Resin sheet and molded container

Abstract

The present invention addresses the problem of providing a resin sheet comprising a polystyrene-based resin and a poly(lactic acid) resin, the resin sheet being excellent in terms of notched-portion foldability and impact resistance. The resin sheet includes a base layer which comprises both a polystyrene-based resin containing butadiene rubber and a poly(lactic acid) resin and in which the butadiene rubber has a median diameter less than 6 μm and the content of the butadiene rubber is 3.0-7.0 mass%.

Description

[Technical Field]

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

[0002] Resin sheets containing polystyrene resins have excellent moldability and have been widely used for a variety of packaging applications, such as food containers, beverage containers, and industrial containers including various trays. In particular, demand for high-impact polystyrene (HIPS), which is made by graft copolymerizing polystyrene onto butadiene rubber, is growing as it can produce resin sheets with excellent impact resistance, and related technological developments are also progressing.

[0003] Japanese Patent Application Laid-Open No. 2011-51264 discloses a deep-draw foam sheet comprising at least one oxygen barrier layer, at least one moisture-proof layer, at least one impact-resistant auxiliary layer, and a polystyrene foam sheet, wherein the oxygen barrier layer contains a modified ethylene-vinyl alcohol copolymer (hereinafter sometimes abbreviated as modified EVOH) containing 0.1 to 20 mol % of structural units (I) other than ethylene units and vinyl alcohol units, the moisture-proof layer is made of polypropylene, and the impact-resistant auxiliary layer is made of high-impact polystyrene. The publication also discloses that the deep-draw foam sheet has excellent gas barrier properties and moisture-proof properties against oxygen and is capable of being deep-drawn and thermoformed at high magnifications, and further discloses that a foam container can be provided by deep-drawing the sheet.

[0004] JP 2015-199311 A describes that in a laminated sheet consisting of a core layer whose main component is a mixture of high-impact polystyrene and polystyrene, and outer layers whose main component is high-impact polystyrene and are arranged on both sides of the core layer, by setting the thickness of the outer layer relative to the total thickness and the amount of polybutadiene in the core layer and outer layer within a specific range, a laminated sheet having excellent notch foldability, impact resistance, and formability can be obtained.

[0005] JP 2020-164600 A describes that in a polystyrene-based resin foam sheet for containers having a foam layer containing a polystyrene-based resin and a polyphenylene ether-based resin, excellent moldability and heat resistance can be obtained by specifying the ratio of each resin component, the average bubble diameter in the foam layer, and the density of the foam layer within predetermined ranges. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-51264 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-199311 [Patent Document 3] Japanese Patent Application Publication No. 2020-164600 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, demand for biomass plastics has been increasing in order to reduce the burden on the environment. Polylactic acid resin, a type of biomass plastic, is inexpensive and has excellent rigidity and high transparency. For these reasons, polylactic acid resin is expected to be used as a material for molded containers such as packs, cups, and trays for beverages, foods, cosmetics, home appliances, and other daily necessities. However, polylactic acid resin has poor compatibility with polystyrene-based resins, and when a resin sheet contains both polystyrene-based resin and polylactic acid resin, it is difficult to achieve both excellent notch foldability and excellent impact resistance.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a resin sheet containing a polystyrene resin and a polylactic acid resin, which resin sheet has both excellent notch foldability and excellent impact resistance. In another embodiment, the present invention is to provide a molded container including such a resin sheet. [Means for solving the problem]

[0009] The present inventors have conducted extensive research to solve the above-mentioned problems and have found that adjusting the median diameter and content of the butadiene rubber contained in the polystyrene-based resin within appropriate ranges is effective in solving the above-mentioned problems, and have arrived at the present invention, which is exemplified below.

[0010] [1] A resin sheet comprising a base layer containing a polystyrene resin containing butadiene rubber and a polylactic acid resin, wherein the median diameter of the butadiene rubber in the base layer is less than 6 μm, and the content of the butadiene rubber in the base layer is 3.0 mass% or more and 7.0 mass% or less. [2] The resin sheet according to [1], wherein the content of the polylactic acid resin in the base layer is 1% by mass or more and 25% by mass or less. [3] The resin sheet according to [1] or [2], wherein in the base layer, the polylactic acid resin constitutes a plurality of dispersed phases dispersed in the polystyrene-based resin. [4] The resin sheet according to any one of [1] to [3], wherein the total content of the polystyrene resin and the polylactic acid resin in the base layer is 90% by mass or more. [5] The resin sheet according to any one of [1] to [4], further comprising: a surface layer containing a polystyrene-based resin laminated on one surface of the base layer; and an underskin layer containing a polystyrene-based resin laminated on the surface of the base layer opposite to the surface having the surface layer. [6] The resin sheet according to [5], wherein the average thickness of the surface layer and the underskin layer is 1% or more and 15% or less of the average total thickness of the resin sheet. [7] The resin sheet according to any one of [1] to [6], having an average total thickness of 200 μm or more and 1300 μm or less. [8] The resin sheet according to any one of [1] to [7], wherein the substrate layer contains a white pigment in an amount of 1 phr or more and 5 phr or less. [9] The resin sheet according to any one of [1] to [8], wherein the biomass content is 0.1% by mass or more and 20% by mass or less.

[10] The resin sheet according to any one of [1] to [9], which has a DuPont impact strength of 2.0 J or more as measured in accordance with JIS K7211-1:2006.

[11] The resin sheet according to any one of [1] to

[10] , wherein when a test piece is taken with its longitudinal direction parallel to the MD direction and subjected to a folding endurance test method in accordance with JIS P8115:2001, the number of reciprocal foldings until breakage occurs is less than 300 on average.

