Laminated sheets for paper containers and paper containers

Abstract

To provide a laminated sheet for a paper container capable of suppressing bubbling due to hot air (heating) during molding of the container while suppressing an increase in the number of manufacturing processes.SOLUTION: In a laminated sheet for a paper container, a bubbling suppressing layer, an adhesive layer, a barrier film layer and a sealant layer are laminated in this order on one surface side of a paper layer, and a thermoplastic resin layer is laminated on the other surface side of the paper layer. The bubbling suppressing layer is composed of a resin containing low density polyethylene or linear low density polyethylene. The melt tension of the resin is 0.04 N or more and 0.09 N or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention relates to a laminated sheet for paper containers and a paper container using the laminated sheet. [Background technology]

[0002] Traditionally, glass bottles, cans, and plastic bottles were commonly used as containers for liquids such as beverages and alcoholic drinks, as well as powders. However, in recent years, with growing awareness of environmental protection, paper containers, which are highly recyclable and have a low environmental impact, have become widely used as containers for beverages, alcoholic drinks, and other similar products. Generally, liquid paper containers used to hold liquids employ packaging materials consisting of laminated sheets made by layering multiple materials to ensure the preservation of the contents, the strength of the container, and gas barrier properties. The packaging materials (laminated sheets) used for these liquid paper containers are known to have a layered structure in which a thermoplastic resin layer, paper layer, adhesive layer, barrier layer, and sealant layer are laminated in that order from the outside of the container. EMAA resin, which exhibits good adhesion to the paper layer and barrier film layer, is commonly used for the adhesive layer.

[0003] When forming a container into the desired shape using such laminated sheets, a heating step is involved in applying hot air to melt the sealant layer. In this heating step, when hot air is applied to the sealant layer, the heat rapidly heats the water contained in the paper layer, turning it into steam. The expansion pressure of this steam can cause a foaming phenomenon (bubbling) that separates the paper layer from the adhesive layer. The EMAA resin used in the adhesive layer has low resistance to expansion pressure, making it prone to bubbling. When bubbling occurs as described above, it can lead to sealing failures and cosmetic defects. Therefore, laminated sheets are required to be resistant to bubbling. Conventionally, methods such as those described in Patent Document 1 and Patent Document 2 have been proposed as techniques to suppress bubbling.

[0004] Patent Document 1 describes a paper container formed from a laminated material mainly consisting of a paper substrate in which a paper layer and a barrier film layer are laminated with a melt-extruded resin layer in between, wherein the adhesive coating surface of the paper substrate has a sizing degree of 400 seconds or more according to the measurement method of JIS P8122, and the adhesive coating surface has an adhesive layer of 0.5 g / m² made of a two-component curing adhesive having urethane bonding. 2 More than 4g / m 2 A paper container has been proposed characterized by forming a laminated material in which a paper layer and a barrier film layer are laminated by applying the adhesive layer with the following amounts and interposing the adhesive layer between the paper layer and the molten extruded resin layer. In this case, by providing the adhesive layer, it is possible to improve heat resistance or to provide strength sufficient to withstand the pressure of water vapor expansion, thereby suppressing bubbling.

[0005] Patent Document 2 proposes a paper container material for liquid packaging, in which at least an outer resin layer is laminated to one side of a main cardboard layer, and an inner sealant resin layer is laminated to the other side of the cardboard layer via an adhesive layer or barrier layer such as a plastic resin layer, characterized in that the outer resin layer is provided with fine, water vapor permeable pores that reach the cardboard layer. According to this method, the pores in the outer resin layer serve as escape routes for water vapor evaporated by hot air, thereby reducing the expansion pressure due to water vapor and suppressing bubbling. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 4577001 [Patent Document 2] Japanese Patent Publication No. 2000-203565 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, the method described in Patent Document 1 requires the provision of an adhesive layer between the paper layer and the molten extruded resin layer. Therefore, the manufacturing cost increases due to the increased material costs and number of steps in the method described in Patent Document 1. Furthermore, the method described in Patent Document 2 requires the step of creating a perforated section, which increases the number of steps, thus requiring further simplification of the process. In addition, with the method described in Patent Document 2, there is a risk that moisture and odors from the air may enter the paper layer through the pores when the paper container is used. This invention was made in view of the above-mentioned points, and aims to provide a laminated sheet for paper containers that can suppress bubbling caused by hot air (heating) during container molding while keeping the number of manufacturing steps low. [Means for solving the problem]

