JP2020164600A - Polystyrene-based resin foam sheet and polystyrene-based resin foam container - Google Patents

Abstract

To provide a polystyrene-based resin foam sheet which is excellent in moldability and heat resistance and can further improve a top to bottom compressive strength of the container, and a polystyrene-based resin foam container.SOLUTION: A polystyrene-based resin foam sheet for a container has a foam layer containing a polystyrene-based resin and a polyphenylene ether-based resin, in which the foam layer has a specific range of an average bubble diameter, a density (A) in an area a1 to 200 μm in a thickness direction from the surface of one surface α is 0.120-0.211 g/cm3, a density (B) in an area a2 to 200 μm in the thickness direction from the surface of another surface β is 0.100-0.190 g/cm3, a density (C) of an area a3 to 200-300 μm in the thickness direction from the surface of the one surface α is 0.062 g/cm3 or more and less than the density (A), and a density difference obtained by subtracting the density (B) from the density (A) is 0.016-0.105 g/cm3.SELECTED DRAWING: Figure 1

Description

The present invention relates to a polystyrene-based resin foam sheet and a polystyrene-based resin foam container.

A polystyrene-based resin foam container formed by molding a polystyrene-based resin foam sheet is widely used as a container that is hard to break because it is lightweight, has high heat insulating properties, and has high strength.
In recent years, polystyrene-based resin foam containers have been widely used as containers for foods to be eaten by heating in a microwave oven with improved heat resistance. For example, there is a cooked food in a container in which cooked food is placed in a polystyrene resin foam container and closed with a lid.

In the field of food packaging containers, there is always a demand for weight reduction of containers, and various attempts are being made to reduce the weight of containers. However, simply reducing the weight reduces the strength (top-bottom compression strength) when the top surface of the container is compressed.
To solve such a problem, for example, Patent Document 1 proposes a laminated foamed sheet in which a non-foamed film having a specific basis weight is laminated on a foamed sheet having a specific basis weight and density. In the laminated foam sheet of Patent Document 1, strengths such as top-bottom compression strength, lip compression strength, and piercing strength are improved.

Patent Document 2 proposes a polystyrene-based resin foam sheet having a specific thickness and density and having a surface layer density and an average cell diameter within a specific range. The polystyrene-based resin foam sheet of Patent Document 2 is lightweight but has improved strength.

JP-A-2005-88200 Japanese Unexamined Patent Publication No. 2013-209449

However, with the conventional technique, the top-bottom compression strength is not satisfactory. For this reason, during the production of cooked food in a container, the top surface of the container body may be deformed when the lid is fitted into the container body. In addition, when the cooked foods in the container are stacked during transportation or storage, the container body may be deformed.
In addition, the container is required to have good moldability.

Therefore, an object of the present invention is a polystyrene-based resin foam sheet and a polystyrene-based resin foam container which are excellent in moldability and heat resistance and can further enhance the top-bottom compression strength of the container.

In order to solve the above problems, the present invention has the following aspects.
[1] A polystyrene-based resin foam sheet for a container having a foamed layer containing a polystyrene-based resin and a polyphenylene ether-based resin, wherein the total amount of the polystyrene-based resin and the polyphenylene ether-based resin is 100 parts by mass. On the other hand, the content of the polyphenylene ether-based resin is 10 to 50 parts by mass, the average cell diameter of the foamed layer is 150 to 400 μm, and the foamed layer is in the thickness direction from the surface of one surface. The density (A) of the region up to 200 μm is 0.120 to 0.211 g / cm ³ , and the foam layer has a density (B) of the region up to 200 μm in the thickness direction from the surface of the other surface. a 100~0.190g / cm ^3, the foam layer, the density of one of 200~300μm from the surface in the thickness direction of the surface area (C) is at 0.062 g / cm ³ or more, the density of (C) is a polystyrene-based resin foam sheet, which is lower than the density (A) and has a density difference of 0.016 to 0.105 g / cm ³ obtained by subtracting the density (B) from the density (A).
[2] The polystyrene-based resin foam sheet according to [1], wherein the density (C) is lower than the density (B).
[3] Extruded and foamed into a tubular body, the inner peripheral surface of the tubular body is cooled along the outer peripheral surface of the mandrel, and then torn to produce, and the inner peripheral surface of the tubular body is one of the above. The polystyrene-based resin foam sheet according to [1] or [2], which forms the surface of.
[4] The thickness of the foamed layer is 0.5 to 5.0 mm, and the overall density (D) of the foamed layer is 0.050 to 0.150 g / cm ³ , [1] to [3]. ]. The polystyrene-based resin foam sheet according to any one of the items.
[5] The polystyrene-based resin according to any one of claims 1 to [4], which has a non-foaming layer on one side or both sides of the foaming layer, and the thickness of the non-foaming layer is 5 to 100 μm. Foam sheet.
[6] A polystyrene-based resin foam container formed by heat-molding with one side of the polystyrene-based resin foam sheet according to any one of [1] to [5] inside the container.
[7] The polystyrene-based resin foam container according to [6], which is a container for food.

According to the polystyrene-based resin foam sheet and the polystyrene-based resin foam container of the present invention, the moldability and heat resistance are excellent, and the top-bottom compression strength of the container can be further increased.

It is sectional drawing which shows an example of the polystyrene-based resin foam sheet which concerns on this invention. It is a schematic diagram which shows an example of the manufacturing apparatus of polystyrene-based resin foam sheet.

[Polystyrene resin foam sheet]
The polystyrene-based resin foamed sheet of the present invention (hereinafter, also simply referred to as “foamed sheet”) has a foamed layer containing a polystyrene-based resin and a polyphenylene ether-based resin.
The foamed sheet may have a single-layer structure consisting of only a foamed layer, or a multi-layered structure having a non-foamed layer on one or both sides of the foamed layer.

Hereinafter, an example of the foam sheet of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the foamed sheet 1 is a foamed sheet for a container, and has one surface α (hereinafter, also referred to as “first surface α”) and the other surface β (hereinafter, “second surface α”). Also referred to as "plane β"). The foam sheet 1 has a single-layer structure composed of only a foam layer.
The foam sheet 1 is formed so that the bubble diameter becomes smaller and the density becomes higher from the central portion in the thickness direction toward the first surface α.
Further, the foam sheet 1 is formed so that the bubble diameter becomes smaller and the density becomes higher from the central portion in the thickness direction toward the second surface β.

