JP7280030B2 - Composition, foamed sheet and molded article - Google Patents

Description

The present invention relates to compositions, foam sheets and molded articles.

Foamed sheets using polystyrene resins are used as materials for food containers, packaging containers, and the like. On the other hand, food containers made only of polystyrene resin may not have sufficient properties such as heat resistance. A proposal is made. For example, Patent Document 1 discloses a resin foam sheet containing predetermined amounts of a styrene-methacrylic acid copolymer, polyphenylene ether, and polystyrene.

JP 2014-205761 A

In order to obtain a molded product of excellent quality, it is desirable that the foam sheet is suppressed in deformation and cracking. Furthermore, since food containers are often heated in a microwave oven, they are also required to have excellent heat resistance.

An object of the present invention is to obtain a foamed sheet having excellent heat resistance and suppressed deformation and cracking.

The present invention provides the composition, foamed sheet and molded article shown below.
(1) Polymer (A) containing styrene and (meth)acrylic acid as monomer units, and polymer containing methyl (meth)acrylate and (meth)acrylic acid alkyl ester other than methyl (meth)acrylate as monomer units A composition containing (B) and, based on the total amount of monomer units contained in the polymer (B), the content of methyl (meth)acrylate is 65 to 85% by mass, and (meth)acrylic acid A composition having an alkyl ester content of 15 to 35% by weight.
(2) The composition according to (1), wherein the composition has a melt tension of 0.19 to 1.0 N at 200°C.
(3) (1) or (2), wherein the content of the polymer (A) is 84 to 97% by mass and the content of the polymer (B) is 3 to 16% by mass, based on the total amount of the composition; The described composition.
(4) The composition according to any one of (1) to (3), which has a melt mass flow rate of 6 to 22 g/10 minutes at 220° C. and a load of 10 kg.
(5) The composition according to any one of (1) to (4), wherein the composition has a Z-average molecular weight of 300,000 to 1,000,000.
(6) A foam sheet made of the composition according to any one of (1) to (5).
(7) The foamed sheet according to (6), which has an expansion ratio of 3 to 30 times.
(8) The foam sheet according to (6) or (7), which has a cell flatness of 1.1 to 9.0.
(9) A molded article obtained by molding the foamed sheet according to any one of (6) to (8).
(10) The molded article according to (9), which is a food container.

According to the present invention, it is possible to obtain a foamed sheet with excellent heat resistance and suppressed deformation and cracking.

1 is a perspective view of a molded body according to one embodiment; FIG.

Embodiments of the present invention will be described below. However, the present invention is not limited to the following embodiments.

"(Meth)acrylic acid" as used herein means acrylic acid and methacrylic acid corresponding thereto. The same applies to similar expressions such as "(meth)acrylic acid alkyl ester".

The weight average molecular weight (Mw) and Z average molecular weight (Mz) in this specification are calculated from the molecular weight distribution measured under the following conditions by gel permeation chromatography (GPC). The molecular weight was calculated as a polystyrene-equivalent molecular weight based on the molecular weight calculated at each elution time from the elution curve of monodisperse polystyrene.
Model: Shodex GPC-101 (manufactured by Showa Denko K.K.)
Column: PLgel 10 μm MIXED-A manufactured by Polymer Laboratories
Mobile phase: Tetrahydrofuran Sample concentration: 0.2% by mass
Temperature: oven 40°C, inlet 35°C, detector 35°C
Detector: Differential Refractometer

A foam sheet according to one embodiment is composed of the following composition. The foamed sheet does not necessarily have to have the same composition as the composition, and depending on the manufacturing conditions and the like, some of the components contained in the composition may be lost due to volatilization or the like during the process of forming the sheet. That is, the foam sheet according to one embodiment is formed using the following composition.

A composition according to one embodiment comprises a polymer (A) containing styrene and (meth)acrylic acid as monomer units (copolymer (A)), methyl (meth)acrylate, and (other than methyl (meth)acrylate) and a polymer (B) (copolymer (B)) containing a meth)acrylic acid alkyl ester as a monomer unit.

