Multilayer sheets and containers using the same

Abstract

To provide a sheet which can suppress occurrence of an adhesive foreign matter while using a polylactic acid as a main raw material, a container using the sheet, and an appropriate method for producing the sheet.SOLUTION: A multilayer sheet has a layer structure including outermost surface layers composed of a styrenic resin or a propylene resin on the outermost surface parts on both surfaces of the multilayer sheet, and a core layer composed of a resin composition containing a polylactic acid and a styrenic resin at an intermediate part of the multilayer sheet. A method for producing the multilayer sheet includes integrating all of the layers of the multilayer sheet in a die, and coextrusion molding the integrated layer.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a multilayer sheet, a container using the same, and a method for manufacturing the multilayer sheet.

Background Art

[0002] Conventionally, in stores such as supermarkets, convenience stores, department stores, and bento shops, containers obtained by molding a synthetic resin sheet are widely used as containers for packaging fresh food products, processed food products, etc.

[0003] Containers made of synthetic resin sheets for packaging fresh food products, processed food products, etc. are generally incinerated after one use, and it is also a situation where waste and dissipation into the natural environment cannot be overlooked. Therefore, in recent years, from the viewpoints of petroleum resource conservation and environmental protection, it has been recommended to reduce the amount of synthetic resin used, or to use a material with less environmental impact, if not for the entire container, at least for a part of it.

[0004] In the art, polylactic acid made from plants has attracted attention as a material that can reduce the environmental load more than before. However, polylactic acid alone has insufficient moldability. For example, when attempting to manufacture a food container by molding a polylactic acid sheet, it is difficult to satisfactorily shape it into the desired container form. Therefore, various resin compositions containing, for example, polylactic acid and styrene-based resins have been developed, and they are disclosed in, for example, Patent Documents 1 to 7.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

[0006] When manufacturing containers obtained by further molding synthetic resin sheets, especially those that come into direct contact with food, such as containers for prepared foods, it is essential from a hygiene and safety standpoint that no foreign matter adheres to the surface of the sheet material. When manufacturing sheets using synthetic resin, sticky foreign matter (sometimes called "eye discharge") originating from the synthetic resin and its additives can accumulate around the discharge port (lip) of the die used for sheet formation. As sheet formation progresses, the amount of sticky foreign matter gradually increases, eventually adhering to the sheet and contaminating its surface. In particular, when using raw materials containing polylactic acid, the amount of sticky foreign matter generated tends to increase, further increasing the risk of contamination of the sheet surface. As a result, the frequency of removing sticky foreign matter accumulated around the lip increases, and production efficiency decreases. Under these circumstances, there has been a need for a sheet that uses polylactic acid as the main raw material but can suppress the generation of sticky foreign matter, a container using the said sheet, and an appropriate method for manufacturing the said sheet. [Means for solving the problem]

[0007] In view of the above circumstances, the inventors considered means to solve the problems and have completed the present invention. That is, the present invention is as follows (1) to (8). (1) A multilayer sheet having a layer structure comprising a top surface layer made of a styrene resin or a propylene resin on the outermost surface of both sides of the multilayer sheet, and a core layer made of a resin composition containing polylactic acid and a styrene resin in the middle of the multilayer sheet. (2) The multilayer sheet according to (1), wherein the amount of polylactic acid in the resin composition of the core layer is 15 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the total of polylactic acid and styrene resin. (3) The multilayer sheet according to (1) or (2), wherein the total mass ratio of polylactic acid and styrene resin in the resin composition of the core layer is 80% by mass or more and 99% by mass or less of the total mass of the resin composition of the core layer. (4) A multilayer sheet as described in any one of items (1) to (3), wherein the core layer is a foamed layer with a foaming ratio of 1.1 times or more and 2.0 times or less. (5) A multilayer sheet as described in any one of items (1) to (4), wherein the thickness ratio of the core layer is 50% or more and 90% or less of the total thickness of the multilayer sheet. (6) A method for manufacturing a multilayer sheet according to any one of (1) to (5), wherein all layers of the multilayer sheet are integrated and co-extruded in a die. (7) A container formed from a multilayer sheet as described in any one of items (1) to (5). (8) The container described in (7), which is a food container. [Effects of the Invention]

