JP7143242B2 - Polystyrene resin foam container - Google Patents

Description

TECHNICAL FIELD The present invention relates to a polystyrene resin foam sheet and a polystyrene resin foam container.

A polystyrene-based resin foamed container formed by molding a polystyrene-based resin foamed sheet is lightweight and has high strength, so that it is widely used as a hard-to-break container. As such a container, for example, food packaging containers such as a tray container and a natto container are known.
A tray container or the like puts contents in the container, wraps it with a film, and puts it on the market in the wrapped state. In such a method of using the tray container, since a large compressive force is applied to the tray container, the tray container is required to have a buckling strength that does not easily bend.

For example, in Patent Document 1, a high-density skin layer is formed only on the inner surface of the container, bulging ribs are arranged between the side wall and the bottom of the container, and the bottom of the container is slightly curved upward. A container is proposed. In the container of Patent Literature 1, buckling is prevented from occurring when a wrap or the like is compressed.
Patent Document 2 proposes a polystyrene-based resin foamed sheet having a specific residual foaming agent amount and a specific density in a portion up to 100 μm in the thickness direction from both surfaces of the sheet. The invention of Patent Document 2 attempts to improve the lip strength (buckling strength) of a molded product obtained by molding a sheet into a shape such as a tray container.

Japanese Utility Model Publication No. 63-6005 JP-A-2004-161804

In recent years, as a device for wrapping a tray container or the like becomes faster, a larger load is applied when wrapping the tray container. For this reason, the conventional technology has a problem that the buckling strength is not sufficient, and wrinkles and cracks occur in the tray container.

Accordingly, an object of the present invention is to provide a polystyrene-based resin foam sheet and a polystyrene-based resin foam container that can further increase the buckling strength of the container.

In order to solve the above problems, the present invention has the following aspects.
[1] A polystyrene resin foam sheet for a container having a foam layer, wherein the foam layer has a density (D0) of 0.045 to 0.165 g/cm ³ , and the foam layer has one surface of The density (D1) in the area from the surface to 200 μm in the thickness direction is 0.085 to 0.446 g/cm ³ , and the foam layer has a density in the area from the surface to 200 μm in the thickness direction on the other side. (D2) is 0.050 to 0.349 g/cm ³ , the ratio represented by the density (D1)/the density (D0) is 1.90 to 2.70, and the density (D2)/ The ratio represented by the density (D0) is 1.11 to 2.11, and the ratio represented by the density (D1) / the density (D2) is 1.28 to 1.71. Resin foam sheet.
[2] The foam layer has a density (D3) of 0.033 to 0.215 g/cm ³ in a region of 200 to 300 μm in the thickness direction from the surface of the one surface, and the density (D3)/the above The polystyrene resin foam sheet according to [1], wherein the ratio represented by density (D0) is 0.75 to 1.30.
[3] The foam layer has a density (D4) of 0.024 to 0.265 g/cm ³ in a region of 200 to 300 μm in the thickness direction from the surface of the other surface, and the density (D4)/the The ratio represented by the density (D0) is 0.54 to 1.61, and the ratio represented by the density (D3)/the density (D4) is 0.81 to 1.38, [2] The polystyrene-based resin foam sheet according to .
[4] The polystyrene resin foam sheet according to any one of [1] to [3], wherein the foam layer has an average cell diameter of 250 to 340 μm.
[5] The polystyrene resin foam sheet according to any one of [1] to [4], which has a non-foamed layer on one or both sides of the foamed layer.
[6] A polystyrene-based resin foamed container obtained by heat-molding the polystyrene-based resin foamed sheet according to any one of [1] to [5] with the one surface inside the container.
[7] The polystyrene-based resin foam container according to [6], which is a food container.

According to the polystyrene resin foam sheet and the polystyrene resin foam container of the present invention, the buckling strength of the container can be further enhanced.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows an example of the polystyrene resin foam sheet which concerns on this invention. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram which shows an example of the manufacturing apparatus of a polystyrene 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.
The foam sheet may have a single layer structure consisting only of a foam layer, or may have a multilayer structure having a non-foam layer on one or both sides of the foam layer.

An example of the foamed sheet of the present invention will be described below with reference to the drawings.
As shown in FIG. 1, the foam sheet 1 is a foam sheet for a container, and includes one surface A (hereinafter also referred to as "first surface A") and the other surface B (hereinafter referred to as "second surface A"). (also referred to as "face B"). The foam sheet 1 has a single-layer structure consisting of only foam layers.
The foam sheet 1 is formed so that the diameter of cells decreases and the density increases from the central portion in the thickness direction toward the first surface A.
Further, the foam sheet 1 is formed so that the cell diameter decreases and the density increases from the center in the thickness direction toward the second surface B. As shown in FIG.

The thickness T ₁ of the foamed sheet 1 is, for example, preferably 0.6 to 5.0 mm, more preferably 0.8 to 4.0 mm, even more preferably 1.0 to 3.0 mm. When the thickness T1 of the foam sheet ₁ is equal to or greater than the above lower limit, the buckling strength of the polystyrene-based resin foam container (hereinafter also simply referred to as "foam container") to be described later can be further enhanced. When the thickness T1 of the foamed sheet ₁ is equal to or less than the above upper limit, the formability of the foamed sheet 1 is likely to be improved.
The thickness T1 of the foamed sheet ₁ is a value obtained by the following method. The thickness of 10 arbitrary points in the TD direction (width direction) of the foam sheet 1 is measured with a microgauge. The thickness T1 of the foam sheet ₁ is obtained by averaging the measured values at 10 points.