[0008] A laminated sheet for paper containers according to one aspect of the present invention is a laminated sheet for paper containers in which a bubbling suppression layer, an adhesive layer, a barrier film layer and a sealant layer are laminated in this order on one side of a paper layer, and a thermoplastic resin layer is laminated on the other side of the paper layer, wherein the bubbling suppression layer is composed of a resin containing low-density polyethylene or linear low-density polyethylene, and the melt tension of the resin is 0.04 N or more and 0.09 N or less.

[0009] Furthermore, the laminated sheet for paper containers may have a total thickness of 20 μm or more and 40 μm or less for the sum of the film thicknesses of the bubbling suppression layer and the adhesive layer, and the thickness of the bubbling suppression layer may be 10 μm or more and 35 μm or less, and the thickness of the adhesive layer may be 5 μm or more and 10 μm or less. Furthermore, the laminated sheet for paper containers may have a lamination strength of 2N / 15mm or more between the adhesive layer and the barrier film layer. Furthermore, the laminated sheet for paper containers described above may have an adhesive layer composed of a resin containing any of the following: additive-free polyethylene, polyethylene containing adhesive components, or an ethylene-acrylic acid copolymer.

[0010] In addition, the laminated sheet for paper containers is the laminated sheet for paper containers according to any one of claims 1 to 4, characterized in that the barrier film layer is any film selected from the following (1) to (3). (1) A PET film provided with a vapor-deposited film of a metal (2) A PET film provided with a vapor-deposited film of an inorganic oxide (3) A laminated film of an aluminum foil and a PET film In addition, the paper container according to one aspect of the present invention is formed by shaping the laminated sheet for paper containers into a container shape. In addition, the shape of the paper container may be any of a go-getter top type shape, a cup shape, or a cylindrical shape. [Advantages of the Invention]

[0011] According to an aspect of the present invention, it is possible to suppress bubbling due to hot air during container molding while suppressing an increase in the number of manufacturing steps. [Brief Description of the Drawings]

[0012] [Figure 1] It is a schematic cross-sectional view for explaining a configuration example of a laminated sheet for paper containers according to an embodiment based on the present invention. [Figure 2] It is a diagram showing an example of a process of manufacturing a paper container according to an embodiment based on the present invention. [Figure 3] It is a conceptual diagram for explaining an example of manufacturing a laminated sheet for paper containers according to an embodiment based on the present invention. [Figure 4] It is a diagram for explaining an example of a manufacturing process of a paper container according to an embodiment based on the present invention. [Modes for Carrying Out the Invention]

[0013] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Each figure is a schematically shown figure, and the size, shape, etc. of each part are exaggerated as appropriate for easy understanding. In addition, the following description relates to an example of the present invention, and the present invention is not limited by these. (Laminated Sheet for Paper Container) Figure 1 is a schematic cross-sectional view for explaining a configuration example of a laminated sheet for a paper container according to an embodiment based on the present invention. The laminated sheet 10 for a paper container in this embodiment has a structure in which a bubbling suppression layer 3, an adhesive layer 4, a barrier film layer 5, and a sealant layer 6 are laminated in this order on one surface side of a paper layer 2, and a thermoplastic resin layer 1 is laminated on the other surface side of the paper layer 2.

[0014] Next, each layer constituting the laminated sheet 10 for a paper container will be individually described. (Paper Layer 2) The paper layer 2 is mainly a layer for imparting formability and rigidity to the container. Examples of the paper layer 2 include surface-treated coated paper and untreated non-coated paper. A known paper material used for paper containers may be used for the paper layer 2. The basis weight of the paper layer 2 is, for example, 200 g / m 2 or more and 500 g / m 2 or less is preferable, but it may be appropriately selected according to the container size. Here, it is preferable that the surface of the paper layer 2 is appropriately subjected to a surface treatment such as corona treatment in order to improve the adhesiveness with the thermoplastic resin layer 1 and the bubbling suppression layer 3.

