JP2015189864A - Polystyrene-based resin foam sheet, polystyrene-based resin laminate foam sheet, and molded container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve brittleness and make handleability good while preventing deformation of a container even with heating by a microwave oven.SOLUTION: There is provided a polystyrene-based resin foam sheet 10 which contains a styrene-methacrylic acid copolymer containing 94 to 98 mass% of a styrene unit and 2 to 6 mass% of a methacrylic acid unit and having a weight average molecular weight of 190,000 to 260,000, and has thickness of 0.5 to 3.0 mm, bulk density of 0.05 to 0.15 g/cm, average bubble diameter of 150 to 500 μm, and total volatile component content of 200 to 800 μg/g. There is provided a polystyrene-based resin laminate foam sheet 1 obtained by laminating resin non-form films 12 consisting of a thermoplastic resin on both face of the polystyrene-based resin foam sheet 10. There is provided a molded container using the polystyrene-based resin foam sheet 10 or the polystyrene-based resin laminate foam sheet 1.

Description

  The present invention relates to a polystyrene resin foam sheet, a polystyrene resin laminated foam sheet, and a molded container.

  Polystyrene resin foam sheets have a beautiful surface, are lightweight yet strong, have excellent moldability, are inexpensive, are hydrophobic, hygienic, and have excellent heat and heat insulation properties. It is shaped into a shape, cup shape, and bowl shape, and is widely used as various food packaging materials and simple containers. Specifically, it is used as a container for instant noodles in cups represented by instant noodles. In molding of such a molded container, a polystyrene resin laminated foam sheet in which a resin non-foamed film made of a thermoplastic resin is laminated and integrated on at least one surface of the polystyrene resin foam sheet is usually used.

In recent years, the above-described molded containers are required to have heat resistance that does not deform even when heated in a microwave oven. Then, the following are proposed as a polystyrene-type resin foam sheet used for a shaping | molding container.
A styrene-methacrylic acid copolymer containing 94 to 96% by mass of styrene units and 4 to 6% by mass of methacrylic acid units, having a weight average molecular weight of 210,000 to 260,000 and a Vicat softening point of 108 to 114 ° C. The union is made of a raw material resin, extruded at a shear rate of 1.0 × 10 ^{3 to} 1.0 × 10 ⁴ seconds ⁻¹ at the die part of the die, and has a thickness of 1.0 to 3.5 mm and an apparent specific gravity of 0 A styrenic resin heat-resistant foamed sheet having a thickness of .050 to 0.105 g / cm ³ (Patent Document 1).

JP 2013-221128 A

  However, the styrene resin heat-resistant foamed sheet of Patent Document 1 has heat resistance to such an extent that the molded container is not deformed by heating in a microwave oven, but may be cracked or cracked (inferior in brittleness). Becomes complicated.

  The present invention provides a polystyrene-based resin foam sheet, a polystyrene-based resin laminated foam sheet, and a molded container that have sufficient heat resistance that can suppress deformation of the container even when heated in a microwave oven, and that are easily brittle and easy to handle. The purpose is to provide.

The polystyrene-based resin foam sheet of the present invention contains a styrene-methacrylic acid copolymer having 94 to 98% by mass of styrene units and 2 to 6% by mass of methacrylic acid units and having a weight average molecular weight of 190,000 to 260,000. In the polystyrene resin foam sheet, the thickness is 0.5 to 3.0 mm, the apparent density is 0.05 to 0.15 g / cm ³ , the average cell diameter is 150 to 500 μm, and the total volatile component amount is 200 to 800 μg / g. is there.

In the polystyrene resin foam sheet of the present invention, the average density of the surface layer having a depth of 0.2 mm from the surfaces of both sheets is preferably 0.10 g / cm ³ or more.

  In the polystyrene-based resin laminated foam sheet of the present invention, a resin non-foamed film made of a thermoplastic resin is laminated on at least one surface of the polystyrene-based resin foam sheet of the present invention.

The molded container of the present invention comprises a foamed layer containing a styrene-methacrylic acid copolymer having 94 to 98% by mass of styrene units and 2 to 6% by mass of methacrylic acid units and having a weight average molecular weight of 190,000 to 260,000. In the molded container, the foam layer has a thickness of 0.5 to 3.0 mm, an apparent density of 0.05 to 0.15 g / cm ³ , an average cell diameter of 150 to 500 μm, and a total amount of volatile components of 200. ˜800 μg / g.

