JP7010782B2 - Polystyrene resin laminated foam sheet and container - Google Patents

Description

The present invention relates to a polystyrene-based resin laminated foam sheet and a container obtained by thermoforming the foam sheet. Specifically, although it is lightweight, it has high strength when the container opening is compressed in the horizontal direction. The present invention relates to a polystyrene-based resin laminated foamed sheet capable of thermoforming a container having a large amount of deflection until it breaks when compressed in the horizontal direction, and a container obtained by thermoforming the foamed sheet.

The molded product obtained by thermoforming a polystyrene resin laminated foam sheet in which a polyethylene resin film or the like is laminated and bonded to a polystyrene resin foam sheet is widely used in supermarkets and convenience stores as food containers such as trays and lunch boxes. Has been done.

From the viewpoint of reducing the price of the container, it is preferable that the basis weight of the laminated foam sheet for thermoforming such a container is small. However, the lightweight thermoformed container obtained from the laminated foam sheet having a small basis weight tends to have low mechanical strength (particularly stiffness strength). Therefore, conventionally, for example, when the foamed sheet is extruded, the mechanical strength of the container obtained by blowing cooling air on the foam immediately after being extruded from the die to increase the density of the surface layer portion of the foamed sheet is obtained. Has been done to improve.

For example, Patent Document 1 describes a polystyrene-based resin foam sheet having a thickness of 1.0 to 2.0 mm and an overall density of 0.06 to 0.11 g / cm ³ after being extruded from a circular die. The density of the surface layer of the foamed sheet is increased by blowing cooling air onto the cylindrical sheet of the above, and the density of the surface layer is in the range of 0.10 to 0.15 g / cm ³ and the average cell diameter of the surface layer is in the range of 20 to 60 μm. As a result, it is disclosed that a polystyrene-based resin foam sheet capable of forming a container that satisfies the required performances of top-bottom compression strength and piercing strength while being lightweight can be obtained.

Japanese Unexamined Patent Publication No. 2013-209449

However, the foamed sheet and the laminated foamed sheet in the prior art such as Cited Document 1 tend to be easily cracked when the opening of the container obtained by thermoforming is compressed in the horizontal direction.
For example, a container obtained by thermoforming a laminated foam sheet may be wrapped with a shrink film by an automatic wrapping machine or the like. Specifically, a food manufacturing company manufactures food, and the obtained food is packaged in a container by an automatic packaging machine (hereinafter, also simply referred to as automatic packaging) to make a final product, and this product is used as a retail store or the like. Outpacks are widely sold in the form of shipment to. When performing this automatic packaging, in order to strengthen the tension of the film after packaging and improve the appearance of the container, it is possible to wrap the container with film with the opening of the container compressed by a certain amount in the horizontal direction. Will be done. However, when a container made by thermoforming a foam sheet as disclosed in Patent Document 1 is packaged by automatic packaging, the container may not be able to withstand the deformation when the opening is compressed by a certain amount and may be cracked. there were.

The present invention has been made in view of the above-mentioned problems of the prior art, and although it is lightweight, it has a high compressive strength when the opening of the container is compressed in the horizontal direction, and the container is broken by compression. The challenge is to obtain a polystyrene-based resin laminated foam sheet that can be thermoformed into a container with a large amount of deflection.

According to the present invention, the following polystyrene-based resin laminated foam sheet and a container obtained by thermoforming the polystyrene-based resin laminated foam sheet are provided.
[1] Polystyrene resin foam layer and
A polystyrene-based resin layer A laminated and adhered to one surface of the foam layer by coextrusion,
A polystyrene-based resin laminated foam sheet having a thermoplastic resin film B laminated and adhered to the other surface of the foam layer.
The polystyrene-based resin laminated foam sheet has an overall apparent density of 0.05 to 0.14 g / cm ³ , an overall basis weight of 100 to 200 g / m ² , and an average thickness of 0.5 to 3.0 mm. ,
The polystyrene-based resin layer A has a basis weight of 3 to 18 g / m ² .
The basis weight of the thermoplastic resin film B is 14 g / m ² or more, and the basis weight is 14 g / m 2.
Breakage per bubble for bubbles existing in a portion up to 50 μm in the thickness direction from the interface between the foam layer and the polystyrene resin layer A in a cross section perpendicular to the extrusion direction of the polystyrene resin foam layer. A polystyrene-based resin laminated foam sheet having an average area value ( _AAS ) of 7000 μm ² / piece or more.
[2] The laminated foam sheet is characterized in that the apparent density of the surface layer portion B, which is a portion up to 200 μm from the surface of the thermoplastic resin film B in the thickness direction, is 0.20 g / cm ³ or more. The polystyrene-based resin laminated foam sheet according to 1 above.
[3] The average value (A _W ) of the cross-sectional area per bubble for the bubbles in the entire foam layer in the cross section perpendicular to the extrusion direction of the polystyrene-based resin foam layer is 20000 to 60,000) μm ² /. The above 1 is characterized in that the ratio (A _AS / A _W ) of the average value A _AS of the cross section to the average value A _W of the cross section is 0.3 or more and 0.5 or less. Alternatively, the polystyrene-based resin laminated foam sheet according to 2.
[4] The polystyrene-based resin laminated foam sheet according to any one of 1 to 3, wherein the thermoplastic resin film B is laminated and adhered to the polystyrene-based resin foam layer by thermal lamination. ..
[5] One bubble for a bubble existing in a portion up to 50 μm in the thickness direction from the interface between the foam layer and the thermoplastic resin film B in a cross section perpendicular to the extrusion direction of the polystyrene resin foam layer. The polystyrene-based resin laminated foam sheet according to any one of 1 to 4, wherein the average value ( _ABS ) of the cross-sectional area per unit is 4000 μm ² / piece or more and less than 7000 μm ² / piece.
[6] The average value (A _W ) of the cross-sectional area per bubble for the bubbles of the entire foam layer in the cross section perpendicular to the extrusion direction of the polystyrene-based resin foam layer is 20000 to 60,000 μm ² / piece. 5 above, wherein the ratio of the average value _ABS of the cross-sectional area ( _ABS / _AW ) to the average value _AW of the cross-sectional area is 0.1 or more and less than 0.3. The polystyrene-based resin laminated foam sheet described.
[7] A container formed by thermoforming the polystyrene-based resin laminated foam sheet according to any one of 1 to 6 above, wherein the polystyrene-based resin layer A is located on the outside of the container. ,container.

The polystyrene-based resin laminated foam sheet of the present invention is laminated on the polystyrene-based resin foamed layer, the polystyrene-based resin layer A laminated and adhered to one surface of the foamed layer by coextrusion, and the other surface of the foamed layer. A polystyrene-based resin laminated foam sheet having an bonded thermoplastic resin film B, the polystyrene-based resin layer A and the thermoplastic resin film B having a specific basis weight, with respect to the extrusion direction of the polystyrene-based resin foamed layer. The average value ( _AS ) of the cross-sectional area per bubble for the bubbles existing in the portion up to 50 μm in the thickness direction from the interface between the foam layer and the polystyrene-based resin layer A in the vertical cross section is a specific value or more. Therefore, despite being lightweight, the strength until buckling when the opening of the container is compressed in the horizontal direction (hereinafter, also referred to as the compression strength in the horizontal direction of the container) is high, and the opening of the container is opened. It has the effect that a container having a large amount of deflection until buckling when the portion is compressed in the horizontal direction (hereinafter, also referred to as the amount of deflection at the time of compression failure in the horizontal direction of the container) can be obtained by thermal molding.

