Packaging materials and containers

Abstract

One aspect of the packaging material disclosed herein has a laminated structure comprising a paper substrate, an adhesive resin layer, a gas barrier layer, and a sealant layer in sequence. The sealant layer comprises an ethylene-methacrylic acid copolymer, and the melt flow rate of the sealant layer, measured at a temperature of 190°C and a load of 2.16 kg, is 3.0 g / 10 min or more and 40 g / 10 min or less.

Description

Technical Field

[0001] This disclosure relates to packaging materials and containers. Background Technology

[0002] For a long time, paper containers for liquids, with paper as the main material, have been used in the field of packaging materials. Patent Document 1 discloses a liquid paper container made by boxing a packaging material formed from a paper substrate, a specific barrier layer (gas barrier layer), an adhesive resin layer of a specific thickness, and a heat-sealing resin layer (sealant layer).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2001-171649 Summary of the Invention

[0006] The technical problem that the invention aims to solve

[0007] Such containers (paper containers) generally have a main body consisting of a top, sides, and a bottom made of packaging material. For example, when the main body is cylindrical, the container is obtained by pre-processing grid lines into the packaging material, bending the material along these lines, and then heating and bonding the material. Alternatively, when the main body is cylindrical, the container is obtained by heating and bonding different components that constitute the top, sides, and bottom. These components are obtained by heating and bending the packaging material to achieve the desired shape.

[0008] When heating and bonding packaging materials, such as when using polyethylene resin as a sealant layer, heat sealing is required at temperatures above 200°C, and above 250°C depending on the thickness of the paper substrate. High-temperature heat sealing can cause thermal shrinkage and cracking of the gas barrier layer, reducing its gas barrier properties.

[0009] Furthermore, during high-temperature heat sealing, moisture in the paper, the main material, can sometimes evaporate, producing water vapor. This water vapor can then penetrate the interface between the paper and the adhesive resin layer, creating voids and causing bubbling. When voids form due to bubbling, continued heating of the packaging material makes it difficult for heat to transfer to the paper from the voided areas. As a result, excess heat accumulates in the gas barrier layer, causing cracks or pinholes and reducing gas barrier properties. Bubbling is also associated with leakage of the contents.

[0010] When the main body of the container is cylindrical, the component is obtained by heating the packaging material while bending it. Therefore, the heat will cause thermal shrinkage or bubbling of the gas barrier layer.

[0011] In addition, packaging materials can be obtained by heating the materials that make up the packaging materials and laminating them. However, heating will cause thermal shrinkage and cracking of the gas barrier layer, which will reduce the gas barrier properties.

[0012] Furthermore, since the main body of the container is constructed from curved packaging material as described above, it has technical problems such as cracks or pinholes in the curved portion and a reduction in gas barrier properties.

[0013] Means for solving technical problems

[0014] This disclosure provides packaging materials that enable the production of containers with excellent gas barrier properties and the ability to suppress leakage of contents, as well as containers obtained using the packaging materials.

[0015] One aspect of the packaging material disclosed herein has a laminated structure comprising a paper substrate, an adhesive resin layer, a gas barrier layer, and a sealant layer in sequence. The sealant layer comprises an ethylene-methacrylic acid copolymer, and the melt flow rate of the sealant layer, measured at a temperature of 190°C and a load of 2.16 kg, is 3.0 g / 10 min or more and 40 g / 10 min or less.

