Multilayer resin sheet and molded container

Abstract

To provide a multilayer resin sheet that can be molded into a molded article that has an oxygen barrier property and excellent rupture resistance that allows suppression of a content leakage phenomenon that possibly occurs due to rupture of a resin layer constituting a packaging container by a weight due to stacking and the like, and provide a molded container comprising the multilayer resin sheet.SOLUTION: A multilayer resin sheet comprises a top layer, an oxygen barrier layer, a substrate layer, and a bottom layer in this order. The oxygen barrier layer is laminated with the top layer and the substrate layer via adhesive layers. The substrate layer and the bottom layers are layers comprising a polystyrene-based resin. The top layer comprises a mixture of low density polyethylene and high density polyethylene, where the proportion of the high density polyethylene relative to a total of the low density polyethylene and the high density polyethylene is 30 mass% or higher and 70 mass% or lower. The thickness of the top layer relative to the whole of the multilayer resin sheet is 5-40%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermoplastic multilayer resin sheet and a molded container including the same. [Background technology]

[0002] In recent years, food packaging containers have generally been manufactured by molding multilayer resin sheets in order to prevent quality deterioration of food due to deterioration of freshness caused by gases such as oxygen, nitrogen, carbon dioxide, and water vapor that permeate from the inside and outside of the packaging container. It has been known that the multilayer resin sheet is provided with an ethylene-vinyl alcohol copolymer resin layer to impart oxygen barrier properties that block oxygen permeation, or a polyolefin resin layer to impart water vapor barrier properties that block water vapor permeation (Patent Documents 1 to 5). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-58619 [Patent Document 2] Japanese Patent Application Publication No. 11-138705 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-112392 [Patent Document 4] Japanese Patent Application Laid-Open No. 2000-108287 [Patent Document 5] Japanese Patent Application Publication No. 2018-12263 Summary of the Invention [Problem to be solved by the invention]

[0004] Some food packaging containers have connecting portions that connect multiple container bodies, and slits (hereinafter referred to as "notches") formed in the connecting portions to separate the individual container bodies. There are also so-called distribution packages, in which a notch is formed in the lid to allow the food packaged inside the packaging container to be discharged to the outside of the packaging container. However, when a notch is formed in a molded product formed using the multilayer resin sheets disclosed in Patent Documents 1 to 5, there is a problem that the folding characteristics, which are important when folding the notch, are poor. Furthermore, when the multilayer resin sheets disclosed in Patent Documents 1 to 5 are molded into food packaging containers and used, there is a problem that if the food packaging products are exposed to an environment in which they are transported, for example, an environment in which they are stacked and subjected to a load during transportation, a portion of the resin layer that constitutes the packaging container may rupture, causing the packaged food to leak.

[0005] The present invention has been made in view of the problems in the prior art described above, and an object of the present invention is to provide, in one embodiment, a multilayer resin sheet that has oxygen barrier properties and can be formed into a molded article having excellent notch foldability, that is, when the packaging container is manually separated into individual container bodies or when packaged food is discharged from the container through a notch formed in the packaging container, regardless of the speed at which the notch is folded, and a molded container including the same. In another embodiment, the present invention has an object to provide, in another embodiment, a multilayer resin sheet that has oxygen barrier properties and can be formed into a molded article having excellent rupture resistance that can suppress content leakage that may occur when the resin layers constituting the packaging container are ruptured due to loads such as those caused by stacking, and a molded container including the same. [Means for solving the problem]

[0006] [1] A multilayer resin sheet having a laminated structure in which a surface layer, an oxygen barrier layer, a base layer, and an underskin layer are laminated in this order, the oxygen barrier layer is laminated on the surface layer and the base layer via an adhesive layer; A multilayer resin sheet in which the base layer and the underskin layer are layers containing a polystyrene resin and a plurality of rubber particles dispersed in the resin, and the average particle size of the rubber particles contained in the base layer and the underskin layer is less than 6 μm. [2] The multilayer resin sheet according to [1], wherein the base layer and the underskin layer each contain less than 7 mass % of rubber particles relative to the total mass of the polystyrene resin and the rubber particles. [3] The multilayer resin sheet according to [1] or [2], wherein the surface layer contains a mixture of low-density polyethylene and high-density polyethylene. [4] The multilayer resin sheet according to [3], wherein the ratio of the high-density polyethylene to the total mass of the low-density polyethylene and the high-density polyethylene in the surface layer is 30% by mass or more and 70% by mass or less. [5] The density of a mixture of low-density polyethylene and high-density polyethylene is 0.91 to 0.97 g / cm 3 The multilayer resin sheet according to [3] or [4], [6] The multilayer resin sheet according to any one of [1] to [5], wherein the surface layer has a thickness of 5 to 40% of the entire multilayer resin sheet. [7] The multilayer resin sheet according to any one of [1] to [6], wherein the underlayer contains 0.04 phr or more and 0.50 phr or less of a pigment suitable for laser marking. [8] The multilayer 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 multilayer resin sheet according to any one of [1] to [8], wherein the multilayer resin sheet has an overall thickness of 100 to 1300 μm.

