Resin sheets and molded containers

Abstract

To provide a resin sheet containing a polystyrene-based resin and a plant-derived polyethylene-based resin which has both excellent notch breaking properties and excellent impact resistance.SOLUTION: A resin sheet has a base material layer containing a polystyrene-based resin, a plant-derived polyethylene-based resin, and a compatibilizer for compatibilizing the polystyrene-based resin and the plant-derived polyethylene-based resin, wherein the polystyrene-based resin may contain a butadiene rubber or no butadiene rubber, when the polystyrene-based resin contains the butadiene rubber, a median size of the butadiene rubber is 3.5 μm or less, and a content of the butadiene rubber in the base material layer is more than 0 mass% and 3 mass% or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a resin sheet containing a polystyrene-based resin and a formed container including the same.

Background Art

[0002] Since a resin sheet containing a polystyrene-based resin has excellent molding processability, it has been widely used in various packaging applications such as food containers, beverage containers, and industrial containers including various trays. In particular, high-impact polystyrene (HIPS) in which polystyrene is graft copolymerized with butadiene rubber has seen growing demand because a resin sheet with excellent impact resistance can be obtained, and related technological developments have also advanced.

[0003] In Japanese Patent Laid-Open No. 2015-199311, in a laminated sheet composed of a core layer mainly composed of a mixture of high-impact polystyrene and polystyrene and outer layers mainly composed of high-impact polystyrene disposed on both sides of the core layer, by setting the thickness of the core layer relative to the total thickness and the amount of polybutadiene in the core layer and the outer layers within a specific range, it is described that a laminated sheet excellent in notch breakage resistance, impact resistance, and moldability can be obtained.

[0004] On the other hand, in recent years, the demand for biomass plastics has been increasing from the perspective of reducing the environmental load. As biomass plastics, plant-derived polyethylene has been put on the market and is expected to contribute to reducing carbon dioxide emissions.

[0005] Japanese Patent Publication No. 2020-193274 describes a resin composition obtained by mixing a polystyrene resin and a polyethylene resin, wherein the polyethylene resin includes plant-derived polyethylene. The publication states that polystyrene and polyethylene have poor compatibility, and when a resin composition mixed with these resins is extruded and molded into a sheet, problems such as unstable shape, brittleness, and low rigidity occur. It also states that a compatibilizer is added to improve the compatibility of polystyrene and polyethylene. The publication states that by including impact-resistant polystyrene and general-purpose polystyrene in the polystyrene resin, a polystyrene resin composition with excellent sheet moldability and good strength can be obtained. Furthermore, Patent Document 2 states that a resin sheet obtained by molding this polystyrene resin composition had good bending resistance and film impact. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-199311 [Patent Document 2] Japanese Patent Publication No. 2020-193274 [Overview of the project] [Problems that the invention aims to solve]

[0007] Although the laminated sheet described in Patent Document 1 is described as having excellent notch-folding properties and impact resistance, the impact resistance is not sufficient in most of the examples described in Patent Document 1, and environmental considerations are also insufficient. Furthermore, the resin composition described in Patent Document 2 contains a plant-derived polyethylene resin and has excellent environmental performance. However, Patent Document 2 aims to improve the strength of polystyrene resin compositions, and improving the notch-folding properties of the polystyrene resin composition described in Patent Document 2 is considered to deviate from the purpose of Patent Document 2.

[0008] The present invention was created in view of the above circumstances, and in one embodiment, aims to provide a resin sheet containing a polystyrene resin and a plant-derived polyethylene resin that possesses both excellent notch-folding properties and excellent impact resistance. In another embodiment, the present invention aims to provide a molded container equipped with such a resin sheet. [Means for solving the problem]

[0009] The inventors of this invention diligently studied to solve the above problems and found that while resin sheets may be composed of a single layer or multiple layers, in either case, in resin layers containing polystyrene resin and plant-derived polyethylene resin, butadiene rubber, which was conventionally included to enhance impact resistance, is unnecessary, and even if butadiene rubber is included, it should be limited to a small amount of fine butadiene rubber. The present invention was completed based on this finding and is illustrated below.

[0010] [1] The material comprises a base layer containing a polystyrene resin, a plant-derived polyethylene resin, and a compatibilizer for compatibilizing the polystyrene resin and the plant-derived polyethylene resin. The polystyrene resin may or may not contain butadiene rubber. If the polystyrene resin contains butadiene rubber, the median diameter of the butadiene rubber is 3.5 μm or less, and the butadiene rubber content in the base layer is greater than 0% by mass and 3% by mass or less. [2] The resin sheet according to [1], wherein the content of plant-derived polyethylene resin in the resin sheet is 0.1% by mass or more and 35% by mass or less. [3] The resin sheet according to [1] or [2], wherein the content of plant-derived polyethylene resin in the base layer is 10 parts by mass or more and 30 parts by mass or less per 100 parts by mass of the total of polystyrene resin and plant-derived polyethylene resin. [4] A resin sheet according to any one of the following [1] to [3], wherein the content of the compatibilizer in the base layer is 0.1% by mass or more and 5% by mass or less. [5] A resin sheet according to any one of the following [1] to [4], wherein the total content of polystyrene resin and plant-derived polyethylene resin in the base layer is 90% by mass or more. [6] A resin sheet according to any one of [1] to [5], further comprising: a surface layer containing a polystyrene resin laminated on one side of a base layer; and a base layer containing a polystyrene resin laminated on the side of the base layer opposite to the side having the surface layer. [7] The resin sheet according to [6], wherein the polystyrene resin constituting the epidermal layer and the subcutaneous layer each contains butadiene rubber with a median diameter of 4.5 μm or less, the butadiene rubber content in the epidermal layer is greater than 0% by mass and 8% by mass or less, and the butadiene rubber content in the subcutaneous layer is greater than 0% by mass and 8% by mass or less. [8] The resin sheet according to [7], wherein the butadiene rubber content in the epidermal layer is 5.0% by mass or more and 7.5% by mass or less, and the butadiene rubber content in the subdermal layer is 5.0% by mass or more and 7.5% by mass or less. [9] The resin sheet according to [7] or [8], wherein the average thickness of the epidermal layer and subdermal layer is 0.1% or more and 15% or less of the average total thickness of the resin sheet, respectively.

[10] A resin sheet as described in any one of the following [1] to [9], having an average total thickness of 200 μm or more and 1300 μm or less.

[11] A resin sheet as described in any one of the following [1] to

[10] , having a biomass content of 0.1% by mass or more and 40% by mass or less.

[12] A resin sheet as described in any one of the following [1] to

[11] , having a DuPont impact strength of 2.0 J or more as measured in accordance with JIS K7211-1:2006.

[13] When a test piece with its longitudinal direction parallel to the MD direction is sampled and the folding strength test method is carried out in accordance with JIS P8115:2001, the resin sheet according to any one of [1] to

[12] in which the average number of reciprocating bending times until breakage is less than 300 times.

[14] When a test piece with its longitudinal direction parallel to the TD direction is sampled and the folding strength test method is carried out in accordance with JIS P8115:2001, the resin sheet according to any one of [1] to

[13] in which the average number of reciprocating bending times until breakage is less than 300 times.

