JP6660218B2 - Polystyrene resin foam sheet, method for producing the same, and molded article and container - Google Patents

Description

  The present invention relates to a polystyrene resin foam sheet, a method for producing the same, and a molded article and a container.

For example, fruits, such as apples, pears, and peaches, are housed in a container for packaging of fruits and vegetables, and are transported or stored in order to minimize the surface damage. In the container for packaging of fruit and vegetables, a plurality of concave portions which are open on one surface of the sheet and bulge in a semi-spherical shape are formed on the other surface of the sheet, and each of the fruits and vegetables is accommodated in the concave portion.
In such a container for packaging fruit and vegetables, a molded article in which a polystyrene resin foam sheet is molded into a predetermined shape is used. The polystyrene-based resin foam sheet is excellent in moldability, heat insulation properties and light weight, has appropriate rigidity, and is suitably used as a material for a container for packing fruit and vegetables.

Conventionally, studies have been made on improving the flexibility of a polystyrene-based resin foam sheet so as not to damage the surface of the fruit vegetables.
For example, Patent Literature 1 proposes a tray for fruits and vegetables (a container for packing vegetables and fruits) obtained by molding a laminated foamed sheet in which a foamed sheet and a thermoplastic resin film are laminated. In the foamed sheet described in Patent Document 1, a mixed resin of a polystyrene resin, a rubber-modified polystyrene resin, and a styrene elastomer resin is used.
Patent Literature 2 proposes a fruit and vegetable packaging container formed by molding a polystyrene resin foam sheet containing a polystyrene resin, a rubber-modified polystyrene resin, and a specific hydrogenated polystyrene elastomer.

JP-A-2004-299075 JP 2012-097190 A

  However, in the fruit and vegetable packaging container described in Patent Document 1, although the flexibility of the foamed sheet is enhanced by blending the elastomer with the foamed sheet, the heat resistance of the foamed sheet may be reduced. In some cases, molding failure due to insufficient melt tension occurred during molding (that is, moldability was sometimes reduced).

  In the fruit and vegetable packaging container described in Patent Document 2, the flexibility was insufficient. For this reason, in the adjacent concave portions of the fruit and vegetable packaging container, when a slightly larger fruit and vegetables are stored in one of the concave portions, the volume of the other concave portion decreases as the volume of the concave portion in which the fruit and vegetables are stored increases. In some cases, the opening becomes narrower, and it becomes difficult to store fruit and vegetables in the other recess. In this case, if the fruit is forcibly stored in the other concave portion, the fruit will be damaged.

  Therefore, the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a foamed polystyrene resin sheet having improved flexibility, heat resistance, and good moldability.

The present invention has the following aspects.
[1] It contains a resin component containing a polystyrene resin, has a complex viscosity of 3500 to 7000 Pa · s determined by viscoelasticity measurement at a temperature of 180 ° C. and a frequency of 1 Hz, and contains a styrene monomer component. A foamed polystyrene resin sheet comprising a foamed resin layer having a particle size of 120 to 320 ppm.
[2] The foamed resin layer contains a resin component having a styrene monomer unit and an ethylene monomer unit,
The foamed resin layer surface of the infrared absorbing styrene obtained from the spectrum monomer units absorbance derived 698cm ^-1 of (D698) ethylene monomer units absorbance derived 2850cm ^-1 (D2850) and the absorbance ratio of (D698 / D2850) is 7.0-15.0, The polystyrene resin foam sheet given in [1].
[3] The foamed resin layer comprises 45 to 85% by mass of a polystyrene-based resin, 5 to 20% by mass of a hydrogenated polystyrene-based elastomer, and 5 to 5% by mass of a polyethylene-based resin based on the total amount of the resin components (100% by mass). The polystyrene resin foam sheet according to [1] or [2], comprising 15% by mass and 0 to 30% by mass of a rubber-modified polystyrene resin.
[4] The method for producing a polystyrene resin foam sheet according to any one of [1] to [3],
A method for producing a foamed polystyrene resin sheet, comprising melt-kneading a raw material composition containing a resin component containing a polystyrene resin and a foaming agent, extruding and foaming.
[5] A molded article obtained by molding the polystyrene resin foam sheet according to any one of [1] to [3].
[6] The molded article according to [5], which is a container for packing fruit and vegetables.
[7] A foamed resin layer having a complex viscosity of 3500 to 7000 Pa · s determined by viscoelasticity measurement at a temperature of 180 ° C. and a frequency of 1 Hz, and a styrene monomer component content of 120 to 320 ppm. ,container.
[8] The container according to [7], which is a container for packing fruit and vegetables.

The foamed polystyrene resin sheet of the present invention has enhanced flexibility, and has excellent heat resistance and moldability.
According to the method for producing a foamed polystyrene resin sheet of the present invention, a foamed polystyrene resin sheet having enhanced flexibility, good heat resistance and good moldability can be produced.
The molded article of the present invention has enhanced flexibility and good heat resistance.
INDUSTRIAL APPLICABILITY The container of the present invention has enhanced flexibility and good heat resistance. For example, fruits and vegetables can be easily stored one by one in a concave portion, and fruits and vegetables are hardly damaged.

It is a perspective view showing one embodiment of a container of the present invention. It is XX sectional drawing of FIG.

(Polystyrene resin foam sheet)
The polystyrene resin foam sheet of the present invention (hereinafter, also simply referred to as “foam sheet”) has a foam resin layer containing a polystyrene resin.
Such a foamed sheet may have a single-layer structure composed of only a foamed resin layer, or may have a laminated structure in which a resin film or the like is provided on at least one surface of the foamed resin layer. In the foamed sheet of the present invention, sufficient flexibility, heat resistance, and moldability are ensured because the foamed resin layer has a predetermined complex viscosity even in a single-layer structure composed of only the foamed resin layer.

  In the present invention, the complex viscosity is determined by measuring viscoelasticity at a temperature of 180 ° C. and a frequency of 1 Hz.

The complex viscosity of the foamed resin layer in the present invention is 3500 to 7000 Pa · s, preferably 4000 to 6500 Pa · s, more preferably 4300 to 6500 Pa · s. s.
When the complex viscosity of the foamed resin layer is at least the lower limit of the above range, the flexibility of the foamed sheet will be enhanced. When the complex viscosity of the foamed resin layer is equal to or less than the upper limit of the above range, heat resistance is easily maintained, and molding failure is less likely to occur.
The complex viscosity of the foamed resin layer is controlled, for example, by adjusting the composition of the resin component. The complex viscosity of the foamed resin layer is specifically determined by a method described in Examples described later.

The content of the styrene monomer component in the foamed resin layer in the present invention is 120 to 320 ppm, more preferably 150 to 250 ppm, and still more preferably 150 to 220 ppm, based on the total mass of the foamed resin layer.
When the content of the styrene monomer component is equal to or more than the lower limit of the above range, the flexibility of the foamed sheet is enhanced. When the content of the styrene-based monomer component is equal to or less than the upper limit of the above range, heat resistance is easily maintained, and molding failure is less likely to occur.
In addition, in this specification, "ppm" is a value based on mass.
The styrene monomer component is a styrene monomer remaining in the resin when a polystyrene resin or the like is synthesized. For example, styrene monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, t-butylstyrene, dimethylstyrene, bromostyrene and the like can be mentioned.
The content of the styrene monomer component can be determined by a method described in Examples described later.

The open cell ratio of the foamed resin layer in the present invention is preferably 20% or less, more preferably 15% or less. If the open cell ratio of the foamed resin layer exceeds the preferred upper limit of the above range, the secondary foamability of the foamed sheet may be deteriorated, and the moldability may be reduced.
In the present invention, the open cell rate of the foamed resin layer can be measured by a method based on an air pycnometer (air comparison specific gravity meter) method (1-1 / 2-1 atmospheric pressure method) specified in ASTM D-2856. .

