JP7448401B2 - How to make natto containers - Google Patents

Description

The present invention relates to a polystyrene resin foam container.

Simple food containers made from polystyrene resin foam sheets (hereinafter simply referred to as foam sheets) by thermoforming can be used, for example, as trays for side dishes, yakisoba, takoyaki, etc., natto containers, and other simple containers for various foods. It is used universally. A method for producing such simple containers involves thermoforming a foam sheet to obtain a sheet molded body in which a plurality of container shapes are formed, and then inserting the sheet molded body into individual containers using a hot wire (for example, a nichrome wire). There is a method to separate it and make it into a product.
When a sheet molded body is continuously cut with a hot wire, there is a problem in that as the number of cuts and the number of sheets increase, foreign matter adhering to the hot wire burns, resulting in a large amount of smoke and odor.

To address these problems, for example, Patent Document 1 proposes a foam sheet containing a specific amount of ash content.
Patent Document 2 proposes a foam sheet having a melt mass flow rate (MFR) and a storage modulus within a specific range.
According to the inventions of Patent Documents 1 and 2, it is possible to suppress the adhesion of foreign matter and the generation of smoke and odor when cutting the nichrome wire.

Japanese Patent Application Publication No. 2004-35712 JP2007-291224A

By the way, when the molding cycle is shortened to improve the productivity of foam sheets, static electricity may accumulate in the molding line. For this reason, there is a need for a foam sheet that has antistatic properties.
As a method for imparting antistatic properties, for example, there is a method of applying an antistatic agent to the surface of a foamed sheet to provide an antistatic layer. If a foam sheet containing an antistatic agent is cut with a hot wire, smoke will increase and the odor will become stronger.

Therefore, the object of the present invention is to provide a polystyrene resin foam container that can reduce smoke and odor generated when cutting with a heated nichrome wire.

[1] An antistatic agent is provided inside or on the surface of the wall having a foamed layer of polystyrene resin, and the content of volatile organic compounds (VOC) excluding styrene measured by the following measurement method 1 is 2. A polystyrene resin foam container with a concentration of 0 μg/L or less.
<Measurement method 1>
A 50 mm square sample was cut out from the bottom wall of a polystyrene resin foam container, and the gas generated when the diagonal of the sample was cut with a nichrome wire heated to 180°C was collected in a 4 L sampling bag, and the gas generated was collected into a 4 L sampling bag. 1 L of the gas from the bag was passed through the adsorption tube at a flow rate of 0.1 mL/min, the VOC components contained in the gas were adsorbed into the adsorption tube, and the adsorption tube was heated at 250°C for 3 minutes to remove the generated volatilization. Components are trapped and concentrated in a cryofocus section maintained at -40°C, and the volatile components are heated to 200°C to be desorbed from the cryofocus section and analyzed using gas chromatography-mass spectrometry (GC/MS). In the chromatogram obtained by measurement, among the peaks detected between the peak retention time of n-hexane and the peak retention time of n-hexadecane, a peak of 0.001 μg/L or more determined in terms of toluene The volatile component having the above-mentioned VOC component is the measurement target, and the sum of the contents of the measurement target is the content of the VOC component.
[2] The polystyrene resin foam container according to [1], wherein the benzene content measured by the measurement method 1 is 0.10 μg/L or less.
[3] The polystyrene resin foam container according to [1] or [2], wherein the content of hexanal measured by the measurement method 1 is 0.005 μg/L or less.
[4] The content of benzene contained in the antistatic agent is less than 0.4 mg/kg based on the total mass of the antistatic agent, according to any one of [1] to [3]. Polystyrene resin foam container.
[5] The polystyrene resin foam container according to any one of [1] to [4], which is a natto container.

According to the polystyrene resin foam container of the present invention, smoke and odor generated when cutting with a heated nichrome wire can be reduced.

1 is a perspective view showing a polystyrene resin foam container according to an embodiment of the present invention.

[Polystyrene resin foam container]
The polystyrene resin foam container (hereinafter also simply referred to as a foam container) of the present invention has an antistatic agent inside or on the surface of the wall portion having a polystyrene resin foam layer.

A foaming container according to an embodiment of the present invention will be described with reference to FIG. 1.
The foam container 10 in FIG. 1 is a natto container used to store natto.
The foam container 10 of this embodiment is obtained by thermoforming a polystyrene resin foam sheet (hereinafter also simply referred to as a foam sheet).
The foaming container 10 includes a container body 11 which is rectangular in plan view and includes a bottom wall portion 14 and a side wall portion 13 erected from the periphery thereof, and a container body 11 which is connected to one side of the container body 11 via a hinge portion 17 in plan view. It consists of a rectangular lid body 12. The lid body 12 is composed of a top wall portion.

A flange is formed at the tip of the side wall portion 13 so as to project outward. When packaging the foam container 10, the flange comes into contact with the periphery of the bent lid 12, so that the protrusion 15 formed on the lid 12 fits into the opening of the container body 11.
A perforation 16 is formed in the hinge portion 17 for separating the lid 12 from the container body 11.
In this embodiment, the "wall" includes the bottom wall 14, side wall 13, and top wall (lid 12) of the foaming container 10.
In this embodiment, the "wall" is composed of a foam layer and an antistatic agent inside or on the surface of the foam layer.

The foaming container 10 has a volatile organic compound (VOC) content other than styrene measured by the following measurement method 1 of 2.0 μg/L or less, preferably 1.8 μg/L or less, and 1.5 μg/L or less. L or less is more preferable, and 1.0 μg/L or less is even more preferable. When the content of VOC components is below the above upper limit value, smoke and odor generated when cutting with a heated nichrome wire can be reduced. The content of VOC components is preferably as low as possible, and most preferably 0 μg/L. The content of VOC components is expressed by the mass per 1 L of gas generated when cutting a sample using measurement method 1 below.
The content of the VOC component can be adjusted by the type and amount of the organic compound and the type and amount of the antistatic agent contained in the resin composition forming the foam layer.