FIG. 1A is an explanatory view of a buckling test in which the opening of the container is compressed in the lateral direction as viewed from the side. FIG. 1B is an explanatory view of a buckling test in which the opening of the container is compressed in the lateral direction as viewed from the front. FIG. 2 is a drawing showing a line drawing created for the laminated foam sheet obtained in Example 1. FIG. 3 is a drawing showing a line drawing created for the laminated foam sheet obtained in Comparative Example 1.

Hereinafter, the polystyrene-based resin laminated foam sheet of the present invention will be described in detail.
The polystyrene-based resin laminated foam sheet (hereinafter, also referred to as a laminated foamed sheet) of the present invention is laminated with a polystyrene-based resin foamed layer (hereinafter, also simply referred to as a foamed layer) by coextrusion on one surface of the foamed layer. The polystyrene-based resin layer A (hereinafter, also simply referred to as resin layer A) to be bonded and the thermoplastic resin film B (hereinafter, also simply referred to as film B) laminated and bonded to the other surface of the foamed layer. And have.

The base resin constituting the polystyrene-based resin foam layer is a polystyrene-based resin. The polystyrene-based resin means a resin containing 50% by weight or more of a styrene-based monomer component unit, for example, polystyrene, rubber-modified polystyrene (impact-resistant polystyrene), styrene-α-methylstyrene copolymer, styrene-p. Methyl styrene copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-maleic anhydride copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene -Methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-acrylonitrile copolymer, a mixture of polystyrene and polyphenylene ether and the like can be mentioned. The polystyrene-based resin may contain a polyfunctional monomer component unit such as divinylbenzene or a polybranched macromonomer.

Further, the base resin constituting the foamed layer may be a mixture of two or more kinds of these polystyrene-based resins, or a mixture of these polystyrene-based resins and other components. Other components include propylene homopolymers, polypropylene resins such as ethylene-propylene copolymers, polyethylene resins such as high density polyethylene and low density polyethylene, styrene-conjugated diene block copolymers and their hydrogenated products. Examples thereof include rubbers such as thermoplastic elastomers, ethylene-propylene rubber, and butadiene rubber.

The melt flow rate (MFR) of the polystyrene-based resin constituting the foam layer is preferably 0.1 to 5 g / 10 minutes, more preferably 1 to 2 g / 10 minutes. When the MFR is within this range, a foamed sheet having a closed cell structure and excellent mechanical strength can be manufactured over a wide range of manufacturing conditions.
The melt flow rate in the present specification means a melt mass flow rate measured by the test method A of JIS K 7210 (1999), and the conditions of a test temperature of 200 ° C. and a load of 5 kg are adopted.

The base resin constituting the polystyrene-based resin layer A is a polystyrene-based resin. Examples of the polystyrene-based resin include the same polystyrene-based resins constituting the foamed layer.
Among them, it is preferable to use a mixture of polystyrene and a thermoplastic elastomer such as a styrene-conjugated diene block copolymer or a hydrogenated product thereof, or impact-resistant polystyrene. These resins have a low melt viscosity in the extrusion temperature range, facilitate coextrusion at an appropriate foaming temperature, and can sufficiently grow bubbles near the surface layer on the resin layer A side of the foam layer, so that desired bubbles can be sufficiently grown. It becomes easy to form a foam layer having a structure. In addition, since the resin layer A is flexible, the surface of the obtained laminated foam sheet on the resin layer A side becomes flexible. As a result, the amount of deflection of the container obtained by thermoforming at the time of compression fracture in the horizontal direction of the container can be increased.

When a mixture of polystyrene and a thermoplastic elastomer is used as the resin layer A, the content of the thermoplastic elastomer in the base resin is preferably about 10 to 50% by weight, more preferably 20 to 40% by weight. Is.

From the viewpoint of facilitating the formation of a foam layer having a desired bubble structure, the melt flow rate (MFR) of the polystyrene-based resin constituting the polystyrene-based resin layer A is preferably 5 to 30 g / 10 minutes, more preferably. Is 7 to 20 g / 10 minutes.

The basis weight of the resin layer A is 3 to 18 g / m ² . If the basis weight is too small, the amount of heat of the molten resin constituting the resin layer A is too small when the resin layer A is laminated on the foam layer by coextrusion, and the surface layer of the foam layer on the resin layer A side during extrusion foaming. It becomes impossible to sufficiently grow the bubbles in the vicinity, and there is a possibility that the amount of deflection of the obtained container at the time of compression failure in the horizontal direction of the container becomes small. On the other hand, if the basis weight is too large, the amount of heat of the molten resin forming the resin layer A is too large when the resin layer A is laminated on the foam layer by coextrusion, and bubbles in the vicinity of the surface layer of the foam layer during extrusion foaming. However, there is a possibility that a good laminated foamed sheet cannot be obtained because the foam tends to break and the surface condition of the obtained foamed sheet tends to deteriorate. From this point of view, the basis weight of the film A is preferably 5 to 15 g / m ² .

In the laminated foam sheet of the present invention, the thermoplastic resin film B (hereinafter, also simply referred to as film B) is laminated and adhered to the other surface of the foam layer (the surface opposite to the one surface).
The base resin constituting the film B includes high-density polyethylene, low-density polyethylene, ethylene-vinyl acetate copolymer, polyolefin resin such as polypropylene, polyester resin such as polyethylene terephthalate, and polystyrene resin such as polystyrene. Can be mentioned. Further, it is also possible to use a multilayer film in which a plurality of films using these resins are laminated.

The basis weight of the film B is 14 g / m ² or more. When the basis weight of the film B is within this range, the compressive fracture strength of the obtained container in the horizontal direction of the container can be increased. From this point of view, the basis weight is preferably 15 g / m ² or more, more preferably 16 g / m ² or more. The upper limit of the basis weight is preferably about 50 g / m ² , more preferably 40 g / m ² , and even more preferably 30 g / m ² .

In general, the strength is improved by laminating the resin layer A, the film B, or the like on both sides of the foam layer, so that the strength of the foam sheet can be increased even if the basis weight of the foam layer is reduced. However, as described above, the problem that the container is easily cracked when the opening of the container is compressed by a certain amount can be solved by the conventional method of laminating and adhering a resin layer or a film on both sides of the foam layer. I didn't.
This problem could only be solved by adjusting the bubble structure near the surface of the foam layer, as described below.