The overall density (D0) of the foam layers in the foam sheet 1 is 0.045-0.165 g/cm ³ , preferably 0.053-0.133 g/cm ³ , more preferably 0.061-0.101 g/cm ³ is more preferred. When the density (D0) is at least the above lower limit, the impact resistance of the foam container can be further enhanced. A foaming container can be made more lightweight as density (D0) is below the said upper limit.
Density (D0) is obtained by measuring in accordance with JIS K 7222:2005 "Foamed plastics and rubbers - Determination of apparent density".
More specifically, the mass and apparent volume of a 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 (D0) (g/cm ³ )=mass of test piece (g)/apparent volume of test piece (cm ³ ) (0)

The density (D1) of the region from the surface of the first surface A to 200 μm in the thickness direction (hereinafter also referred to as “first region a1”) is 0.085 to 0.446 g / cm ³ , and 0 0.106 to 0.349 g/cm ³ is preferred, and 0.128 to 0.257 g/cm ³ is more preferred. When the density (D1) is at least the above lower limit, the buckling strength of the foam container can be further increased. A foaming container can be made more lightweight as density (D1) is below the said upper limit.
How to obtain the density (D1) will be described later.

The density (D2) of the region from the surface of the second surface B to 200 μm in the thickness direction (hereinafter also referred to as “second region a2”) is 0.050 to 0.349 g / cm ³ , 0.064 to 0.273 g/cm ³ is preferred, and 0.080 to 0.201 g/cm ³ is more preferred. When the density (D2) is at least the above lower limit, the buckling strength of the foam container can be further increased. A foaming container can be made more lightweight as density (D2) is below the said upper limit.
How to obtain the density (D2) will be described later.

The density (D3) of the region 200 to 300 μm in the thickness direction from the surface of the first surface A (hereinafter also referred to as “third region a3”) is preferably 0.033 to 0.215 g/cm ³ , 0.041 to 0.168 g/cm ³ is more preferred, and 0.049 to 0.124 g/cm ³ is even more preferred. When the density (D3) is at least the above lower limit, the buckling strength of the foam container can be further increased. A foaming container can be made more lightweight as density (D3) is below the said upper limit.
How to obtain the density (D3) will be described later.

The density (D4) of a region 200 to 300 μm in the thickness direction from the surface of the second surface B (hereinafter also referred to as “fourth region a4”) is preferably 0.024 to 0.265 g/cm ³ , 0.031 to 0.185 g/cm ³ is more preferred, and 0.038 to 0.122 g/cm ³ is even more preferred. When the density (D4) is at least the above lower limit, the buckling strength of the foam container can be further increased. A foaming container can be made more lightweight as density (D4) is below the said upper limit.
How to obtain the density (D4) will be described later.

The density (D5) of the central region in the thickness direction (hereinafter also referred to as “fifth region a5”) excluding the first region a1 to the fourth region a4 from the entire foam sheet 1 is 0.020. ~0.120 g/cm ³ is preferred, 0.025 to 0.100 g/cm ³ is more preferred, and 0.030 to 0.080 g/cm ³ is even more preferred.
How to obtain the density (D5) will be described later.
The thickness of the fifth region a5 is not particularly limited, but is the value obtained by subtracting the total thickness of the first region a1 to the fourth region a4 (that is, 600 μm) from the thickness T1 of the foam sheet ₁ . . The thickness of the fifth region a5 is, for example, preferably 0 to 4400 μm, more preferably 200 to 3400 μm, even more preferably 400 to 2400 μm.

The density (d1) of the region from the surface of the first surface A to 100 μm in the thickness direction (hereinafter also referred to as “sixth region a6”) is preferably, for example, 0.142 to 0.642 g/cm ³ .
The density (d2) of the region from the surface of the second surface B to 100 μm in the thickness direction (hereinafter also referred to as “seventh region a7”) is preferably, for example, 0.073 to 0.453 g/cm ³ .
How to obtain the density (d1) and the density (d2) will be described later.

The above density (d1), density (d2), density (D1), density (D2), density (D3), density (D4) and density (D5) (hereinafter also referred to as "the density of each region") , can be adjusted by the manufacturing conditions of the foam sheet 1 . More specifically, it can be adjusted by adjusting the temperature and flow rate of the air blown when cooling the foam sheet 1, the temperature and flow rate of cooling water for the mandrel, the type and content of the cell control agent in the resin composition, and the like.
Density (D0), density (d1), density (d2), density (D1), density (D2), density (D3), density (D4) and density (D5) are apparent densities.

The ratio represented by density (D1)/density (D0) (hereinafter also referred to as “D1/D0 ratio”) is 1.90 to 2.70, preferably 2.00 to 2.62, and 2 0.10 to 2.54 is more preferred. When the D1/D0 ratio is within the above numerical range, the buckling strength of the foam container can be further enhanced.

The ratio represented by density (D2)/density (D0) (hereinafter also referred to as “D2/D0 ratio”) is 1.11 to 2.11, preferably 1.21 to 2.05, and 1 0.32 to 1.99 is more preferred. When the D2/D0 ratio is within the above numerical range, the buckling strength of the foam container can be further enhanced.

The ratio represented by density (D1)/density (D2) (hereinafter also referred to as “D1/D2 ratio”) is 1.28 to 1.71, preferably 1.28 to 1.65, and 1 0.28 to 1.59 is more preferred. Since the D1/D2 ratio is greater than 1, the first region a1 is denser than the second region a2, forming a high density layer. When the D1/D2 ratio is at least the above lower limit, the buckling strength of the foam container can be further increased. It is believed that this is because the foamed container is formed so that the high-density layer is located inside the container, so that the high-density layer can exhibit a repulsive force against an external force applied to the foamed container. When the D1/D2 ratio is equal to or less than the above upper limit, moldability can be further enhanced.