The thickness _{T 1} of the foamed sheet 1, for example, preferably from 0.5 to 5.0 mm, more preferably 0.8～4.0Mm, more preferably 1.0 to 3.0 mm. If the thickness T ₁ of the foam sheet 1 is not less than the above lower limit, a polystyrene type resin foamed container to be described later (hereinafter, simply referred. To as "foam containers") are the top and bottom compression strength of more enhanced. When the thickness T ₁ of the foamed sheet 1 is not more than the above upper limit value, the moldability of the foamed sheet 1 can be easily improved.
The thickness T ₁ of the foamed sheet 1 is a value determined by the following method. The thickness of any 10 points in the TD direction (width direction) of the foam sheet 1 is measured with a micro gauge. 10 points measurements are averaged, and the thickness T ₁ of the foam sheet 1.

The overall density (D) of the foam layer in the foam sheet 1 is 0.050 to 0.150 g / cm ³ , preferably 0.050 to 0.120 g / cm ³ , and preferably 0.050 to 0.100 g / cm. ³ is more preferable. When the density (D) is at least the above lower limit value, the top-bottom compression strength of the foam container can be further increased. When the density (D) is not more than the above upper limit value, the foam container can be made lighter.
Density (D) is determined by measuring in accordance with JIS K 7222: 2005 "Foam Plastics and Rubber-How to Determine Apparent Density".
More specifically, the mass and apparent volume of the test piece of the foam sheet cut so as not to change the original cell structure are measured and calculated by the following formula (0).
Density (D) (g / cm ³ ) = Mass of test piece (g) / Apparent volume of test piece (cm ³ ) ... (0)

The density (A) of the region (hereinafter, also referred to as “first region a1”) from the surface of the first surface α to 200 μm in the thickness direction is 0.120 to 0.211 g / cm ^3, which is 0. .130 to 0.205 g / cm ³ is preferable, and 0.140 to 0.200 g / cm ³ is more preferable. When the density (A) is at least the above lower limit value, the top-bottom compression strength of the foam container can be further increased. When the density (A) is not more than the above upper limit value, the moldability of the foam container can be further improved.
How to obtain the density (A) will be described later.

The density (B) of the region (hereinafter, also referred to as “second region a2”) from the surface of the second surface β to 200 μm in the thickness direction is 0.100 to 0.190 g / cm ^3, which is 0. .100 to 0.175 g / cm ³ is preferable, and 0.100 to 0.160 g / cm ³ is more preferable. When the density (B) is at least the above lower limit value, the top-bottom compression strength of the foam container can be further increased. When the density (B) is not more than the above upper limit value, the moldability of the foam container can be further improved.
How to obtain the density (B) will be described later.

The density (C) of a region 200 to 300 μm in the thickness direction from the surface of the first surface α (hereinafter, also referred to as “third region a3”) is 0.062 g / cm ³ or more, and 0.066 g. / Cm ³ or more is preferable, and 0.068 g / cm ³ or more is more preferable. When the density (C) is at least the above lower limit value, the top-bottom compression strength of the foam container can be further increased.
Further, the density (C) is lower than the density (A). Since the density (C) is lower than the density (A), the moldability can be further improved.
How to obtain the density (C) will be described later.

The density difference obtained by subtracting the density (B) from the density (A) (hereinafter, also referred to as “density difference (AB)”) is 0.016 to 0.105 g / cm ³ , and is 0.018 to 0. .098 g / cm ³ is preferable, and 0.020 to 0.092 g / cm ³ is more preferable. When the density difference (AB) is at least the above lower limit value, the top-bottom compression strength of the foam container can be further increased. When the density difference (AB) is not more than the above upper limit value, the moldability can be further improved.
The density difference (AB) is obtained by calculating the following equation (1) by obtaining the density (A) and the density (B).
Density difference (AB) (g / cm ³ ) = Density (A) -Density (B) ... (1)

The density difference obtained by subtracting the density (C) from the density (A) (hereinafter, also referred to as “density difference (AC)”) is preferably 0.060 to 0.120 g / cm ³ , preferably 0.070 to 0. .108 g / cm ³ is more preferred. When the density difference (AC) is at least the above lower limit value, the top-bottom compression strength of the foam container can be further increased. When the density difference (AC) is not more than the above upper limit value, the moldability can be further improved.
The density difference (AC) is obtained by obtaining the density (A) and the density (C) by the same calculation as in the equation (1).

The density (C) is preferably lower than the density (B). Since the density (C) is lower than the density (B), the moldability can be further improved.

The density difference obtained by subtracting the density (C) from the density (B) (hereinafter, also referred to as “density difference (BC)”) is preferably 0.012 to 0.060 g / cm ³ , preferably 0.015 to 0. .056 g / cm ³ is more preferred. When the density difference (BC) is at least the above lower limit value, the top-bottom compression strength of the foam container can be further increased. When the density difference (BC) is not more than the above upper limit value, the moldability can be further improved.
The density difference (BC) is obtained by obtaining the density (B) and the density (C) by the same calculation as in the equation (1).

The density (E) of the central portion in the thickness direction (hereinafter, also referred to as “fourth region a4”) excluding the first region a1 to the third region a3 from the entire foam sheet 1 is 0.030. ~ 0.120 g / cm ³ is preferable, 0.035 to 0.100 g / cm ³ is more preferable, and 0.040 to 0.080 g / cm ³ is even more preferable.
How to obtain the density (E) will be described later.
The thickness of the fourth region a4 is not particularly limited, the thickness T ₁ of the foamed sheet 1, the total thickness of the first region a1 to the third region a3 (i.e., 500 [mu] m) is a value obtained by subtracting the .. The thickness of the fourth region a4 is, for example, preferably 0 to 4500 μm, more preferably 300 to 3500 μm, and even more preferably 500 to 2500 μm.

The above-mentioned density (A), density (B), density (C), density (D) and density (E) (hereinafter, also referred to as "density of each region") can be adjusted according to the production conditions of the foamed sheet 1. .. More specifically, the temperature and air volume of the air blown when cooling the foam sheet 1, the temperature and flow rate of the cooling water of the mandrel, the surface in contact with the mandrel, the type and content of the bubble adjusting agent in the resin composition, etc. Can be adjusted by.
The density of each region is the apparent density.