Apparent density of the foamed resin layer in the present invention, from the viewpoint of light weight, preferably ^{0.03~0.21g / cm 3, 0.05~0.09g / cm} 3 is more preferable.
If the apparent density of the foamed resin layer is less than the preferred lower limit of the above range, heat resistance and moldability of the foamed sheet may be reduced. If the apparent density of the foamed resin layer exceeds the preferred upper limit of the above range, the flexibility of the foamed sheet may be reduced.
In the present invention, the apparent density of the foamed resin layer can be measured by a method according to JIS K6767.

The thickness of the foamed resin layer in the present invention is preferably 0.5 to 3.0 mm, more preferably 0.5 to 2.5 mm, and still more preferably 1.0 to 2.5 mm. If the thickness of the foamed resin layer is within the above range, the moldability will be better.
In the present invention, the thickness of the foamed resin layer refers to an arithmetic mean value of the thickness of the foamed resin layer measured at least at five places and measured at five places.

The basis weight of the foamed resin layer in the present invention is preferably ^{75~300g / m 2, 85~200g / m} 2 is more preferable.
When the basis weight of the foamed resin layer is equal to or more than the preferable lower limit of the above range, the heat resistance and the moldability of the foamed sheet are easily maintained. When the basis weight of the foamed resin layer is equal to or less than the preferable upper limit of the above range, the flexibility of the foamed sheet is maintained, and the foamed sheet is likely to have a cushioning property.

The expansion ratio of the foamed resin layer in the present invention is preferably 5 to 30 times, more preferably 8 to 26 times, and still more preferably 12 to 21 times.
When the expansion ratio of the foamed resin layer is equal to or more than the preferred lower limit of the above range, the weight of the foamed sheet can be easily reduced. When the expansion ratio of the foamed resin layer is equal to or less than the preferable upper limit of the above range, the heat resistance and moldability of the foamed sheet are further improved.

<Polystyrene resin>
The foamed resin layer constituting the foamed sheet of the present invention contains a polystyrene resin.
Examples of the polystyrene resin include, for example, polymers of styrene monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, t-butylstyrene, dimethylstyrene, and bromostyrene; Alternatively, a copolymer of such a styrene-based monomer and a monomer other than the styrene-based monomer may be used.
Incidentally, the polystyrene resin mentioned here does not contain a conjugated diene as a monomer component.

  In the polymer of the styrene-based monomer, the styrene-based monomer may be a single homopolymer or a copolymer of two or more styrene-based monomers.

Examples of the monomer other than the styrene-based monomer include vinyl monomers copolymerizable with the styrene-based monomer, for example, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, Alkyl (meth) acrylates such as butyl methacrylate, cetyl acrylate, and cetyl methacrylate; acrylic acid, methacrylic acid; acrylonitrile, methacrylonitrile; maleic anhydride; dimethyl maleate; dimethyl fumarate; diethyl fumarate; ethyl fumarate; Butadiene and the like.
In addition, the said alkyl (meth) acrylate means an alkyl acrylate or an alkyl methacrylate.

When the polystyrene-based resin is a copolymer, 50% by mass or more based on the total amount (100% by mass) of the monomers used in the copolymer is preferably a styrene-based monomer. More preferably, it is 95% by mass or more, and may be 100% by mass.
When a vinyl monomer copolymerizable with a styrene monomer is used for the copolymer, the amount of the vinyl monomer is appropriately determined according to the use of the foamed sheet. It is preferably at most 5% by mass based on the total amount of monomers (100% by mass) used in the polymer.

The melt flow rate (MFR) of the polystyrene resin is preferably from 0.5 to 6.0 g / 10 minutes, more preferably from 0.7 to 3.0 g / 10 minutes.
If the MFR of the polystyrene resin is less than the preferred lower limit of the above range, the thickness of the foamed resin layer may be uneven. When the MFR of the polystyrene-based resin exceeds the preferred upper limit of the above range, the expansion ratio of the foamed resin layer may decrease.

  In the present invention, the melt flow rate (MFR) of the polystyrene resin is described in JIS K 7210: 1999 “Test method for melt mass flow rate (MFR) and melt volume flow rate (MVR) of plastic-thermoplastics” described in Method B. According to the method, it means a value measured under the conditions of a test temperature of 200 ° C., a test load of 49.03 N, and a preheating time of 4 minutes.

The weight average molecular weight of the polystyrene resin is preferably from 200,000 to 450,000, more preferably from 300,000 to 400,000.
If the weight average molecular weight of the polystyrene resin is less than the preferred lower limit of the above range, it becomes difficult to obtain a foamed resin layer having a high expansion ratio and a low open cell ratio. If the weight average molecular weight of the polystyrene resin exceeds the preferred upper limit of the above range, the fluidity at the time of melting may decrease, and the productivity may decrease.

In the present invention, the weight-average molecular weight of the resin is determined by dissolving 30 mg of the resin in 10 ml of chloroform, filtering the solution with a 0.45 μm non-aqueous chromato disk, and measuring the resulting filtrate as a sample by chromatography, in terms of polystyrene. Mean value.
Specifically, it is measured under the following conditions.

Gas chromatograph: high performance liquid chromatography manufactured by Tosoh Corporation (pump: DP-8020, auto sample: AS8020, detector: UV-8020, RI-8020).
Columns: Two Shodex GPC K-806L (φ8.0 × 300 mm) manufactured by Showa Denko KK
Column temperature: 40 ° C.
Carrier gas: chloroform.
Carrier gas flow rate: 1.2 ml / min.
Infusion / pump temperature: room temperature.
Detection: UV 254 nm.
Injection volume: 50 microliter.
Standard polystyrene for calibration curve: trade name “shodex” manufactured by Showa Denko KK, weight average molecular weight 1030000; weight average molecular weight 54800000, 3840000, 355000, 102000, 37900, 9100, 2630, 495 manufactured by Tosoh Corporation.

As the polystyrene resin, a resin produced by a known production method can be used. For example, examples of the polystyrene resin include those produced by a suspension polymerization method, a bulk polymerization method, a solution polymerization method, an emulsion polymerization method, and the like.
When polymerizing a styrene monomer and a vinyl monomer used in combination as required, a known polymerization initiator can be used. For example, as a polymerization initiator, 2,2-bis (4,4-di-t-butylperoxycyclohexyl) propane, benzoyl peroxide, lauryl peroxide, t-butylperoxybenzoate, t-butyl peroxide, t-butylperoxypivalate, t-butylperoxyisopropyl carbonate, t-butylperoxyacetate, 2,2-t-butylperoxybutane, t-butylperoxy-3,3,5 trimethylhexanoate, Organic peroxides such as di-t-butylperoxyhexahydroterephthalate; azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile; The polymerization initiators may be used alone or in combination of two or more.

When producing a polystyrene resin, a crosslinking agent may be used at the time of polymerization. Examples of the crosslinking agent include divinylbenzene and the like. The crosslinking agents may be used alone or in combination of two or more.
The compounding amount of the crosslinking agent is preferably more than 0 parts by mass and 1 part by mass or less based on 100 parts by mass of the total amount of the monomers used for the polystyrene resin.

  The polystyrene-based resin may be used alone or in a combination of two or more.

<Optional components>
When the foamed resin layer constituting the foamed sheet of the present invention has a complex viscosity in the range of 3500 to 7000 Pas and the content of the styrene-based monomer component in the range of 120 to 320 ppm, the polystyrene-based Other components (arbitrary components) may be contained in addition to the resin.
Examples of such optional components include resin components other than the polystyrene-based resin, a cell regulator, a coloring agent, an anti-shrinkage agent, a flame retardant, a lubricant, and a deterioration inhibitor.
Examples of the resin component other than the polystyrene resin include a rubber-modified polystyrene resin, a hydrogenated polystyrene elastomer, and a polyethylene resin.