[0015] (Bubbling Suppression Layer 3) The bubbling suppression layer 3 is a layer provided for suppressing bubbling. Examples of the resin selected for the bubbling suppression layer 3 include low-density polyethylene, linear low-density polyethylene, or resins containing them. The material selected for the bubbling suppression layer 3 preferably has good adhesion to the paper layer 2, is easy to extrude, and is inexpensive. However, polyethylene is easy to co-extrude with the resin used for the adhesive layer 4 described later and has good adhesion, so good adhesive strength can be obtained while having excellent processability. Also, the adhesion to the paper layer 2 is excellent. When resins other than polyethylene are used, it becomes difficult to achieve both adhesion to the paper layer 2 and the adhesive layer 4, and sufficient adhesive strength cannot be obtained at either interface, which may cause delamination or the like.

[0016] The bubbling suppression layer 3 uses polyethylene resin with a melt tension in the range of 0.04 N to 0.09 N. Placing a resin with a melt tension in the above range in the bubbling suppression layer 3 adjacent to the paper layer increases resistance to the expansion pressure caused by the vapor of moisture in the paper, thereby suppressing bubbling. If the melt tension is greater than 0.09 N, the adhesion with the paper layer 2 decreases, making delamination more likely, and thus bubbling will easily occur. Also, if the melt tension is less than 0.04 N, the resin lacks viscosity and cannot withstand the expansion pressure of the vapor.

[0017] The melt tension was measured using a capillary rheometer (NETZSCH Rosand RH-7D) at a temperature of 200°C, a piston speed of 20 mm / min, and a draw speed of 10 m / min. The bubbling suppression layer 3 is preferably 10 μm to 35 μm in thickness. If the thickness is less than 10 μm, adhesion will decrease and delamination may occur, which is necessary for maintaining the adhesion of the paper layer 2 and the adhesive layer 4. If the thickness is 35 μm or more, problems may occur during the container molding process, such as difficulty in creating creases.

[0018] Methods for laminating the bubbling suppression layer 3 include an extrusion coating method and a method of laminating the barrier film layer 5 by co-extrusion lamination with the adhesive layer 4, which will be described later. Co-extrusion lamination with the adhesive layer 4 is preferable because it allows for the lamination of multiple layers at once, simplifying the manufacturing process. When the adhesive layer 4 is extruded and coated in a single layer configuration, corona treatment can be appropriately applied to the bubbling suppression layer 3 to improve adhesion.

[0019] (adhesive layer 4) The adhesive layer 4 is provided on one side of the bubbling suppression layer 3 to adhere to the barrier film layer 5, which will be described later. The lamination strength of the adhesive layer 4 and the barrier film layer 5 is preferably 2N / 15mm or higher. If the lamination strength is 2N / 15mm or higher, leakage due to poor sealing can be prevented when liquid is placed in the container. The adhesive layer 4 is not particularly limited as long as it is a thermoplastic resin that has adhesion to the barrier film layer as well as adhesion to the bubbling suppression layer 3, as described above. The reason for using thermoplastic resin is that the bubbling suppression layer 3 and the co-extrusion lamination method allow for lamination with fewer steps.

[0020] Examples of thermoplastic resins constituting the adhesive layer 4 include low-density polyethylene, medium-density polyethylene, linear low-density polyethylene, polypropylene, copolymer resins of ethylene-α-olefin, copolymers of ethylene-unsaturated carboxylic acids or their ester compounds such as ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, ethylene-methyl acrylate copolymer, and ethylene-methacrylic acid copolymer, as well as ionomer resins. Among these, low-density polyethylene constituting the bubbling suppression layer 3, additive-free polyethylene with good adhesion to linear low-density polyethylene, polyethylene containing adhesive components, and ethylene-acrylic acid copolymer are more preferred.

