JP6546555B2 - Polystyrene-based resin foam sheet, method for producing the same, and molded body - Google Patents

Description

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

For example, fruits, such as apples, pears, and peaches, are stored, transported, and stored in a container for packing fruits and vegetables, in order to minimize damage to the surface. In the container for packaging fruits and vegetables, a plurality of concave portions which are opened on one side of the sheet and swelled in a semispherical shape are formed on the other side of the sheet, and one fruity vegetable is accommodated in each of the concave portions.
The molded object by which the polystyrene-type resin foam sheet was shape | molded in the predetermined | prescribed shape is utilized for such a container for fruit and vegetable packaging. The polystyrene-based resin foam sheet is excellent in moldability, heat insulation and lightness, has appropriate rigidity, and is also suitably used as a material of a fruit vegetable packaging container.

  In recent years, antibacterial properties and deodorizing properties have been required for resin moldings used as daily necessities as well as polystyrene foam foam sheets of this type. For example, in Patent Document 1, sublimation is achieved by using hinokitiol as a derivative thereof in using hinokitiol which has antibacterial properties and insect repellent properties but can not exert the effect over a long period because of high sublimation properties. It has been disclosed that it is possible to suppress the antifungal agent and to maintain the antibacterial and insecticidal effects over a long period of time.

  Also, in recent years, calcium carbonate powder obtained by firing shells containing calcium carbonate as a main component, calcium hydroxide powder obtained by appropriately hydrating the calcium oxide powder, and antibacterial and deodorant powdered shell powder of calcium hydroxide It has been attempted to use it for the purpose. As a specific example of a method for producing a polystyrene-based resin foam-molded article using a shell-fired product, Patent Document 2 describes master pellets in which a scallop shell-fired product powder is dispersed in a polystyrene-based resin, and And a resin component such as a polystyrene-based resin are melt-kneaded.

Unexamined-Japanese-Patent No. 2004-123985 JP 2014-84338 A

  However, when an organic antibacterial agent such as a hinokitiol derivative described in Patent Document 1 is contained in the expandable polystyrene resin particles, the compatibility of the organic antibacterial agent with the polystyrene resin is not sufficient, and the antibacterial agent is a foam. It may bleed out on the surface of the molded product, and the antibacterial effect may be reduced early.

  When using the master pellet described in patent document 2 for manufacture of a polystyrene-type resin foam sheet, a polystyrene-type resin foam sheet with a favorable external appearance and a moldability is not obtained. Specifically, the polystyrene resin foam sheet needs to be relatively coarse cells from the viewpoint of appearance and formability, but when using the master pellet described in Patent Document 2, the polystyrene resin foam sheet is used. Air bubbles become too fine, resulting in poor appearance and formability of the sheet.

  Therefore, the present invention has been made in view of the above circumstances, and it is possible to provide a polystyrene resin foam sheet capable of exhibiting antibacterial properties over a long period of time and having a good appearance and formability. It will be an issue.

The present invention has the following aspects.
[1] A polystyrene-based resin foam sheet comprising a foamed resin layer containing a resin component containing a polystyrene-based resin, wherein 2 to 8 mass of the inorganic antibacterial agent relative to the total amount (100 mass parts) of the resin component The polystyrene-type resin foam sheet which contains part and whose average bubble diameter is 190-400 micrometers.
[2] The foamed resin layer contains a resin component having a styrene-based monomer unit and an ethylene-based 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 as described in [1] whose (D698 / D2850) is 7.0-15.0.
[3] The foamed resin layer contains 45 to 85% by mass of a polystyrene resin, 5 to 20% by mass of a hydrogenated polystyrene elastomer, and 5 to 5% of a polyethylene resin, based on the total amount (100% by mass) of the resin component. The polystyrene resin foamed sheet according to [1] or [2], which contains 15% by mass and 0 to 30% by mass of a rubber-modified polystyrene-based resin.
[4] The polystyrene resin foam sheet according to any one of [1] to [3], wherein the inorganic antibacterial agent contains calcium hydroxide.
[5] The polystyrene resin foam sheet according to any one of [1] to [3], wherein the inorganic antibacterial agent comprises a shell fired product.
[6] The foamed resin layer according to any one of [1] to [5], which has a complex viscosity of 4500 to 8500 Pa · s determined by viscoelastic measurement under conditions of a temperature of 180 ° C. and a frequency of 1 Hz. Polystyrene resin foam sheet.
[7] A method for producing a polystyrene resin foam sheet according to any one of [1] to [6],
Production of polystyrene resin foamed sheet by melt-kneading, extruding and foaming a raw material composition containing a resin component containing a polystyrene resin, a masterbatch containing a polyethylene resin and an inorganic antibacterial agent, and a foaming agent Method.
[8] A molded article obtained by molding the polystyrene resin foam sheet according to any one of [1] to [6].
[9] The molded article according to [8], which is a container for packaging fruits and vegetables.

The polystyrene resin foam sheet of the present invention can exhibit antibacterial properties over a long period of time, and is excellent in appearance and moldability.
According to the method for producing a polystyrene resin foam sheet of the present invention, it is possible to exhibit antibacterial properties over a long period of time, and to produce a polystyrene resin foam sheet having good appearance and moldability.
The molded article of the present invention can exhibit antibacterial properties over a long period of time, and is excellent in appearance.

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 foamed sheet (hereinafter, also simply referred to as "foamed sheet") of the present invention is provided with a foamed resin layer containing a polystyrene resin.
The foam sheet may have a single-layer structure consisting only of a foam resin layer, or may have a laminate structure in which a resin film or the like is provided on at least one surface of the foam resin layer.

20% or less is preferable and 15% or less of the open cell rate of the foamed resin layer in this invention is more preferable. When the open cell ratio of the foamed resin layer exceeds the preferable 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 ratio of the foamed resin layer can be measured by the method according to the air pycnometer (air comparative specific gravity meter) method (1-1 / 2-1 atmospheric pressure method) defined 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 preferable lower limit value of the above range, the heat resistance and the formability of the foamed sheet may be reduced. When the apparent density of the foamed resin layer exceeds the preferable 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 in accordance with JIS K 6767.

0.5-3.0 mm is preferable, as for the thickness of the foamed resin layer in this invention, 0.5-2.5 mm is more preferable, and 1.0-2.5 mm is more preferable. If the thickness of the foamed resin layer is in the above range, the moldability becomes better.
In the present invention, the thickness of the foamed resin layer refers to the arithmetic mean value of the thickness of the five portions where the thickness of an arbitrary part of the foamed resin layer is measured at at least five locations.

75-300 g / m < ² > is preferable and, as for the basic weight of the foaming resin layer in this invention, 85-200 g / m < ² > is more preferable.
If the basis weight of the foamed resin layer is equal to or more than the preferable lower limit value 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 it tends to have buffer property.

5-30 times are preferable, as for the foaming ratio of the foaming resin layer in this invention, 8-26 times are more preferable, and 12-21 times are more preferable.
If the foaming ratio of the foamed resin layer is equal to or more than the preferable lower limit value of the above range, weight reduction of the foamed sheet becomes easy. If 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 the formability of the foamed sheet are further enhanced.