In the polymer (A), the content of styrene, based on the total amount of monomer units contained in the polymer (A), may be 85% by mass or more, 88% by mass or more, or 90% by mass or more, and 97% by mass or less, It may be 95% by mass or less, or 93% by mass or less.

In the polymer (A), the content of (meth)acrylic acid may be 3% by mass or more, 5% by mass or more, or 7% by mass or more based on the total amount of monomer units contained in the polymer (A). % by mass or less, 12% by mass or less, or 10% by mass or less.

The polymer (A) may contain only styrene and (meth)acrylic acid as monomer units, or may contain monomer units other than styrene and (meth)acrylic acid. Other monomer units include (meth)acrylic acid alkyl esters in which the alkyl group has 1 to 8 carbon atoms, maleic anhydride, and the like. (Meth) acrylic acid alkyl esters include methyl (meth) acrylate, ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate (n-butyl (meth) acrylate, (meth) acrylic isobutyl acid, t-butyl (meth)acrylate), and the like.

The content of other monomer units may be 1% by mass or more and 12% by mass or less based on the total amount of monomer units contained in the polymer (A).

Polymerization methods for the polymer (A) include known polymerization methods such as bulk polymerization, solution polymerization and suspension polymerization, which are industrialized for polystyrene and the like. In terms of quality and productivity, bulk polymerization and solution polymerization are preferred, and continuous polymerization of these is preferred. Solvents used in the polymerization may be, for example, alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, and aliphatic hydrocarbons such as hexane and cyclohexane.

When polymerizing the polymer (A), a polymerization initiator and a chain transfer agent can be used as necessary. An organic peroxide can be used as the polymerization initiator. Specific examples of organic peroxides include benzoyl peroxide, t-butylperoxybenzoate, 1,1-di(t-butylperoxy)cyclohexane, 1,1-bis(t-butylperoxy)-3 , 3,5-trimethylcyclohexane, 2,2-bis(4,4-di-t-butylperoxycyclohexyl)propane, t-butylperoxyisopropyl carbonate, dicumyl peroxide, t-butylcumyl peroxide, t -butyl peroxyacetate, t-butylperoxy-2-ethylhexanoate, polyether tetrakis(t-butylperoxycarbonate), ethyl-3,3-di(t-butylperoxy)butyrate, t-butyl and peroxyisobutyrate. Specific examples of chain transfer agents include aliphatic mercaptans, aromatic mercaptans, pentaphenylethane, α-methylstyrene dimer, terpinolene and the like.

The weight-average molecular weight (Mw) of the polymer (A) is preferably 120,000 or more, more preferably 150,000 or more, and still more preferably 180,000 or more, from the viewpoint of improving film-forming properties when producing a foamed sheet. Also, it is preferably 250,000 or less, more preferably 220,000 or less, and still more preferably 200,000 or less.

The content of the polymer (A) contained in the composition may be 84% by mass or more, 88% by mass or more, or 92% by mass or more based on the total amount of the composition, and the content of the polymer (A) is 97% by mass. It may be 96% by mass or less, or 95% by mass or less.

In the polymer (B), the content of methyl (meth)acrylate is the total amount of monomer units contained in the polymer (B), from the viewpoint of making it easier to obtain a foamed sheet with excellent heat resistance and suppressed deformation and cracking. On a basis, it is 65-85% by mass. The content of methyl (meth)acrylate is preferably 67% by mass, based on the total amount of monomer units contained in the polymer (B), from the viewpoint of further suppressing deformation and making it easier to obtain a foamed sheet with further excellent heat resistance. Above, more preferably 70% by mass or more, still more preferably 75% by mass or more. The content of methyl (meth)acrylate is preferably 83% by mass or less, more preferably 82% by mass, based on the total amount of monomer units contained in the polymer (B), from the viewpoint of making it easier to obtain a foamed sheet with further suppressed cracking. % by mass or less, more preferably 81% by mass or less.

(Meth)acrylic acid alkyl esters are esters of (meth)acrylic acid and aliphatic alcohols other than methyl (meth)acrylate. The number of carbon atoms in the alkyl group of the (meth)acrylic acid alkyl ester may be, for example, 2-8 or 3-7. The (meth)acrylic acid alkyl ester is preferably butyl (meth)acrylate (n-butyl (meth)acrylate, isobutyl (meth)acrylate, t (meth)acrylate) in which the alkyl group has 4 carbon atoms. -butyl). (Meth)acrylic acid alkyl esters may be used alone or in combination of two or more.

