JP4848476B1 - Thermoformed product manufacturing method and food container - Google Patents

Abstract

An object of the present invention is to provide a method for producing a thermoformed product effective for imparting toughness to a polystyrene-based resin foam layer, and to provide a food container having excellent strength in which generation of chips is suppressed. .
A method for producing a thermoformed product by thermoforming a resin sheet having a polystyrene resin foam layer, wherein a polyphenylene ether resin and a polystyrene resin are mixed at 10:90 to 50: Using the resin sheet having a polystyrene-based resin foam layer obtained by foaming a mixed resin containing 50 by mass with a foaming agent containing butane, butane is added to a portion formed by the polystyrene-based resin foam layer. Provided is a method for producing a thermoformed product characterized by producing a thermoformed product containing 5% by mass or more.
[Selection] Figure 2

Description

  The present invention relates to a method for producing a thermoformed product and a food container, and more particularly, to a method for producing a thermoformed product for thermoforming a resin sheet, and a food container produced by such a production method.

Conventionally, it has been widely practiced to produce thermoformed products such as food containers by thermoforming a resin sheet, and the resin sheet used as a material for forming this type of thermoformed product includes a resin film and a resin foam. A sheet and a laminated sheet obtained by laminating the resin film on the resin foam sheet are employed.
Among these, laminated sheets are widely used in food containers. For example, in applications where a certain level of strength is required, such as a bowl container containing instant noodles, a resin foam like a resin foam sheet is used. Since it is difficult to obtain a desired strength with a resin sheet having a single layer configuration, a laminated sheet in which a resin film is laminated on one surface of a resin foam sheet is used, and thermoforming is performed so that the resin film side is on the outside is doing.
Also, in containers for instant yakisoba, a certain degree of strength is required on the inner surface side so that the container is not damaged when cooking noodles with a chopstick tip and cooking, and a film layer formed of a resin film The laminated sheet is thermoformed so that is on the inside.

As a resin foam sheet constituting this type of laminated sheet, those having a polyolefin resin as a main material and those having a polystyrene resin as a main material are known.
Among these, the polystyrene-based resin foam sheet is relatively hard and has excellent strength as compared with the polyolefin-based resin foam sheet, and is a forming material as described in Patent Document 1 below. Since it is easy to improve heat resistance by incorporating a polyphenylene ether resin into a polystyrene resin composition, it is widely used as a material for forming food containers.

By the way, as a method for producing a food container by thermoforming a polystyrene resin foam sheet, a plurality of container shapes are formed on the polystyrene resin foam sheet using a mold in which a large number of the food container shapes are arranged. A method is widely adopted in which after the formation, the individual containers are taken out by cutting along the outer periphery of the container shape.
Here, since the polystyrene-based resin is relatively hard as described above, for example, in a thermoformed product obtained by thermoforming a polystyrene-based resin foam sheet, there is a problem that chips are easily generated on the cut end surface. Have.
For the same reason, a thermoformed product obtained by thermoforming a polystyrene resin foam sheet has a problem that it is likely to be cracked when sudden deformation is applied.

This type of problem can also occur in a thermoformed product obtained by thermoforming a laminated sheet in which a polyolefin resin film is laminated on both surfaces of a polystyrene resin foam sheet, for example.
For example, even when a resin sheet having a resin film laminated on both sides of a polystyrene resin foam sheet is thermoformed, if the polystyrene resin foam layer is exposed at the cut end face, the resin sheet is cut from this end face portion. There is no change in the generation of powder, and the reinforcement effect by the resin film can be expected, but there is no change in that the polystyrene resin foam layer is easily cracked against deformation.
In other words, this kind of problem may be a resin foam sheet having a polystyrene resin foam layer, whether it is a resin foam sheet with a single polystyrene resin foam layer or a laminated sheet in which a film layer is laminated on a polystyrene resin foam layer. This is a problem common to thermoformed products obtained by thermoforming.

JP 2008-094919 A

Among the thermoformed products formed by thermoforming a resin sheet, in the case of food containers, if chips are generated from the end face, the chips may be mixed into the food to be stored. The food that is being used cannot be adequately shielded from the external environment and may cause sanitary problems.
Therefore, the problem as described above is strongly required to be solved particularly in food containers.

In order to solve the above problems, it is conceivable to prevent generation of chips by imparting toughness higher than ever to the forming material of the polystyrene-based resin foam layer.
However, in the past, such studies have not been sufficiently conducted, and no solution has been established.

  In view of the above problems, the present invention provides a method for producing a thermoformed product effective for imparting toughness to a polystyrene-based resin foam layer, and consequently, food having excellent strength in which generation of chips is suppressed. The problem is to provide a container for use.

  The inventor of the present invention includes a polystyrene-based resin foam layer by containing a polyphenylene ether-based resin in a predetermined ratio in the forming material of the polystyrene-based resin foam layer and leaving butane in a predetermined ratio after thermoforming. It has been found that excellent toughness can be imparted to a portion, and the present invention has been completed.

  That is, the present invention relating to a method for producing a thermoformed article is a method for producing a thermoformed article by thermoforming a resin sheet having a polystyrene resin foam layer, comprising a polyphenylene ether resin and polystyrene. The polystyrene-based resin foam layer using the resin sheet having a polystyrene-based resin foam layer obtained by foaming a mixed resin containing a resin based on a mass ratio of 10:90 to 50:50 with a foaming agent containing butane A thermoformed product containing 1.5% by mass or more of butane in a portion formed in (1) is produced.

  Further, the present invention relating to a food container is characterized by being manufactured by the method for manufacturing a thermoformed product as described above.

  According to the method for producing a thermoformed product of the present invention, the polystyrene resin foam layer contains a polyphenylene ether-based resin in a predetermined ratio and butane remains in a predetermined ratio after thermoforming, so that the polystyrene Excellent toughness can be imparted to the location formed by the resin foam layer.