The foam sheet of the present invention has an average cell diameter of 190 to 400 μm, preferably 200 to 370 μm, and more preferably 200 to 360 μm. When the average cell diameter is at least the lower limit of the above range, the foamed sheet of the present invention is not only excellent in brittleness and easy to handle, but also effectively exerts the antibacterial property by the inorganic type antibacterial agent, The appearance and formability are good. When the average cell diameter of the foam sheet is equal to or less than the above-mentioned upper limit, the foam sheet becomes soft and it becomes difficult to cause cracking.
The average cell diameter means the average cell diameter (μm) of the foam sheet and can be measured by the following test method.
[Method of measuring average bubble diameter]
The average cell diameter of the polystyrene resin foam sheet is measured by the following test method.
A scanning electron microscope (cross section taken along a direction perpendicular to the sheet surface along a MD direction (extrusion direction) and a TD direction (direction orthogonal to the extrusion direction) of the polystyrene resin foam sheet is taken along a scanning electron microscope The image is magnified 18 times with Hitachi High-Technologies S-3400N or SU1510. At this time, the magnification of the electron microscope is adjusted so that the number of air bubbles present on the 60 mm straight line drawn on the printed image is about 10 to 20. The photographed image is printed on one sheet of A4 sheet oriented in the horizontal direction (an image of two fields of view from the cross section in the MD direction and an image of two fields of view from the cross section in the TD direction). In the case of the cross section in the MD direction, three straight lines (length 60 mm) parallel to the MD direction are drawn in each of the images of the two fields of view. In the case of the cross section in the TD direction, three straight lines (length 60 mm) parallel to the TD direction are drawn in each of the images of the two fields of view. Also, three straight lines parallel to the VD direction (the direction perpendicular to the MD direction or the TD direction, the sheet thickness direction), an image of one field of view in the MD direction cross section and an image of one field of view in the TD direction cross section Draw a length of 60 mm), and draw six 60 mm straight lines parallel to the MD, TD, and VD directions. The number of bubbles counted for six straight lines (length 60 mm) in each direction of MD, TD and VD is arithmetically averaged to obtain the number of bubbles in each direction. From the magnification of the image obtained by counting the number of bubbles and the number of bubbles, the average chord length (t) of the bubbles is calculated by the following equation.
Average chord length t (mm) = 60 / (number of bubbles × image magnification)
However, when the thickness of the test piece is thin and the number of bubbles of 60 mm in the VD direction (sheet thickness direction) can not be counted, the number of bubbles on a 30 mm or 20 mm straight line is used instead of the 60 mm long straight line. Convert to the number of bubbles on a straight line of 60 mm in length (for example, when there are 5 bubbles on a straight line of 30 mm in length, it is considered that there are 10 bubbles on a straight line of 60 mm in length ). The optional straight line allows the bubbles to penetrate as much as possible, rather than contacting the bubbles only at points. If some bubbles contact at a straight point, this bubble is also included in the number of bubbles. If the end point of the straight line is located in a bubble, this bubble is also included in the bubble number.
The magnification of the image is obtained by measuring the scale bar on the image to 1/100 mm with “Digimatic Caliper” manufactured by Mitutoyo Co., Ltd.
Image magnification = Scale bar actual value (mm) / Scale bar display value (mm)
And the bubble diameter in each direction was computed by following Formula.
Bubble diameter D (mm) = t / 0.616
Furthermore, the cube root of those products was made into the average bubble diameter.
Average bubble diameter (mm) = ( _DMD x _DTD x D _VD ) ^1/3
D _MD : Bubble diameter in the MD direction (mm)
D _TD : Bubble diameter in the TD direction (mm)
D _VD : Bubble diameter in the VD direction (mm)
If the MD direction (extrusion direction) or TD direction (direction orthogonal to the extrusion direction on the sheet surface) of the polystyrene resin foam sheet can not be specified, any one direction on the sheet surface is taken as the MD direction and MD on the sheet surface The direction orthogonal to the direction is taken as the TD direction. The value of the average bubble diameter is almost the same whether the direction can be identified or not.

<Polystyrene resin>
The foamed resin layer constituting the foamed sheet of the present invention contains a polystyrene resin.
Examples of polystyrene resins include polymers of styrene monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, isopropylstyrene, t-butylstyrene, dimethylstyrene and bromostyrene, or Copolymers of these styrenic monomers and monomers other than the styrenic monomers may be mentioned.
In addition, the polystyrene resin here does not contain conjugated diene as a monomer component.

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

Examples of monomers other than the above-mentioned styrenic monomers include vinyl monomers copolymerizable with styrenic monomers, such as 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, acrylamide Butadiene etc. are mentioned.
The above alkyl (meth) acrylate means alkyl acrylate or alkyl methacrylate.

When the polystyrene resin is a copolymer, 50% by mass or more based on the total amount (100% by mass) of the monomers used for the copolymer is preferably a styrene monomer. More preferably, it is 95 mass% or more, and 100 mass% may be sufficient.
When a vinyl monomer copolymerizable with a styrenic monomer is used as the copolymer, the compounding amount of the vinyl monomer is appropriately determined according to the application etc. of the foam sheet, for example, 5 mass% or less is preferable with respect to the total amount (100 mass%) of the monomer used for a polymer.

0.5-6.0 g / 10 minutes are preferable and, as for the melt flow rate (MFR) of polystyrene-type resin, 0.7-3.0 g / 10 minutes are more preferable.
When the MFR of the polystyrene resin is less than the preferable lower limit value of the above range, the thickness of the foamed resin layer may be nonuniform. If the MFR of the polystyrene resin exceeds the preferable upper limit of the above range, the expansion ratio of the foamed resin layer may be decreased.

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

The weight average molecular weight of the polystyrene resin is preferably 200,000 or more and 450,000 or less, and more preferably 300,000 or more and 400,000 or less.
When the weight average molecular weight of the polystyrene-based resin is less than the preferable lower limit value of the above range, a foamed resin layer having a high expansion ratio and a low open cell ratio becomes difficult to obtain. When the weight average molecular weight of the polystyrene resin exceeds the preferable upper limit value of the above range, the fluidity at the time of melting may be reduced, and the productivity may be reduced.

In the present invention, the weight average molecular weight of the resin is determined by dissolving 30 mg of resin in 10 ml of chloroform, filtering it through a non-aqueous 0.45 μm chromatography disk, and measuring the filtrate as a sample by chromatography, polystyrene equivalent Means a 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).
Column: Two “Shodex GPC K-806L (φ 8.0 × 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 microliters.
Standard polystyrene for calibration curve: trade name "shodex" manufactured by Showa Denko KK, weight average molecular weight 1030000; weight average molecular weight 5480000, 3840000, 355000, 102000, 37900, 9100, 2630, 495 manufactured by Tosoh Corporation.

As the polystyrene resin, those produced by known production methods can be used. For example, as a polystyrene resin, what was manufactured by the suspension polymerization method, the block polymerization method, the solution polymerization method, the emulsion polymerization method etc. is mentioned.
When polymerizing a styrenic monomer and a vinyl monomer optionally used in combination, 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-butyl peroxybenzoate, t-butyl peroxide, t-Butyl peroxy pivalate, t-butyl peroxy isopropyl carbonate, t-butyl peroxy acetate, 2,2-t-butyl peroxy butane, t-butyl peroxy-3,3,5 trimethylhexanoate, Organic peroxides such as di-t-butylperoxyhexahydro terephthalate; azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. The polymerization initiator may be used alone or in combination of two or more.

Moreover, when manufacturing a polystyrene-type resin, a crosslinking agent may be used at the time of superposition | polymerization. Examples of this crosslinking agent include divinylbenzene and the like. The crosslinking agents may be used alone or in combination of two or more.
The blending amount of the crosslinking agent is preferably more than 0 parts by mass and 1 part by mass or less with respect to 100 parts by mass of the total amount of monomers used for the polystyrene resin.

  A polystyrene resin may be used individually by 1 type, and 2 or more types may be combined and used.