The content of the (meth)acrylic acid alkyl ester is from 15 to 15, based on the total amount of the monomer units contained in the polymer (B), from the viewpoint of making it easier to obtain a foamed sheet with excellent heat resistance and suppressed deformation and cracking. 35% by mass. The content of the (meth)acrylic acid alkyl ester is preferably 17% by mass or more, more preferably 17% by mass or more, based on the total amount of monomer units contained in the polymer (B), from the viewpoint of making it easier to obtain a foamed sheet with further suppressed cracking. It is 18% by mass or more, more preferably 20% by mass or more. The content of the (meth)acrylic acid alkyl ester is preferably 33 mass based on the total amount of the monomer units contained in the polymer (B), from the viewpoint of further suppressing deformation and making it easier to obtain a foamed sheet with further excellent heat resistance. % or less, more preferably 30 mass % or less, and still more preferably 25 mass % or less.

Polymer (B) may contain only methyl (meth)acrylate and the above alkyl (meth)acrylate as monomer units, and in addition to methyl (meth)acrylate and alkyl (meth)acrylate, It may contain other monomeric units. Other monomer units may be aromatic vinyl compounds such as styrene.

The content of other monomer units may be 1% by mass or more and 20% by mass or less based on the total amount of monomer units contained in the polymer (B).

The weight average molecular weight (Mw) of the polymer (B) is preferably 1,000,000 or more, more preferably 1,500,000 or more, and still more preferably 2,000,000 or more, from the viewpoint of facilitating adjustment of the melt tension of the composition to a predetermined range. It is preferably 6 million or less, more preferably 5 million or less, still more preferably 4.5 million or less.

The content of the polymer (B) contained in the composition, based on the total amount of the composition, may be 3% by mass or more, 4% by mass or more, or 5% by mass or more, and 16% by mass or less, 12% by mass or less, or It may be 8% by mass or less.

The method of polymerizing the polymer (B) is not particularly limited, and may be an emulsion polymerization method, a soap-free polymerization method, a suspension polymerization method, a fine suspension polymerization method, a dispersion polymerization method, or the like. The polymerization method of the polymer (B) is preferably an emulsion polymerization method or a soap-free polymerization method. According to these polymerization methods, it is easy to control the structure of the particles such as the core-shell structure. A mixture of these is added and polymerized to produce core-shell type polymer microparticles. Methods for recovering polymer fine particles (polymer (B)) from a latex containing polymer fine particles obtained by the above polymerization methods, particularly emulsion polymerization methods include spray drying (spray drying), freeze drying, dehydration after salting out and coagulation. Various methods such as drying may be used, but spray drying is preferred.

When the polymer (B) is recovered as fine polymer particles, the properties and structure of the fine polymer particles as a dry powder do not matter. For example, a large number of primary particles obtained by polymerization may aggregate to form aggregated particles (secondary particles), or may have a higher order structure. However, in the case of such an aggregated structure, it is preferable that the primary particles are loosely aggregated without being strongly bonded to each other so that the primary particles are finely and uniformly dispersed in the composition.

The composition may contain other components in addition to the polymer (A) and polymer (B). The composition may contain, for example, polymeric processing aids. A polymer processing aid is a compound that exerts an effect on thickness accuracy, film-forming stability, and reduction of fish eyes when the composition is formed into a sheet. Polymeric processing aids are typically polymer particles having a particle size of 0.05 to 0.5 μm, which can be produced by emulsion polymerization methods. The polymeric processing aid may consist of a resin different from polymer (A) and polymer (B) described above, and may contain, for example, an acrylic resin different from polymer (A) and polymer (B). The polymer processing aid may be a monolayer particle composed of a polymer having a single composition ratio and a single intrinsic viscosity, or a multilayer particle composed of two or more polymers having different composition ratios or intrinsic viscosities. good.