The ratio represented by density (D3)/density (D0) (hereinafter also referred to as "D3/D0 ratio") is preferably 0.75 to 1.30, more preferably 0.78 to 1.26, 0.81 to 1.22 is more preferred. When the D3/D0 ratio is within the above numerical range, the buckling strength of the foam container can be further enhanced.

The ratio represented by density (D4)/density (D0) (hereinafter also referred to as "D4/D0 ratio") is preferably 0.54 to 1.61, more preferably 0.58 to 1.39, 0.63 to 1.21 is more preferable. When the D3/D0 ratio is within the above numerical range, the buckling strength of the foam container can be further enhanced.

The ratio represented by density (D3)/density (D4) (hereinafter also referred to as "D3/D4 ratio") is preferably 0.81 to 1.38, more preferably 0.91 to 1.33, 1.01 to 1.28 are more preferred. When the D3/D4 ratio is at least the above lower limit, the buckling strength of the foam container can be further increased. When the D3/D4 ratio is equal to or less than the above upper limit, moldability can be further enhanced.

The ratio represented by density (d1)/density (D0) (hereinafter also referred to as “d1/D0 ratio”) is preferably 3.17 to 3.89, for example. When the D1/D0 ratio is within the above numerical range, the buckling strength of the foam container can be further enhanced.

The ratio represented by density (d2)/density (D0) (hereinafter also referred to as “d2/D0 ratio”) is preferably 1.62 to 2.74. When the d2/D0 ratio is within the above numerical range, the buckling strength of the foam container can be further enhanced.

The ratio represented by density (d1)/density (d2) (hereinafter also referred to as “d1/d2 ratio”) is preferably 1.42 to 1.95. When the d1/d2 ratio is at least the above lower limit, the buckling strength of the foam container can be further increased. If the d1/d2 ratio is equal to or less than the above upper limit, moldability can be further enhanced.

The density of each region can be obtained by measuring the volume and mass of three slices obtained by slicing the foam sheet 1 from the surface of the first surface A at depths of 100 μm, 200 μm, and 300 μm. can.
Similarly, the density of each region was obtained by measuring the volume and mass of three slices obtained by slicing the foam sheet 1 from the surface of the second surface B at depths of 100 μm, 200 μm, and 300 μm. can ask.
More specifically, the value of density (d1) is determined as follows. First, a foamed sheet cut into a size of 2 cm×5 cm is sliced at a depth of 100 μm from the surface of the first surface A to prepare slices (first slices) having a thickness of 100 μm. It can be obtained by calculating the following formula (1) from the apparent volume (Vd1: cm ³ ) and the mass (Wd1: g) of a sample cut into a size of 1 cm×2 cm from the first slice.
“d1”=Wd1/Vd1 (g/cm ³ ) (1)

The density (D1) value is determined as follows. First, a foamed 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 A to prepare slices (second slices) having a thickness of 200 μm. From the apparent volume (VD1: cm ³ ) and the mass (WD1: g) of the sample cut into a size of 1 cm×2 cm from the second slice piece, it can be obtained by calculating the following formula (2).
“D1”=WD1/VD1 (g/cm ³ ) (2)
The density (D3) value is determined as follows. First, a foamed 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 A to prepare slices (third slices) having a thickness of 300 μm. From the apparent volume (VD3: cm ³ ) and mass (WD3: g) of the sample cut out from the third slice into a size of 1 cm×2 cm, it can be obtained by calculating the following formula (3).
"D3" = (WD3-WD1)/(VD3-VD1) (g/cm ³ ) (3)

Density (d2), density (D2), density (D4), and density (D5) can also be obtained by the same method.

The average cell diameter of the entire foam layer in the foam sheet 1 is preferably 250-340 μm, more preferably 260-330 μm, and even more preferably 270-320 μm. The buckling strength of the foam sheet 1 can be further increased when the average cell diameter of the entire foam layer is at least the above lower limit. When the average cell diameter of the entire foam layer is equal to or less than the above upper limit, the beauty of the foam sheet 1 can be further enhanced.
The average cell diameter of the entire foam layer in the foam sheet 1 may be 150 to 400 μm within a range that does not impair the effects of the present invention.
The average cell diameter of the entire foam layer in the foam sheet 1 can be adjusted by the manufacturing conditions of the foam sheet 1 . More specifically, it can be adjusted by adjusting the temperature and flow rate of the air blown when cooling the foam sheet 1, the temperature and flow rate of cooling water for the mandrel, the type and content of the cell control 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.

Along the extrusion direction (MD direction) of the foam sheet 1 and the direction perpendicular to the MD direction on the surface of the foam sheet 1 (width direction, also referred to as TD direction), from the center part of the foam sheet 1 in the TD direction, the foam sheet The foam sheet 1 is cut out in a direction perpendicular to the surface of the foam sheet 1 (also referred to as thickness direction or VD direction).
Using a scanning electron microscope ("S-3400N" or "SU1510" manufactured by Hitachi High-Technologies Corporation), the cut cross section is photographed at a magnification of 20 to 100 times.
At this time, a microscope image is taken so as to obtain a predetermined magnification when printed in a state in which a total of four images are arranged on one sheet of A4 paper in landscape orientation, with two images arranged vertically and horizontally.
More specifically, when arbitrary straight lines with a length of 60 mm parallel to each of the MD, TD, and VD directions are drawn on the microscope image, the number of bubbles present on these straight lines is The imaging magnification of the scanning electron microscope is adjusted so that 5 to 30 are obtained.