<Inorganic antibacterial agent>
The polystyrene resin foam sheet of the present invention contains 2 to 8 parts by mass, preferably 3 to 8 parts by mass, more preferably 3 to 6 parts by mass of the inorganic antibacterial agent based on the total amount (100 parts by mass) of the resin component. Contains part.
Inorganic antibacterial agents include calcium compounds such as calcium carbonate, calcium oxide and calcium hydroxide; metals such as silver, zinc, copper, titanium and molybdenum; these metal ions, silica, zeolite, synthetic zeolite, zirconium phosphate, Supported on inorganic fine particles such as calcium phosphate, zinc calcium phosphate, ceramic, alumina silicon, titanium zeolite, apatite, calcium carbonate, etc .; Other inorganic oxides, complex oxides, etc. on the surface of inorganic compound particles by sol-gel method And those laminated or coated, etc. can be mentioned. Among these, calcium compounds are preferable, and calcium hydroxide is particularly preferable in view of high antibacterial property. Calcium hydroxide may be slaked lime obtained using limestone as a raw material, but it is included in shell fired product powder or eggshell fired product powder from the viewpoints of ease of handling, safety, effective use of resources, sustainability of antibacterial effect, etc. More preferred is calcium hydroxide. More preferably, it is calcium hydroxide contained in shell fired powder.

  The calcined shell material to be used as an inorganic antibacterial agent is not particularly limited, but it is not limited to scallops, spiny snails, flathead clams, asari, salmon, oysters, oyster shell, mussels, salmon, red shellfish, snail shells, It is preferable to use a powder of a baked product obtained by firing a shell of an edible shellfish such as an oyster, a sea bream, a salmon, a conch, a shellfish, and a shellfish. The fired eggshell powder is not particularly limited, but it is preferable to use a powder of a fired material obtained by firing eggshells of birds such as chickens and chicks, reptiles such as crocodiles and turtles.

  In the present embodiment, as the shell fired product powder, the shell which has been washed with water and the like to remove the deposit is fired at a temperature of about 800 to 1300 ° C. for about 3 to 6 hours. It is possible to use a powder that has been pulverized later or a powder that has been further subjected to a hydration treatment.

  In addition, as said shell-fired baked matter powder in this embodiment, there are few impurities other than a calcium carbonate, And the shell of the scallop which is industrially processed and discharged | emitted in large quantities as waste after extract | collecting an edible part It is particularly preferable from the viewpoint of environmental load reduction to use a powder of a baked scallop shell fired product, and it is preferable to adopt a shell fired product powder having a pH of 11 or more.

  The pH of this shell fired powder means a value determined by a method according to JIS Z 8802 by preparing a saturated aqueous solution of the shell fired powder, and it is preferable that the pH is 11 or more. When the powder exhibits strong alkalinity, the foamed molded article can be made excellent in sterilization and sterilization effects, and can be made excellent in antibacterial properties. The pH is more preferably 11.5 to 14 and particularly preferably 12 to 13.5.

In addition to calcium oxide and calcium hydroxide, trace amounts of metal elements such as zinc, iron, magnesium and the like are contained in this kind of shell fired product powder, and an antibacterial effect by the metal element can also be expected.
As a matter of course, the shell fired product powder may not sufficiently exhibit the antibacterial and deodorizing effects if it is contained in a very small amount in the expandable resin particles, but if it is contained excessively, the foamability and molding at the time of prefoaming It has the possibility of adversely affecting the fusion property of the pre-foamed particles at the time, and the lightness and mechanical properties of the finally obtained foam-molded product.
Accordingly, the amount of the shell fired material powder contained in the polystyrene resin foam sheet of the present invention from the viewpoint of exhibiting the excellent antibacterial / deodorant effect more reliably to the foam molded article excellent in lightness and mechanical properties. Usually, it is 2-8 mass parts with respect to 100 mass parts of said resin components, It is more preferable that it is 3-8 mass parts, It is especially preferable that it is 3-6 mass parts.

  As the inorganic antibacterial agent to be contained in the foamable resin particles, one having an average particle diameter of 0.1 to 40 μm can usually be adopted, preferably 0.1 to 20 μm, more preferably 0.1. Those having an average particle diameter of -15 μm can be employed. Here, the average particle size is a value measured using a laser diffraction / scattering particle size analyzer.

<Optional component>
The foamed resin layer constituting the foamed sheet of the present invention preferably has a complex viscosity of 4500 to 8500 Pa · s obtained by viscoelastic measurement under conditions of a temperature of 180 ° C. and a frequency of 1 Hz, and is 5000 to 8000 Pa · s. Is more preferable, and 5500 to 8000 are more preferable. When the complex viscosity is in this range, the foamed resin layer may contain other components (optional components) in addition to the polystyrene resin.
Examples of such optional components include resin components other than polystyrene resins, cell regulators, colorants, shrinkage inhibitors, flame retardants, lubricants, and antidegradants.
Examples of resin components other than polystyrene resins include rubber-modified polystyrene resins, hydrogenated polystyrene elastomers, polyethylene resins, and the like.

«Rubber-modified polystyrene resin»
The rubber-modified polystyrene resin in the present invention is a polymer alloy formed by mixing a conjugated diene polymer with a polystyrene resin, and a graft copolymer obtained by graft copolymerizing a conjugated diene polymer to a polystyrene resin. Each contains
The rubber-modified polystyrene-based resin has a sea-island structure in which particles (islands) composed of a conjugated diene-based polymer having a particle diameter of 0.3 to 10 μm are dispersed in a continuous phase (sea) of polystyrene-based resin Generally referred to as high impact polystyrene.
In the rubber-modified polystyrene resin, hydrogenation of the double bond of the conjugated diene polymer portion (conjugated diene block) is not performed.

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

The content of the styrene-based monomer unit in the rubber-modified polystyrene-based resin is preferably 75 to 99% by mass, and 80 to 97% by mass, with respect to the total amount (100% by mass) of the monomer units constituting the resin. % Is more preferable.
When the content of the styrenic monomer unit is less than the preferable lower limit value of the above range, the formability of the foam sheet may be reduced. When the content of the styrenic monomer unit exceeds the preferable 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 1.5 to 4.0 g / 10 minutes, and more preferably 2.5 to 4.0 g / 10 minutes.
If the MFR of the rubber-modified polystyrene resin is less than the preferable lower limit of the above range, the thickness of the foamed resin layer may be nonuniform. When the MFR of the rubber-modified polystyrene resin exceeds the preferable upper limit of the above range, the expansion ratio of the foamed resin layer may be decreased.
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 150,000 to 350,000, and more preferably 150,000 to 300,000.
If the weight average molecular weight of the rubber-modified polystyrene resin is less than the preferable lower limit value of the above range, the closed cell ratio of the foamed resin layer may be decreased, and the thickness of the foamed resin layer may be insufficient. When the weight average molecular weight of the rubber-modified polystyrene resin exceeds the preferable upper limit value of the above range, the fluidity at the time of melting may be reduced, and the productivity may be reduced.

  The rubber-modified polystyrene resin may be used singly or in combination of two or more.

«Hydrogenated polystyrene based elastomers»
The hydrogenated polystyrene elastomer in the present invention is a hydrogenated product of a styrene-conjugated diene block copolymer.
As a conjugated diene here, butadiene, isoprene, chloroprene etc. are mentioned, and butadiene is preferable.

  Examples of hydrogenated polystyrene elastomers include styrene / butadiene block copolymer (SBR), styrene-ethylene / butadiene-styrene (SEBS) block copolymer, styrene-butadiene / butylene-styrene (SBBS) block copolymer Is preferably mentioned.

The hydrogenation rate of the double bond of the conjugated diene block in the hydrogenated polystyrene elastomer is preferably 60 to 95 mol%, more preferably 65 to 95 mol%.
If the hydrogenation rate is within the above range, the flexibility of the foamed sheet can be enhanced by using a hydrogenated polystyrene elastomer. For example, when transporting a fruit vegetable in a recess of a fruit vegetable packaging container formed by forming a foam sheet, the fruit vegetable is subjected to an impact force such as vibration during transportation while the fruit vegetable contained in the recess is transported, Since there is no rotation (ball rotation) in the recess, the fruit can be prevented from being damaged.

