Multilayer resin sheet and molded container molded therefrom

Abstract

Provided is a multilayer resin sheet having thermoformability, rigidity, oxygen barrier properties, and imparting a heat-formed slit bendability. Also provided is a molded container having a deep drawing shape that is excellent in design and visual recognition. A multilayer resin sheet characterized by comprising an oxygen barrier resin layer and styrene resin layers C and D, the styrene resin layers C and D being laminated on both sides of the oxygen barrier resin layer via modified olefin polymer layers A and B, respectively, the thickness of the multilayer resin sheet as a whole being 500 to 1200 μm, the thickness of the styrene resin layer C being 10 to 35% of the thickness as a whole, the thickness of the styrene resin layer D being 50 to 80% of the thickness as a whole, the surface roughness (Ra) of the side of the styrene resin layers C and D opposite the side facing the modified olefin polymer layers A and B being 0.1 to 2.0 μm, and the styrene resin layer D comprising 15 to 70 mass% of a styrene-conjugated diene block copolymer and 30 to 85 mass% of a polystyrene containing 0.5 to 5 mass% of a conjugated diene rubber formed by graft polymerization of a styrene monomer.

Description

Technical Field

[0001] This invention relates to a multilayer resin sheet and a molded container formed therefrom. Background Technology

[0002] Styrene-based resins and polyolefin-based resins have traditionally been used as containers for soft drinks, fruit juices, and other beverages. However, in recent years, multilayer resin sheets and multilayer containers incorporating such sheets have become widespread. These multilayer resin sheets, with an ethylene-vinyl alcohol copolymer resin layer sandwiched between an adhesive layer such as a modified olefin resin, impart oxygen barrier properties and suppress quality degradation caused by oxidation of the contents (Patent Documents 1-3).

[0003] The manufacture of these containers through a series of processes, including molding, filling, and sealing, has been increasing in recent years. Patent document 1 discloses a multilayer resin sheet that prevents hot plate adhesion during container molding by adjusting the surface roughness of the polystyrene resin layer.

[0004] Furthermore, Patent Document 2 proposes a multilayer resin sheet that combines transparency, rigidity, and oxygen barrier properties by using a transparent styrene-based resin.

[0005] In addition, Patent Document 3 proposes a multilayer resin sheet, which possesses gas barrier properties, formability, and rigidity by combining an olefin resin layer, a gas barrier resin layer, and a resin composition layer composed of styrene resin, styrene-diene copolymer, and olefin resin in a specific order.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 06225159

[0009] Patent Document 2: Japanese Patent Application Publication No. 10-100338

[0010] Patent Document 3: Japanese Patent No. 3967899 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] On the other hand, in recent years, there has been an increase in containers with complex, deep-drawn shapes, leading to the development of products that, for example... Figure 5The container shown is a two-container design where the main dessert is placed in the larger container and the sauce in the smaller container. In this type of container, a slit is pre-cut between the containers. By bending along the slit, the large and small containers do not break apart, allowing the sauce to be added from the small container to the large container, thus enabling tasting according to preference. Furthermore, the containers are required to be transparent, ensuring excellent design and visual visibility of the contents.

[0013] However, the multilayer resin sheets described in Patent Documents 1 and 2 break when bent at the cut section, and are therefore unsuitable for the aforementioned containers. Furthermore, the polypropylene used as the substrate layer in the multilayer resin sheet described in Patent Document 3 has poor moldability and cannot be applied to containers with complex shapes as described above.

[0014] The present invention was made in view of the above circumstances, and its object is to provide a multilayer resin sheet and a molded container formed therefrom, wherein the multilayer resin sheet has thermoformability, rigidity, oxygen barrier properties and is easy to impart slit bending properties after thermoforming, and can also be molded into a deep-drawn shape container with excellent design and visual recognizability after being filled with contents.

[0015] The means to solve the problem

[0016] In other words, the inventors, through in-depth research to develop a multilayer resin sheet with the aforementioned characteristics and suitable for deep drawing, discovered that a multilayer resin sheet formed by laminating a styrene-based resin layer on both sides of an oxygen-barrier resin layer with a modified olefin-based polymer layer in between, wherein at least one side of the styrene-based resin layer is formed with a specific styrene-based resin, and by simultaneously adjusting the surface roughness (Ra) of the opposite sides of the styrene-based resin layers on both sides (i.e., the two surfaces of the multilayer resin sheet) and their respective thickness ratios relative to the overall thickness of the multilayer sheet, can solve the aforementioned problems and complete the present invention.

[0017] The present invention, which solves the above-mentioned problems, is comprised of the following components.

[0018] (1) A multilayer resin sheet comprising an oxygen barrier resin layer and styrene resin layers C and D, wherein the styrene resin layers C and D are laminated on both sides of the oxygen barrier resin layer with a modified olefin polymer layer A and a modified olefin polymer layer B in between, the overall thickness of the multilayer resin sheet is 500-1200 μm, the thickness of the styrene resin layer C is 10-35% of the overall thickness, the thickness of the styrene resin layer D is 50-80% of the overall thickness, the surface roughness (Ra) of the surfaces of the styrene resin layers C and D opposite to the surfaces of the modified olefin polymer layers A and B is 0.1-2.0 μm, and the styrene resin layer D comprises 15-70% by mass of a styrene-conjugated diene block copolymer and 30-85% by mass of polystyrene, wherein the polystyrene contains 0.5-5% by mass of a conjugated diene rubber obtained by graft polymerization of styrene monomers.

[0019] (2) The multilayer resin sheet according to (1), wherein the oxygen barrier resin layer comprises ethylene-vinyl alcohol copolymer resin.

[0020] (3) The multilayer resin sheet according to (1) or (2), wherein the thicknesses of the modified olefin polymer layers A and B are 10 to 50 μm, respectively.

[0021] (4) The multilayer resin sheet according to any one of (1) to (3), wherein the thickness of the oxygen barrier resin layer is 10 to 50 μm.

[0022] (5) A molded article, which is a molded article of any one of (1) to (4) of a multilayer resin sheet.

