Resin sheets and containers

Abstract

To provide a resin sheet that can achieve reduction in environmental load and from which a resin-made container having excellent heat resistance that does not cause deformation by heat sterilization treatment of the content or heat treatment with microwave oven or the like, and to provide a resin-made container using the resin sheet.SOLUTION: Provided is a resin sheet, which is a resin sheet having a blended resin layer that contains a propylene-based resin and a biomass-derived ethylene-based resin, and in which, characterized, the propylene-based resin contains a propylene homopolymer and has a storage elastic modulus at 140°C of 5×107 Pa or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a resin sheet having a blended resin layer containing a propylene-based resin and a biomass-derived ethylene-based resin, and to a container using this resin sheet. [Background technology]

[0002] Resin containers are widely used for food products such as retort foods, seasonings like miso, and confectionery. These resin containers are known to be made by molding resin sheets, for example, by thermoforming. Such resin containers require sufficient heat resistance to prevent deformation during heat sterilization of the contents or heating in a microwave oven. Therefore, the resin sheet used to constitute the container has a resin layer made of propylene-based resin.

[0003] Incidentally, in recent years, in the field of synthetic resin materials, there has been a growing demand to switch from fossil fuel-derived synthetic resin materials to biomass-derived synthetic resin materials, in response to the need to reduce environmental impact through the creation of a circular economy. For these reasons, the use of biomass-derived synthetic resin materials is being considered for resin sheets that make up food containers. For example, Patent Document 1 proposes a resin sheet having a first layer containing a propylene-based resin and a second layer containing a propylene-based resin and a biomass-derived ethylene-based resin. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-163634 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, it was found that when food containers used for retort foods and the like were constructed using resin sheets made from the biomass-derived ethylene resin described above, sufficient heat resistance could not be obtained.

[0006] The present invention has been made based on the circumstances described above, and its purpose is to provide a resin sheet that can reduce the environmental burden and has excellent heat resistance, preventing deformation when the contents are heat-sterilized or when heated by a microwave oven or the like. Another object of the present invention is to provide a resin container that can reduce environmental impact and has excellent heat resistance, preventing deformation when the contents are subjected to heat sterilization or heating by a microwave oven or the like. [Means for solving the problem]

[0007] The resin sheet of the present invention is a resin sheet having a blended resin layer containing a propylene-based resin and a biomass-derived ethylene-based resin, The aforementioned resin sheet is intended to be molded by thermoforming. The resin sheet has two first resin layers, and a gas barrier layer is provided between the two first resin layers. The two first resin layers consist of the blended resin layer, The propylene-based resin contains a propylene homopolymer and has a storage modulus of 5 × 10⁻¹⁶ at 140°C. 7 It is Pa or higher, The biomass-derived ethylene resin has a melt flow rate (MFR) of 0.32 g / 10 min or more and 0.34 g / 10 min or less, measured under conditions of a temperature of 190°C and a load of 2.16 kgf. The proportion of the propylene homopolymer in the blended resin layer is 50% by mass or more. the law of nature, The aforementioned resin sheet has a shrinkage rate of 3% or less at 140°C. It is characterized by the following.

[0008] In the resin sheet of the present invention, The aforementioned resin sheet is it contains a propylene-based resin 2nd resin layer and The second resin layer it is preferable that The second resin layer is the blend resin layer. Also, It is preferable to have an adhesive resin layer. Moreover, it is preferable that the mass of the blend resin layer is 50% or more of the entire resin sheet.

[0009] The container of the present invention is characterized in that the above resin sheet is formed by thermoforming.

Advantages of the Invention

[0010] According to the resin sheet of the present invention, since it has a blend resin layer containing a propylene-based resin and an ethylene-based resin derived from biomass, it is possible to reduce the environmental load. Moreover, the propylene-based resin in the blend resin layer includes homopolypropylene and has a storage elastic modulus of 5×10 7 Pa or more at 140°C, so a resin container with excellent heat resistance that does not deform due to heat sterilization treatment of the contents or heat treatment using a microwave oven or the like can be obtained. Moreover, according to the container of the present invention, since the above resin sheet is used, it is possible to reduce the environmental load, and excellent heat resistance that does not deform due to heat sterilization treatment of the contents or heat treatment using a microwave oven or the like can be obtained.

