JP5898552B2 - Polystyrene resin foam sheet and polystyrene resin molded container - Google Patents

Description

  The present invention relates to a polystyrene-based resin foam sheet used for the production of food packaging containers such as trays and natto containers, and in particular, a polystyrene-based resin foam sheet capable of manufacturing a molded container having a sufficient strength while being lightweight. And a molded container.

Polystyrene resin foam sheets are widely used as lightweight, high-strength containers that are difficult to break, such as food packaging containers such as trays and natto containers. In the field of food packaging containers, there has always been a demand for price reduction and weight reduction of containers, and the demand has become stronger due to recent enforcement of the Container Recycling Law.
In order to meet this requirement, various attempts have been made to reduce the weight of the container. However, as an adverse effect of the weight reduction, there is a problem that the brittleness of the container and the piercing strength are lowered.
Conventionally, for example, techniques disclosed in Patent Documents 1 to 3 have been proposed for containers manufactured using polystyrene-based resin foam sheets.

  In Patent Document 1, it is used for automatic filling and packaging including at least a step of sequentially transporting containers, a step of filling contents into the containers on the transport device, and a step of sliding the bottom surface of the container between and / or on the transport devices. A container obtained by thermoforming a polystyrene-based resin extruded foam sheet, wherein the container is made of a polystyrene-based resin foam at least on the bottom and has a dynamic friction coefficient of 0.9 or less on the bottom of the container. A featured polystyrene resin foam container is disclosed.

  Patent Document 2 discloses a polystyrene resin foam used in a method in which a polystyrene resin foam sheet is thermoformed and a plurality of molded articles are joined to separate molded articles by heat rays to obtain products. In the sheet, there is disclosed a polystyrene-based resin foam sheet characterized in that the ash content in the foam sheet is 0.35% by mass or less.

  Patent Document 3 discloses a container main body in which a storage concave portion for storing natto is formed leaving a flat rectangular flange around the opening, and a lid body connected to the container main body via a hinge portion. The lid body has a rib-like convex part having a U-shaped cross section that can be fitted inside the opening of the housing concave part of the container body, leaving a flange part on the outer peripheral part. It is formed in a flat U shape excluding the hinge side and protrudes on the lower surface side in the closed state, leaving a flat U-shaped flat portion that is flush with the flange portion along the inside of the rib-like convex portion. By forming the side portion bulging to the lower surface side in the closed state, a concave portion for accommodating the seasoning material storage bag is formed on the upper surface side in the closed state, and at least one of the horizontal and vertical insertion dimensions in the opening of the concave portion Is the passing dimension on the bottom lower surface of the container body Natto container, characterized in that it is smaller than the diametral dimension of the corresponding direction is disclosed.

JP-A-8-104386 JP 2004-35712 A JP 2010-179934 A

  However, the conventional polystyrene resin foam sheets described in Patent Documents 1 to 3 described above are formed by extrusion foam molding with approximately the same size of bubbles existing in the sheet thickness direction, and this foam sheet is heated. When the molded container obtained by molding is reduced in weight, the resin density decreases as a whole, so that the strength quality required for the container decreases.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the polystyrene-type resin foam sheet and molded container which can manufacture the molded container which can ensure the required quality of intensity | strength though it is lightweight.

In order to achieve the above object, the present invention provides a polystyrene resin foam sheet having a thickness in the range of 1.0 to 2.0 mm and an overall density in the range of 0.06 to 0.11 g / cm ^3. One or both of the front and back surfaces of the sheet have a surface layer density of 0.10 to 0.15 g / cm ³ from the surface to 20% of the total thickness (where surface layer density> total density). There is provided a polystyrene-based resin foam sheet characterized in that the average cell diameter of the surface layer is in the range of 20 to 60 μm.

  In the polystyrene resin foam sheet of the present invention, when the average cell diameter of the surface layer is D1, and the average cell diameter inside the sheet other than the surface layer is D2, the ratio of the average cell diameter between the surface layer and the inside (D1 / D2) is It is preferable to be within the range of 0.3 to 0.6.

  The present invention also provides a molded container obtained by thermoforming the polystyrene-based resin foam sheet.

In the present invention, the thickness is in the range of 1.5 to 5.0 mm, the overall density is in the range of 0.02 to 0.07) g / cm ³ , and from the surface to 20% of the total thickness. Provided is a molded container having an average cell diameter of 60 to 120 μm in the surface layer.

  In the molded container of the present invention, it is preferable that the molded container has a tray shape.

  In the molded container of the present invention, the molded container is preferably a natto container including a container main body and a lid connected to a part of the container main body via a hinge portion.