The foamed layer in the present invention has a characteristic bubble structure in the vicinity of the surface thereof. Next, regarding the bubble structure, the bubble structure existing in the portion up to 50 μm in the thickness direction from the interface between the foam layer and the resin layer A, the entire bubble structure of the foam layer, and the thickness direction from the interface between the foam layer and the film B. The bubble structure existing in the portion up to 50 μm will be described in this order.
In the present invention, a portion of the cross section perpendicular to the extrusion direction of the foam layer (TD cross section) from the interface between the foam layer and the polystyrene resin layer A (hereinafter, also referred to as interface A) to 50 μm in the thickness direction. The average value ( _AAS ) of the cross-sectional area per bubble for the bubbles existing in is 7000 μm ² / piece or more. If the average value ( _AAS ) is too small, the amount of deflection of the obtained container at the time of compression fracture in the horizontal direction of the container may be small.
From this point of view, the average value ( _AAS ) is preferably 8000 μm ² / piece or more, more preferably 9000 μm ² / piece or more, and further preferably 10000 μm ² / piece or more.
On the other hand, the average value ( _AAS ) is preferably about 14000 μm ² / piece or less, and more preferably 13000 μm ² / piece or less. When the average value ( _AAS ) is within this range, the appearance of the obtained container on the resin layer A side is good.

As described above, by adopting a configuration in which the average value ( _AAS ) is 7000 μm ² / piece or more, the amount of deflection until the container is broken by compression when the container opening is compressed in the horizontal direction. Has become larger, and the automatic packaging can be performed without any problem.

In the laminated foam sheet of the present invention, the average value ( _AW ) of the cross-sectional area per bubble for the entire bubbles of the foam layer in the cross section (TD cross section) perpendicular to the extrusion direction of the foam layer is. It is preferably 20000 to 60,000 μm ² / piece. When the average value (A _W ) is within this range, the laminated foam sheet is excellent in thermoforming property, and the container obtained by thermoforming is excellent in mechanical strength even though it is lightweight. Become. From this point of view, the lower limit of the average value ( _AW ) is more preferably 22000 μm ² / piece, still more preferably 24000 μm ² / piece, and particularly preferably 26000 μm ² / piece. The upper limit of the average value (A _W ) is more preferably 50,000 μm ² / piece, still more preferably 45,000 μm ² / piece, and particularly preferably 40,000 μm ² / piece.

Further, the ratio of the average value A _AS to the average value A _W (A _AS / A _W ) is preferably about 0.3 or more and 0.5 or less, and more preferably 0.3 or more and 0.4 or less. Is. When the ratio (A _AS / A _W ) is within this range, the obtained container has a large amount of deflection at the time of compression fracture in the horizontal direction and has a better appearance.

Further, it exists in a portion from the interface between the foam layer and the thermoplastic resin film B (hereinafter, also referred to as interface B) to 50 μm in the thickness direction in the cross section perpendicular to the extrusion direction of the foam layer (TD cross section). The average cross-sectional area ( _ABS ) per bubble is preferably 4000 μm ² / piece or more and 8000 μm ² / piece or less, and more preferably 4000 μm ² / piece or more and less than 7000 μm ² / piece. More preferably, it is 5000 μm ² / piece or more and less than 7000 μm ² / piece. When the average value ( _ABS ) of the cross-sectional area is within this range, the mechanical properties of the obtained container can be enhanced.
From the same viewpoint, the ratio of the average cross-sectional area A _BS to the average cross-sectional area A _W (A _BS / A _W ) is preferably 0.1 or more and less than 0.3, more preferably. It is 0.2 or more and less than 0.3.

The average value ( _AAS ) is obtained as follows.
First, the laminated foam sheet is cut perpendicular to the extrusion direction of the foam layer, and a cross section (TD cross section) perpendicular to the extrusion direction of the foam layer of the laminated foam sheet is cut out. An enlarged photograph of the obtained TD cross section is taken, and a line drawing of a bubble structure (bubble film) based on the enlarged photograph is created using CAD software. An example of a line drawing is shown in FIG. In FIG. 2, the resin layer A and the film B are not shown, and in the figure, the curve located at the lowermost side is the interface A, and the curve located at the uppermost side is the interface B.
On the obtained line drawing, a straight line a1 connecting both ends of the interface A is drawn along the interface A between the foam layer of the laminated foam sheet and the resin layer A, and at a position 50 μm away from the interface A in the thickness direction. Draw a straight line a2 parallel to the straight line a1 and draw two straight lines c1 and c2 parallel to the thickness direction and having a predetermined interval in the foam layer width direction, and draw four straight lines a1, a2 and c1 from the line drawing. , Cut out the part surrounded by the frame determined by c2. A region excluding bubbles intersecting the straight lines c1 and c2 parallel to the thickness direction of the laminated sheet is extracted from the cut out portion. Bubbles existing in the extracted region are defined as measurement targets. The bubbles intersecting the straight lines a1 and a2 are the measurement targets. That is, if the bubble defined as the measurement target has a portion outside the frame, the portion outside the frame is also subject to the cross-sectional area measurement.
The cross-sectional area of the entire bubble is measured for each bubble in the region thus defined, and the number of the bubbles is further measured.
By dividing the cross-sectional area occupied by the bubbles measured in this way by the number of bubbles, the cross-sectional area per bubble for the bubbles existing in the portion from the interface A to 50 μm in the thickness direction is calculated. The above measurement was performed on 20 or more randomly selected laminated foam sheets, and the arithmetic mean value of the cross-sectional area per bubble calculated in each measurement was perpendicular to the extrusion direction of the foam layer. Let it be the average value ( _AAS ) of the cross-sectional area per bubble for the bubbles existing in the portion from the interface A between the foamed layer and the polystyrene-based resin layer A to 50 μm in the thickness direction in the cross section (TD cross section).

Further, the average value ( _ABS ) is obtained as follows.
A line drawing is created in the same manner as in the measurement of the average value ( _AAS ), and a straight line b1 connecting both ends of the interface B is drawn on the obtained line drawing along the interface B between the foam layer and the film B. A straight line b2 parallel to the straight line b1 is drawn at a position 50 μm away from the interface B in the thickness direction, and two straight lines c1 and c2 parallel to the thickness direction and having a predetermined interval are drawn, and four straight lines c1 and c2 are drawn from the line drawing. Cut out the part surrounded by the frame defined by the straight lines b1, b2, c1 and c2. A region excluding bubbles intersecting the straight lines c1 and c2 parallel to the thickness direction of the laminated sheet is extracted from the cut out portion. Bubbles existing in the extracted region are defined as measurement targets. The bubbles intersecting the straight lines b1 and b2 are the measurement targets. That is, if the bubble defined as the measurement target has a portion outside the frame, the portion outside the frame is also subject to the cross-sectional area measurement.
The cross-sectional area of the entire bubble in the region thus defined is measured, and the number of the bubble is further measured. By dividing the area occupied by the bubbles measured in this way by the number of bubbles, the cross-sectional area per bubble for the bubbles existing in the portion from the interface B to 50 μm in the thickness direction is calculated. The above measurements were performed on 20 or more randomly selected laminated foam sheets, and the arithmetic mean value of the cross-sectional area per bubble calculated in each measurement was perpendicular to the extrusion direction of the foam layer. Let it be the average value ( _ABS ) of the cross-sectional area per bubble for the bubbles existing in the portion of the cross section (TD cross section) from the interface B between the foam layer and the resin layer B to 50 μm in the thickness direction.