[0023] (6) The molded article according to (5) is a molded container having a slit on the surface of the styrene resin layer D.

[0024] The effects of the invention

[0025] According to the present invention, a multilayer resin sheet is provided that possesses thermoformability, rigidity, oxygen barrier properties, and the ability to impart slit bending capability after thermoforming. Furthermore, by using the multilayer resin sheet of the present invention, a deep-drawn shaped molded container with excellent design flexibility and visual recognizability is provided. Attached Figure Description

[0026] Figure 1 This is a longitudinal sectional view schematically illustrating the laminated structure of a multilayer resin sheet according to an embodiment of the present invention.

[0027] Figure 2 This is a perspective view that schematically illustrates an example of the molded container of the present invention.

[0028] Figure 3This is a side view that schematically illustrates an example of the molded container of the present invention.

[0029] Figure 4 This is a schematic diagram used to illustrate the punching process of a container.

[0030] Figure 5 This is a top view and a schematic longitudinal sectional view along line CC, showing another example of the molded container of the present invention. Detailed Implementation

[0031] The following describes various embodiments of the multilayer resin sheet, followed by a method for manufacturing the multilayer resin sheet. In cases where the specific description described in one embodiment also applies to other embodiments, the description is omitted in other embodiments.

[0032] [First Implementation Method]

[0033] like Figure 1 As shown, one embodiment of the present invention relates to a multilayer resin sheet comprising an oxygen barrier resin layer and styrene-based resin layers C and D. The styrene-based resin layers C and D are stacked on opposite sides of the oxygen barrier resin layer, separated by modified olefin polymer layers A and B, respectively. The overall thickness is 500–1200 μm. The thickness of the styrene-based resin layer C is 10–35% of the overall thickness, and the thickness of the styrene-based resin layer D is 50–80% of the overall thickness. The surface roughness (Ra) of the surfaces of the styrene-based resin layers C and D opposite to the surfaces of the modified olefin polymer layers A and B is 0.1–2.0 μm. The styrene-based resin layer D comprises 15–70% by mass of a styrene-conjugated diene block copolymer and 30–85% by mass of polystyrene, wherein the polystyrene contains 0.5–5% by mass of a conjugated diene rubber obtained by graft polymerization of styrene monomers.

[0034] (Oxygen barrier resin layer)

[0035] The oxygen barrier resin layer mainly contains oxygen barrier resins such as ethylene-vinyl alcohol copolymer resin and polyamide resin. Among them, from the perspective of processability and moldability, it is preferred to contain ethylene-vinyl alcohol copolymer resin.

[0036] Here, "mainly contains" means containing 50% by mass or more of the resin. In other embodiments, it may also contain 70% by mass or more, or 90% by mass or more, or be composed solely of the resin.

[0037] Ethylene-vinyl alcohol copolymer resins are typically obtained by saponifying ethylene-vinyl acetate copolymers. To impart oxygen barrier properties, processability, and moldability, the ethylene content is preferably 10–65 mol%, more preferably 20–50 mol%, and even more preferably 25–40%. Furthermore, the degree of saponification is preferably 90% or more, more preferably 95% or more, and even more preferably 97% or more.

[0038] The ethylene content in ethylene-vinyl alcohol copolymer resin can be calculated, for example, by nuclear magnetic resonance spectroscopy (NMR).

[0039] In addition, examples of polyamide resins include: polymers of lactams such as caprolactam and dodecylactam; polymers of aminocarboxylic acids such as 6-aminohexanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid; condensation polymers of aliphatic diamines such as hexamethylenediamine, decamethylenediamine, dodecylmethylenediamine, and 2,2,4- or 2,4,4-trimethylhexamethylenediamine; alicyclic diamines such as 1,3- or 1,4-bis(aminomethyl)cyclohexane and bis(p-aminocyclohexyl)methane; aromatic diamines such as meta- or p-phenylenediamine; and dicarboxylic acid units such as adipic acid, octanoic acid, sebacic acid, alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; and aromatic dicarboxylic acids such as terephthalic acid and isophthalic acid; as well as copolymers thereof.

[0040] Specific 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, nylon 6I / 6T, etc., among which nylon 6 and nylon MXD6 are preferred.

[0041] The thickness of the oxygen barrier resin layer is preferably 10 to 50 μm, more preferably 20 to 40 μm, and even more preferably 30 to 40 μm. If it is 10 μm or more, sufficient oxygen barrier properties can be obtained to suppress the quality degradation caused by oxidation of the contents of the molded container. In addition, if it is 50 μm or less, resin burrs can be sufficiently suppressed during the punching of the thermoformed container.

[0042] The thickness of the oxygen barrier layer relative to the overall thickness of the multilayer resin sheet is preferably 0.5 to 15%, more preferably 1 to 10%, and even more preferably 2 to 8%.

[0043] (Modified olefin polymer layers A and B)

[0044] Modified olefin polymer layers A and B mainly contain modified olefin polymers. These modified olefin polymers are selected from: olefin resins such as homopolymers of olefins with approximately 2 to 8 carbon atoms, copolymers of these olefins with other olefins with approximately 2 to 20 carbon atoms, and vinyl compounds; olefin rubbers such as ethylene-propylene copolymers, ethylene-propylene-diene copolymers, ethylene-butene-1 copolymers, and propylene-butene-1 copolymers are modified by grafting with unsaturated carboxylic acids or their derivatives such as acyl halides, amides, imides, anhydrides, and esters. The olefins with approximately 2 to 8 carbon atoms are ethylene, propylene, and butene-1, etc., and the olefins with approximately 2 to 20 carbon atoms are... The other olefins on the left and right sides are ethylene, propylene, butene-1, 3-methylbutene-1, pentene-1, 4-methylpentene-1, hexene-1, octene-1, decene-1, etc.; the vinyl compounds are vinyl acetate, vinyl chloride, acrylic acid, methacrylic acid, acrylate, methacrylate, styrene, etc.; the unsaturated carboxylic acids are acrylic acid, methacrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, tetrahydrophthalic acid, etc.; and the unsaturated carboxylic acid derivatives are specifically maleic chloride, maleimide, maleic anhydride, citraconic anhydride, monomethyl maleate, dimethyl maleate, glycidyl maleate, etc. The modified olefin polymer constituting the modified olefin polymer layer A can be the same as or different from the modified olefin polymer constituting the modified olefin polymer layer B.