[15] A formed container comprising the resin sheet according to any one of [1] to

[14] .

[16] The formed container according to

[15] , in which a notch is formed in the resin sheet.

Effect of the Invention

[0011] The resin sheet according to an embodiment of the present invention contains a plant-derived polyethylene-based resin, so it is an environmentally friendly resin sheet and has excellent notch breakability and excellent impact resistance. Therefore, by using the resin sheet, it is possible to manufacture various molded products having both environmental performance and practicality, for example, formed containers such as packs and trays for beverages, foods, cosmetics, household electrical appliances, and other daily necessities.

Brief Description of the Drawings

[0012] [Figure 1] It is a cross-sectional view schematically showing the laminated structure of the resin sheet according to an embodiment of the present invention. [Figure 2] It is a cross-sectional view schematically showing the laminated structure of the resin sheet according to another embodiment of the present invention.

Mode for Carrying Out the Invention

[0013] In one embodiment, the resin sheet according to the present invention comprises a base layer containing a polystyrene resin, a plant-derived polyethylene resin, and a compatibilizer for compatibilizing the polystyrene resin and the plant-derived polyethylene resin. The resin sheet may have a single-layer structure consisting only of the base layer, but for reasons such as ensuring heat sealability with the lid material when molding the resin sheet into a molded container, adjusting the appearance of the resin sheet, and / or reducing manufacturing costs, it is preferable to further provide a multilayer structure by comprising a surface layer containing polystyrene resin laminated on one side of the base layer and a sub-surface layer containing polystyrene resin laminated on the side of the base layer opposite to the side with the surface layer.

[0014] Figure 1 schematically shows the cross-sectional structure of a resin sheet 10 according to one embodiment of the present invention. The resin sheet 10 has a laminated structure in which an outer layer 11 / base layer 12 / underlayer 13 are stacked in this order from top to bottom on the paper. In this embodiment, the outer layer 11 and the base layer 12 are directly joined without an adhesive layer, and the base layer 12 and the underlayer 13 are directly joined without an adhesive layer.

[0015] The following describes each layer in the order of base layer 12, surface layer 11, and underlayer 13, and then provides an illustrative explanation of the resin sheet 10 itself and the food packaging container formed from it.

[0016] <Base material layer 12> In one embodiment, the base layer contains a polystyrene resin, a plant-derived polyethylene resin, and a compatibilizer for compatibilizing the polystyrene resin and the plant-derived polyethylene resin.

[0017] The polystyrene resin constituting the base layer may or may not contain butadiene rubber. While butadiene rubber has traditionally been included in polystyrene resins to enhance impact resistance, polyethylene resins provide a similar effect, making it possible to obtain excellent impact resistance even without its inclusion. However, from a manufacturing cost perspective, it may be desirable to include a polystyrene resin containing butadiene rubber and reduce the amount of plant-derived polyethylene resin. When the polystyrene resin contains butadiene rubber, including a small amount of fine butadiene rubber is advantageous in achieving both the desired impact resistance and notch-folding properties.

[0018] Examples of polystyrene resins that do not contain butadiene rubber include homopolymers of styrene monomers such as styrene, α-methylstyrene, p-methylstyrene, dimethylstyrene, pt-butylstyrene, and chlorostyrene, as well as copolymers of these styrene monomers with other monomers. These are available on the market as general-purpose polystyrene (GPPS resin). An example of a copolymer of a styrene monomer with other monomers is polystyrene-acrylonitrile copolymer (AS resin). Polystyrene resins may be used individually or in combination of two or more types.

[0019] One method for producing a polystyrene resin containing butadiene rubber is, but is not limited to, a method of polymerizing a styrene monomer in the presence of polybutadiene. This method makes it possible to directly obtain a graft polymer having a structure in which multiple butadiene rubber particles, formed by graft polymerization of polystyrene monomers, are dispersed in a polystyrene resin. Examples of styrene monomers include styrene, α-methylstyrene, p-methylstyrene, dimethylstyrene, pt-butylstyrene, and chlorostyrene.

[0020] Polystyrene resins containing butadiene rubber are commercially available. Examples include high-impact polystyrene (HIPS resin) and polystyrene-acrylonitrile graft polymer (ABS resin). High-impact polystyrene (HIPS resin) is obtained by polymerizing styrene monomer in the presence of a rubbery polymer (typically polybutadiene), and has a sea-island structure in which the styrene polymer is the continuous phase (sea) and the rubbery polymer, in which a portion of the styrene monomer is graft-polymerized, is the dispersed phase (islands). ABS resin is obtained by polymerizing styrene monomer and acrylonitrile monomer in the presence of a rubbery polymer (typically polybutadiene), and has a sea-island structure in which the styrene-acrylonitrile copolymer (AS resin) is the continuous phase (sea) and the rubbery polymer, in which a portion of the styrene monomer and acrylonitrile monomer is graft-polymerized, is the dispersed phase (islands).

[0021] When using a polystyrene-based resin containing butadiene rubber in the substrate layer, the rubber content can be adjusted by using a mixture of general-purpose polystyrene (GPPS resin) and high-impact polystyrene (HIPS resin). The mixing ratio of GPPS resin should be adjusted according to the desired rubber content. Furthermore, the median diameter of rubber particles in HIPS resin can be adjusted by controlling the shear force through the speed of the rotor blades in the polymerization chamber, controlling the polymerization time, or controlling polymerization with additives.

[0022] The median diameter of the butadiene rubber in the base layer (also called the "rubber median diameter") is preferably 3.5 μm or less, and more preferably 3.4 μm or less. Although no lower limit is set for the rubber median diameter, from the viewpoint of significantly obtaining the advantages of containing butadiene rubber, it is preferably 1 μm or more, and more preferably 2 μm or more. By setting the rubber median diameter preferably to 1 μm or more, and more preferably to 2 μm or more, appropriate impact resistance can be obtained, and molded products such as molded containers obtained by molding resin sheets can be made less likely to break when dropped. Furthermore, by setting the rubber median diameter preferably to 3.5 μm or less, and more preferably to 3.4 μm or less, cracks propagate more easily, so the notch breakability is improved when the resin sheet is molded into a molded product such as a container and a notch is formed. In this specification, the above rubber median diameter refers to the median diameter (D50) based on the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution analyzer.

[0023] Furthermore, when using a polystyrene-based resin containing butadiene rubber in the base layer, it is preferable that the butadiene rubber content in the base layer be greater than 0% by mass and 3% by mass or less. From the viewpoint of obtaining significant advantages from including butadiene rubber, the lower limit of the butadiene rubber content in the base layer is preferably 0.5% by mass or more, more preferably 1% by mass or more. However, in resin sheets containing polyethylene-based resin, if the butadiene rubber content exceeds 3% by mass, the impact resistance tends to deteriorate rapidly. For this reason, the upper limit of the butadiene rubber content in the base layer is preferably 2% by mass or less, more preferably 1.5% by mass or less.

