Laminates and packaging materials

Abstract

To provide a laminate that is highly recyclable and has excellent heat-sealing properties. [Solution] A laminate comprising at least a base layer, an adhesive layer, and a sealant layer in this order, wherein a protective layer is provided on the outermost side of the base layer, the protective layer is made of a thermosetting resin, both the base layer and the sealant layer are made of polyethylene resin, the base layer has a probe drop temperature of 180°C or higher, the proportion of polyethylene in the laminate is 90% by mass or higher, and the adhesive layer is formed from a polyamine-based adhesive or a urethane-based adhesive having gas barrier properties.

Description

Technical Field

[0001] The present invention relates to a laminate and a packaging material using the same. More specifically, the present invention relates to a laminate with excellent recyclability of materials and low environmental load, and a packaging material using the same.

Background Art

[0002] For packaging bags, various materials are combined and used depending on the nature of the contents to be packaged, the amount of the contents, post-treatment for preventing deterioration of the contents, the form of transporting the packaging bag, the method of opening the packaging bag, the method of discarding, etc.

[0003] For example, in the packaging bag of a flexible package using laminated films, biaxially stretched films such as polypropylene and polyester are used to obtain the mechanical strength of the packaging bag, and polyethylene, polypropylene, ethylene vinyl acetate copolymer, etc. are used as heat-sealing materials to seal the contents as a packaging bag. It is used in combinations such as. In addition, in order to suppress deterioration of the contents, aluminum foil, ethylene vinyl alcohol copolymer, etc. are also laminated.

[0004] The laminate using the above various materials with separated functions is designed with emphasis on suitability in each process from packaging of contents to transportation, storage, opening, etc. However, due to the increasing awareness of environmental problems in recent years, emphasis has been placed on functions such as resource saving and recyclability of various products, and the same functions have been required for the laminate used in packaging bags. Generally, it is considered that the recyclability is high when the proportion of the main resin contained in the packaging material is 90% by mass or more. However, most of the conventional packaging materials are composed of a plurality of resin materials and sometimes include paper and metal materials, and since they do not meet this standard, they are not recycled at present.

[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, and a packaging material using the same. [Means for solving the problem]

[0009] As a means to solve the above problems, a first aspect of the present invention is a laminate comprising at least a base layer, an adhesive layer, and a sealant layer in this order, wherein a protective layer is provided on the outermost side of the base layer, the protective layer is made of a thermosetting resin, both the base layer and the sealant layer are made of polyethylene resin, the base layer has a probe drop temperature of 180°C or higher, the proportion of polyethylene in the laminate is 90% by mass or higher, and the adhesive layer is formed from a polyamine-based adhesive or a urethane-based adhesive having gas barrier properties.

[0010] The laminate according to the present invention reduces and mitigates thermal damage during heat sealing on the surface of the laminate by forming a thermosetting resin film that serves as a protective layer on the outermost surface of the base material layer. Furthermore, since the resin base material made of polyethylene, which has a probe drop temperature in the range of 180°C or higher, has good transparency, it also has high visibility even when the printed layer, such as a design or text, is placed on the inner surface of the base material. The printed layer can be appropriately placed on any surface of the base material, but this effect is more easily obtained when the printed layer is placed on the inner surface of the base material.

[0011] Furthermore, a second aspect of the present invention is a laminate according to the first aspect, wherein the adhesive layer is a cured product of a resin composition containing a polyester polyol, an isocyanate compound, and a phosphate-modified compound.

[0012] Furthermore, a third aspect of the present invention is a laminate according to the first or second aspect, wherein the thickness of the adhesive layer is 0.1 μm or more and 20 μm or less.

[0013] Furthermore, a fourth aspect of the present invention is a laminate according to any one of the first to third aspects, wherein the protective layer comprises at least one of a metal alkoxide, a hydrolysate of a metal alkoxide, and a reaction product of a metal alkoxide or a hydrolysate of a metal alkoxide, and a water-soluble polymer.

[0014] Further, a fifth aspect of the present invention is the laminate according to any one of the first to fourth aspects, comprising a gas barrier layer on the surface of the base material layer facing the sealant layer.

[0015] Further, a sixth aspect of the present invention is the laminate according to the fifth aspect, wherein the gas barrier layer comprises an inorganic compound.

[0016] Further, a seventh aspect of the present invention is the laminate according to the sixth aspect, comprising a coating layer on the surface of the gas barrier layer facing the sealant layer.

[0017] Further, an eighth aspect of the present invention is a packaging material composed of the laminate according to any one of the first to seventh aspects.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a laminate excellent in recyclability and heat sealability, and a packaging material using the same.