The composition may have a melt tension of 0.19 to 1.0 N from the viewpoint of facilitating the production of a foamed sheet having excellent appearance and excellent container moldability. The melt tension of the composition is preferably 0.2 N or higher, more preferably 0.23 N or higher, and even more preferably 0.4 or higher, from the viewpoint of easily obtaining a foamed sheet having excellent container moldability. The melt tension of the composition is preferably 0.8 N or less, more preferably 0.7 N or less, still more preferably 0.6 N or less, and particularly preferably 0.5 N or less, from the viewpoint of making it easier to obtain a foamed sheet with excellent appearance. is. The melt tension in the present invention is measured using a capillary rheometer at a temperature of 200°C when a strand of a composition extruded into air at 23°C at a speed of 10 mm/min is taken off at a take-up speed of 15 m/min. refers to the tension of

The composition may have a melt mass flow rate (MFR) of 6 to 22 g/10 minutes at 220° C. and a load of 10 kg. The MFR of the composition is preferably 8 g/10 min or more, more preferably 10 g/10 min or more, still more preferably 12 g/10 min or more. The MFR of the composition is preferably 20 g/10 minutes or less, more preferably 18 g/10 minutes or less, even more preferably 16 g/10 minutes or less. MFR can be measured according to the method of JIS K 7210-1.

The composition may have a Z-average molecular weight (Mz) of 300,000 to 1,000,000. The Z-average molecular weight of the composition is preferably 400,000 or more, more preferably 450,000 or more, and even more preferably 500,000 or more. The Z-average molecular weight of the composition is preferably 900,000 or less, more preferably 800,000 or less, and even more preferably 700,000 or less.

A foam sheet can be obtained using the composition described above. The method for producing the foamed sheet is not particularly limited, and for example, it can be produced by a method of mounting a die (especially a T-die) at the tip of an extruder to perform extrusion foaming, a method of obtaining a foamed molded article by injection molding, or the like. As a manufacturing method, it is preferable to manufacture by extrusion foaming from the viewpoint of suppressing costs.

A foaming agent may be added to the composition during the production of the foamed sheet. Examples of foaming agents include volatile foaming agents and chemical foaming agents. Volatile blowing agents include gases such as carbon dioxide, nitrogen and air; volatile hydrocarbons such as propane, butane and pentane; halogenated hydrocarbons such as methyl chloride; Chemical blowing agents include sodium bicarbonate, anhydrous monosodium citrate, ammonium carbonate, azodicarbonamide, 4,4'-oxybisbenzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, and N,N'-dinitrosopentamethylene. tetramine, trihydrazinotriazine, benzenesulfonyl semicarbazide and the like. A foaming agent may be used individually by 1 type or in combination of 2 or more types.

The expansion ratio of the foam sheet may be 3 to 30 times. The expansion ratio is preferably 5 times or more, more preferably 7 times or more, and still more preferably 10 times or more from the viewpoint of further suppressing cracking of the foam sheet and providing excellent heat insulating properties of the foam sheet. The expansion ratio is preferably 25 times or less, more preferably 20 times or less, and still more preferably 18 times or less from the viewpoints of further improving the appearance and container moldability of the foamed sheet, further suppressing deformation, and improving bending strength. be. The expansion ratio is a value obtained by dividing the specific gravity of the composition before foaming by the specific gravity of the foam sheet measured by the water substitution method (JIS K 7112).

In the foam sheet, the flatness of the cells (also called foam cells or cells) may be from 1.1 to 9.0. The flatness of the cells is preferably 1.5 or more, more preferably 2.0 or more, and still more preferably 2.5 or more, from the viewpoint of further suppressing cracking of the foam sheet. The flatness of the cells is preferably 7.0 or less, more preferably 5.0 or less, and even more preferably 4.0 or less, from the viewpoints of further suppressing deformation of the foam sheet and providing excellent bending strength. The flatness of the cells is a value expressed by the volume average of the ratio of the major axis to the minor axis of the cell diameter, and the observation surface is perpendicular to the main surface of the foam sheet and parallel to the flow direction of the foam sheet. The major axis direction cell diameter D _L and the minor axis direction cell diameter D _S of ni cells having an elliptical cross section which are cut and observed with a microscope are measured, and can be calculated by the following formula (1).

