JP7779019B2 - Laminate, and packaging material and packaging bag using same - Google Patents

Description

The present invention relates to a laminate for packaging, and packaging materials and packaging bags using the same. In particular, it relates to a laminate with excellent material recyclability and a low environmental impact, and packaging materials and packaging bags using the same.

Packaging bags are made from a variety of materials, depending on the nature and quantity of the contents, post-processing to protect the contents from deterioration, the form in which the packaging bag will be transported, the method of opening the packaging bag, and the method of disposal.

For example, in flexible packaging bags that use laminated films, biaxially oriented films such as polypropylene and polyester are used to provide the bag with mechanical strength, and polyethylene, polypropylene, ethylene-vinyl acetate copolymer, etc. are used as heat-sealing materials to seal the contents. Additionally, aluminum foil and ethylene-vinyl alcohol copolymer are also used as laminations to prevent deterioration of the contents.

The above-mentioned laminates of various functionally separated materials are designed with an emphasis on each process, from packaging the contents to transportation, storage, and opening. However, with growing awareness of environmental issues in recent years, emphasis has been placed on resource conservation and recyclability of various products, and similar functions are being sought for the laminates used in packaging bags. Generally, packaging materials are considered highly recyclable if they contain 90% or more of the main resin by mass. However, many conventional packaging materials are composed of multiple resin materials, and in some cases paper and metal materials, and do not meet this standard, so they are not currently recycled.

For example, in order to reduce the environmental impact, a packaging bag made from a laminate of various plastics that have been replaced with plant-based plastics instead of petroleum-based has been proposed (Patent Document 1). This reduces the amount of petroleum resources used and carbon dioxide emissions. However, when a laminate is made up of a combination of various materials, the materials must be separated and sorted in order to be reused. This involves the problem of consuming energy, as the materials must be separated using various thermal, chemical, and mechanical processes, and then sorted using physical processes based on specific gravity or spectroscopic methods that differ for each material.

Therefore, Patent Document 2 describes a laminate comprising a substrate, an adhesive layer, and a heat-sealing layer, in which the substrate and heat-sealing layer are made of polyethylene. Using the same material for the substrate and heat-sealing layer makes it easier to meet the recyclability standards. However, when the laminate described in Patent Document 2 is used in a packaging bag, the bag-making process involves joining the sealant layers of the laminate together and then applying pressure from the outer surface of the substrate layer of the laminate to a high-temperature jig to heat-seal the laminate. The jig of the heat-sealing machine is heated to a high temperature, and the outer surface of the substrate layer that directly contacts the jig is exposed to high temperatures, which can cause problems such as the substrate layer being affected by the heat and adhering to the jig. This has resulted in issues such as a narrow range of optimum bag-making temperatures, poor productivity, and insufficient packaging bag strength.

Furthermore, Patent Document 3 proposes a packaging bag that has excellent blocking resistance and easy opening by providing a resin coating layer on the outer surface of a polyethylene substrate layer. However, this document proposes a simplified layer structure from the perspective of easy recycling, and uses a single-layer structure in which a sealant layer is provided on a substrate layer, or a structure in which substrates are bonded together, so that it is limited to light packaging applications and is difficult to apply to packaging bags containing liquids that require sufficient sealing properties due to insufficient strength.

Patent No. 6699779 Japanese Patent Application Laid-Open No. 2020-55157 Japanese Patent Application Laid-Open No. 2020-196791

The problem that this invention aims to solve is to provide a packaging laminate, packaging material, and packaging bag that have a low environmental impact, are highly recyclable, and have excellent barrier properties while also having sufficient strength and heat resistance.

In order to solve the above problem, the invention of claim 1 of the present invention is a laminate in which a base film, a first adhesive layer, an intermediate film, a second adhesive layer, and a heat seal film are laminated in this order, with a protective layer further laminated on the outermost surface of the base film, wherein the protective layer is made of a thermosetting resin, the base film is a stretched polyethylene film, the intermediate film and the heat seal film are unstretched polyethylene films, one surface of the intermediate film is provided with a vapor-deposited film, and the proportion of polyethylene in the laminate is 90% by weight or more.

Furthermore, claim 2 of the present invention relates to the laminate described in claim 1, characterized in that the thermosetting resin is a cured product of one or more resin compositions selected from urethane, polyester, polyamide, acrylic, and epoxy.

The invention of claim 3 of the present invention is the laminate described in claim 1 or 2, characterized in that the vapor-deposited film is a barrier film made of a metal oxide.