[12] The resin sheet according to any one of [1] to

[11] , wherein when a test piece is taken with its longitudinal direction parallel to the TD direction and subjected to a folding endurance test method in accordance with JIS P8115:2001, the number of reciprocal foldings until breakage occurs is less than 300 on average.

[13] A molded container comprising the resin sheet according to any one of [1] to

[12] .

[14] The molded container according to

[13] , wherein a notch is formed in the resin sheet. [Effects of the Invention]

[0011] A resin sheet according to one embodiment of the present invention contains a polylactic acid resin and has excellent notch foldability and impact resistance, making it possible to manufacture a variety of molded products that combine environmental friendliness and practicality, such as molded containers such as packs and trays for beverages, food, cosmetics, home appliances, and other daily necessities. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view schematically showing a laminated structure of a resin sheet according to one embodiment of the present invention. [Figure 2] FIG. 3 is a cross-sectional view schematically showing a laminated structure of a resin sheet according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] In one embodiment, the resin sheet according to the present invention includes a substrate layer containing a polystyrene-based resin containing butadiene rubber and a polylactic acid resin. Although the resin sheet may have a single-layer structure consisting of only the substrate layer, in order to enhance impact resistance and to prevent deterioration of heat-sealability with a lid material when the resin sheet is molded into a molded container, it is preferable to further include a surface layer containing a polystyrene-based resin laminated on one side of the substrate layer and an underskin layer containing a polystyrene-based resin laminated on the side of the substrate layer opposite to the surface having the surface layer.

[0014] 1 schematically shows a cross-sectional structure of a resin sheet 10 according to one embodiment of the present invention. The resin sheet 10 has a layered structure in which a surface layer 11, a base layer 12, and an underskin layer 13 are layered in this order from top to bottom of the page. In this embodiment, the surface layer 11 and the base layer 12 are directly bonded together without an adhesive layer, and the base layer 12 and the underskin layer 13 are directly bonded together without an adhesive layer.

[0015] Below, the layers of base material layer 12, skin layer 11, and underskin layer 13 will be described in that order, and then the resin sheet 10 itself and a food packaging container as a molded container molded from the resin sheet 10 will be described as an example.

[0016] <Base material layer 12> In one embodiment, the substrate layer contains a polystyrene-based resin containing butadiene rubber and a polylactic acid resin. In one embodiment, the butadiene rubber can be present in a state in which multiple butadiene rubber particles are dispersed in the polystyrene-based resin. Methods for dispersing multiple butadiene rubber particles in the polystyrene-based resin include, but are not limited to, a method of polymerizing a styrene-based 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 are dispersed in the polystyrene-based resin through graft polymerization of the styrene-based monomer. Examples of styrene-based monomers include styrene, α-methylstyrene, p-methylstyrene, dimethylstyrene, pt-butylstyrene, and chlorostyrene.

[0017] The substrate layer may contain a polystyrene-based resin that does not contain butadiene rubber. Examples of polystyrene-based resins include homopolymers of styrene-based monomers such as styrene, α-methylstyrene, p-methylstyrene, dimethylstyrene, pt-butylstyrene, and chlorostyrene, as well as copolymers of these styrene-based monomers with other monomers. Examples of copolymers of styrene-based monomers with other monomers include polystyrene-acrylonitrile copolymers (AS resins). One type of polystyrene-based resin may be used alone, or two or more types may be used in combination.

[0018] Polystyrene-based 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). It has a sea-island structure with the styrene polymer as the continuous phase (sea) and the rubbery polymer grafted with a portion of the styrene monomer as the dispersed phase (islands). ABS resin is obtained by polymerizing styrene monomer and acrylonitrile monomer in the presence of a rubbery polymer (typically polybutadiene). It has a sea-island structure with the styrene-acrylonitrile copolymer (AS resin) as the continuous phase (sea) and the rubbery polymer grafted with a portion of the styrene monomer and acrylonitrile monomer as the dispersed phase (islands).

[0019] In particular, using a mixture of general-purpose polystyrene (GPPS resin) and high-impact polystyrene (HIPS resin) for the base layer is preferred from the standpoint of rigidity and thermoformability of molded products such as molded containers obtained by molding the resin sheet. Mixing with GPPS resin also offers the advantage of being able to adjust the rubber content. The mixing ratio of GPPS resin can be adjusted according to the desired rubber content. The median diameter of the rubber particles in HIPS resin can be adjusted by controlling the shear force, such as the speed of the rotor in the polymerization vessel, controlling the polymerization time, or controlling the polymerization with additives.

[0020] The median diameter of the butadiene rubber in the base layer (also referred to as "rubber median diameter") is preferably less than 6 μm. Furthermore, the rubber median diameter is more preferably 1 μm or more and 5 μm or less, and even more preferably 2 μm or more and 4 μm or less. By setting the rubber median diameter to preferably 1 μm or more, more preferably 2 μm or more, it is possible to obtain appropriate impact resistance, and to make molded articles such as molded containers obtained by molding the resin sheet less susceptible to breakage when dropped. Furthermore, by setting the rubber median diameter to less than 6 μm, preferably 5 μm or less, more preferably 4 μm or less, cracks are more likely to propagate, thereby improving notch foldability when the resin sheet is molded into a molded article such as a container and a notch is formed. In this specification, the rubber median diameter refers to the median diameter (D50) based on the volume-based particle size distribution measured with a Coulter counter.

[0021] Furthermore, the content of butadiene rubber in the base layer is preferably 3.0% by mass or more and 7.0% by mass or less, and more preferably 4.0% by mass or more and 6.5% by mass or less. By making the content of butadiene rubber in the base layer preferably 3.0% by mass or more, more preferably 4.0% by mass or more, it is possible to improve impact resistance, and therefore it is possible to make it more difficult for molded articles such as molded containers obtained by molding a resin sheet to break when dropped. Furthermore, making the content of butadiene rubber in the base layer preferably 7.0% by mass or less, more preferably 6.5% by mass or less, is advantageous for improving crack propagation resistance.