[0045] As a modified olefin polymer, the preferred materials are: ethylene-based resins, propylene-based resins, or ethylene-propylene or butene-1 copolymer rubbers modified with unsaturated dicarboxylic acids or their anhydrides, especially maleic acid or its anhydrides.

[0046] The thicknesses of the modified olefin polymer layers A and B are preferably 10–50 μm, more preferably 20–40 μm, and even more preferably 20–25 μm. A thickness of 10 μm or more provides sufficient interlayer bond strength, while a thickness of 50 μm or less effectively suppresses resin burrs generated during punching of the thermoformed container. The thicknesses of the modified olefin polymer layer A and B may be the same or different.

[0047] The thickness of the modified olefin polymer layers A and B, relative to the overall thickness of the multilayer resin sheet described later, is preferably 0.5 to 15%, more preferably 1 to 10%, and even more preferably 1.5 to 4%.

[0048] (Styrene-based resin layer C)

[0049] For example, without impairing the effects of the present invention, the styrene-based resin layer C mainly contains a styrene-based resin selected from: homopolymers or copolymers of styrene monomers such as styrene, α-methylstyrene, p-methylstyrene, dimethylstyrene, p-tert-butylstyrene, and chlorostyrene; copolymers of these styrene monomers with other monomers (e.g., styrene-acrylonitrile copolymer (AS resin)); or graft polymers formed by grafting one or more of the aforementioned styrene monomers, or further with other monomers, in the presence of conjugated diene rubber polymers such as polybutadiene, styrene-butadiene copolymers, polyisoprene, and polychloroprene (e.g., impact-resistant polystyrene (HIPS resin), styrene-acrylonitrile graft polymer (ABS resin), etc.). The styrene-based resin can be used alone or in combination as a styrene-based resin layer. Alternatively, the styrene-based resin used in the styrene-based resin layer D described later can also be used.

[0050] The thickness of the styrene-based resin layer C is preferably 10-35% of the overall thickness of the multilayer resin sheet described later, more preferably 15-30%, and even more preferably 20-25%. If it is 10% or more, the styrene-based resin layer C will not break off during container molding, exposing the modified olefin polymer layer and damaging the container's appearance. Furthermore, if it is less than 35%, the resistance to bending the container at the cut section will not increase, reducing its flexibility.

[0051] The thickness of the styrene-based resin layer C is preferably 50–420 μm, more preferably 70–260 μm, and even more preferably 150–200 μm.

[0052] The side opposite to the side of the styrene-based resin layer C that is opposite to the side of the modified olefin polymer layer A (i.e., Figure 1 The surface roughness (Ra) of the upper surface (of the molded product) is preferably 0.1 to 2.0 μm, more preferably 0.1 to 1.0 μm, and even more preferably 0.3 to 0.7 μm. If it is 0.1 μm or more, the resin layer will not fuse with the heat source during heat molding; if it is 2.0 μm or less, the problem of loss of transparency and surface gloss in the resulting molded product, which would lead to a decrease in the product's value, will not occur.

[0053] (Styrene-based resin layer D)

[0054] The styrene-based resin layer D contains a styrene-based resin comprising 15-70% by mass of a styrene-conjugated diene block copolymer and 30-85% by mass of polystyrene, wherein the polystyrene contains 0.5-5% by mass of a conjugated diene rubber obtained by graft polymerization of styrene monomers.

[0055] In one embodiment, the styrene-based resin layer D may contain 40-60% by mass of a styrene-conjugated diene block copolymer, or it may contain 45-55% by mass.

[0056] In addition, the styrene-based resin layer D may contain 40-60% by mass of polystyrene, or 45-55% by mass; wherein the polystyrene contains 0.5-5% by mass of conjugated diene rubber formed by graft polymerization of styrene monomers.

[0057] Styrene-conjugated diene block copolymers are polymers whose structure contains polymer blocks mainly composed of styrene monomers and polymer blocks mainly composed of conjugated diene monomers.

[0058] As styrene-based monomers, there are styrene, o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene, 1,1-diphenylethylene, etc. In this embodiment, styrene is the main component, but it may also contain one or more of the above-mentioned components as trace elements.

[0059] Conjugated diene monomers are compounds that have conjugated double bonds in their structure, such as 1,3-butadiene (butadiene), 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and 2-methylpentadiene, among which butadiene and isoprene are preferred. Alternatively, two or more conjugated diene monomers may be used.

[0060] The polymer blocks primarily composed of styrene monomers can be polymer blocks consisting solely of structures derived from styrene monomers, or polymer blocks containing 50% by mass or more, 70% by mass or more, or 90% by mass or more of structures derived from styrene monomers. Similarly, the polymer blocks primarily composed of conjugated diene monomers can be polymer blocks consisting solely of structures derived from conjugated diene monomers, or polymer blocks containing 50% by mass or more, 70% by mass or more, or 90% by mass or more of structures derived from conjugated diene monomers. From the viewpoint of the mechanical properties of the sheet, the conjugated diene content of the styrene-conjugated diene block copolymer is preferably 10 to 40% by mass, more preferably 15 to 35% by mass, and even more preferably 20 to 30% by mass, relative to all monomer units of the styrene-conjugated diene block copolymer. Here, the conjugated diene content refers to the mass percentage of structures derived from conjugated diene monomers in the styrene-conjugated diene block copolymer. It should be noted that the conjugated diene content of styrene-conjugated diene block copolymers can be calculated, for example, by analysis using Fourier transform infrared spectroscopy (FT-IR).