Furthermore, claim 4 of the present invention relates to the laminate described in any one of claims 1 to 3, characterized in that the base film and the intermediate film are made of high-density polyethylene or medium-density polyethylene.

Furthermore, claim 5 of the present invention relates to the laminate described in any one of claims 1 to 4, wherein the heat seal film contains low-density polyethylene.

Furthermore, claim 6 of the present invention relates to a packaging material made from the laminate described in any one of claims 1 to 5.

Furthermore, claim 7 of the present invention relates to a packaging bag characterized by using the laminate described in any one of claims 1 to 5, wherein the thickness of the heat seal film is 20 μm or more and 150 μm or less.

By providing the laminate of the present invention, it is possible to manufacture packaging bags that are easy to recycle, have strength, heat resistance, and barrier properties, and are highly productive.

1 is a cross-sectional view showing an embodiment of a laminate of the present invention.

The following describes in detail the embodiments of the present invention.

Figure 1 is a schematic cross-sectional view of a laminate 1 according to the present invention. The laminate 1 comprises a base film 10, a first adhesive layer 40, an intermediate film 20, a second adhesive layer 50, and a heat seal film 30. The base film 10 has a protective layer 11 on its outermost surface, and the intermediate film 20 has a vapor-deposited film 14 on one surface thereof.

The base film 10 is a stretched film made of polyethylene and serves as the outer surface when the laminate 1 is used to form a packaging material. The base film 10 may be a uniaxially stretched film or a biaxially stretched film. Here, films made of high-density polyethylene (density 0.94 g/cm ³ or higher) or medium-density polyethylene (density 0.925 to 0.945 g/cm ³ ) can be used. These materials may be petroleum-derived, plant-derived, or a mixture thereof. The film can be manufactured by known methods such as casting or inflation, and the film surface can be subjected to a dry surface treatment such as corona treatment or atmospheric pressure plasma treatment to enhance adhesion. Alternatively, a multilayer stretched polyethylene film obtained by coextrusion of polyethylenes with different densities can be used as the base film 10. The thickness of the base film 10 is preferably 10 μm or more and 50 μm or less, more preferably 12 μm or more and 35 μm or less. By making the thickness of the base film 10 10 μm or more, the strength of the laminate 1 can be improved. By setting the thickness of the base film 10 to 50 μm or less, the processability of the laminate 1 can be improved.

The protective layer 11 on the outermost surface of the base film 10 can be formed using a coating agent that produces a cured product of one or more resin compositions made from urethane, polyester, polyamide, acrylic, or epoxy. The thickness of the protective layer 11 is 0.3 to 4.0 μm.

The printed layer 12 can be formed on the outer surface 10a of the base film 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 the intermediate film 20 is laminated. The image formation method is not particularly limited, and can be performed using standard gravure printing or flexographic printing, etc., with the appropriate ink. Both solvent-based and water-based inks are available, but water-based inks are preferred from an environmental perspective. Furthermore, the outer surface 10a or inner surface 10b of the base film 10 may be subjected to a surface treatment such as corona treatment or plasma treatment to improve the adhesion of the printed layer 12.

The base film 10 is a stretched film with excellent transparency, allowing the display on the printing layer 12 provided on the inner surface 10b to be clearly visible. Transparency that allows clear visibility is a haze value of 20% or less, measured in accordance with JIS K 7105, and even better at 10% or less.

Furthermore, in consideration of recyclability, placing the printed layer 12 on the outside of the base film 10 makes deinking easier and prevents the ink on the printed layer 12 from being mixed in as foreign matter with the recycled polyethylene resin during the recycling process.

The intermediate film 20 is an unstretched film made of polyethylene. From the viewpoints of strength and heat resistance, high-density polyethylene and medium-density polyethylene are preferred as the polyethylene contained in the intermediate film 20. Like the base film 10, the intermediate film 20 may be a multilayer film.

The thickness of the intermediate film 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 film 20 9 μm or more, the strength and heat resistance of the laminate can be improved. By making the thickness of the intermediate film 20 50 μm or less, the processability of the laminate can be improved.

The intermediate film 20 can be produced by forming polyethylene using a method such as the T-die method or inflation method. When producing the intermediate film 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, rupture of the produced substrate can be prevented.

When producing the intermediate film 20 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, film formability can be improved.

The unstretched film that will become the intermediate film 20 can be produced using the method described above, or it can be purchased from a commercially available source.