[10] A molded container comprising the multilayer resin sheet according to any one of [1] to [9].

[11] A multilayer resin sheet having a laminated structure in which a surface layer, an oxygen barrier layer, a base layer, and an underskin layer are laminated in this order, the oxygen barrier layer is laminated on the surface layer and the base layer via an adhesive layer; The base layer and the underskin layer are layers containing a polystyrene-based resin, The surface layer contains a mixture of low-density polyethylene and high-density polyethylene, and the ratio of the high-density polyethylene to the total mass of the low-density polyethylene and the high-density polyethylene is 30% by mass or more and 70% by mass or less, and has a thickness of 5 to 40% of the entire multilayer resin sheet. Multi-layer resin sheet.

[12] The density of a mixture of low-density polyethylene and high-density polyethylene is 0.91 to 0.97 g / cm 3 The multilayer resin sheet according to

[11] ,

[13] The multilayer resin sheet according to

[11] or

[12] , wherein the base layer and the underskin layer are layers containing a polystyrene resin and a plurality of rubber particles dispersed in the resin, and the average particle size of the rubber particles contained in the base layer and the underskin layer is less than 6 μm.

[14] The multilayer resin sheet according to any one of

[11] to

[13] , wherein the base layer contains less than 7 mass % of rubber particles relative to the total mass of the polystyrene resin and the rubber particles.

[15] The multilayer resin sheet according to any one of

[11] to

[14] , wherein the underlayer contains 0.04 phr or more and 0.50 phr or less of a pigment suitable for printing by laser marking.

[16] The multilayer resin sheet according to any one of

[11] to

[15] , wherein the substrate layer contains a white pigment in an amount of 1 phr or more and 5 phr or less.

[17] The multilayer resin sheet according to any one of

[11] to

[16] , wherein the thickness of the entire multilayer resin sheet is 100 to 1300 μm.

[18] A molded container comprising the multilayer resin sheet according to any one of

[11] to

[17] . [Effects of the Invention]

[0007] In one embodiment of the multilayer resin sheet according to the present invention, the base layer and the underskin layer contain a polystyrene resin having dispersed therein rubber particles having an average particle size of less than 6 μm. A notch formed in a molded product of the multilayer resin sheet improves crack propagation resistance, thereby imparting excellent notch foldability, which allows the product to fold stably regardless of the speed at which the notch is broken by hand.

[0008] In another embodiment of the multilayer resin sheet of the present invention, the surface layer contains a low-density polyethylene and a high-density polyethylene in a predetermined blend ratio. For example, when the multilayer resin sheet is used to mold a part or all of a molded container, the surface layer, which is the layer that comes into contact with the contents, has improved fracture resistance, thereby preventing leakage of the contents due to loads such as those caused by stacking. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing an example of a laminate structure of a multilayer resin sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] 1, a multilayer resin sheet according to one embodiment of the present invention has a layered structure in which, from top to bottom of the page, a surface layer 10, an adhesive layer 11a, an oxygen barrier layer 12, an adhesive layer 11b, a base layer 13, and an underskin layer 14 are layered in this order. In this embodiment, the oxygen barrier layer 12 is layered on the surface layer 10 and the base layer 13 via the adhesive layers 11a and 11b, while the base layer 13 and the underskin layer 14 are layered directly on each other.

[0011] Below, we will explain each layer in the order of skin layer 10, adhesive layers 11a and 11b, oxygen barrier layer 12, base material layer 13, and underskin layer 14, and then provide an example of the multilayer resin sheet itself and a food packaging container as a molded container formed from it.

[0012] <Epidermal layer 10> The skin layer 10 of this embodiment preferably contains, but is not limited to, a polyolefin resin to impart water vapor barrier properties to the multilayer resin sheet. Among polyolefin resins, the use of a resin mixture of low-density polyethylene and high-density polyethylene can significantly improve the rupture resistance of the skin layer 10. For example, if a multilayer resin sheet is used to mold a part or all of a molded container so that the skin layer 10 is located on the inside, the rupture resistance of the skin layer 10, which is the layer that comes into contact with the contents, is improved, thereby preventing leakage of the contents. While not intending to limit the present invention by theory, it is speculated that this is because the appropriate blending of low-density polyethylene and high-density polyethylene causes appropriate molecular entanglement between the polyethylenes, thereby improving the rupture resistance.

[0013] Examples of polyolefin resins that can be used to form the skin layer 10 include low-density polyethylene, medium-density polyethylene, high-density polyethylene, linear polyethylene, ethylene-α-olefin copolymers polymerized using a metallocene catalyst, ethylene-vinyl acetate copolymers, ethylene-based ionomer resins, ethylene-acrylic acid copolymers, ethylene-ethyl acrylate copolymers, ethylene-methacrylic acid copolymers, ethylene-methyl methacrylate copolymers, ethylene-propylene copolymers, homopolypropylene, block polypropylene, random polypropylene, etc. These polyolefin resins can be used alone or in combination of two or more, but a resin mixture of low-density polyethylene and high-density polyethylene is preferred from the viewpoint of increasing the fracture resistance of the skin layer 10.