[0008] By implementing the present invention, it is possible to provide a multilayer sheet that contains polylactic acid as a main component, which has a low environmental impact, and also reduces hygiene and safety risks, making it particularly suitable for use in food containers. Furthermore, it is possible to provide a manufacturing method suitable for the multilayer sheet of the present invention. [Modes for carrying out the invention]

[0009] Preferred embodiments of the present invention will be described in detail below. However, the embodiments described below are merely examples of typical embodiments of the present invention and should not be interpreted as narrowly limiting the scope of the present invention.

[0010] <Layer structure> The multilayer sheet of the present invention is a multilayer sheet having a layer structure comprising a top surface layer made of a styrene-based resin or a propylene-based resin on the outermost surface of both sides of the multilayer sheet, and a core layer made of a resin composition containing polylactic acid and a styrene-based resin in the middle of the multilayer sheet.

[0011] In the multilayer sheet of the present invention, the outermost layer refers to the two outermost layers on both sides of the sheet, and the outermost layer may be either a styrene-based resin or a propylene-based resin, and the two layers do not necessarily have to be the same. That is, for example, the outermost layer on one side may be a styrene-based resin, and the outermost layer on the opposite side may be a propylene-based resin. Alternatively, for example, the outermost layer on one side may be, for example, general polystyrene (hereinafter referred to as GPPS), and the outermost layer on the opposite side may be high-impact polystyrene (hereinafter referred to as HIPS), which is the same styrene-based resin. Of course, it is also acceptable for both outermost layers to be, for example, GPPS.

[0012] In this invention, the intermediate portion of a multilayer sheet refers to the portion of the multilayer sheet excluding both outermost layers. In this invention, one requirement is that the intermediate portion of the multilayer sheet contains a core layer made of a resin composition containing polylactic acid and a styrene-based resin. The core layer may be any layer made of a resin composition containing polylactic acid and a styrene-based resin. Multiple core layers may be included, as long as they are made of a resin composition containing polylactic acid and a styrene-based resin. Furthermore, if multiple core layers are included, their chemical compositions may be the same or different. Additionally, the intermediate portion of the sheet may contain layers that do not contain polylactic acid, styrene-based resin, or neither, as needed. The simplest layer configuration of this invention is a multilayer sheet with a so-called two-type, three-layer configuration, where one layer with the same chemical composition is provided on each side of the core layer. This is preferable from the viewpoint of ease of manufacture because it is the simplest layer configuration.

[0013] <Styrene-based resin> The outermost layer of the multilayer sheet of the present invention is made of a styrene-based resin or a propylene-based resin. Examples of the styrene-based resin include resins obtained by polymerizing or copolymerizing one or more styrene monomers selected from the group consisting of styrene, methylstyrene, t-butylstyrene, and α-methylstyrene; rubber-modified styrene-based resins known as HIPS or copolymers of styrene and butadiene (hereinafter referred to as SBC); and resins obtained by copolymerizing the styrene-based monomer with one or more monomers that can copolymerize with the styrene-based monomer, such as acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate. Among these, preferred styrene-based resins include GPPS, HIPS, SBC, MS resin, MBS resin, and resin compositions obtained by mixing these resins. Particularly preferred styrene-based resins are GPPS and HIPS. Furthermore, the styrene-based resin forming the outermost layer may contain various additives such as colorants, antioxidants, antistatic agents, lubricants, and plasticizers, in amounts that do not impair the effects of the present invention, as needed. These additives may be included in the styrene-based resin beforehand, or they may be added at the time of forming the multilayer sheet.

