JP7359565B2 - Multilayer sheet and container using the same - Google Patents

Description

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

Containers made from synthetic resin sheets have traditionally been used in stores such as supermarkets, convenience stores, department stores, and bento shops to package fresh foods and processed foods. It is used.

The synthetic resin sheet containers used to package fresh foods, processed foods, etc. are generally incinerated after one use, and their disposal or dissipation into the natural environment cannot be overlooked. From the viewpoint of resource conservation and environmental protection, it has been recommended to reduce the amount of synthetic resin used or to use materials with less environmental impact for part of the container, if not the entire container.

Polylactic acid, which is made from plants, is attracting attention in this field as a material that can reduce the burden on the environment compared to conventional materials. However, the moldability of polylactic acid alone is insufficient, and when attempting to manufacture food containers by molding a sheet of polylactic acid, for example, it is difficult to form it into the desired shape of the container. Accompanied by sadness. Therefore, various resin compositions containing, for example, polylactic acid and styrene resin have been developed, and these are disclosed in, for example, Patent Documents 1 to 7.

JP2006-328318A Japanese Patent Application Publication No. 2014-189748 JP2016-086251A Japanese Patent Application Publication No. 2016-199652 Japanese Patent Application Publication No. 2016-199654 JP2018-048248A International Publication No. 2016/080134

When manufacturing containers obtained by further molding a synthetic resin sheet, especially containers for side dishes that come into direct contact with food, from a hygiene and safety perspective, foreign matter may adhere to the surface of the sheet material. It is assumed that you have not done so. When manufacturing sheets using synthetic resins, sticky foreign matter (sometimes called "eye mucus") derived from the synthetic resins and additives contained therein is generated, and the dies used for sheet deposition are Adhesive foreign matter may accumulate around the periphery of the discharge port (lip), and as sheet film formation progresses, the amount of sticky foreign matter that remains will gradually increase, and it may eventually adhere to the sheet being formed and contaminate its surface. be. In particular, when raw materials containing polylactic acid are used, the amount of sticky foreign matter generated generally tends to increase, increasing the risk of contaminating the sheet surface. Therefore, the frequency of work to remove sticky foreign matter that has accumulated around the lip periphery increases, and production efficiency also decreases. Under these circumstances, there is a need to provide a sheet that uses polylactic acid as a main raw material and can suppress the generation of sticky foreign matter, a container using the sheet, and an appropriate manufacturing method for the sheet. Ta.

In view of this situation, the present inventors have studied means for solving the problems and have completed the present invention. That is, the present invention is (1) to (8) shown below.
(1) An outermost layer made of styrene resin or 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 styrene resin in the middle of the multilayer sheet. A multilayer sheet having a layered structure including.
(2) The multilayer sheet according to (1), wherein in the resin composition of the core layer, the number of parts by mass of polylactic acid based on 100 parts by mass of the total of polylactic acid and styrene resin is 15 parts by mass or more and 50 parts by mass or less.
(3) The ratio of the total mass 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 entire mass of the resin composition of the core layer, (1 ) or the multilayer sheet described in (2).
(4) The multilayer sheet according to any one of (1) to (3), wherein the core layer is a foam layer with an expansion ratio of 1.1 times or more and 2.0 times or less.
(5) The multilayer sheet according to any one of (1) to (4), wherein the ratio of the thickness of the core layer to the thickness of the entire multilayer sheet is 50% or more and 90% or less.
(6) The method for producing a multilayer sheet according to any one of (1) to (5), wherein all layers of the multilayer sheet are integrated and coextruded in a die.
(7) A container formed from the multilayer sheet according to any one of (1) to (5).
(8) The container according to (7), which is a food container.

By carrying out the present invention, it is possible to provide a multilayer sheet that contains polylactic acid, which has a low environmental impact, as a main component, has reduced health and safety risks, and is particularly suitable for use as food containers. Furthermore, a manufacturing method suitable for the multilayer sheet of the present invention can be provided.

Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiment described below shows an example of a typical embodiment of the present invention, and the scope of the present invention should not be construed as being narrowly limited thereby.

