12] . A packaging bag which is a product made from the packaging materials described in

[14]

[13] .

[0101] However, one aspect of the present invention is not limited to the above embodiments and [1] to

[14] above. One aspect of the present invention can be further modified without departing from its spirit. [Examples]

[0102] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0103] (Preparation of anchor coating agent) An 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 solid content (total amount of acrylic polyol and tolylene diisocyanate) of 5% by mass. To the diluted mixture, β-(3,4-epoxycyclohexyl)trimethoxysilane was added 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 then prepared by mixing.

[0104] (Preparation of overcoat agent) An overcoat agent was prepared by mixing the following solutions 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 0.1 N 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 solution (water:methanol mass ratio is 95:5). Solution C: A hydrolysis solution obtained by diluting 1,3,5-tris(3-trimethoxysilylpropyl) isocyanurate with a mixture of water and isopropyl alcohol (water:isopropyl alcohol mass ratio is 1:1) to a solid content of 5% by mass.

[0105] (Preparation of intermediate film A) A 25 μm thick unoriented polyethylene film (HDPE / MDPE / HDPE = 5 μm / 15 μm / 5 μm, 3-layer structure) with corona treatment on both sides, serving as an intermediate layer, was coated with the aforementioned anchor coating agent by gravure coating and dried to form a 0.1 μm thick anchor coating layer. Next, a 30 nm thick transparent vapor-deposited layer made of silicon dioxide was formed on the anchor coating layer using an electron beam heating vacuum deposition apparatus. The O / Si ratio of the vapor-deposited layer was set to 1.8 by adjusting the vapor-deposited material type. The aforementioned overcoat agent was coated on the vapor-deposited layer by gravure coating and dried to form a 0.3 μm thick gas barrier coating layer (overcoat layer) with gas barrier function. Thus, an intermediate film A with a vapor-deposited layer made of silica was obtained.

[0106] (Preparation of intermediate film B) An anchor coating agent was applied to one side of an unoriented polyethylene film identical to that of intermediate film A by gravure coating and dried to form an anchor coating layer with a thickness of 0.1 μm. Next, a transparent vapor-deposited layer of aluminum oxide with a thickness of 10 nm was formed on the anchor coating layer using a vacuum deposition apparatus with an electron beam heating method using aluminum as the deposition source. The O / Al ratio of the vapor-deposited layer was set to 1.5 by adjusting the amount of oxygen introduced. Furthermore, an overcoat agent was applied on top of the vapor-deposited layer by gravure coating and dried to form a gas barrier coating layer (overcoat layer) with a thickness of 0.3 μm that has gas barrier function. As a result, intermediate film B with a vapor-deposited layer made of alumina was obtained.

[0107] (Preparation of intermediate film C) Intermediate film C was obtained in the same manner as intermediate film A, except that a gas barrier coating layer was not formed.

[0108] (Preparation of coating solution (coating agent) for forming a protective layer) The following solutions A, B, and C were prepared. Solution A: A hydrolysis solution with a solid content of 5% by mass (SiO2 equivalent) obtained by adding 72.1 g of 0.1 N 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 solution (water:methanol mass ratio is 95:5). Solution C: A hydrolysis solution obtained by diluting 1,3,5-tris(3-trimethoxysilylpropyl) isocyanurate with a mixture of water and isopropyl alcohol (water:isopropyl alcohol mass ratio is 1:1) to a solid content of 5% by mass.

[0109] (Preparation of adhesive A) Adhesive A, a urethane-based adhesive, was prepared by mixing 100 parts by mass of Takelac A525 manufactured by Mitsui Chemicals, 11 parts by mass of Takenate A52 manufactured by Mitsui Chemicals, and 84 parts by mass of ethyl acetate.

[0110] (Adhesive B) Adhesive B, an epoxy-based gas barrier adhesive, was prepared by mixing 16 parts by mass of Maxive C93T manufactured by Mitsubishi Gas Chemical Company and 5 parts by mass of Maxive M-100 manufactured by Mitsubishi Gas Chemical Company.