[0024] Plant-derived polyethylene resin refers to a resin produced by polymerizing monomers containing plant-derived ethylene. The raw material monomers for plant-derived polyethylene resin do not necessarily have to contain 100% by mass of plant-derived ethylene, but from the viewpoint of improving environmental performance, it is preferable that the biomass content be 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. The biomass content of plant-derived polyethylene resin refers to the ratio of the carbon content of the biobase to the total carbon content (TO) measured by a biobase concentration test in accordance with ASTM D6866-20.

[0025] Examples of plant-derived polyethylene resins include polyethylene resins such as ethylene homopolymers and copolymers of ethylene with other α-olefins, where plant-derived ethylene is used at least partially. The α-olefin is preferably one or more selected from butene, hexene, and octene, although this is not limited to these types. Plant-derived polyethylene resins may be used individually or in combination of two or more types.

[0026] In terms of branching and density, plant-derived polyethylene resins can be classified as high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), or linear low-density polyethylene (LLDPE). These can be used individually or as a blend of two or more types, but it is preferable to include at least LLDPE to improve the DuPont impact strength of the resin sheet.

[0027] In this specification, high-density polyethylene (HDPE) refers to a material with a density of 0.942 g / cm³. 3 More than 0.970g / cm 3 This refers to the following polyethylene products. In this specification, medium-density polyethylene (MDPE) refers to a material with a density of 0.925 g / cm³. 3 More than 0.942g / cm 3This refers to polyethylene less than a certain size. In this specification, low-density polyethylene (LDPE) refers to polyethylene with a density of 0.910 g / cm³. 3 More than 0.925g / cm 3 This refers to polyethylene with a density of less than 1.5 mm. Among low-density polyethylenes (LDPEs), linear low-density polyethylene (LLDPE) is a random copolymer of ethylene and α-olefins with 3 to 8 carbon atoms, and is superior in terms of tensile strength, tear resistance, impact strength, seal strength, and stress cracking resistance. The choice of which of the above resins to use depends on the application, etc.

[0028] In order to improve environmental performance, impact resistance, and notch breakability in a balanced manner, it is preferable that the content of plant-derived polyethylene resin in the base layer is 5 parts by mass or more and 50 parts by mass or less, more preferably 10 parts by mass or more and 40 parts by mass or less, and even more preferably 10 parts by mass or more and 30 parts by mass or less, per 100 parts by mass of the total of polystyrene resin (if butadiene rubber is included, the same applies hereinafter) and plant-derived polyethylene resin.

[0029] The preferred range for the butadiene rubber content in the base layer, as described above, may also vary depending on the content of plant-derived polyethylene resin in the base layer. In the base layer, when the content of plant-derived polyethylene resin is 25 parts by mass or more relative to 100 parts by mass of the total of polystyrene resin and plant-derived polyethylene resin, the content of butadiene rubber in the base layer is preferably 0% by mass or more and 1% by mass or less, and more preferably 0% by mass or more and 0.5% by mass or less. In the base layer, when the content of plant-derived polyethylene resin is less than 25 parts by mass per 100 parts by mass of the total of polystyrene resin and plant-derived polyethylene resin, and particularly when it is 20 parts by mass or less, the content of butadiene rubber in the base layer is preferably more than 1% by mass and 3% by mass or less, and more preferably 1.5% by mass or more and 2.5% by mass or less.

[0030] The content of plant-derived polyethylene resin in the resin sheet is preferably 0.1% by mass or more and 35% by mass or less, more preferably 1% by mass or more and 30% by mass or less, and even more preferably 5% by mass or more and 25% by mass or less, considering the balance between environmental performance and manufacturing costs.

[0031] The impact resistance of the base layer can be improved by containing a compatibilizer for compatibilizing polystyrene resin and plant-derived polyethylene resin. While not limited to these, styrene-based elastomers such as styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-butylene-ethylene block copolymer (SEBC), and styrene-butadiene copolymer (SBC) can be used as the compatibilizer. The content of the compatibilizer in the base layer is preferably 0.1% to 5% by mass, more preferably 0.5% to 4% by mass, and even more preferably 1% to 3% by mass.

[0032] When printing on resin sheets or molded products thereof using laser irradiation or the like, it is preferable that the base layer contains 1 phr to 5 phr of white pigment. Furthermore, it is more preferable that the amount of white pigment contained in the base layer is 1.5 phr to 4 phr. The unit phr used here refers to the parts by mass of white pigment per 100 parts by mass of the total resin components in the base layer. By containing 1 phr or more of white pigment in the base layer, opacity is obtained, which improves the color development of the printed material when printing on resin sheets and molded products thereof, and furthermore, light shielding is obtained, which can suppress discoloration and deterioration of the contents due to light irradiation from outside the molded product. Furthermore, by keeping the amount of white pigment in the substrate layer to 5 phr or less, aggregation of the white pigment can be suppressed, thereby reducing appearance defects such as aggregates in the resin sheet and its molded products. From a cost perspective, it is preferable to use less white pigment.

[0033] Examples of the aforementioned white pigments include titanium dioxide (titanium white), zinc oxide (zinc white), lithopone, and lead white, with titanium dioxide being particularly preferred. The aforementioned white pigments may be used individually or in combination of two or more types.

[0034] Other resins may be mixed into the base layer, as long as they do not hinder the effects of the present invention, and various additive components other than resin components may also be added. Examples of such additive components include, in addition to the white pigment mentioned above, other pigments, colorants such as dyes, mold release agents such as silicone oil and alkyl esters, fibrous reinforcing agents such as glass fibers, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals and polyalkylene glycols, and additives such as ultraviolet absorbers and antibacterial agents. Furthermore, scrap resin generated in the manufacturing process of resin sheets and molded containers according to one embodiment of the present invention may also be mixed in.

[0035] Generally, the total content of polystyrene resin (including butadiene rubber if it is included in the polystyrene resin) and plant-derived polyethylene resin in the base layer is 90% by mass or more, typically 93% by mass or more, for example, 90% by mass or more and 98% by mass or less.

[0036] The thickness of the base layer is preferably 160 to 1200 μm, and more preferably 180 to 1000 μm. A base layer thickness of 160 μm or more is advantageous in that it can ensure the strength of the molded product obtained by molding the resin sheet. A base layer thickness of 1200 μm or less is advantageous in that it can suppress the cost of the resin sheet and the molded product such as the thermoformed container.

[0037] <Epidermal layer 11> The surface layer is laminated on one side of the base layer. The surface layer serves to protect the base layer and is preferably provided for reasons such as ensuring heat sealability with the lid material when molding the resin sheet into a molded container, adjusting the appearance of the resin sheet, and / or reducing manufacturing costs. In one embodiment, the surface layer contains a polystyrene resin. The presence of a polystyrene resin in the surface layer, similar to the base layer, is advantageous in that it enhances the impact resistance of the resin sheet and provides sufficient interlayer adhesion with the base layer. In a preferred embodiment, the surface layer contains a polystyrene resin containing butadiene rubber in order to enhance the effect of improving the impact resistance of the resin sheet.