The density of each region can be determined by measuring the apparent volume and mass of two sliced pieces obtained by slicing the foam sheet 1 from the surface of the first surface α at depths of 200 μm and 300 μm, respectively. ..
Similarly, the density of each region can be determined by measuring the apparent volume and mass of one slice piece obtained by slicing the foamed sheet 1 from the surface of the second surface β at a depth of 200 μm. ..
More specifically, the value of the density (A) is obtained as follows. First, a foam sheet cut into a size of 2 cm × 5 cm is sliced at a depth of 200 μm from the surface of the first surface α to prepare a slice piece (first slice piece). The following formula (2) can be calculated and obtained from the apparent volume (VA: cm ³ ) and mass (WA: g) of the sample cut out from the first slice piece to a size of 1 cm × 2 cm.
"Density (A)" = WA / VA (g / cm ³ ) ... (2)

The value of the density (B) is obtained as follows. First, a foam sheet cut into a size of 2 cm × 5 cm is sliced at a depth of 200 μm from the surface of the second surface β to prepare a slice piece (second slice piece) having a thickness of 200 μm. The following formula (3) can be calculated and obtained from the apparent volume (VB: cm ³ ) and mass (WB: g) of the sample cut out from the second slice piece to a size of 1 cm × 2 cm.
"Density (B)" = WB / VB (g / cm ³ ) ... (3)

The value of the density (C) is obtained as follows. First, a foam sheet cut into a size of 2 cm × 5 cm is sliced at a depth of 300 μm from the surface of the first surface α to prepare a slice piece (third slice piece) having a thickness of 300 μm. The following formula (4) can be calculated and obtained from the apparent volume (VC: cm ³ ) and mass (WC: g) of the sample cut into a size of 1 cm × 2 cm from the third slice piece.
"Density (C)" = (WC-WA) / (VC-VA) (g / cm ³ ) ... (4)

The average cell diameter of the entire foam layer in the foam sheet 1 is 150 to 400 μm, preferably 180 to 380 μm, more preferably 210 to 360 μm, still more preferably 240 to 340 μm. When the average cell diameter of the entire foam layer is at least the above lower limit value, the top-bottom compression strength of the foam container can be further increased. When the average cell diameter of the entire foam layer is not more than the above upper limit value, the surface smoothness of the foam container can be further enhanced.
The average cell diameter of the entire foam layer in the foam sheet 1 can be adjusted according to the manufacturing conditions of the foam sheet 1. More specifically, it can be adjusted by the temperature and air volume of air blown when cooling the foam sheet 1, the water temperature and flow rate of the cooling water of the mandrel, the type and content of the bubble adjusting agent in the resin composition, and the like.
The average cell diameter of the entire foam layer in the foam sheet 1 can be calculated by the following method.

The foamed sheet 1 is extruded in the extrusion direction (MD direction) and the surface of the foamed sheet 1 is orthogonal to the MD direction (also referred to as a width direction or a TD direction) from the central portion of the foamed sheet 1 in the TD direction. The foam sheet 1 is cut out in a direction perpendicular to the surface of 1 (also referred to as a thickness direction or a VD direction).
The cut-out cross section is photographed at a magnification of 20 to 100 times using a scanning electron microscope (“S-3400N” or “SU1510” manufactured by Hitachi High-Technologies Corporation).
At this time, when a total of four images, two images in each of the vertical and horizontal directions, are printed on one sheet of A4 paper in the horizontal orientation, a microscope image is taken so as to have a predetermined magnification.
More specifically, when an arbitrary straight line having a length of 60 mm parallel to each of the MD direction, the TD direction, and the VD direction is drawn on the microscope image, the number of bubbles existing on these straight lines is Adjust the imaging magnification with a scanning electron microscope so that the number is 5 to 30.

A total of two visual fields for each of the cross section cut along the MD direction (hereinafter, also referred to as "MD cross section") and the cross section cut along the TD direction (hereinafter, also referred to as "TD cross section"). A four-field microscopic image is taken and printed on A4 paper as described above.
Draw three arbitrary straight lines (60 mm in length) parallel to the MD direction on each of the two images of the MD cross section, and three arbitrary straight lines parallel to the TD direction on each of the two images of the TD cross section (60 mm in length). Draw a length of 60 mm).
Further, three straight lines (60 mm) parallel to the VD direction are drawn on one image of the MD cross section and one image of the TD cross section. In this way, six arbitrary straight lines of 60 mm parallel to each of the MD direction, the TD direction, and the VD direction are drawn in each direction.
It should be noted that, as much as possible, the arbitrary straight line should not be contacted only by the contacts, and if they are contacted, the number of bubbles is counted in addition to the number of bubbles at this contact as well.

The number of bubbles counted for six arbitrary straight lines in each of the MD direction, the TD direction, and the VD direction is arithmetically averaged to obtain the number of bubbles in each direction.
The average chord length t of the bubbles is calculated from the image magnification obtained by counting the number of bubbles and the number of bubbles from the following formula (5).
Average string length t (mm) = 60 / (number of bubbles x image magnification) ... (5)
However, if the foam sheet 1 is too thin to draw a straight line for a length of 60 mm in the VD direction, draw a straight line with a length of 30 mm or 20 mm instead of a straight line with a length of 60 mm on these straight lines. The number of bubbles is counted and converted into the number of bubbles on a straight line having a length of 60 mm (for example, when there are 5 bubbles on a straight line having a length of 30 mm, there are 10 bubbles on a straight line having a length of 60 mm. (Think of it as a thing).

The image magnification is calculated by measuring the scale bar on the image to 1/100 mm with "Digimatic Caliper" manufactured by Mitutoyo Co., Ltd. and using the following formula (6).
Image magnification = measured value of scale bar (mm) / display value of scale bar (mm) ... (6)

Then, the bubble diameter DMD in the MD direction is calculated by the following formula (7).
DMD (mm) = t / 0.616 ... (7)
The bubble diameter DTD (mm) in the TD direction and the bubble diameter DVD (mm) in the VD direction can be calculated in the same manner as the DMD.

Let the cube root of the product of DMD, DTD, and DVD be the average cell diameter D (mm) (the following formula (8)).
D (mm) = (DMD x DTD x DVD) ^1/3 ... (8)

The basis weight of the whole of the foamed layer in the foamed sheet 1, for example, preferably 80~500g / ^{m 2,} more preferably 90~300g / ^{m 2,} more preferably 100 to 150 g / ^{m 2.} When the total basis weight of the foam layer in the foam sheet 1 is at least the above lower limit value, the top-bottom compression strength of the foam container can be further increased. When the total basis weight of the foam layer in the foam sheet 1 is not more than the above upper limit value, the foam container can be made lighter. In addition, when the total basis weight of the foam layer in the foam sheet 1 is not more than the above upper limit value, the heating time at the time of heat molding does not become too long, and the productivity of the foam container can be further enhanced.