[0016] According to the packaging material disclosed herein, a container with excellent gas barrier properties and the ability to suppress leakage of contents can be obtained. This effect is presumably achieved through the following mechanism: The ethylene-methacrylic acid copolymer contained in the sealant layer has a low melting point, allowing for lamination of the materials constituting the packaging material at low temperatures. Therefore, thermal shrinkage of the gas barrier layer due to heating can be suppressed. Similarly, since the packaging material can be bent and heated during bonding at low temperatures, thermal shrinkage and bubbling of the gas barrier layer due to heating can be suppressed. Furthermore, the ethylene-methacrylic acid copolymer exhibits strong intermolecular bonding due to hydrogen bonds between carboxyl groups in a low-melting-point resin, thus displaying high strength while exhibiting moderate flexibility due to its ethylene-derived structure. Furthermore, by ensuring the melt flow rate of the ethylene-methacrylic acid copolymer is within the aforementioned range, uneven thickness of the sealant layer and improved adhesion between sealant layers can be suppressed. Therefore, the resulting container suppresses leakage of contents and exhibits excellent gas barrier properties.

[0017] From the perspective of excellent water resistance and reusability of the container, the gas barrier layer can be: having a membrane substrate comprising a polypropylene membrane and a vapor-deposited layer comprising an inorganic oxide. From the perspective of even better gas barrier properties, the vapor-deposited layer can also be disposed between the membrane substrate and the adhesive resin layer. From the perspective of even better gas barrier properties of the container, the adhesive resin layer can comprise an ethylene-methacrylic acid copolymer, and the melt flow rate of the adhesive resin layer, measured at a temperature of 190°C and a load of 2.16 kg, can be 3.0 g / 10 min or more and 40 g / 10 min or less.

[0018] The resin contained in the sealant layer, from the perspective of providing superior gas barrier properties for the container, has a melting point below 105°C and a Vicat softening point below 95°C. From the same perspective, the resin contained in the sealant layer can achieve a hardness of 45 or higher using a type D hardness tester at 23°C.

[0019] Another aspect of this disclosure relates to a container made of the aforementioned packaging material. This container maintains excellent gas barrier properties even when tension is applied or bending is performed during its manufacturing process (box-making process).

[0020] Invention Effects

[0021] According to this disclosure, packaging materials that can produce containers that can suppress leakage of contents and have excellent gas barrier properties, and containers obtained using the packaging materials, can be provided. Attached Figure Description

[0022] Figure 1 A cross-sectional view schematically illustrating one embodiment of the packaging material of this disclosure.

[0023] Figure 2 A cross-sectional view schematically illustrating another embodiment of the packaging material of this disclosure.

[0024] Figure 3 A perspective view schematically illustrating one embodiment of the container of this disclosure.

[0025] Figure 4 A perspective view schematically illustrating another embodiment of the container of this disclosure. Detailed Implementation

[0026] The following is a reference to the appendix. Figure 1 The embodiments of this disclosure will be described below. However, this disclosure is not limited to the following embodiments.

[0027] Packaging materials

[0028] <First Implementation Method>

[0029] The packaging materials of the first embodiment are described below. Figure 1 A cross-sectional view schematically illustrating the packaging material of the first embodiment. (Example) Figure 1 As shown, the packaging material 10 of this embodiment has a laminated structure comprising a paper substrate 1, an adhesive resin layer 2, a gas barrier layer 3, and a sealant layer 4 in sequence. A protective layer 5 is disposed on the surface of the paper substrate 1 opposite to the surface that contacts the adhesive resin layer 2. The components of the packaging material 10 will be described below.

[0030] (Paper substrate)

[0031] As the paper substrate 1, for example, paper with properties such as shapeability, bending resistance, rigidity, stiffness, and strength can be used. Such paper can be, for example, highly sized sun-dried or unsun-dried paper, pure white tissue paper, kraft paper, cardboard, and processed paper.

[0032] From the perspective of achieving better gas barrier properties in the resulting container, the weight per unit area of ​​the paper substrate 1 is preferably 80–600 g / m². 2 More preferably, it is 200–450 g / m³. 2 .

[0033] The desired printed patterns, such as text, graphics, designs, and symbols, can be arbitrarily formed on the paper substrate 1 using conventional printing methods.

[0034] (Adhesive resin layer)

[0035] The adhesive resin layer 2 contains an ethylene-methacrylic acid copolymer. The ethylene-methacrylic acid copolymer contained in the adhesive resin layer 2 may be the same as or different from the ethylene-methacrylic acid copolymer contained in the sealant layer 4.