[0038] Examples of polystyrene resins containing butadiene rubber include graft polymers as described in the base layer description, i.e., graft polymers obtained by polymerizing styrene monomers in the presence of polybutadiene, such as high-impact polystyrene (HIPS resin) and polystyrene-acrylonitrile graft polymer (ABS resin). One type of polystyrene resin may be used alone, or two or more types may be used in combination. Also, similar to the base layer, a polystyrene resin that does not contain butadiene rubber may be appropriately blended into the surface layer. In particular, using a mixture of general-purpose polystyrene (GPPS resin) and high-impact polystyrene (HIPS resin) in the surface layer is preferred due to the rigidity and thermoformability of molded containers etc. obtained by molding the resin sheet. The mixing ratio of HIPS resin and GPPS resin can be adjusted according to the desired rubber content.

[0039] The median diameter of the butadiene rubber in the epidermal layer (also called the "rubber median diameter") is preferably 4.5 μm or less, and more preferably 4.2 μm or less. Although no lower limit is set for the rubber median diameter, from the viewpoint of significantly obtaining the advantages of the epidermal layer containing butadiene rubber, it is preferably 1 μm or more, and more preferably 4 μm or more. By setting the rubber median diameter preferably to 1 μm or more, and more preferably to 4 μm or more, appropriate impact resistance can be obtained, making it less likely for molded products such as molded containers obtained by molding resin sheets to break when dropped. Furthermore, by setting the rubber median diameter preferably to 4.5 μm or less, and more preferably to 4.2 μm or less, crack propagation becomes easier, so the notch breakability is improved when the resin sheet is molded into a molded product such as a container and a notch is formed. In this specification, the above-mentioned rubber median diameter refers to the median diameter (D50) based on the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution analyzer.

[0040] Furthermore, when a polystyrene resin containing butadiene rubber is used in the surface layer, the butadiene rubber content in the surface layer is preferably greater than 0% by mass and 8.0% by mass or less. From the viewpoint of obtaining significant advantages from including butadiene rubber, the lower limit of the butadiene rubber content in the surface layer is preferably 1.0% by mass or more, more preferably 3.0% by mass or more, and even more preferably 5.0% by mass or more. Also, from the viewpoint of achieving both notch foldability and impact strength of the container, the upper limit of the butadiene rubber content in the surface layer is preferably 8.0% by mass or less, more preferably 7.5% by mass or less.

[0041] In the surface layer, as with the base layer, other resins may be mixed in, and various additive components other than resin components may be added, as long as they do not hinder the effects of the present invention. Examples of such additive components include compatibilizers that make different components compatible, colorants such as pigments and dyes, release agents such as silicone oil and alkyl esters, fibrous reinforcing agents such as glass fibers, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals and polyalkylene glycols, and additives such as ultraviolet absorbers and antibacterial agents. It is desirable that the surface layer does not contain scrap resin in order to improve the appearance of the resin sheet.

[0042] Generally, the total content of polystyrene resin (including butadiene rubber if it contains polystyrene resin) in the surface layer is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can also be 100% by mass. In preferred embodiments, the total content of HIPS resin and GPPS resin in the surface layer is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can also be 100% by mass.

[0043] The average thickness of the surface layer is preferably 0.1% to 15% of the average total thickness of the resin sheet, more preferably 3% to 13%, and even more preferably 5% to 10%. By setting the average thickness of the surface layer to preferably 0.1% or more, more preferably 3% or more, and even more preferably 5% or more of the average total thickness of the resin sheet, the advantages of providing a surface layer can be significantly realized. Furthermore, by setting the average thickness of the surface layer to preferably 15% or less, more preferably 13% or less, and even more preferably 10% or less of the average total thickness of the resin sheet, the content of plant-derived polyethylene resin in the entire resin sheet increases, resulting in the advantage of containing more biomass plastic material and being environmentally friendly.

[0044] <Hypodermal layer 13> The underlayer is laminated on the side of the base layer opposite to the side with the surface layer. The underlayer, like the surface layer, plays a role in protecting the base layer, and is preferably provided for reasons such as ensuring heat sealability with the lid material when molding the resin sheet into a molded container, adjusting the appearance of the resin sheet, and / or reducing manufacturing costs. In one embodiment, the underlayer contains a polystyrene resin. The inclusion of a polystyrene resin in the underlayer, like the base layer, is advantageous in that it enhances the impact resistance of the resin sheet and provides sufficient interlayer adhesion with the base layer. In a preferred embodiment, to enhance the effect of improving the impact resistance of the resin sheet, the underlayer contains a polystyrene resin containing butadiene rubber. Alternatively, the underlayer may be provided symmetrically with respect to the surface layer, with the base layer in between. This results in a laminated structure that is symmetrical in the thickness direction of the resin sheet, so the resin sheet can be used without worrying about its front or back when attaching it to other articles, improving ease of handling.

[0045] Examples of polystyrene resins containing butadiene rubber include graft polymers as described in the base layer description, i.e., graft polymers obtained by polymerizing styrene monomers in the presence of polybutadiene, such as high-impact polystyrene (HIPS resin) and polystyrene-acrylonitrile graft polymer (ABS resin). One type of polystyrene resin may be used alone, or two or more types may be used in combination. Also, similar to the base layer, a polystyrene resin that does not contain butadiene rubber may be appropriately blended into the underlayer. In particular, using a mixture of general-purpose polystyrene (GPPS resin) and high-impact polystyrene (HIPS resin) in the underlayer is preferred due to the rigidity and thermoformability of molded containers etc. obtained by molding the resin sheet. The mixing ratio of HIPS resin and GPPS resin can be adjusted according to the desired rubber content.

[0046] The median diameter of the butadiene rubber in the sublayer (also called the "rubber median diameter") is preferably 4.5 μm or less, and more preferably 4.2 μm or less. Although no lower limit is set for the rubber median diameter, from the viewpoint of significantly obtaining the advantages of the sublayer containing butadiene rubber, it is preferably 1 μm or more, and more preferably 4 μm or more. By setting the rubber median diameter preferably to 1 μm or more, and more preferably to 4 μm or more, appropriate impact resistance can be obtained, making it less likely for molded products such as molded containers obtained by molding resin sheets to break when dropped. Furthermore, by setting the rubber median diameter preferably to 4.5 μm or less, and more preferably to 4.2 μm or less, cracks propagate more easily, so the notch breakability is improved when the resin sheet is molded into a container or other molded product and a notch is formed. In this specification, the above-mentioned rubber median diameter refers to the median diameter (D50) based on the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution analyzer.

[0047] Furthermore, when using a polystyrene resin containing butadiene rubber in the undercoat, the butadiene rubber content in the undercoat is preferably greater than 0% by mass and less than or equal to 8.0% by mass. From the viewpoint of obtaining significant advantages from including butadiene rubber, the lower limit of the butadiene rubber content in the undercoat is preferably 1.0% by mass or more, more preferably 3.0% by mass or more, and even more preferably 5.0% by mass or more. Also, from the viewpoint of achieving both notch foldability and impact strength of the container, the upper limit of the butadiene rubber content in the undercoat is preferably 8.0% by mass or less, more preferably 7.5% by mass or less.