Further, the average value ( _AW ) is obtained as follows.
A line drawing was created in the same manner as in the measurement of the average value ( _AAS ), and two straight lines parallel to the thickness direction and having a predetermined interval were drawn on the obtained line drawing, and the line drawing was drawn at interface A, interface B, and so on. Cut out the part surrounded by the frame defined by two straight lines. A region excluding air bubbles intersecting a straight line parallel to the thickness direction of the laminated sheet is extracted from the cut out portion. By measuring the cross-sectional area occupied by all bubbles and the number of bubbles in the extracted region and dividing the area occupied by all bubbles by the number of bubbles, the bubbles 1 in the cross section perpendicular to the extrusion direction of the foam layer. Calculate the cross-sectional area per piece.
The above measurement is performed on 10 or more randomly selected laminated foam sheets, and the arithmetic mean value of the cross-sectional area per bubble calculated in each measurement is defined as the average value ( _AW ).

In creating the line drawing, it is assumed that processing with vector data by CAD software or the like is performed and the thickness of the drawn line does not affect the area of the bubble to be measured.

Next, various general physical properties of the laminated foam sheet of the present invention will be described.
In the laminated foam sheet of the present invention, the apparent density of the surface layer portion B, which is a portion from the surface of the film B to 200 μm in the thickness direction, is preferably 0.20 g / cm ³ or more, more preferably 0. 22 g / cm ³ or more. By setting the apparent density of the surface layer portion B in the above range, the compressive strength of the obtained container in the horizontal direction of the container can be further increased.
From the viewpoint of lightness and thermoformability, the apparent density of the surface layer portion B is preferably less than 0.32 g / cm ³ , and more preferably 0.30 g / cm ³ or less.

The apparent density of the surface layer portion B is measured as follows.
The laminated foam sheet is sliced from the surface of the film B to 200 μm in the thickness direction, a test piece having a predetermined size is cut out, and the weight of the test piece is measured. The surface layer density is obtained by dividing the weight of the test piece by the volume of the test piece and converting it into a unit.

The total basis weight of the laminated foam sheet is 100 to 200 g / m ² . If the total basis weight is within this range, a lightweight laminated foam sheet can be obtained, and the weight of the obtained container can be reduced. From this point of view, the total basis weight is preferably 110 to 180 g / m ² , more preferably 120 to 170 g / m ² .

The total basis weight of the laminated foam sheet is measured as follows.
A test piece having a predetermined size (for example, 800 mm × 100 mm) is cut out from the laminated foam sheet, the weight of the test piece is measured, the weight of the test piece is divided by the area obtained from the size of the test piece, and the unit is converted. Obtained by.
The basis weight of the resin layer A can be obtained from the total basis weight of the laminated foamed sheet and the ratio of the discharge amount of the foamed layer and the resin layer A at the time of extrusion.
The basis weight of the film B can be obtained by cutting the film B from the laminated foam sheet, measuring the weight of the film B, and dividing the weight of the film B by the area obtained from the dimensions of the film B.

The average thickness of the laminated foam sheet of the present invention is 0.5 to 3.0 mm. If the thickness is too small, the mechanical strength of the obtained container may decrease. If the thickness is too large, the thermoformability of the laminated foam sheet may decrease. From the above viewpoint, the average thickness of the laminated foam sheet is preferably 0.5 to 2.5 mm, more preferably 0.5 to 2.3 mm.

The overall apparent density of the laminated foam sheet is 0.05 to 0.14 g / cm ³ . If the overall apparent density is too small, the mechanical strength of the resulting container may decrease. If the overall apparent density is too high, the lightness of the container may be lost. From this point of view, the overall apparent density is preferably 0.06 to 0.13 g / cm ³ , and more preferably 0.06 to 0.12 g / cm ³ .

The average thickness of the laminated foam sheet is measured as follows.
First, a strip having a length in the width direction (TD) orthogonal to the extrusion direction and a length in the extrusion direction (MD) having a predetermined dimension (for example, 100 mm) is cut out from the laminated foam sheet, and further in the longitudinal direction of the strip. Both ends of the laminated foam sheet are cut off, and the central portion in the width direction of the laminated foam sheet is cut out as a test piece.
This test piece is further divided into 10 equal parts in the width direction, the thickness near the center of each of the cut test pieces is measured with a micrometer, and the value obtained by arithmetically averaging the thickness of each test piece is taken as the average thickness of the laminated foam sheet.

The measurement of the total apparent density is performed as follows. A test piece having a predetermined size (for example, 800 mm × 100 mm × thickness of the laminated foam sheet) is cut out from the laminated foam sheet, the weight (g) of the test piece is measured, and the weight of the test piece is determined from the size of the test piece. Divide by and convert to the unit to obtain the basis weight (g / m ² ). Next, the value obtained by dividing the obtained basis weight (g / m ² ) of the test piece by the thickness (mm) of the test piece is converted into a unit to obtain the overall apparent density (g / cm ³ ) of the laminated foam sheet.

Next, a method for manufacturing the laminated foam sheet of the present invention will be described.
The laminated foam sheet of the present invention can be obtained, for example, as follows.
A coextrusion die is attached to the outlet of the foam layer forming extruder, and a resin layer is attached to the foam layer by the coextrusion foaming method using a device in which the resin layer A forming extruder is connected to the coextrusion die. A foamed sheet in which A is laminated is manufactured, and the film B is laminated and adhered to a surface of the obtained foamed sheet opposite to the surface on which the film A is laminated by thermal lamination or the like, whereby the laminated foam of the present invention is formed. You can get a sheet.

In the laminated foam sheet of the present invention, as described above, the average value ( _AAS ) of the cross-sectional areas per bubble for the bubbles existing in the portion from the interface A to 50 μm in the thickness direction is 7000 μm ² / piece or more. It is necessary to be. Such a bubble structure having large bubbles in the vicinity of the surface layer can be formed by adopting the coextrusion foaming method. That is, in the foamed sheet having a bubble structure in which bubbles near the surface layer on the resin layer A side are large, the resin layer A is laminated by simultaneously extruding (co-extruding) the foam layer and the resin layer A at the time of extrusion. It can be formed by sufficiently growing bubbles in the vicinity of the surface layer of the foamed layer to be sufficiently grown by the amount of heat of the resin layer A.
By laminating and adhering the resin layer A on one side of the foamed sheet, such a bubble structure is formed, and by further laminating the thermoplastic film B on the other side, a laminated foamed sheet having improved strength is obtained. Can be done. Here is the feature of the present invention. The container obtained by thermally molding the laminated foam sheet is a container having an appropriate elasticity and a large amount of deflection at the time of compression fracture (buckling) in the horizontal direction of the container.