[0014] There are no particular restrictions on the molecular weight of the styrene-based resin, but the weight-average molecular weight (Mw) calculated by gel permeation chromatography and conversion from a calibration curve using GPPS with a standard molecular weight is preferably between 10,000 and 500,000. Particularly preferably, the Mw is between 30,000 and 400,000. Styrene-based resins with an Mw exceeding 500,000 have low fluidity, which reduces sheet moldability and tends to cause rough or moiré patterns on the sheet surface. On the other hand, an Mw of less than 10,000 is undesirable because it results in poor heat resistance and impact resistance of the sheet.

[0015] Further, as an index of the fluidity of the styrene resin during melting, the MFR value at 200°C and 5 kgf measured by a method conforming to the H method of JISK7210 is preferably 1 (g / 10 min) or more and 15 (g / 10 min) or less, and more preferably 2 (g / 10 min) or more and 8 (g / 10 min) or less.

[0016] <Propylene-based resin> The outermost layer of the multilayer sheet of the present invention is made of a styrene resin or a propylene-based resin. Examples of the propylene-based resin include a propylene homopolymer, a propylene random copolymer, that is, a random copolymer of propylene and ethylene and / or butene-1 (however, the propylene monomer unit is numerically more in the molecule), a propylene block copolymer, that is, a mixture of a propylene homopolymer and an ethylene-propylene polymer. It is also possible to further mix and use different types of propylene-based resins as described above. A particularly preferred propylene-based resin is a propylene homopolymer. In addition, various additives such as a colorant, an antioxidant, an antistatic agent, a lubricant, and a plasticizer can be added to these propylene-based resins as needed.

[0017] There is no particular limitation on the molecular weight of the propylene-based resin. However, as an index of the fluidity during melting, the MFR value at 230°C and 2.16 kgf measured by a method conforming to the M method of JISK7210 is preferably 0.2 (g / 10 min) or more and 8 (g / 10 min) or less, and more preferably 0.3 (g / 10 min) or more and 5 (g / 10 min) or less.

[0018] <Core layer, polylactic acid> The core layer of the multilayer sheet of the present invention is made of a resin composition containing polylactic acid and a styrene-based resin. The polylactic acid that can be used in the core layer of the multilayer sheet of the present invention is a polymer formed by the esterification of many lactic acid units. Lactic acid exists in two forms, L-form and D-form, depending on the stereoconfiguration of the functional group bonded to one chiral carbon. Therefore, polylactic acid can be formed with D-form or L-form monomer units bonded almost individually, with a mixture of D-form and L-form monomer units bonded together, and furthermore, the bond between D-form and L-form monomer units can be random, alternating, or block-like. However, from the viewpoint of heat resistance, it is preferable that the polylactic acid contains 95% by mass or more of L-form monomer units. Polylactic acid has recently attracted attention from the viewpoint of environmental protection as a carbon-neutral compound that can be synthesized from plant-derived raw materials, and therefore, it is preferable that the polylactic acid used in the present invention is also plant-derived polylactic acid. There are no particular limitations on the molecular weight of the polylactic acid; it is sufficient if it can be melt-mixed with the styrene-based resin. However, generally, polylactic acid with a molecular weight (Mw) of 50,000 or more is used. Note that the polylactic acid used for the outermost layer and the core layer does not necessarily have to be the same, but it is preferable if there is no particular need to use the same material.

[0019] <Core layer, styrene resin> The core layer of the multilayer sheet of the present invention is made of a resin composition containing polylactic acid and a styrene-based resin. The styrene-based resin that can be used in the core layer of the multilayer sheet of the present invention is the same as the styrene-based resin that can be used in the outermost layer. Particularly preferred styrene-based resins are GPPS and HIPS. Note that the styrene-based resin used in the outermost layer and the styrene-based resin used in the core layer do not necessarily have to be the same. Furthermore, the Mw of the styrene-based resin in the core layer is preferably between 10,000 and 500,000. Particularly preferred is an Mw of 30,000 and 400,000. Using a styrene-based resin with an Mw of less than 10,000 is undesirable because it results in poor heat resistance and impact resistance of the sheet. On the other hand, using a styrene-based resin with an Mw of more than 500,000 has low fluidity, which leads to a decrease in sheet moldability and a new problem of widening variations in sheet film thickness.