The content of VOC components is measured by the following measurement method 1.
<Measurement method 1>
A 50 mm square sample is cut out from the bottom wall portion 14 of the foaming container 10. At this time, the sample is cut out using a knife or the like without heating the bottom wall portion 14. Cut the sample diagonally with a nichrome wire heated to 180°C. The gas generated when cutting the sample is collected in a 4 L sampling bag, and 1 L of gas is passed through the adsorption tube from this sampling bag at a flow rate of 0.1 mL/min. By passing gas through the adsorption tube, VOC components contained in the gas are adsorbed into the adsorption tube. The adsorption tube on which VOC components have been adsorbed is heated at 250° C. for 3 minutes to generate volatile components. The generated volatile components are trapped and concentrated in a cryofocus section maintained at -40° C., and the concentrated volatile components are heated to 200° C. and desorbed from the cryofocus section. The volatile components desorbed from the cryofocus section are measured by gas chromatography-mass spectrometry (GC/MS). In the chromatogram obtained by GC/MS measurement, all peaks of volatile components detected between the peak retention time of n-hexane and the peak retention time of n-hexadecane are extracted. The extracted peaks are quantified in terms of toluene, volatile components having peaks of 0.001 μg/L or more are measured, and the sum of the contents of the measurement objects is defined as the content of VOC components in the foaming container 10.
Note that the amount of volatile components (μg/L) of each volatile component is determined by the following formula.
Volatile component amount (μg/L) = Toluene equivalent amount of each volatile component (μg)/Gas sampling volume (L)

In the above measurement method 1, the sampling bag is preferably a bag made of vinyl fluoride resin, which exhibits excellent resistance to organic solvents. Examples of such bags include Tedlar (registered trademark) bags.
The adsorption tube is not particularly limited, and examples include columns filled with an adsorbent capable of adsorbing VOCs. As the adsorbent, known adsorbents such as activated carbon and zeolite can be used.

The cryofocus section is a component of the GC/MS measurement device, and is a device that heats a trap tube to desorb adsorbed components, and cools it with liquid nitrogen or the like to concentrate the adsorbed components.
In a GC/MS measurement device, the temperature of the trap tube is raised at high speed (for example, 15° C./min), and the desorbed gas is introduced into a GC column and detected by a mass spectrometer.
In the chromatogram obtained at this time, all peaks of volatile components detected between the peak retention time of n-hexane and the peak retention time of n-hexadecane are extracted. The extracted peaks are quantified in terms of toluene, and volatile components having peaks of 0.001 μg/L or more are targeted for measurement.
Examples of the measurement target include benzene, methyl methacrylate, toluene, butyl acetate, siloxane compounds, ethylbenzene, benzaldehyde, propylbenzene, pentanal, n-butyric acid, hexanal, isopentanoic acid, and pentanoic acid.
The sum of the contents of these measurement targets is determined, and the sum is determined as the content of the VOC components of the foaming container 10.
The foam container 10 contains polystyrene resin. Therefore, when the foaming container 10 is cut with a heated nichrome wire, it is natural that styrene is generated, and therefore, in this specification, styrene is excluded from the measurement target.

The content of benzene measured by the above measurement method 1 is preferably 0.10 μg/L or less, more preferably 0.08 μg/L or less, and even more preferably 0.06 μg/L or less. When the content of benzene is below the above upper limit, the odor generated when cutting with a heated nichrome wire can be further reduced. The lower limit of the benzene content is preferably 0 μg/L.

The content of hexanal measured by the above measurement method 1 is preferably 0.005 μg/L or less, more preferably 0.004 μg/L or less, and even more preferably 0.003 μg/L or less. When the content of hexanal is below the above upper limit, the odor generated when cutting with a heated nichrome wire can be further reduced. The lower limit of the content of hexanal is preferably 0 μg/L.

The content of toluene measured by the above measurement method 1 is preferably 1.0 μg/L or less, more preferably 0.8 μg/L or less, and even more preferably 0.6 μg/L or less. When the content of toluene is below the above upper limit, the odor generated when cutting with a heated nichrome wire can be further reduced. The lower limit of the toluene content is preferably 0 μg/L.

The content of ethylbenzene measured by the above measurement method 1 is preferably 0.25 μg/L or less, more preferably 0.20 μg/L or less, and even more preferably 0.13 μg/L or less. When the content of ethylbenzene is below the above upper limit, the odor generated when cutting with a heated nichrome wire can be further reduced. The lower limit of the content of ethylbenzene is preferably 0 μg/L.

The content of benzaldehyde measured by the above measurement method 1 is preferably 0.70 μg/L or less, more preferably 0.60 μg/L or less, and even more preferably 0.50 μg/L or less. When the content of benzaldehyde is below the above upper limit, the odor generated when cutting with a heated nichrome wire can be further reduced. The lower limit of the content of benzaldehyde is preferably 0 μg/L.

The content of each VOC component in the foamed container 10 can be adjusted by the type and amount of the organic compound and the type and amount of the antistatic agent contained in the resin composition forming the foamed layer.

In the foaming container 10, it is preferable that the VOC components measured by the following measurement method 2 are within a specific range.

<Measurement method 2>
The bottom wall portion 14 of the foaming container 10 is cut out and 5 mg is weighed out to be used as a sample. This sample is wrapped in aluminum foil and placed in a glass-lined SUS desorption tube (GLT tube) with an inner diameter of 4 mm and a length of 100 mm. The GLT tube is set in an autosampler and heated at 250° C. for 3 minutes to generate volatile components. The generated volatile components are trapped and concentrated in a cryofocus section maintained at -40° C., and the concentrated volatile components are heated to 200° C. and desorbed from the cryofocus section. The volatile components desorbed from the cryofocus section are measured by gas chromatography-mass spectrometry (GC/MS). In the chromatogram obtained by GC/MS measurement, all peaks of volatile components detected between the peak retention time of n-hexane and the peak retention time of n-hexadecane are extracted. The extracted peaks are quantified in terms of toluene, volatile components having peaks of 0.1 mg/kg or more are measured, and the sum of the contents of the measurement objects is defined as the content of VOC components in the foaming container 10.
Note that the amount of volatile components (mg/kg) of each volatile component is determined by the following formula.
Volatile component amount (mg/kg) = Toluene equivalent amount of each volatile component (mg) / Mass of sample (kg)

In the above measurement method 2, the inner diameter of the GLT tube is preferably 3 to 5 mm. The length of the GLT tube is preferably 80 to 120 mm. The outer diameter of the GLT tube is preferably 4 to 8 mm.
Examples of the autosampler include the one attached to the thermal desorption device "TD-4J" manufactured by LC Science Co., Ltd., and the like.