As a method for producing a laminated foam sheet by a coextrusion foaming method, a method of coextruding a resin melt for forming each layer using a flat die for coextrusion to make a laminated foam sheet, or an annular die for coextrusion is used. There is a method of co-extruding a resin melt for forming each layer using the product to obtain a tubular laminated foam, and then cutting open the tubular foam to form a laminated foam sheet. Among these, the method using an annular die for coextrusion is preferable because a wide laminated foam sheet having a width of 1000 mm or more can be easily produced.

Hereinafter, a case where a laminated foam sheet is manufactured by a coextrusion foaming method using the annular die will be described in detail.
First, a polystyrene-based resin for forming a foam layer and an additive such as a bubble adjusting agent are supplied to an extruder for forming a foam layer, heated, melted, and kneaded, and then a physical foaming agent is press-fitted to further press-fit. Knead and adjust to an appropriate foaming temperature to obtain a resin melt for forming a foam layer.
On the other hand, the polystyrene resin for forming the resin layer A is supplied to the extruder for forming the resin layer A, heated, melted and kneaded, and then a volatile plasticizer is press-fitted as necessary to further knead and extrude. The temperature is adjusted to an appropriate level to obtain a resin melt for forming the resin layer A.
Next, the resin melt for forming the foam layer and the resin melt for forming the resin layer A were introduced into the annular die for coextrusion, and the resin melt for forming the resin layer A was laminated on the resin melt for forming the foam layer. After that, the die is co-extruded into the atmosphere in a tubular shape to foam the resin melt for forming a foam layer. The resin layer A is laminated on one side of the foam layer by cutting open the tubular laminated foam while cooling it while taking it along a cylindrical cooling device (hereinafter, also referred to as a mandrel) to form a sheet. A bonded laminated foam sheet can be obtained.

In the present invention, as described above, the average value ( _AAS ) of the cross-sectional areas per bubble for the bubbles existing in the portion from the interface A to 50 μm in the thickness direction is 7000 μm ² / piece or more. It is necessary to grow bubbles during extrusion foaming. For that purpose, as the resin constituting the resin layer A, a mixture of polystyrene and a thermoplastic elastomer such as a styrene-conjugated diene block copolymer or its hydrogenated product, impact-resistant polystyrene, or the like, and melt viscosity in the extrusion temperature range. It is preferable to perform coextrusion using a resin having a low polystyrene.

Further, it is preferable to cool the tubular body extruded and foamed from the co-extruded die by blowing cooling air. At this time, it is preferable to set the air volume of the cooling air in the range of approximately 1.0 to 4.0 m ³ / m ² with respect to one side of the foamed sheet (foamed layer). By doing so, it becomes easy to appropriately grow bubbles in the vicinity of the surface layer on the resin layer A side of the laminated foam sheet. Further, it becomes easy to adjust the surface layer density of the foamed sheet on the laminated surface side of the film B and the size of bubbles in the vicinity of the surface layer within a desired range.

Examples of the physical foaming agent added to the foamed layer forming resin melt include aliphatic hydrocarbons such as propane, normal butane, isopentane, normal pentane, isopentane, normal hexane and isohexane, and fats such as cyclopentane and cyclohexane. Hydrocarbons such as cyclic hydrocarbons, methyl chloride and ethyl chloride, organic physical foaming agents such as fluorocarbons such as 1,1,1,2-tetrafluoroetan and 1,1-difluoroetan, nitrogen and dioxide. Examples thereof include inorganic physical foaming agents such as carbon, air, and water. Two or more of the above-mentioned physical foaming agents can be used in combination. Of these, it is preferable to use an organic physical foaming agent from the viewpoint that a good foamed sheet can be easily obtained, and it is more preferable to use normal butane, isobutane, or a mixture thereof.

The amount of the physical foaming agent added is adjusted according to the type of foaming agent and the desired apparent density. Further, the amount of the bubble adjusting agent added is adjusted according to the target bubble diameter. For example, when a laminated butane sheet containing 30% by weight of isobutane and 70% by weight of normal butane is used as a foaming agent to obtain a laminated foamed sheet in the apparent density range, the amount of the mixed butane added is approximately 1 per 100 parts by weight of the base resin. It is preferably about 10 parts by weight, more preferably 1.5 to 8 parts by weight, still more preferably 2 to 5 parts by weight.

A bubble adjusting agent is usually added as a main additive added to the foamed layer forming resin melt. As the bubble adjusting agent, either an organic type or an inorganic type can be used. Examples of the inorganic bubble adjusting agent include boric acid metal salts such as zinc borate, magnesium borate, and borax, sodium chloride, aluminum hydroxide, talc, zeolite, silica, calcium carbonate, and sodium bicarbonate. Examples of the organic bubble adjusting agent include sodium phosphate-2,2-methylenebis (4,6-tert-butylphenyl), sodium benzoate, calcium benzoate, aluminum benzoate, sodium stearate and the like. Further, a combination of citric acid and sodium bicarbonate, an alkali salt of citric acid and sodium bicarbonate and the like can also be used as the bubble adjusting agent. Two or more of these bubble regulators can be mixed and used.
The amount of the bubble adjusting agent added is preferably about 0.01 to 3 parts by weight, more preferably 0.03 to 1 part by weight per 100 parts by weight of the base resin.

At the time of coextrusion foaming, it is preferable to add a volatile plasticizer to the resin melt for forming the resin layer A. By adding a volatile thermoplastic to the resin melt, the melt viscosity of the polystyrene-based resin can be appropriately lowered. Therefore, particularly when co-extruding a laminated foam sheet having an apparent density, which is the object of the present invention. It is effective because the extrusion temperature of the resin melt for forming the resin layer A can be brought close to the extrusion temperature of the resin melt for forming the foam layer. As a result, bubbles in the vicinity of the surface layer of the foam layer are less likely to break due to the heat of the resin layer A during coextrusion, and bubbles in the vicinity of the surface layer are easily grown. Therefore, the appearance is good and the bubbles in the vicinity of the surface layer are large. A foam sheet can be stably obtained.

Examples of the volatile plastic agent include aliphatic hydrocarbons such as propane, normal butane, isobutane, pentane, hexane, cyclobutane, and cyclopentane, methyl chloride, ethyl chloride, 1,1,1,2-tetrafluoroethane, and the like. One or more selected from halogenated aliphatic hydrocarbons such as 1,1-difluoroethane, aliphatic alcohols such as methanol, ethanol, propanol and butanol, or aliphatic ethers such as methyl ethyl ether and dimethyl ether. Those composed of are preferably used. Among these, those containing normal butane, isobutane or a mixture thereof as main components can be preferably used.

The boiling point of the volatile plasticizer is preferably 80 ° C. or lower, more preferably 60 ° C. or lower, from the viewpoint that it is easy to handle during extrusion molding and it is easy to obtain a good foamed sheet. The lower limit of the boiling point is approximately −50 ° C.
The volatile plasticizer is preferably added in an amount of approximately 2 to 10 parts by weight with respect to 100 parts by weight of the polystyrene-based resin for forming the resin layer A.