The total basis weight of the foamed layer in the foamed sheet 1 can be measured by the following method.
Except for both ends 20 mm in the width direction of the foam sheet 1, 10 sections of 10 cm × 10 cm are cut out at equal intervals in the width direction, and the mass (g) of each section is measured up to 0.001 g. The value obtained by converting the average value of the mass (g) of each section into the mass per 1 m ^{2 is taken as} the total basis weight (g / m ² ) of the foamed sheet 1.

<Foam layer>
The foamed layer is a layer formed by firing a resin composition containing a polystyrene-based resin, a polyphenylene ether-based resin, and a foaming agent. The foamed sheet 1 exhibits heat insulating properties and impact resistance by having a foamed layer.

Examples of the polystyrene-based resin include homopolymers of styrene-based monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene, or copolymers thereof; A copolymer of a styrene-based monomer as a main component (50% by mass or more) and a styrene-based monomer and a vinyl monomer polymerizable on the styrene-based monomer: a copolymer of a styrene-based monomer and a rubber component such as butadiene, or a styrene-based monomer. Is a so-called high-impact polystyrene, which is a homopolymer of the above, a copolymer thereof, a copolymer of a styrene-based monomer and a vinyl monomer, and a mixture or a polymer of a diene-based rubber-like polymer.
Vinyl monomers that can be polymerized with styrene-based monomers include, for example, alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and cetyl (meth) acrylate, (meth) acrylonitrile, and dimethyl. Bifunctional monomers such as maleate, dimethyl fumarate, diethyl fumarate, ethyl fumarate, divinylbenzene, and alkylene glycol dimethacrylate. One of these vinyl monomers may be used alone, or two or more thereof may be used in combination.
Here, "(meth) acrylate" represents one or both of "acrylate" and "methacrylate", and "(meth) acrylonitrile" represents one or both of "acrylonitrile" and "methacrylonitrile".
Examples of the diene-based rubber-like polymer include polybutadiene, styrene-butadiene copolymer, ethylene-propylene-non-conjugated diene three-dimensional copolymer, and acrylonitrile-butadiene-styrene copolymer.
One of these polystyrene resins may be used alone, or two or more thereof may be used in combination.

The polystyrene-based resin may be a polystyrene-based resin that is not a recycled raw material, such as a commercially available polystyrene-based resin or a polystyrene-based resin newly prepared by a method such as a suspension polymerization method, or may be a polystyrene-based resin that is a recycled raw material.
The recycled raw material is a used polystyrene resin foam molded product. Recycled raw materials include food packaging trays, fish boxes, cushioning materials for home appliances, etc., which are collected and recycled by a limonene melting method or a heating volume reduction method. In addition, the recycled raw materials that can be used are non-foamed polystyrene resin moldings that are separately collected from home appliances (for example, TVs, refrigerators, washing machines, air conditioners, etc.) and office equipment (for example, copiers, facsimiles, printers, etc.). The body may be crushed, melt-kneaded and repelletized.

The content of the polystyrene-based resin in the foamed layer is preferably 50 to 90 parts by mass, more preferably 60 to 90 parts by mass, and 70 to 70 parts by mass with respect to 100 parts by mass of the total amount of the polystyrene-based resin and the polyphenylene ether-based resin. 90 parts by mass is more preferable. When the content of the polystyrene-based resin is at least the above lower limit value, the foamed sheet 1 becomes stiff and the molded product can be handled more easily. When the content of the polystyrene-based resin is not more than the above upper limit value, the characteristics of the other resin are likely to be exhibited when the other resin is blended.

The foamed layer exhibits excellent heat resistance by containing a polyphenylene ether-based resin.
Examples of the polyphenylene ether-based resin include compounds represented by the following formula (I).

In the formula (I), R ¹ and R ² each independently represent an alkyl group or a halogen atom having 1 to 4 carbon atoms. Examples of the halogen atom include fluorine, chlorine, bromine and the like.
In the formula (I), n is a positive integer representing the degree of polymerization. n is, for example, usually 10 to 5000.

Examples of the polyphenylene ether-based resin represented by the formula (I) include poly (2,6-dimethylphenylene-1,4-ether), poly (2,6-diethylphenylene-1,4-ether), and poly. (2,6-Dichlorophenylene-1,4-ether) or modified products thereof and the like can be mentioned.
One of these polyphenylene ether-based resins may be used alone, or two or more thereof may be used in combination.

The content of the polyphenylene ether-based resin in the foam layer is 10 to 50 parts by mass, preferably 10 to 40 parts by mass, preferably 10 to 40 parts by mass with respect to 100 parts by mass of the total amount of the polystyrene-based resin and the polyphenylene ether-based resin. 30 parts by mass is more preferable.
When the content of the polyphenylene ether-based resin is at least the above lower limit value, the heat resistance of the foamed sheet 1 is further enhanced. When the content of the polyphenylene ether-based resin is not more than the above upper limit value, the foamed sheet 1 becomes stiff and the molded product can be handled more easily.

The foamed layer may contain a resin other than the polystyrene-based resin and the polyphenylene ether-based resin (hereinafter, also referred to as “other resin”). Examples of other resins include polyolefin resins and the like.
The polyolefin-based resin is, for example, a homopolymer of an olefin-based monomer such as ethylene or propylene, a copolymer thereof, or an olefin-based monomer as a main component, and the common weight of the olefin-based monomer and a vinyl monomer polymerizable thereby. Coalescence and the like can be mentioned.

The content of the other resin is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and may be 0 parts by mass with respect to 100 parts by mass of the total resin component in the foamed sheet 1. When the content of the other resin is not more than the above upper limit value, the foamed sheet 1 becomes stiff and the molded product can be handled more easily.

Examples of the foaming agent include hydrocarbons such as propane, butane and pentane; halogenated hydrocarbons such as tetrafluoroethane, chlorodifluoroethane and difluoroethane. Of these, butane is preferable as the foaming agent. Butane may be normal butane or isobutane alone, or may be a combination of normal butane and isobutane.
These foaming agents may be used alone or in combination of two or more.
The blending amount of the foaming agent is determined in consideration of the type of foaming agent, the overall density (D) required for the foam sheet 1, and the like. The blending amount of the foaming agent is preferably 1.0 to 7.0 parts by mass with respect to 100 parts by mass of the total resin component in the foam sheet 1.

The foamed layer may contain components other than the polystyrene-based resin, the polyphenylene ether-based resin, and the foaming agent (hereinafter, also referred to as “arbitrary components”). Examples of the optional component include a bubble modifier, a stabilizer, an ultraviolet absorber, an antioxidant, a colorant, a deodorant, a lubricant, a flame retardant, an antistatic agent, and the like.
The type of the optional component is determined in consideration of the physical properties required for the foamed sheet 1. As the optional component, one kind may be used alone, or two or more kinds may be used in combination.