A total of two fields of view for each of a cross section cut along the MD direction (hereinafter also referred to as "MD cross section") and a cross section cut along the TD direction (hereinafter also referred to as "TD cross section"). Microscopic images of 4 fields are taken and printed on A4 paper as described above.
Three arbitrary straight lines (length 60 mm) parallel to the MD direction are drawn on each of the two images of the MD cross section, and three arbitrary straight lines parallel to the TD direction are drawn on each of the two images of the TD cross section ( 60 mm long).
Also, three straight lines (60 mm) parallel to the VD direction are drawn on one image of the MD section and one image of the TD section. In this way, six arbitrary straight lines of 60 mm parallel to each of the MD, TD, and VD directions are drawn in each direction.
It should be noted that the arbitrary straight line is designed so that bubbles do not come into contact only at the points of contact as much as possible.

Arithmetic mean of the number of bubbles counted for six arbitrary straight lines in each direction of MD, TD, and VD is taken as the number of bubbles in each direction.
The average chord length t of bubbles is calculated by the following formula (4) from the image magnification obtained by counting the number of bubbles and the number of bubbles.
Average chord length t (mm) = 60/(number of bubbles x image magnification) (4)
However, if the thickness of the foam sheet 1 is thin and it is not possible to draw a straight line of 60 mm in length 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. Count the number of bubbles and convert to the number of bubbles on a straight line of 60 mm in length (for example, if there are 5 bubbles on a straight line with a length of 30 mm, there are 10 bubbles on a straight line with a length of 60 mm). regarded as a thing).

The image magnification is obtained by measuring the scale bar on the image to 1/100 mm using "Digimatic Caliper" manufactured by Mitutoyo Corporation and using the following formula (5).
Image magnification = measured value of scale bar (mm)/displayed value of scale bar (mm) (5)

Then, the bubble diameter DMD in the MD direction is calculated by the following formula (6).
DMD (mm) = t/0.616 (6)
The bubble diameter DTD (mm) in the TD direction and the bubble diameter DVD (mm) in the VD direction can also be calculated in the same manner as the DMD.

Let the cube root of the product of DMD, DTD, and DVD be the average bubble diameter D (mm) (formula (7) below).
D (mm)=(DMD×DTD×DVD) ^1/3 (7)

The total basis weight of the foam layers in the foam sheet 1 is preferably, for example, 80-500 g/m ² , more preferably 90-300 g/m ² . When the basis weight of the entire foam layer in the foam sheet 1 is at least the above lower limit, the buckling strength of the foam container can be further increased. When the basis weight of the entire foam layer in the foam sheet 1 is equal to or less than the above upper limit, the foam container can be made lighter. In addition, when the basis weight of the entire foam layer in the foam sheet 1 is equal to or less than the above upper limit, the heating time during thermoforming does not become too long, and the productivity of the foam container can be further enhanced.

The basis weight of the entire foam layer in the foam sheet 1 can be measured by the following method.
Ten pieces of 10 cm×10 cm are cut out at equal intervals in the width direction except for 20 mm at both ends in the width direction of the foam sheet 1, and the mass (g) of each piece is measured to the nearest 0.001 g. A value obtained by converting the average value of the mass (g) of each section into mass per 1 m ² is defined as the basis weight (g/m ² ) of the entire foam sheet 1 .

<Foam layer>
The foam layer is a layer formed by foaming a resin composition containing a polystyrene resin and a foaming agent. The foam sheet 1 exhibits heat insulation and impact resistance by having a foam layer.

Examples of polystyrene resins include homopolymers or copolymers of styrene monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene; Copolymers of a styrene-based monomer as a main component (50% by mass or more) and a vinyl monomer polymerizable therewith: a copolymer of a styrene-based monomer and a rubber component such as butadiene, and a styrene-based monomer or copolymers thereof, or mixtures or polymers of copolymers of styrene-based monomers and vinyl monomers with diene-based rubber-like polymers, so-called high-impact polystyrene;
Examples of vinyl monomers polymerizable with styrene monomers include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate and cetyl (meth)acrylate, (meth)acrylonitrile, dimethyl Bifunctional monomers such as maleate, dimethyl fumarate, diethyl fumarate, ethyl fumarate, divinylbenzene, alkylene glycol dimethacrylate, and the like. These vinyl monomers may be used individually by 1 type, and may use 2 or more types together.
Here, "(meth)acrylate" represents one or both of "acrylate" and "methacrylate", and "(meth)acrylonitrile" represents one or both of "acrylonitrile" and "methacrylonitrile".
Examples of diene-based rubber-like polymers include polybutadiene, styrene-butadiene copolymers, ethylene-propylene-nonconjugated diene three-dimensional copolymers, acrylonitrile-butadiene-styrene copolymers, and the like.
These polystyrene-based resins may be used alone or in combination of two or more.

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, a polystyrene-based resin newly prepared by a method such as suspension polymerization, or a polystyrene-based resin that is a recycled raw material.
The recycled raw material is a used polystyrene-based resin foam molding. Recycled raw materials include food packaging trays, fish boxes, cushioning materials for household appliances, etc., which are recovered and regenerated by the limonene dissolution method or the heating volume reduction method. In addition, usable recycled materials are non-foamed polystyrene resin moldings that are sorted and collected from home appliances (e.g., televisions, refrigerators, washing machines, air conditioners, etc.) and office equipment (e.g., copiers, facsimiles, printers, etc.). It may also be obtained by pulverizing the body, melt-kneading it, and repelletizing it.

The foam sheet 1 may contain resins other than polystyrene-based resins (hereinafter also referred to as "other resins"). Other resins include, for example, polyolefin-based resins and polyphenylene ether-based resins.
Polyolefin resins include, for example, homopolymers of olefinic monomers such as ethylene and propylene, copolymers thereof, and copolymerization of olefinic monomers and vinyl monomers polymerizable therewith. A coalescence etc. are mentioned.
Examples of polyphenylene ether resins include poly(2,6-dimethylphenylene-1,4-ether), poly(2,6-diethylphenylene-1,4-ether), poly(2,6-dichlorophenylene -1,4-ether) and the like.