In the resin melt for forming the resin layer A, various additives may be added to the resin forming the melt as long as the object of the present invention is not impaired. Examples of various additives include antioxidants, heat stabilizers, weather resistant agents, ultraviolet absorbers, colorants, fillers, antibacterial agents and the like. When an additive is used, the total amount of the additive is appropriately determined according to the purpose and effect of the additive, but it is preferably about 10 parts by weight or less with respect to 100 parts by weight of the base resin. It is more preferably 5 parts by weight or less.

As the manufacturing apparatus such as the coextruded annular die and the extruder, known ones conventionally used in the field of extrusion foaming can be used.

The laminated foam sheet of the present invention can be obtained by laminating and adhering the film B to the surface opposite to the surface on which the resin layer A of the laminated foam sheet obtained by the coextrusion foaming method is laminated and adhered. can.
As a method for laminating and adhering the film B, for example, a thermal lamination method in which the foamed sheet and the film B are thermally fused by a heated roll or the like, an extrusion lamination method in which the film B is laminated and adhered to the foamed sheet via a molten resin, and the like. Further, a method of coating one side of the film B with an adhesive and laminating and adhering it to a foam sheet can be mentioned. Among these, it is preferable to use the thermal lamination method from the viewpoint that the film B having a small basis weight can be laminated and the total basis weight of the laminated foam sheet can be reduced.

Next, the container of the present invention obtained by thermoforming and thermoforming the laminated foam sheet, that is, the polystyrene-based resin foam layer, the polystyrene-based resin layer A laminated and adhered to one surface of the foamed layer, and the said. A container having a thermoplastic resin film B laminated and adhered to the other surface of the foam layer will be described.
The container of the present invention can be obtained by molding the laminated foam sheet by a conventionally known molding method. Molding methods include vacuum forming, pneumatic forming, and as applications thereof, free drawing forming, plug and ridge forming, ridge forming, matched molding, straight forming, drape forming, reverse drawing forming, air slip forming, etc. Plug-assist molding, plug-assist reverse load molding, etc., and a method combining these are adopted.

The overall apparent density of the container is preferably 0.04 to 0.13 g / cm ³ , more preferably 0.05, from the viewpoint of excellent balance between mechanical strength and lightness of the container. It is ~ 0.12 g / cm ³ and 0.06 to 0.10 g / cm ³ .

The average thickness of the container is preferably 1.0 to 3.5 mm, more preferably 1.5 to 3.0 mm, from the viewpoint of excellent balance between mechanical strength and lightness of the container. Is.

The overall apparent density of the container can be determined as follows.
First, a test piece having a predetermined size is cut out from a flat portion of the foam container other than the flange portion and the specially shaped portion. Next, the mass and thickness of the test piece are measured. Next, the mass is divided by the area of the test piece and converted into units to obtain the basis weight of the test piece. Next, the apparent density of the container can be obtained by dividing the basis weight of the test piece by the thickness of the test piece and converting it into a unit.

The average thickness of the container is calculated as follows. First, the container is cut into two equal parts by passing through the bottom surface of the container and cutting the side surface of the container along a line rising perpendicular to the bottom surface (hereinafter, the method of cutting this container is simply "cutting the container". The thickness of 10 containers was measured and measured at equal intervals from one edge to the other along one of the cut surfaces of the cut container. Let the arithmetic average value of the thickness be the average thickness of the container.
When dividing the container into two equal parts, the container shall be cut so that the weights of the two cut containers are equal.

The average thickness of the resin layer A in the container is preferably 2 to 18 μm. When the average thickness of the resin layer A is within this range, the compressive strength in the horizontal direction of the container can be increased. From this point of view, the average thickness is preferably 3 to 16 μm.

The average thickness of the thermoplastic resin film B in the container is preferably 13 μm or more. When the average thickness of the film B is in this range, the compressive strength in the horizontal direction of the container can be increased. From this point of view, the basis weight is preferably 14 μm or more, more preferably 16 μm or more, still more preferably 18 μm or more. The upper limit of the basis weight is preferably about 45 μm, more preferably 40 μm, still more preferably 30 μm.

The average thickness of the resin layer A and the film B is measured as follows.
First, the container is cut and bisected.
Next, 10 or more magnified photographs of one of the cut surfaces of the cut container are randomly taken. The thickness of the resin layer A or the film B is measured from each enlarged photograph taken as described above, and the arithmetic mean value thereof is taken as the average thickness of the resin layer A or the film B of the container. The measurement shall be performed on a flat portion of the container as much as possible. In addition, when dividing a container into two equal parts, the container shall be cut so that the weights of the two cut containers are equal.

In the container of the present invention, the container is cut and bisected at a portion from the interface between the foam layer and the polystyrene resin layer A (hereinafter, also referred to as interface A2) to 50 μm in the thickness direction. The average value ( _AAS ) of the cross-sectional area per bubble for the bubbles to be formed is 7000 μm ² / piece or more. If the average value ( _AAS ) is too small, the amount of deflection of the obtained container at the time of compression fracture in the horizontal direction of the container may be small.
From this point of view, the average value ( _AAS ) is preferably 8000 μm ² / piece or more, more preferably 9000 μm ² / piece or more, and further preferably 10000 μm ² / piece or more.
On the other hand, the average value ( _AAS ) is preferably about 15,000 μm ² / piece or less, more preferably 14,000 μm ² / piece or less, and further preferably 13000 μm ² / piece or less. When the average value ( _AAS ) is within this range, the appearance of the resin layer A side of the container can be improved.

The average value ( _AW ) of the cross-sectional area per bubble for the bubbles in the entire foam layer in the cross section obtained by cutting the container and dividing it into two equal parts is preferably 20000 to 60,000 μm ² / piece. When the average value (A _W ) is within this range, the container is lightweight and has good mechanical strength. From this point of view, the average value (A _W ) is more preferably 25,000 to 50,000 μm ² / piece, still more preferably 30,000 to 45,000 μm ² / piece.

Further, the ratio ( _AAS / _AW ) of the average value ( _AAS ) to the average value _AW is preferably about 0.3 or more and 0.5 or less, and more preferably 0.3 or more and 0. It is less than 0.4. When the ratio (A _AS / A _W ) is within this range, the amount of deflection at the time of compression fracture in the horizontal direction of the container is large, and the container has a good appearance.

In addition, bubbles 1 for bubbles existing in a portion up to 50 μm in the thickness direction from the interface between the foam layer and the thermoplastic resin film B (hereinafter, also referred to as interface B2) in the cross section obtained by cutting the container and bisected. The average value ( _ABS ) of the cross-sectional area per piece is preferably 4000 μm ² / piece or more and 8000 μm ² / piece or less, and more preferably 5000 μm ² / piece or more and less than 7000 μm ² / piece. When the average value ( _ABS ) is within this range, the mechanical properties of the container can be increased.