In measurement method 2, a larger amount and more types of VOC components are volatilized than in measurement method 1. Therefore, compared to measurement method 1, errors in the measured values of VOC components can be reduced and measurements can be made with higher accuracy.
The content of VOC components other than styrene measured by measurement method 2 is preferably 50 mg/kg or less, more preferably 40 mg/kg or less, and even more preferably 35 mg/kg or less, based on the total mass of the foaming container 10. When the content of the VOC component is below the above upper limit, smoke and odor generated when the foaming container 10 is heated can be further reduced. The content of VOC components is preferably as low as possible, and most preferably 0 mg/kg.

The content of benzene measured by the measurement method 2 is preferably less than 0.3 mg/kg based on the total mass of the foaming container 10. When the benzene content in measurement method 2 is less than the above upper limit, smoke and odor generated when the foaming container 10 is heated can be further reduced. The lower limit of the benzene content in measurement method 2 is preferably 0 mg/kg.

The content of hexanal measured by the above measurement method 2 is preferably less than 1.2 mg/kg, more preferably 1.0 mg/kg or less, and 0.8 mg/kg or less based on the total mass of the foaming container 10. More preferred. When the content of hexanal in measurement method 2 is less than the above upper limit, smoke and odor generated when the foaming container 10 is heated can be further reduced. The lower limit of the content of hexanal in measurement method 2 is preferably 0 mg/kg.

The content of ethylbenzene measured by the measurement method 2 is preferably less than 20 mg/kg based on the total mass of the foaming container 10. When the content of ethylbenzene in measurement method 2 is less than the above upper limit, smoke and odor generated when the foaming container 10 is heated can be further reduced. The lower limit of the ethylbenzene content in measurement method 2 is preferably 0 mg/kg.

The content of benzaldehyde measured by the above measurement method 2 is preferably 20 mg/kg or less, more preferably 15 mg/kg or less, and even more preferably 10 mg/kg or less, based on the total mass of the foaming container 10. When the content of benzaldehyde in measurement method 2 is below the above upper limit value, smoke and odor generated when the foaming container 10 is heated can be further reduced. The lower limit of the content of benzaldehyde in measurement method 2 is preferably 0 mg/kg.

The content of propylbenzene measured by the above measurement method 2 is preferably less than 2.0 mg/kg, more preferably 1.7 mg/kg or less, and more preferably 1.5 mg/kg or less based on the total mass of the foaming container 10. is even more preferable. When the content of propylbenzene in measurement method 2 is less than the above upper limit, smoke and odor generated when the foaming container 10 is heated can be further reduced. The lower limit of the propylbenzene content in measurement method 2 is preferably 0 mg/kg.

The content of isopentanoic acid measured by the above measurement method 2 is preferably 2.0 mg/kg or less, more preferably 1.8 mg/kg or less, and 1.5 mg/kg or less based on the total mass of the foaming container 10. is even more preferable. When the content of isopentanoic acid in measurement method 2 is below the above upper limit, smoke and odor generated when the foaming container 10 is heated can be further reduced. The lower limit of the content of isopentanoic acid in measurement method 2 is preferably 0 mg/kg.

(foam layer)
The container body 11 and the lid 12 of the foamed container 10 have a foamed layer of polystyrene resin. Examples of polystyrene resins include homopolymers of styrene monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene, or copolymers thereof. Polystyrene resins containing 50% by mass or more of styrene are preferred, and polystyrene is more preferred.
The polystyrene resin may be a copolymer containing a styrene monomer as a main component and a vinyl monomer copolymerizable with the styrene monomer. Examples of such vinyl monomer include: Alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, cetyl (meth)acrylate, (meth)acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl fumarate, ethyl fuma In addition to esters, difunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate can be mentioned.
Here, (meth)acrylate means both or one of acrylate and methacrylate, and (meth)acrylonitrile means both or one of acrylonitrile and methacrylonitrile.

The foam layer may contain other resins as long as the polystyrene resin is the main component. Other resins include, for example, rubber-modified polystyrene resins containing diene-based rubbery polymers such as polybutadiene, styrene-butadiene copolymers, ethylene-propylene-nonconjugated diene three-dimensional copolymers, and so-called high-impact polystyrene resins. Examples include polystyrene. Alternatively, polyethylene resins, polypropylene resins, acrylic resins, acrylonitrile-styrene copolymers, acrylonitrile-butadiene-styrene copolymers, etc. may be mentioned. In addition, as the raw material polystyrene resin, it is possible to use commercially available normal polystyrene resins, polystyrene resins that are not recycled raw materials, such as polystyrene resins newly created by methods such as suspension polymerization, and Recycled raw materials obtained by recycling used polystyrene resin foam moldings can be used. As this recycled raw material, used polystyrene resin foam moldings, such as fish boxes, home appliance cushioning materials, food packaging trays, etc., are collected and recycled using a limonene dissolution method or a heating volume reduction method. Can be done. In addition to recycled materials obtained by recycling used polystyrene resin foam moldings, recycled materials that can be used include home appliances (e.g., televisions, refrigerators, washing machines, air conditioners, etc.) and Non-foamed polystyrene-based resin molded bodies separately collected from commercial equipment (for example, copying machines, facsimile machines, printers, etc.) can be crushed, melt-kneaded, and re-pelletized.