Brief Description of the Drawings

[0011] [Figure 1] It is an explanatory cross-sectional view showing the configuration in an example of the resin sheet of the present invention.

Embodiments for Carrying Out the Invention

[0012] Hereinafter, embodiments of the present invention will be described in detail. [Resin Sheet] The resin sheet of the present invention has a blended resin layer containing a propylene-based resin and a biomass-derived ethylene-based resin (hereinafter also referred to as "bioethylene-based resin"). In addition to the propylene-based resin and the bioethylene-based resin, the blended resin layer may also contain a fossil fuel-derived ethylene-based resin.

[0013] The propylene-based resin constituting the blended resin layer has a storage modulus at 140°C (hereinafter also simply referred to as "storage modulus") of 5 × 10⁻¹⁰. 7 The Pa is set to be 10 or higher, preferably 6 × 10 7 The storage modulus of propylene resin is 5 × 10⁻⁶. 7 If the storage modulus is less than Pa, it becomes difficult to obtain a container with excellent heat resistance. There is no particular upper limit to the storage modulus of propylene resin, but considering processability, etc., 1.5 × 10 8 It is preferable that the value is Pa or less. Here, we will explain the storage modulus. Synthetic resins are typical viscoelastic materials, possessing both elastic and viscous properties. Dynamic viscoelasticity measurements allow us to measure the storage modulus G' (Pa) and loss modulus G'' (Pa) by applying a stress or strain that changes (vibrates) over time to a sample and measuring the resulting strain or stress. The storage modulus is the component of energy generated in an object by external force and strain that is stored within the object (i.e., elasticity), while the loss modulus is the component that diffuses to the outside (i.e., viscosity).

[0014] The proportion of propylene-based resin in the blended resin layer is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. If the proportion of propylene-based resin is too low, it may be difficult to obtain a container with excellent heat resistance.

[0015] The propylene-based resin used to constitute the blended resin layer contains a propylene homopolymer (hereinafter also referred to as "homopolypropylene"). Homopolypropylene has a storage modulus of 5 × 10⁻⁶. 7Those of Pa or higher, particularly those of 6×10 7 Pa or higher are preferably used. Also, as the homopolypropylene, from the viewpoint of moldability, the melt flow rate (MFR) measured under the conditions of a temperature of 230°C and a load of 2.16 kgf is preferably 0.3 g / 10 min or more and 5 g / 10 min or less, and from the viewpoint of rigidity, the tensile elastic modulus (JIS K7162) is preferably 1500 MPa or more.

[0016] Also, the proportion of homopolypropylene in the blend resin layer is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 70% by mass or more from the point of ensuring excellent heat resistance.

[0017] In the propylene-based resin constituting the blend resin layer, in addition to the homopolypropylene, a copolymer of propylene and another monomer (hereinafter also referred to as "propylene copolymer") may be contained. As the propylene copolymer, an ethylene-propylene copolymer or the like can be used. The propylene copolymer may be a random copolymer or a block copolymer. The storage elastic modulus of the propylene copolymer is not particularly limited as long as the storage elastic modulus of the entire propylene-based resin satisfies the above value, but from the point of ensuring excellent heat resistance, it is preferably 5×10 7 Pa or higher. Also, as the propylene copolymer, from the viewpoint of moldability, the melt flow rate (MFR) measured under the conditions of a temperature of (230°C) and a load of 2.16 kgf is preferably 0.2 g / 10 min or more and 5 g / 10 min or less, and from the viewpoint of rigidity, the tensile elastic modulus (JIS K7162) is preferably 1500 MPa or more.

[0018] Low-density polyethylene (LDPE), high-density polyethylene (HDPE), and linear low-density polyethylene (LLDPE) can be used as the bioethylene resins that make up the blended resin layer. Furthermore, the bioethylene resin may consist entirely of ethylene monomers derived from biomass, or part of it may be derived from fossil fuels. Furthermore, from the viewpoint of moldability, the bioethylene-based resin preferably has a melt flow rate (MFR) of 0.1 g / 10 min or more and 3 g / 10 min or less, measured under conditions of a temperature of 190°C and a load of 2.16 kgf, and a density of 0.91 g / cm³. 3 More than 0.97g / cm 3 The following is preferable from the standpoint of rigidity.