The figure which shows the cross-section of a polystyrene-type resin foam sheet. The figure which shows the cross-section of the lamination sheet utilized for formation of a thermoformed product.

The preferred embodiments of the present invention will be described below.
In the present embodiment, a laminated sheet having a polystyrene resin foam layer is used as a resin sheet that is a raw material of a thermoformed product.
More specifically, a thermoformed product using the resin sheet having a film layer made of the resin film together with a polystyrene resin foam layer made of the polystyrene resin foam sheet, in which a resin film is laminated on one side of the polystyrene resin foam sheet. Is made.

The polystyrene resin foam sheet is a polystyrene resin obtained by foaming a mixed resin containing a polyphenylene ether resin and a polystyrene resin in a mass ratio of 10:90 to 50:50 with a blowing agent containing butane. The use of the foam sheet is important in forming a thermoformed product that hardly generates chips and is difficult to break by deformation.
In addition, when forming a thermoformed product that hardly generates chips and is difficult to break by deformation, a thermoformed product containing 1.5% by mass or more of butane in the portion formed by the polystyrene resin foam layer is produced. It is important to.

First, a laminated sheet for forming such a thermoformed product will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view schematically showing a cross-sectional structure of a polystyrene resin foam sheet (hereinafter also simply referred to as “foam sheet”) for constituting a polystyrene resin foam layer of a laminated sheet used for thermoforming. 2 is a cross-sectional view of the laminated sheet 1 obtained by laminating a resin film on the foam sheet 10x.

Reference numeral 20 in FIG. 2 represents a film layer formed by laminating a resin film on one surface of the foam sheet 10x.
Thus, in the present embodiment, a laminated sheet having a two-layer structure of the polystyrene-based resin foam layer 10 and the film layer 20 is employed as the resin sheet 1 for producing a thermoformed product.

Examples of the polystyrene resin used as a material for forming the foam sheet 10x include styrene such as styrene, methylstyrene, ethylstyrene, isopropylstyrene, dimethylstyrene, paramethylstyrene, chlorostyrene, bromostyrene, vinyltoluene, and vinylxylene. A homopolymer of a styrene monomer or a copolymer of the styrene monomer and another monomer can be used.
Among these, from the viewpoint of compatibility with the polyphenylene ether resin, a styrene homopolymer known as a so-called general-purpose polystyrene resin (GPPS) can be preferably used.

As said polyphenylene ether-type resin, what is normally represented by the following general formula is employable.

Here, R ¹ and R ² represent an alkyl group having 1 to 4 carbon atoms or a halogen atom, and n is a positive integer representing the degree of polymerization.
For example, poly (2,6-dimethylphenylene-1,4-ether), poly (2,6-diethylphenylene-1,4-ether), poly (2,6-dichlorophenylene-1,4-ether) Ether) or the like may be used in this embodiment.
The degree of polymerization n is usually in the range of 10 to 5000.

  This polyphenylene ether-based resin is an important component for imparting toughness to the foamed sheet 10x. When a thermoformed product is formed using the foamed sheet 10x, the polyphenylene ether-based resin is removed from the portion formed by the foamed sheet 10x. The generation of chips can be suppressed, and excellent toughness can be exhibited in thermoformed products.

  The polyphenylene ether resin is an effective component for improving heat resistance, and the Vicat softening temperature (JIS K7206 B method, 50 ° C./h) of a foamed sheet obtained by foaming a general-purpose polystyrene resin is generally about 102 ° C. In contrast, the polyphenylene ether-based resin and the polystyrene-based resin are contained in a mass ratio of 10:90 to 50:50 (polyphenylene ether-based resin: polystyrene-based resin) as described above. The Vicat softening temperature of the foam sheet 10x can be improved to a range of 110 to 155 ° C.

  In the case where the purpose is simply to impart heat resistance to a product in which a polystyrene resin composition is used, a styrene-methacrylic acid copolymer having a higher Vicat softening temperature than styrene homopolymer, styrene-anhydrous Although it is possible to employ a copolymer such as a maleic acid copolymer, a styrene-maleimide copolymer, or a polyparamethylstyrene resin as the forming material, in this embodiment, it is superior to the case where the copolymer is used. In order to provide the foamed sheet 10x with high toughness, a mixed resin in which the polyphenylene ether resin and the polystyrene resin are mixed at a predetermined ratio as described above is used as the material for forming the foamed sheet 10x.

The mass ratio of the polyphenylene ether resin and the polystyrene resin is 10:90 to 50:50 (polyphenylene ether resin: polystyrene resin) as described above. In the case of containing polyphenylene ether resin, there is a possibility that the addition effect of polyphenylene ether resin may not be sufficiently exerted. Conversely, even if polyphenylene ether resin is contained exceeding the above range, addition of polyphenylene ether resin is further added. This is because the effect may not be exhibited.
In general, the polyphenylene ether resin is more expensive than the polystyrene resin, and therefore, if the polyphenylene ether resin is contained beyond the above range, there is a risk of causing a problem in terms of material cost.

As described above, the method for manufacturing a thermoformed product according to the present embodiment is the one side of the foam sheet 10x obtained by foaming a mixed resin containing a polyphenylene ether resin and a polystyrene resin with a foaming agent containing butane. A thermoformed product is prepared using a laminated sheet 1 laminated with a resin film on the surface, and 1.5% by mass or more of butane is contained in the portion formed by the foamed sheet 10x (polystyrene resin foamed layer 10 in the laminated sheet). In this state, a thermoformed product is produced.
Thus, by adding butane to the portion corresponding to the foamed sheet 10x, butane functions as a plasticizer, and in addition to the effect of adding the polyphenylene ether resin, further toughness can be improved.
In addition, when the butane content in the portion formed by the polystyrene-based resin foam layer 10 is less than 1.5% by mass, it is difficult to expect a further toughness-improving effect. There is a risk that it may be difficult to sufficiently suppress cracking of the thermoformed product due to generation and deformation of chips.
Therefore, the butane content in the polystyrene-based resin foam layer of the thermoformed product is preferably 1.6% by mass or more in terms of more reliably preventing generation of chips and cracking of the thermoformed product. .