Examples of the foaming agent used in producing the foamed layer include nitrogen dioxide, carbon dioxide, propane, n-butane, i-butane, n-pentane, and i-pentane. Among these, n-butane and i-butane are preferred. When using a hydrocarbon blowing agent such as butane, the amount added is preferably within the range of 1 to 10 parts by mass, and preferably within the range of 2 to 8 parts by mass, per 100 parts by mass of the polystyrene resin. More preferred.
One type of blowing agent may be used alone, or two or more types may be used in combination.

The foaming container 10 may contain other components (optional components) in addition to the polystyrene resin, antistatic agent, and foaming agent.
Such optional components include foaming nucleating agents, cell regulators, stabilizers, ultraviolet absorbers, coloring agents, crystallization promoters, lubricants, crosslinking agents, shrinkage inhibitors, flame retardants, deterioration inhibitors, and the like.
Note that the total amount of the polystyrene resin, antistatic agent, and optional components does not exceed 100% by mass.

Examples of the foam nucleating agent used in producing the foam layer include talc, sodium hydrogen carbonate, ammonium hydrogen carbonate, calcium carbonate, clay, and citric acid, and among these, talc is preferred. The amount of the foam nucleating agent added is preferably in the range of 1 to 8 parts by weight, more preferably in the range of 2 to 6 parts by weight, per 100 parts by weight of the polystyrene resin.

The above-mentioned optional components may be used alone or in combination of two or more.
The total amount of optional components contained in the foaming container 10 is preferably 0.1 to 5% by mass, more preferably 0.5 to 3% by mass, based on the total mass of the foaming container 10.

The foaming ratio of the foam layer is, for example, preferably 1.5 to 20 times, more preferably 2 to 18 times, even more preferably 3 to 16 times. When the expansion ratio of the foam layer is at least the above lower limit, the heat insulation properties of the foam container 10 can be further improved. When the expansion ratio of the foam layer is less than or equal to the above upper limit value, the moldability of the foam container 10 is easily improved.
The foaming ratio of the foamed layer is a value obtained by dividing 1 by "apparent density of the foamed layer (g/cm ³ )".

The apparent density of the foam layer is determined by measuring in accordance with JIS K 7222:2005 "Foamed plastics and rubber - How to determine apparent density."
More specifically, the mass and apparent volume of a test piece of the foam layer cut without changing the original cell structure are measured and calculated using the following formula.
Apparent density of foam layer (g/cm ³ ) = Mass of test piece (g) / Apparent volume of test piece (cm ³ )

The average cell diameter of the foamed layer is preferably 95 to 160 μm, more preferably 100 to 155 μm, even more preferably 110 to 150 μm. When the average cell diameter of the foam layer is within the above numerical range, the beautiful appearance of the foam container 10 can be ensured.

(Antistatic agent)
Antistatic agents are agents that prevent the accumulation of static electricity by imparting conductivity to insulators. Examples of the antistatic agent include organic compounds such as surfactants, and agents containing carbon and metal fillers. The antistatic agent may be applied to one or both surfaces of the foam layer, or may be kneaded into the resin composition constituting the foam layer. The antistatic agent may be liquid or solid.
The antistatic agent preferably has a low content of VOC components from the viewpoint of reducing smoke and odor generated when cutting with a heated nichrome wire.
The content of VOC components in the antistatic agent can be measured, for example, by the following measurement method 3.

<Measurement method 3>
Weigh 5 mg of the antistatic agent and use it as a sample. This sample is wrapped in aluminum foil and placed in a glass-lined SUS desorption tube (GLT tube) with an inner diameter of 4 mm and a length of 100 mm. The GLT tube is set in an autosampler and heated at 250° C. for 3 minutes to generate volatile components. The generated volatile components are trapped and concentrated in a cryofocus section maintained at -40° C., and the concentrated volatile components are heated to 200° C. and desorbed from the cryofocus section. The volatile components desorbed from the cryofocus section are measured by gas chromatography-mass spectrometry (GC/MS). In the chromatogram obtained by GC/MS measurement, all peaks of volatile components detected between the peak retention time of n-hexane and the peak retention time of n-hexadecane are extracted. The extracted peaks are quantified in terms of toluene, volatile components having peaks of 0.1 mg/kg or more are measured, and the sum of the contents of the measurement objects is defined as the content of VOC components in the foaming container 10.
Note that the amount of volatile components (mg/kg) of each volatile component is determined by the following formula.
Volatile component amount (mg/kg) = Toluene equivalent amount of each volatile component (mg) / Mass of sample (kg)

In measurement method 3, the same GLT tube and autosampler as in measurement method 2 can be used.

In measurement method 3, the content of VOC components relative to the total mass of the antistatic agent can be measured. That is, the content of VOC components in the antistatic agent itself can be measured. Therefore, it is possible to easily determine what kind of antistatic agent is preferable as the antistatic agent contained in the foaming container.
Note that some antistatic agents contain a large amount of siloxane compounds, but siloxane compounds are components that are difficult to volatilize when cutting a foaming container with a heated nichrome wire. Therefore, the siloxane compound may be excluded from the VOC components of the antistatic agent.

The content of VOC components other than siloxane compounds measured by the above measurement method 3 is preferably less than 0.7 mg/kg, more preferably 0.5 mg/kg or less, and 0.7 mg/kg or less, more preferably 0.5 mg/kg or less, based on the total mass of the antistatic agent. More preferably, it is 3 mg/kg or less. When the content of the VOC component in the antistatic agent is less than the above upper limit, smoke and odor generated when cutting the foaming container 10 with a heated nichrome wire can be further reduced. The content of VOC components in the antistatic agent is preferably as low as possible, most preferably 0 mg/kg.

The content of benzene measured by the above measurement method 3 is preferably less than 0.4 mg/kg based on the total mass of the antistatic agent. When the benzene content in measurement method 3 is less than the above upper limit, smoke and odor generated when cutting the foaming container 10 with a heated nichrome wire can be further reduced. The lower limit of the benzene content in measurement method 3 is preferably 0 mg/kg.