The polystyrene resin foam sheet of the present invention is a polystyrene resin foam sheet having a thickness in the range of 1.0 to 2.0 mm and an overall density in the range of 0.06 to 0.11 g / cm ^3. One or both of the front and back surfaces of the sheet has a surface layer density ranging from the surface to 20% of the total thickness within a range of 0.10 to 0.15 g / cm ³ (where surface layer density> total density). The density of one or both of the surface layers of the front and back surfaces of the sheet is increased by adopting a configuration in which the average cell diameter of the surface layer is in the range of 20 to 60 μm, and even when the foamed sheet is foamed, Since the surface structure side that requires strength can be strengthened while maintaining the characteristics of the cell structure, a molded container that can be reduced in weight while satisfying the required performance of strength can be manufactured.

The molded container of the present invention has a thickness in the range of 1.5 to 5.0 mm, an overall density in the range of 0.02 to 0.07 g / cm ³ , and from the surface to 20% of the total thickness. By adopting a configuration in which the average cell diameter of the surface layer is in the range of 60 to 120 μm, the surface layer side that requires strength can be strengthened, so that weight reduction can be achieved while satisfying the required performance of strength.

It is a block diagram which shows an example of the manufacturing apparatus of a polystyrene-type resin foam sheet. 2 is an enlarged image of a cross section of a foam sheet manufactured in Example 1. FIG. 3 is an enlarged image of a cross section of a foam sheet manufactured in Comparative Example 1. FIG. It is a perspective view which shows the structure of the natto container manufactured in the Example.

(Polystyrene resin foam sheet)
The polystyrene resin foam sheet of the present invention is a polystyrene resin foam sheet having a thickness in the range of 1.0 to 2.0 mm and an overall density in the range of 0.06 to 0.11 g / cm ^3. One or both of the front and back surfaces of the sheet has a surface layer density ranging from the surface to 20% of the total thickness within a range of 0.10 to 0.15 g / cm ³ (where surface layer density> total density). The average cell diameter of the surface layer is in the range of 20 to 60 μm.

FIG. 2 is an enlarged image of a cross section of the polystyrene resin foam sheet produced in Example 1 according to the present invention. The polystyrene resin foam sheet of the present invention shown in FIG. 2 has a cross-sectional cell structure in which the surface layer and the back surface have a surface layer with a density larger than the inside (thickness central portion) and an average cell diameter smaller than the inside. It has a three-layer structure. The density of the surface layer is in the range of 0.10 to 0.15 g / cm ³ , and the average bubble diameter is in the range of 50 μm to 100 μm.
On the other hand, FIG. 3 is an enlarged image of a cross section of the polystyrene-based resin foam sheet manufactured in Comparative Example 1 corresponding to the prior art. In the polystyrene-based resin foam sheet of Comparative Example 1, the cell structure of the cross section is substantially equal in the thickness direction in both the specific gravity and the average cell diameter.

The polystyrene resin foam sheet of the present invention has a thickness in the range of 1.0 to 2.0 mm, preferably in the range of 1.0 to 1.6 mm, and in the range of 1.0 to 1.4 mm. More preferably, it is within.
If the thickness of the polystyrene-based resin foam sheet is within the above range, the polystyrene-based resin foam sheet can be foamed when thermoformed to produce a molded container such as a tray or a natto container having an appropriate thickness. If the thickness is less than the above range, it is difficult to obtain a molded container that satisfies the required quality of strength. If the thickness exceeds the above range, the resulting molded container may be unnecessarily thick, or the problem of providing a lightweight molded container may not be achieved.

Polystyrene-based resin foam sheet of the present invention are within the overall density of 0.06~0.11g / cm ^3, preferably in the range of 0.07~0.11g / cm ^3, 0. More preferably, it is within the range of 08 to 0.11 g / cm ³ .
If the overall density of the polystyrene resin foam sheet is within the above range, the polystyrene resin foam sheet may be foamed when thermoformed to produce a molded container such as a tray or a natto container that satisfies the required quality of strength. it can. If the overall density is less than the above range, it is difficult to obtain a molded container that satisfies the required quality of strength. If the density exceeds the above range, the problem of providing a lightweight molded container may not be achieved.

The polystyrene-based resin foam sheet of the present invention has a density of one or both of the surface layers of the front and back surfaces of the sheet within a range of 0.10 to 0.15 g / cm ³ (where surface layer density> overall density), 0 preferably in the range of .11~0.15g / cm ^3, and more preferably in a range of 0.12~0.15g / cm ^3.
If the density of the surface layer is less than the above range, the difference between the density of the inside (thickness center) and the surface layer density may be reduced, leading to a decrease in strength of the molded container. If the density of the surface layer exceeds the above range, the problem of providing a lightweight molded container may not be achieved.

In the polystyrene resin foam sheet of the present invention, the average cell diameter of one or both of the front and back surfaces of the sheet is in the range of 20 to 60 μm, preferably in the range of 25 to 60 μm, and in the range of 30 to 60 μm. More preferably, it is within.
When the average cell diameter of the surface layer is less than the above range, it is difficult to obtain a molded container that is lightweight and satisfies the required quality of strength. When the average cell diameter of the surface layer exceeds the above range, it is difficult to obtain a molded container that satisfies the required quality of strength.