[0111] (Example 1-1) As the base layer, a 25 μm thick unoriented polyethylene film (HDPE / MDPE / HDPE = 5 μm / 15 μm / 5 μm, 3-layer structure) with both sides corona-treated was prepared. A protective layer-forming coating solution was created by mixing solutions A and B, prepared as described above, in a mass ratio of 65 / 35 on the corona-treated outer surface of the base layer. This solution was applied by gravure coating, dried, and cured to form a 0.5 μm thick protective layer. Furthermore, a printed layer (1 μm thick) was formed on the corona-treated inner surface of the base layer using gravure printing with a urethane-based ink. No image was formed; the entire surface was coated with ink.

[0112] Next, the printed layer of the substrate layer and the corona-treated surface of the intermediate film A, where the vapor deposition layer was not formed, were bonded using a drynate method with adhesive A. This adhesive layer was designated as the first adhesive layer. The thickness of the first adhesive layer was 3 μm.

[0113] Furthermore, a 60 μm thick, single-sided corona-treated, unstretched polyethylene film (LLDPE single layer) was prepared as a sealant layer. The vapor-deposited side of the intermediate film A and the corona-treated side of the sealant layer were bonded using a drynate method with adhesive A as the second adhesive layer. The laminate of Example 1-1 was thus obtained.

[0114] (Examples 1-2) The laminate of Example 1-2 was obtained in the same manner as in Example 1-1, except that the thickness of the protective layer was 2 μm and the thickness of the sealant layer was 150 μm.

[0115] (Examples 1-3) The laminate of Example 1-3 was obtained in the same manner as in Example 1-1, except that intermediate film B was used instead of intermediate film A.

[0116] (Examples 1-4) The laminate of Example 1-4 was obtained in the same manner as in Example 1-1, except that intermediate film C was used instead of intermediate film A, and adhesive B was used as the second adhesive layer.

[0117] (Examples 1-5) The laminate of Example 1-5 was obtained in the same manner as in Example 1-1, except that the thickness of the protective layer was 4 μm, a 25 μm thick unoriented polyethylene film (HDPE / MDPE / HDPE = 5 μm / 15 μm / 5 μm 3-layer structure) with corona treatment on both sides was used instead of intermediate film A, and the thickness of the sealant layer was 150 μm.

[0118] (Example 2-1) The laminate of Example 2-1 was obtained in the same manner as in Example 1-1, except that liquids A, B, and C were mixed in a mass ratio of 65 / 25 / 10, respectively, as a coating solution for forming a protective layer.

[0119] (Example 2-2) The laminate of Example 2-2 was obtained in the same manner as in Example 2-1, except that the thickness of the protective layer was 2 μm and the thickness of the sealant layer was 150 μm.

[0120] (Examples 2-3) The laminate of Example 2-3 was obtained in the same manner as in Example 2-1, except that intermediate film B was used instead of intermediate film A.

[0121] (Examples 2-4) The laminate of Example 2-4 was obtained in the same manner as in Example 2-1, except that intermediate film C was used instead of intermediate film A, and adhesive B was used as the second adhesive layer.

[0122] (Examples 2-5) The laminate of Example 2-5 was obtained in the same manner as in Example 2-1, except that the thickness of the protective layer was 4 μm, a 25 μm thick unoriented polyethylene film (HDPE / MDPE / HDPE = 5 μm / 15 μm / 5 μm 3-layer structure) with corona treatment on both sides was used instead of intermediate film A, and the thickness of the sealant layer was 150 μm.

[0123] (Example 3-1) The laminate of Example 3-1 was obtained in the same manner as in Example 1-1, except that liquids A, B, and C were mixed in a mass ratio of 45 / 45 / 10, respectively, as a coating solution for forming a protective layer.

[0124] (Example 3-2) The laminate of Example 3-2 was obtained in the same manner as in Example 3-1, except that the thickness of the protective layer was 2 μm and the thickness of the sealant layer was 150 μm.

[0125] (Example 3-3) The laminate of Example 3-3 was obtained in the same manner as in Example 3-1, except that intermediate film B was used instead of intermediate film A.

[0126] (Examples 3-4) The laminate of Example 3-4 was obtained in the same manner as in Example 3-1, except that intermediate film C was used instead of intermediate film A, and adhesive B was used as the second adhesive layer.