The content of hexanal measured by the above measurement method 3 is preferably less than 0.3 mg/kg, more preferably 0.2 mg/kg or less, based on the total mass of the antistatic agent. When the content of hexanal in measurement method 3 is less than the above upper limit, smoke and odor generated when cutting the foaming container 10 with a heated nichrome wire can be further reduced. The lower limit of the content of hexanal in measurement method 3 is preferably 0 mg/kg.

The content of the antistatic agent is preferably 0.2×10 ⁻⁵ to 9.0×10 ⁻⁵ % by mass, and 0.5×10 ⁻⁵ to 7.0× with respect to the total mass of the foaming container 10. It is more preferably 10 ⁻⁵ % by mass, and even more preferably 1.0×10 ⁻⁵ to 5.0×10 ⁻⁵ % by mass. When the content of the antistatic agent is at least the above lower limit, sufficient antistatic performance can be imparted to the foam sheet. When the content of the antistatic agent is below the above upper limit, smoke and odor generated when the foaming container 10 is cut with a heated nichrome wire can be further reduced. Note that the content of the antistatic agent is the content when not diluted.

[Method for manufacturing foam containers]
The method for manufacturing a foamed container of the present invention includes a step of obtaining a foam sheet material and a step of molding the foamed sheet.

(Process of obtaining raw material for foam sheet)
As a method for manufacturing the original foam sheet, a conventionally known method for manufacturing a foam sheet can be used.
For example, the original fabric of the foam sheet can be manufactured by the manufacturing method described below, but it is not limited to this manufacturing method.
A tandem extruder consisting of a first extruder and a second extruder connected to the outlet of the first extruder is used as a manufacturing device for the original fabric of the foam sheet, and an annular die is attached to the outlet of the second extruder. Use the equipment provided. A polystyrene resin composition is supplied to a first extruder, melted, and a blowing agent is injected while kneading. Next, in the second extruder, after cooling to an extrusion temperature suitable for foaming, the melted and kneaded polystyrene resin composition is supplied to an annular die, and a cylindrical foam is formed through the slit of the die. do. Immediately thereafter, the cylindrical foam is cooled with air and drawn along the outer surface of the mandrel. Furthermore, it is cut into two sheets along the extrusion direction to obtain the original foam sheet.

A foamed sheet can be obtained by applying or adding an antistatic agent to the original foamed sheet.
The antistatic agent may be applied to the surface of the obtained foam sheet, or may be added to the polystyrene resin composition that is the raw material for the foam sheet.
It is preferable to use the antistatic agent after diluting it with water. The dilution ratio when diluting the antistatic agent with water is preferably 10 to 500 times, more preferably 30 to 300 times, and even more preferably 50 to 200 times. When the dilution ratio of the antistatic agent is equal to or higher than the above lower limit, smoke and odor generated when cutting with a heated nichrome wire can be further reduced. When the dilution ratio of the antistatic agent is at most the above upper limit, sufficient antistatic performance can be imparted to the foam sheet.

When applying the antistatic agent to the surface of the foam sheet, the antistatic agent may be applied to part or all of the surface of the foam sheet using a roll or the like, or the antistatic agent may be applied to part or all of the surface of the foam sheet by spraying or the like. An antistatic agent may be sprayed on the surface.
By applying an antistatic agent to the surface of the foam sheet, a foam sheet having antistatic performance can be obtained.

When applying an antistatic agent to the surface of the foam sheet, the amount of the antistatic agent applied is preferably 0.2 to 10 ^mg , more preferably 0.5 to 7 mg, and even more preferably 1 to 5 mg per 1 m 2 of the foam sheet. . When the amount of the antistatic agent applied is at least the above lower limit, sufficient antistatic performance can be imparted to the foam sheet. When the amount of the antistatic agent applied is less than or equal to the above upper limit, smoke and odor generated when the foaming container 10 is cut with a heated nichrome wire can be further reduced.

When adding the antistatic agent to the polystyrene resin composition, the amount of the antistatic agent added is 0.2×10 ⁻⁵ to 9.0×10 ⁻⁵ % by mass based on the total mass of the foaming container 10. ^{The amount of ​} More preferred. When the amount of the antistatic agent added is at least the above lower limit, sufficient antistatic performance can be imparted to the foam sheet. When the amount of the antistatic agent added is below the above upper limit, smoke and odor generated when the foaming container 10 is cut with a heated nichrome wire can be further reduced.

(Process of forming a foam sheet)
A foamed container is obtained by thermoforming the obtained foamed sheet to obtain a sheet molded body in which a plurality of container shapes are formed, and then separating this sheet molded body into individual containers using a hot wire.

For example, when the foam container is a natto container, the foam container of the present invention can be manufactured by the manufacturing method described below, but is not limited to this manufacturing method.
As a forming machine for natto containers, the product shape is formed so that dozens of natto containers, each consisting of a container body and a lid having the same size as the container body, can be formed in one thermoforming process. Use one equipped with a mold.
During thermoforming, the second surface of the foam sheet, which corresponds to the inside of the cylindrical foam extruded from the circular mold, is brought into contact with the mold, and the container body is opened at the first surface, which corresponds to the outside of the foam. Implement as follows. In addition, the sheet molded body removed from the mold was cut into pieces for each thermoforming process and stacked to create a laminate in which multiple sheet molded bodies were stacked one on top of the other, and the sheet was stretched horizontally. A fusing device with a plurality of nichrome wires arranged in a grid pattern cuts the stack from bottom to top, dividing the natto containers into individual pieces.

Since the foamed container of the present invention contains an antistatic agent, it is possible to suppress the accumulation of static electricity during the production of the foamed sheet that is the raw material for the foamed container.
The foamed container of the present invention has a content of VOC components other than styrene measured by a specific measurement method of 2.0 μg/L or less, which reduces smoke and odor generated when cutting with heated nichrome wire. can.

The foam container of the present invention is not limited to the embodiments described above, and can be used for containers for various purposes, such as containers for foods other than natto, trays for foods, and containers for electronic devices.