[0020] <Mass ratio of polylactic acid to the total mass of polylactic acid and styrene resin in the core layer> The multilayer sheet of the present invention is preferably a multilayer sheet in which, in the core layer, the amount of polylactic acid per 100 parts by mass of the total amount of polylactic acid and styrene resin contained in the resin composition constituting the core layer is 15 parts by mass or more and 50 parts by mass or less, preferably 20 parts by mass or more and 45 parts by mass or less. If the amount of polylactic acid exceeds 50 parts by mass, the heat resistance decreases, which is undesirable, while if it is less than 15 parts by mass, the proportion of polylactic acid is too low, which deviates from the purpose of environmental protection.

[0021] <Mass ratio of polylactic acid + styrene resin to the total composition of the core layer> In the multilayer sheet of the present invention, the resin composition constituting the core layer may further contain, as necessary, a colorant, antioxidant, antistatic agent, lubricant, plasticizer, compatibilizer, fluidizer, antiblocking agent, and crystal nucleating agent, in addition to polylactic acid and styrene-based resin. The total mass ratio of polylactic acid and styrene-based resin contained in the resin composition constituting the core layer is 80% by mass or more and 99% by mass or less of the total mass of the resin composition constituting the core layer, preferably 85% by mass or more and 95% by mass or less. Specifically, examples of the compatibilizer include a block copolymer of styrene and butadiene, a graft copolymer obtained by graft copolymerizing polybutadiene with methyl methacrylate and styrene, and a block copolymer of methyl methacrylate and n-butyl acrylate.

[0022] Furthermore, as an indicator of the fluidity during melting of the resin composition comprising polylactic acid and styrene resin constituting the core layer, the MFR value at 200°C and 5 kgf, measured by a method compliant with JIS K7210 H method, is preferably 1 (g / 10 min) or more and 15 (g / 10 min) or less, and more preferably 5 (g / 10 min) or more and 12 (g / 10 min) or less.

[0023] <Foaming ratio> In the multilayer sheet of the present invention, there are no particular limitations on the foaming state of each layer; foaming may be performed or not performed depending on the intended use. It is also possible to make only specific layers foamed. The foaming ratio is generally 1.1 times or more and 10 times or less, preferably 1.1 times or more and 5 times or less, and more preferably 1.1 times or more and 2 times or less. When foaming is performed, the bubbles may be interconnected, closed, or a mixture of both. For example, by foaming the core layer, it is possible to obtain a multilayer sheet or container that is lighter and has lower thermal conductivity. Also, for example, if the outermost layer is not foamed, it is possible to obtain a multilayer sheet with higher surface smoothness, printability and gloss.

[0024] When a specific layer in a multilayer sheet is to be a foamed layer, it is preferable to add a foaming agent separately from the raw resin of the foamed layer during the film formation of the multilayer sheet. There are no particular limitations on the type of foaming agent, but inorganic or organic chemical foaming agents are preferably used. There are also no particular limitations on the method of adding the foaming agent; for example, the foaming agent can be added alone, or a resin masterbatch containing the foaming agent can be added. The amount of foaming agent added can be adjusted as appropriate depending on the target thickness and foaming ratio of the multilayer sheet, but it is usually added in the range of 0.3 to 3 parts by mass per 100 parts by mass of the resin composition of the core layer.

[0025] In the multilayer sheet of the present invention, there are no particular limitations on the overall thickness of the sheet, but the overall thickness is preferably 0.2 mm or more and 3.0 mm or less, and more preferably 0.4 mm or more and 1.5 mm or less. The multilayer sheet of the present invention is preferably used as a sheet material for food containers, but if the overall thickness is less than 0.2 mm, the absolute strength is insufficient. On the other hand, if it exceeds 3.0 mm, the shapeability and flexibility decrease due to the thickness, making it generally difficult to mold it into food containers, and it also becomes difficult to roll the sheet into a roll.