In the molded container of the present invention, the average density of the surface layer having a depth of 0.2 mm from the inner surface and the outer surface of the foamed layer is preferably 0.10 g / cm ³ or more.
Moreover, it is preferable that the resin non-foamed film which consists of a thermoplastic resin is laminated | stacked on any one or both of the inner surface of the said foaming layer, and an outer surface.

The polystyrene-based resin foam sheet of the present invention has sufficient heat resistance that can suppress deformation of the container even when heated in a microwave oven, and is excellent in brittleness and easy to handle.
The polystyrene-based resin laminated foam sheet of the present invention has sufficient heat resistance that can suppress deformation of the container even when heated in a microwave oven, and is excellent in brittleness and easy to handle.
The molded container of the present invention has sufficient heat resistance that prevents deformation even when heated in a microwave oven, and is excellent in brittleness and easy to handle.

It is sectional drawing which showed an example of the polystyrene-type resin laminated foam sheet of this invention.

<Polystyrene resin foam sheet>
The polystyrene-based resin foam sheet of the present invention (hereinafter referred to as a foam sheet) has 94 to 98% by mass of styrene units and 2 to 6% by mass of methacrylic acid units, and has a weight average molecular weight of 190,000 to 260,000. Contains a methacrylic acid copolymer (hereinafter referred to as copolymer (A)).

[Copolymer (A)]
The copolymer (A) is a copolymer of styrene and methacrylic acid.
The ratio of the styrene unit to the total unit (100% by mass) of the copolymer (A) is 94 to 98% by mass, preferably 94 to 97% by mass, and more preferably 94 to 96% by mass. If the ratio of the styrene unit is at least the lower limit, the brittleness is further improved and the handling becomes easier. If the ratio of the styrene unit is less than or equal to the above upper limit value, sufficient heat resistance that suppresses deformation is easily obtained even when heated in a microwave oven.

  The ratio of the methacrylic acid unit to the total unit (100% by mass) of the copolymer (A) is 2 to 6% by mass, preferably 3 to 6% by mass, and more preferably 4 to 6% by mass. If the ratio of the methacrylic acid unit is equal to or higher than the lower limit, sufficient heat resistance that prevents deformation even when heated in a microwave oven is easily obtained. If the proportion of methacrylic acid units is less than or equal to the above upper limit value, brittleness is further improved and handling becomes easier.

  The weight average molecular weight of the copolymer (A) is 190,000 to 260,000, preferably 200,000 to 260,000, and more preferably 200,000 to 250,000. If the weight average molecular weight of a copolymer (A) is more than the said lower limit, brittleness will be improved and handling will become easier. If the weight average molecular weight of a copolymer (A) is below the said upper limit, manufacture of a foam sheet will become easy.

As the copolymer (A), a commercially available product, a copolymer (A) (virgin polystyrene) that is not a recycle raw material such as a copolymer (A) produced by a method such as a suspension polymerization method can be used and used. Recycled raw materials obtained by regenerating the foamed sheets, molded containers and the like can be used.
A copolymer (A) may be used individually by 1 type, and may use 2 or more types.

[Other ingredients]
The foamed sheet of the present invention may contain a polystyrene resin other than the copolymer (A) as necessary.
As the polystyrene resin other than the copolymer (A), polystyrene is preferable from the viewpoint of moldability and cost. When the foamed sheet of the present invention contains polystyrene, the total proportion of the copolymer (A) and the styrene unit of polystyrene is from 94 to 98 with respect to 100% by mass of the total of all units of the copolymer (A) and polystyrene. More preferably, the proportion of methacrylic acid units in the copolymer (A) is 2 to 6 mass%.

  Examples of the polystyrene resin other than the copolymer (A) include homopolymers or copolymers of styrene monomers (excluding styrene). The polystyrene resin includes a styrene monomer obtained by copolymerizing a styrene monomer (excluding styrene) and a vinyl monomer copolymerizable with the styrene monomer. A copolymer mainly composed of a monomer (excluding styrene) may be used.

Examples of the styrene monomer other than styrene include α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, bromostyrene, and the like. The styrenic monomer may be used alone or in combination of two or more.
Examples of vinyl monomers copolymerizable with styrene monomers include alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and cetyl (meth) acrylate. Bifunctional monomers such as (meth) acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl fumarate, ethyl fumarate, divinyl benzene, alkylene glycol dimethacrylate, and the like. These vinyl monomers may be used alone or in combination of two or more.