A foam sheet can be processed into a molded body having a desired shape, for example, by thermoforming. That is, the foam sheet can be used, for example, as a thermoforming foam sheet. Since the molded foam sheet is excellent in appearance and heat resistance, and deformation and cracking are suppressed, it can be suitably used as a food container or packaging container, and is particularly suitable as a food container. can. The molded foam sheet may be a container that is used by being heated in a microwave oven (container for microwave heating).

The shape and size of the molded foam sheet are not particularly limited. The planar shape of the molded body can be various shapes such as quadrilateral, circle, ellipse, and polygon. The three-dimensional shape of the molded body can be various shapes such as a box shape (especially a lunch box shape), a tray shape and a bowl shape. The molded body is part or all of a container separately provided with a lid and a container body, or part or all of a lidded container in which the lid and container body are connected via a part of the side wall serving as a hinge. may

FIG. 1 is a perspective view showing a molded foam sheet according to one embodiment. A molded body 10 shown in FIG. 1 is composed of a foamed sheet 1 . As shown in FIG. 1, the molded body 10 is molded in the shape of a hollow box with one side open, and can contain items such as foodstuffs therein. The molded body 10 can be suitably used as a container body in a container separately provided with a container body and a lid.

EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

<Production Example 1: Production of styrene-(meth)acrylic acid copolymer (A-1)>
100 kg of pure water and 100 g of polyvinyl alcohol were added to a 200 L jacketed autoclave equipped with a stirrer and stirred at 130 rpm. Subsequently, 72.0 kg of styrene, 4.0 kg of methacrylic acid and 20 g of t-butyl peroxide were charged, the autoclave was sealed, and the temperature was raised to 110° C. for 5 hours of polymerization (Step 1). Further, 4.0 kg of methacrylic acid was added evenly over 2 hours after the polymerization temperature reached 110° C. (Step 2). Further, the temperature was maintained at 140° C. for 3 hours to complete the polymerization (Step 3). The obtained beads were washed, dehydrated, dried and then extruded to obtain a styrene-(meth)acrylic acid copolymer (A-1) in the form of pellets. As a result of analyzing this copolymer using pyrolysis gas chromatography, the mass composition ratio of styrene monomer units/methacrylic acid monomer units was 92/8. Also, the weight average molecular weight (Mw) determined by GPC measurement was 190,000.

<Production Example 2: Production of styrene-(meth)acrylic acid copolymers (A-2) to (A- 6 )>
Styrene-(meth)acrylic acid copolymer (A-2) was prepared in the same manner as in Production Example 1, except that the composition of the monomer units used in the styrene-(meth)acrylic acid copolymer was changed to the composition shown in Table 1. ~ (A- 6 ) was obtained. All weight average molecular weights (Mw) obtained by GPC measurement were 190,000.

<Production Example 3: Production of methyl methacrylate-butyl acrylate copolymer (B-1)>
In a separable flask (capacity 5 L) equipped with a thermometer, a nitrogen inlet tube, a cooling tube and a stirring device, 300 parts by mass (3000 g) of ion-exchanged water as a dispersion medium, 1.1 parts by mass of sodium dodecylbenzenesulfonate as an emulsifier, 0.01 parts by mass of n-octyl mercaptan as a chain transfer agent, 80 parts by mass of methyl methacrylate and 20 parts by mass of butyl acrylate as monomers were added. The atmosphere in the flask was replaced with nitrogen by passing a nitrogen stream through the separable flask. Next, the internal temperature was raised to 60° C., and 0.15 parts by mass of potassium persulfate and 5 parts by mass of deionized water were added. After that, heating and stirring was continued for 2 hours to complete the polymerization, and an acrylic resin latex was obtained.
After cooling the obtained acrylic resin latex to 25° C., it was dropped into 500 parts by mass of hot water at 70° C. containing 5 parts by mass of calcium acetate, and then heated to 90° C. for coagulation. After separating and washing the obtained coagulate, it was dried at 60° C. for 12 hours to obtain a methyl methacrylate-butyl acrylate copolymer (B-1). The glass transition temperature of the methyl methacrylate-butyl acrylate copolymer (B-1) was 60° C. when measured by differential scanning calorimetry (DSC) according to JIS K 7121:2012 Plastic transition temperature measurement method. . Also, the weight average molecular weight (Mw) determined by GPC measurement was 4,000,000.