In the polystyrene resin foam sheet of the present invention, when the average cell diameter of the surface layer is D1, and the average cell diameter inside the sheet other than the surface layer is D2, the ratio of the average cell diameter between the surface layer and the inside (D1 / D2) is It is preferably within the range of 0.3 to 0.6, and more preferably within the range of 0.4 to 0.6.
When the ratio of the average bubble diameter (D1 / D2) is less than the above range, it is difficult to obtain a molded container that is lightweight and satisfies the required quality of strength. When the ratio of the average bubble diameter (D1 / D2) exceeds the above range, it is difficult to obtain a molded container that satisfies the required quality of strength.

  As the polystyrene resin constituting the polystyrene resin foam sheet of the present invention, any resin can be used as long as it can usually be a foam and can be a rigid foam. Examples include styrene, methyl styrene, ethyl styrene, isopropyl styrene, dimethyl styrene, paramethyl styrene, chloro styrene, bromo styrene, vinyl toluene, vinyl xylene homopolymer, or maleic anhydride, acrylic acid, butadiene, etc. Polymers can be used. Of these, polystyrene, styrene-maleic anhydride copolymer, styrene-acrylic acid copolymer, impact-resistant polystyrene, styrene-acrylonitrile copolymer, and acrylonitrile-butadiene-styrene copolymer are preferably used.

  A foaming agent is used to foam the polystyrene resin. As such a blowing agent, nitrogen dioxide, carbon dioxide, propane, n-butane, i-butane, n-pentane, i-pentane, and a mixture of two or more thereof are used. When producing the polystyrene-based resin foam sheet of the present invention, an extruder is used for adding the foaming agent to the polystyrene-based resin to cause foaming. The screw of the extruder may be uniaxial or biaxial. Further, for example, it can be used in a configuration in which two having an inner diameter of 90 mm and one having an inner diameter of 150 mm are connected. An extruder having a structure in which two are connected is preferably used because it has good kneadability between a polystyrene resin and a foaming agent and is excellent in foamability.

  Various additives known in the field of polystyrene resin production can be added to the polystyrene resin foam sheet of the present invention. Additives include, for example, bubble regulators, antioxidants, metal deactivators, flame retardants, UV absorbers, crosslinking agents, chain transfer agents, lubricants, plasticizers, fillers, reinforcing materials, pigments, dyes, charging Examples include inhibitors.

FIG. 1 is a diagram showing an example of a foam sheet manufacturing apparatus used for manufacturing the polystyrene resin foam sheet of the present invention.
The manufacturing apparatus of this example includes a first extruder 1 and a second extruder 2 constituting a tandem type extruder, a die 3 (circular die) attached to a discharge port of the second extruder 2, and a first extruder. A raw material blending device 4 for feeding a thermoplastic resin and an additive to the extruder 1, a hopper 5 for feeding the raw material from the raw material blending device 4, a foaming agent press-fitting pump 6 connected to the first extruder 1, A plug 7 provided adjacent to the outlet of the die 3, a cutter 8 for cutting a tubular sheet provided downstream of the plug 7 in the sheet take-up direction, and two sheets obtained by cutting with the cutter 8. A take-up roll 10 for applying a take-up force to the foamed sheet 9 and a take-up machine for taking up the taken-up foamed sheet 9 as a take-up foamed sheet roll 11 are provided.

  Between the die 3 and the plug 7, an air outlet of a cooling fan (not shown) is provided, and is extruded into a cylindrical shape from the annular opening of the die 3, and is used for cooling inside and outside of the foamed cylindrical foam. The air is blown to guide the outer surface of the plug 7 while cooling the cylindrical foam.

The resin and additive charged into the first extruder 1 of the tandem type extruder from the hopper 5 are melted and mixed in the first extruder 1 to form a resin melt, and a foaming agent press-fitting pump 6 is added to the resin melt. The foaming agent is pressed through and mixed with the resin melt.
Next, this mixture is supplied to the second extruder 2, further kneaded, cooled to an appropriate temperature, and then guided to the resin flow path of the die 3 attached to the discharge port of the second extruder 2. The molten mixture guided to the resin flow path of the die 3 is extruded into the atmosphere in a cylindrical shape with an arbitrary extrusion amount at the outlet of the die 3 (the outlet of the resin flow path), and simultaneously with the extrusion. Foam.

  The cylindrical foamed sheet obtained by this foaming is cooled by a cooling plug 7, and then a predetermined portion is cut by a cutter 8 and developed into a flat shape to form two foamed sheets 9. Each of these foam sheets 9 is pulled by a take-up roll 10 and wound into a roll shape to form a foam sheet roll 11.

The polystyrene resin foam sheet of the present invention is a polystyrene resin foam sheet having a thickness in the range of 1.0 to 2.0 mm and an overall density in the range of 0.06 to 0.11 g / cm ^3. One or both of the front and back surfaces of the sheet has a surface layer density ranging from the surface to 20% of the total thickness within a range of 0.10 to 0.15 g / cm ³ (where surface layer density> total density). The density of one or both of the surface layers of the front and back surfaces of the sheet is increased by adopting a configuration in which the average cell diameter of the surface layer is in the range of 20 to 60 μm, and even when the foamed sheet is foamed, Since the surface structure side that requires strength can be strengthened while maintaining the characteristics of the cell structure, a molded container that can be reduced in weight while satisfying the required performance of strength can be manufactured.