The hydrogenation rate of the conjugated diene block in the hydrogenated polystyrene elastomer can be measured according to the procedure shown below.
Procedure 1) A ¹ H-NMR spectrum of a resin to be measured is obtained using a nuclear magnetic resonance apparatus.
Procedure 2) Calculate the amount of hydrogenated conjugated diene (the amount of hydrogenated conjugated diene) and the amount of non-hydrogenated conjugated diene (the amount of non-hydrogenated conjugated diene) based on the above ¹ H-NMR spectrum Do.
Procedure 3) From the above-mentioned amount of conjugated diene and the amount of unhydrogenated conjugated diene, the hydrogenation rate is calculated from the following equation.
Hydrogenation rate (mol%)
= 100 x (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 Nippon Denshi Co., Ltd.
Measurement nucleus: ¹ H.
Observation range: 8000 (20 ppm).
Pulse width: 45 ° (9.0 μsec).
Pulse interval: 9 seconds.
The number of measurements: 2400 times.
Setting temperature: 55 ° C.
Measurement solvent: CDCl ₃ .
Measurement concentration: 50 mgr / 0.4 mL.
Internal reference material: tetramethylsilane (TMS).

90 or less is preferable and, as for the durometer type A hardness (HDA) of a hydrogenation polystyrene-type elastomer, 50-90 are more preferable.
If the durometer type A hardness (HDA) is equal to or less than the preferable upper limit of the above range, the flexibility of the foam sheet is further enhanced. For example, fruit and vegetable stored in the recess of the container for fruit and vegetable packaging formed by forming a foam sheet are less likely to cause friction with the recess, 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 elastomer refers to a value measured by the method according to JIS K7215.

The melt flow rate (MFR) of the hydrogenated polystyrene elastomer is preferably 2 to 20 g / 10 min, and more preferably 3 to 15 g / 10 min.
When the MFR of the hydrogenated polystyrene elastomer is less than the preferable lower limit of the above range, the thickness of the foamed resin layer may be nonuniform. When the MFR of the hydrogenated polystyrene elastomer exceeds the preferable upper limit of the above range, the expansion ratio of the foamed resin layer may be decreased.
In the present invention, the MFR of the hydrogenated polystyrene elastomer is in accordance with JIS K 7210: 1999 "Plastics-Test methods for melt mass flow rate (MFR) and melt volume flow rate (MVR) of thermoplastics" method B. The test temperature is 230 ° C, the test load is 21.17 N, and the preheating time is 4 minutes.

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

  The hydrogenated polystyrene elastomer may be used singly or in combination of two or more.

«Polyethylene resin»
In the foam sheet of the present invention, when the foam resin layer contains a polyethylene resin, the flexibility of the foam sheet is enhanced, and for example, the fruits and vegetables contained in the recess of the fruit vegetable packaging container formed by molding the foam sheet. It becomes difficult to get hurt.
As a 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-based resin contains an ethylene-based monomer unit. The ethylenic monomer unit is a monomer unit derived from a chain unsaturated hydrocarbon (for example, ethylene, 1-butene, etc.) having a double bond.

0.1-5 g / 10 minutes are preferable and, as for the melt flow rate (MFR) of polyethylene-type resin, 0.4-4 g / 10 minutes are more preferable.
When the MFR of the polyethylene-based resin is less than the preferable lower limit value of the above range, the fluidity at the time of melting may be reduced, and the productivity may be easily reduced. When the MFR of the polyethylene-based resin exceeds the preferable upper limit value of the above range, the foamability or the moldability may be reduced, or the compatibility with polystyrene may be deteriorated.
In the present invention, the MFR of the polyethylene-based resin conforms to the method described in JIS K 7210: 1999 “Test method for melt mass flow rate (MFR) and melt volume flow rate (MVR) of plastic-thermoplastic”, The value measured under the conditions of test temperature 190 ° C, test load 21.17N and preheating time 4 minutes.

50,000-300,000 are preferable and, as for the weight average molecular weight of polyethylene-type resin, 100,000-200,000 are more preferable.
When the weight average molecular weight of the polyethylene-based resin is less than the preferable lower limit value of the above range, a foamed resin layer having a low open cell ratio may be difficult to obtain. When the weight average molecular weight of the polyethylene-based resin exceeds the preferable upper limit value of the above range, the fluidity at the time of melting may be reduced, and the productivity may be reduced.

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

In the polystyrene-based resin foam sheet of the invention, the foamed resin layer preferably contains a resin component having a styrene-based monomer unit and an ethylene-based monomer unit from the viewpoint of imparting flexibility.
The absorbance ratio (D698 / D2850) of the foamed resin layer is preferably 7.0 to 15.0, more preferably 8 from the viewpoint of the balance between flexibility, strength, heat resistance and moldability of the foamed sheet. 0.1 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 value of the above range, the heat resistance of the foam 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 foam sheet is further enhanced.
In the present invention, the absorbance ratio (D698 / D2850) of the foamed resin layer is measured by infrared spectroscopy (IR). The absorbance ratio (D698 / D2850) means the ratio of the absorbance at 698 cm ^-1 derived from styrenic monomer units (D 698) to the absorbance at 2850 cm ^-1 derived from ethylene monomer units (D 2850) . Specifically, it can be determined by the method described in the examples below.

In addition to the resin component, the foamed resin layer preferably further contains a cell regulator. By containing the cell regulator, it is easy to obtain a foam sheet having a low open cell ratio and good moldability.
Examples of the cell regulator include inorganic fillers such as talc, mica, mica, montmorillonite and the like.
The cell regulator may be used alone or in combination of two or more.
0.5-5 mass parts is preferable with respect to 100 mass parts of resin components, and, as for content of the foam | bubble regulator in a foaming resin layer, 0.5-3 mass parts is more preferable.

The complex viscosity of the foamed resin layer in the present invention is preferably 4500 to 8500 Pa · s, more preferably 5000 to 8000 Pa · s, and still more preferably 5500 to 8000 Pa.s. s. In the present invention, the complex viscosity is determined by viscoelastic measurement under conditions of a temperature of 180 ° C. and a frequency of 1 Hz.
If the complex viscosity of the foamed resin layer is at least the lower limit value of the above range, the flexibility of the foamed sheet is enhanced. If the complex viscosity of the foamed resin layer is equal to or less than the upper limit value of the above range, heat resistance is easily maintained, and molding defects are less likely to occur.
The complex viscosity of the foamed resin layer is controlled, for example, by adjusting the composition of the resin component. Specifically, the complex viscosity of the foamed resin layer is determined by the method described in the below-mentioned Examples.

(Production method of polystyrene resin foam sheet)
The method for producing a polystyrene resin foam sheet according to the present invention is a method for producing a polystyrene resin foam sheet according to the present invention described above, comprising: a raw material composition containing a resin component containing a polystyrene resin; This is a method of melt-kneading, extruding and foaming a masterbatch containing an antibacterial agent and a foaming agent.

The masterbatch preferably contains the inorganic antibacterial agent in an amount of 40 to 70 parts by mass, more preferably 45 to 70 parts by mass, and still more preferably 45 to 65 parts by mass with respect to 100 parts by mass of the polyethylene resin. As the inorganic antibacterial agent in the master batch, the same one as described above can be used.
Although there is no restriction | limiting in particular about the shape of a masterbatch, For example, it can be set as the shape of a pellet. Moreover, there is no restriction | limiting in particular also about the manufacturing method of a masterbatch, It can manufacture by a well-known method. For example, the particles of the inorganic antibacterial agent and the polyethylene resin are melt-kneaded using a twin-screw extruder, extruded in the form of strands (round cords), the strands are passed through a water tank and cooled, and then a pelletizer is used. It can be manufactured by the method of cutting.
Regarding the twin-screw extruder, L / D, which is the ratio of screw length L (mm) and screw diameter D (mm), satisfies the relationship of 30 <(L / D) <60. Preferably, 30 <(L / D) <50 is more preferably satisfied. Moreover, it is preferable that it is 190-240 degreeC, and, as for the melting temperature of resin at the time of melt-kneading, it is more preferable that it is 190-220 degreeC. If the melting temperature is less than 190 ° C., the melting is insufficient and the unmelted gel tends to occur frequently. If the temperature exceeds 240 ° C., the resin composition is thermally deteriorated and easily colored.