Brief Description of the Drawings

[0019] [Figure 1] FIG. 1 is a schematic cross-sectional view showing an embodiment of the laminate according to the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of the laminate of Example 1.

Modes for Carrying Out the Invention

[0020] The laminate according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an embodiment of the laminate 10 according to the present invention, and FIG. 2 is a schematic cross-sectional view of the laminate 11 of Example 1.

[0021] As shown in Fig. 1, the laminate 10 according to the present invention is a laminate in which a base material layer 1, a gas barrier layer 5, an adhesive layer 2, and a sealant layer 3 are laminated in this order, and a protective layer 4 is laminated on the outermost surface side of the base material layer 1. Further, in the laminate 11 of Example 1 shown in Fig. 2, a printing layer 6 is provided on the back surface side of the base material layer 1. Both the base material layer 1 and the sealant layer 3, which are the main components, are made of polyethylene resin.

[0022] <Method for Measuring Probe Drop Temperature> Using an atomic force microscope equipped with a nano thermal microscope composed of a cantilever having a heating mechanism, the cantilever is brought into contact with the surface of a resin base material in an individual state fixed to a sample stage, and a constant force (contact pressure) is applied to the cantilever in contact mode. When heating is performed by applying a voltage, the sample surface thermally expands and the cantilever rises. When the cantilever is further heated, the sample surface softens and a large change in hardness is observed, and the cantilever descends and penetrates into the sample surface. The abrupt change in displacement at this time is detected. This change point of displacement is the softening point, and by converting the voltage to temperature, the softening temperature, that is, the probe drop temperature, is obtained.

[0023] The probe drop temperature is the temperature obtained by measuring the rising and falling behavior of the probe by locally performing thermal analysis. To evaluate the probe drop temperature, an atomic force microscope equipped with a nano thermal microscope composed of a cantilever (probe) having a heating mechanism is used. When the cantilever is brought into contact with the surface of a solid sample fixed to a sample stage and a constant force (contact pressure) is applied to the cantilever (probe) in contact mode and heating is performed by applying a voltage, the sample surface thermally expands and the cantilever (probe) rises. When the cantilever (probe) is further heated, the sample surface softens and a large change in hardness is observed, and the cantilever (probe) descends and penetrates into the sample surface. The abrupt change in displacement at this time is detected. This change point of voltage is the probe drop start point, and by converting the voltage to temperature, the probe drop temperature is obtained. By performing such measurement, the probe drop temperature in the nano scale region, locally and near the surface, can be known.

[0024] The atomic force microscope (AFM) used is the MPF-3D-SA (product name) and Ztherm system (product name) manufactured by Oxford Instruments Ltd. However, the system is not limited to these specific instruments; Bruker Japan's Nano Thermal Analysis (product name) series and nanoIR (product name) series are also acceptable. Furthermore, it is possible to attach the Nano Thermal Analysis (product name) as an accessory to AFMs from other manufacturers for measurement.

[0025] The cantilever (probe) used is the AN2-200 (product name) manufactured by Anasis Instruments. However, it is not limited to this cantilever; other cantilevers (probes) that can adequately reflect the laser light and to which voltage can be applied may be used.

[0026] The voltage range applied to the cantilever (probe) depends on the resin or other material being measured, but 1V to 10V is preferable. To minimize damage to the sample and achieve higher spatial resolution, 3V to 8V is more preferable.

[0027] The measurable probe temperature drop range depends on the resin being measured, but generally, measurements can be taken from around 25°C (room temperature) to around 400°C. The temperature range for calculating the probe temperature drop is preferably between 25°C and 300°C.

[0028] In measuring the probe temperature drop, heat is applied to the cantilever (probe) while maintaining a constant contact pressure. The contact pressure must be in contact with the sample but must not damage the surface. The spring constant of the cantilever (probe) is preferably 0.1 to 3.5 N / m, and to perform measurements in both tapping mode and contact mode, it is preferable to use a cantilever (probe) with a spring constant of 0.5 to 3.5 N / m. The contact pressure is preferably 0.1 to 3.0 V.

[0029] The heating rate of the cantilever (probe) depends on the heating mechanism of the cantilever (probe), but generally it is preferable to heat it at a heating rate of 0.1 V / sec to 10 V / sec. More preferably, it is preferable to heat it at a heating rate of 0.2 V / sec to 5 V / sec. When the sample surface softens, the cantilever penetrates the sample and the needle descends. The amount of penetration of the cantilever (probe) needs to be deep enough to recognize the peak top of the softening curve, so 3 to 500 nm is preferable. If the amount of penetration is too large, the cantilever (probe) may break, so more preferably it is 5 to 100 nm.