<Layer composition>
The multilayer sheet of the present invention has an outermost layer made of a styrene resin or a propylene resin on the outermost surface of both sides of the multilayer sheet, and a resin composition containing polylactic acid and a styrene resin in the middle of the multilayer sheet. It is a multilayer sheet having a layered structure including a core layer.

The outermost layer in the multilayer sheet of the present invention refers to the two outermost layers on both sides of the sheet, and the outermost layer may be made of either a styrene resin or a propylene resin, and the two layers are not necessarily the same. It doesn't have to be. That is, for example, the outermost layer on one side may be a styrene resin, and the outermost layer on the opposite side may be a propylene resin. Further, for example, the outermost layer on one side is made of general polystyrene (hereinafter referred to as GPPS), and the outermost layer on the opposite side is made of the same styrene resin (hereinafter referred to as HIPS). It may be. Of course, it is also permissible for both of the outermost layers to be made of GPPS, for example.

The intermediate portion of the multilayer sheet as used in the present invention is the portion of the multilayer sheet from which both outermost layers are removed. One of the requirements for the multilayer sheet of the present invention is that the multilayer sheet includes a core layer made of a resin composition containing polylactic acid and a styrene resin in the middle portion of the multilayer sheet. The core layer may be a layer made of a resin composition containing polylactic acid and styrene resin. A plurality of core layers may be included as long as the layer is made of a resin composition containing polylactic acid and styrene resin. Furthermore, when a plurality of core layers are included, their chemical compositions may be the same or different. Furthermore, a layer containing either polylactic acid or styrene resin or neither may be present in the intermediate portion of the sheet, if necessary. The simplest layer structure of the multilayer sheet of the present invention is a multilayer sheet having a so-called two-type, three-layer structure in which one layer having the same chemical composition is provided on both sides of a core layer. This case is preferable from the viewpoint of ease of manufacture since it has the simplest layer structure.

<Styrenic resin>
The outermost layer of the multilayer sheet of the present invention is made of styrene resin or propylene resin. Examples of the styrene resin include resins obtained by polymerizing or copolymerizing one or more styrene monomers selected from the group of styrene, methylstyrene, t-butylstyrene, and α-methylstyrene, HIPS, and styrene. A rubber-modified styrene resin known as a copolymer of butadiene and butadiene (hereinafter referred to as SBC), the styrene monomer, and a monomer that can be copolymerized with the styrenic monomer, such as , acrylic acid, methacrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, or Examples include resins obtained by copolymerizing two or more types of monomers. Among these, preferable styrenic resins include GPPS, HIPS, SBC, MS resin, MBS resin, and resin compositions obtained by mixing these resins. Particularly preferred styrenic resins are GPPS and HIPS. The styrene resin that forms the outermost layer may contain various additives such as colorants, antioxidants, antistatic agents, lubricants, and plasticizers, if necessary, in amounts that do not impair the effects of the present invention. It is possible to include. These various additives may be included in the styrene resin in advance, or may be newly added at the time of forming the multilayer sheet.

There is no particular restriction on the molecular weight of the styrene resin, but the weight average molecular weight (Mw) calculated by gel permeation chromatography and a calibration curve using GPPS having a standard molecular weight is 10,000. It is preferable that it is above 500,000 or less. Particularly preferably, Mw is 30,000 or more and 400,000 or less. Styrenic resins with an Mw of more than 500,000 have low fluidity, resulting in poor sheet formability and a tendency for shark skin or moire patterns to occur on the sheet surface. On the other hand, if Mw is less than 10,000, the heat resistance and impact resistance of the sheet will be poor, which is not preferable.

Furthermore, as an index of the fluidity of the styrene resin during melting, the MFR value at 200°C and 5 kgf measured by the method H of JIS K7210 is 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.

<Propylene resin>
The outermost layer of the multilayer sheet of the present invention is made of styrene resin or propylene resin. The propylene resin may be a propylene homopolymer, a propylene random copolymer, or a random copolymer of propylene and ethylene and/or butene-1 (provided that the molecule has a large number of propylene monomer units). , propylene block copolymers, ie, mixtures of propylene homopolymers and ethylene-polypropylene polymers. It is also possible to further mix and use the different types of propylene resins. A particularly preferred propylene resin is a propylene homopolymer. Note that various additives such as colorants, antioxidants, antistatic agents, lubricants, and plasticizers can be added to these propylene resins as necessary.