[0026] Furthermore, in the multilayer sheet of the present invention, there are no particular limitations on the ratio of the thickness of each layer to the total thickness of the sheet. However, the core layer of the multilayer sheet of the present invention is a layer that is essential to contain polylactic acid, and it is preferable that the core layer accounts for 50% to 90% of the total thickness of the sheet. If the thickness ratio of the core layer is less than 50%, the proportion of polylactic acid is low, which deviates from the purpose of environmental protection. Also, if the thickness ratio of the core layer exceeds 90%, it becomes easier for the outermost layer to be interrupted, and the appearance of the sheet is likely to be impaired. Note that there are two outermost layers, but these two layers do not necessarily have to be the same thickness.

[0027] The multilayer sheet of the present invention is not particularly limited in its layer structure, as long as it includes a top surface layer made of a styrene-based resin or a propylene-based resin on the outermost surface of both sides of the multilayer sheet, and a core layer made of a resin composition containing polylactic acid and a styrene-based resin in the middle of the multilayer sheet. In other words, it may further include layers other than the top surface layer and the core layer. However, a preferred layer structure for the multilayer sheet is a three-layer structure in which each layer is laminated in the order of top surface layer / core layer / top surface layer. Specifically, it is a two-type, three-layer multilayer sheet consisting of two top surface layers which are either HIPS or PP, and one core layer provided in the middle which is made of a resin composition containing polylactic acid and either GPPS or HIPS. By defining the layer structure of the multilayer sheet as required by the present invention, it is possible to obtain a multilayer sheet in which the adhesion of sticky foreign matter to the lip periphery of the T-die is suppressed during the manufacture of sheets containing a large amount of polylactic acid, which has been a problem until now, and a container using the same.

[0028] <Method of manufacturing the sheet> The present invention provides a manufacturing method for multilayer sheets, which is a common co-extrusion multilayer method such as a feed block method or a multi-manifold method. In this method, all layers of the multilayer sheet are integrated in a die, extruded into a single sheet from the lip of the discharge port, solidified by passing it between cooling rolls, and then wound up. A T-die (also called a T-die) is preferably used as the die. When manufacturing multilayer sheets using a common co-extrusion method, it is preferable to use resins with matching fluidity for each layer.

[0029] <Container> A container obtained by molding the multilayer sheet of the present invention is also one embodiment of the present invention. The method of molding the multilayer sheet is not particularly limited, but it can be obtained by known molding methods such as vacuum forming or pressure forming. The container of the present invention is preferably a container for food. [Examples]

[0030] The multilayer sheet of the present invention will be described in more detail below based on examples, and the results of verifying the effects of the present invention will be presented. The examples described below are representative examples of the present invention, and this should not be interpreted as narrowing the scope of the present invention.

[0031] <Sheet film formation> The multilayer sheets in Examples 1-13 and Comparative Examples 1 and 2 were all multilayer sheets consisting of two types and three layers, and were formed with the layer configurations shown in Table 1. Of these, the multilayer sheets in Example 13 and Comparative Example 2 were multilayer sheets in which the core layer was foamed. The manufacturing method of the multilayer sheets is described in more detail below.

[0032] <Example 1> The resin composition used as the core layer of the multilayer sheet in Example 1 was prepared in advance by the following method. Specifically, 10 parts by mass of polylactic acid (REVODA110, manufactured by Kaisei Biomaterials Co., Ltd.), 90 parts by mass of HIPS (Toyo Styrofoam HI E640N, manufactured by Toyo Styrene Co., Ltd.), 10 parts by mass of compatibilizer (Metablen C-223A, manufactured by Mitsubishi Chemical Corporation), and a total of 3 parts by mass of lubricant and fluidizer were premixed in a Henschel mixer, then melt-kneaded using a twin-screw extruder (Toshiba Machine Co., Ltd., TEM26SS), and the strands were further passed through a pelletizer to obtain pellets of the resin composition for the core layer of the multilayer sheet in Example 1. The twin-screw extruder was operated under the following conditions: cylinder temperature setting of 200°C and resin composition extrusion rate of 30 kg / hour.