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

Examples of the composition of the vapor-deposited film 14 include vapor-deposited films made of metal oxides such as aluminum oxide, silicon oxide, magnesium oxide, and tin oxide. From the standpoint of transparency and barrier properties, the metal oxide may be selected from the group consisting of aluminum oxide, silicon oxide, and magnesium oxide. Furthermore, from the standpoint of cost, it is selected from aluminum oxide and silicon oxide. Furthermore, from the standpoint of excellent tensile elongation during processing, it is more preferable to use a layer made of silicon oxide. By using a metal oxide as the barrier film for the vapor-deposited film 14, high barrier properties can be achieved with an extremely thin layer that does not affect the recyclability of the laminate 1.

A vapor-deposited film made of metal oxide is transparent, and therefore has the advantage that, compared to a vapor-deposited film made of metal, users who handle packaging material made of the laminate are less likely to mistakenly believe that it contains metal foil.

The thickness of the vapor-deposited aluminum oxide film is preferably 5 nm or more and 30 nm or less. A film thickness of 5 nm or more can achieve sufficient gas barrier properties. Furthermore, a film thickness of 30 nm or less can prevent cracks from occurring due to deformation caused by internal stress in the thin film, thereby preventing a decrease in gas barrier properties. However, a film thickness exceeding 30 nm is undesirable from an economic standpoint, as it increases costs due to increased material usage and longer film formation times. From the same perspective as above, it is more preferable that the film thickness be 7 nm or more and 15 nm or less.

The thickness of the vapor-deposited film made of silicon oxide is preferably 10 nm or more and 50 nm or less.
A film thickness of 10 nm or more can provide sufficient gas barrier properties. Furthermore, a film thickness of 50 nm or less can prevent cracks from occurring due to deformation caused by internal stress in the thin film, thereby preventing a decrease in gas barrier properties. A film thickness exceeding 50 nm is undesirable from an economic standpoint, as it increases the amount of material used and the film formation time, leading to increased costs. From the same perspective as above, the film thickness of the vapor-deposited film is more preferably 20 nm or more and 40 nm or less.

The vapor deposition film 14 can be formed, for example, by vacuum deposition. Vacuum deposition can be performed using physical vapor deposition or chemical vapor deposition. Physical vapor deposition methods include, but are not limited to, vacuum deposition, sputtering, and ion plating. Chemical vapor deposition methods include, but are not limited to, thermal CVD, plasma CVD, and photo-CVD.

The most preferred vacuum deposition methods are resistance heating vacuum deposition, EB (Electron Beam) heating vacuum deposition, induction heating vacuum deposition, sputtering, reactive sputtering, dual magnetron sputtering, and plasma enhanced chemical vapor deposition (PECVD). However, considering productivity, vacuum deposition is currently the most superior method. The heating method for vacuum deposition is preferably electron beam heating, resistance heating, or induction heating.

As in this embodiment, an anchor coating layer may be formed on the surface of the intermediate film 20 on which the vapor-deposited film 14 is formed, using a known anchor coating agent. This improves the adhesion of the vapor-deposited film made of metal oxide. Examples of anchor coating agents include polyester-based polyurethane resins and polyether-based polyurethane resins. From the standpoint of heat resistance and interlayer adhesive strength, polyester-based polyurethane resins are preferred.

Furthermore, in order to improve adhesion between the first adhesive layer 40, the second adhesive layer 50, the vapor deposition film 14, and the above-mentioned anchor coat layer, the corresponding surfaces of the intermediate film 20 may be subjected to surface treatment such as corona treatment or plasma treatment.

The heat seal film 30 is made of polyethylene and is bonded by heat fusion (heat sealing) when the laminate 1 is used to form a packaging material such as a packaging bag. From the standpoint of heat sealing properties, low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and very-low-density polyethylene (VLDPE) are preferred as the polyethylene that makes up the heat seal film 30. Furthermore, from the standpoint of environmental impact, it is preferable to use biomass-derived polyethylene or recycled polyethylene for the heat seal film 30.

As the low-density polyethylene, polyethylene having a density of 0.900 g/ ^cm3 or more and less than 0.925 g/ ^cm3 can be used. As the linear low-density polyethylene, polyethylene having a density of 0.900 g/ ^cm3 or more and less than 0.925 g/ ^cm3 can be used. As the ultra-low-density polyethylene, polyethylene having a density less than 0.900 g/ ^cm3 can be used. For the heat-seal film 30, a copolymer of ethylene and other monomers can be used within a range that does not impair the properties of the laminate 1.