  When the foamed sheet of the present invention contains a polystyrene resin other than the copolymer (A), the proportion of the copolymer (A) is determined based on the copolymer (A) and the polystyrene type other than the copolymer (A). 5-50 mass% is preferable with respect to the total 100 mass% of resin, and 10-50 mass% is more preferable. When the proportion of the copolymer (A) is at least the lower limit, sufficient heat resistance that can suppress deformation of the container even when heated in a microwave oven and the effect of improving brittleness are easily obtained. If the ratio of the copolymer (A) is not more than the upper limit, the thermoformability will be good.

  The foamed sheet of the present invention includes a nucleating agent, a crosslinking agent, a filler, a flame retardant, a flame retardant aid, a lubricant (hydrocarbon, fatty acid, fatty acid amide, ester, alcohol within the range that does not impair the physical properties. System, metal soap, silicone oil, wax such as low molecular weight polyethylene, etc.), spreading agents (liquid paraffin, polyethylene glycol, polybutene, etc.), colorants and other additives may be added. Especially, it is preferable that the foam sheet of this invention contains a nucleating agent.

Examples of the nucleating agent include talc, sodium hydrogen carbonate, ammonium hydrogen carbonate, calcium carbonate, clay, citric acid and the like. Of these, talc is preferable as the nucleating agent. A nucleating agent may be used individually by 1 type, and may use 2 or more types together.
The addition amount of the nucleating agent is preferably 0.01 to 5 parts by mass with respect to 100 parts by mass of the copolymer (A).

[Thickness]
The thickness of the foam sheet of the present invention is 0.5 to 3.0 mm, preferably 1.0 to 2.5 mm, and more preferably 1.0 to 2.3 mm. When the thickness of the foamed sheet is within the above range, the foamed sheet is excellent in brittleness and easy to handle. Moreover, if the thickness of a foam sheet is more than the said lower limit, it will be excellent in intensity | strength and heat insulation. If the thickness of the foamed sheet is not more than the above upper limit value, the thermoformability will be good.

[Apparent density]
Apparent density of the foamed sheet of the present invention has an apparent density of 0.05~0.15g / cm ^3, preferably 0.06~0.14g / cm ^3, is 0.07~0.13g / cm ³ More preferred. When the apparent density of the foam sheet is within the above range, the foam sheet is excellent in brittleness and easy to handle. Moreover, if the apparent density of a foam sheet is more than the said lower limit, a foam sheet will become hard and it will be excellent in intensity | strength. If the apparent density of the foamed sheet is not more than the above upper limit value, the heat insulating property is excellent.

[Average bubble diameter]
The average cell diameter of the foamed sheet of the present invention is 150 to 500 μm, preferably 150 to 400 μm, and more preferably 200 to 400 μm. When the average cell ratio of the foam sheet is within the above range, the foam sheet is excellent in brittleness and easy to handle. Moreover, if the average cell diameter of a foam sheet is more than the said lower limit, a moldability is favorable and a favorable molded product is obtained. If the average cell diameter of a foam sheet is below the said upper limit, a foam sheet will become soft and it will become difficult to produce a crack.

[Total amount of volatile components]
The total volatile component amount of the foamed sheet of the present invention is 200 to 800 μg / g, preferably 220 to 800 μg / g, and more preferably 250 to 800 μg / g. When the total amount of volatile components of the foamed sheet is within the above range, the foamed sheet is excellent in brittleness and easy to handle. Moreover, if the total volatile component amount of a foam sheet is more than the said lower limit, a foam sheet will become soft and it will become difficult to produce a crack. If the total amount of volatile components of the foamed sheet is less than or equal to the above upper limit value, the molded product is hardly deformed and excellent in oil resistance.

[Average density of surface layer]
In the foamed sheet of the present invention, the average density of the surface layer having a depth of 0.2 mm from both sheet surfaces is preferably 0.10 g / cm ³ or more. Thereby, the rigidity and toughness of the sheet surface are improved, and the foamed sheet can be easily handled with further improved brittleness.
The average density of the surface layer is more preferably 0.10~0.60g / cm ^3, more preferably 0.10~0.50g / cm ^3.
The above-mentioned “average density of the surface layer having a depth of 0.2 mm from both sheet surfaces” means the density of the surface layer having a depth of 0.2 mm from one sheet surface of the foam sheet and the depth from the other sheet surface. It means the average with the density of the surface layer of 0.2 mm.

[Production method]
The method for producing the foamed sheet of the present invention is not particularly limited. For example, the copolymer (A) and a polystyrene-based resin other than the copolymer (A), a nucleating agent, etc. used as necessary are extruded. Examples include a method of supplying to a machine, heating and melting, adding a foaming agent, kneading, extrusion foaming from a mold attached to the tip of the extruder, and winding up and collecting the obtained foamed sheet.