[0019] Furthermore, it is preferable that the bioethylene-based resin is included in the blended resin layer at a rate such that the biomass content of the blended resin layer is 5% or more, and particularly 10% or more. If the biomass content of the blended resin layer is less than 5%, it may be difficult to sufficiently reduce the environmental impact.

[0020] The resin sheet of the present invention may have a single-layer structure consisting only of the above-described blended resin layer, or it may have a laminated structure with other layers. A laminated resin sheet will be described below, but the resin sheet of the present invention is not limited to the laminated structure described below.

[0021] Figure 1 is an explanatory cross-sectional view showing the configuration of an example of a resin sheet of the present invention. This resin sheet 10 is used to form a resin container and has two first resin layers 11 and two second resin layers 12 arranged inside each of the first resin layers, with the first resin layers 11 being the blended resin layer described above. Inside each of the second resin layers 12, a gas barrier layer 13 is provided to prevent or suppress the permeation of gases such as oxygen gas. An adhesive layer 14 is formed between each of the second resin layers 12 and the gas barrier layer 13. In the configuration shown in Figure 1, the second resin layers 12 are arranged inside the first resin layers 11, but the present invention is not limited to this, and the arrangement positions of the first resin layers 11 and the second resin layers 12 may be swapped, and the first resin layers 11 and the gas barrier layers 13 may be laminated via the adhesive resin layer 14. Alternatively, the first resin layers 11 and the second resin layers 12 may be made of the same resin material and configured as a single resin layer.

[0022] The second resin layer 12 contains a propylene-based resin. As the propylene-based resin, homopolypropylene, propylene copolymer, or a mixture thereof can be used. Furthermore, the second resin layer 12 may be composed solely of a propylene-based resin, or it may be composed of a mixture of a propylene-based resin and other olefin-based resins such as ethylene-based resins. However, from the viewpoint of reducing environmental impact, it is preferable that the second resin layer 12 is the blended resin layer described above.

[0023] As the material constituting the gas barrier layer 13, resin materials such as ethylene-vinyl alcohol copolymer, polyamide, polyvinyl alcohol, and polyvinylidene chloride can be used. Among these, ethylene-vinyl alcohol copolymer is preferred from the viewpoint of moldability.

[0024] As adhesives for forming the adhesive layers 14 and 15, urethane-based adhesives, acid-modified polyolefin-based adhesives, polyester-based adhesives, polyether-based adhesives, polyamide-based adhesives, and the like can be used.

[0025] In a resin sheet 10 having such a laminated structure, the thickness of the first resin layer 11, which is a blended resin layer, is, for example, 100 to 800 μm, the thickness of the second resin layer 12 is, for example, 100 to 800 μm, and the thickness of the gas barrier layer 13 is, for example, 5 to 200 μm. Furthermore, conventionally known methods such as co-extrusion and dry lamination can be used to manufacture the resin sheet 10 having a laminated structure, and from the viewpoint of productivity, it is preferable to manufacture it by co-extrusion.

[0026] Furthermore, a surface layer (not shown) may be provided on the surface of the first resin layer and the second resin layer, respectively. The material constituting the surface layer is not particularly limited, and various resin materials can be used, but from the viewpoint of reducing environmental impact, it is preferable that the surface layer contains a biomass-derived resin material such as biopolyethylene resin.

[0027] [container] The container of the present invention is formed by thermoforming the above-mentioned resin sheet. Specific thermoforming methods include conventionally known methods such as vacuum pressure forming. The molding temperature during thermoforming is appropriately set considering the melting point and softening point of the materials constituting the resin sheet; for example, the heater setting temperature is 300-450°C, and the sheet surface temperature is 150-190°C. Such containers of the present invention are suitable for use with foods that require heat sterilization of their contents or heat treatment during cooking, such as retort foods, seasonings such as miso, and confectionery.

[0028] According to the present invention, since the blended resin layer contains a propylene-based resin and a biomass-derived ethylene-based resin, the environmental impact can be reduced. Moreover, the propylene-based resin in the blended resin layer contains homopolypropylene, and the storage modulus at 140°C is 5 × 10⁻⁶. 7Because the heat resistance is above Pa, a resin container with excellent heat resistance can be obtained that will not deform when the contents are heat-sterilized or when heated in a microwave oven or the like. [Examples]

[0029] The following describes specific embodiments of the present invention, but the present invention is not limited to these. , reference example The propylene-based resin and ethylene-based resin used in the comparative examples have the properties shown in Table 1 below.