There is no particular restriction on the molecular weight of the propylene resin, but as an index of fluidity during melting, the MFR value at 230°C and 2.16 kgf measured by the method M of JIS K7210 is 0.2 ( g/10 minutes) or more and 8 (g/10 minutes) or less, and more preferably 0.3 (g/10 minutes) or more and 5 (g/10 minutes) or less.

<Middle 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 styrene resin. The polylactic acid that can be used in the core layer of the multilayer sheet of the present invention is a polymer made of a large number of lactic acids bonded together with esters. There are two types of lactic acid, L-form and D-form, due to differences in the steric configuration of the functional group bonded to one asymmetric carbon. Therefore, polylactic acid also has D- or L-form monomer units. Regarding the combination of almost alone, the combination of D-form monomer unit and L-form monomer unit, and the combination of D-form monomer unit and L-form monomer unit. Also, it is possible to use any of those in which they are combined randomly, in an alternating manner, or in a block shape. However, from the viewpoint of heat resistance, polylactic acid containing 95% by mass or more of L monomer units is preferable. Polylactic acid has recently attracted attention from the perspective of environmental protection as a carbon-neutral compound that can be synthesized from plant-derived raw materials, and therefore the polylactic acid used in the present invention must also be plant-derived polylactic acid. is preferred. The molecular weight of polylactic acid is not particularly limited as long as it can be melt-mixed with the styrene resin, but polylactic acid with an Mw of 50,000 or more is generally used. Note that the polylactic acids used in the outermost layer and the core layer do not necessarily have to be the same, but it is preferable that they are the same unless there is a particular need.

<Middle 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 styrene resin. The styrene resin that can be used in the core layer of the multilayer sheet of the present invention is the same as the styrene resin that can be used in the outermost layer. Particularly preferred styrenic resins are GPPS and HIPS. Note that the styrene resin used for the outermost layer and the styrene resin used for the middle core layer do not necessarily have to be the same. Further, the Mw of the styrene resin of the core layer is also preferably 10,000 or more and 500,000 or less. Particularly preferably, Mw is 30,000 or more and 400,000 or less. Using a styrene resin with an Mw of less than 10,000 is undesirable because the heat resistance and impact resistance of the sheet will be poor, while a styrenic resin with an Mw of more than 500,000 has low fluidity, resulting in poor sheet formability. As a result, a new problem arises in that the variation in sheet film thickness widens.

<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 further characterized in that, in the core layer, the number of parts by mass of polylactic acid is 15 parts by mass or more and 50 parts by mass based on the total of 100 parts by mass of polylactic acid and styrene resin contained in the resin composition constituting the core layer. parts, preferably 20 parts by mass or more and 45 parts by mass or less. If the number of parts by mass of polylactic acid exceeds 50 parts by mass, it is undesirable because the heat resistance will decrease, while if it is less than 15 parts by mass, the proportion of polylactic acid will be small and will deviate from the purpose of environmental protection.

<Mass percentage of polylactic acid + styrene resin in the entire composition of the core layer>
In the multilayer sheet of the present invention, in addition to polylactic acid and styrene resin, the resin composition constituting the core layer may optionally contain colorants, antioxidants, antistatic agents, lubricants, plasticizers, etc. It can be a resin composition containing a compatibilizing agent, a fluidizing agent, an anti-blocking material, and a crystal nucleating material, and the total mass of polylactic acid and styrene resin contained in the resin composition constituting the core layer can be A multilayer sheet can be obtained in which the ratio is 80% by mass or more and 99% by mass or less, preferably 85% by mass or more and 95% by mass or less, based on the mass of the entire resin composition constituting the core layer. In particular, examples of the compatibilizer include block copolymers of styrene and butadiene, graft copolymers of polybutadiene with methyl methacrylate and styrene, and methyl methacrylate and n-butyl acrylate. Block copolymers, etc. can be mentioned.

In addition, as an index of the fluidity at the time of melting of the resin composition containing polylactic acid and styrene resin constituting the core layer, the fluidity at 200°C and 5 kgf measured by a method based on JIS K7210 H method is used. The MFR value is preferably 1 (g/10 minutes) or more and 15 (g/10 minutes) or less, and more preferably 5 (g/10 minutes) or more and 12 (g/10 minutes) or less.