As the foaming agent, a physical foaming agent is preferable.
As the physical foaming agent, hydrocarbons having 6 or less carbon atoms (for example, aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, neopentane, and cyclopentane) are preferable, and normal butane, isobutane, normal pentane, and isopentane. Is more preferable. A foaming agent may be used individually by 1 type, and may use 2 or more types together.
1.0-8.0 mass parts is preferable with respect to 100 mass parts of all the resin components to be used, and 1.0-7.0 mass parts is more preferable.

As a metal mold | die attached to the front-end | tip of an extruder, the cyclic | annular metal mold | die (circular die) which has cyclic | annular opening, T-die, etc. are mentioned, for example.
As a specific mode in the case of using an annular mold, for example, the cylindrical foam extruded from the annular mold is placed along the cooling mandrel, and the cylinder is formed by cutters provided on both sides of the tip of the cooling mandrel. A mode in which a slit is cut in the axial direction in the shape of the foamed material to form two foam sheets.

  The expansion ratio is preferably 7 to 18 times, and more preferably 8 to 17 times. If the expansion ratio is equal to or greater than the lower limit, the molded container can be easily reduced in weight. If the expansion ratio is equal to or less than the upper limit, a molded container having high strength can be easily obtained.

The method for controlling the thickness, the apparent density, the average cell diameter and the total volatile component amount of the foam sheet is not particularly limited.
For example, the apparent density of a foam sheet becomes small by increasing the usage-amount of a nucleating agent. Moreover, the apparent density of a foam sheet becomes large by reducing the usage-amount of a foaming agent. By increasing the melt kneading temperature of the resin component containing the copolymer (A) in the extruder, the amount of the volatile component of the foamed sheet is increased. By changing the amount and type of the foaming agent, the thickness of the foamed sheet can be controlled. Further, the average bubble diameter is increased by reducing the amount of the nucleating agent used. Further, for example, by applying cooling air to a cylindrical foam extruded from an annular mold, the average density of the surface layer is increased.

[Function and effect]
The foamed sheet of the present invention described above controls the ratio of the methacrylic acid unit and the weight average molecular weight of the copolymer (A), the sheet thickness, the apparent density, the average cell diameter, and the total volatile component amount to a specific range. Therefore, it has sufficient heat resistance that can suppress deformation of the container even when heated in a microwave oven, and is excellent in brittleness and easy to handle.

<Polystyrene resin laminated foam sheet>
Hereinafter, an example of the polystyrene-based resin laminated foam sheet of the present invention will be described and described.
As shown in FIG. 1, a polystyrene-based resin laminated foam sheet 1 (hereinafter referred to as “laminated foam sheet 1”) of the present embodiment includes a polystyrene-based resin foam sheet 10 (hereinafter referred to as a foamed sheet 10) and a foamed sheet 10. The resin non-foamed films 12 and 12 are laminated on both surfaces.
The foam sheet 10 is the above-described foam sheet of the present invention.

The resin non-foamed film 12 is a non-foamed film made of a thermoplastic resin. By laminating the resin non-foamed film 12, the surface of the laminated foamed sheet 1 becomes more beautiful, the rigidity becomes higher, and the heat resistance and oil resistance are further improved.
Examples of the thermoplastic resin that forms the resin non-foamed film 12 include polystyrene resins, impact-resistant polystyrene resins, polyethylene resins, polypropylene resins, polyethylene terephthalate resins, polyphenylene ether resins, and polyvinylidene chloride resins. And ethylene-vinyl alcohol copolymer resin. Moreover, these may be used individually by 1 type, and 2 or more types may be laminated | stacked by dry lamination etc.
The resin non-foamed film 12 may be colored in various colors by adding colorants (pigments, dyes, etc.), and may display various patterns and designs by printing on the surface.

  10-150 micrometers is preferable and, as for the thickness of the resin non-foaming film 12, 10-100 micrometers is more preferable. If the thickness of the resin non-foamed film 12 is equal to or more than the lower limit value, the film is easily stretched at the time of heat molding, and defects are hardly generated. If the thickness of the resin non-foamed film 12 is equal to or less than the above upper limit, the cost does not increase, and the film can be laminated at a low temperature and the glossiness is not lost.