[0014] The method for mixing the resin mixture is not particularly limited, and any common mixing method can be used, such as a dry blending method in which individual pellets are simply mixed using a mixer / stirrer such as a tumbler, or a compounding method in which resin pellets are heated using an extruder or the like to melt and knead them.

[0015] When a resin mixture combining low-density polyethylene and high-density polyethylene is used, the ratio of high-density polyethylene to the total mass of low-density polyethylene and high-density polyethylene is preferably 30% by mass or more and 70% by mass or less. By setting the ratio of high-density polyethylene to 30% by mass or more, the breakage resistance can be significantly improved. As a result, for example, when the multilayer resin sheet is molded into a packaging container, the skin layer constituting the packaging container can obtain breakage resistance against the load caused by stacking. Furthermore, by setting the ratio to 70% by mass or less, the breakage resistance of the multilayer resin sheet can be appropriately prevented from becoming too high, and punching defects such as the multilayer resin sheet not ripping during the punching process when molding into a container or the like can be prevented. The ratio of high-density polyethylene is more preferably 40% by mass or more and 60% by mass or less.

[0016] When a resin mixture of low-density polyethylene and high-density polyethylene is used, the density of the low-density polyethylene is, but not limited to, 0.91 to 0.93 g / cm 3 and the density can be 0.915 to 0.925 g / cm 3 The density of the high density polyethylene is preferably, but not limited to, 0.94 to 0.97 g / cm 3 and the density can be 0.955 to 0.965 g / cm 3 The density of the resin mixture of low-density polyethylene and high-density polyethylene is preferably 0.91 to 0.97 g / cm. 3 and the density can be 0.93 to 0.95 g / cm 3 It is preferable to set the following.

[0017] The skin layer 10 may contain resins other than the polyolefin-based 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, granular 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 polyolefin-based resin content in the skin layer 10 is generally 80% by weight or more, typically 90% by weight or more, more typically 95% by weight or more, and can be 100% by weight. In a preferred embodiment, the total content of low-density polyethylene and high-density polyethylene in the skin layer 10 is 80% by weight or more, typically 90% by weight or more, more typically 95% by weight or more, and can be 100% by weight.

[0018] The thickness of the skin layer 10 is preferably 5 to 40% of the overall thickness of the multilayer resin sheet, and more preferably 10% to 30%. The ratio of the thickness of the skin layer 10 to the overall thickness of the multilayer resin sheet is the value obtained by dividing the thickness of the skin layer 10 by the overall thickness of the multilayer resin sheet, expressed as a percentage. By setting the thickness ratio of the skin layer 10 to 5% or more, a sufficient thickness of the skin layer 10 can be ensured, which is advantageous for exhibiting water vapor barrier properties and breakage resistance. Furthermore, by setting the thickness ratio of the skin layer 10 to 40% or less, punching defects, such as failure to rupture the multilayer resin sheet during the punching process when the multilayer resin sheet is molded into a container or the like, and problems such as burrs caused by stretching the resin can be further suppressed.

[0019] <Adhesive layer 11a, 11b> The adhesive layers 11a and 11b 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 about 2 to 8 carbon atoms, such as ethylene, propylene, and butene-1; modified copolymers of these olefins with other olefins (e.g., olefins having about 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.

[0020] 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.

[0021] The thickness of each of the adhesive layers 11a and 11b is preferably 2 to 30 μm, and more preferably 5 to 20 μm. By making the thickness of the adhesive layers 11a and 11b 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.

[0022] Various additives other than the adhesive may be added to the adhesive layers 11a and 11b 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 11a and 11b is generally 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 modified polyolefin polymer content in the adhesive layers 11a and 11b 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.

[0023] <Oxygen barrier layer 12> The oxygen barrier layer 12 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] The oxygen barrier layer 12 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 12 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 12 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.

[0028] The thickness of the oxygen barrier layer 12 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 12 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 a better appearance.

[0029] <Base material layer 13> The base layer 13 of this embodiment contains a polystyrene resin and a plurality of rubber particles dispersed in the resin. Methods for dispersing a plurality of rubber particles in a polystyrene resin include, but are not limited to, graft polymerization in the presence of a styrene monomer and another polymer. This method makes it possible to directly obtain a graft polymer having a structure in which a plurality of rubber particles are dispersed in a polystyrene resin. Examples of styrene monomers include styrene, α-methylstyrene, p-methylstyrene, dimethylstyrene, pt-butylstyrene, and chlorostyrene. Examples of other polymers include diene-based rubber polymers such as polybutadiene, polystyrene-butadiene copolymers (e.g., random copolymers, block copolymers), polyisoprene, and polychloroprene.

[0030] The base layer 13 may be appropriately blended with a polystyrene-based resin without dispersed rubber particles. Examples of polystyrene-based resins include homopolymers or copolymers of styrene-based monomers such as styrene, α-methylstyrene, p-methylstyrene, dimethylstyrene, pt-butylstyrene, and chlorostyrene, and copolymers of these styrene-based monomers with other monomers. Examples of copolymers of styrene-based monomers and 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.