[0021] The sum of the film thicknesses of the bubbling suppression layer 3 and the adhesive layer 4 is preferably 20 μm or more and 40 μm or less. If the sum of the film thicknesses of the bubbling suppression layer 3 and the adhesive layer 4 is less than 20 μm, heat transfer to the paper, which is the site of bubbling, will be faster when heated with hot air, making bubbling more likely to occur. If the sum of the film thicknesses of the bubbling suppression layer 3 and the adhesive layer 4 is thicker than 40 μm, problems such as difficulty in creating creases for container molding are more likely to occur. The thickness of the adhesive layer 4 is preferably 5 μm or more and 10 μm or less. If it is thinner than 5 μm, the adhesion between the bubbling suppression layer 3 and the barrier film layer 5 will decrease, and delamination will be more likely to occur. If the thickness of the adhesive layer 4 is thicker than 10 μm, when the sum of the film thicknesses of the bubbling suppression layer 3 and the adhesive layer 4 is designed to be within the aforementioned preferred range, it becomes impossible to ensure a sufficient thickness for the bubbling suppression layer 3.

[0022] Known methods for laminating the adhesive layer 4 include extrusion lamination, in which the adhesive layer 4 is sandwiched in a molten state between the bubbling suppression layer 3 and the barrier film layer 5. Alternatively, a co-extrusion lamination method can be applied in which the bubbling suppression layer 3 and the adhesive layer 4 are co-extruded and sandwiched in a molten state between the paper layer 2 and the barrier film layer 5. A two-layer co-extrusion lamination method is more preferable because it allows for the lamination of the barrier film layer 3 and the adhesive layer 4 to be performed simultaneously, thus eliminating the need for additional steps.

[0023] (Barrier film layer 5) The barrier film layer 5 is provided to give the container gas barrier properties. For the barrier film layer 5, a film can be used in which an inorganic substance such as silica, alumina, or aluminum is deposited onto a base film such as a biaxially oriented polyester film, nylon film, polycarbonate film, polyvinyl alcohol film, or ethylene-vinyl alcohol copolymer resin. The thickness of this base film is appropriately about 5 to 30 μm. The thickness of the deposited film itself only needs to be thick enough to exhibit the required gas barrier properties; for example, when depositing silica, a thickness of about 30 to 200 nm is preferable.

[0024] Alternatively, the barrier film layer 5 may be manufactured by bonding aluminum foil and the aforementioned base film using a dry lamination method. When the barrier film layer 5 is laminated with the adhesive layer 4 and the sealant layer 6, the surface can be appropriately treated with corona to improve adhesion. The barrier film layer 5 is preferably one of the films selected from (1) to (3) below. (1) PET film with a metal vapor-deposited film (2) PET film with an inorganic oxide vapor-deposited film (3) Laminated film of aluminum foil and PET film Here, "provided" includes not only cases where it is provided on one side of the PET film, but also cases where it is provided on both sides.

[0025] (Sealant layer 6) The sealant layer 6 can use resins commonly used as sealant layers. Examples of resins that make up the sealant layer 6 include polyethylene-based resins such as low-density polyethylene, medium-density polyethylene, linear low-density polyethylene, ethylene-α-olefin copolymer resins, and ethylene-vinyl acetate copolymers, as well as polypropylene. The sealant layer 6 can be used as a single layer or as a multilayer by combining multiple resins.

[0026] The thickness of the sealant layer 6 is not particularly limited as long as it provides sufficient sealing performance during container molding, and any known thickness can be used. For example, a suitable thickness for the sealant layer 6 is 30 μm to 100 μm. The method of laminating the sealant layer 6 is not particularly limited, but common methods include a dry lamination method using a two-component curing adhesive with urethane bonding after film formation, and an extrusion coating method in which the sealant layer 6 is laminated onto the barrier film layer 5 in a molten state. For extrusion coating, in order to improve adhesion with the barrier film layer 5, the adhesive may be applied to the barrier film layer 5 in advance, and then the sealant layer 6 may be laminated in a molten state.