≪Rubber-modified polystyrene resin≫
The rubber-modified polystyrene resin in the present invention is a polymer alloy obtained by mixing a conjugated diene polymer with a polystyrene resin, and a graft copolymer obtained by graft copolymerizing a conjugated diene polymer with a polystyrene resin. Respectively.
The rubber-modified polystyrene resin has a sea-island structure in which particles (islands) of a conjugated diene polymer having a particle size of 0.3 to 10 μm are dispersed in a continuous phase (sea) of the polystyrene resin, Generally referred to as high impact polystyrene.
In the rubber-modified polystyrene resin, no hydrogenation is performed on the double bond of the conjugated diene polymer portion (conjugated diene block).

As the polystyrene resin in the rubber-modified polystyrene resin, the same polystyrene resin as described above is used.
Examples of the conjugated diene-based polymer include a conjugated diene polymer or copolymer and a copolymer of a conjugated diene and an aromatic vinyl compound. When the conjugated diene-based polymer is a copolymer of a conjugated diene or a copolymer of a conjugated diene and an aromatic vinyl compound, the conjugated diene-based polymer may be a block copolymer or a random copolymer. Any of polymers may be used. Examples of the conjugated diene include butadiene, isoprene, chloroprene, and the like, butadiene is preferred. Examples of the aromatic vinyl compound include styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, t-butylstyrene, dimethylstyrene, bromostyrene and the like, and styrene is preferred.

The content of the styrene monomer unit in the rubber-modified polystyrene resin is preferably from 75 to 99% by mass, and preferably from 80 to 97% by mass, based on the total amount (100% by mass) of the monomer units constituting the resin. % Is more preferred.
If the content of the styrene monomer unit is less than the preferred lower limit of the above range, the moldability of the foamed sheet may be reduced. When the content of the styrene-based monomer unit exceeds the preferred upper limit of the above range, the impact resistance of the foamed sheet or the molded article thereof may be reduced.

The MFR of the rubber-modified polystyrene resin is preferably from 1.5 to 4.0 g / 10 minutes, and more preferably from 2.5 to 4.0 g / 10 minutes.
When the MFR of the rubber-modified polystyrene-based resin is less than the preferred lower limit of the above range, the thickness of the foamed resin layer may be uneven. If the MFR of the rubber-modified polystyrene-based resin exceeds the preferred upper limit of the above range, the expansion ratio of the foamed resin layer may decrease.
The MFR of the rubber-modified polystyrene resin is measured under the same conditions as the MFR of the polystyrene resin.

The weight-average molecular weight of the rubber-modified polystyrene resin is preferably from 150,000 to 350,000, and more preferably from 150,000 to 300,000.
If the weight-average molecular weight of the rubber-modified polystyrene resin is less than the preferred lower limit of the above range, the closed cell rate of the foamed resin layer may decrease, and the thickness of the foamed resin layer may be insufficient. When the weight-average molecular weight of the rubber-modified polystyrene-based resin exceeds the preferred upper limit of the above range, the fluidity at the time of melting may decrease, and the productivity may decrease.

  The rubber-modified polystyrene-based resin may be used alone, or two or more kinds may be used in combination.

≪Hydrogenated polystyrene elastomer≫
The hydrogenated polystyrene-based elastomer in the present invention is a hydrogenated product of a styrene-conjugated diene block copolymer.
As the conjugated diene here, butadiene, isoprene, chloroprene and the like can be mentioned, butadiene is preferred.

  Examples of the hydrogenated polystyrene-based elastomer include a styrene / butadiene block copolymer (SBR), a styrene-ethylene / butadiene-styrene (SEBS) block copolymer, and a styrene-butadiene / butylene-styrene (SBBS) block copolymer. Are preferred.

The hydrogenation rate of the double bond of the conjugated diene block in the hydrogenated polystyrene-based elastomer is preferably from 60 to 95 mol%, more preferably from 65 to 95 mol%.
When the hydrogenation ratio is within the above range, the flexibility of the foamed sheet is enhanced by using the hydrogenated polystyrene-based elastomer. For example, when transporting fruits and vegetables housed in a concave portion of a container for packaging fruit and vegetables formed of a foamed sheet, even if the fruits and vegetables contained in the concave portions are subjected to an impact force such as vibration during transportation, the fruits and vegetables are Since there is no rotation (ball rotation) in the concave portion, it is possible to prevent the fruit vegetables from being damaged.

The hydrogenation rate of the conjugated diene block in the hydrogenated polystyrene-based elastomer can be measured according to the following procedure.
Procedure 1) Using a nuclear magnetic resonance apparatus, obtain a ¹ H-NMR spectrum of the resin to be measured.
Procedure 2) Based on the above ¹ H-NMR spectrum, the amount of hydrogenated conjugated diene (the amount of hydrogenated conjugated diene) and the amount of the conjugated diene that is not hydrogenated (the amount of unhydrogenated conjugated diene) are calculated. I do.
Step 3) The hydrogenation rate is calculated from the following formula based on the amount of the added conjugated diene and the amount of the unhydrogenated conjugated diene.
Hydrogenation rate (mol%)
= 100 × (amount of hydrogenated conjugated diene) / {(amount of hydrogenated conjugated diene) + (amount of unhydrogenated conjugated diene)}

The measurement by the nuclear magnetic resonance apparatus in the procedure 1 is performed under the following conditions.
Nuclear magnetic resonance apparatus: trade name “ECX-400P type” manufactured by JEOL Ltd.
Measurement ^nucleus: 1 H.
Observation range: 8000 (20 ppm).
Pulse width: 45 ° (9.0 μsec).
Pulse interval: 9 sec.
Number of measurements: 2400 times.
Set temperature: 55 ° C.
Measurement solvent: CDCl ₃ .
Measurement concentration: 50 mgr / 0.4 mL.
Internal reference material: tetramethylsilane (TMS).

The durometer type A hardness (HDA) of the hydrogenated polystyrene elastomer is preferably 90 or less, more preferably 50 to 90.
When the durometer type A hardness (HDA) is equal to or less than the preferred upper limit of the above range, the flexibility of the foamed sheet is further enhanced. For example, fruits and vegetables contained in a concave portion of a fruit and vegetable packaging container formed by molding a foam sheet are less likely to cause friction with the concave portions, and the fruit and vegetables are less likely to be damaged.
In the present invention, the durometer type A hardness (HDA) of the hydrogenated polystyrene-based elastomer refers to a value measured by a method based on JIS K7215.

The MFR of the hydrogenated polystyrene-based elastomer is preferably 2 to 20 g / 10 minutes, and more preferably 3 to 15 g / 10 minutes.
In the present invention, the melt flow rate (MFR) of the hydrogenated polystyrene-based elastomer is determined according to JIS K 7210: 1999 “Test method for melt mass flow rate (MFR) and melt volume flow rate (MVR) of plastic-thermoplastic”. A value measured under the conditions of a test temperature of 230 ° C., a test load of 21.17 N, and a preheating time of 4 minutes in accordance with the described method.
If the MFR of the hydrogenated polystyrene-based elastomer is less than the preferred lower limit of the above range, the thickness of the foamed resin layer may be uneven. If the MFR of the hydrogenated polystyrene-based elastomer exceeds the preferred upper limit of the above range, the expansion ratio of the foamed resin layer may decrease.

The weight average molecular weight of the hydrogenated polystyrene elastomer is preferably from 100,000 to 350,000, more preferably from 150,000 to 250,000.
When the weight average molecular weight of the hydrogenated polystyrene-based elastomer is less than the preferred lower limit of the above range, the closed cell ratio of the foamed resin layer may be reduced, and the thickness of the foamed resin layer may be insufficient. If the weight-average molecular weight of the hydrogenated polystyrene-based elastomer exceeds the preferred upper limit of the above range, the fluidity at the time of melting may decrease, and the productivity may decrease.

  The hydrogenated polystyrene-based elastomer may be used alone, or two or more kinds may be used in combination.