  In order to contain butane in the form as described above in the thermoformed product, for example, the laminated sheet 1 is formed using a foamed sheet containing 1.5% by mass or more of butane as the foamed sheet 10x. The method of implementing thermoforming so that content of butane in the polystyrene-type resin foam layer 10 of 1 may be maintained with 1.5 mass% or more is mentioned.

  The polystyrene resin foam sheet is generally continuously produced by extrusion foaming. In such a production method, it is difficult to contain butane in an excessive content in the polystyrene resin foam sheet. Usually, the butane content in the stage used for thermoforming is about 1.5% by mass to 3.5% by mass.

Therefore, the upper limit of butane to be contained in the polystyrene resin foam sheet is usually 3.5% by mass, and 1.5% by mass or more of butane is contained in the portion formed by the polystyrene resin foam layer 10. In order to obtain a thermoformed product, it is preferable to prevent the dissipation of butane from the polystyrene resin foam sheet as much as possible.
In that respect, the method of performing the thermoforming in the state of the laminated sheet 1 laminated with the resin film as in the present embodiment is thermoforming from at least the surface on which the resin film is laminated as compared with the case of thermoforming the foam sheet 10x alone. It can be said that the butane can be prevented from being occasionally dissipated, and the butane content in the polystyrene-based resin foam layer of the thermoformed product can be more reliably set to 1.5% by mass or more.

For the above reasons, as the resin film laminated on the foam sheet 10x, it is preferable to select and use a general-purpose resin film having a gas barrier property against butane to some extent, a polyethylene terephthalate resin film, stretched It is preferable to select any one of a polypropylene resin film and an unstretched polypropylene resin film.
In addition, the resin film does not need to be a single layer film, and may be a resin film in which a plurality of resin films are laminated and integrated.
Usually, those resin films having a thickness of 5 μm to 100 μm can be adopted.

Further, both the surface portions of the foam sheet 10x are made to be lower foamed than the central portion in the thickness direction, and high density portions called “surface skin layers” are formed on both surface portions to further prevent butane from being dissipated. Is also possible.
That is, a polystyrene-based resin foam sheet used for thermoforming, typically, has a thickness of about 1Mm～3.5Mm, although the overall apparent density of about ^{0.06g / cm 3 ~0.20g / cm 3} , It is preferable to make the average density of both surface portions higher than the overall average density.
In addition, if the average density of the surface portion is not more than a certain level as an absolute value, there is a possibility that it will not be effective in preventing butane dissipation only by being higher than the average density of the whole.
Therefore, as the foam sheet 10x of the present embodiment, specifically, the average density from both surfaces to the depth of 0.2 mm in the thickness direction (“A” and “B” portions in FIG. 1) is 0.10 g / cm ^3. It is preferable to employ the above foam sheet.
Further, it is preferable that the surface cell layer thickness of the surface skin layer (the thickness of the cell membrane forming the surface of the foam sheet) has a predetermined thickness or more, specifically, a surface layer cell of 7 μm or more. It is preferable to have a film thickness.

The foam sheet 10x having such a surface skin layer is formed by, for example, extruding and foaming a melt-kneaded product made of a resin composition containing a polystyrene resin, a polyphenylene ether resin, and butane as a foaming agent. At this time, it can be produced by a method in which cooling air is blown on both sides of the foam sheet immediately after extrusion to suppress the growth of bubbles in the vicinity of the surface after extrusion.
Specifically, when the glass transition temperature observed by differential scanning calorimetry (DSC) of the forming material of the foam sheet is Tg (° C.), the extruder is used as an extrusion foaming mold such as a circular die. temperature of the melt-kneaded product is supplied from the, (Tg + 45 ℃) ~ (Tg + 75 ℃) performed extruded foam so as to be in the range of, 0.01m ³ ~0.15m ³ per foam sheet 1 m ² made The above-mentioned surface skin layer can be formed on the surface of the foamed sheet by cooling the foamed sheet immediately after extrusion by blowing cooling air at room temperature to about 40 ° C.
In addition, the temperature of the melt-kneaded material supplied to this metal mold | die can be calculated | required by the temperature measurement in the breaker hole of the head part installed between the extruder and the metal mold | die in the general extrusion line.

The surface skin layer as described above can also be adjusted by the temperature of the mold used for extrusion.
For example, as described above, extrusion foaming is performed so that the resin temperature is in the range of (Tg + 45 ° C.) to (Tg + 75 ° C.), and the melt kneaded product is discharged from the discharge port to the extruder side. The surface as above by setting the mold temperature at a position 15 mm away from the resin flow path at a position retracted 100 to 150 mm in the horizontal direction to a temperature within the range of (resin temperature −50 ° C.) to (resin temperature) The skin layer can be more reliably formed on the foamed sheet.

Further, extrusion under the above temperature conditions and cooling with the cooling air are also effective in preventing butane dissipation during extrusion, compared with the case where the content of butane in the foam sheet is not cooled. Can be improved.
As the foaming agent, two types of butanes, normal butane and isobutane, can be appropriately selected and used from the relationship between the diffusion rate in the molten resin and the contribution to foaming, and the adjustment of the state of bubbles in the foamed sheet 10x can be used. And butane content can be adjusted, it is preferable to use mixed butane mixed with these as the blowing agent.

In order to prevent butane from escaping from the foam sheet 10x, it is important not only to provide the surface skin layer as described above but also to suppress the formation of open cells.
That is, as the foam sheet 10x in the present embodiment, it is preferable that the open cell ratio is less than 15%.