[0033] Next, as the core layer of the multilayer sheet of Example 1, a 65 mm extruder was used to extrude pellets of the resin composition for the core layer. Additionally, two 40 mm extruders were used to extrude HIPS (Toyo Styrene HI E640N, manufactured by Toyo Styrene Co., Ltd.) as the two outermost layers of the multilayer sheet of Example 1. The molten resins were fed through a feed block into a 700 mm wide T-die, integrating the core layer and the outermost layer into a single 3-layer structure. The resulting sheet had a total thickness of 0.4 mm after cooling, and the ratio of the outermost layer / core layer / outermost layer thicknesses to the total sheet thickness was 15% / 70% / 15%. The layer structure of Example 1 is also shown in Table 1. The multilayer sheet of Example 1 extruded from the lip of the T-die was then cooled using three rolls and wound onto a winding machine. The film formation of the multilayer sheet of Example 1 was carried out continuously for 1 hour without interruption.

[0034] <Examples 2-11> For the multilayer sheets of Examples 2 to 11, the chemical composition of the resin composition of the core layer and the thickness of the outermost layer / core layer / outermost layer relative to the total thickness of the sheet were set as shown in Table 1. The heater temperature, discharge rate, and lip width of the film deposition apparatus were adjusted as appropriate, but basically the same procedure and apparatus as in Example 1 were used to deposit the multilayer sheets of Examples 2 to 11. The extrusion of the multilayer sheets of Examples 2 to 11 from the T-die was also carried out continuously for 1 hour without interruption, as in Example 1. The layer configurations of Examples 2 to 9 are shown in Tables 1 and 2, and the layer configurations of Examples 10 to 11 are shown in Table 3.

[0035] <Example 12> The multilayer sheet of Example 12 was formed using the same procedure and apparatus as in Example 3, except that both surface layers were made of PP (PL400A, manufactured by Sun Allomer Co., Ltd.). The extrusion of the multilayer sheet of Example 12 from the T-die was also carried out continuously for 1 hour without interruption, as in Example 1. The layer structure of Example 12 is also shown in Table 3.

[0036] <Comparative Example 1> In Comparative Example 1, the resin for both outermost layers was not supplied, and only the core layer used the same resin composition as in Example 3. The heater temperature, discharge volume, and lip width of the film deposition apparatus were finely adjusted as appropriate, but basically the same apparatus as in Example 3 was used to deposit a single-layer sheet in which the entire sheet was made up of a resin composition containing polylactic acid and HIPS. The sheet extrusion from the T-die in Comparative Example 1 was also carried out continuously for 1 hour without interruption, in the same manner as in Example 1. The layer structure of Comparative Example 1 is also shown in Table 3.

[0037] <Example 13> The multilayer sheet of Example 13 was prepared using the same raw materials, procedures, and equipment as in Example 12, but with the addition of 0.8 parts by mass of a foaming agent masterbatch (Polyslene ES405, manufactured by Eiwa Kasei Co., Ltd.) as the resin composition of the core layer. The heater temperature, discharge rate, and lip width of the film deposition apparatus were adjusted as appropriate to deposit a multilayer sheet with an overall thickness of 0.6 mm and a core layer foamed to 1.3 times its original volume. The extrusion of the multilayer sheet of Example 13 from the T-die was also carried out continuously for 1 hour without interruption. The layer configuration of Example 13 is shown in Table 4.

[0038] <Comparative Example 2> Similar to Comparative Example 1, the resin for both outermost layers of the multilayer sheet in Comparative Example 2 was not supplied. Only the core layer used the same resin composition as in Example 13. The heater temperatures, discharge volume, and lip width of the film deposition apparatus were adjusted as appropriate, but basically the same apparatus as in Example 13 was used to deposit a single-layer foamed sheet in which the entire sheet was made of a resin composition containing polylactic acid and HIPS. Sheet extrusion from the T-die in Comparative Example 2 was also carried out continuously for 1 hour without interruption, similar to Example 13. The layer structure of Comparative Example 2 is also shown in Table 4.