[0061] In one embodiment of the present invention, one or more styrene-conjugated diene block copolymers may be used. Alternatively, for example, when the conjugated diene is butadiene, the styrene-conjugated diene block copolymer may be either a styrene-butadiene (SB) binary copolymer or a styrene-butadiene-styrene (SBS) terpolymer (SBS), or it may be a resin composed of multiple blocks having three or more styrene blocks and two or more butadiene blocks. Furthermore, it may be a so-called tapered block structure having a continuously varying styrene to butadiene ratio between the blocks. The styrene-conjugated diene block copolymer can be manufactured by conventionally known polymerization methods such as emulsion polymerization and solution polymerization, or commercially available products can be used directly.

[0062] Polystyrene containing styrene monomers grafted into conjugated diene rubber (hereinafter sometimes referred to as "grafted rubber") is so-called high-impact polystyrene (HIPS). It is obtained by polymerizing styrene monomers in the presence of conjugated diene rubber polymers. The particulate rubber component formed by grafting styrene monomers is dispersed in an island-like manner in the resin phase containing polystyrene.

[0063] Here, without impairing the effects of the present invention, the styrene monomer may also contain one or more aromatic vinyl compounds such as o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene, and 1,1-diphenylethylene.

[0064] Examples of conjugated diene-based rubber polymers include those using monomers such as 1,3-butadiene (butadiene), 2-methyl-1,3-butadiene (isoprene), 2,3-dimethyl-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, and 2-methylpentadiene. Additionally, thermoplastic elastomers such as styrene-conjugated diene block copolymers with a conjugated diene content of 50% by mass or more can also be used. Among these, polybutadiene and styrene-butadiene block copolymers are preferred.

[0065] The polystyrene contains 0.5 to 5% by mass, preferably 0.5 to 3.0% by mass, and more preferably 1.0 to 2.5% by mass of grafted rubber. If the content of grafted rubber is 0.5% by mass or more, the adhesion of the sheets to each other can be sufficiently suppressed, and if it is 5% by mass or less, the transparency of the container can be sufficiently ensured.

[0066] The content of the grafted rubber relative to all the styrene-based resin used in the styrene-based resin layer is preferably 0.3 to 3% by mass, more preferably 0.3 to 2.5% by mass, and even more preferably 0.5 to 2.0% by mass.

[0067] The content of grafted rubber in polystyrene can be adjusted during the HIPS manufacturing stage, but a simple method is to prepare HIPS with a grafted rubber content greater than the target content beforehand, and adjust it by mixing polystyrene (general purpose polystyrene, GPPS). Here, GPPS generally means a homopolymer of styrene monomers, but without impairing the effects of the present invention, it may also contain one or more aromatic vinyl compounds other than styrene, such as o-methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1,3-dimethylstyrene, α-methylstyrene, vinylnaphthalene, vinylanthracene, 1,1-diphenylethylene. Furthermore, the grafted rubber content can be determined by dissolving HIPS in chloroform, adding a certain amount of iodine monochloride / carbon tetrachloride solution, and placing it in the dark for about 1 hour, then adding potassium iodide solution, titrating the excess iodine monochloride with a 0.1N sodium thiosulfate / ethanol aqueous solution, and determining the amount of iodine monochloride added.

[0068] From the viewpoint of transparency and strength of the sheet, the particle size of the grafted rubber is preferably 1.0 μm or more and 3.0 μm or less, more preferably 1.0 μm or more and 2.8 μm or less, and even more preferably 1.0 μm or more and 2.5 μm or less. Here, the particle size of the grafted rubber refers to the average particle size of the grafted rubber portion as measured by a laser diffraction particle analyzer.

[0069] The thickness of the styrene-based resin layer D is 50-80% of the overall thickness of the sheet material described later, preferably 60-80%, and more preferably 70-75%. If it is 50% or more, the styrene-based resin layer D will not break during the cutting process, exposing the modified olefin polymer layer and damaging the appearance of the container. Furthermore, if it is 80% or less, the container will not experience increased resistance and reduced flexibility when bent at the cut section. Moreover, by relatively increasing the thickness of the oxygen-barrier resin layer, the oxygen-barrier performance can be improved; or by relatively increasing the thickness of the styrene-based resin layer C, the styrene-based resin layer C can be prevented from breaking during container molding, exposing the modified olefin polymer layer and damaging the appearance of the container.

[0070] The thickness of the styrene-based resin layer D is preferably 250–850 μm, more preferably 340–750 μm, and even more preferably 500–580 μm.

[0071] The side opposite to the side of the styrene-based resin layer D that is opposite to the side of the modified olefin-based polymer layer B (i.e., Figure 1The surface roughness (Ra) of the lower surface (of the resin layer) is 0.1 to 2.0 μm, preferably 0.1 to 1.0 μm, and more preferably 0.3 to 0.7 μm. If it is 0.1 μm or more, the resin layer will not fuse with the heat source during heat molding. If it is 2.0 μm or less, the problem of loss of transparency and surface gloss in the resulting molded article, which would reduce the value of the product, will not occur.

[0072] (Multi-layer resin sheet)

[0073] The multilayer resin sheet of this embodiment can be used for deep drawing. Here, "for deep drawing" means having characteristics suitable for deep drawing. Deep drawing is defined as the ratio of the depth to the width (or the maximum width if the shape has multiple widths), i.e., the drawing ratio, of the formed container, regardless of its shape. The deep-drawn container here is one with a drawing ratio of 0.5 or more, preferably 0.9 or more, more preferably 1 or more, and most preferably 1.5 or more.

[0074] Furthermore, the multilayer resin sheet of this embodiment can also be used for slit formation. Here, "for slit formation" means having characteristics suitable for forming slits, defined as being able to be easily bent by hand when forming a slit and repeatedly bent to the opposite side of the surface where the slit is formed, and not breaking after being bent more than 5 times. The depth of the formed slit is not particularly limited as long as it can be easily bent by hand, for example, it can be 100 to 400 μm, preferably 150 to 350 μm, and more preferably 200 to 300 μm.