(Molded container)
The molded container of the present invention has a thickness in the range of 1.5 to 5.0 mm, an overall density in the range of 0.02 to 0.07 g / cm ³ , and from the surface to 20% of the total thickness. The average cell diameter of the surface layer is in the range of 60 to 120 μm.
Moreover, it is preferable that the shaping | molding container of this invention is a thing obtained by thermoforming the polystyrene-type resin foam sheet of this invention mentioned above. The molded container obtained by thermoforming the polystyrene resin foam sheet maintains the characteristics of the cell structure of the polystyrene resin foam sheet even after thermoforming, and can strengthen the surface layer side that requires strength, It is possible to reduce the weight while satisfying the required strength performance.

  The shape of the molded container of the present invention is not particularly limited. For example, a rectangular, circular, elliptical, semi-circular, fan-shaped or other tray, square-shaped, cup-shaped, rectangular-shaped container with a lid such as a natto container And various shapes of molded containers.

FIG. 4 is a view showing a natto container A which is an example of the molded container of the present invention.
The natto container A in this example has a concave cross-section opening on the upper surface, and a storage recess 22 for storing natto B as the contents is formed around the opening 23 leaving a flat rectangular flange portion 24. A container body 21 and a lid body 25 that is connected to one side end of the container body 21 via a hinge portion 26 so as to be freely opened and closed. Usually, the flange part 24 of the said container main body 21 is utilized as a receiving part by the support member, arm member, etc. for a transfer in a natto production line. The hinge portion 26 is formed so that it can be bent by 180 ° by two parallel V-shaped grooves as shown in the figure, for example.

The lid 25 has a flange-shaped projection 28 having a U-shaped cross section of an inner / outer double wall that can be fitted inside the opening 23 of the storage recess 22, leaving a flange 27 on the outer periphery. Except for the part 26 side, it is formed so as to protrude on the lower surface side (container inner surface side) facing the container main body 25 when the lid is closed so as to form a substantially U-shape. Further, the inner portion swells to the lower surface side (the container inner surface side) when the lid is closed, leaving a flat portion 29 having a planar U-shape that is flush with the flange portion 27 along the inside of the rib-shaped convex portion 28. Recess 30 for accommodating a seasoning storage bag formed by storing the seasoning material such as soy sauce sauce and eggplant in an openable bag on the upper surface side (container outer surface side) when closed. Is formed. The concave portion 30 is not formed with the flat portion 29 and the rib-shaped convex portion 28 on the hinge portion 26 side, so that it is expanded on the hinge portion 26 side, whereby a space for accommodating the seasoning material storage bag can be accommodated. Is secured.
In order to take in air necessary for fermentation and ripening of the natto B stored in the storage recess 2 in the closed state, the lid 25 includes, for example, the recess 30, the flat portion 29, the rib-shaped protrusion 28, etc. Ventilation pores 31 such as needle holes that have air permeability but can suppress the entry of dust and the like are formed at appropriate intervals at required portions of the portion.

The molded container of the present invention has a thickness in the range of 1.5 to 5.0 mm, and preferably in the range of 1.5 to 3.5 mm.
If the thickness of the molded container is less than the above range, the strength of the molded container may be reduced. If the thickness of the molded container exceeds the above range, the thickness of the molded container may become unnecessarily thick or the problem of providing a lightweight molded container may not be achieved.

Molded container of the present invention, the entire density is in the range of 0.02~0.07g / cm ^3, preferably in the range of 0.02~0.05g / cm ^3.
If the total density of the molded container is less than the above range, the strength of the molded container may be reduced. If the overall density of the molded container exceeds the above range, the problem of providing a lightweight molded container may not be achieved.

In the molded container of the present invention, the average cell diameter of the surface layer from the surface to 20% of the total thickness is in the range of 60 to 120 μm, and preferably in the range of 80 to 120 μm.
When the average cell diameter of the surface layer is less than the above range, it is difficult to obtain a molded container that is lightweight and satisfies the required quality of strength. When the average cell diameter of the surface layer exceeds the above range, it is difficult to obtain a molded container that satisfies the required quality of strength.

  Since the molded container of the present invention can strengthen the surface layer side that requires strength, the weight can be reduced while satisfying the required performance of strength.