The content of other resins is preferably 40 parts by mass or less, more preferably 30 parts by mass or less, still more preferably 20 parts by mass or less, and 10 parts by mass or less, based on 100 parts by mass of all resin components in the foam sheet 1. It is particularly preferable, and may be 0 parts by mass. When the content of the other resin is equal to or less than the above upper limit, the foamed sheet 1 becomes rigid, and the molded article becomes easier to handle.

Examples of foaming agents include hydrocarbons such as propane, butane, and pentane; and halogenated hydrocarbons such as tetrafluoroethane, chlorodifluoroethane, and difluoroethane. Among them, butane is suitable as the foaming agent. The butane may be normal butane or isobutane alone, or may be a combination of normal butane and isobutane.
These foaming agents may be used individually by 1 type, and may use 2 or more types together.
The blending amount of the foaming agent is determined in consideration of the type of the foaming agent, the overall density (D0) required for the foamed 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 all the resin components in the foamed sheet 1 .

The foam sheet 1 may contain components other than the polystyrene-based resin and the foaming agent (hereinafter also referred to as "optional components"). Examples of optional components include cell regulators, stabilizers, ultraviolet absorbers, antioxidants, colorants, deodorants, lubricants, flame retardants, antistatic agents, and the like.
The type of optional component is determined in consideration of the physical properties required for the foamed sheet 1 and the like. Optional components may be used singly or in combination of two or more.

Examples of cell control agents include mixtures of inorganic powders such as talc and silica. These cell control agents increase the closed cell ratio of the foam layer, making it easier to form the foam layer.
Examples of stabilizers include calcium-zinc heat stabilizers, tin heat stabilizers, lead heat stabilizers, and the like.
Examples of the ultraviolet absorber include cesium oxide-based ultraviolet absorbers, titanium oxide-based ultraviolet absorbers, and the like.
Antioxidants include, for example, cerium oxide, cerium oxide/zirconia solid solution, cerium hydroxide, carbon, carbon nanotubes, titanium oxide, and fullerene.
Examples of coloring agents include titanium oxide, carbon black, titanium yellow, iron oxide, ultramarine blue, cobalt blue, baked pigments, metallic pigments, mica, pearl pigments, zinc white, precipitated silica, cadmium red, and the like.
Examples of deodorants include silica, zeolite, zirconium phosphate, hydrotalcite calcined products, 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, more preferably 0.3 to 0.3 to 5.0 parts by mass is more preferable. When the content of the optional component is at least the above lower limit, the effect derived from the optional component can be exhibited. When the content of the optional component is equal to or less than the above upper limit, clogging of the die or the like can be better prevented, and the appearance of the foam sheet 1 can be improved.

When the foam layer contains a cell control agent, the content of the cell control agent is preferably 0.01 to 5.0 parts by mass, more preferably 0.02 to 3 parts by mass, with respect to 100 parts by mass of all the resin components in the foam sheet 1. 0.0 parts by weight is more preferred, and 0.03 to 2.0 parts by weight is even more preferred. When the content of the cell adjusting agent is at least the above lower limit, the closed cell ratio of the foam layer can be further increased. When the content of the cell adjusting agent is equal to or less than the above upper limit, clogging of the die or the like can be better prevented, and the appearance of the foam sheet 1 can be improved.

The closed cell ratio of the foam layer is preferably 70% or more, more preferably 80% or more, still more preferably 90% or more, and may be 100%. The closed cell rate of the foam layer is a value measured by the method described in JIS K7138:2006 "Rigid Foamed Plastics - Determination of Open Cell Rate and Closed Cell Rate".

The foamed sheet of the present invention preferably has a non-foamed layer on one side or both sides of the foamed layer. A foamed container having a non-foamed layer can increase the buckling strength of the container. In addition, a foamed container having a non-foamed layer can enhance the aesthetics of the container.
The resin constituting the non-foamed layer is not particularly limited, and examples thereof include the same resins as those constituting the foamed layer.
The resin forming the non-foamed layer may be the same as or different from the resin forming the foamed layer.
In addition, a printed 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 printed layer.

The thickness of the non-foamed layer is determined in consideration of the usage of the foamed sheet, and is preferably 5 to 300 μm, more preferably 10 to 200 μm. When the thickness of the non-foamed layer is at least the above lower limit, the buckling strength of the foamed sheet can be further improved. In addition, when the thickness of the non-foamed layer is equal to or more than the above lower limit, "irregularities caused by air bubbles" on the surface of the foamed container can be improved, and beauty can be further improved. When the thickness of the non-foamed layer is equal to or less than the upper limit, the weight of the foamed sheet can be reduced.

Examples of the resin constituting the non-foamed layer include general-purpose polystyrene resin (GPPS) films, high-impact polystyrene resin (HIPS) films, and laminated films obtained by dry-laminating these films with polyolefin resin films or the like. be done.
These resin films include unstretched films, weakly stretched films, uniaxially stretched films, and
Any biaxially stretched film may be used.
In the case of forming a laminated film as described above, the polyolefin resin film to be dry-laminated is, for example, a high density polyethylene resin (HDPE) film, a polypropylene resin (PP) film, a cycloolefin polymer (COP) film, a cycloolefin A copolymer (COC) film and the like are included. Other resins include, for example, polyamide resin films, polyethylene terephthalate resin (PET) films, ethylene vinyl alcohol resin (EVOH) films, and the like.
The non-foamed layer may have a single-layer structure or a multi-layer structure of 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 that bonds the outer layer and the inner layer. preferable. In this multilayer film, the outer layer is positioned on the surface (exposed surface) and the inner layer is positioned on the foam layer side.