[0048] In the sublayer, as with the base layer, other resins may be mixed in, as long as they do not hinder the effects of the present invention, and various additive components other than resin components may also be added. Examples of such additive components include compatibilizers that make different components compatible, colorants such as pigments and dyes, release agents such as silicone oil and alkyl esters, fibrous reinforcing agents such as glass fibers, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals and polyalkylene glycols, and additives such as ultraviolet absorbers and antibacterial agents. It is desirable that the sublayer does not contain scrap resin in order to improve the appearance of the resin sheet.

[0049] Generally, the total content of polystyrene resin (including butadiene rubber if it contains polystyrene resin) in the undercoat is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can also be 100% by mass. In preferred embodiments, the total content of HIPS and GPPS in the undercoat is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can also be 100% by mass.

[0050] The average thickness of the underlayer is preferably 0.1% to 15% of the average total thickness of the resin sheet, more preferably 3% to 13%, and even more preferably 5% to 10%. By setting the average thickness of the underlayer to preferably 0.1% or more, more preferably 3% or more, and even more preferably 5% or more of the average total thickness of the resin sheet, a significant improvement in the impact resistance of the resin sheet can be achieved. Furthermore, by setting the average thickness of the underlayer to preferably 15% or less, more preferably 13% or less, and even more preferably 10% or less of the average total thickness of the resin sheet, the content of plant-derived polyethylene resin contained in the entire resin sheet increases, resulting in the advantage of containing more biomass plastic material and being environmentally friendly. In one embodiment, the average thickness of the underlayer can be made to match the average thickness of the epidermal layer.

[0051] <Resin sheet 10> The average total thickness of the resin sheet is preferably 200 μm to 1300 μm, more preferably 300 μm to 1200 μm, and even more preferably 500 μm to 900 μm, regardless of whether the resin sheet has a single-layer or multi-layer structure. By setting the average total thickness of the resin sheet to preferably 200 μm or more, more preferably 300 μm or more, and even more preferably 500 μm or more, the strength of the molded product obtained by molding the resin sheet can be ensured. For example, sufficient thickness can be obtained for the sides or bottom of a container obtained by thermoforming, thereby ensuring sufficient strength of the container. By setting the thickness of the resin sheet to 1300 μm or less, more preferably 1200 μm or less, and even more preferably 900 μm or less, the cost of the resin sheet and molded products such as thermoformed containers can be suppressed.

[0052] The resin sheet preferably has a biomass content of 0.1% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 35% by mass or less, and even more preferably 10% by mass or more and 30% by mass or less. The environmental performance of the resin sheet can be improved by having a biomass content of 0.1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. However, considering the balance between manufacturing cost and performance, the biomass content of the resin sheet is preferably 40% by mass or less, more preferably 35% by mass or less, and even more preferably 30% by mass or less. The biomass content of the resin sheet refers to the ratio of the carbon content of the biobase to the total carbon content (TO) measured by a biobase concentration test in accordance with ASTM D6866-20.

[0053] The resin sheet preferably has a DuPont impact strength of 2.0 J or higher, more preferably 2.5 J or higher, and even more preferably 2.9 J or higher, as measured in accordance with JIS K7211-1:2006. This provides sufficient impact resistance when the resin sheet is molded into a container, and has the advantage of being less prone to breakage when dropped. There is no particular upper limit to the DuPont impact strength, but it can be, for example, 4.0 J or lower, and typically 3.5 J or lower. Therefore, in one embodiment, the resin sheet has a DuPont impact strength of 2.0 to 4.0 J as measured in accordance with JIS K7211-1:2006. Here, DuPont impact strength refers to the 50% fracture energy E50 (J) when a DuPont impact test is performed with a drop load of 300g under a measurement environment of 23℃ × 50%RH.

[0054] When a resin sheet is subjected to a bending strength test using a test specimen taken in accordance with JIS P8115:2001, with the longitudinal direction parallel to the MD direction, it is preferable that the average number of back-and-forth bending cycles before fracture is less than 300, more preferably less than 200, even more preferably less than 100, even more preferably less than 50, and most preferably less than 10.

[0055] When a resin sheet is subjected to a bending strength test using a test specimen taken with its longitudinal direction parallel to the TD direction in accordance with JIS P8115:2001, it is preferable that the average number of back-and-forth bending cycles before fracture is less than 300, more preferably less than 200, even more preferably less than 100, even more preferably less than 50, and most preferably less than 10.

[0056] In the resin sheet according to the embodiment of the present invention, when uniaxially stretched, the bending strength (hereinafter also referred to as "bending strength in the MD direction") obtained by taking a test piece from the resin sheet with its longitudinal direction parallel to the MD direction and performing the bending strength test method described above tends to be greater than the bending strength (hereinafter also referred to as "bending strength in the TD direction") obtained by taking a test piece from the resin sheet with its longitudinal direction parallel to the TD direction and performing the bending strength test method described above. In order to reduce the difference in bending strength between the TD direction and the MD direction, biaxial stretching is preferable.

[0057] The layer structure of the resin sheet is not limited to the laminated structure shown in Figure 1. For example, each layer may consist of two or more layers. Furthermore, a new layer may be added to the resin sheet structure in which scrap materials, which are generated in the process of manufacturing molded products such as resin sheets and molded containers, are finely crushed and returned, or recycled material that has been repelled after thermal melting is returned to the resin sheet structure.

[0058] Figure 2 schematically shows the cross-sectional structure of a resin sheet 20 according to another embodiment of the present invention. The resin sheet 20 has a laminated structure in which the surface layer 11 / adhesive layer 14a / oxygen barrier layer 15 / adhesive layer 14b / base layer 12 / underlayer 13 are laminated in this order from top to bottom on the paper. In this embodiment, the oxygen barrier layer 15 is laminated to the surface layer 11 and base layer 12 via adhesive layers 14a and 14b, while the base layer 12 and underlayer 13 are laminated directly.

[0059] The epidermal layer 11, base material layer 12, and underlayer 13 are described in detail in relation to the embodiment shown in Figure 1, so their explanation will be omitted here.

[0060] <Adhesive layer 14a, 14b> The adhesive layers 14a and 14b of this embodiment contain an adhesive. While not limited to adhesives, polyolefin adhesives are preferred from the viewpoint of laminating different resin layers. Polyolefin adhesives preferably contain modified polyolefin polymers. Typical examples include modified homopolymers of olefins having about 2 to 8 carbon atoms, such as ethylene, propylene, and butene-1; modified copolymers of these olefins with other olefins (e.g., ethylene, propylene, butene-1, 3-methylbutene-1, pentene-1, 4-methylpentene-1, hexene-1, octene-1, and decene-1, etc., having about 2 to 20 carbon atoms) and / or vinyl compounds (e.g., vinyl acetate, vinyl chloride, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, and polystyrene, etc.); and modified polyolefin rubbers such as ethylene-butene-1 copolymer and propylene-butene-1 copolymer. Methods of modification include acid modification under graft reaction conditions using unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, and tetrahydrophthalic acid, or their acid halides, amides, imides, anhydrides, esters, etc. Specifically, malenyl chloride, maleimide, maleic anhydride, citraconic anhydride, monomethyl maleate, dimethyl maleate, glycidyl maleate, etc. The adhesive may be used alone or in combination of two or more types.