<Foaming ratio>
In the multilayer sheet of the present invention, the foaming state in each layer is not particularly limited, and may or may not be foamed depending on the intended use. It is also possible to make only a specific layer a foam layer. The expansion 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. In the case of foaming, the foam may be continuous foam, closed foam, or a mixture of both. For example, by foaming the core layer, it becomes possible to obtain multilayer sheets and containers that are lighter and have lower thermal conductivity. Further, for example, if the outermost surface layer is a non-foamed layer, a multilayer sheet with higher sheet surface smoothness and excellent printability and gloss can be obtained.

When forming a specific layer in a multilayer sheet as a foam layer, it is recommended to add a foaming agent in addition to the raw material resin for the foam layer when forming the multilayer sheet. This is a preferred manufacturing method. Although there is no particular limitation on the type of blowing agent, inorganic chemical blowing agents and organic chemical blowing agents are preferably used. Further, there is no particular limitation on the method of adding the blowing agent, and for example, it is possible to add the blowing agent alone or to add a resin masterbatch containing the blowing agent. The amount of the foaming agent added can be adjusted as appropriate depending on the target thickness and expansion ratio of the multilayer sheet, but it is usually 0.3 or more or more than 3 parts by mass per 100 parts by mass of the resin composition of the core layer. Add in a range of 100% or less.

In the multilayer sheet of the present invention, there is no particular limitation on the thickness of the entire sheet, but the overall thickness is preferably 0.2 mm or more and 3.0 mm or less, and 0.4 mm or more and 1.5 mm or less. is more preferable. The multilayer sheet of the present invention is preferably used as a sheet material for food containers, but if the total thickness is less than 0.2 mm, the absolute strength will be insufficient. On the other hand, if the thickness exceeds 3.0 mm, the shapeability and flexibility decrease due to the thickness, making it generally difficult to form into food containers and also making it difficult to wind the sheet into a roll.

Furthermore, in the multilayer sheet of the present invention, there is no particular limitation on the ratio of the thickness of each layer to the thickness of the entire sheet. However, the core layer of the multilayer sheet of the present invention is a layer that must particularly contain polylactic acid, and the core layer preferably accounts for 50% or more and 90% or less of the total thickness of the sheet. . If the thickness ratio of the core layer is less than 50%, the ratio of polylactic acid will be small, which will deviate from the purpose of environmental protection. Furthermore, if the thickness ratio of the core layer exceeds 90%, the outermost layer is likely to have discontinuous portions, increasing the possibility that the appearance of the sheet will be impaired. Note that although there are two outermost layers, these two layers do not necessarily have to have the same thickness.

The multilayer sheet of the present invention has a layer structure including an outermost layer made of styrene resin or propylene resin on the outermost surface of both sides of the multilayer sheet, and polylactic acid and styrene resin in the middle of the multilayer sheet. There is no particular limitation in other respects as long as the core layer is made of a resin composition containing the above-mentioned resin composition. In other words, layers other than the outermost surface layer and the core layer may be further included. However, the preferred layer structure of the multilayer sheet is a three-layer structure in which the layers are laminated in the order of outermost layer/center layer/uppermost layer, and specifically, the layer structure is one in which each layer is laminated in the order of outermost layer/center layer/uppermost layer. A two-layer three-layer structure consisting of two surface layers and a core layer made of a resin composition containing polylactic acid and either GPPS or HIPS, which is provided in the middle. It is a multilayer sheet. By specifying the layer structure of the multilayer sheet as required by the present invention, it is possible to eliminate the adhesion of sticky foreign matter to the lip periphery of the T-die during the production of sheets containing a large amount of polylactic acid, which has been a problem in the past. It is possible to obtain a multilayer sheet with suppressed oxidation and a container using the same.

<Sheet manufacturing method>
The method for manufacturing a multilayer sheet of the present invention is to integrate all the layers of the multilayer sheet in a die using a feed block method or a multi-manifold method, which are common coextrusion multilayer methods, and to A preferred manufacturing method is to extrude it into a sheet, solidify it by passing it between cooling rolls, and then wind up the sheet. As for the dice, T dice (also referred to as T-dies) are preferably used. In addition, when manufacturing a multilayer sheet by a general coextrusion method, it is preferable to use resins that match the fluidity of each layer.