[Example 1]
(Manufacture of polystyrene resin foam sheets)
As shown in FIG. 1, a polystyrene resin foam sheet was manufactured using a manufacturing apparatus including a tandem extruder in which an inner diameter 115 mm extruder and a 180 mm extruder were connected as an extruder.
100% by mass of G9305 (trade name) manufactured by PS Japan as polystyrene resin, and 0.5 parts by mass of DSM-1401A (trade name) manufactured by Toyo Styrene Co., Ltd. as a foam nucleating agent was added to 100 parts by mass of the resin. The raw material was supplied to the first extruder, melted and kneaded at 200 to 230 ° C. in the extruder, and then butane (iso / normal = 70/30% by mass) as a foaming agent was 4.0 with respect to 100 parts by mass of the resin. A part by mass was added and further kneaded. Then, it cooled to resin temperature 148 degreeC suitable for foaming.
Further, a foaming agent-containing resin is extruded at a discharge rate of 350 kg / h from a circular die set at a diameter of 170 mm and a slit clearance of 0.25 mm attached to the tip of the second extruder. A foam sheet was obtained.
At this time, the air volume is the outer circumferential side (Table) 0.032m ³ / ^{m 2,} the inner surface side (back) 0.032m ³ / m of air for cooling the cylindrical sheet after being extruded (temperature 32 ° C.) ² .
Subsequently, the cylindrical foamed sheet was cut by a cutter provided on the left and right sides to obtain two primary sheets. Each primary sheet was wound around a winding roll while stretching between multiple rolls. At the time of winding, the drawing speed was set to 26.0 m / min in order to add stretching in the MD direction of the primary sheet. A polystyrene resin foam sheet having a sheet width of 1050 mm, a sheet thickness of 1.2 mm, and an overall density of 0.09 g / cm ³ (expansion ratio: 11.5 times) was obtained.

(Manufacture of molded containers)
Male-female fitting gold that was heated using a small single molding machine for molding polystyrene foam sheets so that the sheet thickness immediately before molding the sheet was 2.0 to 2.2 times, and the surface temperature was adjusted to 80 ° C. A container having an opening of 80 mm × 80 mm, a bottom of 60 mm × 60 mm, a depth of 25 mm, and a wall thickness of about 2.3 mm was formed with a mold, and the obtained container was cut out with a nichrome wire so that the outer shape would be 100 mm × 100 mm.

  About the polystyrene resin foam sheet and the natto container manufactured as described above, <Measurement of sheet thickness>, <Measurement of density>, <Measurement of average bubble diameter>, <Measurement of top and bottom compression strength>, <Measurement of piercing strength >, <Evaluation of formability>, and <Evaluation of brittleness> were carried out under the following methods and conditions. The results are shown in Table 1.

<Measurement of sheet thickness>
Measure the thickness of the part of the polystyrene resin foam sheet excluding both ends of 20 mm in the width direction using a dial thickness gauge SM-112 (manufactured by Teclock Co.) at 9 or more points in the width direction. The average thickness was determined by arithmetic averaging.

<Measurement of density>
-Whole density: The part except 20 mm of the both ends of the width direction of a polystyrene-type resin foam sheet is cut out to 9 cm or more and 10 cm x 10 cm at equal intervals in the width direction, and the mass of each section | slice is measured. Further, the thickness of each slice was measured using a dial thickness gauge SM-112 (manufactured by Teclock), the volume was measured, the density was calculated from the following formula, and the value obtained by arithmetically averaging the density of each slice was The total density was taken.
Density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm ³ )
-Surface layer density: width obtained by slicing with a slicer (split machine manufactured by Fortuna (Germany), model AB-320-D) from the sheet surface so as to be 20% of the sheet thickness measured by measuring the sheet thickness After cutting to 25 mm and a length of 150 mm, the mass and volume were measured, and the surface layer density was calculated from the following formula.
Surface layer density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm ³ )
However, the test specimen for measurement is cut out from a sample that has passed 72 hours or more after molding, and is subjected to atmospheric conditions of 23 ° C. ± 2 ° C./50 RH% ± 5 RH% or 27 ° C. ± 2 ° C./65 RH% ± 5 RH% for 16 hours or more It is what was left.
Internal density: The internal density is a test piece obtained by cutting the remaining part of the sample obtained by slicing 20% of the total thickness from the front and back surface layers at the surface layer density into a width of 25 mm and a length of 150 mm. The internal density was calculated in the same manner as the surface layer density.
Internal density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm ³ )
-Surface density of the bottom of the container: A flat position at the bottom of the molded container is cut out to 25 mm x 25 mm, and the thickness is measured using a dial thickness gauge SM-112 (manufactured by Teclock Corporation), so that the thickness becomes 20% of the thickness. The slice is sliced from the surface with a slicer (Fortuna (Germany) splitting machine, model AB-320-D). The mass and volume of the sliced piece were measured, and the bottom surface layer density was determined from the following measurement formula.
Bottom surface layer density (g / cm ³ ) = Test piece mass (g) / Test piece volume (cm ³ )
-Flange surface layer density: The flat portion of the flange portion of the molded container is cut into 5 mm x 50 mm, and the thickness is measured using a dial thickness gauge SM-112 (manufactured by Teclock Corporation), and becomes 20% of the thickness. In this manner, the slicer is sliced from the surface with a slicer (a splitting machine manufactured by Fortuna (Germany), model AB-320-D). The mass and volume of the slice piece were measured, and the flange layer surface density was determined from the following measurement formula.
Flange surface layer density (g / cm ³ ) = test piece mass (g) / test piece volume (cm ³ )