≪Polyethylene resin≫
In the foamed sheet of the present invention, the foamed resin layer contains a polyethylene-based resin, whereby the flexibility of the foamed sheet is enhanced. For example, fruits and vegetables contained in the concave portion of the fruit and vegetable packaging container formed by molding the foamed sheet Is less likely to be scratched.
As the polyethylene resin, for example, ultra-low density polyethylene resin, low density polyethylene resin, medium density polyethylene resin, high density polyethylene resin, linear low density polyethylene resin, linear medium density polyethylene resin And linear high-density polyethylene resins.
The polyethylene resin contains an ethylene monomer unit. The ethylene-based monomer unit is a monomer unit derived from a chain unsaturated hydrocarbon having a double bond (eg, ethylene, 1-butene, etc.).

The MFR of the polyethylene resin is preferably from 0.1 to 5 g / 10 min, more preferably from 0.4 to 4 g / 10 min.
In the present invention, the melt flow rate (MFR) of the polyethylene resin is described in JIS K 7210: 1999 “Test method for melt mass flow rate (MFR) and melt volume flow rate (MVR) of plastic-thermoplastic” described in Method B. According to the method, it means a value measured under the conditions of a test temperature of 190 ° C., a test load of 21.17 N, and a preheating time of 4 minutes.
If the MFR of the polyethylene resin is less than the preferred lower limit of the above range, the fluidity at the time of melting may be reduced, and the productivity may be easily reduced. If the MFR of the polyethylene resin exceeds the preferred upper limit of the above range, foamability or moldability may decrease, or compatibility with polystyrene may deteriorate.

The weight average molecular weight of the polyethylene resin is preferably 50,000 to 300,000, more preferably 100,000 to 200,000.
When the weight average molecular weight of the polyethylene resin is less than the preferred lower limit of the above range, a foamed resin layer having a low open cell ratio may be difficult to obtain. If the weight average molecular weight of the polyethylene resin exceeds the preferred upper limit of the above range, the fluidity at the time of melting may decrease, and the productivity may decrease.

  The polyethylene resin may be used alone or in combination of two or more.

In the polystyrene resin foam sheet of the present invention, such a foamed resin layer preferably contains a resin component having a styrene monomer unit and an ethylene monomer unit from the viewpoint of imparting flexibility.
The absorbance ratio (D698 / D2850) of the foamed resin layer is preferably from 7.0 to 15.0, more preferably 8 from the viewpoint of the balance of flexibility, strength, heat resistance and moldability of the foamed sheet. 0.0 to 15.0, and more preferably 8.0 to 14.0.
When the absorbance ratio (D698 / D2850) is equal to or more than the preferable lower limit of the above range, the heat resistance of the foamed sheet is easily maintained, and the moldability is further improved. When the absorbance ratio (D698 / D2850) is equal to or less than the preferable upper limit of the above range, the flexibility of the foamed sheet is further increased.
In the present invention, the absorbance ratio (D698 / D2850) of the foamed resin layer is measured by infrared spectroscopy (IR). Absorbance ratio (D698 / D2850) means the absorbance of the styrene-based monomer unit derived from 698cm ^-1 and (D698), the absorbance of 2850 cm ^-1 derived from ethylene monomer units and (D2850), the ratio of . Specifically, it is determined by a method described in Examples described later.

It is preferable that the foamed resin layer further contains a cell regulator in addition to the resin component. By including the cell regulator, a foamed sheet having a low open cell ratio and good moldability can be easily obtained.
Examples of the cell regulator include inorganic fillers such as talc, mica, mica, and montmorillonite.
The foam control agents may be used alone or in combination of two or more.
The content of the cell regulator in the foamed resin layer is preferably from 0.5 to 5 parts by mass, more preferably from 0.5 to 3 parts by mass, per 100 parts by mass of the resin component.

  As described above, the foamed polystyrene resin sheet of the present invention has a complex viscosity determined by viscoelasticity measurement at a temperature of 180 ° C. and a frequency of 1 Hz of 3500 to 7000 Pa · s, and contains a styrene monomer component. By providing the foamed resin layer having an amount of 120 to 320 ppm, flexibility is enhanced, and sufficient heat resistance and moldability are also excellent.

(Production method of polystyrene resin foam sheet)
The method for producing a foamed polystyrene-based resin sheet of the present invention is the method for producing a foamed polystyrene-based resin sheet of the present invention described above, wherein a raw material composition containing a resin component containing a polystyrene-based resin, and a foaming agent, This is a method of melt-kneading, extruding and foaming.
As a suitable method for producing such a polystyrene-based resin foam sheet, a known method for producing a foam sheet can be employed, and examples thereof include a production method (A) and a production method (B) shown below. Among these, the production method (A) is more preferable as a method for producing such a polystyrene resin foam sheet from the viewpoint of extrusion foaming properties and thermoformability.

Production method (A):
After supplying a raw material composition containing a resin component including a polystyrene resin and other resins and other components, and a physical foaming agent to an extruder and melt-kneading the same, a circular die attached to a tip of the extruder After extrusion foaming to obtain a cylindrical foam, then, after expanding the diameter of the cylindrical foam and supplying it to a mandrel and cooling, the cylindrical foam is interposed between its inner and outer peripheral surfaces. A method for producing a polystyrene-based resin foam sheet by continuously cutting and developing in the extrusion direction.

Production method (B):
After melt-kneading the raw material composition and the chemical foaming agent in an extruder, extruding from a T-die attached to the tip of the extruder to produce a foamable sheet, and heating and foaming the foamable sheet , A method for producing a polystyrene resin foam sheet.

In the production method (A), the physical foaming agent is not particularly limited, and examples thereof include hydrocarbons such as propane, butane, and pentane; and inert gases such as nitrogen and carbon dioxide.
The physical foaming agents may be used alone or in combination of two or more.
The blending amount of the physical foaming agent is preferably 2 to 7 parts by mass, more preferably 2 to 6 parts by mass, based on 100 parts by mass of the raw material composition.

In the production method (B), the chemical foaming agent is not particularly limited, and examples thereof include azodicarbonamide.
The chemical foaming agents may be used alone or in combination of two or more.
The compounding amount of the chemical foaming agent is preferably 2 to 7 parts by mass, more preferably 2 to 6 parts by mass, per 100 parts by mass of the raw material composition.

The blending amount of the polystyrene resin is preferably 45 to 85% by mass, more preferably 50 to 80% by mass, based on the total amount of the resin components (100% by mass).
When the blending amount of the polystyrene-based resin is equal to or more than the preferred lower limit of the above range, the heat resistance of the foamed sheet is increased, and the moldability is further improved. When the amount of the polystyrene resin is equal to or less than the preferable upper limit of the above range, the flexibility of the foamed sheet is easily maintained.

When a rubber-modified polystyrene-based resin is used as a resin component other than the polystyrene-based resin, the amount of the rubber-modified polystyrene-based resin is preferably from 0 to 30% by mass, and more preferably from 5 to 30% by mass, based on the total amount of the resin component (100% by mass). 30 mass% is more preferable, and 10 to 25 mass% is further preferable.
When the compounding amount of the rubber-modified polystyrene-based resin is equal to or more than the preferable lower limit of the above range, an impact force such as vibration applied to the foamed sheet is easily absorbed. When the compounding amount of the rubber-modified polystyrene-based resin is equal to or less than the preferred upper limit of the above range, the rubber-modified polystyrene-based resin is less likely to aggregate, and the appearance of the foamed sheet is further improved.

The mixing ratio of the polystyrene-based resin (PS-based) and the rubber-modified polystyrene-based resin (rubber-modified) is represented by a mass ratio represented by polystyrene-based resin / rubber-modified polystyrene-based resin (hereinafter, also referred to as “PS-based / rubber-modified”). ) Is preferably from 1.5 to 14.0, and more preferably from 1.5 to 7.0.
When the PS system / rubber modification is at least the preferred lower limit of the above range, the flexibility of the foamed sheet is easily maintained. If the PS system / rubber modification is below the preferred upper limit of the above range, the heat resistance of the foamed sheet is easily maintained, and the moldability is further improved.