  The open cell ratio of the foam sheet 10x can be adjusted by using a cell regulator, and specifically, a polystyrene resin, a polyphenylene ether resin, and a resin containing butane as a foaming agent. The composition may further contain a bubble regulator, and the composition can be adjusted according to the type and amount of the bubble regulator.

  In the present embodiment, the blowing agent is not limited to butane, but other aliphatic hydrocarbons such as propane and pentane may be used in combination with butane. Ammonium carbonate, sodium bicarbonate, bicarbonate Inorganic decomposable foaming agents such as ammonium, ammonium nitrite, calcium azide, sodium azide, sodium borohydride, azodicarbonamide, azobisformamide, azobisisobutyronitrile, diazoaminobenzene, N, N'-di Nitrosopentamethylenetetramine, N, N′-dimethyl-N, N′-dinitrosotephthalamide, benzenesulfonyl hydrazide, p-toluenesulfonyl hydrazide, p, p′-oxybisbenzenesulfonyl semicarbazide, p-toluenesulfonyl semicarbazide, trihydrazino Triazine, may also be used in combination decomposable foaming agent also functions as the nucleating agent such as an organic decomposable foaming agent such as barium azodicarboxylate butane.

  Examples of the air conditioner include talc, mica, silica, diatomaceous earth, aluminum oxide, titanium oxide, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, calcium hydroxide, potassium carbonate, calcium carbonate, and carbonic acid. Examples thereof include inorganic compound particles such as magnesium, potassium sulfate, barium sulfate, and glass beads, and organic compound particles such as polytetrafluoroethylene.

  Thus, in the method for manufacturing a thermoformed product according to this embodiment, a method of laminating a resin film, a method of forming a predetermined surface skin layer on a foamed sheet, and an open cell ratio are adjusted to a predetermined value or less. It is preferable to employ one or more methods among the methods so that more butane contained in the foamed sheet 10x as a starting material of the thermoformed product is retained in the thermoformed product. It is preferable that the butane content in is 0.8 to 1.0 times the butane content in the resin sheet.

As for the ratio of the butane content in the resin sheet and the butane content in the thermoformed product, when the resin sheet is a foamed sheet, the butane content may be simply compared. However, when the resin sheet is a laminated sheet, strictly speaking, it is necessary to isolate and compare only the portion of the polystyrene resin foam layer.
However, the resin film laminated to the foam sheet usually does not contain butane, and the butane contained in the polystyrene resin foam layer moves to the film layer side when the laminated sheet is thermoformed. Even when using a laminated sheet as the resin sheet, even if the transition is negligible, even if it is migrated, the proportion can be determined by comparing the butane content of the laminated sheet and the thermoformed product. As described above, it can be confirmed whether or not it is within the range of 0.8 times to 1.0 times.

  In addition, about the density of a surface skin layer, the open cell rate of a foam sheet (polystyrene-type resin foam layer), and the content of butane in the polystyrene-type resin foam layer and foam sheet of a thermoformed product, the measuring method described in an Example Can be measured.

  In this embodiment, the laminated sheet 1 as described above is exemplified as a resin sheet to be thermoformed in that the butane contained in the foamed sheet 10x can be prevented from being dissipated before being processed into a thermoformed product. However, instead of this, a laminated sheet in which a resin film is laminated on both surfaces of the foamed sheet 10x can also be adopted.

In that case, the type and thickness of the resin film may be different between the one side and the other side, and the laminating method for the foam sheet 10x may be different between the one side and the other side.
For example, a stretched or non-stretched polypropylene resin film may be dry-laminated on one side and a polyethylene terephthalate resin film may be laminated on the other side via an adhesive.

Further, for example, a laminated sheet obtained by laminating a resin film on a foamed sheet in which a plurality of polystyrene-based resin foamed layers are laminated by coextrusion can be used, and conversely, the foamed sheet 10x itself becomes a raw material of a thermoformed product. It is also possible to employ as a resin sheet.
That is, even when a resin sheet having a single polystyrene-based resin foam layer or a resin sheet having a plurality of polystyrene-based resin foam layers is used, a polystyrene-based resin containing a polyphenylene ether-based resin and butane at a predetermined ratio In the point that the effect of the present invention that the resin foam layer is formed in a thermoformed product and the toughness of the polystyrene resin foam layer is improved is exhibited, the laminated sheet 1 illustrated above is used. Same as when used.

Furthermore, in the present invention, the resin sheet forming material is not limited to the above-described examples, and colorants and various chemicals are appropriately used as the resin sheet forming material as long as the effects of the present invention are not significantly impaired. It is possible.
For example, since the polyphenylene ether resin has a peculiar odor, when the thermoformed product to be produced is a food container, a deodorant should be employed as the foam sheet forming material. It is preferable to include zeolite-based or zirconium phosphate-based inorganic particles as a deodorant.

Since this zirconium phosphate-based inorganic particles are excellent in the effect of preventing the generation of odors derived from polyphenylene ether-based resins, by adopting the foamed sheet forming material, the odors cause discomfort to the user. The risk of giving can be reduced.
In addition, zirconium phosphate-based inorganic particles prevent the generation of odors when a foamed sheet is produced by extrusion foaming or when the foamed sheet or a laminated sheet using the foamed sheet is thermoformed. Therefore, the possibility of giving discomfort to not only the user of the thermoformed product but also the worker of the thermoformed product can be reduced.