[0036] The melt flow rate of the adhesive resin layer 2, measured at a temperature of 190°C and a load of 2.16 kg, is 3.0 g / 10 min or more and 40 g / 10 min or less. Alternatively, the melt flow rate of the adhesive resin layer 2 may not be within the above range. The method for measuring the melt flow rate and the preferred numerical range are the same as those for the sealant layer 4.

[0037] The melting point, Vicat softening point, and hardness of the ethylene-methacrylic acid copolymer contained in the adhesive resin layer 2 are determined by the same method as those for measuring hardness using a hardness tester, and the preferred numerical ranges are also the same as those for the ethylene-methacrylic acid copolymer contained in the sealant layer 4.

[0038] The thickness of the adhesive resin layer 2 is preferably 1 to 40 μm, more preferably 10 to 40 μm, and even more preferably 15 to 25 μm, from the perspective of improving the gas barrier properties of the resulting container.

[0039] The material of the adhesive resin layer 2 is not limited to ethylene-methacrylic acid copolymer. Examples of such materials include low-density polyethylene, linear low-density polyethylene, polypropylene, and copolymers of polyethylene and polyvinyl acetate. When the material of the adhesive resin layer 2 is a resin other than ethylene-methacrylic acid copolymer, the melting point, Vicat softening point, and hardness of the relevant resin can be the same as those of the ethylene-methacrylic acid copolymer. When the adhesive resin layer 2 is a composition comprising two or more resins, the melting point, Vicat softening point, and hardness are values ​​based on the entire resin composition.

[0040] When the adhesive resin layer 2 contains a resin other than ethylene-methacrylic acid copolymer, the content of ethylene-methacrylic acid copolymer in the adhesive resin layer 2 may be 80% or more by weight, 90% or more by weight, or 95% or more by weight, based on the total amount of the adhesive resin layer.

[0041] (Gas barrier layer)

[0042] The gas barrier layer 3 is a polypropylene film. From the viewpoint of ease of processing, such as lamination, the thickness of the gas barrier layer 3 is preferably 15–30 μm, more preferably 18–20 μm. The gas barrier layer 3 can be made of materials other than polypropylene film. Examples of such materials include polyethylene film, polyethylene terephthalate film, and nylon film. Furthermore, the film material used as the gas barrier layer 3 can be a uniaxially stretched film or a biaxially stretched film.

[0043] (Sealant layer)

[0044] The sealant layer 4 contains an ethylene-methacrylic acid copolymer.

[0045] The melt flow rate of sealant layer 4, measured at a temperature of 190°C and a load of 2.16 kg, is 3.0 g / 10 min or more and 40 g / 10 min or less. From the perspective of achieving superior gas barrier properties in the resulting container, this melt flow rate is preferably 10 g / 10 min or more, more preferably 20 g / 10 min or more, and even more preferably 30 g / 10 min or more. The melt flow rate was measured according to JIS K7210-1.

[0046] From the perspective of enabling low-temperature lamination and resulting in a more superior gas barrier property, the melting point of the ethylene-methacrylic acid copolymer is preferably below 105°C. The melting point of the ethylene-methacrylic acid copolymer can be determined using a differential scanning calorimeter (DSC).

[0047] The Vicat softening point of the ethylene-methacrylic acid copolymer is preferably below 95°C, and more preferably below 85°C, from the perspective of improving the gas barrier properties of the resulting container. The Vicat softening point is determined according to JIS K7206:1999.

[0048] The hardness of the ethylene-methacrylic acid copolymer, obtained using a type D hardness tester at 23°C, is preferably 45 or higher, but can also be below 60, considering that the packaging material has sufficient extensibility and elasticity, and the resulting container has better gas barrier properties. The hardness of the hardness tester is the value measured at 23°C according to JIS K7215:1986.