  As a method of laminating the resin non-foamed film 12 on one side or both sides of the foamed sheet 10, a method of co-extrusion of the foamed sheet 10 and the resin non-foamed film 12, a heating roll, a binder, an adhesive, etc. And a method of laminating the resin non-foamed film 12 on the foamed sheet 10.

[Function and effect]
In the laminated foam sheet of the present invention described above, the ratio of the methacrylic acid unit and the weight average molecular weight of the copolymer (A), the sheet thickness, the apparent density, the average cell diameter, and the total volatile component amount are controlled within a specific range. By using the foamed sheet, it has sufficient heat resistance that can suppress deformation of the container even when heated in a microwave oven, and is excellent in brittleness and easy to handle.
The laminated foam sheet of the present invention is not limited to the laminated foam sheet 1 described above. For example, the laminated foam sheet of the present invention may be a sheet in which a resin non-foamed film is laminated only on one surface of the foam sheet.

<Molded container>
The molded container of the present invention has a foam layer containing the copolymer (A), and a resin non-resin made of a thermoplastic resin on one or both of the inner surface and the outer surface of the foam layer as necessary. A molded container in which foamed films are laminated. The foamed layer has a thickness of 0.5 to 3.0 mm, preferably 1.0 to 2.5 mm, an apparent density of 0.05 to 0.15 g / cm ³ , and an average cell diameter of 150. ˜500 μm, and the total amount of volatile components is 200 to 800 μg / g. That is, the molded container of the present invention is a molded container obtained by molding the above-described foamed sheet or laminated foamed sheet of the present invention. The foam layer of the molded container of the present invention is formed by the foam sheet of the present invention.
The average density of the surface layer having a depth of 0.2 mm from the inner surface and the outer surface of the foam layer is preferably 0.10 g / cm ³ or more.

The shape and dimensions of the molded container of the present invention are not particularly limited, and examples thereof include cups and bowls for instant noodles with cups.
The molded container of the present invention can be obtained by thermoforming the foamed sheet or laminated foamed sheet of the present invention. In that case, when using a laminated foam sheet, it is preferable to thermoform so that at least the inside of the container becomes a resin non-foamed film from the viewpoint of further improving the mechanical strength, heat resistance, and oil resistance of the container.

  Examples of thermoforming methods include vacuum forming and pressure forming, or free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, air Conventionally known general molding methods such as slip molding, plug assist molding, plug assist reverse load molding and the like can be mentioned.

[Function and effect]
In the molded container of the present invention described above, the ratio of the methacrylic acid unit and the weight average molecular weight of the copolymer (A), the thickness of the foamed layer, the apparent density, the average cell diameter, and the total amount of volatile components are controlled within specific ranges. Therefore, it has sufficient heat resistance that prevents deformation even when heated in a microwave oven, is excellent in brittleness, and is easy to handle.

EXAMPLES Hereinafter, although an Example demonstrates this invention in detail, this invention is not limited by the following description.
[material]
Raw material resin A-1: T040 which is a styrene-methacrylic acid copolymer (manufactured by Toyo Styrene Co., Ltd., styrene unit 96.0% by mass, methacrylic acid unit: 4.0% by mass, weight average molecular weight: 250,000).
Raw material resin A-2: The end material after punching the food packaging lid, etc., when a non-foamed sheet made from T040, which is a styrene-methacrylic acid copolymer, is used as the raw material resin, is formed into a food packaging lid, etc. Recycled raw material pulverized, melt-kneaded and re-pelletized (styrene unit 95.5% by mass, methacrylic acid unit: 4.5% by mass, weight average molecular weight: 210,000).
Raw material resin A-3: T060 which is a styrene-methacrylic acid copolymer (manufactured by Toyo Styrene Co., Ltd., styrene unit 94.0% by mass, methacrylic acid unit: 6.0% by mass, weight average molecular weight: 200,000).
Raw material resin B-1: T080 which is a styrene-methacrylic acid copolymer (manufactured by Toyo Styrene Co., Ltd., styrene unit 92.0% by mass, methacrylic acid amount: 8.0% by mass, weight average molecular weight: 180,000).

