Laminated sheet and food packaging container

Abstract

To provide a laminated sheet having improved poor appearance.SOLUTION: A laminated sheet includes a layer (A), and a layer (B) provided on one surface side of the layer (A), wherein the layer (B) constitutes one surface of the laminated sheet, the layer (A) contains an inorganic substance and a thermoplastic resin, the layer (B) contains a polypropylene resin and a polyethylene resin, and the polyethylene resin contains high density polyethylene.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a laminate sheet and a food packaging container. [Background technology]

[0002] In recent years, attempts have been made to reduce the amount of petroleum-derived resin components used in resin products by replacing them with biomass-derived materials and reducing the volume of the products, thereby reducing the amount of carbon dioxide emissions during incineration. One such attempt has been to incorporate more inorganic substances such as calcium carbonate than before. Inorganic substances such as calcium carbonate are cheaper to obtain than biomass-derived materials, and for example, container packaging formed from a sheet containing 50% or more inorganic substances is not classified as plastic container packaging as defined by the Container and Packaging Recycling Law, and can be disposed of as burnable or non-burnable waste, resulting in low disposal costs.

[0003] For example, Patent Document 1 discloses a multilayer resin sheet material having an intermediate layer and surface layers formed on the front and back surfaces of the intermediate layer, the surface layer being a resin layer made of a polypropylene-based resin, the intermediate layer containing calcium carbonate and a resin, and having a tensile elongation of 500% to 600%. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2021-112862 A Summary of the Invention [Problem to be solved by the invention]

[0005] According to the study by the present inventors, in the laminate sheet as described in the above Patent Document 1, air bubbles may be mixed in during the production of the laminate sheet, and the air bubbles may cause a defective appearance. Therefore, an object of one aspect of the present invention is to provide a laminate sheet with improved defective appearance. [Means for solving the problem]

[0006] As a result of extensive investigations, the present inventors have found that when the outermost layer of a laminate sheet is made of polypropylene resin, the sheet may stick to a sheet forming part (e.g., a roll) during the production of the laminate sheet, which is one of the causes of air bubbles being mixed into the laminate sheet. They have also found that by using a combination of polypropylene resin and high-density polyethylene in the outermost layer, the sticking of the sheet to the roll can be reduced, and as a result, the mixing of air bubbles can be suppressed and poor appearance can be improved.

[0007] In some aspects, the present invention provides the following [1] to

[10] . [1] A laminate sheet comprising a layer (A) and a layer (B) provided on one side of the layer (A), the layer (B) constituting one surface of the laminate sheet, the layer (A) containing an inorganic substance and a thermoplastic resin, the layer (B) containing a polypropylene resin and a polyethylene resin, the polyethylene resin containing a high-density polyethylene. [2] The laminate sheet according to [1], wherein the polyethylene resin further contains low-density polyethylene. [3] The laminate sheet according to [2], wherein the mass ratio of the high-density polyethylene content to the low-density polyethylene content is 1 or more and 3 or less. [4] The laminate sheet according to any one of [1] to [3], wherein the mass ratio of the polypropylene resin content to the polyethylene resin content is 60 / 40 or more and 80 / 20 or less. [5] The laminate sheet according to any one of [1] to [4], wherein the content of the inorganic substance is 30 mass % or more based on the total mass of the laminate sheet. [6] The laminate sheet according to any one of [1] to [5], wherein the thickness of the laminate sheet is 350 μm or more and 450 μm or less. [7] The laminate sheet according to any one of [1] to [6], further comprising a layer (C) provided on the other side of the layer (A) and constituting the other surface of the laminate sheet, the layer (C) containing a polypropylene resin and a polyethylene resin. [8] The laminate sheet according to any one of [1] to [7], which is used for forming a food packaging container. [9] A laminate sheet according to any one of [1] to [8], which is used for vacuum forming.

[10] A food packaging container formed from the laminate sheet according to any one of [1] to [9]. Effect of the Invention

[0008] According to one aspect of the present invention, it is possible to provide a laminate sheet with improved appearance defects. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic cross-sectional view showing one embodiment of a laminate sheet. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing another embodiment of the laminate sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments.

[0011] Fig. 1 is a schematic cross-sectional view showing one embodiment of a laminate sheet. The laminate sheet 1 shown in Fig. 1 includes a layer (A) 11 and a layer (B) 12 provided on one side of the layer (A) 11. In the laminate sheet 1, the layer (B) 12 constitutes one surface of the laminate sheet 1.