<Production Example 4: Production of methyl methacrylate-butyl acrylate copolymers (B-2) to (B-7)>
Methyl methacrylate-butyl acrylate copolymers (B-2) to (B-7) were obtained in the same manner as in Production Example 3, except that the charged amounts of methyl methacrylate and butyl acrylate were changed as shown in Table 2. . All the weight average molecular weights (Mw) determined by GPC measurement were 4,000,000.

<Examples 1 to 18 , Comparative Examples 1 to 2>
[Preparation of composition]
Based on the compositions shown in Tables 3 to 5, the copolymers obtained in Production Examples 1 to 4 were supplied to a twin-screw extruder (TEM-58SX (φ58 mm, L/D = 58), manufactured by Toshiba Machine Co., Ltd.) and melted. The mixture was kneaded to form a composition. At this time, by adjusting the blending amount of copolymer (A) and copolymer (B), screw configuration, extrusion rate, rotation speed, and barrel temperature, melt tension, MFR, and Z average molecular weight are shown in Tables 3 to 5. adjusted accordingly.

[Measurement of physical properties of composition]
(melt tension)
Using a capillary rheometer (Capilograph 1D, manufactured by Toyo Seiki Seisakusho), a strand of the composition extruded into the air at 23°C at a speed of 10 mm/min from a capillary (caliber 1 mm, inner diameter 40 mm) at a temperature of 200°C, The tension at the time of taking off at a take-off speed of 15 m/min was measured and used as the melt tension. The measurement results are shown in Tables 3-5.

(MFR)
The MFR of the composition was measured by the method of JIS K 7210-1 (test temperature 220°C, load 10 kg). The measurement results are shown in Tables 3-5.

(Z average molecular weight)
The Z-average molecular weight of the composition was calculated by GPC measurement. The results are shown in Tables 3-6.

[Preparation of foam sheet]
5.3 parts by mass of butane gas (isobutane/n-butane = 68/32 (mass ratio)) as a foaming agent per 100 parts by mass of the composition is pressurized into the composition in a molten state, so that the butane gas is injected into the composition. evenly distributed in the The composition is applied to a 600 mm wide T die (coat hanger type A sheet-like foam was obtained by extruding and foaming from a horizontal discharge type) with a clearance of 0.5 mm. Subsequently, this sheet-like foam was supplied to cast rolls, sandwiched between nip rolls, and cooled. At this time, the foaming ratio was adjusted as shown in Tables 3 to 6 by adjusting the addition amount of the foaming agent. When confirming the expansion ratio, the specific gravity of the foamed sheet was measured using an electronic balance (MDS-300, manufactured by Alpha Mirage).
After cooling, the ends of the sheet-like foam were continuously cut in the extrusion direction to obtain a foam sheet (thickness: 4 mm, width: 500 mm) cut to a predetermined sheet width.
Moreover, the flatness of the obtained foam sheet was calculated. The results are shown in Tables 3-5.

[Evaluation of foam sheet]
(Heat-resistant)
Using a foam sheet, a lunch container (length: 20 cm, width: 13 cm, Container depth: 3 cm) was molded. After the lunch container was placed in a hot air dryer set at 110° C. for 60 minutes, the length of the long side of the bottom of the container was compared with the length before heating, and evaluated based on the following criteria. If the evaluation result is S, A or B, it can be said that the heat resistance is excellent. The results are shown in Tables 3-5.
S: No deformation A: Less than 3% outer dimension change B: 3% to 5% outer dimension change
C: Outer dimension change of 5% or more

(degree of deformation)
A weight of 500 g was placed in the molded lunch box containers, and the covered lunch containers were piled up in five layers. evaluated. If the evaluation result is S, A or B, it can be said that deformation is sufficiently suppressed. The results are shown in Tables 3-5.
S: No change in shape and no change in appearance A: A wrinkled pattern on the surface of the container, but no deformation of the entire container B: Slight deformation of the entire container C: Deformation of the container , or cracking occurs

(crack resistance)
A 500-g weight was put in, and a lidded bento container was dropped from a height of 1 m. The test was performed 10 times, and the number of times the container was damaged was evaluated. The evaluation criteria were as follows. If the evaluation result is S, A or B, it can be said that cracking is sufficiently suppressed. The results are shown in Tables 3-5.
S: No container breakage observed A: 1-2 broken containers B: 3-4 broken containers C: 5 or more broken containers

Furthermore, the following evaluations were performed on the foamed sheet or lunch box container of each example. The evaluation results are shown in Tables 6-8.