Examples of the bubble adjusting agent include a mixture of inorganic powders such as talc and silica. These bubble modifiers increase the closed cell ratio of the foam layer and facilitate the formation of the foam layer.
Examples of the stabilizer include a calcium-zinc heat stabilizer, a tin heat stabilizer, a lead heat stabilizer and the like.
Examples of the ultraviolet absorber include a cesium oxide-based ultraviolet absorber and a titanium oxide-based ultraviolet absorber.
Examples of the antioxidant include cerium oxide, cerium oxide / zirconia solid solution, cerium hydroxide, carbon, carbon nanotubes, titanium oxide, fullerene and the like.
Examples of the colorant include titanium oxide, carbon black, titanium yellow, iron oxide, ultramarine blue, cobalt blue, fired pigment, metallic pigment, mica, pearl pigment, zinc oxide, precipitated silica, cadmium red and the like.
Examples of the deodorant include silica, zeolite, zirconium phosphate, hydrotalcite calcined product and the like.

The content of the optional component in the foam layer is preferably 0.05 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, and 0.3 to 10 parts by mass with respect to 100 parts by mass of the total resin component in the foam sheet 1. 5.0 parts by mass is more preferable. When the content of the arbitrary component is at least the above lower limit value, the effect derived from the arbitrary component can be exhibited. When the content of the optional component is not more than the above upper limit value, clogging to the die or the like can be better prevented, and the appearance of the foamed sheet 1 can be improved.

When the foamed layer contains a bubble adjusting agent, the content of the bubble adjusting agent is preferably 0.01 to 5.0 parts by mass, and 0.02 to 3 parts by mass, based on 100 parts by mass of the total resin component in the foam sheet 1. .0 parts by mass is more preferable, and 0.03 to 2.0 parts by mass is further preferable. When the content of the bubble adjusting agent is not more than the above lower limit value, the closed cell ratio of the foam layer can be further increased. When the content of the bubble adjusting agent is not more than the above upper limit value, clogging of the die or the like can be better prevented and the appearance of the foamed sheet 1 can be improved.

The closed cell ratio of the foam layer is preferably 70% or more, more preferably 80% or more, further preferably 90% or more, and may be 100%. The closed cell ratio of the foamed layer is a value measured by the method described in JIS K7138: 2006 "Hard foamed plastic-How to obtain open cell ratio and closed cell ratio".

The thickness of the foam layer can be determined in consideration of the use of the foam sheet and the like. The thickness of the foam layer is, for example, preferably 0.5 to 5.0 mm, more preferably 0.5 to 4.0 mm, still more preferably 1.0 to 3.0 mm. When the thickness of the foam layer is at least the above lower limit value, the top-bottom compression strength of the foam container can be further increased. When the thickness of the foam layer is not more than the above upper limit value, the foam container can be made lighter.

The foamed sheet of the present invention preferably has a non-foamed layer on one side or both sides of the foamed layer. A foam container having a non-foam layer can further increase the top-bottom compression strength of the container. In addition, a foam container having a non-foam layer can further enhance the surface smoothness of the container.
The resin constituting the non-foamed layer is not particularly limited, and examples thereof include resins similar to the resin constituting the foamed layer.
The resin constituting the non-foamed layer may be the same as or different from the resin constituting the foamed layer.
In addition, a printing layer may be provided on the surface of the non-foaming layer, and a non-foaming layer may be further provided on the surface of the printing layer.

The thickness of the non-foamed layer is determined in consideration of the use of the foamed sheet and the like. For example, 5 to 100 μm is preferable, 10 to 80 μm is more preferable, and 15 to 60 μm is further preferable. When the thickness of the non-foamed layer is at least the above lower limit value, the top-bottom compression strength of the foam container can be further improved. In addition, when the thickness of the non-foamed layer is at least the above lower limit value, the surface smoothness of the foamed container can be further improved. When the thickness of the non-foamed layer is not more than the above upper limit value, the weight of the foamed container can be reduced.

Examples of the resin constituting the non-foamed layer include a general-purpose polystyrene resin (GPPS) film, a high-impact polystyrene resin (HIPS) film, and a laminated film in which a polyolefin resin film or the like is dry-laminated on these films. Be done.
These resin films include non-stretched films, weakly stretched films, uniaxially stretched films, and
It may be any biaxially stretched film.
When the laminated film as described above is used, the polyolefin-based resin film to be dry-laminated is, for example, a high-density polyethylene resin (HDPE) film, a polypropylene-based resin (PP) film, a cycloolefin polymer (COP) film, or a cycloolefin. Examples include polypropylene (COC) film. Examples of other resins include polyamide resin films, polyethylene terephthalate resin (PET) films, and ethylene vinyl alcohol resins (EVOH) films.
The non-foamed layer may have a single layer structure or a multi-layer structure having two or more layers.
When the non-foamed layer has a multilayer structure, for example, a multilayer film having an outer layer of a polypropylene resin (PP) film, an inner layer of a general-purpose polystyrene resin (GPPS) film, and an adhesive layer for adhering the outer layer and the inner layer. preferable. In this multilayer film, the outer layer is located on the surface (exposed surface) and the inner layer is located on the foam layer side.

[Manufacturing method of foam sheet]
The foamed sheet is manufactured by a conventionally known manufacturing method.
The method for producing the foamed sheet will be described by taking as an example the method for producing the single-layer foamed sheet 1.
The foam sheet manufacturing apparatus 100 of FIG. 2 is an apparatus for obtaining a foam sheet by extrusion molding. The manufacturing apparatus 100 includes an extruder 10, a foaming agent supply source 18, a circular die 20, a mandrel 30, and two winders 40.
The extruder 10 is a so-called tandem extruder. The extruder 10 includes a first extrusion section 11 and a second extrusion section 12 connected to the first extrusion section 11 by a pipe 16. The first extrusion portion 11 includes a hopper 14. A foaming agent supply source 18 is connected to the first extrusion portion 11.
A circular die 20 is connected to the second extrusion section 12. A mandrel 30 including a cutter 32 is provided downstream of the circular die 20. A cooling blower (not shown) is provided between the circular die 20 and the mandrel 30.