From the same viewpoint, the ratio ( _ABS / _AW ) of the average value _ABS of the cross-sectional area to the average value _AW of the cross-sectional area is approximately 0.1 or more and less than 0.3, and more preferably 0. It is 1 or more and 0.2 or less.

In the container, the average value of the cross-sectional area per bubble ( _AAS ) for the bubbles existing in the portion from the interface A2 to 50 μm in the thickness direction, and the bubbles existing in the portion from the interface B2 to 50 μm in the thickness direction. The average value of the cross-sectional area per bubble ( _ABS ) and the average value ( _AW ) of the entire foam layer of the above-mentioned laminated foam sheet are obtained by the same method as the measurement of the average value of each cross-sectional area in the laminated foam sheet. be able to.
The measurement points of the average value ( _AAS ), ( _ABS ), and ( _AW ) of each cross-sectional area in the container are determined as follows. The container is cut and bisected, and measurements are taken at 20 points at equal intervals from one edge to the other along one of the cut surfaces of the cut container. In addition, when dividing a container into two equal parts, the container shall be cut so that the weights of the two cut containers are equal.

The container of the present invention has the above-mentioned bubble structure, and since the resin layer A is laminated on one surface and the film B is laminated on the other surface, the container has an appropriate elasticity and is horizontal to the container. A container with a large amount of deflection during compression failure in the direction.

In the container of the present invention, the polystyrene-based resin layer A is located on the outside of the container. That is, at the time of thermoforming, the resin layer A is thermoformed so as to be located on the outside of the container.
When the resin layer A is located on the outside of the container, the effect that the compressive strength (buckling strength) in the horizontal direction of the container is high and the amount of deflection at the time of compression fracture (buckling) is large is exhibited more remarkably. Can be done. The possible reasons for this are as follows.

When the resin layer A is located on the outside of the container, the container has a characteristic bubble structure near the interface A, so that when a horizontal compressive load is applied to the opening of the container, the resin layer A is on the resin layer A side. Bubbles near the surface layer are easily deformed flexibly. Therefore, when a compressive load is applied to the container, the outside of the container (foam layer near the interface A of the container) can be stretched against the bending deformation of the container. As a result, it is possible to suppress a rapid increase in compressive stress generated inside the container (foam layer near the interface B of the container), especially near the boundary between the bottom and the side wall of the container, and during compression failure in the horizontal direction of the container. It is thought that the amount of deflection will increase.

Examples of the container formed by using the laminated foam sheet of the present invention include a tray, a bowl shape, a cup shape, and a natto container. The shape of the container is not particularly limited, and examples thereof include various shapes such as a square shape, a circular shape, an elliptical shape, a semicircular shape, and a fan shape.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples. However, the present invention is not limited to the examples.

The following polystyrene-based resin was used to form the foam layer.
(1) Polystyrene "GX154" made by "PS Japan" (MFR: 1.5g / 10min)

As a physical foaming agent and a volatile plasticizer, mixed butane composed of 70% by weight of normal butane and 30% by weight of isobutane was used.

As the bubble adjusting agent, a bubble adjusting agent masterbatch containing 35% by weight of talc (trade name "High Filler # 12" manufactured by Matsumura Sangyo Co., Ltd.) was used.

The polystyrene-based resin and the thermoplastic resin elastomer used for forming the polystyrene-based resin film A in Examples and Comparative Examples are shown below.
(1) Abbreviation "PS1": Polystyrene "679" manufactured by PS Japan Corporation (MFR: 18g / 10min)
(2) Abbreviation "PS2": Impact-resistant polystyrene "408" manufactured by PS Japan Co., Ltd. (MFR: 7g / 10min)
(3) Abbreviation "PS3": Asahi Kasei Chemicals Co., Ltd. styrene-butadiene block copolymer "Flex 835" (MFR: 5 g / 10 min)
The MFR is a value measured under condition H (200 ° C., load 5 kg) based on JIS K7210-1999.

As an extruder for forming a foam layer, a tandem extruder consisting of a first extruder having a diameter of 115 mm and a second extruder having a diameter of 180 mm is used, and an extruder having a diameter of 65 mm and L / D = 50 is used as an extruder for forming the resin layer A. A three extruder was used. Further, the outlets of the second extruder and the third extruder were connected to the annular die for coextrusion so that the respective resin melts could be laminated in the annular die for coextrusion.

Examples 1-5
The polystyrene-based resin for forming the foam layer and 1.2 parts by weight of the bubble adjusting agent masterbatch with respect to 100 parts by weight of the polystyrene-based resin are supplied to the raw material input port of the first extruder, and heated and melted. It was kneaded to obtain a resin melt at about 200 ° C. Next, 4.7 parts by weight of mixed butane was press-fitted into the resin melt, and then the resin melt was transferred to a second extruder connected to the downstream side of the first extruder. Next, the extrusion resin temperature was adjusted to 148 ° C. to obtain a foam layer forming resin melt, and the foam layer forming resin melt was introduced into the coextrusion annular die at a discharge rate of 328 kg / hr.

On the other hand, the polystyrene-based resins of the types shown in Table 1 are supplied to a third extruder, heated, melted, and kneaded, and mixed butane as a volatile plasticizer is 4.0 parts by weight with respect to 100 parts by weight of the polystyrene-based resin. It was press-fitted into a resin melt. Then, the resin melt was further kneaded, and the extruded resin temperature was adjusted to 169 ° C. to obtain a resin melt for forming the resin layer A. Next, the resin melt for forming the resin layer A was introduced into the annular die for coextrusion at a discharge rate of 17 kg / hr.

The resin melt for forming the resin layer A was laminated on the outside of the resin melt for forming the foam layer in the annular die for coextrusion, and the laminate of the melt was extruded into the atmosphere from a die having a lip diameter of 180 mm. A two-layer tubular laminated foam composed of an extruded resin layer A / foam layer is widened (blow-up ratio: 3.7), picked up along the mandrel at the pick-up speed shown in Table 1, and cut open. As a result, a laminated foam sheet in which the resin layer A was laminated and adhered to one surface of the foam layer (the surface opposite to the surface taken along the mandrel surface) was obtained.

In addition, cooling air (outside air) is blown to the outside (resin layer A laminated side) of the tubular laminated foam immediately after being extruded from the annular die for coextrusion at an air volume of 2.5 m ³ / min (20 ° C.). The laminated foam sheet was cooled by blowing cooling air on the inside of the tubular laminated foam (resin layer A non-laminated side) at an air volume of 3.2 m ³ / min (30 ° C.).

Next, after curing the obtained foamed sheet at a temperature of 25 ° C. for 30 days, polystyrene having a basis weight shown in Table 3 is formed on the surface of the foamed sheet opposite to the surface on which the resin layer A is laminated and adhered. A film (non-stretched inflation film manufactured by Oishi Sangyo Co., Ltd.) was laminated by heat-sealing at a rate of 20 m / min with a heating roll whose temperature was adjusted to 200 ° C. to obtain a laminated foam sheet.
In Example 5, a polystyrene film having a basis weight of 21 g / m ² was further laminated and adhered to the resin layer A side of the obtained laminated foam sheet by thermal lamination.