In the foam container 10 of this embodiment, the foam layer forming the wall is a single layer, but the wall of the foam container may have a skin layer or a non-foam layer may be laminated. .
The skin layer is a layer formed on the surface when manufacturing a foam sheet, and refers to a thin skin portion that does not contain air bubbles.
Examples of the resin constituting the non-foamed layer include polystyrene resin, polyolefin resin, and the like.

EXAMPLES Hereinafter, the present invention will be explained in detail with reference to Examples, but the present invention is not limited by the following description.

<Manufacture of foam sheet material>
The foam sheet manufacturing device is a tandem extruder consisting of a first extruder (screw diameter 115 mm) and a second extruder (screw diameter 150 mm) connected to the outlet of the first extruder. A manufacturing apparatus was used in which an annular die with a diameter of 170 mm was attached to the outlet of the mold.
To 100 parts by mass of polystyrene resin (trade name "XC-515", manufactured by DIC Corporation), talc was added as a cell regulator so that the average cell diameter was adjusted to 137 μm, and the mixture was supplied to the first extruder. did. The cylinder temperature of the first extruder was set at a maximum temperature of 240°C, and 4.0 parts by mass of butane gas was injected as a foaming agent into 100 parts by mass of polystyrene resin, followed by foaming in the second extruder. Cooled to suitable extrusion temperature. The foamed mixture was fed into an annular die and passed through the slit of the die to form a cylindrical foam. Immediately after that, air is applied to the cylindrical foam to adjust and cool it, and it is taken along the outer surface of a cooling device (mandrel) with a diameter of 675 mm, and then cut into two pieces along the extrusion direction to make a width of 1050 mm. A foamed sheet material A was obtained so that the sheet basis weight was 105 g/m ² and the thickness was 1.33 mm.

A foam sheet material B was obtained in the same manner as the foam sheet material A except that the average cell diameter was 125 μm and the thickness was 1.22 mm.

(Average bubble diameter)
The average cell diameter of the original foam sheet was determined as follows.
Cut perpendicularly to the surface of the original foam sheet along the MD direction (extrusion direction) and TD direction (direction orthogonal to the extrusion direction on the surface of the original foam sheet) from the center in the width direction of the original foam sheet. I put it out.
The cross section was photographed using a scanning electron microscope (SU1510, manufactured by Hitachi High-Technologies) with a magnification of 50 times. At this time, the microscopic images were taken so that they would have a predetermined magnification when printed with two images (total 4 images) lined up vertically and horizontally on one A4 sheet of horizontally oriented paper.
Specifically, an arbitrary straight line of 60 mm parallel to each of the MD and TD directions and a straight line of 60 mm in a direction perpendicular to each direction (VD direction) are drawn on the image, and a cross section cut along the MD direction ( For each of the cross section cut along the TD direction (referred to as MD cross section) and the cross section cut along the TD direction (referred to as TD cross section), microscopic images of a total of 4 fields of view, 2 fields of view each, were taken and printed on A4 paper. Draw three arbitrary straight lines (length 60 mm) parallel to the MD direction on each of the two images of the MD cross section, and draw three arbitrary straight lines (length 60 mm) parallel to the TD direction on each of the two images of the TD cross section. A length of 60 mm) was drawn. Also, draw three straight lines (60 mm) parallel to the VD direction in one image of the MD cross section and one image of the TD cross section, and draw any straight line of 60 mm parallel to the MD direction, TD direction, and VD direction. I drew six lines in each direction. In addition, as much as possible, the arbitrary straight lines were made so that bubbles did not touch only at the points of contact, and when they did touch, these bubbles were also added to the number. The number of bubbles D counted for six arbitrary straight lines in each of the MD direction, TD direction, and VD direction was arithmetic averaged to determine the number of bubbles in each direction. The average chord length t of the bubbles was calculated from the image magnification at which the number of bubbles was counted and the number of bubbles using the following formula.
Average chord length t (mm) = 60/(number of bubbles x image magnification)
The image magnification was determined by measuring the scale bar on the image to 1/100 mm using a Digimatic Caliper (manufactured by Mitutoyo) and using the following formula.
・Image magnification = Scale bar actual value (mm) / Scale bar display value (mm)
The bubble diameter in each direction was calculated using the following formula.
・Bubble diameter D (mm) = t/0.616
Furthermore, the cube root of their product was taken as the average bubble diameter.
・Average bubble diameter (mm) = (D _MD × D _TD × D _VD ) ^1/3
D _MD : Bubble diameter in MD direction (mm).
D _TD : Bubble diameter in TD direction (mm).
_DVD : Bubble diameter in VD direction (mm).

<Antistatic agent>
Antistatic agent A: Antistatic agent A listed in Table 1.
Antistatic agent B: Antistatic agent B listed in Table 1.
Antistatic agent C: Antistatic agent C listed in Table 1.
Antistatic agent D: mixture of antistatic agent A and antistatic agent B (mixing ratio (mass ratio) of antistatic agent A and antistatic agent B, 1:1).
Antistatic agent E: mixture of antistatic agent B and antistatic agent C (mixing ratio (mass ratio) of antistatic agent B and antistatic agent C, 1:1).

[Experiment Examples 1 to 3]
Three types of antistatic agents (antistatic agent A, antistatic agent B, and antistatic agent C) were prepared, and 5 mg of each was weighed and used as a sample. After wrapping this sample in aluminum foil and placing it in a GLT tube, it was placed in the autosampler attached to the thermal desorption device "TD-4J model" manufactured by LC Science Co., Ltd., and heated at 250°C for 3 minutes to evaporate it. generated the ingredients. The generated volatile components were trapped and concentrated in the cryofocus section maintained at -40°C, and the concentrated volatile components were heated to 200°C and desorbed from the cryofocus section. Volatile components desorbed from the cryofocus section were measured by gas chromatography-mass spectrometry (GC/MS). The measurement conditions for GC/MS are shown below.