[0012] <Layer(A)> The layer (A) 11 contains an inorganic material and a thermoplastic resin. In the layer (A) 11, the inorganic material may be dispersed in the thermoplastic resin.

[0013] Examples of inorganic substances include metal salts, oxides, hydroxides, and hydrates thereof, as well as elemental metals, which may be calcium, magnesium, sodium, barium, aluminum, titanium, iron, zinc, molybdenum, and the like.

[0014] Examples of metal salts include metal carbonates, sulfates, sulfites, silicates, phosphates, and borates, as well as titanates. Examples of metal carbonates include calcium carbonate, magnesium carbonate, dolomite, and hydrotalcite. Examples of metal sulfates include calcium sulfate, magnesium sulfate, sodium sulfate, barium sulfate, and aluminum sulfate. Examples of metal sulfites include calcium sulfite. Examples of metal silicates include calcium silicate, magnesium silicate, aluminum silicate, talc, clay, bentonite, kaolin, zeolite, sericite, and mica. Examples of metal phosphates include calcium phosphate, magnesium phosphate, and aluminum phosphate. Examples of titanates include potassium titanate and calcium titanate.

[0015] Examples of metal oxides include magnesium oxide, alumina, titanium oxide, and zinc oxide. Examples of metal hydroxides include magnesium hydroxide and aluminum hydroxide.

[0016] Other examples of inorganic substances include silica (quartz sand), diatomaceous earth, pumice, shirasu, glass beads, glass flakes, glass fibers, boron fibers, carbon fibers, carbon black, graphite, etc. The layer (A) 11 may contain only one type of the inorganic substances described above, or may contain two or more types.

[0017] The inorganic substance may be, for example, particulate. The average particle size of the particulate inorganic substance may be 0.1 μm or more, 0.3 μm or more, or 0.5 μm or more, and may be 15 μm or less, 13 μm or less, 10 μm or less, or 8 μm or less. In this specification, the average particle size means the median size measured by a laser diffraction method.

[0018] The content of the inorganic substance may be 30% by mass or more, 40% by mass or more, 50% by mass or more, or 60% by mass or more, and may be 90% by mass or less, 85% by mass or less, or 80% by mass or less, based on the total mass of layer (A) 11.

[0019] Examples of the thermoplastic resin include polyolefin resin, polyester resin, polystyrene resin, polyamide resin, ABS resin, etc. The thermoplastic resin in the layer (A) 11 may contain only one of these, or may contain two or more of these. Examples of the polyolefin resin include polypropylene resin and polyethylene resin. The thermoplastic resin in the layer (A) 11 preferably contains polypropylene resin. As the polypropylene resin and polyethylene resin in the layer (A) 11, those described below as the polypropylene resin and polyethylene resin in the layer (B) 12 can be used without any particular limitation.

[0020] When the thermoplastic resin in layer (A) 11 contains a polypropylene resin, the content of the polypropylene resin may be 80 parts by mass or more, 90 parts by mass or more, 95 parts by mass or more, or 98 parts by mass or more, relative to 100 parts by mass of the total thermoplastic resins contained in layer (A) 11, or may be 100 parts by mass or less.

[0021] The content of the thermoplastic resin in the layer (A) 11 may be 10 mass% or more, 20 mass% or more, or 25 mass% or more, and may be 70 mass% or less, 60 mass% or less, 50 mass% or less, 40 mass% or less, or 35 mass% or less, based on the total mass of the layer (A) 11.

[0022] The layer (A) 11 may contain other components in addition to the inorganic material and the thermoplastic resin, such as a colorant, a lubricant, a dispersant, an antistatic agent, an antioxidant, a heat stabilizer, and an ultraviolet absorbing agent.

[0023] In the layer (A) 11, the content of other components may be, for example, 10 mass % or less, 5 mass % or less, 3 mass % or less, or 1 mass % or less, based on the total mass of the layer (A) 11.

[0024] The thickness of layer (A) 11 may be 100 μm or more, 150 μm or more, 200 μm or more, 230 μm or more, 250 μm or more, or 270 μm or more, and may be 500 μm or less, 450 μm or less, 400 μm or less, or 350 μm or less. In this specification, the thickness of the layers constituting the laminate sheet and the thickness of the entire laminate sheet refer to values ​​measured using a micrometer in accordance with JIS K7130:1999.

[0025] The thickness of layer (A) 11 may be 50% or more, 60% or more, 65% or more, or 70% or more, and may be 99% or less, 95% or less, 90% or less, 80% or less, or 75% or less, of the total thickness of the laminate sheet taken as 100%.