[Method for manufacturing foam sheet]
A foam sheet is manufactured by a conventionally known manufacturing method.
A method for manufacturing a foam sheet will be described by taking a method for manufacturing a single-layer foam sheet 1 as an example.
A foam sheet manufacturing apparatus 100 in FIG. 2 is an apparatus for obtaining a foam sheet by extrusion molding. The manufacturing apparatus 100 comprises an extruder 10 , a blowing agent 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 section 11 comprises a hopper 14 . A blowing agent supply source 18 is connected to the first extrusion section 11 .
A circular die 20 is connected to the second extrusion part 12 . A mandrel 30 with 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 .

A raw material for forming the foam layer is fed from the hopper 14 into the first extrusion section 11 . The raw materials charged from the hopper 14 are the resin constituting the foam layer and optional components blended as necessary.
In the first extrusion section 11, the raw materials are heated to an arbitrary temperature and mixed to form a resin melt. are mixed to form a resin composition.
The heating temperature is appropriately determined in consideration of the type of resin, etc., within a range in which the resin is melted and optional components are not denatured. The heating temperature is, for example, preferably 150 to 350°C, more preferably 170 to 330°C.

The resin composition is supplied from the first extrusion section 11 through the pipe 16 to the second extrusion section 12 and further mixed. After that, the resin composition is cooled to an arbitrary temperature and then guided to the resin flow path inside the circular die 20 .
The resin composition guided to the resin flow path is extruded from the circular die 20, and the foaming agent is foamed to form a cylindrical foamed sheet 1a.
The discharge rate of the resin composition extruded from the circular die 20 is, for example, preferably 100-800 kg/h, more preferably 150-700 kg/h. When the discharge amount of the resin composition is at least the above lower limit, the resin composition is not cooled too much, and it is possible to prevent 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, the productivity of the cylindrical foam sheet 1a can be enhanced. When the discharge amount of the resin composition is equal to or less than the above upper limit, the resin composition is sufficiently cooled, and the cylindrical foamed sheet 1a having a desired density is easily obtained.

The cylindrical foam sheet 1a is guided to the mandrel 30 while being blown with cooling air blown from a cooling blower. Cylindrical foam sheet 1a passes through the outer peripheral surface of mandrel 30 and is cooled to an arbitrary temperature.
Cooling water flows through the inside of the mandrel 30, forming a mechanism capable of cooling the inner peripheral surface of the cylindrical foamed sheet 1a.
The temperature of the cooling water is, for example, preferably 10 to 60°C, more preferably 15 to 50°C. When the temperature of the cooling water is within the above numerical range, the inner peripheral surface of the cylindrical foamed sheet 1a can be cooled to a desired density.
The flow rate of cooling water is, for example, preferably 5 to 35 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 foamed sheet 1a can be cooled to 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 to the inner peripheral surface of the cylindrical foamed sheet 1a (hereinafter also referred to as “air volume 1”) is, for example, preferably 0.3 to 5.0 Nm ³ /min, and preferably 0.5 to 5.0 Nm 3 /min. 4.5 Nm ³ /min is more preferred. When the air volume 1 is within the above numerical range, the inner peripheral surface of the cylindrical foamed sheet 1a can be cooled to a desired density.
The air volume for blowing cooling air to the outer peripheral surface of the cylindrical foamed sheet 1a (hereinafter also referred to as “air volume 2”) is, for example, preferably 0.1 to 4.5 Nm ³ /min, and 0.3 to 4.0 Nm 3 /min. 0 Nm ³ /min is more preferred. When the air volume 2 is within the above numerical range, the outer peripheral surface of the cylindrical foam sheet 1a can be cooled to a desired density.
The temperature of the cooling air blown onto the cylindrical foamed sheet 1a is, for example, preferably 10 to 50.degree. C., more preferably 15 to 40.degree. When the temperature of the cooling air is equal to or higher than the lower limit, it is possible to prevent the cylindrical foam sheet 1a from being cooled more than necessary. In addition, when the temperature of the air for cooling is equal to or higher than the above lower limit, energy for cooling the air can be saved. When the temperature of the cooling air is equal to or lower than the above upper limit, the cylindrical foamed sheet 1a can be sufficiently cooled.

The cooled cylindrical foam sheet 1 a is cut into two sheets by a cutter 32 to form the foam sheet 1 . At this time, it is preferable that the inner peripheral surface of the cylindrical foam sheet 1 a is the first surface A of the foam sheet 1 and the outer peripheral surface of the cylindrical foam sheet 1 a is the second surface B of the foam sheet 1 . By forming the inner peripheral surface of the cylindrical foam sheet 1a as the first surface A of the foam sheet 1, the first surface A can be easily placed on the high-density layer side.
The foam sheet 1 is wound around a guide roll 42 and a guide roll 44 , respectively, and wound up by a winder 40 to form a foam sheet roll 4 .
Thus, a foamed sheet 1 having a single layer structure is obtained.
The foam layer of the foam sheet 1 described here is a single-layer foam layer, but the foam layer of the foam sheet may be, for example, a laminate of two or more foam layers by coextrusion, and may be heat-sealed. Alternatively, two or more foam layers laminated by adhesion may be used.

As a method of forming a non-foamed layer on a foamed sheet, for example, a method of obtaining a foamed layer by the above-described production method, thermally laminating a resin film having a single-layer structure or a multi-layer structure on the surface of the foamed layer, and forming a non-foamed layer; For example, a foamed layer is obtained by the above-described manufacturing method, and a non-foamed layer is formed on the surface thereof by a T-die method.