[0127] (Examples 3-5) The laminate of Example 3-5 was obtained in the same manner as in Example 3-1, except that the thickness of the protective layer was 4 μm, a 25 μm thick unoriented polyethylene film (HDPE / MDPE / HDPE = 5 μm / 15 μm / 5 μm 3-layer structure) with corona treatment on both sides was used instead of intermediate film A, and the thickness of the sealant layer was 150 μm.

[0128] (Comparative Examples 1-5) Laminates of Comparative Examples 1 to 5 were obtained in the same manner as in Examples 1-1 to 1-5, except that the protective layer forming coating solution was replaced with only solution B.

[0129] (Comparative Examples 6-10) Laminates of Comparative Examples 6 to 10 were obtained in the same manner as in Examples 1-1 to 1-5, except that a protective layer was not formed.

[0130] (Example 4-1) As a base layer, a 25 μm thick unoriented polyethylene film (HDPE / MDPE / HDPE = 5 μm / 15 μm / 5 μm, 3-layer structure) was prepared, with both sides corona-treated. The above-mentioned anchor coating agent was applied to one side of the base layer by gravure coating and dried to form a 0.1 μm thick anchor coating layer. Next, a 30 nm thick transparent vapor-deposited layer made of silicon oxide was formed on the anchor coating layer using an electron beam heating vacuum deposition apparatus. The O / Si ratio of the vapor-deposited layer was set to 1.8 by adjusting the vapor-deposited material type. The above-mentioned overcoat agent was applied to the vapor-deposited layer by gravure coating and dried to form a 0.3 μm thick gas barrier coating layer (overcoat layer) with gas barrier function.

[0131] Next, a protective layer-forming coating solution was prepared by mixing solutions A and B, prepared as a coating solution for forming a protective layer, in a mass ratio of 65 / 35 on the corona-treated surface of the substrate layer opposite to the side where the vapor-deposited layer was formed. This coating solution was then applied by gravure coating, dried, and cured to form a protective layer with a thickness of 0.3 μm. Furthermore, a 20 μm thick unstretched polyethylene film (single-layer LLDPE structure) that had been corona-treated on one side was prepared as a sealant layer. The gas barrier coating layer and the corona-treated surface of the sealant layer were joined by a dry-nate method using adhesive A as the adhesive layer. The laminate of Example 4-1 was thus obtained.

[0132] (Example 4-2) The laminate of Example 4-2 was obtained in the same manner as in Example 4-1, except that the vapor-deposited layer was changed to a transparent vapor-deposited layer made of aluminum oxide with a thickness of 10 nm.

[0133] (Example 4-3) The laminate of Example 4-3 was obtained in the same manner as in Example 4-1, except that adhesive A was replaced with adhesive B as described above, without providing a gas barrier coating layer.

[0134] (Example 4-4) The laminate of Example 4-4 was obtained in the same manner as in Example 4-1, except that the base layer did not have a vapor-deposited layer and a gas barrier coating layer (overcoat layer).

[0135] (Example 5-1) The laminate of Example 5-1 was obtained in the same manner as in Example 4-1, except that liquids A, B, and C were mixed in a mass ratio of 65 / 25 / 10, respectively, as a coating solution for forming a protective layer.

[0136] (Example 5-2) The laminate of Example 5-2 was obtained in the same manner as in Example 5-1, except that the vapor-deposited layer was changed to a transparent vapor-deposited layer made of aluminum oxide with a thickness of 10 nm.

[0137] (Example 5-3) The laminate of Example 5-3 was obtained in the same manner as in Example 5-1, except that adhesive A was replaced with adhesive B as described above, without providing a gas barrier coating layer.

[0138] (Examples 5-4) The laminate of Example 5-4 was obtained in the same manner as in Example 5-1, except that a vapor-deposited layer and a gas barrier coating layer (overcoat layer) were not provided on the base layer.

[0139] (Example 6-1) The laminate of Example 6-1 was obtained in the same manner as in Example 4-1, except that liquids A, B, and C were mixed in a mass ratio of 45 / 45 / 10, respectively, as a coating solution for forming a protective layer.