[Example 1]
A nucleating agent (manufactured by Toyo Styrene Co., Ltd., product name: “DSM1401A”) is added to 100 parts by mass of a resin composition comprising 50 parts by mass of the raw material resin A-1 and 50 parts by mass of the raw material resin A-2. 0 parts by mass was added, charged into a first extruder (diameter φ115 mm), heated at 250 ° C. and melt-kneaded.
Subsequently, from an injection port provided in the middle of the first extruder, 3.5 parts by mass of butane gas (isobutane / normal butane (mass ratio) = 70/30) as a foaming agent with respect to 100 parts by mass of the resin composition Press-fitted and mixed with the resin composition.
Then, the resin composition kneaded with the nucleating agent and the foaming agent is supplied from the first extruder to the second extruder (diameter 180 mm), cooled to 165 ° C., extruded and foamed using a circular die, and the discharge amount A cylindrical body was obtained at 350 kg / h (shear rate: 6.63 × 10 ³ sec ⁻¹ ). The obtained cylindrical body was cut at two locations along the extrusion direction to obtain two polystyrene resin foam sheets. The obtained polystyrene-based resin foam sheet has a total amount of volatile components of 405 μg / g, a thickness of 1.80 mm, an apparent density of 0.08 g / cm ³ , an average density of the surface layers on both sides of 0.14 g / cm ³ , and an average The bubble diameter was 352 μm.

[Example 2]
A polystyrene resin foam sheet was obtained in the same manner as in Example 1 except that 100 parts by mass of the resin composition consisting only of the raw material resin A-1 was used.

[Example 3]
A polystyrene-based resin foam sheet was obtained in the same manner as in Example 1, except that the resin composition consisting of only the raw material resin A-2 was 100 parts by mass.

[Example 4]
A polystyrene-based resin foam sheet was obtained in the same manner as in Example 1 except that the resin composition consisting of only the raw material resin A-3 was 100 parts by mass.

[Example 5]
100 parts by mass of the resin composition consisting of 50 parts by mass of the raw material resin A-1 and 50 parts by mass of HRM26 (manufactured by Toyo Styrene Co., Ltd.) as the polystyrene-based resin is used, and the total of styrene units and methacrylic acid units in the entire raw material resin A polystyrene-based resin foam sheet was obtained in the same manner as in Example 1 except that the ratio of the methacrylic acid unit to 2% by mass was used.

[Example 6]
A heat-resistant polystyrene-based resin foam sheet was obtained in the same manner as in Example 1 except that the nucleating agent was 2.0 parts by mass and the take-up speed was adjusted so that the apparent density of the sheet was 0.06 g / cm ³ . .

[Example 7]
After changing the circular die to another, the same as in Example 1 except that the foaming agent was changed to 2.3 parts by mass and the take-up speed was adjusted so that the apparent density of the sheet was 0.13 g / cm ^3. Thus, a polystyrene resin foam sheet was obtained.

[Example 8]
A polystyrene-based resin foam sheet is obtained in the same manner as in Example 1 except that the temperature of the first extruder is 280 ° C. and the decomposition of the styrene-methacrylic acid copolymer is promoted to adjust the volatile component to increase. It was.

[Example 9]
After changing the circular die to a different one and changing the clearance of the mouthpiece, the extrusion conditions were adjusted so that the discharge rate was 410 kg / h (shear rate: 1.51 × 10 ⁴ sec ⁻¹ ). Except for the above, a polystyrene-based resin foam sheet was obtained in the same manner as in Example 1.

[Comparative Example 1]
A polystyrene-based resin foam sheet is obtained in the same manner as in Example 1 except that the temperature of the first extruder is 310 ° C. and that the decomposition of the styrene-methacrylic acid copolymer is promoted to increase the volatile components. It was.

[Comparative Example 2]
100 parts by mass of a resin composition comprising 50 parts by mass of the raw material resin A-1 and 50 parts by mass of HRM52 (manufactured by Toyo Styrene Co., Ltd.) as a polystyrene resin, and 98% by mass of styrene units of the styrene-methacrylic acid copolymer A polystyrene-based resin foamed sheet was obtained in the same manner as in Example 1 except that the methacrylic acid unit was changed to 2% by mass.

[Comparative Example 3]
A polystyrene resin foam sheet was obtained in the same manner as in Example 1 except that 100 parts by mass of the resin composition consisting only of the raw material resin B-1 was used. However, when the cylindrical body obtained at the time of extrusion foaming was cut along the extrusion direction, the foamed sheet was torn and it was difficult to obtain a good foamed sheet.

[Comparative Example 4]
A polystyrene-based resin foam sheet was obtained in the same manner as in Example 1, except that the nucleating agent was adjusted to 0.3 parts by mass and the foaming agent was adjusted to 5.0 parts by mass so that the average cell diameter was increased.

[Measuring method of methacrylic acid unit content]
The sample resin copolymer was weighed and dissolved in 100 mL of a mixed reagent in which toluene and ethanol were mixed at a ratio of 2: 1 (volume ratio), and then neutralized titration with a 0.1 mol / L ethanol potassium hydroxide solution. The methacrylic acid unit content was calculated.