It is preferable that it is 60-140 rpm, and, as for screw rotation speed at the time of melt-kneading, 80-120 rpm is more preferable. When the screw rotation speed is less than 60 rpm, the particles of the inorganic antibacterial agent tend to be hardly dispersed in the polyethylene resin, and when it exceeds 140 rpm, the load on the extruder may increase, which is not preferable.
The shape of the pellet thus produced is preferably 1.0 to 3.0 mm in diameter, more preferably 1.5 to 3.0 mm, still more preferably 2.0 to 3.0 mm in the case of a cylindrical shape. The length is preferably 2.0 to 5.0 mm, more preferably 2.0 to 4.0 mm, still more preferably 2.0 to 3.5 mm.

  The weight-average molecular weight of the polyethylene-based resin contained in the polyethylene-based resin composition is preferably 70,000 to 150,000, more preferably 80,000 to 140,000, and still more preferably 90,000 to 120,000. It is further preferred that When the weight average molecular weight is at least the above lower limit value, a polystyrene resin foam sheet excellent in mechanical properties can be easily obtained, and when the weight average molecular weight is at most the above upper limit value, the polystyrene resin foam sheet can be produced. It is easy to improve the formability.

  As a suitable manufacturing method of a polystyrene resin foam sheet, the manufacturing method of a well-known foam sheet can be employ | adopted, for example, the manufacturing method (A) and the manufacturing method (B) which are shown below are mentioned. Among these, as a manufacturing method of this polystyrene resin foam sheet, a manufacturing method (A) is more preferable from the point of extrusion foamability and a thermoforming property.

Production method (A):
Supply extruder with a resin composition containing polystyrene resin (and resin other than this), a raw material composition containing other components, a masterbatch containing polyethylene resin and inorganic antibacterial agent, and a physical foaming agent The mixture is melt-kneaded, extruded and foamed from a circular die attached to the tip of the extruder to obtain a cylindrical foam, and then the cylindrical foam is expanded and then supplied to a mandrel. A method of producing a polystyrene resin foam sheet by continuously cutting and developing a cylindrical foam in the extrusion direction across the inner and outer peripheral surfaces after cooling.

Production method (B):
The raw material composition, the masterbatch, and the chemical foaming agent are melt-kneaded in an extruder, and then extruded from a T-die attached to the tip of the extruder to produce a foamable sheet, and this foamable sheet is prepared A method of producing a polystyrene resin foam sheet by heating and foaming.

The physical blowing agent in the production method (A) 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 blowing agents may be used alone or in combination of two or more.
2-7 mass parts is preferable with respect to 100 mass parts of raw material compositions, and, as for the compounding quantity of a physical foaming agent, 2-6 mass parts is more preferable.

In the production method (B), the chemical blowing agent is not particularly limited, and examples thereof include azodicarbonamide and the like.
The chemical blowing agents may be used alone or in combination of two or more.
2-7 mass parts is preferable with respect to 100 mass parts of raw material compositions, and, as for the compounding quantity of a chemical foaming agent, 2-6 mass parts is more preferable.

45-85 mass% is preferable with respect to the total amount (100 mass%) of a resin component, and, as for the compounding quantity of polystyrene-type resin, 50-70 mass% is more preferable.
If the blending amount of the polystyrene-based resin is equal to or more than the preferable lower limit value of the above range, the heat resistance of the foam sheet is enhanced, and the moldability is further enhanced. If the blending amount of the polystyrene-based resin is equal to or less than the preferable upper limit of the above range, the flexibility of the foam sheet is easily maintained.

When a rubber-modified polystyrene resin is used as a resin component other than a polystyrene resin, the compounding amount of the rubber-modified polystyrene resin is preferably 0 to 30% by mass with respect to the total amount (100% by mass) of the resin component. 30 mass% is more preferable, and 10 to 25 mass% is more preferable.
When the blending amount of the rubber-modified polystyrene resin is equal to or more than the preferable lower limit value of the above range, an impact force such as vibration applied to the foam sheet is easily absorbed. When the blending amount of the rubber-modified polystyrene resin is not more than the preferable upper limit value of the above range, the rubber-modified polystyrene resin is less likely to be aggregated, and the appearance of the foam sheet is further improved.

The compounding ratio of the polystyrene resin (PS resin) to the rubber modified polystyrene resin (rubber modified) is also expressed as a mass ratio represented by polystyrene resin / rubber modified polystyrene resin (hereinafter also referred to as “PS resin / rubber modified”). ) Is preferably 1.5 to 14.0, and more preferably 1.5 to 7.0.
When the PS system / rubber modification is at least the preferable lower limit value of the above range, the flexibility of the foamed sheet is easily maintained. If the PS system / rubber modification is not more 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.

When using a hydrogenated polystyrene-based elastomer as a resin component other than a polystyrene-based resin, the blending amount of the hydrogenated polystyrene-based elastomer is preferably 5 to 20% by mass with respect to the total amount (100% by mass) of the resin component. 20 mass% is more preferable.
The flexibility of the foamed sheet is easily maintained when the blending amount of the hydrogenated polystyrene-based elastomer is equal to or more than the preferable lower limit value in the above range, and for example, the foamed sheet is accommodated in the recess of the fruit vegetable packaging container Fruity vegetables are less likely to be damaged. The heat resistance of a foaming sheet becomes it easy to be maintained as the compounding quantity of a hydrogenation polystyrene-type elastomer is below the preferable upper limit of the said range, and a moldability also improves more.

The blending ratio of the polystyrene resin (PS) to the hydrogenated polystyrene elastomer (hydrogenated) is also expressed as a mass ratio represented by polystyrene resin / hydrogenated polystyrene elastomer (hereinafter also referred to as "PS based / hydrogenated"). 2.0 to 5.0 is preferable, and 2.5 to 5.0 is more preferable.
When the PS system / hydrogenation is at least the preferable lower limit value of the above range, the heat resistance of the foam sheet is easily maintained, and the flexibility is further improved. If the PS system / hydrogenation is not more than the preferable upper limit value of the above range, the compatibility between the polystyrene resin and the polyethylene resin is further enhanced, and the foamability and the thermoforming property are further improved.

When using polyethylene-type resin as resin components other than a polystyrene-type resin, 5-15 mass% is preferable with respect to the total amount (100 mass%) of a resin component, and 5-10-5 mass% of polyethylene-type resin is blended. More preferable.
When the blending amount of the polyethylene-based resin is equal to or more than the preferable lower limit of the above range, the flexibility of the foam sheet is easily maintained, and for example, the fruits and vegetables contained in the recess of the vegetable packaging container formed by molding the foam sheet It becomes hard to hurt. The heat resistance of a foaming sheet becomes it easy to be maintained as the compounding quantity of a polyethylene-type resin is below the preferable upper limit of the said range, and a moldability also improves more.

The blending ratio of the polystyrene resin (PS) to the polyethylene resin (PE) is 4 by the mass ratio represented by polystyrene resin / polyethylene resin (hereinafter also referred to as “PS system / PE system ratio”). 0 to 50.0 are preferable, and 7.0 to 15.0 are more preferable.
If the PS-based / PE-based ratio is equal to or more than the preferable lower limit value of the above range, the formability of the foam sheet is 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 foam sheet is easily maintained.