[0140] (Example 6-2) The laminate of Example 6-2 was obtained in the same manner as in Example 6-1, except that the vapor-deposited layer was changed to a transparent vapor-deposited layer made of aluminum oxide with a thickness of 10 nm.

[0141] (Example 6-3) The laminate of Example 6-3 was obtained in the same manner as in Example 6-1, except that adhesive A was replaced with adhesive B as described above, without providing a gas barrier coating layer.

[0142] (Example 6-4) The laminate of Example 6-4 was obtained in the same manner as in Example 6-1, except that the base layer did not have a vapor-deposited layer and a gas barrier coating layer (overcoat layer).

[0143] (Comparative Examples 11-14) Laminates of Comparative Examples 11 to 14 were obtained in the same manner as in Examples 4-1 to 4-4, except that the protective layer forming coating solution was replaced with only solution B.

[0144] (Comparative Examples 15-18) Laminates of Comparative Examples 15 to 18 were obtained in the same manner as in Examples 4-1 to 4-4, except that a protective layer was not formed.

[0145] <Rating> The following evaluations were performed on the laminates of each example and comparative example. The results are shown in Tables 1 to 10.

[0146] (Ratio of silicon atoms to carbon atoms (Si / C)) To determine the Si / C ratio, a spectrum was first obtained by performing narrow-field analysis on the exposed surface of the protective layer using the following measuring instruments and under the following measurement conditions. The ratio of Si to C was calculated from the obtained spectrum. Note that the ratio of silicon atoms to carbon atoms (Si / C) is expressed as a molar ratio. <Measuring equipment> JEOL Ltd. JPS-9030 Photoelectron Spectrometer <Measurement conditions> (Spectrum sampling conditions) Incident X-ray: MgKα (monochromatic X-ray, hν=1253.6eV) X-ray output: 10W (10kV 10mA) X-ray scanning area (measurement area): Circular area with a diameter of 6 mm Photoelectron capture angle: 90°

[0147] (Recyclability) Based on formula (1) above, the percentage (by mass) of polyethylene in the laminate for each example was calculated. The evaluation was conducted in the following two stages. A: The polyethylene content is 90% by mass or more. C: Polyethylene content is less than 90% by mass.

[0148] (Evaluation of heat sealability) Each prepared laminate was cut into 10 cm squares, folded in half with the sealant layer facing inward, and heat-sealed using a heat seal tester under the conditions of 140°C, 0.1 MPa pressure, and 1 second heating time. However, the heating time for Examples 1-2, 1-5, 2-2, 2-5, 3-2, 3-5, Comparative Example 2, 5, 7, and 10 was 3 seconds. The heat-sealed portion of the obtained samples was visually observed, and the heat sealability was evaluated based on whether or not the laminate adhered to the heat seal bar and whether or not there were wrinkles in the heat-sealed portion. The evaluation was performed based on the following criteria. (1) Adhesion to the heat seal bar A: No molten adhesion of the laminate to the heat seal bar was observed. B: The laminate is pseudo-adhered to the heat seal bar, but no melting or adhesion is observed, and it can be separated. C: The laminate melted and adhered to the heat seal bar. (2) Wrinkles in the heat-sealed area A: No wrinkles are observed in the heat-sealed area. C: Wrinkles are observed in the heat-sealed area.

[0149] (Impact resistance) Ten 100mm x 150mm packaging bags were prepared using the laminates from each example, with the edges heat-sealed. Heat sealing was performed under the same conditions as the heat-sealability evaluation described above. 200g of distilled water was filled into each packaging bag, sealed by heat sealing, and stored at 5°C for one day. After storage, each packaging bag was dropped 50 times from a height of 1.5m, and the number of bags that ruptured was recorded.

[0150] (Hot water resistance) Ten 100mm x 150mm packaging bags with heat-sealed edges were prepared using the laminates from each example. Heat sealing was performed under the same conditions as the heat-sealability evaluation described above. 200g of distilled water was filled into these packaging bags, sealed by heat sealing, and immersed in 80°C hot water for 30 minutes for boiling sterilization. The surface condition of the packaging after treatment was observed. The evaluation was performed based on the following criteria. A: No difference was observed in the protective layer before and after treatment. B: Slight lifting and roughness of the protective layer are observed. C: Peeling, lifting, and roughness are observed in the protective layer.