<GC/MS measurement conditions>
(measuring device)
・Mass spectrometer "JMS-Q1000GCMkII", manufactured by JEOL Ltd.
- Gas chromatograph device "7890A", manufactured by Agilent Technologies.
- Column: Capillary column "ZB-1" (film thickness 1.0 μm, inner diameter 0.25 mm, length 60 m), manufactured by Phenomenex.
(GC oven temperature increase conditions)
・Initial temperature: 40℃, held for 3 minutes.
- 1st stage temperature increase rate: 15°C/min (up to 200°C).
- Second stage temperature increase rate: 25°C/min (up to 250°C).
・Final temperature: 250°C, held for 6 minutes and 20 seconds.
- Carrier gas: helium (He), flow rate 1 mL/min, injection port temperature 250°C.
・Interface temperature: 250℃.
・Detector voltage: -1100V.
・Split ratio: 1/50.
- Ion source temperature: 250°C.
- Ionization current: 300μA.
- Ionization energy: 70eV.
・Detection method: Scan method (m/z=40-400).

<Thermal desorption conditions>
(Device)
・Thermal desorption device "TD-4J type" manufactured by LC Science Co., Ltd.
(Purge & trap conditions)
・Purge time: 10 seconds.
- Injection time: 20 seconds.
-Desorption time: 3 minutes.
・Delay time: 10 seconds.
・Desorption temperature: 250℃.
・Cryofocus section heating temperature: 200℃.
・Cryofocus section cooling temperature: -40℃.

In the chromatogram obtained by GC/MS measurement, all peaks of volatile components detected between the peak retention time of n-hexane and the peak retention time of n-hexadecane were extracted. The extracted peaks are quantified in terms of toluene, and among the volatile components having a peak of 0.1 mg/kg or more, volatile components other than siloxane compounds are measured, and the total content of these measurement objects is determined as the antistatic agent. (Measurement method 3).
In addition, the volatile component amount (mg/kg) of each volatile component was calculated|required by the following formula.
Volatile component amount (mg/kg) = Toluene equivalent amount of each volatile component (mg) / Mass of sample (kg)
The results of the GC/MS measurements are shown in Table 1. In the table, "<0.2" indicates that the content of the component is less than 0.2 mg/kg, which is the detection limit of the measuring device.

As shown in Table 1, antistatic agent A was found to be a preferable antistatic agent since all components to be measured were below the detection limit of 0.2 mg/kg.
Antistatic agent B had a significantly high content of siloxane compounds, and the content of other components was less than the detection limit of 0.2 mg/kg.
Antistatic agent C contained benzene at 0.4 mg/kg and hexanal at 0.3 mg/kg.

[Experiment Examples 4 to 8]
The antistatic agent listed in Table 2 is diluted 100 times with water, and applied to the foam sheet in an amount of 50 mg per 1 m ² when the foam sheet listed in Table 2 is rolled up after extrusion. Got a sheet. The obtained foam sheet was molded using a single-shot molding machine (FM-6AS (manufactured by Tosei Sangyo Co., Ltd.)).
The molding conditions were as follows: A foam sheet was set, heated at an oven heater temperature of 230° C., and then a foam container (natto container) having a container body size of 85×85×28 mm was molded in the shape shown in FIG. The bottom wall of the resulting natto container was cut out and 5 mg was weighed out to be used as a sample. After wrapping this sample in aluminum foil and placing it in a GLT tube, it was placed in the autosampler attached to the thermal desorption device "TD-4J model" manufactured by LC Science Co., Ltd., and heated at 250°C for 3 minutes to evaporate it. generated the ingredients. The generated volatile components were trapped and concentrated in a cryofocus section maintained at -40° C., and the concentrated volatile components were heated to 200° C. and desorbed from the cryofocus section. Volatile components desorbed from the cryofocus section were measured by gas chromatography-mass spectrometry (GC/MS). The measurement conditions for GC/MS were the same as those for Experimental Examples 1 to 3. The thermal desorption conditions were the same as those in Experimental Examples 1 to 3.

In the chromatogram obtained by GC/MS measurement, all peaks of volatile components detected between the peak retention time of n-hexane and the peak retention time of n-hexadecane were extracted. The extracted peaks are quantified in terms of toluene, and among the volatile components having a peak of 0.1 mg/kg or more, volatile components other than styrene are measured, and the total content of these measurement objects is determined as the VOC of the natto container. It was taken as the content of the component (Measurement method 2). The results of the GC/MS measurements are shown in Table 2. In the table, "<0.2" indicates that the content of the component is less than 0.2 mg/kg, which is the detection limit of the measuring device.

[Examples 1 to 4, Comparative Examples 1 to 3]
The antistatic agent listed in Table 3 is diluted with water at the dilution ratio listed in Table 3, and when the original foam sheet listed in Table 3 is extruded and rolled up, the amount of the antistatic agent listed in Table ³ will be 50 mg per 1 m2. A foamed sheet was obtained by coating the original fabric described in . The obtained foam sheet was molded using a single-shot molding machine (FM-6AS (manufactured by Tosei Sangyo Co., Ltd.)).
The molding conditions were as follows: A foam sheet was set, heated at an oven heater temperature of 230° C., and then a foam container (natto container) having a container body size of 85×85×28 mm was molded in the shape shown in FIG. A 50 mm square sample was cut out from the bottom wall of the obtained natto container and used as a sample. The diagonal of this sample was cut with a nichrome wire heated to 180° C., and the generated gas was collected into a 4L Tedra bag using an “ADPAC-SYSTEM” gas collection pump manufactured by Adtec Corporation. 1 L of gas collected from this Tedra bag was passed through the Tenax adsorption tube at a flow rate of 0.1 mL/min to adsorb VOC components. After accurately weighing the Tenax adsorption tube that adsorbed VOC components into a GLT tube, it was set in the autosampler attached to the thermal desorption device "TD-4J model" manufactured by LC Science Co., Ltd., and heated at 250 ° C. for 3 minutes. Volatile components were generated. The generated volatile components were trapped and concentrated in a cryofocus section maintained at -40° C., and the concentrated volatile components were heated to 200° C. and desorbed from the cryofocus section. Volatile components desorbed from the cryofocus section were measured by gas chromatography-mass spectrometry (GC/MS). The measurement conditions for GC/MS were the same as those for Experimental Examples 1 to 3. The thermal desorption conditions were the same as those in Experimental Examples 1 to 3.