[0031] Polystyrene-based resins and resins containing multiple rubber particles dispersed therein 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 formed by graft polymerization of a portion of the styrene monomer as dispersed layers (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 formed by graft polymerization of a portion of the styrene monomer and the acrylonitrile monomer as dispersed layers (islands).

[0032] In particular, a mixture of general-purpose polystyrene (GPPS resin) and high-impact polystyrene (HIPS resin) is preferably used for the base layer 13 in terms of the rigidity and thermoformability of molded products, such as molded containers, obtained by molding a multilayer resin sheet. Mixing with GPPS resin also offers the advantage of being able to adjust the rubber particle content. The mixing ratio of GPPS resin can be adjusted according to the desired rubber content. The average particle size of the rubber particles in the HIPS resin can be adjusted by controlling the shear force, such as the speed of the rotor blades in the polymerization tank, controlling the polymerization time, or controlling the polymerization with additives.

[0033] The average particle size of the multiple rubber particles dispersed in the polystyrene resin (also referred to as the "average rubber particle size") is preferably less than 6 μm. Furthermore, the average particle size of the rubber particles is more preferably 1 μm or more and 3 μm or less. By setting the average particle size of the rubber particles to 1 μm or more, appropriate impact resistance can be achieved, making it less likely for molded articles, such as molded containers obtained by molding the multilayer resin sheet, to break when dropped. Furthermore, by setting the average particle size of the rubber particles to less than 6 μm, preferably 3 μm or less, cracks can be easily propagated. Therefore, when the multilayer resin sheet is molded into a molded article such as a container and the formed notch is broken by hand, it can be easily broken regardless of the folding speed. In this specification, the average particle size of the rubber particles refers to the arithmetic average particle size based on the volume-based particle size distribution measured by a laser diffraction / scattering particle size distribution analyzer.

[0034] Furthermore, the content of rubber particles (also referred to as "rubber content") relative to the total mass of the polystyrene resin and rubber particles in the base layer 13 is preferably less than 7% by mass, and more preferably 3% to 6% by mass. By making the rubber content of the polystyrene resin 3% by mass or more, further impact resistance can be achieved, making it less likely that a molded product such as a molded container obtained by molding the multilayer resin sheet will break when dropped. Furthermore, making the rubber content less than 7% by mass, or even 6% by mass or less, is advantageous for further improving crack propagation resistance.

[0035] Furthermore, when performing printing processing on the multilayer resin sheet or its molded article by laser irradiation or the like, the base layer 13 preferably contains a white pigment of 1 phr to 5 phr. Furthermore, the white pigment contained in the base layer 13 is more preferably 1.5 phr to 4 phr. The unit phr used here refers to the parts by mass of the white pigment per 100 parts by mass of all resin components in the base layer. By including a white pigment of 1 phr or more in the base layer 13, opacity is achieved, improving the color development of the print when printing on the multilayer resin sheet or its molded article. Furthermore, light-blocking properties are achieved, preventing discoloration and deterioration of the contents due to light irradiation from outside the molded article. Furthermore, by keeping the white pigment content in the base layer 13 at 5 phr or less, aggregation of the white pigment can be suppressed, preventing poor appearance of the multilayer resin sheet or its molded article due to aggregation, etc. Furthermore, from a cost perspective, a lower amount of white pigment is preferable.

[0036] Examples of the white pigment include titanium oxide (titanium white), zinc oxide (zinc white), lithopone, and white lead, with titanium oxide being particularly preferred.

[0037] As with other layers, the base layer 13 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 that allow different components to be compatible with each other, 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. Scrap resin generated during the manufacturing process of the multilayer resin sheet or food packaging container according to one embodiment of the present invention may also be mixed and used. However, the total content of polystyrene resin and rubber particles in the base layer 13 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 total content of HIPS (including rubber particles) and GPPS in the base layer 13 is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and can even be 100% by mass.

[0038] The thickness of the base layer 13 is preferably 100 to 800 μm, and more preferably 150 to 700 μm. Having a thickness of 100 μm or more for the base layer 13 is advantageous for improving the rigidity of molded articles such as containers obtained by molding the multilayer resin sheet. By having a thickness of 800 μm or less for the base layer 13, heat is easily transferred in the thickness direction of the sheet when the multilayer resin sheet is thermoformed, improving thermoformability and allowing molded articles with better appearance to be obtained.

[0039] <Hypodermal layer 14> The underskin layer 14 of this embodiment contains a polystyrene-based resin and a plurality of rubber particles dispersed in the resin. The underskin layer 14 is preferably composed of the same or similar resin as the base layer 13. Therefore, although detailed description is omitted, the polystyrene-based resin with dispersed rubber particles used in the underskin layer 14 may be the graft polymer described in the description of the base layer 13, i.e., a graft polymer obtained by graft polymerization in the presence of a styrene-based monomer and another polymer (e.g., a diene-based rubber polymer such as polybutadiene, polystyrene-butadiene copolymer, polyisoprene, or polychloroprene), 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 base layer 13, the underskin layer 14 may also contain a polystyrene-based resin without dispersed rubber particles. Among these, it is preferable to use a mixture of general-purpose polystyrene (GPPS resin) and high-impact polystyrene (HIPS resin) for the underskin layer 14 in terms of the rigidity and thermoformability of the molded container, etc. obtained by molding the multilayer resin sheet. Note that the preferred properties of the rubber particles in the underskin layer 14, including the average particle size and rubber content, are the same as those of the base layer 13, and therefore will not be described here.