<Measurement of average bubble diameter>
-Average bubble diameter of sheet: The average bubble diameter (D) of the sheet was obtained by photographing a cross section perpendicular to the extrusion direction with a microscope at 10 points at equal intervals in the width direction of the sheet, and the sheet thickness (t ). Next, a straight line is drawn in the thickness direction of each cross-sectional photograph, and the number of all bubbles (N) intersecting the straight line is counted. The bubble diameter (t / N) is calculated for each cross-sectional photograph from t and N thus obtained, and the average of 10 (t / N) is taken as the average bubble diameter (D). When drawing a straight line, the straight line should be penetrated as much as possible without making point contact with the bubbles. In addition, when some bubbles are in point contact with a straight line, these bubbles are also included in the number of bubbles.
-Inner cell diameter of the sheet: The inner cell diameter (D2) of the sheet is the surface layer thickness (t1) of 20% from the sheet surface on both sides of the sheet from the sheet thickness (t) measured by the average cell diameter measurement. The removed length (t2) is measured. Next, of the bubbles intersecting with the straight line drawn in the thickness direction of each cross-sectional photograph in the average bubble diameter measurement, the number of bubbles (N2) between t2 is counted. The bubble diameter (t2 / N2) is calculated for each cross-sectional photograph from t2 and N2 obtained in this way, and the average of 10 (t2 / N2) is defined as the surface layer bubble diameter (D2). In addition, in the period between t2, when both ends of the straight line do not penetrate the bubbles and are positioned in the bubbles, the bubbles in which both ends of the straight line are positioned are included in the number of bubbles. In addition, when some bubbles are in point contact with a straight line, these bubbles are also included in the number of bubbles.
-Surface cell bubble diameter of the sheet: The surface cell bubble diameter (D1) of the sheet is 20% from the sheet surface of the sheet thickness (t) measured by the average cell diameter measurement (t1). Next, the number of bubbles (N1) between t1 among the bubbles intersecting the straight line drawn in the thickness direction of each cross-sectional photograph in the average bubble diameter measurement is counted. The bubble diameter (t1 / N1) is calculated for each cross-sectional photograph from t1 and N1 thus obtained, and the average of 10 (t1 / N1) points is defined as the surface layer bubble diameter (D1). In addition, when the end of the straight line does not penetrate the bubble and is positioned in the bubble during t1, the bubble in which the end of the straight line is positioned is included in the number of bubbles. In addition, when some bubbles are in point contact with a straight line, these bubbles are also included in the number of bubbles.
-Container bottom part average bubble diameter: The container bottom part average bubble diameter (D3) measures the container bottom part thickness (t3) about each cross-sectional photograph by image | photographing the container bottom part cross section which cut | disconnected the shaping | molding container arbitrarily 10 places. . Next, a straight line is drawn in the thickness direction of each cross-sectional photograph, and the number of all bubbles (N3) crossing the straight line is counted. The bubble diameter (t3 / N3) is calculated for each cross-sectional photograph from t3 and N3 obtained in this manner, and the average of the 10 (t3 / N3) is taken as the vessel bottom average bubble diameter (D3). When drawing a straight line, the straight line should be penetrated as much as possible without making point contact with the bubbles. In addition, when some bubbles are in point contact with a straight line, these bubbles are also included in the number of bubbles.
-Container bottom surface bubble diameter: The container bottom surface bubble diameter (D4) has a thickness of 20% from the surface of the bottom thickness (t3) measured by the above-mentioned container bottom average bubble diameter measurement (t4). Next, of the bubbles intersecting with the straight line drawn in the thickness direction of each cross-sectional photograph in the measurement of the average bubble diameter at the bottom of the container, the number of bubbles (N4) between t4 is counted. The bubble diameter (t4 / N4) is calculated for each cross-sectional photograph from t4 and N4 thus obtained, and the average of the 10 (t4 / N4) points is taken as the vessel bottom surface bubble diameter (D4). In addition, in the period between t4, when the end portion of the straight line does not penetrate the bubble and is located in the bubble, the bubble in which the end portion of the straight line is positioned is included in the number of bubbles. In addition, when some bubbles are in point contact with a straight line, these bubbles are also included in the number of bubbles.
-Flange part average bubble diameter: Container flange part average bubble diameter (D5) cut | disconnects a container flange part arbitrarily 10 places, the cross section is image | photographed with a microscope, and flange thickness (t5) is measured about each cross-sectional photograph. . Next, a straight line is drawn in the thickness direction of each cross-sectional photograph, and the number of all bubbles (N5) crossing the straight line is counted. The bubble diameter (t5 / N5) is calculated for each cross-sectional photograph from t5 and N5 thus obtained, and the average of 10 (t5 / N5) is defined as the flange part average bubble diameter (D5). When drawing a straight line, the straight line should be penetrated as much as possible without making point contact with the bubbles. In addition, when some bubbles are in point contact with a straight line, these bubbles are also included in the number of bubbles.
-Flange part surface bubble diameter: The container flange part surface bubble diameter (D6) is a flange part surface layer thickness of 20% from the surface of the flange thickness (t5) measured by the flange part average bubble diameter measurement (t6). . Next, of the bubbles intersecting with the straight line drawn in the thickness direction of each cross-sectional photograph in the measurement of the average bubble diameter of the flange portion, the number of bubbles (N6) between t6 is counted. The bubble diameter (t6 / N6) is calculated for each cross-sectional photograph from t6 and N6 obtained in this manner, and the average of the 10 (t6 / N6) points is defined as the surface layer bubble diameter (D6). In addition, in the period between t6, when the end portion of the straight line does not penetrate the bubble and is located in the bubble, the bubble in which the end portion of the straight line is positioned is included in the number of bubbles. In addition, when some bubbles are in point contact with a straight line, these bubbles are also included in the number of bubbles.