[0075] The multilayer resin sheet of this embodiment uses a styrene-based resin as the styrene-based resin layer D. The styrene-based resin contains 15-70% by mass of a styrene-conjugated diene block copolymer and 30-85% by mass of polystyrene. The polystyrene contains 0.5-5% by mass of a conjugated diene rubber obtained by graft polymerization of styrene monomers. As a result, a sheet material that satisfies the requirements of transparency, rigidity, and kerf bending is obtained. Furthermore, adverse conditions such as the reduction in container strength due to the wall thickness of the formed container being biased towards the bottom surface during deep drawing are suppressed.

[0076] The multilayer resin sheet of this embodiment, when molded into the form shown in the embodiment... Figure 2 and Figure 3 Taking a container with a slit on one side as an example, a styrene-based resin layer D is disposed on the side with the slit, and a styrene-based resin layer C is disposed on the side without the slit.

[0077] The overall thickness of the multilayer resin sheet in this embodiment is preferably 500 to 1200 μm, more preferably 700 to 1000 μm, and even more preferably 800 to 900 μm. By making it 500 μm or more, the container obtained by thermoforming can obtain sufficient strength, and by making it 1200 μm or less, the manufacturing cost of the container can be reduced.

[0078] (Manufacturing method of multilayer resin sheet)

[0079] The method for manufacturing the multilayer resin sheet in this embodiment is not particularly limited, and general methods can be used. Examples include: using three or more single-screw extruders to melt-extrude the various raw material resins and obtaining the multilayer resin sheet through a feed block and a T-die; and using a multi-manifold die to obtain the multilayer resin sheet.

[0080] There is no particular limitation on the method for imparting a predetermined surface roughness to both sides of the multilayer resin sheet of this embodiment, and general methods can be used. Examples include: using rollers or conveyor belts with embossed surfaces to draw molten resin.

[0081] [Second Implementation]

[0082] The second embodiment of the present invention relates to a molded container formed by thermoforming the multilayer resin sheet of the first embodiment, and it is a molded container having a slit formed on one side.

[0083] (Molded container)

[0084] The molding container of this embodiment is formed by thermoforming the multilayer resin sheet of the first embodiment described above. Figure 2 and Figure 3 The image shows an example of a molded container according to an embodiment of the present invention. Examples of thermoforming methods include: general vacuum forming, pneumatic forming, and plug-assist forming, where the mold plug is formed by contacting one side of the sheet; and so-called match mold forming methods, where a pair of male and female molds are formed by contacting both sides of the sheet, etc., but are not limited to these. Furthermore, as a method for softening the sheet by heating before forming, known sheet heating methods such as radiation heating using infrared heaters, which are non-contact heating methods, can be used.

[0085] The molding temperature during thermoforming can be appropriately set considering factors such as the melting point of the resin. However, when using the multilayer resin sheet according to the first embodiment for deep drawing with a drawing ratio of 0.5 or higher, the hot plate temperature should be set to 170°C or higher, preferably 175-180°C. If the hot plate temperature is less than 170°C, insufficient heating will result in an inadequate forming state of the container. If it is too high, adverse situations such as fusion with the hot plate may occur, which is therefore not preferred.

[0086] Furthermore, the molded container of the present invention has a slit. The cross-section of the slit is V-shaped, and it can be formed by heating one side, namely the D side of the styrene-based resin layer, using a hot plate or the like, and inserting a V-shaped blade.

[0087] Example

[0088] The present invention will be described in more detail below with examples and comparative examples, but the present invention is not limited to the content of the examples, etc.

[0089] The resin raw materials used in the examples and comparative examples are described below.

[0090] (1) Oxygen barrier resin layer

[0091] Ethylene-vinyl alcohol copolymer "EVAL J-171B" (manufactured by Kuraray Co., Ltd., ethylene content 32 mol%, saponification degree ≥ 99%)

[0092] (2) Modified olefin polymer layer

[0093] "MODIC F502" (manufactured by Mitsubishi Chemical Corporation)

[0094] (3) Styrene-based resin layer

[0095] Impact-resistant polystyrene resin: "TOYOSTYROL H870" (manufactured by Toyo Styrene Co., Ltd., with a grafted rubber content of 8.6% by mass and a grafted rubber particle size of 2.5 μm).

[0096] Polystyrene resin: "HRM23" (manufactured by Toyo Styrene Co., Ltd.)

[0097] Styrene-conjugated diene block copolymer: "730L" (manufactured by Denka Co., Ltd., conjugated diene content 25% by mass)

[0098] <Example 1>

[0099] Two 40mm single-screw extruders were used for the oxygen barrier resin layer and modified olefin polymer layers A and B, and one 65mm single-screw extruder was used for the styrene resin layers C and D. Using a feed block method, a multilayer resin sheet with a total thickness of 800μm was obtained, consisting of a 160μm styrene resin layer C, a 20μm modified olefin polymer layer A, a 30μm oxygen barrier resin layer, a 20μm modified olefin polymer layer B, and a 570μm styrene resin layer D. For the multilayer resin sheet, metal rollers with a surface roughness (Ra) of 0.5μm were used as traction rollers (contact rollers and casting rollers). The surface of the styrene resin layer C was clamped onto the contact roller side, and the surface of the styrene resin layer D was clamped onto the casting roller side, thereby imparting a surface roughness (Ra) of 0.3μm to the surface of the styrene resin layer C and 0.15μm to the surface of the styrene resin layer D. In styrene-based resin layers C and D, a dry blend of 17% by weight styrene-butadiene block copolymer, 71% by weight polystyrene resin, and 12% by weight impact-resistant polystyrene resin is used. In this case, the content of grafted rubber in the polystyrene is 1.2% by weight.

[0100] <Examples 2-10>

[0101] Except for the polystyrene resin blending ratio of the styrene resin layers C and D as shown in Table 1, multilayer resin sheets were obtained using the same method as in Example 1.

[0102] <Example 11>

[0103] Using metal rollers (contact rollers and casting rollers) with an embossed surface roughness (Ra) of 0.3 μm, a surface roughness (Ra) of 0.2 μm is applied to the C side of the styrene-based resin layer and 0.1 μm to the D side of the styrene-based resin layer. Otherwise, a multilayer resin sheet is obtained using the same method as in Example 2.