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

[Measurement condition]
· Heating (590 ° C-5 sec)
・ Oven temperature (300 ° C)
・ Needle temperature (300 ° C)
・ Column (Inter Cap 5 (φ 0.25 mm × 30 m (film thickness 0.25 μm): GL Science Inc.))
Temperature conditions (Hold at 50 ° C. for 0.5 minutes, then heat up to 200 ° C. at 10 ° C./min, then heat up to 320 ° C. at 20 ° C./min, hold at 320 ° C. for 0.5 minutes)
・ Carrier gas (He)
・ He flow rate (25 ml / min)
・ Inlet pressure (100 KPa)
・ Inlet temperature (300 ° C)
・ Detector temperature (300 ° C)
Split ratio (1/30)
The standard sample for preparation of a standard curve is POLYSCIENCES. It is preferred to use INC St / BD = 85/15 (CAT # 07073) resin.

The raw material composition contains a resin component containing a polystyrene resin.
It is also preferable that the resin component contains a polystyrene-based resin, a hydrogenated polystyrene-based elastomer, and one or more selected from the group consisting of a polyethylene-based resin and a rubber-modified polystyrene-based resin.

  As the raw material composition (resin component), since the effect of the present invention is further enhanced, 45 to 85 mass% of polystyrene resin and hydrogenated polystyrene compound are included with respect to the total amount (100 mass%) of the resin component. Those containing 5 to 20% by mass of elastomer, 5 to 15% by mass of polyethylene resin, and 0 to 30% by mass of rubber modified polystyrene resin are preferable. However, the total of these resins does not exceed 100% by mass.

  It is preferable that the compounding quantity of the said masterbatch is 5-15, More preferably, it is 7-15, More preferably, it is 7-13. When the blending amount of the master batch is equal to or more than the above lower limit value, a polystyrene resin foam sheet having sufficient antibacterial properties can be easily obtained. When the blending amount of the masterbatch is equal to or less than the above upper limit value, a polystyrene resin foam sheet having sufficient moldability can be obtained.

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

(Molded body)
The molded article of the present invention is formed by molding the polystyrene resin foam sheet of the present invention into a desired shape using a known molding method or the like.
Examples of the 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 forming, straight forming, drape forming, reverse draw forming, air slip forming, plug assist forming, plug assist reverse draw forming Etc.
The molded product of the present invention has enhanced flexibility and good heat resistance, and for example, a sheet-like cushioning material, a container for packaging electric home appliances, a container for packaging machine parts, a container for confectionery packaging, fruit packaging The container is used as a container such as a container, but is particularly useful as a container for packaging fruits and vegetables having a plurality of recesses formed on one side of the sheet for containing the vegetables. In addition, the polystyrene resin foam sheet of the present invention is not only used as various containers, but is cut by, for example, a punching blade, etc., and used as a partition material, interleaf paper, etc. It can also be suitably used.

FIG. 1 shows one embodiment of the container of the present invention, and FIG. 2 is a cross-sectional view taken along the line X-X of FIG.
The container (container for packaging fruits and vegetables) 10 of the present embodiment is, for example, for containing fruits and vegetables such as apples, pears and peaches.
The container 10 is substantially rectangular in a plan view, and is formed with twelve concave portions 12 which are opened on one surface 10 a of the sheet and which expand in a semispherical shape on the other surface 10 b of the sheet.
One recess 12 is sized to fill about half of one fruit and vegetable.
As shown in FIG. 2, partition portions 15 are formed between adjacent concave portions 12. The partition part 15 consists of each surrounding wall 12b of the recessed part 12 which adjoins, and the connection part 14 provided between the recessed parts 12. As shown in FIG.
At the center of the inner bottom surface of the recess 12, a protrusion 12a is formed which protrudes in the direction of the opening surface 10a and which follows the recess of the fruit.

  The container 10 is manufactured by thermoforming the polystyrene resin foam sheet of the present invention described above into a predetermined shape.

  When fruits and vegetables are accommodated in the recess 12, about the lower half of the fruits and vegetables is buried in the recess 12. The flexibility of the container 10 is enhanced, and the peripheral wall 12b of the recess 12 is in contact with the fruit vegetable so that the fruit can be stably accommodated in the recess 12 in close contact with the peripheral wall 12b.

When a fruit vegetable having a size larger than the opening diameter of the recess is accommodated in one of the adjacent recesses, in the conventional container, the recess containing the fruit vegetable having a large size has a large volume, and the opening expands. Accordingly, the partition portion falls into the other recess, the opening of the other recess is narrowed, and it is difficult to accommodate the fruits and vegetables in the other recess.
In the container 10 of the present embodiment, since the flexibility of the peripheral wall 12b and the connection portion 14 (partition portion 15) is enhanced, the opening portion of the concave portion 12 is obtained even when such large-sized fruit vegetables are accommodated in the concave portion 12 The partition portion 15 is compressed as the As a result, the volume of the other adjacent recess is maintained and the opening does not narrow. For this reason, it is possible to easily accommodate fruits and vegetables in the adjacent recesses 12 respectively.

  In addition, the foamed resin layer constituting the container 10 may be appropriately elastically deformed as the flexibility is enhanced. For this reason, the fruits and vegetables stored in the recess 12 in close contact with the peripheral wall 12b are less likely to produce balls and the like even when subjected to an impact force such as vibration during transportation or storage, and the fruits are less damaged.

Hereinafter, the present invention will be described in detail by way of examples, but the present invention is not limited by the following description.
Raw materials used in this example are shown below.

<Resin component>
Polystyrene A (MFR: 2.3 g / 10 min, weight average molecular weight: 340,000, product name: HRM 48 N, manufactured by Toyo Styrene Co., Ltd.).
Polystyrene B (MFR: 1.5 g / 10 min, weight average molecular weight: 320,000, product name: G9305, manufactured by PS Japan Co., Ltd.).
Polystyrene C (MFR: 1.2 g / 10 min, weight average molecular weight: 587,000, product name: HP555, manufactured by DIC Corporation).

  Polyethylene-based resin (very 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 (styrene-ethylene / butadiene-styrene block copolymer, hydrogenation rate: 95 mol%, resilience modulus: 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 about the above-mentioned raw material was measured as follows.

[Durometer Type A Hardness]
The durometer type A hardness of the hydrogenated polystyrene elastomer was measured by a method based on JIS K7215 using a durometer ASKER A type (manufactured by Kobunshi Keiki Co., Ltd.) and a constant pressure load device to which a load of 10 N is applied.
Specifically, 12 flat rectangular test pieces of 30 mm long × 50 mm wide × 4 mm thick made of a hydrogenated polystyrene-based elastomer are prepared, two of them are stacked, and a measurement sample having a thickness of 8 mm is measured. Individually produced.
For each measurement sample, the value of durometer type A hardness (HDA) was measured six times to calculate the arithmetic mean value.

  Rubber-modified polystyrene-based resin (styrene-based monomer unit: 94% by mass, MFR: 3.1 g / 10 min, weight average molecular weight: 240,000, product name: E641N, manufactured by Toyo Styrene Co., Ltd.).

<Inorganic antibacterial agent>
・ Calcined shell powder (Scallop shell calcined product, average particle size: 7 μm, pH of saturated aqueous solution = 13, Product name: Scarow, manufactured by Antibacterial Research Institute, Inc.)

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

Example 1
[Preparation of master batch (master pellet)]
The above-described calcined shell powder and the above-mentioned polyethylene resin are supplied to a twin screw extruder (L / D = 47) with a diameter of 30 mm, and melt-blended in a twin screw extruder at a resin temperature of 200 ° C. and a rotational speed of 100 rpm. The melt-kneaded product was extruded in the form of a strand (round cord) at a discharge rate of 10 kg / h from a die of 4 mm in diameter, 5 mm in land, and 2 holes with 2 holes attached to the tip of a twin-screw extruder.
Next, the extruded melt-kneaded product (string-like body) is passed through a 2 m-long cooling water tank containing water at 30 ° C., cooled, and cut by a pelletizer to contain 60% by mass of shell fired product The master pellet was made.