[0049] The thickness of the sealant layer 4 is preferably 30 to 150 μm, more preferably 50 to 80 μm, from the perspective of improving the gas barrier properties of the resulting container.

[0050] The sealant layer 4 may further comprise a resin other than an ethylene-methacrylic acid copolymer. Examples of such resins include low-density polyethylene, linear low-density polyethylene, polypropylene, and copolymers of polyethylene and polyvinyl acetate.

[0051] When the sealant layer 4 contains a resin other than ethylene-methacrylic acid copolymer, the melting point, Vicat softening point, and hardness of the resin are values ​​based on the resin composition as a whole, including the relevant resin.

[0052] When the sealant layer 4 contains a resin other than ethylene-methacrylic acid copolymer, the content of ethylene-methacrylic acid copolymer in the sealant layer 4 may be 80% or more by weight, 90% or more by weight, or 95% or more by weight, based on the total amount of the sealant layer.

[0053] (protective layer)

[0054] The material of the protective layer 5 can be, for example, polyethylene resin. Using polyethylene resin for the protective layer 5 improves the reusability of the resulting container. From the perspective of high physical strength and superior gas barrier properties of the resulting container, medium-density polyethylene and high-density polyethylene are preferred. From the perspective of superior gas barrier properties of the resulting container, the thickness of the protective layer 5 is preferably 10–30 μm, more preferably 15–20 μm.

[0055] Packaging material 10 is obtained by laminating layers. Examples of methods for laminating layers include extrusion lamination, T-die extrusion molding, co-extrusion lamination, blow molding, and co-extrusion blow molding. The main surfaces of each layer may also undergo treatments such as corona treatment, plasma treatment, and ozone treatment before lamination.

[0056] The packaging material 10 constructed as described above achieves the following effects: Because polypropylene film has lower heat resistance than polyethylene terephthalate film, it experiences greater shrinkage due to heat during lamination. However, the ethylene-methacrylic acid copolymer contained in the sealant layer 4 and the adhesive resin layer 2 has a low melting point, allowing lamination of the packaging material materials to be performed at low temperatures. Therefore, heat shrinkage of the polypropylene film due to heating can be suppressed. Similarly, because the packaging material can be bent and heated during bonding at low temperatures, heat shrinkage and bubbling of the polypropylene film due to heating can be suppressed.

[0057] Furthermore, when the gas barrier layer is a polypropylene film, the rigidity of the packaging material increases compared to the case where it is a polyethylene terephthalate film. This results in greater forces being applied to the curved portions of the packaging material. However, the ethylene-methacrylic acid copolymer contained in the sealant layer 4 and the adhesive resin layer 2 exhibits strong intermolecular bonding due to hydrogen bonds between carboxyl groups in a low-melting-point resin, thus displaying both high strength and moderate flexibility due to its ethylene-derived structure. Furthermore, by controlling the melt flow rate of the ethylene-methacrylic acid copolymer within a specific range, the sealant layer 4 can suppress uneven thickness and improve the adhesion between sealant layers. Therefore, even if the gas barrier layer 3 is a polypropylene film, the resulting container can effectively prevent leakage of contents and exhibits excellent gas barrier properties. Additionally, since the sealant layer 4, gas barrier layer 3, and adhesive resin layer 2 all use the same olefin-based resin, the resulting container has excellent reusability. In addition, compared with low-density polyethylene, ethylene-methacrylic acid copolymer has the characteristic of obtaining thermal adhesion in a wide heat-sealing temperature range from low to high temperature, so the packaging material 10 tends to have excellent foreign matter trapping and sealing properties.

[0058] <Second Implementation Method>

[0059] The packaging materials of the second embodiment are described below. Unless otherwise stated, aspects not described herein are the same as those of the packaging materials of the first embodiment.