[0061] As the modified polyolefin polymer, it is preferable to use one or more selected from ethylene resins, propylene resins, ethylene-propylene copolymer rubbers, or ethylene-butene-1 copolymer rubbers, which are modified with unsaturated dicarboxylic acids or their anhydrides, particularly maleic acid or its anhydride.

[0062] The thickness of the adhesive layers 14a and 14b is preferably 2 to 30 μm, and more preferably 5 to 20 μm, respectively. By making the thickness of the adhesive layers 14a and 14b 2 μm or more, sufficient interlayer adhesive strength can be obtained in the multilayer resin sheet, and by making the thickness 30 μm or less, the problem of appearance defects called burrs that occur during die-cutting of containers and the like after molding can be suppressed.

[0063] Various additive components other than adhesives may be added to the adhesive layers 14a and 14b, as long as they do not hinder the effects of the present invention. Examples of such additive components include colorants such as pigments and dyes, release agents such as silicone oil and alkyl esters, fibrous reinforcing agents such as glass fibers, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals and polyalkylene glycols, and additives such as ultraviolet absorbers and antibacterial agents. However, generally, the adhesive content in the adhesive layers 14a and 14b is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can also be 100% by mass. In preferred embodiments, the modified polyolefin polymer content in the adhesive layers 14a and 14b is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can also be 100% by mass.

[0064] <Oxygen barrier layer 15> The oxygen barrier layer 15 of this embodiment contains an oxygen barrier resin to impart oxygen barrier properties to the multilayer resin sheet. Typical oxygen barrier resins include, but are not limited to, ethylene-vinyl alcohol copolymers, polyamides, polyvinyl alcohol, and polyvinylidene chloride. The oxygen barrier resin may be used alone or in combination of two or more types. Among these, ethylene-vinyl alcohol copolymers are preferred in terms of extrusion moldability.

[0065] Ethylene-vinyl alcohol copolymers are typically obtained by saponifying ethylene-vinyl acetate copolymers. To provide oxygen barrier properties and extrudeability, it is preferable that the ethylene content is 10 to 65 mol%, preferably 20 to 50 mol%, and the degree of saponification is 90 mol% or more, preferably 95 mol% or more.

[0066] Furthermore, examples of polyamides include polymers of lactams such as caprolactam and laurolactam, polymers of aminocarboxylic acids such as 6-aminocaproic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid, aliphatic diamines such as hexamethylenediamine, decamethylenediamine, dodecamethylenediamine, and 2,2,4- or 2,4,4-trimethylhexamethylenediamine, alicyclic diamines such as 1,3- or 1,4-bis(aminomethyl)cyclohexane and bis(p-aminocyclohexylmethane), and aromatic diamines such as m- or p-xylylenediamine, as well as polycondensates of dicarboxylic acid units such as adipic acid, suberic acid, and sebacic acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid, and aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid, and copolymers thereof.

[0067] Examples of polyamides include nylon 6, nylon 9, nylon 11, nylon 12, nylon 66, nylon 610, nylon 611, nylon 612, nylon 6T, nylon 6I, nylon MXD6, nylon 6 / 66, nylon 6 / 610, nylon 6 / 6T, nylon 6I / 6T, etc., with nylon 6 and nylon MXD6 being particularly preferred.

[0068] The oxygen barrier layer 15 may contain resins other than the oxygen barrier resin described above, as long as they do not impair the effects of the present invention, and various additive components other than resin components may also be added. Examples of such additive components include colorants such as pigments and dyes, release agents such as silicone oil and alkyl esters, fibrous reinforcing agents such as glass fibers, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals and polyalkylene glycols, and additives such as ultraviolet absorbers and antibacterial agents. However, generally, the content of the oxygen barrier resin in the oxygen barrier layer 15 is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can also be 100% by mass. In preferred embodiments, the content of the ethylene-vinyl alcohol copolymer in the oxygen barrier layer 15 is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can also be 100% by mass.

[0069] The thickness of the oxygen barrier layer 15 is preferably 1 to 50 μm, more preferably 5 to 30 μm. A thickness of 1 μm or more for the oxygen barrier layer 15 is advantageous in terms of improving the oxygen barrier properties of the multilayer resin sheet. Furthermore, a thickness of 50 μm or less for the oxygen barrier layer 15 allows for easier heat stretching of the oxygen barrier layer 15 when the multilayer resin sheet is molded into a container or the like, ensuring a smoother molded product thickness and resulting in a molded product with a better appearance.

[0070] <Manufacturing method for resin sheets> The method for manufacturing a resin sheet according to the present invention is not particularly limited, and general resin sheet molding methods can be used. For example, it can be manufactured by a melt extrusion molding method or a melt co-extrusion molding method in which one or more types of resins are bonded and laminated in a molten state using one or more extrusion molding machines. Specifically, when obtaining a multilayer resin sheet, examples include a method in which the raw materials for each layer are melt-extruded using three or more single-screw or twin-screw extruders, and a multilayer resin sheet is obtained using a feed block with a selector plug and a T-die, or a method in which a multilayer resin sheet is obtained using a multi-manifold die.

[0071] <Molded container> The resin sheet according to the present invention is thermoformable. Accordingly, according to one embodiment of the present invention, a molded article comprising a resin sheet is provided. There are no particular restrictions on the type of molded article, but examples include molded containers such as packs, cups and trays for beverages, food (including seasonings), cosmetics, home appliances and other daily necessities. In one embodiment, the resin sheet can constitute part or all of the molded container. Among molded containers, food packaging containers are a preferred embodiment. Some food packaging containers have a connecting part that connects multiple container bodies, and a notch (hereinafter referred to as "notch") is formed in the connecting part to separate each container body. There are also dispensing packaging bodies, which have a notch formed in the lid for discharging the food packaged inside the packaging container to the outside of the packaging container. Dispensing packaging bodies are small food packaging containers that can easily dispense liquid, paste, granular, or powdery contents such as seasonings and beverages, as well as cosmetics and pharmaceuticals, by pinching and bending them with one's fingers.

[0072] The resin sheet constituting the molded container according to one embodiment of the present invention may have a notch. In the case of a single-layer resin sheet, the notch may be formed from either surface of the base layer, and in the case of a multilayer resin sheet, it may be formed from either the surface layer or the underlayer.