When a hydrogenated polystyrene-based elastomer is used as a resin component other than the polystyrene-based resin, the amount of the hydrogenated polystyrene-based elastomer is preferably 5 to 20% by mass, and more preferably 10 to 10% by mass, based on the total amount of the resin component (100% by mass). 20 mass% is more preferable.
When the amount of the hydrogenated polystyrene-based elastomer is equal to or more than the preferred lower limit of the above range, the flexibility of the foamed sheet is easily maintained, and for example, the foamed sheet is housed in the concave portion of the fruit and vegetable packaging container formed by molding the foamed sheet. Fruit vegetables are less likely to be damaged. When the amount of the hydrogenated polystyrene-based elastomer is equal to or less than the preferable upper limit of the above range, the heat resistance of the foamed sheet is easily maintained, and the moldability is further improved.

The mixing ratio of the polystyrene-based resin (PS-based) and the hydrogenated polystyrene-based elastomer (hydrogenated) is represented by a mass ratio represented by polystyrene-based resin / hydrogenated polystyrene-based elastomer (hereinafter also referred to as “PS-based / hydrogenated”). ) Is preferably 2.0 to 5.0, and more preferably 2.5 to 5.0.
When the PS system / hydrogenation is equal to or more than the preferable lower limit of the above range, the heat resistance of the foamed sheet is easily maintained, and the flexibility is further improved. When the ratio of PS / hydrogenation is equal to or less than the preferred upper limit of the above range, the compatibility between the polystyrene-based resin and the polyethylene-based resin is further increased, and the foamability and thermoformability are further improved.

When a polyethylene resin is used as a resin component other than the polystyrene resin, the blending amount of the polyethylene resin is preferably 5 to 15% by mass, and more preferably 5 to 10% by mass based on the total amount of the resin component (100% by mass). More preferred.
When the blending amount of the polyethylene resin is equal to or more than the preferred lower limit of the above range, the flexibility of the foamed sheet is easily maintained, and for example, the fruit and vegetables contained in the concave portion of the fruit and vegetable packaging container formed by molding the foamed sheet can be used. It is hard to be damaged. When the blending amount of the polyethylene resin is equal to or less than the preferred upper limit of the above range, the heat resistance of the foamed sheet is easily maintained, and the moldability is further improved.

The mixing ratio of the polystyrene-based resin (PS-based) to the polyethylene-based resin (PE-based) is represented by a mass ratio expressed by polystyrene-based resin / polyethylene-based resin (hereinafter also referred to as “PS-based / PE-based ratio”) of 4 0.0-50.0 are preferable, and 7.0-15.0 are more preferable.
If the PS / PE ratio is at least the preferred lower limit of the above range, the formability of the foamed sheet will be easily maintained. When the PS-based / PE-based ratio is equal to or less than the preferable upper limit of the above range, the flexibility of the foamed sheet is easily maintained.

The rubber content of the rubber-modified polystyrene-based resin is preferably 3 to 12% by mass, and more preferably 5 to 10% by mass, based on the total amount (100% by mass) of the rubber-modified polystyrene-based resin component. When the rubber content is within the above numerical range, the moldability is easily improved.
The rubber content can be measured by the following method.
[Method of measuring rubber content]
A sample of 0.1 to 0.5 mg is precisely weighed and wrapped with a ferromagnetic metal having a Curie point of 590 ° C (pyrofoil: manufactured by Nippon Kagaku Kogyo Co., Ltd.) so as to be pressed. The sample wrapped in pyrofoil is decomposed by a Curie Point Pyrolyzer JPS-700 (manufactured by Nippon Kagaku Kogyo Co., Ltd.). The butadiene monomer and 4-vinylcyclohexene generated from the decomposed sample are measured with a gas chromatograph GC7820 (manufactured by Agilent Technologies, Inc., detector: FID). The total butadiene amount is calculated from the obtained total peak area and an absolute calibration curve prepared in advance, and this is defined as a rubber component.
The measurement conditions are preferably, for example, the following conditions.

[Measurement condition]
・ Heating (590 ℃ -5sec)
・ Oven temperature (300 ℃)
・ Needle temperature (300 ℃)
Column (Inter Cap5 (φ0.25 mm × 30 m (film thickness 0.25 μm): GL Sciences Corporation)
Temperature conditions (after holding at 50 ° C for 0.5 minutes, the temperature is raised to 200 ° C at 10 ° C / minute, then to 320 ° C at 20 ° C / minute, and held at 320 ° C for 0.5 minutes)
・ Carrier gas (He)
・ He flow rate (25ml / min)
・ Injection port pressure (100KPa)
・ Injection port temperature (300 ℃)
・ Detector temperature (300 ℃)
・ Split ratio (1/30)
The standard sample for preparing the calibration curve was POLYSCIENCES. It is preferable to use St / BD = 85/15 (CAT # 07073) resin manufactured by INC.

The raw material composition contains a resin component containing a polystyrene resin.
The resin component also preferably contains a polystyrene-based resin, a hydrogenated polystyrene-based elastomer, and at least one selected from the group consisting of a polyethylene-based resin and a rubber-modified polystyrene-based resin.

  As the raw material composition (resin component), the effect of the present invention is further enhanced, so that 45 to 85% by mass of a polystyrene-based resin and hydrogenated polystyrene-based resin are added to the total amount of the resin component (100% by mass). What contains an elastomer 5-20 mass%, a polyethylene resin 5-15 mass%, and a rubber modified polystyrene resin 0-30 mass% is preferable. However, the sum of these resins does not exceed 100% by mass.

  According to the method for producing a polystyrene-based resin foam sheet of the present invention described above, it is possible to produce a polystyrene-based resin foam sheet having enhanced flexibility, good heat resistance and good moldability.

(Molded body)
The molded article of the present invention is obtained by molding the above-mentioned foamed polystyrene resin sheet of the present invention into a desired shape using a known molding method or the like.
Examples of a method for forming the polystyrene resin foam sheet include vacuum forming and pressure forming. As vacuum forming or pressure forming, plug forming, free drawing forming, plug and ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, air slip forming, plug assist forming, plug assist reverse draw forming And the like.
The molded product of the present invention has enhanced flexibility and good heat resistance. For example, in addition to a sheet-like cushioning material, a container for packaging home appliances, a container for packaging mechanical parts, a container for packaging confectionery, and a container for packaging fruit and vegetables. Although it is used as a container such as a container, it is particularly useful as a container for packaging fruit and vegetables having a plurality of recesses for accommodating fruit and vegetables on one surface of the sheet. Further, the polystyrene resin foam sheet of the present invention is not only used as various containers, but also cut and processed by, for example, a punching blade and the like, and is used as a partitioning material, interleaving paper and the like, as a packaging material for building materials such as fruits and vegetables, machine parts, and sashes. Can also be suitably used.

(container)
The container of the present invention is a foamed resin having a complex viscosity of 3500 to 7000 Pa · s determined by viscoelasticity measurement at a temperature of 180 ° C. and a frequency of 1 Hz, and a styrene monomer component content of 120 to 320 ppm. It has a layer.
The container of the present invention can be used as a container for packing household appliances, a container for packing machine parts, a container for packing confectionery, a container for packing fruit and vegetables, and among others, a container for packing fruit and vegetables is preferable.

FIG. 1 shows an embodiment of the container of the present invention, and FIG. 2 is a sectional view taken along line XX of FIG.
The container (container for fruit and vegetable packaging) 10 of the present embodiment is for accommodating fruit and vegetables such as apples, pears, and peaches, for example.
The container 10 has a substantially rectangular shape in a plan view, and has 12 concave portions 12 which are open on one surface 10a of the sheet and bulge in a semi-spherical shape on the other surface 10b of the sheet.
One recess 12 is large enough to fill about half of one fruit vegetable.
As shown in FIG. 2, a partition 15 is formed between adjacent recesses 12. The partition part 15 includes the peripheral walls 12 b of the adjacent concave parts 12 and the connecting parts 14 provided between the concave parts 12.
At the center of the inner bottom surface of the concave portion 12, a convex portion 12a projecting in the direction of the opening surface 10a and having a shape along the concave portion of the fruit and vegetable is formed.