[0039] [Table 1]

[0040] [Table 2]

[0041] [Table 3]

[0042] [Table 4]

[0043] <Status of occurrence of sticky foreign matter> During the film formation extrusion of each multilayer sheet in Examples 1-13 and Comparative Examples 1 and 2, the occurrence of sticky foreign matter accumulating around the lip of the T-die, and whether or not this sticky foreign matter adhered to the surface of the sheet during extrusion, were visually observed using video camera recordings as a supplement. Naturally, the less sticky foreign matter is generated, the more the multilayer sheet reflects the effects of the present invention. In terms of evaluation stages, the best result was "A" if no sticky foreign matter was observed at all around the T-lip from immediately after the start of film formation until the end of film formation, and "E" if sticky foreign matter was significantly observed around the lip and adhered to the surface of the sheet even once during film formation. Intermediate stages, specifically when slight adhesion of sticky foreign matter to the lip was observed, were rated "B". When more lip adhesion was observed than in "B", it was rated "C". Even if no adhesion of sticky foreign matter occurred to the sheet, when there was significant accumulation of sticky foreign matter around the lip, it was rated "D". An evaluation of "A" to "C" indicated that the effects of the present invention were being demonstrated.

[0044] <Evaluation of the formability of multilayer sheets> For the multilayer sheets of Examples 1-13 and Comparative Examples 1 and 2, rectangular container samples were prepared by vacuum forming using a mold that molds the opening to a rectangular container with a width of 270 mm, a length of 200 mm, and a depth of 30 mm, with rounded corners, under heater temperature (indirect heating) conditions of 500°C above / below. The prepared rectangular containers were rated "A" if they were molded according to the mold design, and "B" if they were molded but the reproducibility of the corners etc. did not meet the standards of "A". Furthermore, the formability was evaluated in four stages: "C" if the formability did not reach "B" but was molded without cracking, and "D" if cracks or tears occurred on the surface of the container. Since formability is also affected by the shape of the container, in this test, an evaluation of "A" to "C" was considered to indicate that the effects of the present invention were being demonstrated.

[0045] The evaluation results for Examples 1-13 and Comparative Examples 1 and 2 are described in the corresponding columns in Tables 1-3. These evaluation results confirm that the present invention provides a multilayer sheet that contains polylactic acid as a component, has a low environmental impact, exhibits less adhesion of sticky foreign matter to the lip periphery during film formation, and reduces hygiene and safety risks, making it particularly suitable for food container applications.

Claims

1. On both sides of the multilayer sheet, the outermost layer and the outermost layer, The intermediate part of the multilayer sheet is a core layer made of a resin composition containing polylactic acid and a styrene-based resin, Includes, In the resin composition of the core layer, the amount of polylactic acid per 100 parts by mass of the total of polylactic acid and styrene resin is 45 parts by mass or less. A multilayer sheet (excluding multilayer sheets having a marble pattern) in which the thickness ratio of the core layer is 70% or less of the total thickness of the multilayer sheet.

2. The multilayer sheet according to claim 1, wherein the outermost layer is made of a resin composition containing a styrene-based resin or a propylene-based resin.

3. A multilayer sheet according to claim 1 or 2, having a layered structure integrated by co-extrusion molding.

4. The multilayer sheet according to any one of claims 1 to 3, wherein the total mass ratio of polylactic acid and styrene resin in the resin composition of the core layer is 80% by mass or more and 99% by mass or less of the total mass of the resin composition of the core layer.

5. The total mass ratio of polylactic acid and styrene resin in the resin composition of the core layer is 88.5% by mass or more of the total mass of the resin composition of the core layer. The multilayer sheet according to any one of claims 1 to 4, wherein the amount of polylactic acid in the resin composition of the core layer is 15 parts by mass or more and 45 parts by mass or less, relative to 100 parts by mass of the total of polylactic acid and styrene resin.

6. A container formed from a multilayer sheet according to any one of claims 1 to 5.

7. The container according to claim 6, which is a container for food.

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