[0040] In order to perform marking processing on the multilayer resin sheet and its molded products by laser irradiation, the underskin layer 14 preferably contains 0.04 phr to 0.50 phr of a pigment suitable for laser marking. Furthermore, the pigment contained in the underskin layer 14 is more preferably 0.07 phr or more and 0.15 phr or less. The unit phr used here refers to the parts by mass of pigment per 100 parts by mass of all resin components in the underskin layer. A pigment content of 0.04 phr or more in the underskin layer 14 is advantageous for achieving laser marking processability, while a content of 0.50 phr or less can reduce the costs of the multilayer resin sheet and its molded products, such as thermoformed containers.

[0041] Pigments suitable for marking by laser processing include mica, titanium oxide, antimony oxide, metal salts such as copper phosphates and sulfates, and black pigments such as carbon black, and among these, antimony oxide is preferred because it can enhance the contrast of markings made by laser processing.

[0042] As with the other layers, in the lower layer 14, as long as it is within the range that does not inhibit the effects of the present invention, other resins may be mixed, and various additive components other than the resin components are also permitted. Such additives include compatibility agents that allow different ingredients to be compatible with each other, coloring agents such as pigments and dyes, mold release agents such as silicon oils and alkyl ester systems, fibrous reinforcers such as glass fibers, granular lubricants such as talc, clay, and silica, salt compounds of sulfonic acids and alkali metals, and additives such as polyalkylene glycols, and ultraviolet absorbers, and antibacterial agents. However, in general, the total content of the polystyrene resin and rubber particles in the lower layer 14 is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and may be 100% by mass. In a preferred embodiment, the total content of HIPS (including rubber particles) and GPPS in the lower layer 14 is 80% by mass or more, typically 90% by mass or more, more typically 95% by mass or more, and may be 100% by mass.

[0043] The thickness of the lower layer 14 is preferably 5 to 100 μm, more preferably 10 to 60 μm. By setting the thickness of the lower layer 14 to 5 μm or more, even when the substrate layer 13 has a defect in appearance due to the fact that it contains scrap resin, etc., the surface of the multilayer resin sheet does not reveal such defects in appearance, and a multilayer resin sheet with a better appearance can be obtained. By setting the thickness of the lower layer 14 to 100 μm or less, the content of pigments suitable for printing by laser processing in the multilayer resin sheet can be reduced, which reduces costs.

[0044] <Multi-layer resin sheet> As shown in Fig. 1, the layer structure of a multilayer resin sheet according to one embodiment of the present invention is basically skin layer 10 / adhesive layer 11a / oxygen barrier layer 12 / adhesive layer 11b / base layer 13 / underskin layer 14, but the layer structure is not limited to this. For example, each layer may be configured to have two or more layers. Furthermore, scrap generated in the process of producing the multilayer resin sheet of the present invention or a molded product such as a molded container may not be discarded, but may be finely crushed and returned, or a new layer may be provided in which recycled material repelletized after thermal melting is returned to the multilayer resin sheet structure.

[0045] The thickness of the entire multilayer resin sheet is preferably 100 to 1300 μm. By making the thickness of the entire multilayer resin sheet 100 μm or more, the strength of the molded product obtained by molding the multilayer resin sheet can be ensured. For example, the side or bottom of a container obtained by thermoforming can be made sufficiently thick, thereby ensuring sufficient container strength. By making the thickness of the entire multilayer resin sheet 1300 μm or less, the costs of the multilayer resin sheet and molded products such as thermoformed containers can be reduced.

[0046] The method for producing a multilayer resin sheet is not particularly limited, and a general method can be used. For example, it can be produced by a melt coextrusion molding method in which multiple resins are bonded and laminated in a molten state using multiple extruders. More specifically, it can be produced by melt-extruding the raw materials for each layer using four or more single-screw or twin-screw extruders, and then using a feed block and a T-die equipped with a selector plug to produce a multilayer resin sheet, or by using a multi-manifold die to produce a multilayer resin sheet.

[0047] <Food packaging containers> The multilayer resin sheet according to the present invention is thermoformable. Therefore, according to one embodiment of the present invention, a molded article is provided that includes the multilayer resin sheet according to the present invention. The type of molded article is not particularly limited, but examples include molded containers, and food packaging containers are particularly preferred embodiments. The multilayer resin sheet according to the present invention can constitute part or all of the molded container. In this case, it is preferable that the multilayer resin sheet constitutes part or all of the molded container such that the surface layer 10 is located on the inner surface side of the molded container and the underskin layer 14 is located on the outer surface side of the molded container.