The container 10 is, for example, foamed having a complex viscosity of 3500 to 7000 Pa · s determined by viscoelasticity measurement at a temperature of 180 ° C. and a frequency of 1 Hz, and a styrene monomer component content of 120 to 320 ppm. It is manufactured by thermoforming a polystyrene resin foam sheet having a resin layer into a predetermined shape.
The preferred range of the complex viscosity is 4000 to 6500 Pa.s. s, and a more preferred range is 4300 to 6500 Pa.s. s.
The container 10 is provided with a foamed resin layer having a complex viscosity of 3500 to 7000 Pa · s, whereby high flexibility is exhibited and sufficient heat resistance is obtained.

The content of the styrene monomer component in the container is 120 to 320 ppm, preferably 150 to 250 ppm, more preferably 150 to 220 ppm, based on the total mass of the container.
When the content of the styrene monomer component is equal to or more than the lower limit of the above range, the flexibility of the container is increased. When the content of the styrene-based monomer component is equal to or less than the upper limit of the above range, heat resistance is easily maintained, and molding failure is less likely to occur.

  When the fruits and vegetables are accommodated in the concave portions 12, the lower half of the fruits and vegetables is buried in the concave portions 12. Since the flexibility of the container 10 is enhanced, the peripheral wall 12b of the concave portion 12 comes into contact with the fruit and vegetables, so that the fruit and vegetables are stably housed in the concave portion 12 in a state of being in close contact with the peripheral wall 12b.

In the case where fruit or vegetables having a size larger than the opening diameter of the concave portion are accommodated in one of the adjacent concave portions, in the conventional container, the concave portion in which the large-sized fruit or vegetable is accommodated has a large volume and the opening portion is widened. As a result, the partition part falls down into the other concave part, the opening of the other concave part becomes narrow, and it is difficult to store fruit and vegetables in the other concave part.
In the container 10 of the present embodiment, since the flexibility of the peripheral wall 12b and the connecting portion 14 (the partition portion 15) is enhanced, even when such a large-sized fruit and vegetable is stored in the concave portion 12, the opening of the concave portion 12 is formed. The partitioning part 15 is compressed with the spread. Thus, the volume of the other adjacent concave portion is maintained, and the opening does not become narrow. For this reason, fruit vegetables can be easily accommodated in the adjacent concave portions 12 respectively.

  In addition, the foamed resin layer constituting the container 10 can be appropriately elastically deformed as the flexibility is enhanced. For this reason, the fruits and vegetables housed in the recessed portion 12 in close contact with the peripheral wall 12b are less likely to rotate around even if subjected to an impact force such as vibration during transportation or storage, and the fruits and vegetables are hardly damaged.

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

<Resin component>
-Polystyrene resin A (MFR: 1.6 g / 10 min, weight average molecular weight: 320,000, product name: HRM26, manufactured by Toyo Styrene Co., Ltd.).
-Polystyrene resin B (MFR: 2.3 g / 10 min, weight average molecular weight: 340,000, product name: HRM48N, manufactured by Toyo Styrene Co., Ltd.).
-Polystyrene resin C (MFR: 1.5 g / 10 min, weight average molecular weight: 320,000, product name: G9305, manufactured by PS Japan Co., Ltd.).
-Polystyrene resin D (MFR: 1.2 g / 10 min, weight average molecular weight: 340,000, product name: HRM40Z, manufactured by Toyo Styrene Co., Ltd.).
-Polystyrene resin E (MFR: 1.6 g / 10 min, weight average molecular weight: 290,000, product name: G0002, manufactured by PS Japan Co., Ltd.).
-Polystyrene resin F (styrene / butadiene block copolymer, durometer type A hardness: 88, MFR: 20 g / 10 min, product name: Tufpre 125, manufactured by Asahi Kasei Chemicals Corporation).

  Polyethylene resin (ultra low density polyethylene, MFR: 0.8 g / 10 min, weight average molecular weight: 110,000, product name: Lumitac 12-1, manufactured by Tosoh Corporation).

-Hydrogenated polystyrene-based elastomer A (styrene-ethylene / butadiene-styrene block copolymer, hydrogenation rate: 95 mol%, rebound resilience: 65%, durometer type A hardness: 67, MFR: 4.0 g / 10 min. , Weight average molecular weight: 150,000, product name: SOE-S1606, manufactured by Asahi Kasei Chemicals Corporation).
Hydrogenated polystyrene elastomer B (styrene-ethylene / butadiene-styrene block copolymer, hydrogenation rate: 95 mol%, rebound resilience: 4%, durometer type A hardness: 87, MFR: 3.5 g / 10 min. , Weight average molecular weight: 150,000, product name: SOE-S1605, manufactured by Asahi Kasei Chemicals Corporation).
In addition, the durometer type A hardness of the above-mentioned raw materials was measured as follows.

[Durometer type A hardness]
The durometer type A hardness of the hydrogenated polystyrene elastomer was measured using a durometer ASKER type A (manufactured by Kobunshi Keiki Co., Ltd.) and a constant-pressure loader capable of applying a load of 10 N according to a method in accordance with JIS K7215.
Specifically, twelve planar rectangular test pieces of 30 mm long × 50 mm wide × 4 mm thick made of a hydrogenated polystyrene-based elastomer were prepared, and two of these were stacked to form a 6 mm thick measurement sample. This was produced.
The durometer type A hardness value (HDA) was measured six times for each measurement sample, and the arithmetic mean value was calculated.

Rubber-modified polystyrene resin A (styrene monomer unit: 92% by mass, MFR: 3.7 g / 10 min, weight average molecular weight: 200,000, product name: HPS-851, Takafuku Kagaku Kogyo Co., Ltd.) Co., Ltd.).
Rubber-modified polystyrene resin B (styrene monomer unit: 94% by mass, MFR: 2.7 g / 10 minutes, weight average molecular weight: 240,000, product name: E640N, manufactured by Toyo Styrene Co., Ltd.).

<Air bubble adjuster>
Talc (powder talc, product name: DSM-1401A, manufactured by Toyo Styrene Co., Ltd.).

(Example 1)
[Manufacture of polystyrene resin foam sheet]
A resin component containing polystyrene resin A (56% by mass), polyethylene resin (10% by mass), hydrogenated polystyrene elastomer A (16% by mass), and rubber-modified polystyrene resin A (18% by mass), and bubbles A raw material composition containing talc (1.1 parts by mass with respect to 100 parts by mass of the resin component) as a modifier was prepared.
Next, the raw material composition is supplied to an extruder, melt-kneaded so that the maximum temperature is 245 ° C., and butane gas (isobutane / normal butane = 68/32) is added as a physical foaming agent to the raw material composition in a molten state. (Mass ratio)) 5.6 parts by mass (based on 100 parts by mass of the raw material composition) were press-fitted, and butane gas was uniformly dispersed in the raw material composition.
Thereafter, the raw material composition was cooled to a temperature of 143 ° C., and then extruded and foamed with a clearance of 0.28 mm from a circular die having a diameter of 180 mm attached to the end of the extruder to form a cylindrical foam. I got a body. Subsequently, after expanding the diameter of the cylindrical foam, the cylindrical foam was supplied to a cooling mandrel and cooled.
After cooling, the two polystyrene resin foam sheets are continuously cut and expanded in the extrusion direction between the inner and outer peripheral surfaces at two locations opposing each other in the diametrical direction, thereby forming two polystyrene resin foam sheets. Obtained.

(Examples 2 to 7 and Comparative Examples 1 to 6)
A polystyrene resin foam sheet was produced in the same manner as in Example 1, except that the composition of the resin component was changed as shown in Tables 1 and 2.
In Tables 1 and 2, the amount of each component is represented by mass%. Talc is represented by parts by mass (phr: per hundred resin) with respect to 100 parts by mass of the resin component.

About the manufactured polystyrene resin foam sheet, complex viscosity (Pa · s), thickness (mm), basis weight (g / m ² ), expansion ratio (times), absorbance ratio (D698 / D2850), styrene monomer Body content was determined for each. In addition, heat resistance, flexibility, and moldability of the produced polystyrene resin foam sheet were evaluated.
The results are shown in Tables 1 and 2.