[Production of polystyrene-based resin foam sheet]
Resin components including polystyrene A, polyethylene-based resin, hydrogenated polystyrene-based elastomer A, and rubber-modified polystyrene-based resin A, the above-mentioned master pellet, and talc as a cell regulator, are mixed at the ratio shown in Table 1 The raw material mixture was prepared.
Next, the raw material mixture is supplied to an extruder, and the mixture is melt-kneaded to a maximum temperature of 230 ° C., and butane gas (isobutane / normal butane = 68/32 (mass) as a physical blowing agent in the molten raw material mixture. Ratio)) 5.3 parts by mass (relative to 100 parts by mass of the raw material mixture) was injected, and butane gas was uniformly dispersed in the raw material mixture.
Thereafter, the raw material mixture is cooled to a temperature of 149 ° C., and extruded and foamed with a clearance of 0.25 mm from a 200 mm diameter circular die attached to the tip of the extruder to obtain a cylindrical foam. I got Subsequently, the cylindrical foam was expanded in diameter, supplied to a cooling mandrel, and cooled.
After cooling, the cylindrical foam is continuously cut in the extrusion direction and developed between the inner and outer peripheral surfaces at two locations opposed in the diameter direction, so that two polystyrene resin foam sheets are obtained. Obtained.

(Examples 2 to 5 and Comparative Examples 1 to 5)
A polystyrene resin foam sheet was produced in the same manner as in Example 1 except that the composition of the master pellet and the blending ratio of each component were changed as shown in Tables 1 and 2. Moreover, the master pellet used in Comparative Example 3 and Comparative Example 4 was prepared using polystyrene resin (polystyrene B) instead of polyethylene resin.
In Tables 1 and 2, the blending amounts of the respective components are represented by mass%. Talc is expressed in parts by mass (phr) based on 100 parts by mass of the resin component.

Average cell diameter, complex viscosity (Pa · s), thickness (mm), basis weight (g / m ² ), expansion ratio (fold), absorbance ratio (D698 / D2850), for the polystyrene resin foam sheet produced The styrenic monomer content was determined respectively. In addition, heat resistance, flexibility, and moldability were evaluated for the produced polystyrene resin foam sheet.
The above results are shown in Tables 1 and 2.

[Complex viscosity of polystyrene resin foam sheet]
With respect to the foam sheet, dynamic viscoelasticity measurement was performed by combining a viscoelasticity measuring apparatus “PHYSICA MCR301” manufactured by Anton Paar, a temperature control system “CTD450” and software “Leoplus”, and complex viscosity (粘度 *) was determined. .
Specifically, dynamic viscoelasticity measurement was performed according to the following procedure.
The raw material composition used for the production of the foam sheet or a sample collected from the foam sheet was heated at 150 ° C. for 5 minutes with a heat press, under a press pressure (10 MPa), with a press frequency of 5 times, a diameter of 25 mm , A disc-shaped sample of 3 mm in thickness was produced.
Next, the sample was set on a plate of a viscoelasticity measuring device heated to a measurement start temperature of 200 ° C., and allowed to melt for 5 minutes under a nitrogen atmosphere.
Then, the space | interval was crushed to 2.0 mm with the parallel plate of diameter 25 mm, and the molten material which overflowed from the plate was removed.
Furthermore, after leaving for 5 minutes after reaching the measurement start temperature of 200 ± 1 ° C, the condition of strain 5%, frequency 1 Hz, temperature decrease rate 2 ° C / minute, measurement interval 30 seconds, normal force 0 N, measurement temperature 200 to 100 ° C The complex viscosity ** (Pa · s) was measured below, and the complex viscosity η * (Pa · s) value at 180 ° C was read.
The measured complex viscosity ** (Pa · s) values are shown in Tables 1 and 2 as “complex viscosity (Pa · s)”.

[Thickness of polystyrene resin foam sheet]
The thickness (mm) of the foam sheet was determined by measuring the thickness of an arbitrary part of the foam sheet at five locations and calculating the arithmetic mean of the thicknesses at the five locations.

[Basic weight of polystyrene resin foam sheet]
The basis weight of the foam sheet was determined as follows.
Ten pieces of 10 cm × 10 cm were cut at equal intervals in the width direction except for 20 mm at both ends in the width direction of the foam sheet, and the mass (g) of each piece was measured to 0.001 g unit. A value of the average value was converted into mass per 1 m ² of the mass (g) of each section, and the basis weight of the foam sheet (g / m ^2).

[Expansion ratio of polystyrene resin foam sheet]
The expansion ratio (fold) of the foam sheet was determined as follows.
The size (area: S) and thickness (t) of a sample obtained by cutting a foam sheet into a predetermined size are measured and multiplied by these to obtain the apparent volume of the sample (V = S × t (cm ^3). ) Was determined, and the apparent density (d = M / V (g / cm ³ )) of the foamed sheet was calculated from this and the mass of the sample (M (g)).
Then, the density of the mixed resin forming the foam sheet (ρ: 1.05 g / cm ³ ) is divided by the apparent density (d) of the foam sheet to determine the foam magnification (fold) of the foam sheet. The
Expansion ratio (fold) = 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 foam sheet was determined as follows.
The surface of the foam sheet (foamed resin layer) of each of the three randomly selected samples was subjected to surface analysis by an infrared spectroscopy ATR measurement method to obtain an infrared absorption spectrum.
The absorbance ratio (D698 / D2850) was calculated from each infrared absorption spectrum, the arithmetic mean of the calculated absorbance ratio was determined, and this was taken as the absorbance ratio (D698 / D2850) of the foam sheet.
The absorbance (D698) and the absorbance (D2850) are respectively the measuring instruments sold by Nicolet under the trade name “Fourier Transform Infrared Spectrophotometer MAGN-560”, and “The Thunder Dome made by Spectra-Tech as an ATR accessory. It connected and measured.

ATR-FTIR measurement was performed under the following conditions.
High refractive index crystal species: Ge (germanium).
Incident angle: 45 ° ± 1 °.
Measurement area: 4000 cm ^{−1 to} 675 cm ⁻¹ .
Fractional dependence of measurement depth: No correction.
Number of reflections: 1 time.
Detector: DTGS KBr.
Resolution: 4 cm ⁻¹ .
Integration count: 32 times.
Others: The infrared absorption spectrum measured without contacting with the sample is used as the background to perform processing that does not involve the measurement spectrum.
In the ATR method, the intensity of the infrared absorption spectrum obtained varies 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 “Animation ATR accessory”, and the degree of adhesion was controlled almost uniformly and the measurement was performed. The foam sheet was used without pre-treatment and was set on a sander dome to perform such measurements.

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

The absorbance at 698 cm ⁻¹ (D 698) obtained from the infrared absorption spectrum is an absorbance corresponding to an absorption spectrum derived from out-of-plane bending vibration of the benzene ring contained in the styrenic monomer unit. In this measurement of absorbance, no peak separation was performed even when other absorption spectra 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 (D2850) at 2850 cm ⁻¹ obtained from the infrared absorption spectrum is an absorbance corresponding to the absorption spectrum derived from the C—H stretching vibration contained in the ethylene-based monomer unit. In this measurement of absorbance, no peak separation was performed even if other absorption spectra overlapped at 2850 cm ⁻¹ . Absorbance (D2850) is a straight line connecting the 3130Cm ^-1 and 2620cm ^-1 as a baseline, it 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).