[0048] A specific example of a food packaging container is a distribution package. A distribution package is a small food packaging container that allows easy extraction of liquid, paste, granular, or powder contents, such as food products like seasonings and beverages, as well as cosmetics and medicines, by pinching and folding the container with the fingers. Such a distribution package typically comprises a hard lid body with a fold line with a notch (called a half-cut portion) in the center of the surface and a protrusion for facilitating extraction of the contents, and a flexible container body with a peripheral portion fixed to the back surface of the lid body, forming pockets on both sides of the fold line. For example, the multilayer resin sheet according to the present invention can be molded into the lid body of the distribution package. In this case, the distribution package is preferably manufactured so that the surface skin layer 10 is located on the back side (the side that comes into contact with the food) of the lid body and the underskin layer 14 is located on the front side of the lid body.

[0049] Methods for thermoforming multilayer resin sheets include, but are not limited to, general vacuum forming and pressure forming, as well as applications of these methods such as a plug-assisted method in which thermoforming is performed by contacting one side of the multilayer resin sheet with a plug, and a method known as matched mold forming in which thermoforming is performed by contacting both sides of the multilayer resin sheet with a pair of male and female molds. 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 multilayer resin sheet before thermoforming. [Example]

[0050] 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.

[0051] The raw materials used in the examples and comparative examples are as follows. (1) Epidermal layer Low-density polyethylene resin (LDPE resin): "Q400" (Manufactured by China Petrochemical Shanghai Petrochemical Industry Co., Ltd., density: 0.923g / cm 3 , MI:4.0g / 10min.(190℃, 2.16kgf)) High-density polyethylene resin (HDPE resin): "8050" (Manufactured by Taiwan Plastics Industry Co., Ltd., density: 0.959g / cm 3 , MI:6.0g / 10min.(190℃, 2.16kgf)) (2) Oxygen barrier layer Ethylene-vinyl alcohol copolymer (EVOH): "EVAL J171B" (Kuraray Co., Ltd., MI: 1.7g / 10min. (190℃, 2.16kgf), Ethylene content 32 mol%) (3) Adhesive layer Modified polyolefin polymer (modified PO): "Modic F502C" (Mitsubishi Chemical Corporation, MI: 1.3g / 10min. (190℃, 2.16kgf)) (4) Base material layer and hypodermis layer HIPS resin (a resin produced by graft polymerization of styrene and polybutadiene): "6351" (Manufactured by Total Petrochemicals, MI: 3.5g / 10min. (200℃, 5.0kgf), average rubber particle size: 1μm) HIPS resin (a resin produced by graft polymerization of styrene and polybutadiene): "4241" (Manufactured by Total Petrochemicals, MI: 3.5g / 10min. (200℃, 5.0kgf), average rubber particle size: 6μm) HIPS resin (resin produced by graft polymerization of styrene and polybutadiene): "#532P" (Manufactured by SINOPEC, MI: 4.5g / 10min. (200℃, 5.0kgf), average rubber particle size: 5μm) GPPS resin (resin produced by homopolymerization of styrene monomer): "1050" (Total Petrochemicals, MI: 2.8g / 10min. (200℃, 5.0kgf)) (5) Pigments Titanium oxide-containing masterbatch: "HMM 1HR480A" (titanium oxide concentration in masterbatch: 50% by mass) (Manufactured by Shanghai Rare Beauty New Material Technology Co., Ltd.) Masterbatch for laser marking: "HEM 1HR1771" (pigment concentration in masterbatch: 1.5% by mass) (Manufactured by Shanghai Rare Beauty New Material Technology Co., Ltd.)