[0026] <Layer (B)> The layer (B) 12 contains polypropylene resin and polyethylene resin. When the layer constituting the surface of the laminate sheet contains only polypropylene resin, the sheet may stick to the parts for sheet molding during the production of the laminate sheet. More specifically, during the production of the laminate sheet, the layer-constituting material in a molten state extruded from an extruder into a sheet shape is cooled while passing through a plurality of rolls to obtain a sheet molded to a predetermined thickness, and the sheet may stick to the rolls. However, the layer (B) 12 contains polyethylene resin in addition to polypropylene resin. As a result, the surface roughness of the surface of the laminate sheet 1 (the surface constituted by the layer (B) 12) is larger than when the layer (B) 12 contains only polypropylene resin. In particular, since the polyethylene resin in the layer (B) contains high density polyethylene, the surface roughness of the surface of the laminate sheet 1 is larger than when the polyethylene resin in the layer (B) does not contain high density polyethylene but contains low density polyethylene. Therefore, the sticking of the sheet to the parts for sheet molding (rolls, etc.) during the production of the laminate sheet 1 is suppressed. As a result, the inclusion of air bubbles in the laminate sheet 1 is suppressed, and the appearance defect of the laminate sheet 1 is improved. Furthermore, since the layer (B) 12 contains a polyethylene resin in addition to a polypropylene resin, the laminate sheet 1 also has excellent cold resistance, compared to a case in which the layer (B) 12 contains only a polypropylene resin.

[0027] The polypropylene resin is a polymer mainly containing propylene as a monomer unit. The melting point of the polypropylene resin may be 150° C. or higher, and more preferably 160° C. or higher. The polypropylene resin may be a homopolymer of propylene, or a copolymer of propylene and another monomer copolymerizable with propylene (polypropylene copolymer).

[0028] Examples of other monomers copolymerizable with propylene include α-olefins other than propylene. The α-olefins other than propylene may be, for example, an α-olefin having 2 carbon atoms (ethylene) or an α-olefin having 4 to 10 carbon atoms. Examples of the α-olefins having 4 to 10 carbon atoms include 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, 1-nonene, and 1-decene.

[0029] The polypropylene copolymer may be, for example, a binary copolymer or a terpolymer. An example of a binary copolymer is an ethylene-propylene copolymer. An example of a terpolymer is an ethylene-propylene-1-butene copolymer. These copolymers may be random copolymers or block copolymers.

[0030] The content of propylene (propylene unit) in the polypropylene resin may be more than 50% by mass based on the total mass of the polypropylene resin. From the viewpoint of excellent rigidity and heat resistance of the laminated sheet (and food packaging containers formed from the laminated sheet), the content of propylene (propylene unit) in the polypropylene resin may be 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more based on the total mass of the polypropylene resin. In particular, the polypropylene resin is preferably a homocopolymer of propylene.

[0031] The melt mass flow rate (MFR) of the polypropylene resin may be 1.0 g / 10 min or more, 1.4 g / 10 min or more, or 1.6 g / 10 min or more, and may be 3.0 g / 10 min or less, or 2.5 g / 10 min or less. In this specification, MFR means a value measured according to JIS K7210-1:2014 A method at a test temperature of 230°C and a nominal load of 2.16 kg.

[0032] The melt tension of the polypropylene resin at 210° C. may be 10 mN or more, 15 mN or more, or 20 mN or more, and may be 60 mN or less, 50 mN or less, 40 mN or less, 30 mN or less, or 25 mN or less. In this specification, the melt tension at 210° C. (hereinafter, simply referred to as "melt tension") means a value measured using a Capillograph (e.g., 1D, Toyo Seiki Seisakusho Co., Ltd.) at a test temperature of 210° C., a cylinder extrusion speed of 20 mm / min, and a take-up speed of 5 m / min.

[0033] The content of polypropylene resin in layer (B) 12 may be 10% by mass or more, 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, or 55% by mass or more, based on the total mass of layer (B) 12, from the viewpoint of excellent rigidity and heat resistance of the laminate sheet (and food packaging containers formed from the laminate sheet), and may be 99% by mass or less, 95% by mass or less, 92% by mass or less, or 90% by mass or less, from the viewpoint of improving the impact resistance of food packaging containers formed from the laminate sheet.

[0034] The polyethylene resin is a polymer mainly containing ethylene as a monomer unit. The melting point of the polyethylene resin may be less than 150°C, and more preferably is 140°C or less. Examples of the polyethylene resin include high density polyethylene (HDPE), medium density polyethylene (MDPE), low density polyethylene (LDPE), and linear low density polyethylene (LLDPE). The polyethylene resin in the layer (B) 12 includes at least high density polyethylene (HDPE).