[0030] [Table 1]

[0031] In Table 1, the storage modulus at 140°C is the value measured under the following conditions. Test specimen: A 10mm wide, 1mm thick film made by hot pressing. Measurement device: Dynamic viscoelasticity analyzer "DHR-2" (TA Instruments Co., Ltd.) Measurement length: 20mm Temperature conditions: Heating from 20°C to 160°C at a rate of 5°C / min. Measurement mode: Torsion, frequency 1Hz, strain 0.1% Furthermore, the MFR values ​​were measured according to JIS K7210 for propylene-based resins and JIS K6922-1 for ethylene-based resins. Specifically, the MFR for propylene-based resins was measured under conditions of 230°C and 2.16 kgf of load, while the MFR for ethylene-based resins was measured under conditions of 190°C and 2.16 kgf of load.

[0032] <Example 1> Using a multilayer extrusion molding machine capable of forming a multilayer structure of 7 layers of 4 types, consisting of a first resin layer / second resin layer / adhesive layer / gas barrier layer / adhesive layer / second resin layer / first resin layer as shown in Figure 1, a resin sheet with the configuration shown in Figure 1 was manufactured as follows. A resin material common to both the first and second resin layers was prepared by mixing 85% by mass of propylene resin (1) and 15% by mass of ethylene resin (1). The obtained resin material was supplied to single-screw extruders for the first and second resin layers, acid-modified polypropylene resin was supplied to a single-screw extruder for the adhesive layer, and ethylene-vinyl alcohol copolymer was supplied to a single-screw extruder for the gas barrier layer. Each material was melt-kneaded in each single-screw extruder, extruded from a T-die molding device connected to each single-screw extruder, and the molten resins extruded into films were cooled by a cooling roll while being laminated to produce a resin sheet with a thickness of 500 μm. In the above, the cylinder temperature of the single-screw extruders for the first and second resin layers was 230°C, the cylinder temperature of the single-screw extruders for the adhesive layer and gas barrier layer was 210°C, the T-die head temperature was 230°C, and the cooling roll temperature was 50°C. The mass ratios of each layer in the obtained resin sheet are as follows: the first resin layer is 18% by mass in total for both layers, the second resin layer is 74% by mass in total for both layers, the gas barrier layer is 4% by mass, and the adhesive layer is 4% by mass in total for both layers. The resulting resin sheet was used to manufacture a container by vacuum compression molding using a vacuum pressure molding machine at a heater temperature of 350°C. The resulting container has a rectangular base measuring 150 mm x 115 mm and a depth of 30 mm.

[0033] The biomass content of the obtained resin sheets was measured as follows. Furthermore, the shrinkage rate of the obtained containers at 140°C was measured as follows. The results are shown in Table 2 below. [Biomass content] Biomass content is an index that represents the mixing ratio of raw materials derived from fossil fuels and raw materials derived from biomass, and radioactive carbon ( 14 It is determined by measuring the concentration of C). The biomass content was measured according to ASTM 6866 Method B. The sample was burned to generate carbon dioxide, and the carbon dioxide was purified in a vacuum line. The purified carbon dioxide was reduced with hydrogen using iron as a catalyst to produce graphite. The graphite was then processed using a tandem accelerator-based method. 14It is installed in a dedicated C-AMS device (manufactured by NEC Corporation), 14 The coefficient of C, 13 C concentration ( 13 C / 12 C), 14 C concentration ( 14 C / 12 Measurement C) was performed. For the measurement, oxalic acid provided by the U.S. National Institute of Standards (NIST) was used as the standard sample. [Shrinkage rate at 140℃] The containers were heated in an oven at 140°C for 30 minutes. The internal volume of each container before and after heating was measured as follows, and the volume shrinkage rate was calculated using the formula below. This value was defined as the shrinkage rate at 140°C. If the shrinkage rate at 140°C is 3% or less, the container is judged to have high heat resistance, as it does not deform when heated. Measurement of internal volume: The opening of the container was sealed with an acrylic plate having a hole with an inner diameter of 5 mm. Pure water was poured into the container through the hole in the acrylic plate to fill the container with pure water, and the internal volume of the container was calculated from the mass of the injected pure water and the specific gravity of the pure water. Calculation formula: Volume shrinkage rate (%) = (Vb - Va) / Va × 100 Va = internal volume of the container before heat treatment. Vb = internal volume of the container after heat treatment

[0034] <Example 2> Except for changing 85% by mass of propylene resin (1) to 85% by mass of propylene resin (2), resin sheets and containers were manufactured in the same manner as in Example 1, and the biomass content of the resin sheets and the heat shrinkage rate of the containers at 140°C were measured. The results are shown in Table 2 below.