[0060] Figure 2 This is a schematic cross-sectional view illustrating the packaging material of the second embodiment. (Example) Figure 2 As shown, the packaging material 20 of this embodiment has a stacked structure comprising a protective layer 5, a paper substrate 1, an adhesive resin layer 2, a primer layer 11, a gas barrier layer 3 formed by a vapor deposition layer 3a and a film substrate 3b, and a sealant layer 4 in sequence.

[0061] In packaging material 20, vapor-deposited layer 3a is disposed between film substrate 3b and adhesive resin layer 2. The hardest of the three layers, vapor-deposited layer 3a, by being disposed between film substrate 3b and adhesive resin layer 2, has the ability to suppress the warping tendency of packaging material 20. Therefore, the resulting packaging material 20 has superior gas barrier properties. Furthermore, the stacking order of film substrate 3b and vapor-deposited layer 3a in packaging material 20 can also be interchanged.

[0062] (Vapor-deposited layer)

[0063] Evaporated layer 3a is coated with silicon oxide (SiO2). x The packaging material 20 exhibits excellent water resistance. The thickness of the vapor-deposited layer 3a can be appropriately set according to the application, preferably 1 to 300 nm, more preferably 10 to 300 nm, and even more preferably 30 to 100 nm. By making the thickness of the vapor-deposited layer 3a 1 nm or more, it is easy to achieve sufficient continuity of the vapor-deposited layer 3a; by making it 300 nm or less, the occurrence of curling or cracking can be effectively suppressed, and sufficient gas barrier performance and flexibility can be easily achieved.

[0064] The vapor-deposited layer 3a can also be coated with silicon oxide (SiO2). x A layer of inorganic compounds or metals other than aluminum oxide (AlO2). As a vapor-deposited layer, it can be, for example, a layer obtained by vapor-depositing aluminum, or a layer containing aluminum oxide (AlO2). x () layer.

[0065] From the viewpoint of oxygen barrier properties or film uniformity, the vapor-deposited layer 3a is preferably formed using a vacuum deposition method. Known methods include vacuum deposition, sputtering, and chemical vapor deposition (CVD), but vacuum deposition is preferred due to its fast deposition speed and high productivity. Furthermore, vacuum deposition methods, especially those utilizing electron beam heating, are effective because the deposition rate can be easily controlled by adjusting the irradiation area or electron beam current, or because the temperature of the vapor-deposited material can be raised and lowered in a short time.

[0066] (Membrane substrate)

[0067] The membrane substrate 3b is a polypropylene film. The thickness and material of the membrane substrate 3b can be the same as the gas barrier layer 3 in the packaging material 10 of the above embodiment.

[0068] (Primer layer)

[0069] The primer layer 11 improves the adhesion between the adhesive resin layer 2 and the vapor-deposited layer 3a. Materials for the primer layer 11 may include, for example, anchoring agents and laminating adhesives. Examples of anchoring agents include isocyanate resins, urethane resins, polyethyleneimine resins, polybutadiene resins, and organotitanium compounds. Examples of laminating adhesives include polyurethane resins, polyacrylic resins, polyester resins, epoxy resins, polyvinyl acetate resins, and cellulose resins.

[0070] The primer layer 11 is formed by applying a coating liquid to the surface of the vapor-deposited layer 3a. Commonly known methods such as casting, dipping, roller coating, gravure coating, screen printing, reverse coating, spraying, kit coating, mold coating, bar coating, closed-loop blade coating, and curtain coating can be used for this coating process. The primer layer 11 is formed by heating and drying the coating film formed using the coating liquid. The thickness of the primer layer 11 is, for example, about 0.01 to 10 μm.

[0071] [container]

[0072] <First Implementation Method>

[0073] The container (paper container) of the first embodiment is described below. Figure 3 The container 50 shown is made using packaging material 10. Container 50 can also be made using packaging material 20.

[0074] Container 50 can be used to fill and package various food and beverage products, adhesives and other chemicals, cosmetics, pharmaceuticals, and other general merchandise. Due to its excellent gas barrier properties, container 50 is particularly preferred for filling and packaging liquid condiments such as wine, milk, fruit juice, mineral water, soy sauce, and sauces, as well as liquid food and beverages such as curry, stews, and soups.