[0022] Polylactic acid resins can be produced from plants such as corn, sugarcane, and sugar radish, without using petroleum as a raw material, and are completely biodegradable into water and carbon dioxide by microorganisms in the soil, making them environmentally friendly. Examples of polylactic acid resins include homopolymers such as poly(L-lactic acid) and poly(D-lactic acid), copolymers containing both L-lactic acid and D-lactic acid structural units (DL-lactic acid), and mixtures of these.

[0023] Polylactic acid resins can be polymerized by known methods such as condensation polymerization and ring-opening polymerization. For example, in condensation polymerization, L-lactic acid, D-lactic acid, or a mixture thereof can be directly subjected to dehydration condensation polymerization to obtain polylactic acid resins of any composition. Various additives may be added during polymerization to the extent that they do not impair the effects of the present invention. For example, non-aliphatic dicarboxylic acids such as terephthalic acid and non-aliphatic diols such as ethylene oxide adducts of bisphenol A can be added as needed to improve heat resistance. Furthermore, chain extenders such as diisocyanate compounds, epoxy compounds, and acid anhydrides can be added as needed to increase the molecular weight.

[0024] The content of polylactic acid resin in the base layer is preferably 1% by mass or more and 25% by mass or less, more preferably 5% by mass or more and 20% by mass or less, and even more preferably 10% by mass or more and 15% by mass or less. By making the content of polylactic acid resin in the base layer preferably 1% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more, the environmental performance of the resin sheet can be improved. Furthermore, by making the content of polylactic acid resin in the base layer preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less, notch fold resistance and impact resistance are likely to be improved.

[0025] When the content of the polylactic acid resin in the base layer is within the above range, the polylactic acid resin and the polystyrene-based resin are mixed together, so that the polylactic acid resin is present in the base layer as a plurality of dispersed phases dispersed in the polystyrene-based resin. The presence of the polylactic acid resin as a plurality of dispersed phases is advantageous in that a molded product with a good appearance can be obtained when the container is molded.

[0026] When printing is performed on a resin sheet or a molded product thereof using laser irradiation or the like, the base layer preferably contains 1 phr to 5 phr of white pigment. Furthermore, it is even more preferable that the base layer contains 1.5 phr to 4 phr of white pigment. The unit phr used here refers to the parts by mass of white pigment per 100 parts by mass of all resin components in the base layer. By including 1 phr or more of white pigment in the base layer, opacity is achieved, improving the color development of printed characters when printing on the resin sheet and its molded products. Light-blocking properties are also achieved, preventing discoloration and deterioration of the contents due to light irradiation from outside the molded product. Furthermore, by keeping the white pigment content in the base layer at 5 phr or less, aggregation of the white pigment can be suppressed, preventing poor appearance of the resin sheet and its molded products due to aggregation. Considering costs, a lower amount of white pigment is preferable.

[0027] Examples of the white pigment include titanium oxide (titanium white), zinc oxide (zinc white), lithopone, white lead, etc. Among these, titanium oxide is preferred. The white pigment may be used alone or in combination of two or more.

[0028] The base layer may contain other resins, or various additives other than the resin components, as long as they do not impair the effects of the present invention. Examples of such additives include, in addition to the white pigment described above, nucleating agents for promoting crystallization of the polylactic acid resin, compatibilizers for miscible components, colorants such as other pigments and dyes, release agents such as silicone oil and alkyl esters, fibrous reinforcing agents such as glass fiber, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals or polyalkylene glycols, ultraviolet absorbers, and antibacterial agents. Scrap resin generated during the manufacturing process of the resin sheet and molded container according to one embodiment of the present invention may also be mixed.

[0029] Generally, the total content of polystyrene-based resin (if butadiene rubber is contained, the butadiene rubber is also included in the polystyrene-based resin) and polylactic acid resin in the base layer is 90% by mass or more, typically 95% by mass or more, more typically 98% by mass or more, and can also be 100% by mass.

[0030] The thickness of the substrate layer is preferably 160 to 1200 μm, more preferably 180 to 1000 μm. Setting the thickness of the substrate layer to 160 μm or more is advantageous in that it ensures the strength of the molded product obtained by molding the resin sheet. Setting the thickness of the substrate layer to 1200 μm or less is advantageous in that it reduces the costs of the resin sheet and its molded products, such as thermoformed containers.

[0031] <Epidermal layer 11> The skin layer is laminated on one surface of the base layer. The skin layer serves to protect the base layer, and is preferably provided from the viewpoint of improving the impact resistance of the resin sheet. In one embodiment, the skin layer contains a polystyrene-based resin. The skin layer containing a polystyrene-based resin, like the base layer, is advantageous in terms of increasing the impact resistance of the molded container and obtaining sufficient interlayer adhesion with the base layer. In a preferred embodiment, the skin layer contains a polystyrene-based resin containing butadiene rubber in order to enhance the effect of improving the impact resistance of the resin sheet.

[0032] The polystyrene-based resin suitable for the skin layer is similar to the polystyrene-based resin containing butadiene rubber for the substrate layer, and detailed description thereof will be omitted. For example, the polystyrene-based resin containing butadiene rubber suitable for the skin layer may be the graft polymer described in the description of the substrate layer, i.e., a graft polymer obtained by polymerizing a styrene-based monomer in the presence of polybutadiene, such as high-impact polystyrene (HIPS resin) or polystyrene-acrylonitrile graft polymer (ABS resin). One type of polystyrene-based resin may be used alone, or two or more types may be used in combination. Similarly to the substrate layer, the skin layer may also contain a polystyrene-based resin that does not contain butadiene rubber. In particular, a mixture of general-purpose polystyrene (GPPS resin) and high-impact polystyrene (HIPS resin) is preferred for the skin layer in terms of the rigidity and thermoformability of molded containers and the like obtained by molding the resin sheet. The preferred embodiments of the butadiene rubber in the skin layer, including the median diameter and content of the butadiene rubber, are the same as those for the substrate layer, and therefore description thereof will be omitted.