[0035] HDPE is 0.942g / cm 3 MDPE is a polyethylene with a density of 0.930 g / cm or more. 3 More than 0.942g / cm 3 LDPE is polyethylene with a density of less than 0.910 g / cm 3 More than 0.930g / cm 3 LLDPE is a polyethylene with a density of less than 0.911 g / cm3 and a long chain branching structure. 3More than 0.940g / cm 3 It is a polyethylene having a density of less than 100% and having no long chain branching structure. The density of polyethylene is determined from the specific gravity measured under standard conditions in accordance with JIS K7112:1999 Method A.

[0036] The melting point of LDPE may be 95°C or higher and 115°C or lower. The melting point of LLDPE may be 115°C or higher and 125°C or lower. LDPE may have a side chain with 6 or more carbon atoms, and LLDPE may not have a side chain with 6 or more carbon atoms. The presence or absence of a side chain with 6 or more carbon atoms is 13 This can be confirmed by C-NMR measurement.

[0037] The MFR of the HDPE may be 0.1 g / 10 min or more, 0.2 g / 10 min or more, or 0.3 g / 10 min or more, and may be 1.5 g / 10 min or less, 1.0 g / 10 min or less, 0.8 g / 10 min or less, or 0.6 g / 10 min or less.

[0038] The melt tension of the HDPE may be 40 mN or more, 50 mN or more, or 60 mN or more, and may be 110 mN or less, 100 mN or less, 90 mN or less, 80 mN or less, or 70 mN or less.

[0039] The MFR of the LDPE may be 0.3 g / 10 min or more, 0.5 g / 10 min or more, or 0.8 g / 10 min or more, and may be 2.0 g / 10 min or less, 1.5 g / 10 min or less, or 1.0 g / 10 min or less.

[0040] The melt tension of the LDPE may be 100 mN or more, 110 mN or more, or 115 mN or more, and may be 140 mN or less, 130 mN or less, or 125 mN or less.

[0041] The polyethylene resin (such as HDPE or LDPE) may be a homopolymer of ethylene, or a copolymer of ethylene and another monomer copolymerizable with ethylene (polyethylene copolymer).

[0042] Examples of other monomers copolymerizable with ethylene include α-olefins other than ethylene and vinyl acetate. The α-olefin may be, for example, an α-olefin having 3 to 10 carbon atoms. Examples of the α-olefin having 3 to 10 carbon atoms include propylene, 1-butene, isobutylene, 1-pentene, 3-methyl-1-butene, 1-hexene, 3,4-dimethyl-1-butene, 1-heptene, 3-methyl-1-hexene, 1-octene, 1-nonene, and 1-decene.

[0043] Examples of polyethylene copolymers include ethylene-vinyl acetate copolymers, ethylene-propylene copolymers, ethylene-propylene-1-butene copolymers, ethylene-1-butene copolymers, ethylene-1-hexene copolymers, ethylene-4 methyl-1-pentene copolymers, and ethylene-1-octene copolymers.

[0044] The HDPE content in layer (B) 12 may be 5 mass % or more, 8 mass % or more, 10 mass % or more, or 12 mass % or more, based on the total mass of layer (B) 12, from the viewpoint of improving the impact resistance of the laminate sheet (and food packaging containers formed from the laminate sheet), and may be 50 mass % or less, 40 mass % or less, 30 mass % or less, 25 mass % or less, or 23 mass % or less, from the viewpoint of excellent rigidity and heat resistance of the laminate sheet (and food packaging containers formed from the laminate sheet).

[0045] The polyethylene resin in the layer (B) 12 may contain only HDPE, or may further contain other polyethylene resins other than HDPE. Examples of other polyethylene resins other than HDPE include the above-mentioned LDPE, MDPE, and LLDPE.

[0046] In one embodiment, the polyethylene resin in layer (B) 12 may further contain LDPE. The MER and melt tension of the LDPE may be within the numerical ranges described above for the MER and melt tension of the LDPE that may be contained in layer (A) 11. In one embodiment, the polyethylene resin in layer (B) 12 may contain only HDPE and LDPE (i.e., it may not contain MDPE and LLDPE).