The thickness of the heat seal film 30 can be changed appropriately depending on the weight of the contents to be filled into the packaging material to be produced. For example, when producing a packaging bag to be filled with contents of 1 g or more and 200 g or less, the thickness of the heat seal film 30 is preferably 20 μm or more and 60 μm or less. By making the thickness 20 μm or more, it is possible to prevent the filled contents from leaking due to damage to the heat seal film 30. By making the thickness 60 μm or less, it is possible to improve the processability of the laminate 1.

As another example, when producing a standing pouch to be filled with contents of 50 g or more and 2000 g or less, the thickness of the heat seal film 30 is preferably 50 μm or more and 200 μm or less. A thickness of 50 μm or more can prevent the filled contents from leaking due to damage to the heat seal film 30. Furthermore, a thickness of 200 μm or less can improve the processability of the laminate 1, and a thickness of 150 μm is even more preferable.

Additives such as antioxidants, antistatic agents, nucleating agents, and ultraviolet absorbers may be added to the polyethylene used for the base film 10, the intermediate film 20, and the heat seal film 30.

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

The first adhesive layer 40 and the second adhesive layer 50 can also be formed using an adhesive that exhibits gas barrier properties after curing. In particular, forming the second adhesive layer 50 that comes into contact with the vapor-deposited film using an adhesive that exhibits gas barrier properties can further suppress deterioration of the gas barrier properties due to cracking of the vapor-deposited film 14. This can further improve the gas barrier performance of the laminate 1. Examples of such gas barrier adhesives include epoxy-based adhesives and polyester/polyurethane-based adhesives. Specific examples include "Maxieve" manufactured by Mitsubishi Gas Chemical Company, Inc. and "Paslim" manufactured by DIC Corporation.

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 making the thickness of the first adhesive layer 40 and the second adhesive layer 50 0.5 μm or more, the adhesiveness of the first adhesive layer 40 and the second adhesive layer 50 can be improved. By making the thickness of the first adhesive layer 40 and the second adhesive layer 50 6 μm or less, the processability of the laminate 1 can be improved.

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

In the laminate 1 of this embodiment configured as described above, the base film 10, intermediate film 20, and heat seal film 30 are made of polyethylene, so the proportion of polyethylene in the laminate 1 is 90% by mass (wt%) or more. This gives the laminate 1 high recyclability. The proportion (wt%) of polyethylene in the laminate 1 can be calculated using the following formula (1):

(mass of base film + mass of intermediate film 20 + mass of heat seal film 30) / mass of entire laminate 1 × 100 (1)
A packaging bag can be formed from the laminate 1 by folding one sheet of the laminate 1 with the heat seal films 30 facing each other, or by stacking two sheets of the laminate 1 with the heat seal films 30 facing each other, and then joining the peripheral heat seal films 30 by heat sealing, leaving the portion filled with the contents. A standing pouch can be formed by joining the above-mentioned portions while sandwiching the folded bottom film. It can also be used for various other packaging bags, such as pillow packaging, four-sided sealing, three-sided sealing, and gusset bags. In this way, the laminate 1 can be applied to various packaging bags.

The laminate of the present invention has a base film 10 made of stretched high-density polyethylene film and a protective layer 11 made of a thermosetting resin on the outermost layer, which enhances the heat resistance of the heat-sealed portion, enabling bag production under appropriate conditions and improving the strength and appearance required of packaging bags. Furthermore, by combining this with an intermediate film 20 made of a non-stretched film with a vapor-deposited film 14, the bag is less likely to rupture due to impact when dropped after being filled with liquid, and the strength of the packaging bag is increased.