[0033] As with the base layer, the skin layer may contain other resins or various additives other than the resin components, provided that the effects of the present invention are not impaired. Examples of such additives include compatibilizers for miscible components, colorants such as pigments and dyes, release agents such as silicone oils and alkyl esters, fibrous reinforcing agents such as glass fiber, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals or polyalkylene glycols, UV absorbers, and antibacterial agents. However, from the perspective of improving impact resistance and notch breakability, it is desirable for the skin layer to not contain polylactic acid resin. Furthermore, it is desirable for the skin layer to not contain scrap resin in order to improve the appearance of the resin sheet.

[0034] Generally, the total content of polystyrene-based resins (when butadiene rubber is contained, the butadiene rubber is also included in the polystyrene-based resins) in the skin layer is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can be 100% by mass. In a preferred embodiment, the total content of HIPS and GPPS in the skin layer is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can be 100% by mass.

[0035] The average thickness of the skin layer is preferably 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 making the average thickness of the skin layer preferably 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 impact resistance of the resin sheet can be significantly improved. Furthermore, by making the average thickness of the skin layer 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 polylactic acid resin content in the entire sheet is increased, resulting in a higher biomass plastic material content and environmentally friendly benefits.

[0036] <Hypodermal layer 13> The underskin layer is laminated on the surface of the substrate layer opposite to the surface having the surface skin layer. The underskin layer, like the surface skin layer, serves to protect the substrate layer, and is preferably provided from the viewpoint of improving the impact resistance of the resin sheet. In one embodiment, the underskin layer contains a polystyrene-based resin. The underskin layer containing a polystyrene-based resin, like the substrate layer, is advantageous in terms of increasing the impact resistance of the molded container and obtaining sufficient interlayer adhesion with the substrate layer. In a preferred embodiment, the underskin layer contains a polystyrene-based resin containing butadiene rubber to enhance the effect of improving the impact resistance of the resin sheet. The underskin layer may also be provided symmetrically with the surface skin layer across the substrate layer. This results in the resin sheet having a symmetrical laminate structure in the thickness direction, which allows the resin sheet to be attached to another article without having to worry about the front and back sides, improving ease of handling.

[0037] The polystyrene-based resin suitable for the underskin layer is similar to the polystyrene-based resin containing butadiene rubber for the substrate layer, and detailed description thereof will be omitted. For example, the polystyrene-based resin containing butadiene rubber suitable for the underskin layer may be the graft polymer described in the description of the substrate layer, i.e., a graft polymer obtained by polymerizing a styrene-based monomer in the presence of polybutadiene, such as high-impact polystyrene (HIPS resin) or polystyrene-acrylonitrile graft polymer (ABS resin). One type of polystyrene-based resin may be used alone, or two or more types may be used in combination. Similarly to the substrate layer, the underskin layer may be appropriately blended with a polystyrene-based resin that does not contain butadiene rubber. In particular, a mixture of general-purpose polystyrene (GPPS resin) and high-impact polystyrene (HIPS resin) is preferred for the underskin layer in terms of the rigidity and thermoformability of molded containers and the like obtained by molding the resin sheet. The preferred butadiene rubber for the underskin layer, including the median diameter and content of the butadiene rubber, is the same as for the substrate layer, and detailed description thereof will be omitted.

[0038] As with the substrate layer, the underskin layer may contain other resins or various additives other than the resin components, provided that the effects of the present invention are not impaired. Examples of such additives include compatibilizers for miscible components, colorants such as pigments and dyes, release agents such as silicone oils and alkyl esters, fibrous reinforcing agents such as glass fiber, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals or polyalkylene glycols, UV absorbers, and antibacterial agents. However, from the perspective of improving impact resistance and notch break resistance, it is desirable for the underskin layer to not contain polylactic acid resin. Furthermore, it is desirable for the underskin layer to not contain scrap resin in order to improve the appearance of the resin sheet.

[0039] Generally, the total content of polystyrene-based resins (when butadiene rubber is contained, the butadiene rubber is also included in the polystyrene-based resins) in the underskin layer is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can be 100% by mass. In a preferred embodiment, the total content of HIPS and GPPS in the underskin layer is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can be 100% by mass.

[0040] The average thickness of the underskin layer is preferably 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 making the average thickness of the underskin layer preferably 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 impact resistance of the resin sheet can be significantly improved. Furthermore, by making the average thickness of the underskin layer 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 polylactic acid resin content in the entire sheet is increased, resulting in a higher content of biomass plastic material and environmental friendliness. In one embodiment, the average thickness of the underskin layer can be the same as the average thickness of the surface layer.

[0041] <Resin sheet 10> The average total thickness of the resin sheet, regardless of whether the resin sheet has a single-layer structure or a multilayer structure, is preferably 200 μm or more and 1300 μm or less, more preferably 300 μm or more and 1200 μm or less, and even more preferably 500 μm or more and 900 μm or less. By making the average total thickness of the resin sheet 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, a sufficient thickness can be obtained on the side or bottom of a container obtained by thermoforming, thereby ensuring sufficient container strength. By making the thickness of the resin sheet 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 its molded product, such as a thermoformed container, can be reduced.