[0047] The LDPE content in layer (B) 12 may be 5% by mass or more, 8% by mass or more, 10% by mass or more, or 12% by mass or more, based on the total mass of layer (B) 12, from the viewpoint of improving the uniformity of the thickness of the laminate sheet and the moldability when forming a container, and may be 50% by mass or less, 40% by mass or less, 30% by mass or less, 25% by mass or less, or 23% by mass or less, from the viewpoint of excellent rigidity and heat resistance of the laminate sheet (and food packaging containers formed from the laminate sheet).

[0048] In layer (B) 12, the mass ratio of the HDPE content to the LDPE content (HDPE content / LDPE content) may be 0.8 or more, 0.9 or more, or 1 or more, from the viewpoint of improving the uniformity of the thickness of the laminate sheet and the moldability during container molding, and may be, for example, 5 or less, 4 or less, 3 or less, or 2.5 or less.

[0049] The content of the polyethylene resin in layer (B) 12 (when multiple types of polyethylene are contained, the total content of them) may be 10 mass % or more, 14 mass % or more, 18 mass % or more, 22 mass % or more, or 25 mass % or more, based on the total mass of layer (B) 12, from the viewpoint of improving the impact resistance of a food packaging container obtained by molding the laminate sheet, and may be 60 mass % or less, 50 mass % or less, 40 mass % or less, or 35 mass % or less, from the viewpoint of excellent rigidity and heat resistance of the laminate sheet (and food packaging containers obtained by molding the laminate sheet).

[0050] In layer (B) 12, the mass ratio of the polypropylene resin content to the polyethylene resin content (polypropylene resin content / polyethylene resin content) may be 50 / 50 or more, 55 / 45 or more, 60 / 40 or more, 64 / 36 or more, or 67 / 33 or more, from the viewpoint of excellent rigidity and heat resistance of the laminate sheet (and food packaging containers formed from the laminate sheet), and may be 90 / 10 or less, 80 / 20 or less, 75 / 25 or less, or 72 / 28 or less, from the viewpoint of improving the impact resistance of the food packaging containers formed from the laminate sheet and further improving poor appearance of the laminate sheet (and food packaging containers formed from the laminate sheet).

[0051] The layer (B) 12 may contain a thermoplastic resin other than a polyethylene resin and a polypropylene resin. Examples of the other thermoplastic resin include an olefin resin other than a polyethylene resin and a polypropylene resin, a polyester resin, a polystyrene resin, a polyamide resin, an ABS resin, and the like.

[0052] When layer (B) 12 contains a thermoplastic resin other than a polyethylene resin and a polypropylene resin, the content of the other thermoplastic resin may be, for example, 10 mass% or less, 5 mass% or less, 3 mass% or less, or 1 mass% or less, based on the total mass of layer (B) 12.

[0053] The layer (B) 12 may be made of a thermoplastic resin, or may contain other components other than the thermoplastic resin, such as colorants, lubricants, dispersants, antistatic agents, antioxidants, heat stabilizers, and ultraviolet absorbing agents.

[0054] The content of other components may be, for example, 10 mass % or less, 5 mass % or less, 3 mass % or less, or 1 mass % or less based on the total mass of the layer (B) 12.

[0055] Layer (B) 12 may not contain an inorganic substance. Layer (B) 12 containing no inorganic substance means that layer (B) 12 does not contain any inorganic substance at all, or layer (B) 12 contains only inorganic substances as unavoidable impurities. Layer (B) 12 may contain an inorganic substance. From the viewpoint of further improving the acid resistance and safety of the laminated sheet (and the food packaging container formed from the laminated sheet), the content of the inorganic substance in layer (B) 12 may be 10 mass % or less, 5 mass % or less, 3 mass % or less, or 1 mass % or less based on the total mass of layer (B) 12.

[0056] The thickness of layer (B) 12 may be 2 μm or more, 5 μm or more, 10 μm or more, 20 μm or more, 30 μm or more, 40 μm or more, or 50 μm or more, and may be 100 μm or less, 80 μm or less, 70 μm or less, or 60 μm or less.

[0057] The thickness of layer (B) 12 may be 1% or more, 2% or more, 3% or more, 5% or more, 10% or more, or 13% or more, and may be 50% or less, 40% or less, 30% or less, or 20% or less, relative to the total thickness of the laminate sheet being 100%.

[0058] 1 is composed of two layers, a layer (A) and a layer (B) provided on one side of the layer (A), but the configuration of the laminate sheet is not limited to this. The laminate sheet may be composed of three or more layers.