In addition, in the manufacturing method of the thermoformed product according to the present embodiment, a conventionally known thermoforming method such as vacuum forming, pressure forming, vacuum pressure forming, press forming can be adopted, and the resin sheet as described above is used as the above. The thermoformed product such as a food container can be manufactured by using the thermoforming method as described above.
At this time, when the foam sheet 10x illustrated in FIG. 1 is employed as the resin sheet, thermoforming is performed so that the content of butane in the entire food container is 1.5% by mass or more. This is important for obtaining a food container having excellent toughness.
When the laminated sheet 1 illustrated in FIG. 2 is adopted as the resin sheet, the butane content in the portion occupied by the polystyrene-based resin foam layer 10 in the food container is 1. In order to obtain a food container having excellent toughness, it is important to carry out thermoforming so as to be 5% by mass or more.

This will be described in more detail. A general thermoformed product is formed by forming a plurality of product shapes on a resin sheet using a mold in which a large number of molded product shapes are arranged, and then using a Thomson blade mold or the like. The product is manufactured by a method in which individual products are taken out by cutting along the outer periphery of the product shape.
For example, in a food container called a food pack or the like in which a tray for a food or a tray portion and a lid portion are connected in series, a plurality of stacked bodies in which a plurality of products are stacked in a rod shape are collected. They are packed and transported from container manufacturers to consumption areas.

  Here, since a general polystyrene resin sheet is relatively hard, for example, when punching with the Thomson blade mold, the side surface of the Thomson blade and the cut end surface of the container rub against each other to generate fine chips. Or, when the food container constituting the rod-shaped laminated body is conveyed in the state as described above, the edges of the food container constituting the adjacent laminated body are separated from each other by the vibration of the conveyance. There are cases where fine chips are generated due to rubbing.

On the other hand, in the food container produced by the method for producing a thermoformed product according to the present embodiment, a polyphenylene ether-based resin is contained in the forming material of the polystyrene-based resin foam layer, and the resin has a general tenacity. In addition to being improved compared to polystyrene resin, butane is contained in the polystyrene resin foam layer in a predetermined amount or more, so that the plasticizing action by butane functions in the polystyrene resin foam layer and is finely cut. It is in a state where powder is more difficult to be generated.
For the same reason, the food container produced by the method for producing a thermoformed product according to the present embodiment is abruptly deformed to cause cracking in a food container formed by thermoforming a general polystyrene resin sheet. Even if it is a case where it adds, it is suppressed that the said food container cracks following the deformation | transformation.
As described above, according to the method for manufacturing a thermoformed product according to the present embodiment, the toughness of the polystyrene resin foam layer is improved as compared with the conventional manufacturing method, thereby suppressing generation of chips. Thus, a food container having excellent strength can be provided.

In addition, the food container obtained by the method for producing a thermoformed product of the present embodiment has excellent strength and heat resistance because it contains a polyphenylene ether resin as a material for forming a polystyrene resin foam layer. Is also excellent.
Therefore, although the use aspect is not limited as said container for foodstuffs, For example, the range up container for heating the foodstuff accommodated with a microwave oven etc. are mentioned as a suitable aspect.

  Here, a food container is illustrated as a thermoformed product in that the effects of the present invention are more remarkably exhibited. However, in the method for manufacturing a thermoformed product of the present invention, the thermoformed product to be manufactured is used for food. It is not limited to containers.

  EXAMPLES Next, although an Example is given and this invention is demonstrated in more detail, this invention is not limited to these.

(Preliminary experiment)
The following shows an example of evaluating the difficulty of cracking in a polystyrene resin foam sheet whose resin component is only a polystyrene resin and a polystyrene resin foam sheet made of a polystyrene resin composition containing a polyphenylene ether resin. .

(Sheet 1)
70% by mass of a polystyrene resin (DICPS GPPS (styrene homopolymer), trade name “XC-515”), and a mixed resin of polyphenylene ether resin (PPE) and polystyrene resin (PS) (manufactured by Subic, 1 part by mass of an air conditioner masterbatch (polystyrene resin base, 40% by mass of talc) with respect to 100 parts by mass of the resin component consisting of 30% by mass of the trade name “Noryl EFN 4230”, PPE / PS = 70/30) A resin composition containing 0.5 parts by mass of a zirconium phosphate-based deodorant (trade name “Kesmon NS-10”) manufactured by Toa Gosei Co., Ltd. as an odor eliminating component is extruded and foamed to a thickness of 2.0 mm. A 180 g / m ² polystyrene-based resin foam sheet (sheet 1) was produced.

(Sheet 2)
Instead of a resin composition containing GPPS, PPE, and a deodorizing component, a copolymer (heat-resistant polystyrene) of an acrylic monomer and a styrene monomer is extruded and foamed to have the same thickness and the same basis weight as the sheet 1 A foam sheet (sheet 2) was produced.

(Sheet 3)
Instead of the resin composition containing GPPS, PPE, and deodorant components, only GPPS was extruded and foamed to produce a polystyrene resin foam sheet (sheet 3) having the same thickness and the same basis weight as sheet 1.

(Heat resistance evaluation: differential scanning calorimetry)
A sample of 6.5 ± 0.5 mg was taken from the above sheet, and differential scanning calorimetry was performed based on JIS K7121 (device used: differential scanning calorimeter, manufactured by SII Nanotechnology, model name “DSC6220” ").
As a result, in the samples of Sheet 1 and Sheet 2, the “midpoint glass transition temperature (Tmg)” described in JIS K7121 9.3 (1) was observed around 120 ° C., and in the sample of Sheet 3, 106 ° C. Observed.

(Toughness evaluation: Dynatap impact test)
A 100 × 100 mm test piece was collected from the sheets 1 to 3 and subjected to a Dynatap impact test based on ASTM D3763 on the test piece (device used: General Research Corp., Dynatap impact) Test device, model name “GRC8250”).
As a result, for the test piece of the sheet 2, the maximum point displacement was 3.2 mm and the maximum load was 29 N, and for the test piece of the sheet 3, the maximum point displacement was 4.0 mm and the maximum load was 36 N.
On the other hand, for the test piece of the sheet 1, the maximum point displacement was 4.4 mm and the maximum load was 42 N.
This also shows that the sheet 1 is in a state in which displacement and load are large and cracking is difficult due to the inclusion of the polyphenylene ether resin.