[0027] (Thermoplastic resin layer 1) The thermoplastic resin layer 1 is the outermost layer after container molding and is provided to protect the paper layer and for printing. The thermoplastic resin layer 1 is required to have properties such as heat sealability and printability to heat-seal the thermoplastic resin layers together when molding the laminated sheets into various container shapes such as square or round. Examples of resins selected for the thermoplastic resin layer 1 include low-density polyethylene, linear low-density polyethylene, copolymer resins of ethylene-α-olefins, ethylene-vinyl acetate copolymers, ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers, ethylene-methyl acrylate copolymers, ethylene-methyl methacrylate copolymers, ionomer resins, and copolymers of ethylene-unsaturated carboxylic acids or their ester compounds.

[0028] The thickness of the thermoplastic resin layer 1 can be any known thickness used for the thermoplastic resin layer of a paper container. The thickness of the thermoplastic resin layer 1 should be such that it is the minimum thickness necessary to heat-seal the thermoplastic resin layers together during container molding and withstand impacts such as dropping after container molding. Generally, the thickness of the thermoplastic resin layer 1 is between 10 μm and 30 μm. For laminating the thermoplastic resin layer 1, an extrusion coating method can be used, in which the layer is laminated onto the paper layer in a molten state. When using the dry lamination method, the adhesive layer blocks the escape route for water vapor generated in the paper layer 2 during hot air heating, which tends to increase the internal pressure in the paper layer 2 and makes bubbling more likely, so this is undesirable. The order in which each layer is laminated relative to the paper layer 2 is not particularly limited; the thermoplastic resin layer 1 may be laminated first, followed by the bubbling suppression layer 3, or the order may be reversed. The surface of the thermoplastic resin layer 1 can be subjected to surface treatments such as corona treatment as needed, and then printing can be performed.

[0029] (Paper container) Figure 2 shows an example of a paper container manufacturing process according to one embodiment of the present invention. The paper container is formed using the laminated sheet 10 for paper containers described in the above embodiment. The manufacturing process 20 for producing a paper container with the desired container shape from the laminated sheet 10 for paper containers includes a heating process 20A and a molding process 20B, as shown in Figure 2. The heating step 20A is a process in which heat is applied from both sides of the laminated sheet 10 for paper containers, which will be on the inside of the paper container, on the side with the sealant layer 6, and on the side with the thermoplastic resin layer 1, which will be on the outside of the paper container, to temporarily melt the sealant layer 6 and the thermoplastic resin layer 1. The heating process in heating step 20A is performed, for example, by blowing hot air at a temperature of 340°C for 1 second. In molding process 20B, a load is applied to the sealant layer 6 and thermoplastic resin layer 1, which have been temporarily melted after heating process 20A, to seal them and simultaneously mold them into a three-dimensional container shape. The heating process 20A and molding process 20B are first performed on the bottom of the container. After the bottom of the container is molded, the contents are filled in, and then the heating process 20A and molding process 20B are performed again to seal and mold the top of the container.

[0030] (Example of manufacturing process) This figure shows an example of a method for manufacturing a laminated sheet for paper containers and a paper container according to this embodiment. Figure 3 is a conceptual diagram illustrating an example of manufacturing a laminated sheet for paper containers according to one embodiment of the present invention. Figure 4 is a diagram illustrating an example of the manufacturing process for a paper container according to one embodiment of the present invention.

[0031] <Manufacturing example of laminated sheet 10 for paper containers> First, as shown in Figure 3(a), a laminated sheet (5,6) is manufactured by laminating a resin constituting the sealant layer 6 onto a barrier film layer 5 that has been pre-coated with adhesive using an extrusion coating method. Next, as shown in Figure 3(b), the laminated sheets (5,6) manufactured above and the paper layer 2 are co-extruded and laminated with the bubbling suppression layer 3 and the adhesive layer 4 to produce laminated sheets (2-6). Next, as shown in Figure 3(c), the manufactured laminated sheets (2-6) and the thermoplastic resin layer 1 are laminated sequentially by extrusion molding to form laminated sheets 10 for paper containers, and these laminated sheets 10 for paper containers are then rolled into a roll.