[0059] Fig. 2 is a schematic cross-sectional view showing another embodiment of the laminate sheet. The laminate sheet 2 shown in Fig. 2 includes a layer (A) 11, a layer (B) 12 provided on one side of the layer (A) 11, and a layer (C) 13 provided on the other side of the layer (A) 11. In the laminate sheet 2, the layer (B) 12 constitutes one surface of the laminate sheet 2, and the layer (C) 13 constitutes the other surface of the laminate sheet 2.

[0060] The composition and thickness of the layer (C) 13 are not particularly limited. The layer (C) 13 may be, for example, a layer containing a polypropylene resin and a polyethylene resin. As the polypropylene resin and the polyethylene resin, the polypropylene resin and the polypropylene resin described above for the layer (B) 12 can be used without any particular limitation. The layer (C) 13 may or may not contain an inorganic substance. The layer (C) 13 may have the same composition and thickness as the layer (B) 12.

[0061] Layer (C) 13 may also be a layer containing a thermoplastic resin and an inorganic substance. Details of the thermoplastic resin and the inorganic substance may be the same as those described above for the thermoplastic resin and the inorganic substance contained in layer (A) 11. In this case, layer (C) 13 may have a composition (type and content of thermoplastic resin and inorganic substance) different from that of layer (A) 11. The thermoplastic resin in layer (C) 13 may include, for example, a polypropylene resin and a polyethylene resin.

[0062] The laminate sheet composed of three layers is not limited to the laminate sheet 2 shown in FIG. 2. For example, in a laminate sheet composed of three layers, the layer (B) may constitute one surface of the laminate sheet, and the layer (A) may constitute the other surface of the laminate sheet. In this case, the laminate sheet includes an intermediate layer, a layer (B) provided on one surface of the intermediate layer, and a layer (A) provided on the other surface of the intermediate layer. The intermediate layer may be, for example, a layer made of polypropylene resin, or a layer containing polypropylene resin, polyethylene resin, and an inorganic substance. When the intermediate layer is a layer containing polypropylene resin, polyethylene resin, and an inorganic substance, the intermediate layer may have a composition (type and content of resin and inorganic substance) different from that of the layer (A) 11. The details of the polypropylene resin, polyethylene resin, and inorganic substance may be the same as those described above as the thermoplastic resin and inorganic substance contained in the layer (A) 11.

[0063] In another embodiment, the laminate sheet may be composed of four or more layers. In this case, the laminate sheet includes a layer (A) and a layer (B) constituting one surface of the laminate sheet, as well as a plurality of other layers.

[0064] A specific example of a four-layer laminate sheet is a laminate sheet including a layer (A), a layer (B) provided on one side of the layer (A) and constituting one surface of the laminate sheet, a layer (D) provided on the other side of the layer (A), and a layer (C) provided on the surface of the layer (D) opposite to the layer (A) and constituting the other surface of the laminate sheet. The layer (D) in this laminate sheet may contain, for example, a thermoplastic resin and an inorganic substance. The details of the thermoplastic resin and the inorganic substance may be the same as those described above for the thermoplastic resin and the inorganic substance contained in the layer (A). The layer (D) may have a composition (type and content of the thermoplastic resin and the inorganic substance) different from that of the layer (A).

[0065] In the laminate sheet of each of the above embodiments, the content of the inorganic substance may be 10 mass% or more, 20 mass% or more, 30 mass% or more, 40 mass% or more, or 50 mass% or more, based on the total mass of the laminate sheet, and may be 80 mass% or less, 70 mass% or less, or 65 mass% or less.

[0066] The thickness of the laminate sheet in each of the above embodiments may be 200 μm or more, 300 μm or more, or 350 μm or more, and may be 500 μm or less, or 450 μm or less.

[0067] The density of the laminated sheet in each of the above embodiments is 1.0 g / cm 3 or more than 1.2g / cm 3 or more, and 3 or less than 1.8g / cm 3 It may be the following:

[0068] The impact strength of the laminate sheet of each of the above embodiments may be 3.0 J / mm or more, 3.5 J / mm or more, or 4.0 J / mm or more, and may be 10.0 J / mm or less, 8.0 J / mm or less, or 6.0 J / mm or less. In this specification, the impact strength of the laminate sheet means a value obtained according to ASTM-D3420.

[0069] The laminated sheet described above can be produced, for example, by a multi-layer T-die method. Specifically, it can be produced by a method including a step of preparing the material of layer (A), the material of layer (B), and, if necessary, the material of other layers such as layer (C), and a step of melting the materials of each layer and co-extruding them to obtain a laminated sheet.