[0042] The resin sheet preferably has a biomass degree of 0.1% by mass or more and 20% by mass or less, more preferably 3% by mass or more and 15% by mass or less, and even more preferably 5% by mass or more and 13% by mass or less. The biomass degree of the resin sheet is preferably 0.1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, thereby improving the environmental performance of the resin sheet. However, in consideration of the balance between the impact resistance and notch foldability required of the resin sheet, the biomass degree of the resin sheet is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 13% by mass or less.

[0043] Here, the biomass content of the resin sheet refers to the ratio of the biobased carbon content to the total carbon content (TO) measured by the biobased concentration test in accordance with ASTM D6866-05.

[0044] The resin sheet preferably has a DuPont impact strength of 2.0 J or more, more preferably 2.5 J or more, and even more preferably 2.9 J or more, as measured in accordance with JIS K7211-1:2006. This provides sufficient impact resistance when molded into a container from the resin sheet, resulting in the advantage that the container is less likely to break when dropped. There is no particular upper limit to the DuPont impact strength, but it can be, for example, 4.0 J or less, and typically 3.5 J or less. 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, the DuPont impact strength refers to the 50% breaking energy E50 (J) when a DuPont impact test is performed under a drop load of 300 g and in a measurement environment of 23°C x 50% RH.

[0045] When a resin sheet is subjected to a folding endurance test in accordance with JIS P8115:2001 using a test piece with the longitudinal direction parallel to the MD direction, the resin sheet is preferably bent back and forth an average of less than 300 times, more preferably less than 200 times, even more preferably less than 100 times, even more preferably less than 50 times, and most preferably less than 10 times until it breaks.

[0046] When a resin sheet is subjected to a folding endurance test in accordance with JIS P8115:2001 using a test piece with its longitudinal direction parallel to the TD direction, the resin sheet is preferably bent back and forth an average of less than 300 times, more preferably less than 200 times, even more preferably less than 100 times, even more preferably less than 50 times, and most preferably less than 10 times until it breaks.

[0047] When a resin sheet contains polylactic acid resin, the polylactic acid resin in the resin sheet tends to form a dispersed phase elongated in the MD direction during sheet formation. Therefore, when a test piece whose longitudinal direction is parallel to the MD direction is taken from the resin sheet and subjected to the above-mentioned folding strength test method, the folding strength (hereinafter also referred to as "MD folding strength") tends to be higher than the folding strength (hereinafter also referred to as "TD folding strength") when a test piece whose longitudinal direction is parallel to the TD direction is taken from the resin sheet and subjected to the above-mentioned folding strength test method. To reduce the MD folding strength, it is preferable to reduce the content of polylactic acid resin and butadiene rubber and to reduce the particle size of the butadiene rubber.

[0048] The layer structure of the resin sheet is not limited to the laminated structure shown in Fig. 1. For example, each layer may be composed of two or more layers. Furthermore, scrap generated in the process of manufacturing molded products such as resin sheets and molded containers may be finely crushed and returned instead of being discarded, or a new layer may be provided in which recycled material re-pelletized after thermal melting is returned to the resin sheet structure.

[0049] 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 layered structure in which, from top to bottom of the page, a surface layer 11, an adhesive layer 14a, an oxygen barrier layer 15, an adhesive layer 14b, a base layer 12, and an underskin layer 13 are layered in this order. In this embodiment, the oxygen barrier layer 15 is layered on the surface layer 11 and the base layer 12 via the adhesive layers 14a and 14b, while the base layer 12 and the underskin layer 13 are layered directly on each other.

[0050] The skin layer 11, the base layer 12 and the underskin layer 13 have been described in detail in relation to the embodiment shown in FIG. 1, and therefore further description thereof will be omitted.

[0051] <Adhesive layer 14a, 14b> The adhesive layers 14a and 14b of this embodiment contain an adhesive. The adhesive is not limited to, but is preferably a polyolefin-based adhesive from the viewpoint of laminating different resin layers. The polyolefin-based adhesive preferably contains a modified polyolefin-based polymer. Representative examples include modified homopolymers of olefins having approximately 2 to 8 carbon atoms, such as ethylene, propylene, and butene-1; modified copolymers of these olefins with other olefins (e.g., olefins having approximately 2 to 20 carbon atoms, such as ethylene, propylene, butene-1, 3-methylbutene-1, pentene-1, 4-methylpentene-1, hexene-1, octene-1, and decene-1) and / or vinyl compounds (e.g., vinyl acetate, vinyl chloride, acrylic acid, methacrylic acid, acrylic acid esters, methacrylic acid esters, and polystyrene); and modified polyolefin-based rubbers, such as ethylene-butene-1 copolymers and propylene-butene-1 copolymers. Examples of the modification method include a method of 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, tetrahydrophthalic acid, etc., or derivatives thereof such as 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.

[0052] As the modified polyolefin polymer, it is preferable to use one or more selected from ethylene resins, propylene resins, ethylene-propylene copolymer rubbers, and ethylene-butene-1 copolymer rubbers, which are modified with an unsaturated dicarboxylic acid or an anhydride thereof, particularly maleic acid or an anhydride thereof.

[0053] The thickness of each of the adhesive layers 14a, 14b is preferably 2 to 30 μm, more preferably 5 to 20 μm. By making the thickness of the adhesive layers 14a, 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, it is possible to suppress the problem of poor appearance called whisker burrs that occur during punching of containers and the like that is performed after molding.

[0054] Various additives other than the adhesive may be added to the adhesive layers 14a and 14b as long as they do not impair the effects of the present invention. Examples of such additives include colorants such as pigments and dyes, release agents such as silicone oils and alkyl esters, fibrous reinforcing agents such as glass fiber, granular lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid and alkali metals or polyalkylene glycols, UV absorbers, and antibacterial agents. However, the adhesive content in the adhesive layers 14a and 14b is generally 80% by weight or more, typically 90% by weight or more, more typically 95% by weight or more, and can be as high as 100% by weight. In a preferred embodiment, the modified polyolefin polymer content in the adhesive layers 14a and 14b is 80% by weight or more, typically 90% by weight or more, more typically 95% by weight or more, and can be as high as 100% by weight.