In the chromatogram obtained by GC/MS measurement, all peaks of volatile components detected between the peak retention time of n-hexane and the peak retention time of n-hexadecane were extracted. The extracted peaks are quantified in terms of toluene, and among the volatile components having a peak of 0.001 μg/L or more, volatile components other than styrene are measured, and the total content of these measurement objects is determined as the VOC of the natto container. It was taken as the content of the component (Measurement method 1).
In addition, the amount of volatile components (μg/L) of each volatile component was determined by the following formula.
Volatile component amount (μg/L) = Toluene equivalent amount of each volatile component (μg)/Gas sampling volume (L)
The results of the GC/MS measurements are shown in Table 3. In the table, "<0.001" indicates that the content of the component is less than 0.001 μg/L, which is the detection limit of the measuring device.

<Odor evaluation>
50 container bodies of the foamed containers obtained in Examples 1 to 4 and Comparative Examples 1 to 3 were stacked together, and the smoke generated when the stacked container bodies were cut with a nichrome wire heated to 180°C. The odor was smelled and scored by 10 people according to the following evaluation criteria.
The scores of 10 people were averaged, and the decimal points were rounded off to obtain a judgment value. The average value was classified according to the following criteria and used as an odor evaluation. The results are shown in Table 3.

"Evaluation criteria"
5 points: No strange odor detected.
3 points: A slight strange odor is felt.
1 point: A strange odor is clearly felt.

"Judgment criteria"
◎: Judgment value is 4 to 5 points.
○: Judgment value is 2 to 3 points.
×: Judgment value is 1 point.

As shown in Table 3, in Examples 1 to 4 to which the present invention was applied, the odor evaluation results were "◎" to "○".
In Comparative Examples 1 to 3, in which the content of VOC components was outside the range of the present invention, the odor evaluation result was "x".
From these results, it was found that by applying the present invention, smoke and odor generated when cutting with a heated nichrome wire can be reduced.

10 Foaming container 11 Container body 12 Lid 13 Side wall 14 Bottom wall 15 Projection 16 Perforation 17 Hinge

Claims (2)

It has an antistatic agent on the surface of the wall that has a foam layer of polystyrene resin,
The content of volatile organic compound (VOC) components other than styrene measured by the following measurement method 1 is 2.0 μg/L or less, and the benzene content measured by the following measurement method 1 is 0.10 μg/L. L or less, the toluene content measured by measurement method 1 below is 1.0 μg/L or less, the ethylbenzene content measured by measurement method 1 below is 0.25 μg/L or less, and A method for producing a natto container in which the styrene content measured by the following measurement method 1 is 49 μg/L or less,
The content of VOC components in the antistatic agent is measured by the following measurement method 3, and the content of VOC components is less than 0.7 mg/kg with respect to the total mass of the antistatic agent, and the content of benzene is confirming that it is less than 0.4 mg/kg, and then applying the antistatic agent to the original fabric of the foam sheet to obtain a foam sheet;
A method for producing a natto container, comprising thermoforming the foamed sheet to obtain a sheet molded body in which a plurality of container shapes are formed, and separating the sheet molded body into individual containers using a hot wire to obtain the natto container.
<Measurement method 1>
A 50 mm square sample was cut out from the bottom wall of the natto container, and the gas generated when the diagonal of the sample was cut with a nichrome wire heated to 180°C was collected in a 4L sampling bag. 1 L of gas is passed through the adsorption tube at a flow rate of 0.1 mL/min, the VOC components contained in the gas are adsorbed into the adsorption tube, the adsorption tube is set in an autosampler of a thermal desorption device, and the adsorption tube is placed in the autosampler. The set adsorption tube was heated at 250°C for 3 minutes, the volatile components generated were trapped and concentrated in the cryofocus section maintained at -40°C, and the volatile components were heated to 200°C with a delay time of 10 seconds. In the chromatogram obtained by heating and desorbing from the cryofocus section and measuring by gas chromatography-mass spectrometry (GC/MS), the peak retention time of n-hexane and the peak retention time of n-hexadecane are determined. Among the peaks detected during this period, the volatile components having a peak of 0.001 μg/L or more determined in terms of toluene are the measurement target , and the total content of the measurement target excluding styrene is the VOC component. The amount of volatile components (μg/L) of each volatile component is determined by the following formula.
Volatile component amount (μg/L) = Toluene equivalent amount of each volatile component (μg)/Gas sampling volume (L)
<Measurement method 3>
Weigh out 5 mg of antistatic agent as a sample, wrap the sample in aluminum foil, and place it in a glass-lined SUS desorption tube (GLT tube).The GLT tube is then set in the autosampler of a thermal desorption device, and the GLT The tube was heated at 250°C for 3 minutes, the volatile components generated were trapped and concentrated in the cryofocus section maintained at -40°C, the delay time was 10 seconds, and the volatile components were heated to 200°C to concentrate the volatile components. In the chromatogram obtained by desorbing from the cryofocus section and measuring with gas chromatography-mass spectrometry (GC/MS), it was detected between the peak retention time of n-hexane and the peak retention time of n-hexadecane. Of the volatile components that have peaks of 0.1 mg/kg or more determined in toluene terms, the volatile components excluding siloxane compounds are the measurement target, and the total content of the measurement target is the antistatic component. The amount of volatile components (mg/kg) of each volatile component is determined by the following formula, with the content of VOC components in the agent as the content.
Amount of volatile components (mg/kg) = Toluene equivalent amount of each volatile component (mg)/mass of sample (kg) The method for manufacturing a natto container according to claim 1 , wherein the natto container has a hexanal content of 0.005 μg/L or less as measured by the measurement method 1.

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