[Complex viscosity of polystyrene resin foam sheet]
For the foamed sheet, a dynamic viscoelasticity measurement was performed by combining a viscoelasticity measuring device “PHYSICA MCR301” manufactured by Anton Paar, a temperature control system “CTD450” and software “Leoplus” to determine a complex viscosity (η *). .
Specifically, dynamic viscoelasticity was measured according to the following procedure.
The raw material composition used for the production of the foamed sheet, or a sample collected from the foamed sheet, was subjected to a hot press at a temperature of 150 ° C. for 5 minutes, a pressure of 10 MPa, and a number of presses of 5 times. And a disk-shaped sample having a thickness of 3 mm was prepared.
Next, the sample was set on a plate of a viscoelasticity measuring apparatus heated to a measurement start temperature of 200 ° C., and left under a nitrogen atmosphere for 5 minutes to be melted.
Thereafter, the gap was crushed to a gap of 2.0 mm with a parallel plate having a diameter of 25 mm, and the melt protruding from the plate was removed.
Furthermore, after leaving for 5 minutes after reaching the measurement start temperature of 200 ± 1 ° C., the conditions of strain 5%, frequency 1 Hz, temperature drop rate 2 ° C./min, measurement interval 30 seconds, normal force 0N, and measurement temperature 200 to 100 ° C. The complex viscosity η * (Pa · s) was measured below, and the value of the complex viscosity η * (Pa · s) at 180 ° C. was read.
The measured complex viscosity η * (Pa · s) value is shown in Tables 1 and 2 as “complex viscosity (Pa · s)”.

[Thickness of polystyrene resin foam sheet]
The thickness (mm) of the foamed sheet was determined by measuring the thickness of an arbitrary portion of the foamed sheet at five places and calculating the arithmetic average of the thicknesses at the five places.

[Basic weight of polystyrene resin foam sheet]
The basis weight of the foam sheet was determined as follows.
Except for 20 mm at both ends in the width direction of the 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 the nearest 0.001 g. The value obtained by converting the average value of the mass (g) of each section into the mass per 1 m ² was defined as the basis weight (g / m ² ) of the foamed sheet.

[Expansion ratio of polystyrene resin foam sheet]
The expansion ratio (times) of the foamed sheet was determined as follows.
The size (area: S) and thickness (t) of a sample obtained by cutting the foamed sheet into a predetermined size are measured, and the measured values are multiplied to obtain the apparent volume of the sample (V = S × t (cm ^3)). )), And the apparent density (d = M / V (g / cm ³ )) of the foamed sheet was calculated from this and the mass (M (g)) of the sample.
Then, the density (×) of the foamed sheet is obtained by dividing the density (ρ: 1.05 g / cm ³ ) of the mixed resin forming the foamed sheet by the apparent density (d) of the foamed sheet. Was.
Expansion ratio (times) = density of mixed resin (ρ) / apparent density of foam sheet (d)

[Absorbance ratio of polystyrene resin foam sheet (D698 / D2850)]
The absorbance ratio (D698 / D2850) of the foamed sheet was determined as follows.
The surface of each of the three randomly selected foamed sheets (foamed resin layers) was subjected to surface analysis by an infrared spectroscopic analysis ATR measurement method to obtain an infrared absorption spectrum.
The absorbance ratio (D698 / D2850) was calculated from each infrared absorption spectrum, and the arithmetic mean of the calculated absorbance ratio was determined, and this was defined as the absorbance ratio of the foamed sheet (D698 / D2850).
The absorbance (D698) and the absorbance (D2850) were measured with a measuring device sold by Nicolet under the trade name “Fourier transform infrared spectrophotometer MAGN-560”, respectively. Was connected and measured.

ATR-FTIR measurement was performed under the following conditions.
High refractive index crystal seed: Ge (germanium).
Incident angle: 45 ° ± 1 °.
Measurement area: 4000 cm ^{-1 to} 675 cm ^-1 .
Fractional dependence of measurement depth: uncorrected.
Number of reflections: once.
Detector: DTGS KBr.
Resolution: 4 cm ^-1 .
Number of integration: 32 times.
Others: The infrared absorption spectrum measured without contacting with the sample is used as a background to perform processing not related to the measurement spectrum.
In the ATR method, the intensity of the obtained infrared absorption spectrum changes depending on the degree of adhesion between the sample and the high refractive index crystal. For this reason, the maximum load was applied by the “Thunder Dome” of the ATR accessory to control the degree of adhesion almost uniformly, and the measurement was performed. The foamed sheet was set in a sander dome without performing pretreatment, and the measurement was performed.

  Absorbance (D698) and absorbance (D2850) were obtained by subjecting the infrared absorption spectrum obtained under the above conditions to peak processing as follows.

The absorbance at 698 cm ⁻¹ (D698) obtained from the infrared absorption spectrum is an absorbance corresponding to the absorption spectrum derived from out-of-plane bending vibration of the benzene ring contained in the styrene monomer unit. In the measurement of the absorbance, no peak separation was performed even when another absorption spectrum overlapped at 698 cm ^-1 . Absorbance (D698) is a straight line connecting the 2000 cm ^-1 and 815 cm ^-1 as a baseline, means the maximum absorbance between 710 cm ^-1 and 685cm ^-1.

The absorbance at 2850 cm ⁻¹ (D2850) obtained from the infrared absorption spectrum is an absorbance corresponding to the absorption spectrum derived from C—H stretching vibration contained in the ethylene monomer unit. In the measurement of the absorbance, no peak separation was performed even when another absorption spectrum overlapped at 2850 cm ⁻¹ . Absorbance (D2850) is a straight line connecting the 3130Cm ^-1 and 2620cm ^-1 as a baseline, means the maximum absorbance between 2875cm ^-1 and 2800 cm ^-1.
The absorbance ratio (D698 / D2850) is a value obtained by dividing the absorbance (D698) by the absorbance (D2850).

[Content of styrene monomer component in polystyrene resin foam sheet]
The styrene monomer component of the polystyrene resin foam sheet was measured by the following test method.
Approximately 0.1 g of a polystyrene resin foam sheet was precisely weighed in a 20 mL vial, dissolved in 1 mL of DMF (dimethylformamide) containing DEB (diethylbenzene), covered with a septum and an aluminum cap, and sealed with an aluminum cap fastener. After setting the vial in an HT2000H type autosampler manufactured by YL, 2 mL of a volatile component generated by heating at 90 ° C. for 60 minutes was collected with a gas tight syringe, and measured by a gas chromatograph GC2025AF manufactured by Shimadzu Corporation. The GC measurement conditions were as shown below, and the obtained chromatogram was quantified by the internal standard method.
(GC measurement conditions)
Gas chromatograph: GC-2025AF (manufactured by Shimadzu Corporation)
Column: ZB-WAX (φ0.25 mm × 30 m (film thickness 0.25 μm): manufactured by PHENOMENEX)
Detector: FID
GC oven heating condition: Initial temperature 60 ° C (hold 3 minutes)
First stage heating rate 20 ° C / min (hold 3min to 100 ° C)
Second stage heating rate 40 ° C / min (up to 220 ° C)
Final temperature 220 ° C (hold 0.5min)
Inlet temperature: 150 ° C
Detector temperature: 250 ° C
Measurement sample liquid injection volume: 2 mL
Split ratio = 70: 1
Column flow rate = 1.6 mL / min (He)
Gas pressure = 122 kPa
(Head space measurement conditions)
Measuring device: Headspace autosampler YL2000H (manufactured by YL)
Heating temperature: 90 ° C
Heating time: 60min
Quantitative method: Internal standard method = DEB
(Calculation conditions)
Standard samples: cyclohexane, toluene, ethylbenzene, m-xylene, isopropylbenzene, o-xylene, normal-propylbenzene, styrene Calculation method: Each standard sample (8 types) in DMF (dimethylformamide) solution containing DEB (diethylbenzene) It was calculated using the area coefficient per concentration of the prepared standard solution.