[0070] The laminate sheet according to one embodiment includes a layer (A) containing an inorganic substance, so that the environmental impact when the laminate sheet (and the food packaging container formed from the laminate sheet) is small when it is disposed of. Furthermore, at least one surface of the laminate sheet is composed of a layer (B) containing a polypropylene resin and a polyethylene resin, so that appearance defects are improved. Therefore, the laminate sheet according to one embodiment is particularly suitable as a food packaging material such as a food packaging container. The laminate sheet may be one used for forming a food packaging container.

[0071] Another embodiment of the present invention is a food packaging container formed by molding a laminated sheet. A known method can be adopted as a method for producing a food packaging container from a laminated sheet, and for example, a thermoforming method such as a vacuum forming method or a pressure forming method can be used. The laminated sheet may be one used for vacuum forming. EXAMPLES

[0072] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0073] [Laminated sheet manufacturing] <Material> In the examples and comparative examples, the materials shown below were used. Calcium carbonate: Calcium carbonate particles (average particle size: 0.7 to 6.0 μm) PP: Homopolypropylene resin (pellet type, MFR: 1.8g / 10min, melt tension: 22mN) HDPE: High density polyethylene (pellet form, density: 0.96 g / cm 3 , MFR: 0.4g / 10min, Melt tension: 64mN) LDPE: Low-density polyethylene (pellet type, density: 0.92 g / cm 3 , Melting point: 110℃, MFR: 0.9g / 10min, Melt tension: 120mN) The MFR and melt tension were measured by the following methods.

[0074] (Melt Mass Flow Rate (MFR) Measurement) The MFR was measured using a melt indexer (G-02, manufactured by Toyo Seiki Seisakusho Co., Ltd.) in accordance with JIS K7210-1:2014 Method A at a test temperature of 230°C and a nominal load of 2.16 kg.

[0075] (Melt tension measurement) The melt tension was measured using a Capillograph (1D, Toyo Seiki Seisakusho Co., Ltd.). A capillary with a diameter of 2.0 mm and a length of 20 mm (L / D=20 / 2) and a cylinder with an aperture of 9.55 mm were used for the measurement. The test temperature was 210°C, the cylinder extrusion speed was 20 mm / min, and the take-up speed was 5 m / min.

[0076] <Masterbatch production> A master batch was prepared by melt-kneading PP (20.0% by mass) and calcium carbonate particles (80.0% by mass) at 230°C using a twin-screw kneader (Shibaura Machine Co., Ltd., TEM-35B), extruding the mixture into strands, and pelletizing the mixture. The MFR of the obtained master batch, as measured by the above method, was 0.2 g / 10 min. The melt viscosity was measured using a Toyo Seiki Co., Ltd. Capillograph, using a capillary with a diameter of 2.0 mm and a length of 20 mm and a cylinder with an aperture of 9.55 mm, at a measurement temperature of 230°C and a cylinder extrusion speed of 10 mm / min, and was found to be 11.4 kPa s.

[0077] <Examples 1 to 6 and Comparative Examples 1, 3, and 4> As the material for layer (A), a master batch and PP were hand-blended so that the compounding ratio of PP to calcium carbonate was the value shown in Table 1. For example, in Example 1, 87.5 mass% of the master batch and 12.5 mass% of PP were hand-blended. In addition, as the material for layer (B) and layer (C), a hand-blended material of each component was prepared at the compounding ratio shown in Table 1. Using a 40 mmφ single-screw extruder for producing layer (A), a 40 mmφ single-screw extruder for producing layers (B) and (C), and a two-kind three-layer feed block, each molten material was laminated, and three-layer co-extrusion molding was performed using a coat hanger die to produce a laminated sheet in which layers (B), (A), and (C) were laminated in this order. The thickness ratio of each layer was adjusted by adjusting the screw rotation speed of the extruder for producing each layer. The thickness of the entire laminated sheet obtained was 400 μm. The thickness of layer (A) was 280 μm (70% of the total thickness of the laminate sheet), and the thicknesses of layers (B) and (C) were each 60 μm (15% of the total thickness of the laminate sheet). The calcium carbonate content based on the total mass of the laminate sheet was as shown in Table 1.

[0078] <Example 7> As the material for layer (A), a hand blend of master batch and PP was prepared so that the compounding ratio of PP to calcium carbonate was the value shown in Table 1. As the material for layer (B), a hand blend of each component was prepared at the compounding ratio shown in Table 1. A laminated sheet in which layers (B) and (A) were laminated in this order was produced by using a 2-kind 2-layer feed block instead of a 2-kind 3-layer feed block, and by the same procedure as in Example 1 above. The thickness ratio of each layer was adjusted by adjusting the screw rotation speed of the extruder that produced each layer. The thickness of the entire laminated sheet obtained was 400 μm. The thickness of layer (A) was 280 μm (70% of the thickness of the entire laminated sheet), and the thickness of layer (B) was 120 μm (30% of the thickness of the entire laminated sheet). The content of calcium carbonate based on the total mass of the laminated sheet was as shown in Table 1.