[0055] <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. Representative examples of oxygen barrier resins include, but are not limited to, ethylene-vinyl alcohol copolymers, polyamides, polyvinyl alcohols, and polyvinylidene chloride. The oxygen barrier resins may be used alone or in combination of two or more. Among these, ethylene-vinyl alcohol copolymer resins are preferred in terms of extrusion moldability.

[0056] Ethylene-vinyl alcohol copolymers are usually obtained by saponifying ethylene-vinyl acetate copolymers, and in order to provide oxygen barrier properties and extrusion moldability, they preferably have an ethylene content of 10 to 65 mol%, preferably 20 to 50 mol%, and a saponification degree of 90 mol% or more, preferably 95 mol% or more.

[0057] Examples of polyamides include lactam polymers such as caprolactam and laurolactam; polymers of aminocarboxylic acids such as 6-aminocaproic acid, 11-aminoundecanoic acid and 12-aminododecanoic acid; polycondensates of diamine units such as 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, and dicarboxylic acid units such as aliphatic dicarboxylic acids 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.

[0058] Specific examples of polyamide resins 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, and nylon 6I / 6T, with nylon 6 and nylon MXD6 being particularly preferred.

[0059] The oxygen barrier layer 15 may contain resins other than the oxygen barrier resins described above, and various additives other than the resin components may also be added, as long as the effects of the present invention are not impaired. Examples of such additives include colorants such as pigments and dyes, release agents such as silicone oils and alkyl esters, fibrous reinforcing agents such as glass fiber, particulate lubricants such as talc, clay, and silica, antistatic agents such as salt compounds of sulfonic acid with alkali metals and polyalkylene glycols, UV absorbers, and antibacterial agents. However, the content of the oxygen barrier resin in the oxygen barrier layer 15 is generally 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can be as high as 100% by mass. In a preferred embodiment, the content of the ethylene-vinyl alcohol copolymer 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 be as high as 100% by mass.

[0060] The thickness of the oxygen barrier layer 15 is preferably 1 to 50 μm, more preferably 5 to 30 μm. Having a thickness of 1 μm or more is advantageous from the viewpoint of enhancing the oxygen barrier properties of the multilayer resin sheet. Furthermore, having a thickness of 50 μm or less makes the oxygen barrier layer 15 more susceptible to thermal stretching when the multilayer resin sheet is molded into a container or the like, ensuring a smoother molded product thickness and enabling the production of molded products with better appearance.

[0061] <Resin sheet manufacturing method> The method for producing the resin sheet according to the present invention is not particularly limited, and a general resin sheet molding method can be used. For example, the resin sheet can be produced by a melt extrusion molding method or a melt coextrusion molding method in which one or more types of resins are adhesively laminated in a molten state using one or more extruders. Specific examples of a method for producing a multilayer resin sheet 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 the multilayer resin sheet is obtained using a feed block and a T-die equipped with a selector plug, and a method in which a multilayer resin sheet is obtained using a multi-manifold die.

[0062] <Molded container> The resin sheet according to the present invention is thermoformable. Therefore, according to one embodiment of the present invention, a molded product including a resin sheet is provided. The type of molded product is not particularly limited, and 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 a part or all of the molded container. Among molded containers, a food packaging container is a preferred embodiment. Some food packaging containers have a connecting portion that connects multiple container bodies, and a notch (hereinafter referred to as a "notch") formed in the connecting portion for separating the individual container bodies. There are also so-called dispensing packages, in which a notch is formed in the lid to allow the food packaged inside the packaging container to be discharged outside the packaging container. Dispensing packages are small food packaging containers that allow easy extraction of liquid, paste, granular, or powdery contents, such as food products such as seasonings and beverages, as well as cosmetics and medicines, by pinching and folding them with the fingers.

[0063] 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 on either surface of the base layer, and in the case of a multi-layer resin sheet, the notch may be formed on either side of the skin layer or the underskin layer.

[0064] When a multilayer resin sheet is used as a material for a molded container, either the surface skin layer 11 or the underskin layer 13 may be located on the outer surface. However, when an oxygen barrier layer 15 is provided as in the embodiment shown in FIG. 2 , it is preferable to configure a portion or all of the molded container so that the surface skin layer 11 is located on the outer surface side of the molded container and the underskin layer 13 is located on the inner surface side of the molded container. Furthermore, a distribution package generally comprises a lid body made of a hard material having a fold line with a notch called a "half-cut portion" in the center of the surface and protrusions to facilitate extraction of the contents, and a container body made of a flexible material whose peripheral edge is fixed to the back surface of the lid body and forms pockets on both sides of the fold line. For example, the resin sheet according to the present invention can be molded into the lid body of a distribution package. When a multilayer resin sheet is used as a material for the lid body of a distribution package, it is preferable to manufacture the distribution package so that the surface skin layer 11 is located on the back surface side of the lid body (the side that comes into contact with food) and the underskin layer 13 is located on the front surface side of the lid body.

[0065] Thermoforming methods for resin sheets include, but are not limited to, general vacuum forming and pressure forming, as well as applications of these, such as a plug-assisted method in which thermoforming is performed by contacting one side of a resin sheet with a plug, and a method known as matched mold forming in which thermoforming is performed by contacting both sides of a resin sheet with a pair of male and female molds, etc. Furthermore, known sheet heating methods, such as non-contact heating using an infrared heater or the like, can be used to heat and soften the resin sheet before thermoforming.