[0030] While not limited to these methods, one could also approximate the expansion curve and the softening curve using functions as needed, and calculate their intersection point to determine the probe descent start point and probe descent temperature. Alternatively, one could use an analytical method where the peak top of the displacement is used as the probe descent start point and probe descent temperature. In expansion or softening, the change could be defined as the displacement from the steady state up to a certain value.

[0031] To accurately measure the temperature of the samples, a calibration curve was created after the sample measurement. Four types of samples were used for calibration: polycaprolactone (melting point: 55°C), low-density polyethylene (LDPE, melting point: 110°C), polypropylene (PP, melting point: 164°C), and polyethylene terephthalate (PET, melting point: 235°C). Each sample was measured twice at different measurement positions, and the average value was used to create a calibration curve, which in turn created the calibration curve. Using this calibration curve, the voltage was used as the probe drop start point, and this was converted to temperature to obtain the probe drop temperature.

[0032] <Base material layer> The base layer 1 has a density of 0.925 g / cm³. 3The material consists of high-density polyethylene and medium-density polyethylene. The thickness of the base layer 1 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 1 10 μm or more, the strength of the laminate 10 can be improved. By making the thickness of the base layer 1 50 μm or less, the processability of the laminate 10 can be improved.

[0033] Furthermore, the base layer 1 may be subjected to surface treatment such as corona treatment in order to improve its adhesion with the protective layer 4 and the gas barrier layer 5.

[0034] In this invention, the probe temperature drop was measured for various polyethylene resins, and it was found that when the probe temperature drop was 180°C or higher, the haze of the base material 1 was small, transparency was achieved, and sufficient visibility was ensured, and when it was 200°C or higher, the transparency improved even further. This makes it possible to place the printed layer 6 on the inner surface side of the base material layer 1. The position of the printed layer 6 does not necessarily have to be on the back side of the base material layer 1, but this effect is more easily obtained when the printed layer 6 is placed on the inner surface side of the base material.

[0035] <Gas barrier layer> In the layer configuration shown in Figure 1, it is desirable that the substrate layer 1 has an inorganic compound layer or a gas barrier layer 5 consisting of an inorganic compound layer and a coating layer on the side facing the sealant layer 3. The gas barrier layer 5 functions as a barrier layer that suppresses the permeation of oxygen and water vapor.

[0036] Examples of inorganic compounds contained in the inorganic compound layer include vapor-deposited films made of metal oxides such as aluminum oxide, silicon oxide, magnesium oxide, and 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 can be selected from aluminum oxide and silicon oxide. By using a metal oxide as the barrier film for the inorganic compound layer, high barrier properties can be obtained with a very thin layer that does not affect the recyclability of the laminate 10.

[0037] Inorganic compound layers can be formed, for example, by vacuum deposition. Vacuum deposition can utilize either physical vapor deposition (CVD) or chemical vapor deposition (CVD). Examples of physical vapor deposition include vacuum evaporation, 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.

[0038] The thickness of the inorganic compound 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. 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 for the inorganic compound layer.

[0039] The thickness of the inorganic compound layer made of silicon dioxide is preferably between 10 nm and 50 nm. A thickness of 10 nm or more provides sufficient gas barrier properties. Furthermore, a thickness of 50 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 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.

[0040] An anchor coat layer may be formed on the side of the base layer 1 where the inorganic compound layer is formed, using a known anchor coat agent. This improves the adhesion of the inorganic compound layer made of metal oxides. Examples of anchor coat agents include polyester polyurethane resins and polyether polyurethane resins. From the viewpoint of heat resistance and interlayer adhesion strength, polyester polyurethane resins are preferred.

[0041] The coating layer protects the inorganic compound layer and exhibits barrier properties independently of the inorganic compound layer. The coating layer can be formed using an aqueous solution containing at least one selected from the group consisting of hydroxyl group-containing polymer compounds, metal alkoxides, silane coupling agents, and their hydrolysates.

[0042] The thickness of the 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.

[0043] <Protective layer> One main surface of the protective layer 4 constitutes the outermost surface of the laminate 10. The protective layer 4 contains a thermosetting resin and has excellent heat resistance. Examples of thermosetting resins include polyurethane resin, polyester resin, polyamide resin, polyamide-imide resin, acrylic resin, epoxy resin, hydroxyl group-containing polymer, organosilicon compounds, etc. The protective layer 4 may contain one of the above thermosetting resins or two or more. When the film thickness of the protective layer 4 is thin, it tends to become difficult to achieve high heat resistance. In order to reduce and mitigate thermal damage during heat sealing, the film thickness of the protective layer 4 is preferably 0.3 μm or more. Also, when the film thickness of the protective layer 4 is thick, it tends to become difficult to sufficiently dry the resin coating during the manufacturing process of the laminate 10. From the viewpoint of productivity, the film thickness of the protective layer 4 is preferably 3 μm or less.