[0032] <Examples of paper container manufacturing> As shown in Figure 4(a), the manufactured laminated paper container sheet 10 is cut into sheets to obtain a blank material as shown in Figure 4(b) (punching process). Next, as shown in Figure 4(c), a creasing process is performed on the blank material to create creases for easier assembly. Next, the material is formed into a cylindrical shape as shown in Figure 4(d). Next, as shown in Figure 4(e), the bottom side of the cylindrical molded product is heated with hot air on the sealant layer 6 side (inner surface) and the thermoplastic resin 1 side (outer surface) to seal and perform a molding process that closes the bottom of the container (molding process 20B). Next, as shown in Figure 4(f), the contents are filled from the top side (filling process). Next, as shown in Figure 4(g), the top side of the sealant layer 6 (inner surface) and the thermoplastic resin 1 (outer surface) are heated with hot air (heating step 20A), and a molding process is performed to seal and close the top of the container (molding step 20B).

[0033] [Example 1] A 55 μm thick LDPE film with one side pre-treated with corona was prepared as the sealant layer 6, and a 12 μm thick PET film with silica deposition on one side and corona treatment on the other side was prepared as the barrier film layer 5. The silica-deposited side and the corona-treated side of the LDPE film were laminated using a urethane-based adhesive by dry lamination to create a laminated sheet of barrier film layer 5 / sealant layer 6. In addition, the PET surface exposed on the barrier film layer 5 side of the laminated sheet of barrier film layer 5 / sealant layer 6 was subjected to corona treatment.

[0034] Paper layer 2 with a basis weight of 380 g / m² 2Uncoated paper was prepared, and after corona treatment was performed on both sides of paper layer 2, LDPE (Suntech L2340 manufactured by Asahi Kasei Corporation) was extruded to a thickness of 18 μm onto one side of the paper substrate using the first T-die of a tandem extruder, and thermoplastic resin layer 1 was laminated on top of paper layer 2. Subsequently, LDPE (L2340 manufactured by Asahi Kasei Corporation, melt tension 0.08 N, thickness 20 μm) as a bubbling suppression layer 3 and EMAA (AN4228C manufactured by Mitsui DuPont Polychemical Co., Ltd., thickness 10 μm) as an adhesive layer 4 were co-extruded from the second T-die onto the opposite side of the paper substrate where thermoplastic resin layer 1 was formed and the PET film side of the laminated film of barrier film layer 5 / sealant layer 6 to perform sand lamination and produce a laminated sheet.

[0035] The resulting laminated sheet consists of LDPE (L2340, thickness 18 μm) (1) / paper (basis weight 380 g / m²). 2 (2) LDPE (L2340, melt tension 0.08N, thickness 20μm) (3) EMAA (AN4228C, thickness 10μm) (4) Silica vapor-deposited PET film (thickness 12μm) (5) LDPE (thickness 55μm) (6). (See Figure 1).

[0036] [Example 2] A laminated sheet was prepared in the same manner as in Example 1, except that the resin of the bubbling suppression layer 3 was changed to LDPE (Asahi Kasei Corporation, L1640, melt tension 0.05N). The resulting laminated sheet consists of L2340 (L2340, thickness 18 μm) / paper (basis weight 380 g / m²). 2 The materials are: ) / LDPE (L1640, melt tension 0.05N, thickness 20μm) / EMAA (AN4228C, thickness 10μm) / silica vapor-deposited PET film (thickness 12μm) / LDPE (thickness 55μm).

[0037] [Example 3] A laminated sheet was prepared in the same manner as in Example 1, except that the resin of the bubbling suppression layer 3 was changed to LDPE (LC500 manufactured by Asahi Kasei Corporation, melt tension 0.04N). The structure of the obtained laminated sheet is LDPE (L2340, thickness 18 μm) / paper (basis weight 380 g / m 2 ) / LDPE (LC500, melt tension 0.04 N, thickness 20 μm) / EMAA (AN4228C, thickness 10 μm) / silica-deposited PET film (thickness 12 μm) / LDPE (thickness 55 μm).