[0066] In one embodiment, the resin sheet is suitable for use in so-called form-fill-seal (FFS) packaging, which involves an integrated process of thermoforming, filling the contents, heat-sealing a cover film as a lid, and then punching out the packaging container to produce the finished product. [Example]

[0067] EXAMPLES The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the contents of the examples or the like.

[0068] <1. Preparation of resin sheet> The raw materials used in the examples and comparative examples are as follows. HIPS resin (a resin produced by graft polymerization of styrene and butadiene rubber): Product name "H850N" (Toyo Styrene Co., Ltd.), rubber median diameter: 2.8 μm, butadiene rubber content: 9.0% by mass HIPS resin (a resin produced by graft polymerization of styrene and butadiene rubber): Product name "4241" (Total Petrochemicals), rubber median diameter: 6.0 μm, butadiene rubber content: 7.0% by mass HIPS resin (a resin produced 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 GPPS resin (resin produced by homopolymerization of styrene monomer): Product name "HRM23" (Toyo Styrene Co., Ltd.) Alloy resin of HIPS resin (70% by mass) and polylactic acid resin (30% by mass) made from plant-derived materials: Product name "BM600" (Toyo Styrene Co., Ltd.), rubber median diameter in HIPS resin: 2.4 μm, butadiene rubber content in HIPS resin: 6.2% by mass, biomass content based on ASTM D6866-05: 27% by mass White pigment masterbatch: Product name "ET3627" (Nikko Bix Co., Ltd.), titanium oxide concentration in the masterbatch: 50% by mass

[0069] (Examples 1 to 8, Comparative Examples 1 and 2) Using a φ65 mm single-screw extruder (for the base layer), a φ40 mm single-screw extruder (for the skin layer), and a φ40 mm single-screw extruder (for the underskin layer), the raw materials for each layer listed in Tables 1 and 2 corresponding to the test number were melt-extruded by the feedblock method, cooled and solidified on a cooling roll, transported by a take-up machine, and wound into a roll on a winding machine. This resulted in a multilayer resin sheet having the layer structure listed in Tables 1 and 2 and measuring 30 m in the machine direction (MD) and 800 mm in the width direction (TD).

[0070] (Example 9, Comparative Examples 3 to 5) Using a φ65 mm single-screw extruder, each raw material for the base layer listed in Tables 1 and 2 corresponding to the test number was melt-extruded by the T-die method, cooled and solidified on a cooling roll, transported by a take-up machine, and wound into a roll on a winding machine. This produced a single-layer resin sheet 30 m in the machine direction (MD) and 800 mm in the width direction (TD).

[0071] <2. Characterization> The resin sheets obtained according to the examples and comparative examples were evaluated in the following manner. The results are shown in Tables 1 and 2. (A) Thickness of each layer Test pieces were cut out at five equally spaced positions across the entire width direction (TD), which is perpendicular to the machine direction (MD) of the resin sheet, and the cross-sections of the test pieces were excised using a single-edged knife, and the thickness of each layer was measured using an electron microscope. The thickness value of each layer was the average value of the thicknesses of each layer at the above five points on the resin sheet. Measuring equipment: Electron microscope KH7700 (Hirox) As a result of observation under an electron microscope during thickness measurement, it was confirmed that in all Examples and Comparative Examples, the polylactic acid resin was present in the substrate layer so as to constitute a plurality of dispersed phases. (B) Median diameter of rubber in the epidermis, base material, and subdermis layers Test pieces were cut from the resin sheet at a desired position, and the layer to be analyzed was scraped off from the test piece with a single-edged knife. The scraped sample was then dissolved and dispersed in an electrolyte (tetra-n-butylammonium / N,N-dimethylformamide). Specifically, all components except the rubber particles were dissolved in the liquid, and the rubber particles were dispersed in the liquid. The resulting dispersion was then further diluted with the same electrolyte, and the median diameter (D50) of the rubber particles in each layer was measured using a Beckman Coulter Coulter Counter (Multisizer II). (C) Content of rubber particles in the surface layer, base layer, and subskin layer (rubber content) Measurements were carried out using pyrolysis gas chromatography. Test pieces were cut out at random positions from the resin sheet, and the layers to be analyzed were scraped out of the test pieces with a single-edged knife. Next, the test pieces were placed in a pyrolysis gas chromatograph (Gas chromatograph: Shimadzu Corporation, Model GC-2010plus; Pyrolysis apparatus: Japan Analytical Industry Co., Ltd., Model JCI-22) heated to a constant high temperature, and each layer was pyrolyzed. The gas peak areas of the generated butadiene monomer and styrene monomer were determined, and the rubber content of each layer was calculated based on a calibration curve for other resins with known rubber content. (D) Biomass ratio Since no biomass is used except for the above-mentioned "BM600," the biomass degree of the entire resin sheet was calculated from the biomass degree of "BM600" and the composition of the resin sheet. (E) Folding endurance Test pieces (15 mm x 110 mm) were cut out at random positions from the resin sheet, and both ends of the test piece in the longitudinal direction were chucked and subjected to a folding strength test method conforming to JIS P8115: 2001 using an MIT testing machine. Two types of test pieces were prepared: one with the longitudinal direction in MD (labeled "MD" in the table) and one with the longitudinal direction in TD (labeled "TD" in the table), and tests were performed on each. MIT testing machine: Toyo Seiki Co., Ltd. Model MIT-D Measurement conditions: With a load (500 g) applied, the test piece was bent back and forth at an angle of 135 ± 2° to the left and right of the vertical line at a rate of 175 ± 10 times per minute, and the number of times it could be bent back and forth (folding endurance) until it broke was measured. Five test pieces were tested, and the average value was calculated. Here, the folding endurance of the resin sheet before thermoforming was evaluated, but it has been found that the folding endurance of the resin sheet before thermoforming tends to be the same as the foldability of thermoformed products that include the resin sheet. The folding endurance was evaluated according to the following three levels. 1) ◎: The number of bending times is less than 50 times in both MD and TD. 2) 〇: The number of bending times in both MD and TD was less than 300 times. And the number of bending times in at least one of MD and TD is 50 or more 3) ×: The number of bending times in at least one of MD and TD is 300 or more. (F) DuPont impact strength Test pieces measuring 100mm long x 500mm wide were prepared from the resin sheets, and the 50% fracture energy E50 (J) of these test pieces was measured using a DuPont impact tester (Yasuda Seiki Seisakusho, Model No. 517) in accordance with JIS K7211-1:2006. A weight was dropped onto the lower skin layer with a drop load of 300g, and the measurement was carried out in an environment of 23°C x 50% RH. The results were evaluated according to the following three levels. 1) ◎: E50 exceeds 3.0J 2) 〇: E50 is 2.0J or more and 3.0J or less 3) ×: E50 is less than 2.0J