The laminate of this embodiment will be further described using examples and comparative examples, but the present invention is not limited to the specific contents of the examples and comparative examples.
(Preparation of anchor coating agent)
Acrylic polyol and tolylene diisocyanate were mixed so that the number of NCO groups in tolylene diisocyanate was equal to the number of OH groups in the acrylic polyol, and the mixture was diluted with ethyl acetate so that the total solids content (total amount of acrylic polyol and tolylene diisocyanate) was 5 mass%. β-(3,4-epoxycyclohexyl)trimethoxysilane was further added to the diluted mixture in an amount of 5 parts by mass per 100 parts by mass of the total amount of acrylic polyol and tolylene diisocyanate, and these were mixed to prepare an anchor coating agent.
(Preparation of Overcoat Agent)
An overcoat agent was prepared by mixing the following liquids A, B, and C in a mass ratio of 70/20/10, respectively.
Solution A: A hydrolysis solution with a solid content of 5% by mass ( _{SiO2 equivalent} ) obtained by adding 72.1 g of 0.1 N hydrochloric acid to 17.9 g of tetraethoxysilane (Si( _OC2H5 ) ₄ ) and 10 g of methanol and stirring for 30 minutes to hydrolyze the mixture.
Solution B: a 5% by mass water/methanol solution of polyvinyl alcohol (water:methanol mass ratio 95:5).
Liquid C: A hydrolysis solution obtained by diluting 1,3,5-tris(3-trialkoxysilylpropyl)isocyanurate with a mixed liquid of water and isopropyl alcohol (water:isopropyl alcohol mass ratio 1:1) to a solids content of 5 mass %.
(Preparation of intermediate film A)
The anchor coating agent described above was applied by gravure coating to one side of a 25 μm-thick unstretched polyethylene film (three-layer structure: HDPE/MDPE/HDPE) that had been corona-treated on both sides, followed by drying to form a 0.1 μm-thick anchor coating layer. Next, a 30 nm-thick transparent vapor-deposited film made of silicon oxide was formed on the anchor coating layer using a vacuum deposition device employing an electron beam heating system. The O/Si ratio of the vapor-deposited film was adjusted to 1.8 by adjusting the type of vapor-deposited material. The overcoat agent described above was applied by gravure coating to the vapor-deposited film and dried to form a 0.3 μm-thick overcoat layer with gas barrier properties. This resulted in intermediate film A, on which a vapor-deposited film made of silica was formed.
(Preparation of intermediate film B)
An anchor coating agent was applied to one side of the same unstretched polyethylene film as intermediate film A by gravure coating and dried to form a 0.1 μm thick anchor coating layer. Next, a 10 nm thick transparent vapor deposition film made of aluminum oxide was formed on the anchor coating layer using an electron beam heating vacuum deposition device. The O/Al ratio of the vapor deposition film was set to 1.5 by adjusting the type of vapor deposition material. Furthermore, an overcoat agent was applied to the vapor deposition film by gravure coating and dried to form a 0.3 μm thick overcoat layer with gas barrier function. In this way, intermediate film B was obtained, on which a vapor deposition film made of alumina was formed. (Preparation of intermediate film C)
An anchor coating agent was applied by gravure coating to a 25 μm-thick biaxially oriented polyethylene film (three-layer structure: HDPE/MDPE/HDPE) that had been corona-treated on both sides, followed by drying to form a 0.1 μm-thick anchor coating layer. Next, a 30 nm-thick transparent vapor-deposited film made of silicon oxide was formed using a vacuum deposition device employing an electron beam heating system. The O/Si ratio of the vapor-deposited film was adjusted to 1.8 by adjusting the type of vapor-deposited material. The above-described overcoat agent was applied by gravure coating to the vapor-deposited film and dried to form a 0.3 μm-thick overcoat layer with gas barrier properties. This resulted in intermediate film C, on which a vapor-deposited film made of silica was formed.
(Coating liquid for forming protective layer)
An organic solvent-based coating solution containing polyamideimide (Viromax HR-15ET, manufactured by Toyobo) with a non-volatile component concentration of 5% by mass was used as the coating solution for forming the protective layer.
Example 1
A 25 μm-thick biaxially oriented polyethylene film (with a three-layer structure of HDPE/MDPE/HDPE) with both sides corona-treated was prepared as the substrate film. The coating solution for forming the protective layer described above was applied to the corona-treated outer surface of the substrate film by gravure coating and dried to form a 0.5 μm-thick protective layer. Furthermore, an image was formed on the corona-treated inner surface of the substrate film by flexographic printing using aqueous flexographic ink.

Next, the ink layer-formed surface of the base film was bonded to the corona-treated surface of intermediate film A, where no vapor-deposited film was formed, using a non-sol lamination method with a two-component curing urethane adhesive. This adhesive layer was designated the first adhesive layer.

Furthermore, a 40 μm-thick unstretched polyethylene film (single layer of LLDPE) was prepared as a heat seal film, and a two-component curing urethane adhesive was used as a second adhesive layer, and the surface of intermediate film A facing the vapor-deposited film was bonded to the heat seal film by a non-sol lamination method. In this way, a laminate according to Example 1 was obtained.
Example 2
A laminate according to Example 2 was obtained in the same manner as in Example 1, except that Intermediate Film B was used instead of Intermediate Film A.
(Comparative Example 1)
A laminate according to Comparative Example 1 was obtained in the same manner as in Example 1, except that no protective layer was formed and intermediate film C was used instead of intermediate film A.
(Comparative Example 2)
A laminate according to Comparative Example 2 was obtained in the same manner as in Example 1, except that a 25 μm-thick unstretched polyethylene film (three-layer structure of HDPE/MDPE/HDPE) with one side corona-treated was used as the base film, no protective layer was formed, and intermediate film C was used instead of intermediate film A.