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

EXAMPLES Hereinafter, the multilayer sheet of the present invention will be explained in more detail based on Examples, and the results of verifying the effects of the present invention will be shown. Note that the examples described below are representative examples of the present invention, and the scope of the present invention should not be interpreted narrowly thereby.

<Sheet film formation>
The multilayer sheets of Examples 1 to 13 and Comparative Examples 1 and 2 were all multilayer sheets of two types and three layers, and were formed with the layer configurations shown in Table 1. Among these, the multilayer sheets of Example 13 and Comparative Example 2 are multilayer sheets in which the core layer is particularly foamed. The method for manufacturing the multilayer sheet will be described in more detail below.

<Example 1>
A resin composition used as the core layer of the multilayer sheet of Example 1 was prepared in advance by the following method. That is, 10 parts by mass of polylactic acid (REVODA110, manufactured by Kaisho Biological Materials Co., Ltd.), 90 parts by mass of HIPS (Toyostyrene HI E640N, manufactured by Toyo Styrene Co., Ltd.), and a compatibilizer (Metablen C-223A, manufactured by Mitsubishi Chemical Corporation). A total of 3 parts by mass of a lubricant and a fluidizing agent were premixed using a Henschel mixer, and then melt-kneaded using a twin-screw extruder (TEM26SS, manufactured by Toshiba Machinery Co., Ltd.) to form strands. The resin composition for the core layer of the multilayer sheet of Example 1 was passed through a pelletizer to obtain pellets. The twin-screw extruder was operated under conditions such that the cylinder temperature was set at 200° C. and the amount of resin composition ejected was 30 kg/hour.

Next, as the core layer of the multilayer sheet of Example 1, pellets of the resin composition for the core layer were extruded using a 65 mm extruder, and as both outermost layers of the multilayer sheet of Example 1, a 40 mm extruder was used to extrude the pellets of the resin composition for the core layer. HIPS (Toyo Styrene HI E640N, manufactured by Toyo Styrene Co., Ltd.) is extruded using two units, and each molten resin is sent through a feed block into a T-die with a width of 700 mm to separate the core layer and the outermost layer. The two types and three layers are all integrated, and the thickness of the entire sheet after cooling is 0.4 mm, and the ratio of the thickness of the outermost layer / center layer / outermost layer to the thickness of the entire sheet is 15 A multilayer sheet with a layer structure of %/70%/15% was extruded. 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 up using a winding machine. The multilayer sheet of Example 1 was continuously formed for one hour without interruption.

<Examples 2 to 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/center layer/uppermost layer relative to the thickness of the entire sheet were set as shown in Table 1. However, the temperature of each heater, discharge amount, and lip width of the film forming apparatus were adjusted as appropriate, but basically the multilayer sheets of Examples 2 to 11 were formed using the same procedure and the same apparatus as in Example 1. . Extrusion of the multilayer sheets of Examples 2 to 11 through the T-die was also carried out continuously for 1 hour in the same manner as in Example 1 without interruption. The layer structures of Examples 2 to 9 are shown in Tables 1 and 2, and the layer structures of Examples 10 to 11 are shown in Table 3.

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

<Comparative example 1>
In Comparative Example 1, the resin for both outermost layers was not supplied, and the same resin composition as in Example 3 was used only for the core layer, and the temperature, discharge amount, and lip width of each heater of the film forming apparatus were finely adjusted as appropriate. Basically, using the same apparatus as in Example 3, a single-layer sheet was formed, the entire sheet being a resin composition containing polylactic acid and HIPS. Sheet extrusion from the T-die in Comparative Example 1 was also carried out continuously for 1 hour in the same manner as in Example 1 without interruption. The layer structure of Comparative Example 1 is also shown in Table 3.

<Example 13>
The multilayer sheet of Example 13 uses the same raw materials, procedures, and equipment as Example 12, except that 0.8 mass of a blowing agent masterbatch (Polysrene ES405, manufactured by Eiwa Kasei Co., Ltd.) was added as the resin composition of the core layer. The temperature of each heater, discharge amount, and lip width of the film forming apparatus were adjusted appropriately to form a multilayer sheet with an overall thickness of 0.6 mm and a core layer foamed 1.3 times. It was filmed. 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 structure of Example 13 is shown in Table 4.