<Measurement of top and bottom compression strength>
Using a Tensilon universal testing machine RTG-1310 (manufactured by Orientec Co., Ltd.), a container is placed on a dedicated plate with a groove for air venting on the surface so that the bottom is on the top. The container is compressed at a test speed of 100 mm / min with a compression plate of φ120 mm. Compress up to a maximum of 10 mm, and let the average value of the maximum load at this time be the vertical compression strength (unit: N) of the container.

<Measurement of puncture strength>
It was measured in accordance with “2. Test methods for strength, etc.” in “Standards for Foods, Additives, etc. 3: Equipment and Containers and Packaging” in the Food Sanitation Law (Ministry of Health and Welfare Notification No. 20 of 1982). That is, using a Tensilon universal testing machine RTG-1310 (Orientec Co., Ltd.), a needle having a diameter of 1 mm and a tip diameter of 0.5 mm was pierced at the center of the bottom surface inside the container at a piercing speed of 50 mm / min. The strength at the time of penetrating was measured to determine the puncture strength.

<Evaluation of formability>
From the state of the heat-molded container, the moldability was evaluated in light of the following evaluation criteria.
Good (O): No perforation, crack or wrinkle is generated.
Slightly poor (Δ): No holes or cracks occur, but it is not uniform overall.
Defect (x): Perforations, cracks, and wrinkles occur.

<Evaluation of brittleness>
The container obtained by heat molding was allowed to stand in a natural state for 24 hours or more, and when a force was momentarily applied to the container, the brittleness was evaluated in light of the following evaluation criteria.
Good (O): Does not easily break and does not crack.
Defect (x): chipped easily and cracked.

[Example 2]
The air volume of air to cool the cylindrical sheet, 0.038 m ³ / ^{m 2} the outer peripheral side, except that the inner surface side and 0.032m ³ / ^{m 2,} a polystyrene resin foam sheet in the same manner as in Example 1, And manufactured a natto container. The obtained polystyrene resin foam sheet and natto container were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Example 3]
The air volume of air to cool the cylindrical seat, 0.032m ³ / ^{m 2} the outer peripheral side, except that the inner surface side and 0.035 m ³ / ^{m 2,} a polystyrene resin foam sheet in the same manner as in Example 1, And manufactured a natto container. The obtained polystyrene resin foam sheet and natto container were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Example 4]
A polystyrene resin foam sheet and a natto container were produced in the same manner as in Example 1 except that the amount of the foam nucleating agent added was changed to 0.65 parts by mass. The obtained polystyrene resin foam sheet and natto container were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Example 5]
The foam nucleating agent added amount is 0.43 parts by mass, the air volume of air to cool the cylindrical sheet, 0.036 m ³ / ^{m 2} the outer peripheral side, except that the inner surface side and 0.034 m ³ / ^{m 2} In the same manner as in Example 1, a polystyrene resin foam sheet and a natto container were produced. The obtained polystyrene resin foam sheet and natto container were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
The foam nucleating agent added amount is 0.32 parts by mass, the air volume of air to cool the cylindrical sheet, 0.020 m ³ / ^{m 2} the outer peripheral side, except that the inner surface side and 0.025 m ³ / ^{m 2} In the same manner as in Example 1, a polystyrene resin foam sheet and a natto container were produced. The obtained polystyrene resin foam sheet and natto container were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 2]
The air volume of air to cool the cylindrical sheet, 0.055 m ³ / ^{m 2} the outer peripheral side, except that the inner surface side and 0.055 m ³ / ^{m 2,} a polystyrene resin foam sheet in the same manner as in Example 1, And manufactured a natto container. The obtained polystyrene resin foam sheet and natto container were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 3]
A polystyrene resin foam sheet and a natto container were produced in the same manner as in Example 1 except that the overall density of the polystyrene resin foam sheet was 0.14 g / cm ³ (expansion ratio: 7.0 times). The obtained polystyrene resin foam sheet and natto container were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 4]
The air volume of air to cool the cylindrical seat, 0.031m ³ / ^{m 2} the outer peripheral side, the inner surface side and 0.031m ³ / ^{m 2,} the entire density 0.05 g / cm ³ (foamed polystyrene resin foam sheet A polystyrene resin foam sheet and a natto container were produced in the same manner as in Example 1 except that the ratio was 18.5 times. The obtained polystyrene resin foam sheet and natto container were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 5]
The foam nucleating agent added amount is 1.00 parts by mass, the air volume of air to cool the cylindrical sheet, 0.014 m ³ / ^{m 2} the outer peripheral side, except that the inner surface side and 0.014 m ³ / ^{m 2} In the same manner as in Example 1, a polystyrene resin foam sheet and a natto container were produced. The obtained polystyrene resin foam sheet and natto container were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1.