(Evaluation)
Next, examples of various evaluations performed on thermoformed products are shown.
First, an evaluation method for a foamed sheet, a laminated sheet, and a thermoformed product will be described.

(Butane content)
A sample 10-20 mg was precisely weighed and sealed in a 20 ml glass vial, set in a headspace sampler “TurboMatrix HS40” manufactured by Perkins Elmer, heated at 160 ° C. for 20 minutes, and then a gas chromatograph “Claras500GC” manufactured by Perkins Elmer (detector: FID) and quantified by the MHE method.
The measurement conditions in the headspace sampler were a needle temperature of 160 ° C., a sample introduction time of 0.08 minutes, and a transfer line temperature of 180 ° C. The measurement conditions in the gas chromatograph were as follows. DB-1 (0.25 mmφ × 60 m, film thickness 1 μm, column temperature: 6 minutes at 50 ° C., temperature rise to 270 ° C. at 40 ° C./min, 1 column at 270 ° C. Minute), carrier gas helium (introduction conditions: 10 psi at 18 psi, increased to 24 psi at 0.5 psi / min), inlet temperature 200 ° C., detector temperature 250 ° C., range = 20, Att = 1 .

(Average density from surface to 0.2 mm depth)
The foam sheet was sliced at a position of a depth of 0.2 mm from both surfaces of the foam sheet, and the average density of the sliced pieces was measured based on JIS K 7222: 2005 “How to Obtain Foamed Plastic and Rubber—Apparent Density”.

(Surface bubble film thickness)
The foam sheet is cut in the sheet width direction (direction orthogonal to the extrusion direction) at an arbitrary position, and the cut surface is 200 times magnification using a scanning electron microscope, model name “S-3000N” manufactured by Hitachi, Ltd. The thickness of the bubble film forming the foam sheet surface was measured at 10 arbitrary positions, and the average value was defined as the surface layer bubble film thickness.

(Open cell ratio)
In addition, the open cell ratio of the foam sheet was measured by the 1-1 / 2-1 atmospheric pressure method in accordance with ASTM D-2856-87.
Specifically, the foamed sheet was cut into a planar square shape with a side of 25 mm, and a plurality of the cut pieces were overlapped in the thickness direction to prepare a test piece having a thickness of about 25 mm.
Five test pieces were prepared in this manner, and the open cell ratio of each test piece was determined by using the air comparison type hydrometer (trade name “1000 type” manufactured by Tokyo Science Co., Ltd.). The arithmetic average value was defined as the open cell ratio of the foamed sheet.

Example 1
70% by mass of a polystyrene resin (DIC (GPPS), trade name “XC-515”), a mixture of a polyphenylene ether resin (PPE) and a polystyrene resin (PS) (savic product, trade name “ "Noryl EFN4230", PPE / PS = 70/30 (mass ratio)) in a proportion of 30% by mass with respect to 100 parts by mass of the mixed resin, the blowing agent (mixed butane: isobutane (i-butane) / normal butane (n- A resin composition containing 3.5 parts by weight of butane) = 68/32) was extruded and foamed to produce a polystyrene-based resin foam sheet having a thickness of 1.80 mm and a basis weight of 150 g / m ² .
At this time, the surface of the foam sheet immediately after extrusion was air-cooled, the average density from the surface to a depth of 0.2 mm was 0.13 g / cm ³ , the surface layer cell thickness was 16 μm, and the open cell rate was 8.5%. Was made.

A dry laminate film (polystyrene resin film layer / polystyrene resin film layer / layer having a three-layer structure in which a polystyrene resin film and an unstretched polypropylene resin film are bonded to one side of the foamed sheet (the inner surface of the container to be produced) via an adhesive. Adhesive layer / unstretched polypropylene resin film layer = 15 μm / 2 μm / 30 μm, total: 47 μm (CPPS) is dry-laminated, and a weakly stretched PS film (CPS film) on the opposite surface (the surface that is the outside of the container to be produced) 20 μ) was heat laminated to prepare a laminated sheet.
The laminated sheet was thermoformed to form a food container.
Specifically, a rectangular tray having a depth of 40 mm having a rectangular opening of 165 mm × 115 mm and a rectangular bottom of 110 mm × 70 mm is formed so that the extrusion direction (MD direction) of the foam sheet is the longitudinal direction. I let you.
In addition, the said thermoforming was implemented in the time over 2 months with respect to the manufacture time of a foam sheet.
The i-butane content in the obtained food container was 1.65% by mass, and the n-butane content was 0.39% by mass.
That is, the butane content of the container was 2.04% by mass.

Here, the butane content of the polystyrene resin foam layer was not measured, but at least the butane content in the polystyrene resin foam layer is the butane content of the entire container because no butane is contained in the dry laminate film or the like. It turns out that it is more than content (2.04 mass%).
Further, the butane content of the laminated sheet before thermoforming was similarly measured and compared with the butane content of this container. As a result, the butane content of the container relative to the butane content of the laminated sheet was about 103%. I understood it.
In addition, since it cannot be considered that it exceeds 100% originally, 3% is considered to be a measurement error.
That is, it was found that even if the error was taken into account, the butane present at the time of the laminated sheet remained almost completely.

(Example 2)
A container was prepared in the same manner as in Example 1 except that the dry laminate film was laminated only on one side.
The i-butane content in the container of Example 2 was 1.41% by mass, and the n-butane content was 0.38% by mass (total butane content: 1.79% by mass).
The butane content of the container relative to the laminated sheet before thermoforming was about 89%.
Considering the result of Example 2 and the result of Example 1 above, it can be seen that laminating both surfaces of the foamed sheet with a resin film is more advantageous in preventing butane dissipation.