[0038] [Example 4] A laminated sheet was produced in the same manner as in Example 1, except that the resin of the bubbling suppression layer 3 in Example 1 was changed to LDPE (M2629 with a melt tension of 0.09 N, manufactured by Asahi Kasei Corporation). The structure of the obtained laminated sheet is LDPE (L2340, thickness 18 μm) / paper (basis weight 380 g / m 2 ) / LDPE (M2629, melt tension 0.09 N, thickness 20 μm) / EMAA (AN4228C, melt tension 0.02 N, thickness 10 μm) / silica-deposited PET film (thickness 12 μm) / LDPE (thickness 55 μm).

[0039] [Example 5] A laminated sheet was produced in the same manner as in Example 1, except that the resin of the bubbling suppression layer 3 in Example 1 was changed to LDPE (LC522 with a melt tension of 0.09 N, manufactured by Nippon Polyethylene Co., Ltd.). The structure of the obtained laminated sheet is LDPE (L2340, thickness 18 μm) / paper (basis weight 380 g / m 2 ) / LDPE (LC522, melt tension 0.09 N, thickness 20 μm) / EMAA (AN4228C, melt tension 0.02 N, thickness 10 μm) / silica-deposited PET film (thickness 12 μm) / LDPE (thickness 55 μm).

[0040] [Comparative Example 1] A laminated sheet was produced in the same manner as in Example 1, except that the resin of the bubbling suppression layer 3 in Example 1 was changed to EMAA (AN4228C with a melt tension of 0.02 N, manufactured by Mitsui DuPont Polychemicals Co., Ltd.). The structure of the obtained laminated sheet is LDPE (L2340, thickness 18 μm) / paper (basis weight 380 g / m 2The materials are ) / EMAA (AN4228C, melt tension 0.02N, thickness 20μm) / EMAA (AN4228C, melt tension 0.02N, thickness 10μm) / silica vapor-deposited PET film (thickness 12μm) / LDPE (thickness 55μm).

[0041] [Comparative Example 2] A laminated sheet was prepared in the same manner as in Example 1, except that the resin of the bubbling suppression layer 3 was changed to LDPE (Asahi Kasei Corporation, L6810, melt tension 0.03N). The resulting laminated sheet consists of LDPE (L2340, thickness 18 μm) / paper (basis weight 380 g / m²). 2 The materials are: ) / LDPE (L6810, melt tension 0.03N, thickness 20μm) / EMAA (AN4228C, thickness 10μm) / silica vapor-deposited PET film (thickness 12μm) / LDPE (thickness 55μm).

[0042] [Comparative Example 3] A laminated sheet was prepared in the same manner as in Example 1, except that the resin of the bubbling suppression layer 3 was changed to LDPE (M6520, manufactured by Asahi Kasei Corporation, melt tension 0.007N). The resulting laminated sheet consists of LDPE (L2340, thickness 18 μm) / paper (basis weight 380 g / m²). 2 The materials are: ) / LDPE (M6520, melt tension 0.007N, thickness 20μm) / EMAA (AN4228C, thickness 10μm) / silica vapor-deposited PET film (thickness 12μm) / LDPE (thickness 55μm).

[0043] [Comparative Example 4] A laminated sheet was prepared in the same manner as in Example 1, except that the resin of the bubbling suppression layer 3 was changed to PP (MFX3, manufactured by Nippon Polypropylene Co., Ltd., melt tension 0.007N). The resulting laminated sheet consists of LDPE (L2340, thickness 18 μm) / paper (basis weight 380 g / m²). 2 The materials are ) / PP (MFX3, melt tension 0.16N, thickness 20μm) / EMAA (AN4228C, thickness 10μm) / silica vapor-deposited PET film (thickness 12μm) / LDPE (thickness 55μm). Table 1 shows the results of evaluating the bubbling resistance of Examples 1-5 and Comparative Examples 1-4 prepared above.