[0151] (water resistance) Ten 100mm x 150mm packaging bags with heat-sealed edges were prepared using the laminates from each example. Heat sealing was performed under the same conditions as the heat-sealability evaluation described above. 200g of distilled water was filled into these packaging bags, sealed by heat sealing, and immersed in tap water (without temperature control). After 12 hours, the bags were removed, and the surface condition after immersion was observed. The evaluation was performed based on the following criteria. A: No difference was observed in the protective layer before and after treatment. B: Slight lifting and roughness of the protective layer are observed. C: Peeling, lifting, and roughness are observed in the protective layer.

[0152] (Oxygen permeability: OTR) Oxygen permeability was measured using the Mocon method under conditions of 30°C and 70% RH (relative humidity). However, oxygen permeability was not measured for laminates without a vapor-deposited layer.

[0153] (Water vapor transmission rate: WVTR) Water vapor transmission was measured using the Mocon method under conditions of 40°C and 90% RH (relative humidity). However, water vapor transmission was not measured for laminates without a vapor-deposited layer.

[0154] [Table 1]

[0155] Table 2

[0156] Table 3

[0157] Table 4

[0158] Table 5

[0159] Table 6

[0160] Table 7

[0161] Table 8

[0162] Table 9

[0163] Table 10

[0164] As shown in Tables 1 to 10, all of the examples and comparative examples exhibited high recyclability and excellent impact resistance and gas barrier properties. However, when the protective layer consisted only of PVA, the protective layer had poor heat and water resistance, and the laminates of the comparative examples without a protective layer had poor heat sealability. Examples 2-1 to 2-5, 3-1 to 3-5, 5-1 to 5-4, and 6-1 to 6-4, which contained liquid C as the coating agent, showed a result of A in the heat and water resistance test. [Explanation of Symbols]

[0165] 1,2...Laminate, 10...Base layer, 10a...Outer surface of base layer, 10b...Inner surface of base layer, 11...Protective layer, 12...Printed layer, 14...Vaporized layer, 15...Gas barrier coating layer, 20...Intermediate layer, 30...Sealant layer, 40...First adhesive layer, 50,60...Second adhesive layer.

Claims

1. A laminate having a structure in which a protective layer, a base layer, and a sealant layer are stacked in this order, The base layer and the sealant layer contain polyethylene. The aforementioned protective layer At least one of a hydroxyl group-containing polymer compound and its hydrolysate, A heat-dried product of a composition containing at least one selected from the group consisting of metal alkoxides, silane coupling agents, and hydrolysates thereof, A laminate in which the proportion of polyethylene in the laminate is 90% by mass or more.

2. The laminate according to claim 1, wherein the composition contains a silane coupling agent.

3. The laminate according to claim 2, wherein the silane coupling agent comprises 1,3,5-tris(3-trialkoxysilylalkyl) isocyanurate.

4. The laminate according to claim 1, further comprising a vapor-deposited layer located between the substrate layer and the sealant layer.

5. The laminate according to claim 4, wherein the vapor-deposited layer contains a metal oxide.

6. The laminate according to claim 1, wherein the thickness of the protective layer is 0.4% or more and 2.0% or less of the total thickness of the laminate.

7. The laminate according to claim 1, wherein the base layer comprises high-density polyethylene or medium-density polyethylene.

8. The laminate according to claim 1, wherein the sealant layer contains low-density polyethylene.

9. The laminate according to claim 1, wherein at least one of the base layer and the sealant layer is a layer made of unstretched polyethylene film.

10. The laminate according to claim 1, further comprising an intermediate layer located between the base material layer and the sealant layer, wherein the intermediate layer contains polyethylene.

11. The laminate according to claim 10, wherein the intermediate layer comprises high-density polyethylene or medium-density polyethylene.

12. The laminate according to claim 10, wherein the intermediate layer is a layer made of an unstretched polyethylene film.

13. A packaging material comprising a laminate according to any one of claims 1 to 12.

14. A packaging bag which is a bag made of the packaging material described in claim 13.

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