(Comparative Example 1)
A container was formed in the same manner using a general polystyrene resin foam sheet (weight per unit area: 105 g / m ² ) that was not laminated on the surface and did not contain a polyphenylene ether resin.
Although this container contained 2.44% by mass of butane, it was easier to break than the containers obtained in Examples 1 and 2, and chips were easily generated.
From this, it can be seen that not only the butane content but also the presence of a predetermined amount of polyphenylene ether-based resin is difficult to break and is important in forming a thermoformed product in which the generation of chips is suppressed.

(Evaluation of containers: occurrence of “cracking” and occurrence of “chip”)
In each of the examples and comparative examples, 40 square trays were prepared, and 20 of them were oriented in the longitudinal direction (MD direction) so that the length of the opening was reduced by 30 mm (165 mm → 135 mm). The remaining 20 pieces are compressed so that the length of the opening is shortened by 30 mm (115 mm⇒85 mm) in the short direction (TD direction), and the occurrence of “cracking” at the opening edge is checked. evaluated.
Those having an occurrence rate of cracks of 10% or more were judged as “x”, and those less than 10% were judged as “◯”.
Moreover, the generation | occurrence | production situation of "chip" was evaluated by the method of confirming whether the chip has adhered to the inner and outer surfaces of 100 molded articles.
Based on the obtained results, when the number of molded products in which chips are found is 0 (when the adhesion of chips is not seen in all molded products), “○” indicates that even one or more chips. The case where there was a molded product in which was seen was judged as “x”.
The results are shown in Table 1 below.

(Example 3)
A container was prepared in the same manner as in Example 1 except that a simple foam sheet was used without laminating a dry laminate film, and the container was evaluated in the same manner.
The i-butane content in the container of Example 3 was 1.21% by mass, and the n-butane content was 0.33% by mass (total butane content: 1.54% by mass).
The butane content of the container relative to the foamed sheet before thermoforming was about 80%.
From the results of Example 3, it can be seen that laminating a foam sheet with a resin film is more advantageous for preventing butane from escaping.

(Examples 4 to 6)
The ratio of polystyrene resin (trade name “XC-515”) to mixed resin (trade name “Noryl EFN4230”, PPE / PS = 70/30) is changed to 70:30 instead of 70:30, and polyphenylene ether A foamed sheet (laminated sheet) is produced in the same manner as in Examples 1 to 3 except that the content of the resin is about 14% by mass, and a container is produced in the same manner as in Examples 1 to 3, and evaluated in the same manner. did.
However, in the case of using a laminated sheet laminated with a dry lamination film, the film was peeled off immediately before the measurement of the butane content, and the measurement was performed with only the polystyrene resin foam layer.
As a result, as in Example 1, in Example 4 using a laminated sheet laminated with a dry laminate film on both sides, the i-butane content in the polystyrene resin foam layer of the container is 1.72% by mass, The n-butane content was 0.43% by mass (total butane content: 2.15% by mass).
The butane content of this container was about 96% with respect to the butane content in the polystyrene resin foam layer of the laminated sheet before thermoforming.
Moreover, similarly to Example 2, in Example 5 using a laminated sheet laminated with a dry laminate film on one side, the i-butane content in the polystyrene resin foam layer of the container is 1.51% by mass, The n-butane content was 0.44% by mass (total butane content: 1.95% by mass).
Moreover, the butane content of this container was about 87% with respect to the butane content in the polystyrene resin foam layer of the laminated sheet before thermoforming.
Furthermore, similarly to Example 3, in Example 6 using the foamed sheet itself, the i-butane content in the container was 1.47% by mass, and the n-butane content was 0.34% by mass ( Total butane content: 1.81% by mass).
Further, the butane content of this container relative to the butane content in the foamed sheet before thermoforming was about 81%.

(Comparative Examples 2 to 4)
The ratio of polystyrene resin (trade name “XC-515”) to mixed resin (trade name “Noryl EFN4230”, PPE / PS = 70/30) is changed to 70:30 instead of 70:30, and polyphenylene ether occupies the whole A foamed sheet (laminated sheet) was produced in the same manner as in Examples 1 to 3 except that the content of the system resin was about 7% by mass, and a container was produced in the same manner as in Examples 1 to 3.
Similar to Example 1, in Comparative Example 2 using a laminated sheet laminated with a dry laminate film on both sides, the i-butane content in the polystyrene resin foam layer of the container was 1.81% by mass, and n- The butane content was 0.45% by mass (total butane content: 2.26% by mass).
The butane content of this container was about 97% with respect to the butane content in the polystyrene resin foam layer of the laminated sheet before thermoforming.
In addition, as in Example 2, in Comparative Example 3 using a laminated sheet laminated with a dry lamination film on one side, the i-butane content in the polystyrene-based resin foam layer of the container is 1.67% by mass, The n-butane content was 0.39% by mass (total butane content: 2.06% by mass).
Moreover, the butane content of the container was about 88% with respect to the butane content in the polystyrene resin foam layer of the laminated sheet before thermoforming.
Furthermore, similarly to Example 3, in Comparative Example 4 using the foamed sheet itself, the i-butane content in the container was 1.47% by mass, and the n-butane content was 0.39% by mass ( Total butane content: 1.86% by mass).
Further, the butane content of this container relative to the butane content in the foamed sheet before thermoforming was about 80%.