[0073] When using a multilayer resin sheet as a material for a molded container, either the outer layer 11 or the underlayer 13 may be on the outer surface. However, when an oxygen barrier layer 15 is provided as in the embodiment shown in Figure 2, it is preferable to configure part or all of the molded container so that the outer layer 11 is located on the outer surface and the underlayer 13 is located on the inner surface. Generally, a dispensing package comprises a lid made of a rigid material having a fold line with a notch called a "half-cut portion" in the center of the surface and protrusions to facilitate the extraction of contents, and a container body made of a flexible member whose peripheral edge is fixed to the back surface of the lid and which forms pocket portions on both sides of the fold line. Exemplarily, the resin sheet according to the present invention can be molded into the lid of a dispensing package. When using a multilayer resin sheet as a material for the lid of a dispensing package, it is preferable to manufacture the dispensing package so that the outer layer 11 is located on the back surface (the side that contacts food) of the lid and the underlayer 13 is located on the front surface of the lid.

[0074] Methods for thermoforming resin sheets include, but are not limited to, general vacuum forming and pressure forming, as well as applications of these, such as the plug-assisted method, in which a plug is brought into contact with one side of the resin sheet for thermoforming, and the so-called match-mold method, in which a pair of male and female molds are brought into contact with both sides of the resin sheet for thermoforming. Furthermore, known sheet heating methods, such as radiant heating using infrared heaters, which are non-contact heating methods, can be applied to heat and soften the resin sheet before thermoforming.

[0075] In one embodiment, the resin sheet is suitable for use in so-called foam-fill-seal (FFS) packaging, in which the processes of thermoforming, filling with contents, heat-sealing a cover film as a lid material, and then punching out the packaging container to produce the final product are carried out in an integrated manner. [Examples]

[0076] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited in any way to the contents of the examples, etc.

[0077] <1. Fabrication of resin sheets> The raw materials used in the examples and comparative examples are as follows: • HIPS resin (resin manufactured by graft polymerization of styrene and butadiene rubber): Product name "H850N" (Toyo Styrene Co., Ltd.), rubber median diameter: 4.2 μm, butadiene rubber content: 9.0% by mass • HIPS resin (resin manufactured by graft polymerization of styrene and butadiene rubber): Product name "E640N" (Toyo Styrene Co., Ltd.), rubber median diameter: 3.4 μm, butadiene rubber content: 6.2% by mass • HIPS resin (resin manufactured by graft polymerization of styrene and butadiene rubber): Product name "H309" (Toyo Styrene Co., Ltd.), rubber median diameter: 4.5 μm, butadiene rubber content: 4.3% by mass • HIPS resin (resin manufactured by graft polymerization of styrene and butadiene rubber): Product name "GH-8300" (DIC Corporation), rubber median diameter: 3.8 μm, butadiene rubber content: 5.7% by mass • GPPS resin (resin produced by homopolymerization of styrene monomers): Product name "HRM23" (Toyo Styrene Co., Ltd.) • Linear low-density polyethylene (Green LLDPE) manufactured using plant-derived ethylene: Product name "SLH218" (Braskem), Biomass content according to ASTM D6866: 84% by mass or more, Density: 0.916 g / cm³ 3 • Compatibilizer (hydrogenated styrene-based thermoplastic elastomer (SEBS)): Product name "ToughTec (registered trademark) H1043" (Asahi Kasei Corporation) • White pigment masterbatch: Product name "ET3627" (Nikko Bix Co., Ltd.), Titanium dioxide concentration in masterbatch: 50% by mass

[0078] (Examples 1-7, Comparative Examples 1, 6-8) Using a φ65mm single-screw extruder (for the base layer), a φ40mm single-screw extruder (for the surface layer), and a φ40mm single-screw extruder (for the underlayer), each raw material for each layer listed in Tables 1 and 2 according to the test number was melt-co-extruded using the feed block method. After cooling and solidification with a cooling roll, the material was transported by a take-up machine and wound into a roll shape with a winding machine. As a result, a multilayer resin sheet with the layer configuration described in Tables 1 and 2 was obtained, with a flow direction (MD direction) of 30m and a width direction (TD direction) of 800mm.

[0079] (Example 8, Comparative Examples 2-5) Using a φ65mm single-screw extruder, each raw material for the base layer listed in Tables 1 and 2 according to the test number was melt-extruded using the T-die method. After cooling and solidification with a cooling roll, it was transported by a take-up machine and wound into a roll by a winding machine. This yielded a single-layer resin sheet with a flow direction (MD direction) of 30m and a width direction (TD direction) of 800mm.

[0080] <2. Characteristic Evaluation> The resin sheets obtained in the examples and comparative examples were evaluated using the following methods. The results are shown in Tables 1 and 2. (A) Thickness of each layer Test specimens were cut at five evenly spaced points along the entire width direction (TD), which is perpendicular to the flow direction (MD) of the resin sheet. The specimens were cross-sectioned using a single-edged knife, and the thickness of each layer was measured using an electron microscope. The thickness value for each layer was the average of the thicknesses of each layer at the five points mentioned above on the resin sheet. Measuring instrument: Electron microscope KH7700 (Hirox) (B) Rubber median diameter in the epidermal layer, base layer and subdermal layer Test specimens were cut from a resin sheet at arbitrary positions, and the layer to be analyzed was scraped off the specimen using a single-edged knife. Next, all materials except the rubber particles were dissolved with a solvent (N,N-dimethylformamide) to separate the rubber particles. Then, the median diameter (D50) of the rubber particles in each layer was measured using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd., model: LA-920). (C) Rubber particle content in the epidermal layer, base layer and subcutaneous layer (rubber content) Measurements were performed using pyrolysis gas chromatography. Test specimens were cut from a resin sheet at arbitrary positions, and the layer to be analyzed was scraped off the specimen using a single-edged knife. Next, each layer was subjected to thermal decomposition in an environment heated to a constant high temperature using a pyrolysis gas chromatograph (gas chromatograph / Shimadzu Corporation: model GC-2010plus, pyrolysis apparatus / Nippon Analytical Industry Co., Ltd.: model JCI-22). The gas peak areas of the generated butadiene monomer and styrene monomer were determined, and the rubber content in each layer was calculated based on calibration curves for other resins whose rubber content was known. (D) Biomass content Since no biomass is used in any product other than the "Green LLDPE" mentioned above, the biomass content of the entire resin sheet was calculated from the biomass content of the "Green LLDPE" and the composition of the resin sheet. (E) Folding strength Test specimens (15 mm x 110 mm) were cut from the resin sheet at arbitrary positions, and both ends of the specimen in the longitudinal direction were chucked. A bending strength test method in accordance with JIS P8115:2001 was performed using an MIT testing machine. Two types of test specimens were prepared: one with the longitudinal direction as MD (indicated as "MD" in the table) and one with the longitudinal direction as TD (indicated as "TD" in the table). Tests were performed on each type. MIT Test Machine: Manufactured by Toyo Seiki Seisakusho Co., Ltd., Model MIT-D Measurement conditions: With a load (500g) applied, the test specimen was bent back and forth at a speed of 175±10 times per minute at an angle of 135±2° to the left and right of a line perpendicular to the specimen. The number of back-and-forth bends until the test specimen broke (bending endurance) was measured. Each test was performed on 5 test specimens, and the average value was calculated. Note that here the bending endurance of the resin sheet before thermoforming was evaluated, but it has been found that the bending endurance of the resin sheet before thermoforming tends to be the same as the ease of bending of the thermoformed product with the resin sheet attached. Folding strength was evaluated using the following four levels. 1) ◎: Less than 50 flexion repetitions 2) ○: Number of flexion repetitions is 50 or more but less than 300 3) △: Number of flexions is between 300 and 1000 4) ×: Number of flexions exceeds 1000 (F) DuPont impact strength A test specimen measuring 100 mm in length and 500 mm in width was prepared from a resin sheet, and the 50% fracture energy E50 (J) was measured for this specimen using a DuPont impact tester (model No. 517, manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in accordance with JIS K7211-1:2006. The weight was applied to the lower layer in the case of a multilayer resin sheet, and to the base layer in the case of a single-layer resin sheet, with a drop load of 300 g and a measurement environment of 23°C × 50% RH. The results were evaluated using the following four levels. 1) ◎: E50 exceeds 3.0J 2) ○: E50 is 2.0J or more and 3.0J or less 3) △: E50 is 1.0J or more and less than 2.0J 4) ×: E50 is less than 1.0J