The raw material constituting the foam layer is charged from the hopper 14 into the first extrusion section 11. The raw material input from the hopper 14 is a resin constituting the foam layer and an optional component to be blended as needed.
In the first extrusion section 11, the raw materials are mixed while being heated to an arbitrary temperature to form a resin melt, and the foaming agent is supplied from the foaming agent supply source 18 to the first extrusion section 11, and the foaming agent is added to the resin melt. To obtain a resin composition.
The heating temperature is appropriately determined within a range in which the resin is melted and arbitrary components are not denatured in consideration of the type of resin and the like. The heating temperature is, for example, preferably 200 to 350 ° C, more preferably 250 to 320 ° C.

The resin composition is supplied from the first extrusion section 11 to the second extrusion section 12 via the pipe 16 and further mixed. After that, the resin composition is cooled to an arbitrary temperature and then guided to the resin flow path in the circular die 20.
The resin composition guided to the resin flow path is extruded from the circular die 20, and the foaming agent foams to form a cylindrical foam sheet 1a. That is, a tubular body is obtained by extrusion foaming.
The discharge amount of the resin composition extruded from the circular die 20 is, for example, preferably 100 to 500 kg / h, more preferably 200 to 400 kg / h. When the discharge amount of the resin composition is not more than the above lower limit value, it is possible to prevent the resin composition from being cooled too much and the density of the cylindrical foam sheet 1a from becoming too high. In addition, when the discharge amount of the resin composition is at least the above lower limit value, the productivity of the cylindrical foam sheet 1a can be increased. When the discharge amount of the resin composition is not more than the above upper limit value, the resin composition is sufficiently cooled, and a cylindrical foam sheet 1a having a desired density can be easily obtained.

The cylindrical foam sheet 1a is guided to the mandrel 30 while being blown with the cooling air blown from the cooling blower. The inner peripheral surface of the cylindrical foam sheet 1a passes through the outer peripheral surface of the mandrel 30, and is cooled to an arbitrary temperature along the outer peripheral surface of the mandrel 30.
Cooling water flows through the inside of the mandrel 30 to cool the inner peripheral surface of the cylindrical foam sheet 1a.
The temperature of the cooling water is, for example, preferably 10 to 40 ° C, more preferably 15 to 30 ° C. When the temperature of the cooling water is within the above numerical range, the inner peripheral surface of the cylindrical foam sheet 1a can be cooled so as to have a desired density.
The flow rate of the cooling water is, for example, preferably 5 to 40 L / min, more preferably 10 to 30 L / min. When the flow rate of the cooling water is within the above numerical range, the inner peripheral surface of the cylindrical foam sheet 1a can be cooled so as to have a desired density.

The inner peripheral surface of the cylindrical foam sheet 1a and the outer peripheral surface of the cylindrical foam sheet 1a are cooled by blowing cooling air. The air volume for blowing cooling air onto the inner peripheral surface of the cylindrical foam sheet 1a (hereinafter, also referred to as “air volume 1”) is preferably, for example, 0.01 to 0.08 m ³ / m ² , preferably 0.02. ~ 0.05 m ³ / m ² is more preferable. When the air volume 1 is within the above numerical range, the inner peripheral surface of the cylindrical foam sheet 1a can be cooled so as to have a desired density.
The air volume for blowing cooling air onto the outer peripheral surface of the cylindrical foam sheet 1a (hereinafter, also referred to as “air volume 2”) is preferably, for example, 0.01 to 0.08 m ³ / m ² , preferably 0.015 to 0.015. More preferably 0.07 m ³ / m ² . When the air volume 2 is within the above numerical range, the outer peripheral surface of the cylindrical foam sheet 1a can be cooled so as to have a desired density.
The unit of air volume "m ³ / m ² " indicates the volume (m ³ ) of air to be blown per unit area (m ² ) of the foam sheet 1.

The temperature of the cooling air blown onto the cylindrical foam sheet 1a is, for example, preferably 10 to 40 ° C, more preferably 15 to 35 ° C. When the temperature of the cooling air is equal to or higher than the above lower limit value, it is possible to prevent the cylindrical foam sheet 1a from being cooled more than necessary. In addition, when the temperature of the cooling air is equal to or higher than the above lower limit, the energy for cooling the air can be saved. When the temperature of the cooling air is not more than the above upper limit value, the cylindrical foam sheet 1a can be sufficiently cooled.

The cooled cylindrical foam sheet 1a is cut into two by the cutter 32 to become the foam sheet 1. At this time, it is preferable that the inner peripheral surface of the cylindrical foam sheet 1a is the first surface α of the foam sheet 1, and the outer peripheral surface of the cylindrical foam sheet 1a is the second surface β of the foam sheet 1. Since the inner peripheral surface of the tubular body forms the first surface α, the top-bottom compression strength of the foam container can be further increased.
The foam sheet 1 is wound around the guide roll 42 and the guide roll 44, respectively, and wound by the winder 40 to become the foam sheet roll 4.
In this way, the foam sheet 1 having a single layer structure can be obtained.
The foamed layer of the foamed sheet 1 described here is a single-layered foamed layer, but the foamed layer of the foamed sheet may be, for example, a laminated layer of two or more foamed layers by coextrusion, and is heat-sealed. Alternatively, two or more foam layers may be laminated by adhesion.

As a method of forming a non-foaming layer on a foamed sheet, for example, a foaming layer is obtained by the above-mentioned manufacturing method, and a resin film having a single-layer structure or a multi-layer structure is heat-laminated on the surface thereof to form a non-foaming layer; Examples thereof include a method in which a foamed layer is obtained by the above-mentioned production method and a non-foamed layer is formed on the surface of the foamed layer by the T-die method.

[Polystyrene resin foam container]
The polystyrene-based resin foam container of the present invention (also simply referred to as “foam container”) is formed by heat molding with one side of the foam sheet of the present invention described above inside the container. Here, one surface of the foamed sheet refers to the surface on the side of the first region a1 (the region having the density (A)) that forms the high-density layer.
Examples of the foam container include a tray having a perfect circular shape, an elliptical shape, a semicircular shape, a polygonal shape, a fan shape, etc., a bowl-shaped container, a container having a bottomed cylindrical shape or a bottomed square cylinder shape, and a container for natto. Various containers such as containers with lids; lids and the like attached to the container body.
As the use of these containers, for example, food products are preferable.