[0052] The multilayer resin sheet was evaluated in various ways by the following methods. (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 multilayer 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 calculated as an average value of the thickness of each layer at five positions in the width direction of the multilayer resin sheet. Measuring equipment: Electron microscope KH7700 (Hirox) (B) Average particle size of rubber in the polystyrene resin in the base layer and the underskin layer A test piece was cut out at a random position from the multilayer resin sheet, and layers not to be analyzed were scraped off with a single-edged knife to separate the substrate layer and the underskin layer. Next, all components except the rubber particles were dissolved in a solvent (N,N-dimethylformamide) to separate the rubber particles, and the average particle size of the rubber particles in the substrate layer and the underskin layer was measured using a laser diffraction / scattering particle size distribution analyzer (Horiba, Ltd., Model: LA-920). (C) The content of rubber particles in the base layer and the underskin layer relative to the total mass of polystyrene resin and rubber particles (rubber content) Measurements were performed using pyrolysis gas chromatography. Test pieces were cut out at random positions from the multilayer resin sheet, and layers not to be analyzed were scraped off with a single-edged knife to separate the substrate layer and underskin layer. The test pieces were then 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, whereupon the substrate layer and underskin layer were pyrolyzed. The gas peak areas of the generated butadiene monomer and styrene monomer were determined, and the rubber content in the substrate layer and underskin layer was calculated based on the calibration curves of other resins with known rubber content. (D) Break resistance of the epidermis A square sealing material made of ethylene-vinyl acetate copolymer was placed on the surface of the skin layer of the multilayer resin sheet, and a square frame (seal width 1.5 mm, square size 60 mm x 60 mm) was heat-sealed along each side of the sealing material. After leaving it in an atmosphere of 23°C and 50% relative humidity for 24 hours, one corner of the sealing material was used as the peel starting point, and the sealing material was peeled diagonally to check whether or not the skin layer had ruptured. Heat sealing conditions Sealing temperature: 175℃ Sealing pressure: 0.1MPa Sealing time: 1.6 seconds 〇Peeling conditions Peeling speed: 830~1700mm / sec (manual peeling) Peeling angle: 90° The fracture resistance was evaluated according to the following four levels based on the results of performing the above test 30 times. 1) ◎: No breakage, stretching or cracks were observed in any of the tests. 2) 〇: No fractures were observed in any of the tests, but some stretching or cracks were observed in at least some of the tests. 3) △: Minor fractures (less than 2mm x 2mm) were found in at least some tests. 4) ×: Significant fractures (greater than 2mm x 2mm) were found in at least some of the tests. (E) Bending resistance A test piece (15 mm x 100 mm) was cut out at an arbitrary position from the multilayer resin sheet, and both ends of the test piece in the longitudinal direction were chucked, and a folding strength test was carried out using a folding tester. Folding endurance tester: FPC folding endurance tester (Model MY-FPC-01, manufactured by Shenzhen Mingyu Instrument and Equipment Co., Ltd.) Measurement conditions: The test piece was bent at a bending angle (135°) under a load (1600 g) at three different bending speeds, and the number of times it was bent until the multilayer resin sheet broke (meaning it broke in two) was measured. Note that the bending resistance of the multilayer resin sheet before thermoforming was evaluated here, but it has been found that the bending resistance of the multilayer resin sheet before thermoforming tends to be the same as the notch fold resistance of a thermoformed product including the multilayer resin sheet. Bending speed level 1) High speed: 135rpm 2) Medium speed: 70rpm 3) Low speed: 10rpm The bending resistance was evaluated according to the following four levels. 1) ◎: Less than 50 bending times 2) 〇: Number of bending times is 50 or more but less than 100 3) △: Number of bending times: 100 to 1000 4) ×: The number of bending times exceeds 1000 (F) Laser marking ability Using a laser marking machine (LS-MFP / 20) manufactured by Suzhou Laisai Gekko Co., Ltd., laser irradiation was performed from the lower skin layer side of the multilayer resin sheet, and printability was confirmed visually. Laser type: YAG ·Wavelength: 1064nm Frequency: 20KHz The printability was evaluated according to the following four levels. 1) ◎: Printed clearly 2) 〇: The print is not blurred, but the color is weak. 3) △: Printed, but partially faded 4) ×: Not printed

[0053] Example 1 The raw materials for each layer were melt-extruded using two φ45 mm single-screw extruders (for the adhesive layer and oxygen barrier layer), one φ65 mm single-screw extruder (for the underskin layer), one φ75 mm single-screw extruder (for the skin layer), and one φ120 mm single-screw extruder (for the base layer), and a feed block method was used to obtain a multilayer resin sheet having a thickness of 330 μm and a width of 640 mm, and having a layer structure of skin layer 10 60 μm / adhesive layer 11a 10 μm / oxygen barrier layer 12 15 μm / adhesive layer 11b 10 μm / base layer 13 185 μm / underskin layer 14 50 μm.

[0054] Here, the skin layer 10 was made of a resin mixture of high-density polyethylene resin and low-density polyethylene resin, a mixture of HDPE resin "8050" and LDPE resin "Q400" in a mass ratio of 50 / 50; the adhesive layers 11a and 11b were made of modified polyolefin polymer "Modic F502C;" the oxygen barrier layer 12 was made of ethylene-vinyl alcohol copolymer "EVAL J171B;" the base material layer 13 was made of a mixture of HIPS resin "6351" and GPPS resin "1050" in a mass ratio of 80 / 20, to which 5 phr of titanium oxide-containing masterbatch "HMM 1HR480A" had been added; and the underskin layer 14 was made of HIPS resin "6351" to which 7 phr of laser marking masterbatch "HEM 1HR1771" had been added.

[0055] <Examples 2 to 12 and Comparative Examples 1 to 3> A multilayer resin sheet was molded in the same manner as in Example 1, except that the raw material mixing ratios of the surface layer 10, the base layer 13, and the underlayer 14 and the thickness of each layer were changed as shown in Table 1, and the HIPS resin type was changed appropriately.

[0056] The obtained multilayer resin sheets according to the examples and comparative examples were evaluated in various ways using the methods for evaluating multilayer resin sheets described above. The results are shown in Tables 1 to 3.

[0057] [Table 1]

[0058] [Table 2]

[0059] [Table 3]

[0060] <Consideration> The multilayer resin sheet of Example 1 contained a moderate blending ratio of low-density polyethylene resin and high-density polyethylene resin, so no cracking occurred in the skin layer. Furthermore, because the average particle size of the rubber particles dispersed in the polystyrene resin in the base layer was small and the rubber content was moderate, the number of folding cycles, which is a flexural characteristic, met the standard at all bending speeds. Furthermore, the laser marking was clearly printed, meeting the standard. Here, the evaluation shown above was judged to meet the standard if it was rated as ◎ or ◯, and judged to not meet the standard if it was rated as △ or ×. The same applies below.