<Comparative example 2>
In the multilayer sheet of Comparative Example 2, as in Comparative Example 1, the resins for both outermost layers were not supplied, and the same resin composition as in Example 13 was used only for the core layer, and the temperature and discharge amount of each heater of the film forming apparatus were adjusted. Although the lip width was adjusted as appropriate, basically the same apparatus as in Example 13 was used to form 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 in the same manner as in Example 13 without interruption. The layer structure of Comparative Example 2 is also shown in Table 4.

<Occurrence status of sticky foreign matter>
During the film formation and extrusion of each multilayer sheet of Examples 1 to 13 and Comparative Examples 1 and 2, the state of occurrence of adhesive foreign matter that remained at the lip periphery of the T-die, and the adhesive that accumulated at the lip periphery. Visual observation was made to determine whether or not the foreign matter had adhered to the surface of the sheet during extrusion, with supplementary use of recordings taken by a video camera. Of course, the less the occurrence of sticky foreign matter, the more the multilayer sheet reflects the effects of the present invention. The best evaluation stage is "A" when no adhesive foreign matter is observed on the T-lip periphery immediately after the start of film formation until the end of film formation, and the case where adhesive foreign matter on the lip periphery is noticeable. It was rated "E" if even one occurrence occurred where the film was observed and also adhered to the surface of the sheet during film formation. At the intermediate stage, if there is a slight amount of sticky foreign matter adhering to the lip, it is rated "B", if more lip adhesion is observed than "B", it is "C", until no sticky foreign matter is attached to the sheet. Also, when there was significant retention of sticky foreign matter on the lip periphery, it was rated "D". Evaluations of "A" to "C" indicate that the effects of the present invention are being achieved.

<Evaluation of formability of multilayer sheet>
The multilayer sheets of Examples 1 to 13 and Comparative Examples 1 and 2 were molded into a rectangular container with an opening width of 270 mm, an opening length of 200 mm, and a depth of 30 mm, each corner being rounded. Using the mold to be processed, a rectangular container sample was produced by vacuum forming under conditions of heater temperature (indirect heating) up/down 500°C. Regarding the manufactured square container, if it was molded according to the design of the mold, it was rated "A", and if it was molded, but the reproducibility of the corners etc. was not as good as "A", it was rated "B". . Furthermore, the formability is compared on a four-level scale: "C" if the shapeability does not reach "B" but can be molded without cracking, and "D" if cracks or tears occur on the surface of the container. evaluated. Regarding formability, since it also depends on the shape of the container, in this test, evaluations of "A" to "C" were considered to indicate that the effects of the present invention were being expressed.

The evaluation results of Examples 1 to 13 and Comparative Examples 1 and 2 are listed in the corresponding columns of Tables 1 to 3. From these evaluation results, it was found that by implementing the present invention, the film contained polylactic acid with a low environmental impact as a component, less sticky foreign matter adhered to the lip periphery during film formation, and the health and safety risks were also reduced. It was confirmed that a multilayer sheet particularly suitable for food container applications can be provided.

Claims (6)

An outermost 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. It has a layered structure integrated by coextrusion ,
The core layer is a foam layer with a foaming ratio of 1.1 times or more and 2.0 times or less,
A multilayer sheet, wherein in the resin composition of the core layer, the number of parts by mass of polylactic acid is from 15 parts by mass to 50 parts by mass, based on 100 parts by mass of the total of polylactic acid and styrene resin. 2. The resin composition according to claim 1 , wherein the ratio of the total mass 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 entire mass of the resin composition of the core layer. Multilayer sheet. The multilayer sheet according to claim 1 or 2 , wherein the ratio of the thickness of the core layer to the thickness of the entire multilayer sheet is 50% or more and 90% or less. The method for producing a multilayer sheet according to any one of claims 1 to 3 , wherein all layers of the multilayer sheet are integrated and coextruded in a die. A container formed from the multilayer sheet according to any one of claims 1 to 3 . The container according to claim 5 , which is a container for food.