(Comparative Examples 5-7)
As in Examples 1 to 3, a polystyrene resin (trade name “XC-515”) and a mixed resin (trade name “Noryl EFN4230”, PPE / PS = 70/30) are contained at a ratio of 70:30. A container was produced in the same manner as in Examples 1 to 3, using a foam sheet and a laminated sheet obtained by laminating a dry laminate film on the foam sheet.
In Comparative Examples 5 to 7, the butane content is lower than the laminated sheets and foamed sheets used in Examples 1 to 3 by reducing the sheet surface cooling air amount immediately after extrusion and adjusting the injection gas amount. The container was produced using few laminated sheets and foam sheets.
As in Example 1, in Comparative Example 5 using a laminated sheet having a dry laminate film laminated on both sides, the i-butane content in the polystyrene resin foam layer of the container was 1.30% by mass, and n- The butane content was 0.18% by mass (total butane content: 1.48% by mass).
The butane content of this container was about 90% with respect to the butane content in the polystyrene resin foam layer of the laminated sheet before thermoforming.
Moreover, similarly to Example 2, in Comparative Example 6 using a laminated sheet laminated with a dry laminate film on one side, the i-butane content in the polystyrene resin foam layer of the container is 1.29% by mass, The n-butane content was 0.11% by mass (total butane content: 1.40% by mass).
Moreover, the butane content of the container was about 82% with respect to the butane content in the polystyrene resin foam layer of the laminated sheet before thermoforming.
Furthermore, similarly to Example 3, in Comparative Example 7 using the foamed sheet itself, the i-butane content in the container was 1.07% by mass, and the n-butane content was 0.19% by mass ( Total butane content: 1.26% by mass).
Moreover, the butane content of this container with respect to the butane content in the foamed sheet before thermoforming was about 75%.

(Comparative Example 8)
In Comparative Example 8, a container was produced using a laminated sheet having a dry laminate film laminated on both sides.
The i-butane content in the polystyrene resin foam layer of the container of Comparative Example 8 is 1.25% by mass, and the n-butane content is 0.22% by mass (total butane content: 1.47% by mass). %)Met.
Further, the butane content of this container relative to the butane content in the polystyrene resin foam layer of the laminated sheet before thermoforming was about 78%.
These evaluation results are shown in Tables 2 and 3 below.

From the above, it can be cut by adding 1.5% by mass or more of butane to the polystyrene resin foam layer containing the polyphenylene ether resin so that the ratio to the total with the polystyrene resin is 10% by mass or more. It turns out that generation | occurrence | production of powder | flour can be suppressed and the outstanding intensity | strength can be provided to the container for foodstuffs.
That is, according to the present invention, a method for producing a thermoformed product effective for imparting toughness to the polystyrene-based resin foam layer is provided, food having excellent strength, and generation of chips is suppressed. It can be seen that a container is provided.

(Reference experiment)
A polystyrene resin composition containing a polyphenylene ether resin and a polystyrene resin composition not containing a polyphenylene ether resin are coextruded to correspond to the layer corresponding to the foam sheet in Example 1 and the foam sheet in Comparative Example 1. A foam sheet having a two-layer structure of layers to be manufactured was prepared.
Similarly to Examples 1 and 2, a laminated sheet obtained by laminating a double-sided film on this foamed sheet and a laminated sheet obtained by subjecting only one side to dry lamination were produced, and a thermoformed product was produced in the same manner as in Examples 1 and 2. .

  As a result, the butane content of the double-sided laminate was 2.34% by mass (i-butane: 1.99% by mass, n-butane: 0.35% by mass), and the butane content of the single-sided laminate was 2.31. It is mass% (i-butane: 1.93 mass%, n-butane: 0.38 mass%), and both-sided laminates contain more butane in the thermoformed product. all right.

  Further, the same comparison was carried out with the period from the production of the foam sheet to thermoforming being about one month, but the butane content of the double-sided laminate was 2.57% by mass (i-butane: 1.98% by mass). %, N-butane: 0.59% by mass), butane content of the single-sided laminate is 2.44% by mass (i-butane: 1.90% by mass, n-butane: 0.54% by mass) Thus, it was found that the one laminated on both sides contained more butane in the thermoformed product.

1: Laminated sheet (resin sheet), 10: polystyrene resin foam layer, 10x: polystyrene resin foam sheet, 20: film layer, A, B: surface skin layer

Claims (7)

A method for producing a thermoformed product by thermoforming a resin sheet having a polystyrene resin foam layer to produce a thermoformed product,
Using the resin sheet having a polystyrene resin foam layer obtained by foaming a mixed resin containing a polyphenylene ether resin and a polystyrene resin in a mass ratio of 10:90 to 50:50 with a foaming agent containing butane, A method for producing a thermoformed product, comprising producing a thermoformed product containing 1.5% by mass or more of butane at a location formed by the polystyrene resin foam layer.   The thermoformed article according to claim 1, wherein the thermoforming is performed so that the butane content in the thermoformed article is 0.8 times to 1.0 times the butane content in the resin sheet. Method.   A resin film is laminated on at least one surface of a polystyrene resin foam sheet obtained by extruding and foaming a mixed resin containing a polyphenylene ether resin and a polystyrene resin in a mass ratio of 10:90 to 50:50 together with a foaming agent containing butane. The method for producing a thermoformed product according to claim 1 or 2, wherein the resin sheet having a film layer made of the resin film together with the polystyrene resin foam layer is thermoformed.   The method for producing a thermoformed article according to claim 3, wherein the resin film is any one of a polyethylene terephthalate resin film, a stretched polypropylene resin film, and an unstretched polypropylene resin film. The average density of both surfaces of the polystyrene resin foam sheet is higher than the average density of the entire polystyrene resin foam sheet, and the average density from the both surfaces to the depth of 0.2 mm in the thickness direction is 0.10 g / cm ³ or more. The method for producing a thermoformed article according to claim 3 or 4, wherein the surface bubble film thickness is 7 µm or more.   The method for producing a thermoformed product according to any one of claims 3 to 5, wherein an open cell ratio of the polystyrene-based resin foam sheet is less than 15%.   A food container produced by the method for producing a thermoformed product according to any one of claims 1 to 6.

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