[0075] Container 50 is a roof-type container. Container 50 comprises a cylindrical container body 52 having an upper portion 52a, sides 52b, and a bottom 52c with an opening 51, and a lid 55 for closing the opening 51. The container body 52 has a protective layer 5 of packaging material 10 as its outermost layer and a sealing layer 4 as its innermost layer. The container body 52 has locations where the packaging material 10 is bent (bending portions B1 and B2). Bending portion B1 is where the packaging material 10 is folded when viewed from the innermost layer side, while bending portion B2 is where the packaging material 10 is folded when viewed from the innermost layer side.

[0076] The container 50 is made of packaging material 10 that maintains sufficient gas barrier properties even under tension and can suppress leakage of the contents after heat sealing. Therefore, it can effectively suppress the deterioration and leakage of the contents for a long period of time.

[0077] <Second Implementation Method>

[0078] The container (paper container) of the second embodiment will be described. For aspects not described below, they are the same as those of the container of the first embodiment, unless there is a contradiction. Figure 4 The container 60 shown is made using packaging material 10. Container 60 can also be made using packaging material 20.

[0079] The container 60 comprises a cylindrical container body 62 having an upper part 62a, a side part 62b, and a bottom part 62c with an opening 61, and a sealing part 65 for closing the opening 61. The container body 62 has a protective layer 5 of packaging material 10 as the outermost layer and a sealing layer 4 as the innermost layer. The side part 62b is made of packaging material 10 that is bent while being heated.

[0080] The packaging material 10 is constructed such that it is bendable at low temperatures, maintains sufficient gas barrier properties even after tension is applied due to bending, and can suppress leakage of the contents after heat sealing. Therefore, it can effectively suppress the deterioration and leakage of the contents for a long period of time.

[0081] The embodiments of this disclosure have been described in detail above, but this disclosure is not limited to the above embodiments. For example, the primer layer 11 may not be provided in the packaging material 20. In addition, although the container 50 has an opening 51 at the top 52a, the opening 51 may not be provided. Furthermore, the shape of the container is not limited to the shapes of the containers 50 and 60; for example, it may also be brick-shaped or triangular pyramid-shaped.

[0082] Example

[0083] The present disclosure will be described in more detail below with reference to embodiments and comparative examples, but the present disclosure is not limited to the following embodiments.

[0084] Prepare the following materials as adhesive resin layers and sealant layers.

[0085] • Ethylene-methacrylic acid copolymer A: N0908C (trade name, manufactured by DOW-MITSUI POLYCHEMICALS Co., Ltd., melting point: 99°C, Vicat softening point: 82°C, melt flow rate: 8 g / 10 min, hardness tester hardness: 57)

[0086] • Ethylene-methacrylic acid copolymer B: AN4213C (trade name, manufactured by DOW-MITSUI POLYCHEMICALS Co., Ltd., melting point: 88℃, Vicat softening point: 62℃, melt flow rate: 10g / 10min, hardness tester hardness: 47)

[0087] • Ethylene-methacrylic acid copolymer C: N1035 (trade name, manufactured by DOW-MITSUI POLYCHEMICALS Co., Ltd., melting point: 95°C, Vicat softening point: 71°C, melt flow rate: 35 g / 10 min, hardness tester hardness: 54)

[0088] • Ethylene-methacrylic acid copolymer D: N1110H (trade name, manufactured by DOW-MITSUI POLYCHEMICALS Co., Ltd., melting point: 95°C, Vicat softening point: 68°C, melt flow rate: 100g / 10min, hardness tester hardness: 53)

[0089] • Low-density polyethylene resin: LC600A (trade name, manufactured by Japan Polyethylene Co., Ltd., melting point: 109℃, Vicat softening point: 93℃, melt flow rate: 0.9g / 10min, hardness tester hardness: 48)

[0090] The melt flow rate was determined according to JIS K7210-1 at a temperature of 190°C and a load of 2.16 kg. The melting point was determined using a differential scanning calorimeter. The Vicat softening point was determined according to JIS K7206-1999. The hardness was determined according to JIS K7215:1986 at 23°C.