[0072] [Table 1]

[0073] [Table 2]

[0074] <3. Consideration> The multilayer resin sheets of Comparative Examples 1 and 2 contain polylactic acid resin and are excellent in environmental performance. However, the multilayer resin sheets of Comparative Examples 1 and 2 had an excessive amount of butadiene rubber in the base layer, resulting in a high number of folding cycles (i.e., poor notch fold resistance). On the other hand, the multilayer resin sheets of Examples 1 to 8 had appropriate butadiene rubber content and median diameter in the base layer, and therefore contained polylactic acid resin, which gave them excellent environmental performance, low folding endurance (i.e., good notch fold resistance), and high impact strength.

[0075] The single-layer resin sheets of Comparative Examples 3 and 4 contain polylactic acid resin and are excellent in environmental performance. However, the single-layer resin sheet of Comparative Example 3 had an excessive amount of butadiene rubber in the substrate layer, which inhibited crack propagation during bending, resulting in increased folding strength. Conversely, the single-layer resin sheet of Comparative Example 4 had an insufficient amount of butadiene rubber in the substrate layer, resulting in insufficient impact strength. The single-layer resin sheet of Comparative Example 5 had a biomass content of 0% and was therefore insufficient in environmental performance. In addition, the median diameter of the butadiene rubber in the substrate layer was large, resulting in a large number of folding cycles (i.e., poor notch folding resistance). On the other hand, the content and median diameter of butadiene rubber in the base layer were both appropriate for the single-layer resin sheet of Example 9. This indicates that the single-layer resin sheet of Example 9 had excellent environmental performance, a low number of folding cycles (i.e., good notch foldability), and high impact strength.

[0076] Comparing the multilayer resin sheets of Examples 1 to 8 with the single-layer resin sheet of Example 9, it can be seen that the multilayer resin sheets of Examples 1 to 8 have improved impact resistance compared to Example 9 because they have a surface layer and a subskin layer. Furthermore, when comparing the Examples, it can be seen that Examples with a lower content of polylactic acid resin tend to have a lower number of folding cycles. [Explanation of symbols]

[0077] 10, 20 Resin sheet 11 Epidermal layer 12 Base material layer 13 Hypodermal layer 14a, 14b adhesive layer 15 Oxygen barrier layer

Claims

1. a base layer containing a polystyrene-based resin containing butadiene rubber and a polylactic acid resin; a surface layer laminated on one surface of the base layer, the surface layer containing a polystyrene-based resin containing butadiene rubber but not containing a polylactic acid resin; and an underskin layer laminated on the surface of the base layer opposite to the surface having the skin layer, the underskin layer containing a polystyrene-based resin containing butadiene rubber but not containing a polylactic acid resin; wherein the median diameter of the butadiene rubber in the base layer is less than 6 μm, the content of the butadiene rubber in the base layer is 3.0% by mass or more and 7.0% by mass or less, and the average thicknesses of the surface layer and the underskin layer are each 1% or more and 15% or less of the average total thickness of the resin sheet.

2. 2. The resin sheet according to claim 1, wherein the content of the polylactic acid resin in the base layer is 1% by mass or more and 25% by mass or less.

3. 3. The resin sheet according to claim 1, wherein in the base layer, the polylactic acid resin constitutes a plurality of dispersed phases dispersed in the polystyrene-based resin.

4. 3. The resin sheet according to claim 1, wherein the total content of the polystyrene resin and the polylactic acid resin in the base layer is 90% by mass or more.

5. 3. The resin sheet according to claim 1, having an average total thickness of 200 μm or more and 1300 μm or less.

6. 3. The resin sheet according to claim 1, wherein the substrate layer contains a white pigment in an amount of 1 phr or more and 5 phr or less.

7. The resin sheet according to claim 1 or 2, having a biomass content of 0.1% by mass or more and 20% by mass or less.

8. The resin sheet according to claim 1 or 2, having a DuPont impact strength measured in accordance with JIS K7211-1:2006 of 2.0 J or more.

9. 3. The resin sheet according to claim 1 or 2, wherein when a test piece is taken with its longitudinal direction parallel to the MD direction and subjected to a folding endurance test method in accordance with JIS P8115:2001, the number of reciprocal foldings until breakage occurs is less than 300 on average.

10. 3. The resin sheet according to claim 1 or 2, wherein when a test piece whose longitudinal direction is parallel to the TD direction is taken and subjected to a folding endurance test method in accordance with JIS P8115:2001, the number of reciprocal foldings until breakage occurs is less than 300 on average.

11. A molded container comprising the resin sheet according to claim 1 or 2.

12. The molded container according to claim 11, wherein the resin sheet has a notch formed therein.

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