[Heat resistance of polystyrene resin foam sheet]
From the foamed sheet of each example, five pieces of 10 cm × 10 cm were cut out, each of the five pieces was overlapped, and further placed at 70 ° C. with two pieces of aluminum having a thickness of about 1 mm having the same size sandwiched therebetween. The sample was placed horizontally in the set oven. Next, a weight of 5 kg was placed on the upper aluminum plate and heated in that state for 24 hours.
Thereafter, the pieces were taken out of the oven, and the releasability (fusing and releasability) between the sections (foamed sheets) was examined. The stacked five pieces (foamed sheet) are peeled off one by one, and the degree of peeling at that time is determined in four stages of ◎, 段 階, Δ, and × according to the following evaluation criteria, and the heat resistance of the foamed sheet is determined. Was evaluated.
Evaluation criteria A: The sections peeled off with little force, and almost no sound was produced (very good).
：: A slight force is required to start peeling the pieces, but after the pieces start peeling, almost no sound is produced and no force is required (further good).
Δ: The sound is almost crispy when the pieces are peeled off, but the force is not so much needed to peel off the pieces (good).
×: A noise was generated when the pieces came off, and the pieces did not come off without applying force (poor).

[Flexibility of polystyrene resin foam sheet]
Using Tensilon UCT-10 manufactured by Orientec, a partial compression test was performed as follows to evaluate the flexibility of the foamed sheet.
The foam sheet was cut out to 50 mm x 50 mm to obtain a sample sample.
For the partial compression displacement measurement, a load cell with a maximum load of 25 kgf was used, and a hemispherical φ20 mm tip and a 25 mm long straight rod-shaped pressing jig were attached to the load cell, and a partial compression test was performed. went.
The four sample samples described above were stacked, and the sample sample in which the four samples were stacked was set in close contact with the measurement device carrier so that there was no gap in the measurement device carrier. The thickness at this time was defined as a measurement sample thickness (unit: mm).
Starting from a state where the lower end of the pressing jig was in contact with the upper end in the thickness direction of the sample, the pressing jig was lowered at a speed of 10 mm / min to compress the sample.
At this time, the displacement (mm) from the base point of the jig when the load on the sample sample was 1 kgf was defined as the partial compressive displacement amount of the sample sample when the load was 1 kgf. The average of the measured values of five samples was defined as the partial compression displacement (unit: mm) of the sample sample under a load of 1 kgf.
Then, the flexibility (%) of the foam sheet was determined by the following equation.
Flexibility (%) = partial compressive displacement of sample sample under 1 kgf load (unit: mm) / measured sample thickness (unit: mm) × 100
The higher the numerical value of the flexibility (%), the higher the flexibility of the foamed sheet.
Evaluation criteria A: Flexibility 13% or more, extremely good.
：: Flexibility of 11% or more and less than 13%, good.
Δ: Flexibility of 9% or more and less than 11%, slightly poor.
×: Flexibility is less than 9%, which is poor.

[Moldability of polystyrene resin foam sheet]
Using a mold having 12 recesses having an opening diameter of 100 mm and a depth of 40 mm, the temperature of the heating furnace was set to 130 ° C., and the foamed sheet was thermoformed. As a formed body, the container for fruit and vegetable packaging of the embodiment shown in FIG. I got
The state of the surface of the molded article and the thickness of the molded article were observed, and the moldability of the foamed sheet was evaluated according to the following evaluation criteria.
Evaluation criteria A: No defects were observed on the surface of the molded product and the thickness of the molded product (very good).
：: Defects were hardly recognized on the surface of the molded product and the thickness of the molded product (good).
Δ: There was no problem on the surface of the molded body, but a part where the thickness of the molded body was thin was partially observed (slightly poor).
X: The surface of the molded article was in a hot state, cracked, or the molded article was thin and insufficiently obtained (defective).

[Comprehensive judgment]
Based on the evaluation results of flexibility, heat resistance, and moldability, comprehensive judgment was made according to the following evaluation criteria.
Comprehensive evaluation criteria A: Three of the three evaluation results (very good).
：: Three evaluation results did not have × or Δ, and even one 良好 (good).
Δ: Three evaluation results did not include x and even one Δ (slightly poor).
X: Out of the three evaluation results, at least one x was found (poor).

From the results shown in Tables 1 and 2, the polystyrene-based resin foam sheets of Examples 1 to 7 to which the present invention was applied were excellent in all of flexibility, heat resistance, and moldability.
Comparative Examples 1 and 2 having a complex viscosity of more than 7000 Pa · s were poor in heat resistance and moldability.
Comparative Example 3 having a complex viscosity of less than 3500 Pa · s was poor in moldability.
Comparative Example 4, in which the complex viscosity was less than 3500 Pa · s and the content of the styrene monomer component was less than 120 ppm, was poor in flexibility and moldability.
Comparative Example 5, in which the content of the styrene monomer component was less than 120 ppm, was poor in moldability.
Comparative Example 6, in which the content of the styrene monomer component was more than 320 ppm, was poor in moldability.

10 container, 12 recess, 14 connection, 15 partition

Claims (10)

It contains a resin component containing a polystyrene resin, has a complex viscosity of 3500 to 7000 Pa · s determined by viscoelasticity measurement at a temperature of 180 ° C. and a frequency of 1 Hz, and has a styrene monomer component content of 120 to 7000 Pa · s. With a foamed resin layer of 320 ppm ,
The foamed resin layer contains 45 to 85% by mass of a polystyrene-based resin, 5 to 20% by mass of a hydrogenated polystyrene-based elastomer, and 0 to 30% by mass of a rubber-modified polystyrene-based resin based on the total amount of the resin components (100% by mass). %, And a foamed polystyrene resin sheet. The foamed resin layer contains a resin component having a styrene monomer unit and an ethylene monomer unit,
The foamed resin layer surface of the infrared absorbing styrene obtained from the spectrum monomer units absorbance derived 698cm ^-1 of (D698) ethylene monomer units absorbance derived 2850cm ^-1 (D2850) and the absorbance ratio of The polystyrene resin foam sheet according to claim 1, wherein (D698 / D2850) is 7.0 to 15.0. The polystyrene resin foam sheet according to claim 1 or 2, wherein the foam resin layer further contains 5 to 15% by mass of a polyethylene resin. The said foamed resin layer further contains talc, The content of the said talc is 0.5-5 mass parts with respect to 100 mass parts of said resin components, The Claims any one of Claims 1-3. Polystyrene resin foam sheet. A method for producing a polystyrene resin foam sheet according to any one of claims 1 to 4 ,
A method for producing a foamed polystyrene resin sheet, comprising melt-kneading a raw material composition containing a resin component containing a polystyrene resin and a foaming agent, extruding and foaming. A molded article formed by molding the polystyrene resin foam sheet according to any one of claims 1 to 4 . The molded article according to claim 6 , which is a container for packing fruit and vegetables. It contains a resin component containing a polystyrene resin, has a complex viscosity of 3500 to 7000 Pa · s determined by viscoelasticity measurement at a temperature of 180 ° C. and a frequency of 1 Hz, and has a styrene monomer component content of 120 to 7000 Pa · s. With a foamed resin layer of 320 ppm ,
The foamed resin layer contains 45 to 85% by mass of a polystyrene-based resin, 5 to 20% by mass of a hydrogenated polystyrene-based elastomer, and 0 to 30% by mass of a rubber-modified polystyrene-based resin based on the total amount of the resin components (100% by mass). % By mass .   The foamed resin layer contains a resin component having a styrene monomer unit and an ethylene monomer unit,
  698 cm derived from a styrene monomer unit obtained from an infrared absorption spectrum of the surface of the foamed resin layer ^-1 Absorbance (D698) and 2850 cm derived from ethylene monomer unit ^-1 The container according to claim 8, wherein the absorbance ratio (D698 / D2850) to the absorbance (D2850) is 7.0 to 15.0. The container according to claim 8 or 9 , which is a container for packing fruit and vegetables.

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