[0044] Even when polyethylene with poor heat resistance is used as the base layer 1, the protective layer 4 made of thermosetting resin on the outermost surface reduces and mitigates thermal damage to the surface of the laminate 10 during heat sealing. This prevents the occurrence of appearance defects such as thermal shrinkage and distortion in the heat-sealed area, eliminating the need for measures such as slowing down the bag-making speed and preventing a decrease in productivity.

[0045] <Print layer> A printing layer 6 can be provided on the gas barrier layer 5. The printing layer 6 is a layer composed of ink, which is made by adding various pigments, extenders, plasticizers, drying agents, and stabilizers to conventionally used ink binder resins such as urethane, acrylic, nitrocellulose, rubber, and vinyl chloride, and displays patterns such as characters and images. It is preferable to use biomass-derived ink as the ink.

[0046] As a method for forming the printed layer 6, well-known printing methods such as offset printing, gravure printing, flexographic printing, and screen printing, as well as well-known coating methods such as roll coating, knife-edge coating, and gravure coating, can be used. In particular, water-based flexographic printing is preferable because it places a small printing load on the substrate layer and is also environmentally friendly.

[0047] <Adhesive layer> The adhesive layer 2 contains at least one type of adhesive. The adhesive may be a one-component curing adhesive, a two-component curing adhesive, or a non-curing adhesive. The adhesive may also be a solvent-free adhesive or a solvent-based adhesive.

[0048] Examples of adhesives include polyether-based adhesives, polyester-based adhesives, silicone-based adhesives, epoxy-based adhesives such as polyamine-based adhesives, urethane-based adhesives, rubber-based adhesives, vinyl-based adhesives, silicone-based adhesives, epoxy-based adhesives, phenol-based adhesives, and olefin-based adhesives. Preferably, the adhesive is a polyamine-based adhesive or a urethane-based adhesive that has gas barrier properties.

[0049] The adhesive layer 2 may be a cured product of a resin composition containing a polyester polyol, an isocyanate compound, and a phosphate-modified compound. Such an adhesive layer 2 can further improve the oxygen barrier and water vapor barrier properties of the laminate 10.

[0050] The thickness of the adhesive layer 2 is preferably in the range of 0.1 μm to 20 μm, more preferably in the range of 0.5 μm to 10 μm, and even more preferably in the range of 1 to 5 μm.

[0051] The adhesive layer 2 can be formed by applying and drying it on the sealant layer 6 using conventionally 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.

[0052] <Heat seal layer> As described above, a heat-seal layer 3 can be added to the barrier-type laminate to form a packaging material. The heat-seal layer 3 is made of polyethylene and is joined by heat sealing when forming a packaging material such as a packaging bag using the laminate. 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 heat-seal layer 3.

[0053] 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 3Polyethylene of less than 500 kg can be used. The heat seal layer may be a single layer or have a multilayer structure. By using a multilayer structure, bag-making suitability and strength can be further improved while maintaining heat sealability. From the viewpoint of environmental impact, biomass-derived polyethylene or recycled polyethylene is preferred. The thickness of the heat seal layer 3 can be set appropriately considering the shape of the packaging bag to be manufactured and the mass of the contents to be contained, but for example it can be 30 to 150 μm. [Examples]

[0054] The tests conducted in connection with the present invention are described below. (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. (Preparation of coating solution for forming protective and protective layers) 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-trialkoxysilylpropyl) 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.

[0055] <Example 1> The laminate 10 shown in Figure 1 was manufactured by the following method. First, a film (manufactured by Tokyo Ink Co., Ltd.) sold under the product name "SMUQ" was prepared as the base layer 1. The film sold under the product name "SMUQ" is made of polyethylene, and the probe drop temperature measured by the method described above was 211°C, the haze was 1.6%, the thickness was 25 μm, and the density was 0.950 g / cm³. 3 The substrate layer 1 is corona treated on one side. After corona treatment of one surface of the substrate layer 1, the coating solution for forming the protective layer described above is applied by gravure coating and dried to form a protective layer with a thickness of 0.5 μm.

[0056] Next, on the corona-treated surface opposite to the substrate layer 1, an inorganic compound layer with a thickness of 40 nm, composed of a silicon oxide (SiOx) deposited film, was formed as a gas barrier layer 5 using an electron beam heating type vacuum deposition apparatus. Furthermore, the coating solution for forming the coating layer described above was applied to form a coating layer with a thickness of 0.3 μm.