[0035] < Reference example 1 > Resin sheets and containers were manufactured in the same manner as in Example 1, except that 85% by mass of propylene resin (1) was replaced with 80% by mass of propylene resin (3), and 15% by mass of ethylene resin (1) was replaced with 20% by mass of ethylene resin (2). The biomass content of the resin sheets and the heat shrinkage rate of the containers at 140°C were measured. The results are shown in Table 2 below.

[0036] <Examples> 3 > Except for changing the propylene resin (1) 85% by mass to propylene resin (1) 70% by mass and the ethylene resin (1) 15% by mass to ethylene resin (1) 30% by mass in the resin material for the second resin layer, a resin sheet and a container were manufactured in the same manner as in Example 1, and the biomass content of the resin sheet and the heat shrinkage rate of the container at 140°C were measured. The results are shown in Table 2 below.

[0037] <Examples> 4 > Except for changing 85% by mass of propylene resin (1) to 60% by mass of propylene resin (3) in the resin material for the second resin layer, and changing 15% by mass of ethylene resin (1) to 30% by mass of ethylene resin (1) and 10% by mass of ethylene resin (3), a resin sheet and a container were manufactured in the same manner as in Example 1, and the biomass content of the resin sheet and the heat shrinkage rate of the container at 140°C were measured. The results are shown in Table 2 below.

[0038] <Comparative Example 1> Resin sheets and containers were manufactured in the same manner as in Example 1, except that 85% by mass of propylene resin (1) and 15% by mass of ethylene resin (1) were replaced with 100% by mass of propylene resin (4). The biomass content of the resin sheets and the heat shrinkage rate of the containers at 140°C were measured. The results are shown in Table 2 below.

[0039] <Comparative Example 2> Resin sheets and containers were manufactured in the same manner as in Example 1, except that 85% by mass of propylene resin (1) was replaced with 80% by mass of propylene resin (5), and 15% by mass of ethylene resin (1) was replaced with 20% by mass of ethylene resin (3). The biomass content of the resin sheets and the heat shrinkage rate of the containers at 140°C were measured. The results are shown in Table 2 below.

[0040] [Table 2]

[0041] As is clear from the results in Table 2, Example 1~ 4 According to the study, it was confirmed that a resin container with superior heat resistance compared to Comparative Example 2 could be obtained, even with a biomass content of 10% or more. [Explanation of symbols]

[0042] 10 Resin Sheets 11 First resin layer 12 Second resin layer 13. Gas barrier layer 14 Adhesive layer

Claims

1. A resin sheet having a blended resin layer containing a propylene-based resin and a biomass-derived ethylene-based resin, The aforementioned resin sheet is intended to be molded by thermoforming. The resin sheet has two first resin layers, and a gas barrier layer is provided between the two first resin layers. The two first resin layers consist of the blended resin layer, The propylene-based resin contains a propylene homopolymer and has a storage modulus of 5 × 10⁻¹⁶ at 140°C. 7 Pa or higher, The biomass-derived ethylene resin has a melt flow rate (MFR) of 0.32 g / 10 min or more and 0.34 g / 10 min or less, measured under conditions of a temperature of 190°C and a load of 2.16 kgf. The proportion of the propylene homopolymer in the blended resin layer is 50% by mass or more. The aforementioned resin sheet is characterized by having a shrinkage rate of 3% or less at 140°C.

2. The resin sheet according to claim 1, wherein the resin sheet has a second resin layer containing a propylene-based resin, and the second resin layer is the blended resin layer.

3. The resin sheet according to claim 2, characterized by having an adhesive layer.

4. The resin sheet according to any one of claims 1 to 3, characterized in that the mass of the blended resin layer is 50% or more of the total mass of the resin sheet.

5. A container characterized in that the resin sheet described in claims 1 to 4 is formed by thermoforming.

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