[0091] [Manufacturing of packaging materials and containers]

[0092] (Example 1)

[0093] The packaging material of this example was obtained through the following process. Specifically, a gas barrier film was prepared by forming a vapor-deposited layer (silica vapor-deposited layer, thickness: 50 nm) with silica as the main component on one surface of a film substrate (material: polypropylene resin, thickness: 18 μm). For the stretch evaluation described later, two marks were applied to the polypropylene film at 100 mm intervals along the MD direction during subsequent extrusion lamination. A sealant layer (material: ethylene-methacrylic acid copolymer A, thickness: 30 μm) was formed on the other surface of the film substrate by extrusion lamination, obtaining a laminate 1 containing the vapor-deposited layer. The lamination temperatures were those shown in Table 1. On the other hand, a paper substrate (weight per unit area: 260 g / m²) was prepared. 2 A protective layer (material: polyethylene, thickness: 15 μm) is formed on one surface of the laminate to obtain a laminate 2 containing a paper substrate. The laminates 1 and 2 are extruded and laminated with the vapor-deposited layer of laminate 1 facing the paper substrate of laminate 2, and bonded together with ethylene-methacrylic acid copolymer A (adhesive resin layer). The thickness of the adhesive resin layer is 15 μm. The extrusion lamination temperatures are those shown in Table 1.

[0094] The obtained packaging material is then boxed into gable-top containers. The heat-sealing temperature is the temperature listed in Table 1. The temperatures listed in Table 1 are the lowest possible temperatures within the range that will not cause leakage of the contents. Leakage of the contents is confirmed by spraying Ageless Seal Check liquid (trade name, manufactured by Mitsubishi Gas Chemical Co., Ltd.).

[0095] (Example 2)

[0096] Except that ethylene-methacrylic acid copolymer B is used instead of ethylene-methacrylic acid copolymer A as a sealant layer and adhesive resin layer, the packaging materials and containers are manufactured in the same manner as in Example 1.

[0097] (Example 3)

[0098] Except that ethylene-methacrylic acid copolymer C is used instead of ethylene-methacrylic acid copolymer A as a sealant layer and adhesive resin layer, the packaging materials and containers are manufactured in the same manner as in Example 1.

[0099] (Comparative Example 1)

[0100] Except that low-density polyethylene resin is used instead of ethylene-methacrylic acid copolymer A as a sealant layer and adhesive resin layer, the packaging materials and containers are manufactured in the same manner as in Example 1.

[0101] (Comparative Example 2)

[0102] Except that low-density polyethylene resin is used instead of ethylene-methacrylic acid copolymer A as a sealant layer, the packaging materials and containers are manufactured in the same manner as in Example 1.

[0103] (Comparative Example 3)

[0104] Except that ethylene-methacrylic acid copolymer D was used instead of ethylene-methacrylic acid copolymer A as a sealing layer, the packaging material was manufactured in the same manner as in Example 1. Although it was intended to form the resulting packaging material into a gable-top container, the sealing layer was poorly sealed, resulting in leakage of the contents.

[0105] [Evaluation of the stretchability of the barrier membrane]

[0106] (Examples 1-3 and Comparative Examples 1-3)

[0107] In the obtained packaging material, the interval between two marks pre-applied to the polypropylene film was measured. The obtained measured value (mm) was substituted into the following formula (1) to calculate the shrinkage rate of the polypropylene film. The results are shown in Table 1.