[Heat resistance of polystyrene resin foam sheet]
Five pieces of 10 cm × 10 cm pieces are cut out from the foam sheet of each example, 5 pieces of the pieces are stacked, and further, at 70 ° C. with two aluminum plates of the same size of about 1 mm in thickness sandwiched vertically. Placed horizontally in the set oven. Next, a 5 kg weight was placed on the upper aluminum plate and heated in that state for 24 hours.
Then, it took out from oven and the peelability (fusion peelability) of the sections (foamed sheet) was investigated. The stacked five sections (foamed sheet) are peeled off one by one, and the degree of peeling at that time is judged in four stages of 基準, 段 階, Δ, and × according to the following evaluation criteria, and the heat resistance of the foamed sheet Was evaluated.
Evaluation criteria ◎: The sections peel off with little force, and there is almost no sound (very good).
:: A slight force is required to start peeling the sections, but after the sections start to peel, almost no sound is generated and no force is required (more favorable).
Fair: A sound like crispness is produced when the sections are peeled off, but not so much force is required to peel the sections (good).
X: When the sections are peeled off, a buzzing sound is generated, and the sections do not separate unless a force is applied (defect).

[Flexibility of polystyrene resin foam sheet]
A partial compression test was conducted as follows using Tensilon UCT-10 manufactured by ORIENTEC Co., Ltd. to evaluate the flexibility of the foamed sheet.
The foamed sheet was cut into 50 mm × 50 mm and used as a sample sample.
A partial compression test is carried out by using a load cell with a maximum load of 25 kgf and measuring the partial compression displacement amount, mounting a straight rod shaped push jig with a diameter of 20 mm and a length of 25 mm with a hemispherical tip of R = 10 mm on the load cell. went.
The four sample samples described above were stacked, and the four stacked sample samples were set in close contact with the measuring instrument loading platform so that no gap was created in the measuring instrument loading platform. The thickness at this time was taken as the measurement sample thickness (unit: mm).
The pressing jig was lowered at a speed of 10 mm / min to compress the sample sample, with the lower end of the pressing jig in contact with the upper end in the thickness direction of the sample as the base point.
At that time, the displacement (mm) from the base point of the jig at a load of 1 kgf on the sample sample was taken as the partial compression displacement amount at a load of 1 kgf of the sample sample. The average of measured values of 5 samples was taken as the partial compression displacement amount (unit: mm) under 1 kgf load of the sample.
And the softness | flexibility (%) of the foamed sheet was calculated | required by the following Formula.
Flexibility (%) = Partial compression displacement of sample sample under 1 kgf load (unit: mm) / Measurement sample thickness (unit: mm) x 100
The higher the value of this flexibility (%), the higher the flexibility of the foam sheet.
Evaluation criteria ◎: The flexibility is 13% or more, which is extremely good.
Good: Flexibility is 11% or more and less than 13%.
:: The flexibility is 9% or more and less than 11%, and is somewhat poor.
X: The flexibility is less than 9% and defective.

[Moldability of polystyrene-based resin foam sheet]
Using the mold having 12 recesses with an opening diameter of 100 mm and a depth of 40 mm, the temperature in the heating furnace is set to 130 ° C., the foam sheet is thermoformed, and the container for fruit vegetable packaging of the embodiment shown in FIG. I got
Then, the state of the surface of the formed body and the thickness of the formed body were observed, and the formability of the foam sheet was evaluated according to the following evaluation criteria.
Evaluation criteria A: No defect was observed on the surface of the molded product and the thickness of the molded product (very good).
○: Almost no defects were observed on the surface of the molded product and the thickness of the molded product (good).
Fair: No defect was found on the surface of the molded product, but a part where the thickness of the molded product was thin was partially observed (slightly poor).
X: The surface of the molded product was in a state of heat burnt, tearing occurred, or only a thin molded product with insufficient thickness was obtained (defect).

[Antibacterial property of polystyrene resin foam sheet]
According to JIS Z 2801 (2010), an antibacterial test was carried out as a bacterium used for the test in S. aureus and E. coli.
The higher the antimicrobial activity value obtained by this test method, the higher the antimicrobial activity. The antimicrobial properties of the foam sheet were evaluated according to the following evaluation criteria.
Evaluation criteria ◎: The antibacterial activity value of E. coli and S. aureus also exceeds 3.0 (very good).
○: E. coli and Staphylococcus aureus both have antibacterial activity values of 2.0 to 3.0 (good).
Δ: only one of E. coli and S. aureus has an antibacterial activity of 2.0 or more (slightly poor).
X: E. coli and Staphylococcus aureus both have antibacterial activity values less than 2.0 (defective).

[Comprehensive judgment]
Based on the evaluation results of flexibility, heat resistance, moldability, and antibacterial properties, comprehensive judgment was performed according to the following evaluation criteria.
Overall evaluation criteria ◎: There were four に in the four evaluation results (very good).
○: In the four evaluation results, there was no x or 、, and there was even one ○ (good).
Fair: In the four evaluation results, there was no x, and there was even one Δ (slightly poor).
X: In one of the four evaluation results, x was even one (defect).

From the results shown in Tables 1 and 2, the polystyrene resin foam sheets of Examples 1 to 5 to which the present invention is applied were excellent not only in flexibility and heat resistance but also in moldability and antibacterial property.
In Comparative Example 1 in which the amount of the inorganic type antibacterial agent was less than 2 parts by mass, the antibacterial property was significantly inferior.
In Comparative Example 2 in which the amount of the inorganic antibacterial agent exceeds 8 parts by mass, the formability was poor.
In Comparative Examples 3 and 4 in which one containing a polystyrene-based resin instead of a polyethylene-based resin was used as a master pellet containing a shell fired product powder, the formability was significantly inferior.
In Comparative Example 5 in which the average cell diameter was less than 190 μm, the formability and the antibacterial property were significantly inferior.
In Comparative Example 6 in which the average cell diameter exceeds 400 μm, the result was inferior in moldability and flexibility.

10 containers, 12 recesses, 14 connections, 15 partitions

Claims (7)

A polystyrene resin foam sheet comprising a foam resin layer containing a resin component containing a polystyrene resin,
The inorganic antibacterial agent is contained in an amount of 2 to 8 parts by mass with respect to the total amount (100 parts by mass) of the resin component,
The inorganic antibacterial agent contains calcium hydroxide,
Ri average bubble diameter is 190~400μm der,
The polystyrene resin foamed sheet, wherein the foamed resin layer has a complex viscosity of 4500 to 8500 Pa · s determined by viscoelastic measurement under conditions of a temperature of 180 ° C. and a frequency of 1 Hz . The foamed resin layer contains a resin component having a styrene-based monomer unit and an ethylene-based 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 foamed sheet according to claim 1, wherein (D698 / D2850) is 7.0 to 15.0.   The foamed resin layer contains 45 to 85% by mass of a polystyrene resin, 5 to 20% by mass of a hydrogenated polystyrene elastomer, and 5 to 15% by mass of a polyethylene resin based on the total amount (100% by mass) of the resin component. The polystyrene resin foamed sheet according to claim 1 or 2, containing 0 to 30% by mass of a rubber-modified polystyrene resin. The polystyrene resin foam sheet according to any one of claims 1 to 3, wherein the calcium hydroxide is calcium hydroxide contained in a shell fired powder . It is a manufacturing method of the polystyrene resin foam sheet as described in any one of Claims 1-4 , Comprising:
A polystyrene resin foam sheet, wherein a raw material composition containing a resin component containing a polystyrene resin, a masterbatch containing a polyethylene resin and the inorganic antibacterial agent, and a foaming agent are melt-kneaded, extruded and foamed. Production method. The molded object formed by shape | molding the polystyrene resin foam sheet as described in any one of Claims 1-4 . The molded article according to claim 6 , which is a container for packaging fruits and vegetables.

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