[0104] <Example 12>

[0105] Using metal rollers (contact rollers and casting rollers) with an embossed surface roughness (Ra) of 1 μm, a surface roughness (Ra) of 0.95 μm is applied to the C side of the styrene-based resin layer and 0.5 μm to the D side of the styrene-based resin layer. Otherwise, a multilayer resin sheet is obtained using the same method as in Example 2.

[0106] <Example 13>

[0107] Using metal rollers (contact rollers and casting rollers) with an embossed surface roughness (Ra) of 1.5 μm, a surface roughness (Ra) of 1.3 μm is applied to the C side of the styrene-based resin layer and 1.0 μm to the D side of the styrene-based resin layer. Otherwise, a multilayer resin sheet is obtained using the same method as in Example 2.

[0108] <Example 14>

[0109] Using metal rollers (contact rollers and casting rollers) with an embossed surface roughness (Ra) of 2 μm, a surface roughness (Ra) of 1.9 μm is applied to the C side of the styrene-based resin layer and 1.2 μm to the D side of the styrene-based resin layer. Otherwise, a multilayer resin sheet is obtained using the same method as in Example 2.

[0110] <Example 15>

[0111] A multilayer resin sheet is formed by a layer consisting of a styrene-based resin layer C (180 μm), a modified olefin polymer layer A (25 μm), an oxygen barrier resin layer (40 μm), a modified olefin polymer layer B (25 μm), and a styrene-based resin layer D (350 μm), with an overall thickness of 620 μm. Otherwise, a multilayer resin sheet is obtained using the same method as in Example 2. Furthermore, the overall thickness of the multilayer resin sheet and the thickness of each resin layer are varied by adjusting the discharge rate of molten resin feedstock from each extruder, adjusting the outlet (lip) spacing of the T-die, and adjusting the winding speed of the multilayer resin sheet.

[0112] <Example 16>

[0113] A multilayer resin sheet is formed having a layer structure of 100 μm styrene-based resin layer C, 25 μm modified olefin polymer layer A, 40 μm oxygen barrier resin layer, 25 μm modified olefin polymer layer B, and 350 μm styrene-based resin layer D, with an overall thickness of 540 μm. Otherwise, a multilayer resin sheet is obtained using the same method as in Example 2.

[0114] <Example 17>

[0115] A multilayer resin sheet is formed having a layer structure of 100 μm styrene-based resin layer C, 20 μm modified olefin polymer layer A, 30 μm oxygen barrier resin layer, 20 μm modified olefin polymer layer B, and 630 μm styrene-based resin layer D, with an overall thickness of 800 μm. Otherwise, a multilayer resin sheet is obtained using the same method as in Example 2.

[0116] <Example 18>

[0117] A multilayer resin sheet was obtained by means of a styrene-based resin layer C 150 μm / a modified olefin polymer layer A 20 μm / an oxygen barrier resin layer 30 μm / a modified olefin polymer layer B 20 μm / a styrene-based resin layer D 800 μm, with an overall thickness of 1020 μm.

[0118] <Example 19>

[0119] A multilayer resin sheet is formed having a layer structure of 80 μm styrene-based resin layer C, 20 μm modified olefin polymer layer A, 30 μm oxygen barrier resin layer, 20 μm modified olefin polymer layer B, and 500 μm styrene-based resin layer D, with an overall thickness of 650 μm. Otherwise, a multilayer resin sheet is obtained using the same method as in Example 2.

[0120] <Example 20>

[0121] A multilayer resin sheet is formed having a layer structure of 100 μm styrene-based resin layer C, 20 μm modified olefin polymer layer A, 30 μm oxygen barrier resin layer, 20 μm modified olefin polymer layer B, and 500 μm styrene-based resin layer D, with an overall thickness of 670 μm. Otherwise, a multilayer resin sheet is obtained using the same method as in Example 2.

[0122] <Example 21>

[0123] A multilayer resin sheet is formed having a layer structure of 200 μm styrene-based resin layer C, 20 μm modified olefin polymer layer A, 30 μm oxygen barrier resin layer, 20 μm modified olefin polymer layer B, and 500 μm styrene-based resin layer D, with an overall thickness of 770 μm. Otherwise, a multilayer resin sheet is obtained using the same method as in Example 2.

[0124] <Example 22>

[0125] A multilayer resin sheet was obtained by means of a layer consisting of a 250 μm styrene-based resin layer C, a 20 μm modified olefin polymer layer A, a 30 μm oxygen barrier resin layer, a 20 μm modified olefin polymer layer B, and a 500 μm styrene-based resin layer D, with an overall thickness of 820 μm.

[0126] <Comparative Example 1>

[0127] The styrene-butadiene block copolymer, 78% polystyrene resin, and 10% impact-resistant polystyrene resin were dry-blended in styrene resin layers C and D. Otherwise, a multilayer resin sheet was obtained by the same method as in Example 1.

[0128] <Comparative Example 2>

[0129] The styrene-butadiene block copolymer, 17% polystyrene resin, and 10% impact-resistant polystyrene resin were dry-blended in styrene resin layers C and D. Otherwise, a multilayer resin sheet was obtained by the same method as in Example 1.

[0130] <Comparative Example 3>

[0131] The styrene-butadiene block copolymer, 24% polystyrene resin, and 3% impact-resistant polystyrene resin were dry-blended in styrene resin layers C and D. Otherwise, a multilayer resin sheet was obtained by the same method as in Example 1.

[0132] <Comparative Example 4>

[0133] The styrene-based resin layers C and D are dry-blended with 10% by weight of styrene-butadiene block copolymer, 40% by weight of polystyrene resin, and 50% by weight of impact-resistant polystyrene resin. Otherwise, a multilayer resin sheet is obtained by the same method as in Example 1.