[0108] Shrinkage rate (%) = {(100 - measured value) / 100} × 100

[0109] [Determination of oxygen permeability]

[0110] (Examples 1-3 and Comparative Examples 1 and 2)

[0111] The oxygen permeability was measured using an oxygen permeability measuring device (Mocon, trade name: "OX-TRAN 2 / 22") at a temperature of 30°C and a relative humidity of 70%. Measurements were performed on freshly boxed containers. The results are shown in Table 1. Measured values ​​are expressed as [(cc / pkg·day)].

[0112] [Evaluation of the bubbling phenomenon]

[0113] (Examples 1-3 and Comparative Examples 1 and 2)

[0114] The presence of bubbling from the paper substrate during heat sealing and boxing of packaging materials into containers was evaluated. The evaluation was conducted visually. The results are shown in Table 1.

[0115] [Table 1]

[0116]

[0117] The main points of this disclosure are contained in the following [1] to [7].

[0118] [1] A packaging material having a laminated structure comprising, in sequence, a paper substrate, an adhesive resin layer, a gas barrier layer, and a sealant layer, wherein,

[0119] The above-mentioned sealant layer contains an ethylene-methacrylic acid copolymer.

[0120] The melt flow rate of the above-mentioned sealant layer, measured at a temperature of 190°C and a load of 2.16 kg, was 3.0 g / 10 min or more and 40 g / 10 min or less.

[0121] [2] According to the packaging material of [1], the gas barrier layer has a film substrate and a vapor-deposited layer, the film substrate comprising a polypropylene film and the vapor-deposited layer comprising an inorganic oxide.

[0122] [3] According to the packaging material of [2], wherein the vapor-deposited layer is disposed between the film substrate and the adhesive resin layer.

[0123] [4] The packaging material according to [1] or [2], wherein the adhesive resin layer comprises an ethylene-methacrylic acid copolymer, and the melt flow rate of the adhesive resin layer, measured at a temperature of 190°C and a load of 2.16 kg, is 3.0 g / 10 min or more and 40 g / 10 min or less.

[0124] [5] According to the packaging material of [1] or [2], wherein the resin contained in the above-mentioned sealant layer has a melting point of less than 105°C and a Vicat softening point of less than 95°C.

[0125] [6] According to the packaging material described in [1] or [2], wherein the resin contained in the above-mentioned sealant layer has a hardness of 45 or higher obtained by a D-type hardness tester at 23°C.

[0126] [7] A container made of the packaging material described in [1] or [2].

[0127] Symbol Explanation

[0128] 1. Paper substrate, 2. Adhesive resin layer, 3. Gas barrier layer, 4. Sealant layer, 5. Protective layer

[0129] 11. Primer layer, 10, 20. Packaging materials, 50, 60. Container.

Claims

1. A packaging material having a layered structure provided with a paper base material, an adhesive resin layer, a gas barrier layer, and a sealant layer in this order, wherein the sealant layer contains an ethylene-methacrylic acid copolymer, and a melt flow rate of the sealant layer measured at a temperature of 190°C and a load of 2.16 Kg is 20 g / 10 min or more and 40 g / 10 min or less.

2. The packaging material according to claim 1, wherein the gas barrier layer has a film base material and a vapor deposition layer, the film base material contains a polypropylene film, and the vapor deposition layer contains an inorganic oxide.

3. The packaging material according to claim 2, wherein the vapor deposition layer is disposed between the film base material and the adhesive resin layer.

4. The packaging material according to any one of claims 1 to 3, wherein the adhesive resin layer contains an ethylene-methacrylic acid copolymer, and a melt flow rate of the adhesive resin layer measured at a temperature of 190°C and a load of 2.16 Kg is 3.0 g / 10 min or more and 40 g / 10 min or less.

5. The packaging material according to any one of claims 1 to 4, wherein a melting point of the resin contained in the sealant layer is 105°C or less and a Vicat softening point is 95°C or less.

6. The packaging material according to any one of claims 1 to 5, wherein a durometer hardness of the resin contained in the sealant layer obtained using a type D durometer at 23°C is 45 or more.

7. A container constituted by the packaging material according to any one of claims 1 to 6. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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