[0081] [Table 1]

[0082] [Table 2]

[0083] <3. Consideration> The multilayer resin sheets of Comparative Examples 1, 6, 7, and 8 contain plant-derived polyethylene resin and exhibit excellent environmental performance. However, the multilayer resin sheet of Comparative Example 1 had low impact strength because the median diameter of the butadiene rubber in the base layer was too large, and furthermore, the base layer did not contain a compatibilizer. The multilayer resin sheets of Comparative Examples 6 and 7 contained a compatibilizer in the base layer, but as a result of the median diameter of the butadiene rubber in the base layer being too large, they had high impact strength but also a high number of folds (i.e., poor notch breakability). The multilayer resin sheet of Comparative Example 8 contained a compatibilizer in the base layer, but as a result of the excessive content of butadiene rubber in the base layer, it had high impact strength but also a high number of folds (i.e., poor notch breakability). On the other hand, the multilayer resin sheets of Examples 1 to 7 contained a compatibilizer, and the butadiene rubber content and median diameter in the base layer were appropriate. As a result, they contained plant-derived polyethylene resin, which provided excellent environmental performance, while also having a low fold resistance (i.e., good notch foldability) and high impact strength.

[0084] The single-layer resin sheets of Comparative Examples 2-5 contained plant-derived polyethylene resin and exhibited excellent environmental performance. However, the single-layer resin sheets of Comparative Examples 2 and 5 had low impact strength because the median diameter of the butadiene rubber in the base layer was too large, and furthermore, the base layer did not contain a compatibilizer. The single-layer resin sheets of Comparative Examples 3 and 4 contained a compatibilizer in the base layer, but the butadiene rubber content in the base layer was high, and furthermore, the median diameter of the butadiene rubber in the base layer was too large. As a result, while the impact strength was high, the number of folds it could withstand was also high (i.e., it had poor notch-breaking ability). On the other hand, the single-layer resin sheet of Example 8 contained a compatibilizer, and the butadiene rubber content and median diameter in the base layer were appropriate. As a result, the single-layer resin sheet of Example 8 had excellent environmental performance, a low number of folding cycles (i.e., good notch breakability), and high impact strength.

[0085] Comparing Example 2 and Example 4, it can be seen that Example 2, which has a lower compatibilizer content, tends to have fewer folding cycles. This can also be understood by comparing Example 6 and Example 7.

[0086] Comparing Example 1 and Example 6, Example 1, in which the content of plant-derived polyethylene resin was 10 to 30 parts by mass relative to the total of 100 parts by mass of polystyrene resin and plant-derived polyethylene resin in the substrate layer, had fewer folding resistance (i.e., better notch breakability) and higher impact strength. [Explanation of Symbols]

[0087] 10, 20 resin sheets 11 Epidermal layer 12 Base material layer 13 Hypodermal layer 14a, 14b adhesive layer 15. Oxygen barrier layer

Claims

1. The material comprises a base layer containing a polystyrene resin, a plant-derived polyethylene resin, and a compatibilizer for compatibilizing the polystyrene resin and the plant-derived polyethylene resin. The polystyrene resin may or may not contain butadiene rubber. If the polystyrene resin contains butadiene rubber, the median diameter of the butadiene rubber is 3.5 μm or less, and the butadiene rubber content in the substrate layer is greater than 0% by mass and 3% by mass or less. The DuPont impact strength, measured in accordance with JIS K7211-1:2006, is 2.0 J or higher. A resin sheet that, in accordance with JIS P8115:2001, when a test specimen with its longitudinal direction parallel to the medium-density direction is taken and the bending strength test method is performed, has an average of fewer than 300 back-and-forth bending cycles before fracture.

2. The resin sheet according to claim 1, wherein the content of plant-derived polyethylene resin in the resin sheet is 0.1% by mass or more and 35% by mass or less.

3. The resin sheet according to claim 1 or 2, wherein in the base layer, the content of plant-derived polyethylene resin is 10 parts by mass or more and 30 parts by mass or less with respect to a total of 100 parts by mass of polystyrene resin and plant-derived polyethylene resin.

4. A resin sheet according to any one of claims 1 to 3, wherein the content of the compatibilizer in the base layer is 0.1% by mass or more and 5% by mass or less.

5. A resin sheet according to any one of claims 1 to 4, wherein the total content of polystyrene resin and plant-derived polyethylene resin in the base layer is 90% by mass or more.

6. A resin sheet according to any one of claims 1 to 5, further comprising: a surface layer containing a polystyrene resin laminated on one side of a base layer; and a base layer containing a polystyrene resin laminated on the side of the base layer opposite to the side having the surface layer.

7. The resin sheet according to claim 6, wherein the polystyrene resin constituting the epidermal layer and the subcutaneous layer each contains butadiene rubber with a median diameter of 4.5 μm or less, the butadiene rubber content in the epidermal layer is greater than 0% by mass and 8.0% by mass or less, and the butadiene rubber content in the subcutaneous layer is greater than 0% by mass and 8.0% by mass or less.

8. The resin sheet according to claim 7, wherein the butadiene rubber content in the epidermal layer is 5.0% by mass or more and 7.5% by mass or less, and the butadiene rubber content in the subdermal layer is 5.0% by mass or more and 7.5% by mass or less.

9. The resin sheet according to claim 7 or 8, wherein the average thickness of the epidermal layer and the subcutaneous layer is 0.1% or more and 15% or less of the average total thickness of the resin sheet, respectively.

10. A resin sheet according to any one of claims 1 to 9, wherein the average total thickness is 200 μm or more and 1300 μm or less.

11. A resin sheet according to any one of claims 1 to 10, wherein the biomass content is 0.1% by mass or more and 40% by mass or less.

12. A resin sheet according to any one of claims 1 to 11, wherein, in accordance with JIS P8115:2001, when a test specimen with its longitudinal direction parallel to the TD direction is taken and the bending strength test method is performed, the average number of back-and-forth bending cycles until fracture is less than 300.

13. A molded container comprising a resin sheet according to any one of claims 1 to 12.

14. The molding container according to claim 13, wherein a notch is formed in the resin sheet.

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