The thickness of the foam container is determined in consideration of the application and the like. For example, 0.5 to 5.0 mm is preferable, 0.8 to 4.0 mm is more preferable, and 1.0 to 3.0 mm is further preferable. When the thickness of the foam container is at least the above lower limit value, the top-bottom compression strength of the foam container can be further increased. When the thickness of the foam container is not more than the above upper limit value, the foam container can be made lighter.
The overall density of the foam layer in the foam container is determined in consideration of the application and the like, and is the same as the overall density (D) of the foam layer in the foam sheet.
The density of the foam layer in the region from the surface of one surface of the foam container to 200 μm in the thickness direction is the same as the density (A) of the first region a1 in the foam sheet.
The density of the foam layer in the region from the surface of the other surface of the foam container to 200 μm in the thickness direction is the same as the density (B) of the second region a2 in the foam sheet.
The density of the foam layer in the region 200 to 300 μm in the thickness direction from the surface of one surface of the foam container is the same as the density (C) of the third region a3 in the foam sheet.
The density of the foam layer in the region from 300 μm in the thickness direction from the surface of one surface of the foam container to 200 μm in the thickness direction from the surface of the other surface of the foam container is the density of the fourth region a4 in the foam sheet. Same as E).
In addition, the density difference of each region in the foam container is the same as the density difference of each region in the foam sheet.
The average cell diameter of the foam layer in the foam container is the same as the average cell diameter of the foam layer in the foam sheet.

When manufacturing a foam container, it is preferable to heat-mold so that the first surface α of the foam sheet forms the inside of the container. By manufacturing the foam container in this way, the top-bottom compression strength of the foam container can be further increased.

As described above, according to the foamed sheet of the present invention, the density (A) of the region from the surface of one surface of the foamed layer to 200 μm in the thickness direction and the thickness direction from the surface of the other surface of the foamed layer. By controlling the density (B) of the region up to 200 μm so that the density (A) becomes high, the top-bottom compression strength of the foam container can be further increased.
In addition, by controlling the density (C) in the region of 200 to 300 μm in the thickness direction from the surface of one surface of the foam layer so as not to cause an extreme decrease in density, there is no locally weak foam layer. Therefore, the top-bottom compression strength of the foam container can be further increased.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to the following description.
The raw materials used in this example are as follows.

[Ingredients used]
· A-1: polystyrene resin (PS ^{resin), MW = 323 × 10 3} , DIC Co., Ltd., product name "XC-515".
-A-2: Mixture of 70% by mass of polyphenylene ether resin (PPE resin) and 30% by mass of PS resin, manufactured by SABIC, product name: "Noril EFN4230".
-Bubble conditioner: A talc-containing resin composition (containing 40% by mass of talc (average specific surface area 10 to 40 m ² / g), manufactured by Toyo Styrene Co., Ltd., product name "DSM1401A").
-Deodorant: Hydrotile site fired product (average specific surface area 125-190 m ² / g).
Foaming agent: butane (isobutane: normal butane = 68:32 (mass ratio) mixture).

[Examples 1 to 7, Comparative Examples 1 to 7]
(Manufacturing of foam sheet)
Using the same manufacturing apparatus as the foamed sheet manufacturing apparatus of FIG. 2, a single-layer foamed sheet was obtained as follows.
According to the composition of Tables 1 and 2, the resin raw material: A-1, the resin raw material: A-2, the bubble adjusting agent, and the deodorant were mixed. The composition in the table represents a part by mass.
A mixture of raw materials was supplied from a hopper to a first mixing portion (screw diameter: 115 mm), heated at a maximum temperature of 300 ° C., and melt-kneaded to obtain a resin melt.
A foaming agent (isobutane: normal butane = 70:30 (mass ratio) mixture) was supplied to the first extrusion section, and the resin melt and the foaming agent were mixed to obtain a resin composition. The blending amount of the foaming agent was 100 parts by mass of the polystyrene resin and parts by mass shown in Tables 1 and 2.
The resin composition is supplied from the first mixing portion to the second mixing portion (screw diameter: 180 mm), cooled to 190 ° C., extruded from a circular die (diameter 160 mm), foamed, and molded with a cooling mandrel. , A cylindrical foam sheet was obtained. At this time, immediately after being extruded from the circular die, the inner peripheral surface and the outer peripheral surface of the cylindrical foam sheet were cooled by blowing air (28 ° C.) for cooling with the air volume shown in Tables 1 and 2. In addition, the cylindrical foam sheet was cooled by passing it through the inner peripheral surface of the cylindrical foam sheet so as to follow the outer peripheral surface of the cooling mandrel. In Examples 1 to 6 and Comparative Examples 1 to 7, the inner peripheral surface of the cylindrical foam sheet was cooled so as to form a high-density layer. In Example 7, the outer peripheral surface of the cylindrical foam sheet was cooled so as to form a high-density layer. The temperature of the cooling water flowing through the mandrel was 25 ° C. (Comparative Example 7 was 42 ° C.), and the flow rate of the cooling water was 25 L / min.
The cooled cylindrical foam sheet was torn along the extrusion direction to obtain a foam sheet composed of the foam layers shown in Tables 1 and 2.
Regarding the obtained foamed sheet, the thickness, the average cell diameter, the overall density (D), the density of the region 200 μm thick from the sheet surface (density (A), density (B)), the region of the sheet surface 200 μm to 300 μm. Density (density (C)) was measured. In addition, the density difference in each region was calculated. The results are shown in Tables 1-2. The unit of the average cell diameter in the table is μm.

(Manufacturing of laminated foam sheet)
A CPPS dry lami film (thickness 50 μm: dry lami film of unstretched PP film and non-stretched PS film) was heat-laminated on one surface of the obtained foamed sheet, and a CPS film (thickness 20 μm) was formed on the other surface. : Non-stretched PS film) was heat-laminated to obtain a laminated foam sheet having non-foam layers on both sides of the foam layer.
The CPPS dry lami film is brought into contact with a heat roll at 180 ° C., the CPS film is brought into contact with a heat roll at 160 ° C., and then a foamed sheet at 25 ° C. at a laminating pressure of 0.5 MPa and a laminating speed of 4.0 m / min. Laminated in. The non-stretched PS film side of the CPPS dry lami film was laminated on one surface, that is, the surface of the region having the density (A) forming the high density layer. The CPS film was laminated on the other surface, that is, the surface of the region having the density (B).
The density and density difference of each region in the foamed layer of the obtained laminated foam sheet was the same as the density and density difference of each region in the foamed sheet before laminating.

(Manufacturing of foam container)
The obtained laminated foam sheet was heat-molded by a single-shot molding machine. By heat molding, a foam container having a circular bottom surface and a side surface rising from the peripheral edge of the bottom surface and having an open upper portion was obtained. The diameter of the opening of this foam container was 20 cm, the diameter of the bottom surface was 17 cm, and the height was 4 cm.
The foam container was heat molded so that one side of the container formed the inside of the container. A foam container was obtained by heat-molding with one surface, that is, the surface on the region side having the density (A) forming the high-density layer, inside the container.