[0044] [Evaluation Method] The time it took for bubbling to occur was measured when 240°C hot air was sprayed from a distance of 2 cm from the sealant layer 6 side using a heat gun 7 (Earthman HG-1450B, manufactured by Takagi Co., Ltd.). The time it took for bubbling to occur was used as a baseline, and a longer time until bubbling occurred was judged as ○, and a shorter time as ×.

[0045] [Table 1]

[0046] As shown in Table 1, it was confirmed that using a resin with a melt tension of 0.04 to 0.09 N in the bubbling suppression layer 3 delayed the time it took for bubbling to occur, demonstrating that the bubbling resistance was improved. [Explanation of symbols]

[0047] 1...Thermoplastic resin layer 2…Paper layer 3…Bubbling suppression layer 4...adhesive layer 5… Barrier film layer 6…Sealant layer 10…Laminated sheets for paper containers

Claims

1. A laminated sheet for paper containers, wherein a bubbling suppression layer, an adhesive layer, a barrier film layer, and a sealant layer are laminated in this order on one side of the paper layer, and a thermoplastic resin layer is laminated on the other side of the paper layer, The bubbling suppression layer is made of a resin containing low-density polyethylene. The melt tension of the aforementioned resin is 0.04 N or more and 0.09 N or less. The basis weight of the aforementioned paper layer is 200 g / m². ２ More than 500g / m ２ The following: A laminated sheet for paper containers, characterized in that the sum of the film thicknesses of the bubbling suppression layer and the adhesive layer is 20 μm or more and 40 μm or less.

2. The laminated sheet for paper containers according to Claim 1, characterized in that the thickness of the bubbling suppression layer is 10 μm or more and 35 μm or less, and the thickness of the adhesive layer is 5 μm or more and 10 μm or less.

3. The laminated sheet for paper containers according to claim 1, characterized in that the thickness of the bubbling suppression layer is 10 μm or more and 35 μm or less.

4. The laminated sheet for paper containers according to any one of claims 1 to 3, characterized in that the lamination strength of the adhesive layer and the barrier film layer is 2 N / 15 mm or more.

5. The laminated sheet for paper containers according to any one of claims 1 to 4, characterized in that the adhesive layer is composed of a resin containing one of the following: additive-free polyethylene, polyethylene containing an adhesive component, or an ethylene-acrylic acid copolymer.

6. The laminated sheet for paper containers according to any one of claims 1 to 4, characterized in that the adhesive layer is composed of a resin containing any of the following: low-density polyethylene, medium-density polyethylene, linear low-density polyethylene, polypropylene, copolymer resin of ethylene-α-olefin, copolymer resin of ethylene-vinyl acetate, copolymer resin of ethylene-acrylic acid, copolymer resin of ethylene-methacrylic acid, copolymer resin of ethylene-methyl acrylate, copolymer resin of ethylene-methacrylic acid or its ester compound, or ionomer resin (excluding resin in which linear low-density polyethylene and low-density polyethylene are blended).

7. The laminated sheet for paper containers according to any one of claims 1 to 6, characterized in that the barrier film layer is one of the films selected from (1) to (3) below. (1) PET film with a metal vapor-deposited film (2) PET film with an inorganic oxide vapor-deposited film (3) Laminated film of aluminum foil and PET film

8. The laminated sheet for paper containers according to any one of claims 1 to 6, characterized in that the barrier film layer is one of a biaxially oriented polyester film, nylon film, polycarbonate film, polyvinyl alcohol film, or ethylene-vinyl alcohol copolymer resin film.

9. The laminated sheet for paper containers according to claim 8, characterized in that the barrier film layer is a film on which an inorganic substance, either silica, alumina, or aluminum, has been vapor-deposited.

10. The laminated sheet for paper containers according to any one of claims 1 to 9, characterized in that the adhesive layer and the barrier film layer are in contact with each other.

11. A paper container formed by molding a laminated sheet for paper containers according to any one of claims 1 to 10 into a container shape.

12. The paper container according to claim 11, characterized in that the shape of the paper container is a gable-top shape, a cup shape, or a cylindrical shape.

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