[0134] <Comparative Example 5>

[0135] The styrene-butadiene block copolymer, 68% polystyrene resin, and 3% impact-resistant polystyrene resin are dry-blended in styrene resin layers C and D. The styrene resin layer C is 160 μm thick, the modified olefin polymer layer A is 15 μm thick, the oxygen barrier resin layer is 20 μm thick, the modified olefin polymer layer B is 15 μm thick, and the styrene resin layer D is 590 μm thick, with an overall thickness of 800 μm. Otherwise, a multilayer resin sheet is obtained by the same method as in Example 1.

[0136] <Comparative Example 6>

[0137] The styrene-butadiene block copolymer, 15% polystyrene resin, and 27% impact-resistant polystyrene resin were dry-blended in styrene resin layers C and D. Otherwise, a multilayer resin sheet was obtained by the same method as in Example 1.

[0138] <Comparative Example 7>

[0139] The styrene-butadiene block copolymer, 30% polystyrene resin, and 12% impact-resistant polystyrene resin were dry-blended in styrene-based resin layers C and D. A metal roller (contact roller and casting roller) with a surface roughness (Ra) of 0.2 μm was used to impart a surface roughness (Ra) of 0.1 μm to the surface of styrene-based resin layer C and 0.07 μm to the surface of styrene-based resin layer D. Otherwise, a multilayer resin sheet was obtained by the same method as in Example 1.

[0140] <Comparative Example 8>

[0141] Using metal rollers (contact rollers and casting rollers) with a surface roughness (Ra) of 5 μm, a surface roughness (Ra) of 2.4 μm is applied to the C side of the styrene-based resin layer and 2.1 μm to the D side of the styrene-based resin layer. Otherwise, a multilayer resin sheet is obtained in the same manner as in Comparative Example 7.

[0142] <Comparative Example 9>

[0143] The styrene-butadiene block copolymer, polystyrene resin, and impact-resistant polystyrene resin are dry-blended in styrene resin layers C and D. The styrene resin layer C is 250 μm thick, the modified olefin polymer layer A is 20 μm thick, the oxygen barrier resin layer is 30 μm thick, the modified olefin polymer layer B is 20 μm thick, and the styrene resin layer D is 250 μm thick, with an overall thickness of 570 μm. Otherwise, a multilayer resin sheet is obtained by the same method as in Example 1.

[0144] <Comparative Example 10>

[0145] A multilayer resin sheet was obtained having a layer structure consisting of a styrene-based resin layer C 100 μm, a modified olefin polymer layer A 20 μm, an oxygen barrier resin layer 20 μm, a modified olefin polymer layer B 20 μm, and a styrene-based resin layer D 800 μm, with an overall thickness of 960 μm. Otherwise, the multilayer resin sheet was obtained using the same method as Comparative Example 9.

[0146] <Comparative Example 11>

[0147] The styrene-butadiene block copolymer, polystyrene resin, and impact-resistant polystyrene resin are dry-blended in styrene resin layers C and D. The styrene resin layer C is 40 μm thick, the modified olefin polymer layer A is 20 μm thick, the oxygen barrier resin layer is 30 μm thick, the modified olefin polymer layer B is 20 μm thick, and the styrene resin layer D is 390 μm thick, with an overall thickness of 500 μm. Otherwise, a multilayer resin sheet is obtained by the same method as in Example 1.

[0148] <Comparative Example 12>

[0149] A multilayer resin sheet is formed having a layer structure of 350 μm styrene-based resin layer C, 20 μm modified olefin polymer layer A, 30 μm oxygen barrier resin layer, 20 μm modified olefin polymer layer B, and 480 μm styrene-based resin layer D, with an overall thickness of 900 μm. Otherwise, a multilayer resin sheet is obtained using the same method as in Example 12.

[0150] The evaluation methods and criteria for the fabricated multilayer sheets are described below. The results are shown in Tables 1-3.

[0151] <Thickness of each layer of the sheet>

[0152] The sheet material was cut into pieces approximately 2mm x 5mm, and cross-sections were created using a single-edged blade. The resulting cross-sections were magnified and observed using a VK-8500 laser microscope manufactured by KEYENCE Corporation, and the thickness of each layer was measured.

[0153] <Surface Roughness (Ra)>

[0154] The surface roughness (Ra) of the sheet is measured using the following method.

[0155] [Measurement Method] The method described in JIS B0601

[0156] Equipment used: KEYENCE Co., Ltd. VK-8500

[0157] Transparency

[0158] The total light transmittance of the sheet was measured using the following method and evaluated according to the following criteria.

[0159] [Measurement Method] The method described in JIS K7105

[0160] Equipment used: NDH-5000 haze meter from Nippon Denshoku Kogyo Co., Ltd.

[0161] [Evaluation Criteria]

[0162] ○: Total light transmittance of 80% or more

[0163] ×: Total light transmittance is less than 80%.

[0164] <Glossiness>

[0165] The gloss of the sheet was measured using the following method and evaluated according to the following criteria.

[0166] [Measurement Method] The method described in JIS Z8741

[0167] Equipment used: GLOSS METER VG7000, Nippon Denshoku Kogyo Co., Ltd.

[0168] Measurement angle: 60°

[0169] [Evaluation Criteria]

[0170] ○: Gloss level 80 or higher

[0171] ×: Gloss level less than 80

[0172] <Anti-blocking properties>

[0173] The sheet material was cut into 10×10cm pieces, and the inner and outer surfaces of the roll were overlapped. A 5×5cm metal sheet and a 10kg weight were then sequentially placed on top, and the mixture was placed at 23°C and 50% humidity for 3 days. After 3 days, the weight and metal sheet were removed, and the samples were peeled apart to check for adhesion. The adhesion resistance was evaluated according to the following criteria. Furthermore, the results of this evaluation method confirmed that it effectively addresses the adhesion state to the rollers after the sheet material has been film-formed and left for an extended period.

[0174] ○: Samples can be peeled off without any resistance.

[0175] ×: Unable to peel off the sample.

[0176] Multilayer resin sheets are processed under the following conditions, from molding and slit formation to container punching. Figure 4 It undergoes a series of processes to obtain Figure 2 The container shown. Furthermore, regarding the slit, it is formed from the surface of the styrene-based resin layer D, and the heating temperature of the slit-forming portion is adjusted to 160°C to impart a slit depth of 250 μm.