The obtained foam container was evaluated for container strength, moldability, and heat resistance shown in the following evaluation methods. The results are shown in Tables 1-2.

[Evaluation of container strength]
The obtained foam container was used as a measurement sample. Using a Tensilon universal material tester (manufactured by Orientec Co., Ltd., model number "UCT-10T"), the top-bottom compression strength of the foam container was measured for the measurement samples of each example. When measuring the top-bottom compression strength, the measurement sample was placed on a special plate provided with a groove for venting air on the surface so that the bottom surface was facing up. The measurement sample was compressed using a compression plate having a diameter of 200 mm at a test speed of 400 mm / min, and the maximum load and displacement amount up to the yield point were measured. Ten measurement samples were measured, and the arithmetic mean value was calculated. Based on the calculated arithmetic mean value, the top-bottom compression strength was evaluated according to the following evaluation criteria.
"Evaluation criteria"
◯: Maximum load 20 kgf or more and displacement amount 5.0 mm or more.
Δ: The maximum load is 20 kgf or more, and the displacement amount is 4.5 mm or more and less than 5.0 mm.
X: Maximum load less than 20 kgf or displacement amount less than 4.5 mm.

[Evaluation of moldability]
The appearance of the obtained foam container was visually observed, and the moldability was evaluated according to the following evaluation criteria.
"Evaluation criteria"
◯: No holes or cracks are found on the surface of the container.
X: There are holes or cracks on the surface of the container.

[Evaluation of heat resistance]
A rectangular test piece having a length of 700 mm and a width of 1040 mm was cut out from the laminated foam sheet of each example. The average temperature of the upper heater of the single-engine molding machine (manufactured by Tosei Sangyo Co., Ltd., trade name "UNIC automatic molding machine FM-3A") is 280 ° C, the average temperature of the lower heater is 230 ° C, and the upper atmosphere temperature is 185 ° C. The side atmosphere temperature was set to 175 ° C.
Next, the test piece was introduced into the single-shot molding machine, the laminated foam sheet was foamed, and the heating time was adjusted so that the thickness was approximately 3.5 mm to obtain a secondary foam plate. The surface condition of the non-foamed layer of the obtained secondary foam plate was visually observed, and the heat resistance was evaluated according to the following evaluation criteria. In the test piece in which bubbles are found to be generated, the laminated film floats up, resulting in a so-called "lame float" state, which is inferior in heat resistance.
"Evaluation criteria"
◯: No bubble is observed.
X: Many minute bubbles having a bubble diameter of 5 mm or less were observed, or one or more bubbles having a bubble diameter of more than 5 mm were observed.

[Comprehensive evaluation]
Based on the above evaluation results of container strength, moldability, and heat resistance, a comprehensive evaluation was performed according to the following evaluation criteria. "A" and "B" were accepted.
"Evaluation criteria"
A: Container strength, moldability, heat resistance, all evaluations are "○".
B: The evaluation of container strength is "Δ", and the evaluation of moldability and heat resistance is "○".
C: The evaluation of container strength, moldability, and heat resistance is "x".

In Examples 1 to 7 to which the present invention was applied, the overall evaluation was "A" or "B".
On the other hand, in Comparative Example 1 in which the density (B) was outside the range of the present invention, the evaluation of moldability was “x”. In Comparative Example 2 in which the density difference (AB) was outside the range of the present invention, the evaluation of the container strength was “x”. In Comparative Example 3 in which the density (C) was outside the range of the present invention, the evaluation of the container strength was “x”. In Comparative Example 4 in which the density (A) and the density difference (AB) were outside the range of the present invention, the evaluation of moldability and the evaluation of heat resistance were “x”. In Comparative Example 5 in which the average cell diameter of the foamed layer was outside the range of the present invention, the evaluation of the container strength and the evaluation of the heat resistance were “x”. In Comparative Example 6 in which the average cell diameter of the foamed layer was outside the range of the present invention, the moldability was evaluated as “x”. In Comparative Example 7 in which the density (C) was outside the range of the present invention, the evaluation of the container strength was “x”.

From these results, it was found that the polystyrene-based resin foam sheet and the polystyrene-based resin foam container of the present invention are excellent in moldability and heat resistance, and the top-bottom compression strength of the container can be further enhanced.

1 Polystyrene resin foam sheet (foam sheet)
α One side β The other side

Claims (7)

A polystyrene-based resin foamed sheet for a container having a foamed layer containing a polystyrene-based resin and a polyphenylene ether-based resin.
The content of the polyphenylene ether resin is 10 to 50 parts by mass with respect to 100 parts by mass of the total amount of the polystyrene resin and the polyphenylene ether resin.
The average cell diameter of the foamed layer is 150 to 400 μm.
The foamed layer has a density (A) of 0.120 to 0.211 g / cm ³ in a region from the surface of one surface to 200 μm in the thickness direction.
The foam layer has a density (B) of 0.100 to 0.190 g / cm ³ in a region from the surface of the other surface to 200 μm in the thickness direction.
The foamed layer has a density (C) of 0.062 g / cm ³ or more in a region of 200 to 300 μm in the thickness direction from the surface of one of the surfaces.
The density (C) is lower than the density (A),
The density difference obtained by subtracting the density (B) from the density (A) is 0.016 to 0.105 g / cm ³ .
Polystyrene resin foam sheet. The polystyrene-based resin foam sheet according to claim 1, wherein the density (C) is lower than the density (B). Extruded and foamed into a tubular body, the inner peripheral surface of the tubular body is cooled along the outer peripheral surface of the mandrel, and then torn to produce.
The polystyrene-based resin foam sheet according to claim 1 or 2, wherein the inner peripheral surface of the tubular body forms one of the surfaces. The foam layer has a thickness of 0.5 to 5.0 mm and has a thickness of 0.5 to 5.0 mm.
The polystyrene-based resin foam sheet according to any one of claims 1 to ³ , wherein the overall density (D) of the foamed layer is 0.050 to 0.150 g / cm ³ . Having a non-foamed layer on one or both sides of the foamed layer
The polystyrene-based resin foam sheet according to any one of claims 1 to 4, wherein the thickness of the non-foamed layer is 5 to 100 μm. A polystyrene-based resin foam container, which is heat-molded with one side of the polystyrene-based resin foam sheet according to any one of claims 1 to 5 inside the container. The polystyrene-based resin foam container according to claim 6, which is a container for food.

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