From the results in Table 1, the natto containers (molded containers) produced in Examples 1 to 5 according to the present invention have a surface layer density of 0.10 to 0.15 g / cm ³ from the surface to 20% of the total thickness. It is produced by thermoforming the polystyrene-based resin foam sheet according to the present invention within the range (however, the surface layer density> the overall density) and the average cell diameter of the surface layer is within the range of 20 to 60 μm. The obtained natto container was lightweight and excellent in strength. Further, the obtained natto container had high puncture strength and was good in terms of moldability and brittleness.

On the other hand, Comparative Example 1 is a polystyrene-based resin foam sheet having an average cell diameter of approximately the same size in the thickness direction, and the obtained natto container is inferior to those of Examples 1 to 5 in terms of compression strength and piercing strength. Further, the brittleness was poor.
Moreover, the comparative example 2 became a polystyrene-type resin foam sheet whose surface layer density is larger than the range of this invention, and the obtained natto container became inferior in moldability and brittleness.
Moreover, the comparative example 3 became a polystyrene-type resin foam sheet whose whole density exceeded the range of this invention, and the obtained natto container was not able to be reduced in weight.
Moreover, the comparative example 4 turns into a polystyrene-type resin foam sheet with a low whole density, and the obtained natto container is inferior to the thing of Examples 1-5 in the top and bottom compression strength and the piercing strength, and a moldability is a little inferior. The brittleness was poor.
Moreover, the comparative example 5 turns into a polystyrene-type resin foam sheet whose surface layer density is smaller than the range of this invention, and the obtained natto container is inferior to the thing of Examples 1-5 in the top and bottom compression strength and the piercing strength. The moldability was slightly poor.

  The present invention relates to a polystyrene-based resin foam sheet used for the production of food packaging containers such as trays and natto containers, and in particular, a polystyrene-based resin foam sheet capable of manufacturing a molded container having a sufficient strength while being lightweight. , And a molded container molded using the same.

  DESCRIPTION OF SYMBOLS 1 ... 1st extruder, 2 ... 2nd extruder, 3 ... Die, 4 ... Raw material compounding apparatus, 5 ... Hopper, 6 ... Foaming agent press injection pump, 7 ... Plug, 8 ... Cutter, 9 ... Foam sheet, 10 ... Take-up roll, 11 ... Foamed sheet roll, A ... Natto container (molded container), 21 ... Container body, 22 ... Storage recess, 23 ... Opening part, 24 ... Flange part, 25 ... Lid, 26 ... Hinge part, 27 ... flange part, 28 ... rib-like convex part, 29 ... flat part, 30 ... concave part, 31 ... pore.

Claims (6)

A polystyrene-based resin foam sheet having a thickness in the range of 1.0 to 2.0 mm and an overall density in the range of 0.06 to 0.11 g / cm ³ ,
One or both of the front and back surfaces of the sheet has a surface layer density of 0.10 to 0.15 g / cm ³ from the surface to 20% of the total thickness (where surface layer density> total density),
The average cell diameter of the surface layer (D1) is Ri range der of 20 to 60 [mu] m,
The average bubble diameter (D2) inside other than the surface layer is 111 μm or less,
A polystyrene-based resin foam sheet, wherein the ratio of the average cell diameter between the surface layer and the inside (D1 / D2) is in the range of 0.3 to 0.6 . The thickness is in the range of 1.5 to 5.0 mm,
The overall density is in the range of 0.02 to 0.07 g / cm ³ ;
A molded container made of polystyrene resin in which the average cell diameter of the surface layer from the surface to 20% of the total thickness is in the range of 60 to 120 μm. The molded container made of polystyrene-based resin according to claim 2 , which has a tray shape. The molded container made of polystyrene resin according to claim 2 or 3 , which is a natto container comprising a container main body and a lid connected to a part of the container main body via a hinge portion.   The density of the surface layer is 0.08 g / cm ³ The molded container made of polystyrene resin according to any one of claims 2 to 4, which is described above.   The molded container made of polystyrene resin according to any one of claims 2 to 5, wherein the average average cell diameter is 128 µm or more.