[0177] Equipment used: CFF-300 (manufactured by CKD Corporation)

[0178] Upper heating plate temperature: 170℃

[0179] Lower heating plate temperature: 170℃

[0180] Upper structure of the container punching blade: outer blade

[0181] Lower structure of the container punching blade: inner blade

[0182] The gap between the upper and lower sides of the container punching blade: 20μm

[0183] <Molding State>

[0184] The formability of containers during thermoforming should be evaluated according to the following criteria.

[0185] ○: Good formability

[0186] ×: Confirmed that poor molding and surface layer cracking are caused by hot plate adhesion.

[0187] <Wall thickness distribution>

[0188] Touch and inspect the sides and bottom of the container to determine if the wall thickness is uneven, based on the following criteria.

[0189] ○: The wall thickness is not biased towards the bottom surface, and the wall thickness of the side portion is sufficient.

[0190] ×: The wall thickness is biased towards the bottom surface, while the wall thickness on the side surface is thinner.

[0191] <Knife bending properties>

[0192] Hold the container by one side, as... Figure 3 As shown, the slit portion is repeatedly bent toward the opposite side of the surface where the slit is formed, and the quality of the slit bending performance is evaluated according to the following criteria.

[0193] ○: It can be easily bent by hand, and it will not break even after being bent more than 5 times.

[0194] ×: It cannot be easily bent by hand, or it will break after being bent once.

[0195] <Comprehensive Judgment>

[0196] Those who receive all of the above evaluation results as ○ are considered ○, and those who receive all other results are considered ×.

[0197] [Table 1]

[0198]

[0199] [Table 2]

[0200]

[0201] [Table 3]

[0202]

[0203] As can be confirmed from Examples 1 to 22, the multilayer resin sheet for deep drawing of the present invention can easily impart slit bending properties after thermoforming, and the sheet also has good transparency, gloss and anti-adhesion properties, and good formability when thermoformed into a container, and there is no uneven wall thickness distribution. Therefore, a deep-drawn molded container with excellent design and visual recognizability can be obtained.

[0204] Compared to Examples 1-22, Comparative Examples 1 and 4, which have a lower content of styrene-conjugated diene block copolymer in the styrene-based resin layer D (and a higher content of polystyrene containing grafted rubber), experienced breakage after only one bend in terms of cut bending performance. On the other hand, Comparative Examples 2 and 3, which have a higher content of styrene-conjugated diene block copolymer (and a lower content of polystyrene containing grafted rubber), showed uneven wall thickness distribution in the containers. Furthermore, Comparative Example 5, with a lower content of grafted rubber in the polystyrene resin, exhibited poor adhesion resistance, while Comparative Example 6, with a higher content of grafted rubber in the polystyrene resin, showed poor transparency and gloss. Additionally, Comparative Example 7, with a lower surface roughness (Ra) on the styrene-based resin layer D side, experienced poor molding due to hot plate adhesion during container molding. Conversely, Comparative Example 8, with a higher surface roughness (Ra) on both the styrene-based resin layer C side and the styrene-based resin layer D side, exhibited poor transparency and gloss. In Comparative Example 9, where the styrene-based resin layer D has a smaller proportion of thickness, the styrene-based resin layer D breaks off during the cutting process, exposing the modified olefin polymer layer B. On the other hand, in Comparative Example 10, where the styrene-based resin layer D has a larger proportion of thickness, the cut is not easily bendable by hand. Similarly, in Comparative Example 11, where the styrene-based resin layer C has a smaller proportion of thickness, the styrene-based resin layer C breaks off during container molding, exposing the modified olefin polymer layer A. On the other hand, in Comparative Example 12, where the styrene-based resin layer C has a larger proportion of thickness, the cut is not easily bendable by hand.

[0205] Explanation of reference numerals in the attached figures

[0206] 1: Oxygen barrier resin layer

[0207] 2: Modified olefin polymer layer A

[0208] 3: Modified olefin polymer layer B

[0209] 4: Styrene-based resin layer C

[0210] 5: Styrene-based resin layer D

Claims

1. A multilayer resin sheet comprising an oxygen barrier resin layer and styrene-based resin layers C and D, wherein the styrene-based resin layers C and D are laminated on opposite sides of the oxygen barrier resin layer, respectively, with modified olefin polymer layers A and B as intermediates. The overall thickness of the multilayer resin sheet is 500-1200 μm. The thickness of the oxygen barrier resin layer relative to the overall thickness of the multilayer resin sheet is 0.5-8%. The thicknesses of the modified olefin polymer layers A and B are each 0.5-4% of the overall thickness of the multilayer resin sheet. The thickness of the styrene-based resin layer C is 10-35% of the overall thickness. The thickness of the resin layer D is 50-80% of the overall thickness. The surface roughness (Ra) of the surfaces of the styrene resin layers C and D opposite to the surfaces of the modified olefin polymer layers A and B is 0.1-2.0 μm. The styrene resin layer D contains 15-70% by mass of styrene-conjugated diene block copolymer and 30-85% by mass of polystyrene. The polystyrene contains 0.5-5% by mass of conjugated diene rubber obtained by graft polymerization of styrene monomers. The content of the conjugated diene rubber obtained by graft polymerization of styrene monomers is 0.3-3% by mass relative to the total styrene resin used in the styrene resin layer D.

2. The multilayer resin sheet according to claim 1, wherein, The oxygen barrier resin layer comprises an ethylene-vinyl alcohol copolymer resin.

3. The multilayer resin sheet according to claim 1 or 2, wherein, The thicknesses of the modified olefin polymer layers A and B are 10~50μm, respectively.

4. The multilayer resin sheet according to claim 1 or 2, wherein, The thickness of the oxygen barrier resin layer is 10~50μm.

5. A molded article, which is a molded article of the multilayer resin sheet according to any one of claims 1 to 4.

6. The molded article according to claim 5, wherein it is a molded container having a slit on the surface of the styrene resin layer D side.

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