The laminates according to the examples and comparative examples were evaluated as follows.
(Recyclability)
The wt % of polyethylene in the laminate of each example was calculated based on the above formula (1). Evaluation was based on the following two levels.
◯ (good): Contains 90 wt % or more of polyethylene.
× (bad): The polyethylene content is less than 90 wt %.
(Evaluation of heat sealability)
The prepared laminates were each cut into 10 cm squares, folded in half with the heat seal film facing inward, and heat sealed using a heat seal tester at a temperature of 140°C, a pressure of 0.1 MPa, and a time of 1 second. The heat-sealed portions of the obtained samples were visually observed and subjected to a sensory evaluation. The evaluation was based on the following two levels.
◯ (good): There are no wrinkles on the surface of the packaging material, and no melting or adhesion to the seal bar is observed.
× (bad): Wrinkles were observed on the surface of the packaging material, and melting and adhesion to the seal bar was observed.
(Puncture strength)
The puncture strength was measured in accordance with JIS Z 1707: 2019. The laminate according to each example was held flat under tension, and a hemispherical needle having a diameter of 1.0 mm and a tip radius of 0.5 mm was pressed against the laminate from the substrate side at a rate of 50 mm/min, and the force (Newton: N) at the time of puncture was measured.
(Impact resistance)
Using the laminate according to each example, ten packaging bags measuring 100 mm x 150 mm were prepared, the edges of which were heat-sealed. These packaging bags were filled with 200 g of distilled water, heat-sealed, and stored at 5°C for one day. After storage, each packaging bag was dropped 50 times from a height of 1.5 m, and the number of packaging bags that broke was recorded.
(Oxygen Transmission Rate: OTR)
Measurement was carried out by the Mocon method under conditions of 30° and 70% RH (relative humidity).
(Water vapor transmission rate: WVTR)
Measurement was carried out by the Mocon method under conditions of 40° and 90% RH.

The evaluation results are shown in Table 1.

As shown in Table 1, all of the Examples and Comparative Examples had high recyclability, but the laminates of Comparative Examples 1 and 2, which did not have a protective layer, had poor heat sealability, and the laminates of Comparative Examples 1 and 2, in which the intermediate film was made of a stretched polyethylene film, did not have sufficient impact resistance.

DESCRIPTION OF SYMBOLS 1 Laminate 10 Base film 10a Base film outer surface 10b Base film inner surface 11 Protective layer 14 Vapor deposition film 20 Intermediate film 30 Heat seal film 40 First adhesive layer 50 Second adhesive layer

Claims (11)

A laminate comprising a base film, a first adhesive layer, an intermediate film, a second adhesive layer, and a heat seal film laminated in this order, with a protective layer further laminated on the outermost surface of the base film, wherein the protective layer is made of a thermosetting resin, the base film is an oriented polyethylene film, the intermediate film and the heat seal film are unoriented polyethylene films, one surface of the intermediate film is provided with a vapor-deposited film, and the proportion of polyethylene in the laminate is 90% by weight or more. The laminate according to claim 1, characterized in that the thermosetting resin is a cured product of one or more resin compositions selected from urethane, polyester, polyamide, acrylic, and epoxy. The thermosetting resin is a cured product of polyamideimide.
The laminate according to claim 1 . 4. The laminate according to claim 1, wherein the vapor-deposited film is a barrier film made of a metal oxide. 5. The laminate according to claim 1 , wherein the base film and the intermediate film are made of high-density polyethylene or medium-density polyethylene. The laminate according to any one of claims 1 to 5 , wherein the heat seal film contains low density polyethylene. The substrate film has a single-layer structure or a three-layer structure.
The laminate according to any one of claims 1 to 6. The haze value of the base film is 20% or less.
The laminate according to any one of claims 1 to 7. A printing layer is provided on the outer side of the base film.
The laminate according to any one of claims 1 to 8. A packaging material comprising the laminate according to any one of claims 1 to 9 . A packaging bag using the laminate according to any one of claims 1 to 9 , wherein the heat seal film has a thickness of 20 µm or more and 150 µm or less.