[Method for measuring weight average molecular weight]
4 mg of the sample resin was dissolved in 4 mL of tetrahydrofuran, followed by filtration with a non-aqueous 0.45 μm chromatodisc (13N). The obtained filtrate was used as a sample solution, and the weight average molecular weight was measured under the following measurement conditions.
Equipment: Tosoh HLC-8320GPC (gel permeation chromatography),
Column: SuperMultipore HZ-H,
Column temperature: 40 ° C
Carrier: tetrahydrofuran (THF) 0.2 mL / min,
Detector: RI,
Calibration curve: Standard polystyrene (PS) manufactured by Tosoh Corporation is used.

[Method for measuring thickness]
Excluding 20 mm at both ends in the width direction of the polystyrene resin foam sheet, 21 points were measured at intervals of 50 mm in the width direction. The thickness of this measurement point was measured to a minimum unit of 0.01 mm using a dial thickness gauge SM-112 (manufactured by Teclock Corporation). The average value of these measured values was defined as the thickness T (mm) of the polystyrene resin foam sheet.

[Measuring method of sheet basis weight]
Except 20 mm in both ends in the width direction of the polystyrene-based resin foam sheet, 10 pieces of 10 cm × 10 cm were cut out at equal intervals in the width direction, and the mass (g) of each piece was measured to 0.001 g unit. A value obtained by converting an average value of mass (g) of each section into mass per 1 m ² was defined as a basis weight M (g / m ² ).

[Apparent density]
From the thickness T and the basis weight M, the apparent density ρ (g / cm ³ ) was determined by the following formula.
ρ = M / (T × 10 ³ )

[Measurement method of average bubble diameter]
The average cell diameter of the polystyrene resin foam sheet was calculated based on the average chord length measured according to the test method of ASTM D2842-69. Specifically, the polystyrene-based resin foam sheet was cut in a direction perpendicular to the surface (thickness direction). Using a scanning electron microscope (manufactured by Hitachi, Ltd., S-3000N), a portion corresponding to approximately half the thickness in the thickness direction of the cut surface and approximately half the thickness in the center is 17 to The picture was taken at 20x (200x in some cases).
Next, in the photograph taken, the average chord length (t) of each bubble is calculated from the following formula (1) from the number of bubbles on the straight line that is 60 mm in length and oriented in the thickness direction of the polystyrene resin foam sheet. ). And the average bubble diameter D was computed by the following Formula (2). In addition, when the layer of the polystyrene resin foam sheet is thin and a straight line having a length of 60 mm cannot be drawn on the photograph, a straight line as long as possible is drawn on the photograph, and the length of this straight line is converted to 60 mm and averaged. The bubble diameter D was calculated.
Average chord length (t) = 60 / (number of bubbles × photo magnification) (1)
Average bubble diameter D = t / 0.616 (2)

[Method for measuring the amount of volatile components]
From the obtained polystyrene resin foam sheet, 0.1 g was weighed into a test piece, and the sample piece was stored in a 20 mL bottomed cylindrical container. Then, 1 mL of dimethylformamide containing 50 ppm of diethylbenzene was supplied into the container to dissolve the test piece, and the opening of the container was sealed with a lid member.
Next, the container was heated at 90 ± 1 ° C. for 1 hour, and 2 mL of gas in the container was collected so that the gas in the container did not leak to the outside. Then, the content of volatile components (styrene monomer, toluene, ethylbenzene, cyclohexane, xylene) in the collected gas was measured using a gas chromatograph. The measurement was performed by the internal standard method, and other conditions were as shown below.
(Measurement condition)
Apparatus: GC (Shimadzu Corporation GC-2025 + HTA HS Autosampler HT200H).
Column: ZB-WAX (0.25 μm × 0.25 mmφ × 30 m).
Column temperature: After maintaining at 60 ° C. for 3 minutes, the temperature was increased to 100 ° C. at a temperature increase rate of 20 ° C./min, and further increased to 220 ° C. at a temperature increase rate of 40 ° C./min and maintained for 0.5 minutes.
Inlet temperature: 150 ° C.
Detector (FID) temperature: 250 ° C.
Carrier gas: helium (moving flow rate: 1.6 mL / min pressure: 122 kPa).
Split ratio: 70: 1.