(bending strength)
The bending strength of the foamed sheet was measured in accordance with ASTM D2176 in the sheet extrusion direction (longitudinal direction) and in the direction perpendicular to it (lateral direction), and the minimum value was determined and evaluated based on the following criteria. If the result is A or B, it can be said that the bending strength is excellent.
A: 5 times or more B: 2 times or more and less than 5 times C: Less than 2 times

(Thermal insulation properties)
The thermal conductivity of the foamed sheet is measured using a quick thermal conductivity meter (QTM-710, manufactured by Kyoto Electronics Industry Co., Ltd.), and is divided by the sheet thickness at the measurement point (measured using a micrometer). was taken as the thermal resistance value. Thermal resistance was evaluated based on the following criteria from the thermal resistance value. If the evaluation result is A or B, it can be said that the heat insulating property is excellent.
A: Thermal resistance value of 8×10 ⁻² (m ² K/W) or more B: Thermal resistance value of 4×10 ⁻² (m ² K/W) or more 8×10 ⁻² (m ² K /W) C: Thermal resistance value is less than 4×10 ⁻² (m ²・K/W)

(exterior)
The appearance (surface condition) of the foamed sheet was visually observed and evaluated based on the following criteria. If the evaluation result is A or B, it can be said that the appearance is excellent.
A: The unevenness on the surface is minute, and no cell breakage is observed.
B: Little unevenness on the surface, or slight breakage of the cells.
C: Appearance is impaired due to significant surface unevenness or cell breakage.

(Container formability)
The appearance of the bento box container after molding was evaluated based on the following criteria. If the result is A or B, it can be said that the moldability of the container is excellent.
A: Surface roughness does not occur at any part of the container B: Surface roughness at corners is slight C: Surface roughness at corners is significant or holes are generated

1... Foamed sheet, 10... Molded body.

Claims (9)

a polymer (A) containing styrene and (meth)acrylic acid as monomer units;
A foamed sheet made of a composition containing methyl (meth)acrylate and a polymer (B) containing (meth)acrylic acid alkyl esters other than methyl (meth)acrylate as monomer units,
Based on the total amount of monomer units contained in the polymer (B), the content of the methyl (meth)acrylate is 65 to 85% by mass, and the content of the alkyl (meth)acrylate is 15 to 35% by mass. (Excluding the case where the content of methyl methacrylate is 80% by mass and the content of 2-ethylhexyl acrylate is 20% by mass based on the total amount of monomer units contained in the polymer ( B ). ),
A foam sheet, wherein the content of the polymer (A) is 80 to 99% by mass and the content of the polymer (B) is 1 to 20% by mass, based on the total amount of the composition. The foam sheet according to claim 1, wherein the composition has a melt tension of 0.19 to 1.0N at 200°C. The foaming according to claim 1 or 2, wherein the content of the polymer (A) is 84 to 97% by mass and the content of the polymer (B) is 3 to 16% by mass, based on the total amount of the composition. sheet. The foam sheet according to any one of claims 1 to 3, wherein the composition has a melt mass flow rate of 6 to 22 g/10 minutes at 220°C and a load of 10 kg. The foam sheet according to any one of claims 1 to 4, wherein the composition has a Z-average molecular weight of 300,000 to 1,000,000. The foamed sheet according to any one of claims 1 to 5, which has an expansion ratio of 3 to 30 times. The foam sheet according to any one of claims 1 to 6, wherein the flatness of cells is 1.1 to 9.0. A molded article obtained by molding the foamed sheet according to any one of claims 1 to 7. The molded article according to claim 8, which is a food container.

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