[0079] <Example 8 and Comparative Examples 2 and 5> As the materials for layers (A) and (D), a hand blend of master batch and PP was prepared so that the PP content and calcium carbonate content were the values ​​shown in Table 1. As the materials for layers (B) and (C), hand blends of each component were prepared in the compounding ratios shown in Table 1. A laminated sheet was produced in which layers (B), (A), (D), and (C) were laminated in this order using a 4-kind 4-layer feed block instead of a 2-kind 3-layer feed block, in the same procedure as in Example 1 above. The thickness ratio of each layer was adjusted by adjusting the screw rotation speed of the extruder that produced each layer. The thickness of the entire laminated sheet obtained was 400 μm. The thickness of layer (B) was 56 μm (14% of the total thickness of the laminate sheet), the thickness of layer (A) was 280 μm (70% of the total thickness of the laminate sheet), the thickness of layer (D) was 56 μm (14% of the total thickness of the laminate sheet), and the thickness of layer (C) was 8 μm (2% of the total thickness of the laminate sheet). The calcium carbonate content based on the total mass of the laminate sheet was as shown in Table 1.

[0080] <Density measurement> The density of the laminated sheets of Examples 1 to 8 and Comparative Examples 1 to 5 was measured in accordance with JIS K7112:1999 Method A under the standard conditions defined in JIS K 7100:1999. The results are shown in Table 1.

[0081] <Evaluation of appearance defects (surface roughness)> The surface of each of the laminated sheets of Examples 1 to 8 and Comparative Examples 1 to 5 was observed in a range of 0.95 mm x 0.95 mm using a confocal laser scanning microscope (OLS4000, manufactured by Olympus Corporation). In the roughness curve obtained with a cutoff period λc = 0.8 mm and λs = 2.5 μm, a reference length (L) was cut out in the direction of the average line, and the roughness curve was expressed as y = f(x) by taking the x-axis in the direction of the average line of the cut out portion and the y-axis in the direction of the longitudinal magnification, and the arithmetic mean roughness Ra was calculated by the following formula. The reference length (L) was set to 1 mm.

number

[0082] [Table 1]

[0083] <Impact resistance measurement> The impact strength of the laminated sheets of Examples 1 to 8 was measured. Measurement samples were prepared by cutting each of the laminated sheets of Examples 1 to 8 into 70 mm x 70 mm pieces. The impact strength of each measurement sample was measured using a film impact tester in accordance with ASTM-D3420. The results are shown in Table 2.

[0084] [Table 2] [Explanation of symbols]

[0085] 1,2...laminated sheet, 11...layer (A), 12...layer (B), 13...layer (C).

Claims

1. A laminated sheet comprising a layer (A) and a layer (B) provided on one side of the layer (A), The layer (B) constitutes one surface of the laminate sheet, The layer (A) contains an inorganic substance and a thermoplastic resin, The layer (B) contains a polypropylene resin and a polyethylene resin, The polyethylene resin comprises high density polyethylene.

2. The laminate sheet of claim 1 , wherein the polyethylene resin further comprises a low density polyethylene.

3. 3. The laminate sheet according to claim 2, wherein a mass ratio of a content of the high density polyethylene to a content of the low density polyethylene is 1 or more and 3 or less.

4. 2. The laminate sheet according to claim 1, wherein a mass ratio of a content of the polypropylene resin to a content of the polyethylene resin is 60 / 40 or more and 80 / 20 or less.

5. The laminate sheet according to claim 1 , wherein the content of the inorganic substance is 30% by mass or more based on the total mass of the laminate sheet.

6. The laminate sheet according to claim 1 , wherein the thickness of the laminate sheet is 350 μm or more and 450 μm or less.

7. Further comprising a layer (C) provided on the other side of the layer (A) and constituting the other surface of the laminate sheet, The laminate sheet according to claim 1 , wherein the layer (C) comprises a polypropylene resin and a polyethylene resin.

8. The laminate sheet according to any one of claims 1 to 7, which is used for forming a food packaging container.

9. The laminate sheet according to any one of claims 1 to 7, which is used for vacuum forming.

10. A food packaging container formed from the laminate sheet according to any one of claims 1 to 7.

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