[0057] Next, a print layer 6 was formed by printing a design onto the gas barrier layer 5 using gravure ink. Then, a urethane-based adhesive for dry lamination (Takelac A525 / Takenate A52, manufactured by Mitsui Chemicals) was applied to the print layer surface as an adhesive, and a linear low-density polyethylene resin (LLDPE) film (TUX, manufactured by Mitsui Tohcello, 60 μm thick) was laminated as a sealant layer 3 to create a laminate 11. The thickness of the adhesive layer 2 was 3 μm. Figure 2 shows a schematic cross-sectional view of the laminate 11 of Example 1.

[0058] <Example 2> The laminate according to Example 2 was prepared and evaluated in the same manner as the laminate according to Example 1, except that a film commercially available under the trade name "HD200" (manufactured by Jindal Films, Inc.) was used as the base layer 1 instead of a film commercially available under the trade name "SMUQ". The film commercially available under the trade name "HD200" is made of polyethylene, and the probe drop temperature measured by the method described above was 203°C, the haze was 5.9%, the thickness was 25 μm, and the density was 0.950 g / cm³. 3 It has been corona-treated on one side.

[0059] <Comparative Example 1> The laminate was prepared and evaluated in the same manner as in Example 2, except that protective layer 4 was not formed.

[0060] <Comparative Example 2> A laminate according to Comparative Example 2 was prepared and evaluated in the same manner as the laminate according to Example 1, except that a film commercially available under the trade name "GAP" (manufactured by Charter Next Generation, Inc.) was used as the base layer 1, instead of the film commercially available under the trade name "SMUQ", and protective layer 4 was omitted. The film commercially available under the trade name "GAP" is made of polyethylene, and the probe drop temperature measured by the method described above was 160°C, the haze was 21.5%, the thickness was 25 μm, and the density was 0.950 g / cm³. 3 It has been corona-treated on one side.

[0061] (Evaluation of sealing properties, print visibility, and recyclability) Small pieces of the laminated sample were folded in half with the sealant layer facing inward and heat-sealed. The sealing performance, print visibility, and recyclability of the sealed surface were evaluated. • Sealing properties ○: The surface is wrinkle-free and does not adhere to the seal bar. ×: The surface is wrinkled and adheres to the seal bar. • Print visibility ○: The printed pattern is clearly visible. ×: The printed pattern is blurry or appears faint. • Recyclability ○: Polyethylene content of 90% by mass or more ×: Polyethylene percentage less than 90% by mass

[0062] The results above are summarized in Table 1.

[0063] [Table 1]

[0064] As shown in Table 1, all of the examples and comparative examples exhibited high recyclability. However, the laminates of Comparative Examples 1 and 2, which lacked a protective layer, had poor sealing properties. In contrast, the laminates of Examples 1 and 2 according to the present invention exhibited excellent sealing properties and print visibility, demonstrating their high value as packaging materials. [Explanation of Symbols]

[0065] 1...Base material layer 2...Adhesive layer 3. Sealant layer 4...Protective layer 5. Gas barrier layer 6...printing layer 10, 11... Laminate

Claims

1. In a laminate comprising at least a substrate layer, an adhesive layer, and a sealant layer in this order, A protective layer is provided on the outermost side of the base layer. The aforementioned protective layer is made of a thermosetting resin. The base layer and the sealant layer are both made of polyethylene resin. The substrate layer has a probe drop temperature of 180°C or higher. The proportion of polyethylene in the laminate is 90% by mass or more. A laminate in which the adhesive layer is formed from a polyamine-based adhesive or a urethane-based adhesive having gas barrier properties.

2. The laminate according to claim 1, wherein the adhesive layer is a cured product of a resin composition comprising a polyester polyol, an isocyanate compound, and a phosphate-modified compound.

3. The laminate according to claim 1 or 2, wherein the thickness of the adhesive layer is 0.1 μm or more and 20 μm or less.

4. The laminate according to any one of claims 1 to 3, wherein the protective layer comprises at least one of a metal alkoxide, a hydrolysate of a metal alkoxide, and a reaction product of a metal alkoxide or a hydrolysate of a metal alkoxide, and a water-soluble polymer.

5. The laminate according to any one of claims 1 to 4, wherein a gas barrier layer is provided on the surface of the substrate layer facing the sealant layer.

6. The laminate according to claim 5, wherein the gas barrier layer comprises an inorganic compound.

7. The laminate according to claim 6, further comprising a coating layer on the surface of the gas barrier layer facing the sealant layer.

8. A packaging material comprising a laminate according to any one of claims 1 to 7.

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