[Polystyrene resin foam container]
The polystyrene-based resin foamed container of the present invention (also simply referred to as a "foamed container") is formed by heat-molding the above-described foamed sheet of the present invention with one surface inside the container. Here, one surface of the foam sheet refers to the surface on the side of the first area a1 (the area having the density (D1)) forming the high-density layer.
Examples of foaming containers include trays with a plan view shape of a perfect circle, ellipse, semicircle, polygon, fan, etc., bowl-shaped containers, bottomed cylindrical or bottomed rectangular cylinders, and natto containers. various containers such as containers with lids such as;
These containers are preferably used for foods, for example.

The thickness of the foaming container is determined in consideration of the application, and is preferably 0.6 to 5.0 mm, more preferably 0.8 to 4.0 mm, and even more preferably 1.0 to 3.0 mm.
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 (D0) of the foam layer in the foam sheet.
The density of the foam layer in the region from the surface of one side of the foam container to 200 μm in the thickness direction is the same as the density (D1) of the first region a1 in the foam sheet.
The density of the foam layer in the area up to 200 μm in the thickness direction from the surface of the other surface of the foam container is the same as the density (D2) of the second area 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 side of the foam container is the same as the density (D3) of the third region a3 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 the other side of the foam container is the same as the density (D4) of the fourth region a4 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 300 μm in the thickness direction from the surface of the other surface of the foam container is the density of the fifth region a5 in the foam sheet ( D5).
The density of the foam layer in the region from the surface of one side of the foam container to 100 μm in the thickness direction is the same as the density (d1) of the sixth region a6 in the foam sheet.
The density of the foam layer in the area up to 100 μm in the thickness direction from the surface of the other surface of the foam container is the same as the density (d2) of the seventh area a7 in the foam sheet.
In addition, the density ratio of each region in the foam container is the same as the density ratio of each region in the foam sheet.

As described above, according to the foamed sheet of the present invention, the density (D1) of the area up to 200 μm in the thickness direction from the surface of one surface of the foam layer and the thickness direction from the surface of the other surface of the foam layer By controlling the density (D2) in the area up to 200 μm and the density (D1) to be high, the buckling strength of the foamed container can be further increased.
In addition, by controlling the density (D3) in a region of 200 to 300 μm in the thickness direction from the surface of one side of the foam layer so that there is no extreme decrease in density, there is no locally weak foam layer. Therefore, the buckling strength of the foam container can be further increased.

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

[raw materials used]
Resin: Polystyrene resin, MW=323×10 ³ , manufactured by DIC Corporation, product name “XC-515”.
Cell control agent: talc-containing resin composition (contains 40% by mass of talc (average specific surface area: 10 to 40 m ² /g); manufactured by Toyo Styrene Co., Ltd., product name: "DSM1401A").
- Foaming agent: butane (mixture of isobutane: normal butane = 68:32 (mass ratio)).

[Examples 1 to 7, Comparative Examples 1 to 3]
(Manufacture of foam sheet)
A single-layer foam sheet was obtained in the following manner using a manufacturing apparatus similar to the foam sheet manufacturing apparatus of FIG.
A polystyrene resin and a cell control agent were mixed according to the composition shown in Table 1. Compositions in the table represent parts by mass.
A mixture of raw materials was supplied from a hopper to a first mixing section (screw diameter: 115 mm), heated at a maximum temperature of 275° C., and melt-kneaded to obtain a resin melt.
A foaming agent (a mixture of isobutane:n-butane=68:32 (mass ratio)) 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 set to parts by mass shown in Table 1 with respect to 100 parts by mass of the polystyrene resin.
The resin composition is supplied from the first mixing section to the second mixing section (screw diameter: 180 mm), cooled to 153 ° C., extruded from a circular die (diameter 175 mm) at the discharge rate shown in Table 1, and foamed. A cylindrical foam sheet was obtained. At this time, immediately after being extruded from the circular die, the inner and outer peripheral surfaces of the cylindrical foamed sheet were cooled by blowing cooling air (30° C.) at the air volume shown in Table 1. In addition, the cylindrical foam sheet was cooled by allowing the inner peripheral surface of the cylindrical foam sheet to come into contact with the outer peripheral surface of the mandrel through which the cooling water flowed. In Examples 1 to 6 and Comparative Examples 1 to 3, the inner peripheral surface of the cylindrical foam sheet was cooled to form a high-density layer. In Example 7, the outer peripheral surface of the cylindrical foam sheet was cooled to form a high-density layer. The cooling water flowing through the mandrel had a temperature of 25° C. and a cooling water flow rate of 25 L/min.
The cylindrical foamed sheet after cooling was cut along the extrusion direction to obtain a foamed sheet having an expansion ratio of 15.1 times and a thickness of 1.8 mm. The density of each region was obtained by slicing this foam sheet. Also, using this foamed sheet, the basis weight and the average cell diameter were measured. The unit of average bubble diameter in the table is μm.

(Manufacture of laminated foam sheet)
A polystyrene resin film having a thickness of 15 μm was brought into contact with a hot roll at 160° C. as a non-foamed layer on both sides of the resulting foamed sheet. After that, it was laminated on a foamed sheet at 25° C. at a lamination pressure of 0.5 MPa and a lamination speed of 8.0 m/min to obtain a laminated foamed sheet having non-foamed layers on both sides of the foamed layer. The density and density ratio of each region in the foam layer of the obtained laminated foam sheet were the same as the density and density ratio of each region in the foam sheet before lamination.

(Manufacture of foaming container)
The obtained laminated foamed sheet was thermoformed by a single-shot molding machine. A rectangular tray (foamed container) having a length of 200 mm, a width of 200 mm and a depth of 30 mm was obtained by hot molding. At this time, one surface, that is, the surface on the side of the region having the density (D1) forming the high-density layer was placed inside the container, and heat molding was performed to obtain a foamed container.