[0061] In Example 2, compared to Example 1, only the average particle size of the rubber in the substrate layer was changed by changing the type of HIPS resin constituting the substrate layer from "6351" to "#532P." The obtained multilayer resin sheet satisfied the criteria for the break resistance, flex resistance, and laser markability of the surface layer.

[0062] In Examples 3 and 4, only the blending ratio of the high-density polyethylene resin in the composition of the skin layer was changed from Example 1. The obtained multilayer resin sheet satisfied the criteria for the break resistance, flex resistance, and laser marking property of the skin layer.

[0063] In Example 5, only the amount of titanium oxide-containing masterbatch added to the composition of the base layer was changed from Example 1. The obtained multilayer resin sheet satisfied the standards for the break resistance, flex resistance, and laser marking property of the surface layer.

[0064] In Example 6, only the amount of the laser marking masterbatch added to the underskin layer composition was changed from Example 1. The obtained multilayer resin sheet satisfied the criteria for the break resistance, flex resistance, and laser markability of the surface layer.

[0065] In Examples 7 and 8, only the thickness of each layer was changed compared to Example 1. The obtained multilayer resin sheet satisfied the criteria for the break resistance, flex resistance, and laser marking property of the surface layer.

[0066] In Example 9, the HIPS resin type constituting the substrate layer was changed from "6351" to "4241" to change the average particle size of the rubber in the substrate layer, as compared to Example 1. The resulting multilayer resin sheet met the standards for both the fracture resistance and laser markability of the skin layer. However, it was found that the crack propagation resistance deteriorated as the average particle size of the rubber particles increased, and the number of flexions required to break increased.

[0067] In Example 10, the HIPS resin type constituting the substrate layer was changed from "6351" to "4241" compared to Example 1, and the GPPS resin was not blended into the substrate layer, thereby changing the rubber content and average particle size of the rubber in the substrate layer. The obtained multilayer resin sheet met the standards for both the break resistance and laser markability of the skin layer. However, it can be seen that the increased rubber content worsened crack propagation, increasing the number of flexions required until breakage occurred.

[0068] In Comparative Examples 1, 2, and 3, the compounding ratio of the high-density polyethylene resin and the low-density polyethylene resin in the composition of the skin layer was changed compared to Example 1, and further, the HIPS resin type constituting the base layer was changed from "6351" to "4241," thereby changing the average particle size of the rubber in the base layer. It can be seen that the fracture resistance of the obtained skin layer was reduced, and further, the number of flexions until breakage occurred was increased.

[0069] In Example 11, the amount of laser marking masterbatch added to the underskin layer was changed compared to Example 1. The HIPS resin type constituting the substrate layer was changed from "6351" to "4241," and the GPPS resin was not blended into the substrate layer, thereby changing the rubber content and average particle size of the rubber in the substrate layer. The resulting multilayer resin sheet met the standards for the break resistance of the surface layer. However, it was found that the laser marking property was reduced due to an insufficient amount of laser marking masterbatch added. It was also found that the number of flexions required to break increased.

[0070] In Example 12, the thicknesses of the skin layer and the base layer were changed compared to Example 1. The obtained multilayer resin sheet satisfied the standards for both bending resistance and laser marking property. However, it was found that the fracture resistance of the skin layer decreased as the thickness ratio of the skin layer in the multilayer resin sheet decreased. [Explanation of symbols]

[0071] 10 Epidermal layer 11a, 11b adhesive layer 12 Oxygen barrier layer 13 Base material layer 14 Hypodermal layer

Claims

1. A multilayer resin sheet having a laminated structure in which a surface layer, an oxygen barrier layer, a base layer, and an underskin layer are laminated in this order, the oxygen barrier layer is laminated on the surface layer and the base layer via an adhesive layer; The base layer and the underskin layer are layers containing a polystyrene-based resin, the surface layer contains a mixture of low-density polyethylene and high-density polyethylene, the ratio of the high-density polyethylene to the total mass of the low-density polyethylene and the high-density polyethylene is 30% by mass or more and 70% by mass or less, and the surface layer has a thickness of 5 to 40% of the entire multilayer resin sheet; Multi-layer resin sheet.

2. The density of the mixture of low-density polyethylene and high-density polyethylene is 0.91 to 0.97 g / cm 3 The multilayer resin sheet according to claim 1,

3. 3. The multilayer resin sheet according to claim 1, wherein the substrate layer and the underskin layer are layers containing a polystyrene-based resin and a plurality of rubber particles dispersed in the resin, and the average particle size of the rubber particles contained in the substrate layer and the underskin layer is less than 6 μm.

4. 4. The multilayer resin sheet according to claim 1, wherein the base layer contains less than 7% by mass of rubber particles relative to the total mass of the polystyrene resin and the rubber particles.

5. 5. The multilayer resin sheet according to claim 1, wherein the lower skin layer contains 0.04 phr to 0.50 phr of a pigment suitable for printing by laser marking.

6. 6. The multilayer 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 multilayer resin sheet according to any one of claims 1 to 6, wherein the thickness of the entire multilayer resin sheet is 100 to 1300 µm.

8. A molded container comprising the multilayer resin sheet according to any one of claims 1 to 7.

Images