[Measurement method of average density of surface layer]
The polystyrene resin foam sheet is sliced at a depth of 0.2 mm from both sheet surfaces, and the average density of the two slices is determined according to JIS K 7222: 2005 “Method of Obtaining Apparent Density”. Measured based on

[Evaluation method of heat resistance]
Dry laminate of unstretched polypropylene film (CPP film) (Osaka Resin Kako Co., Ltd., trade name “ALT”, thickness 20 μm) and unstretched polystyrene film (CPS film) (trade name “TO” 20 μm thickness, manufactured by Oishi Sangyo Co., Ltd.) Thus, a laminated film was obtained. On one surface of the polystyrene resin foam sheet, the polystyrene film in the laminate film was placed on the side of the polystyrene resin foam sheet, and the laminate film was superposed and pressure-bonded with heating to be laminated and integrated to obtain a polystyrene resin laminate foam sheet.
Using a polystyrene-based resin laminated foam sheet, 100 mL of hot water of about 50 ° C. is put into a heat-resistant container obtained by thermoforming into a bowl-shaped container having a diameter of 179 mm and a depth of 55 mm so that the laminated film becomes the inner surface of the container, The glass plate was put on and covered with a microwave oven (500 W) for 3 minutes. Thereafter, the dimensional change amount was obtained by measuring the respective diameters in the directions orthogonal to each other in the bag container, the deformation state of the bag edge portion was confirmed, and the determination was made according to the following criteria.
A: The dimensional change is less than 10 mm.
X: The amount of dimensional change is 10 mm or more, and the deformation is so large that it cannot be used.

[Evaluation method of drop test]
Twenty heat-resistant containers obtained by heat-molding into a bowl-shaped container having a diameter of 179 mm and a depth of 55 mm were prepared using a polystyrene-based resin laminated foam sheet obtained in the same manner as the heat resistance evaluation method. 300 g of water was put into these heat-resistant containers and dropped from a height of 70 cm, and the shape change (cracking, tearing, dent, etc.) at the bottom of the container was confirmed, and the brittleness was determined according to the following criteria.
○: No abnormality in shape in all heat-resistant containers.
X: One or more containers have shape changes such as cracks, tears, and dents.

Table 1 shows the evaluation results in Examples and Comparative Examples, and the shear rate during extrusion foaming in sheet production.
In Table 1, “St unit” means a styrene unit, and “MA unit” means a methacrylic acid unit.

  As shown in Table 1, in Examples 1 to 9 using the foamed sheet of the present invention, the obtained molded container was prevented from being deformed even by heating with a microwave oven, and also had a shape such as crack, tear, dent, etc. even in a drop test. No change and excellent brittleness. On the other hand, in Comparative Examples 1 to 4 that did not satisfy the conditions of the present invention, deformation due to heating in a microwave oven and a decrease in brittleness were observed.

1 Polystyrene resin laminated foam sheet 10 Polystyrene resin foam sheet 12 Resin non-foamed film

Claims (6)

In a polystyrene resin foam sheet containing a styrene-methacrylic acid copolymer having 94 to 98% by mass of styrene units and 2 to 6% by mass of methacrylic acid units and having a weight average molecular weight of 190,000 to 260,000,
A polystyrene-based resin foam sheet having a thickness of 0.5 to 3.0 mm, an apparent density of 0.05 to 0.15 g / cm ³ , an average cell diameter of 150 to 500 μm, and a total amount of volatile components of 200 to 800 μg / g. . 2. The polystyrene-based resin foamed sheet according to claim 1, wherein an average density of a surface layer having a depth of 0.2 mm from both sheet surfaces is 0.10 g / cm ³ or more.   A polystyrene-based resin laminated foamed sheet in which a resin non-foamed film made of a thermoplastic resin is laminated on at least one surface of the polystyrene-based resin foamed sheet according to claim 1 or 2. In a molded container having a foamed layer containing a styrene-methacrylic acid copolymer having 94 to 98% by mass of styrene units and 2 to 6% by mass of methacrylic acid units and having a weight average molecular weight of 190,000 to 260,000,
The foam layer has a thickness of 0.5 to 3.0 mm, an apparent density of 0.05 to 0.15 g / cm ³ , an average cell diameter of 150 to 500 μm, and a total amount of volatile components of 200 to 800 μg / g. Molded container. The molded container according to claim 4, wherein an average density of a surface layer having a depth of 0.2 mm from the inner surface and the outer surface of the foam layer is 0.10 g / cm ³ or more.   The molded container according to claim 4 or 5, wherein a resin non-foamed film made of a thermoplastic resin is laminated on one or both of the inner surface and the outer surface of the foam layer.

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