The resulting foamed container was evaluated for container strength, beauty, and moldability according to the following evaluation methods. Table 1 shows the results.

[Evaluation of container strength]
The obtained foam container (rectangular tray) was used as a measurement sample. Using a Tensilon universal material testing machine (RTC-1310A, manufactured by Orientec Co., Ltd.), the center of both horizontal sides of the measurement sample of each example is set to 400 mm / min so that the opposing horizontal sides are close to each other. was compressed until buckling occurred, and the maximum load and displacement were measured. The maximum load/displacement was measured for 30 measurement samples for each example, and the arithmetic mean of 30 samples was obtained. Next, the central portions of both vertical sides were compressed at a rate of 400 mm/min until buckling occurred, and the maximum load and displacement were measured. The maximum load/displacement was measured for 30 measurement samples for each example, and the arithmetic mean of 30 samples was obtained. The buckling strength of the foamed container and the buckling displacement of the foamed container were defined as the higher arithmetic mean value of the arithmetic mean value measured for the horizontal sides and the arithmetic mean value measured for the vertical sides. From the buckling strength of the foamed container and the value of the buckling displacement of the foamed container, the strength of the container was evaluated based on the following evaluation criteria. "⊚", "○", and "△" were regarded as passed.
"Evaluation criteria"
A: Buckling strength of 1.50 kgf or more and buckling displacement of 30 mm or more.
◯: Buckling strength of 1.50 kgf or more and buckling displacement of 25 mm or more and less than 30 mm.
Δ: Buckling strength of 1.40 kgf or more and less than 1.50 kgf, and buckling displacement of 25 mm or more and less than 30 mm.
x: Buckling displacement less than 1.40 kgf.

[Evaluation of beauty]
The surface of the obtained foamed container was visually observed for "irregularities derived from air bubbles", and the beauty was evaluated based on the following evaluation criteria. "○" and "Δ" were regarded as acceptable.
"Evaluation criteria"
◯: "Unevenness derived from air bubbles" is not observed on the surface.
Δ: "Unevenness derived from air bubbles" is slightly observed on the surface.
x: "Irregularities derived from air bubbles" are clearly observed on the surface.

[Evaluation of moldability]
"Deformation wrinkles caused by molding" on the surface of the obtained foamed container were visually observed, and moldability was evaluated based on the following evaluation criteria. "○" and "Δ" were regarded as acceptable.
"Evaluation criteria"
◯: No "deformation wrinkles due to molding" were observed on the surface of the foamed container.
Δ: Slight "deformation wrinkles due to molding" are observed on the surface of the foamed container.
x: "Deformation wrinkles derived from molding" are clearly observed on the surface of the foamed container.

[Comprehensive evaluation]
Based on the above evaluation results of container strength, beauty, and formability, a comprehensive evaluation was performed based on the following evaluation criteria. "A", "B", and "C" were regarded as passing.
"Evaluation criteria"
A: The evaluation of container strength was "⊚", and the evaluation of beauty and moldability was "◯".
B: The evaluation of container strength is "⊚" or "◯", and the evaluation of beauty and moldability is "◯" or "Δ".
C: The evaluation of container strength is "Δ", and the evaluation of beauty and moldability is "◯" or "Δ".
D: There is "x" in one of the evaluations.

Examples 1 to 7, to which the present invention was applied, received an overall evaluation of "A", "B" or "C".
On the other hand, Comparative Examples 1 and 2, in which the D1/D0 ratio and the D1/D2 ratio are outside the range of the present invention, received an overall evaluation of "D". Comparative Example 3, in which the D1/D2 ratio was outside the scope of the present invention, received an overall evaluation of "D".

From these results, it was found that the polystyrene resin foam sheet and the polystyrene resin foam container of the present invention can further increase the buckling strength of the container.

1 Polystyrene resin foam sheet (foam sheet)
A One side B The other side

Claims (6)

A polystyrene resin foam container formed by heat molding with one surface of a polystyrene resin foam sheet for a container having a foam layer inside the container,
The foam layer has a density (D0) of 0.045 to 0.165 g/cm ³ ,
The foam layer has a density (D1) of 0.085 to 0.446 g/cm ³ in a region from the surface of the one surface to 200 μm in the thickness direction,
The foam layer has a density (D2) of 0.050 to 0.349 g/cm ³ in a region from the surface of the other side to 200 μm in the thickness direction,
The ratio represented by the density (D1) / the density (D0) is 1.90 to 2.70,
The ratio represented by the density (D2) / the density (D0) is 1.11 to 2.11,
The ratio represented by the density (D1) / the density (D2) is 1.28 to 1.71,
Polystyrene resin foam container . The foam layer has a density (D3) of 0.033 to 0.215 g/cm ³ in a region of 200 to 300 μm in the thickness direction from the surface of the one surface,
2. The polystyrene-based resin foam container according to claim 1, wherein the density (D3)/the density (D0) ratio is 0.75 to 1.30. The foam layer has a density (D4) of 0.024 to 0.265 g/cm ³ in a region of 200 to 300 μm in the thickness direction from the other surface,
The ratio represented by the density (D4) / the density (D0) is 0.54 to 1.61,
3. The polystyrene-based resin foam container according to claim 2, wherein the density (D3)/the density (D4) ratio is 0.81 to 1.38. The polystyrene-based resin foam container according to any one of claims 1 to 3, wherein the foam layer has an average cell diameter of 250 to 340 µm. The polystyrene-based resin foam container according to any one of claims 1 to 4, which has a non-foam layer on one side or both sides of the foam layer. The polystyrene-based resin foam container according to any one of claims 1 to 5 , which is a container for food.

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