Comparative Example 1
The foamed layer (single-layer foamed sheet) was extruded in the same manner as in Example 1 except that the resin layer A was not laminated. After curing the obtained foamed sheet at a temperature of 25 ° C. for 30 days, the polystyrene-based resin film B having a basis weight shown in Table 2 was subjected to thermal lamination on the surface taken along the mandrel surface of the obtained foamed sheet. Laminated adhesion was obtained to obtain a laminated foam sheet. Next, the unstretched polystyrene-based resin film having the basis weight shown in Table 2 (CPS film: corresponding to the resin layer A) was placed on the surface of the obtained laminated foam sheet opposite to the surface on which the film B was laminated and adhered. Was laminated and adhered by thermal lamination to obtain a laminated foam sheet in which a film was laminated on both sides.
The thermal lamination was carried out in the same manner as the thermal lamination conditions for the polystyrene film in Example 1.

Comparative Example 2
The foamed layer (single-layer foamed sheet) was extruded in the same manner as in Example 1 except that the resin layer A was not laminated. After curing the obtained foamed sheet at a temperature of 25 ° C. for 30 days, the unstretched polystyrene resin film B having a basis weight shown in Table 3 was heated on the surface taken along the mandrel surface of the obtained foamed sheet. By laminating and adhering by lamination, a laminated foam sheet in which only the film B was laminated and adhered was obtained.

Comparative Example 3
The laminated foam sheet to which the resin layer A was laminated and adhered was extruded in the same manner as in Example 1 except that the basis weight of the resin layer A was 20 g / m ² . After curing the obtained foamed sheet at a temperature of 25 ° C. for 30 days, the unstretched polystyrene-based resin having a basis weight shown in Table 3 is formed on a surface opposite to the surface on which the resin layer A of the foamed sheet is laminated and adhered. The film B was laminated and bonded by thermal lamination to obtain a laminated foam sheet in which only the film B was laminated and bonded.

Comparative Example 4
A laminated foam sheet in which only the resin layer A was laminated and adhered was obtained in the same manner as in Example 1 except that the film B was not laminated.

Next, after curing the laminated foam sheets obtained in Examples 1 to 5 and Comparative Examples 1 to 4 at a temperature of 25 ° C. for 3 days, a molding machine manufactured by Asano Laboratories Co., Ltd. (product number FKS-0631-10) was used. By thermoforming so that the resin layer A is located on the outside of the container, a container (food tray) having a square shape with a flange portion was obtained. The external dimensions of the container are 18 cm x 18 cm for the long side x short side (top view) of the container, 3 cm for the height of the container, and 2.8 mm for the thickness of the container (thickness of the laminated foam sheet after molding). The heating conditions were a heater temperature of 330 ° C. and a heating time of 8 seconds ± 1 second.

Table 2 shows the physical characteristics of the obtained laminated foam sheet, and Table 3 shows the physical characteristics of the obtained container.
In Comparative Example 3, the surface condition on the resin layer A side was poor, and it was not possible to obtain a laminated foam sheet having a good appearance. Further, in Comparative Example 3, when the film B was laminated on the thermal lamination, the foam layer on the resin layer A side was crushed and the bubble structure was deteriorated. Therefore, in the laminated foam sheet of Comparative Example 3, a container having a good appearance could not be obtained.

The average thickness of the laminated foam sheet was measured as follows.
First, a strip having a width direction (TD) orthogonal to the extrusion direction and a length of 100 mm in the extrusion direction (MD) is cut out from the laminated foam sheet, and both ends of the strip in the longitudinal direction are 25 mm each. It was excised, and a portion of the laminated foam sheet having a central portion of 800 mm in the width direction was cut out as a test piece.
This test piece was further divided into 10 equal parts in the width direction, and the thickness near the center of each of the cut test pieces was measured with a micrometer. The value obtained by arithmetically averaging the thicknesses of each test piece was taken as the thickness of the laminated foam sheet.

The measurement of the total basis weight of the laminated foam sheet and the basis weight of the resin layer A were performed as follows.
In the measurement of the thickness, the mass of the cut-out test piece was measured, the mass was divided by the area of the test piece (specifically, 800 mm × 100 mm), and the unit was converted into g / m ² .

Further, the basis weight of the resin layer A was determined by distributing the basis weight of the foamed sheet to which the resin layer A was laminated and adhered by the ratio of the discharge amount of the foamed layer and the resin layer A.

The overall apparent density of the laminated foam sheet was obtained by dividing the total basis weight of the laminated foam sheet by the thickness of the laminated foam sheet and converting it into a unit as described above.

Specifically, the apparent density of the surface layer portion B was measured as follows.
A portion from the surface of the film B of the laminated foam sheet (in Comparative Example 4, the surface of the foam sheet on the opposite side of the resin layer A) to 200 μm in the thickness direction is sliced, and the length (extrusion direction of the sheet) 20 mm × It was cut into test pieces having a width (in the width direction of the sheet) of 5 mm, the mass of the obtained test pieces was measured, and the thickness was measured with a gauge. The mass of the test piece was divided by the volume of the test piece (width x length x thickness) and converted into units to obtain the apparent density of the test piece. The above measurement was performed on 10 points at equal intervals in the width direction of the laminated foam sheet, and the arithmetic mean value thereof was taken as the apparent density of the surface layer portion B.

The average value ( _AAS ) of the cross-sectional areas of bubbles existing in the portion from the interface A to 50 μm in the thickness direction was measured by the above method.
The enlarged photograph of the TD cross section (magnification: 100 to 200 times) was taken using Keyence's "VHX-6000 (lens: VH-Z20R)" and based on the enlarged photograph using "CAD software: JwCAD". A line drawing of the bubble structure (bubble film) was created. As an example of the line drawing, FIG. 2 shows a line drawing created for the laminated foam sheet obtained in Example 1, and FIG. 3 shows a line drawing created for the laminated foam sheet obtained in Comparative Example 1. In FIGS. 2 and 3, the resin layer A and the film B are not shown.
Next, a straight line a1 connecting both ends of the interface A is drawn on the line drawing along the interface A, and a straight line a2 parallel to the straight line a1 is further drawn at a position 50 μm away from the interface A in the thickness direction to further increase the thickness. Two straight lines c1 and c2 that are parallel to the direction and have an actual size interval of 2.0 mm are drawn, and the part surrounded by the frame defined by the four straight lines a1, a2, c1 and c2 is cut out from the line drawing. As described above, the measurement target is specified, the cross-sectional area occupied by the bubbles and the number of bubbles are measured as described above, the cross-sectional area is divided by the number of the bubbles, and the portion from the interface A to 50 μm in the thickness direction is formed. The cross-sectional area of each existing bubble was calculated. Furthermore, as mentioned above,
This measurement was performed on 20 randomly selected laminated foam sheets, and the arithmetic mean value of each measured value obtained was taken as the average value ( _AAS ).
In Comparative Example 2, the same method was used for air bubbles existing in the portion up to 50 μm in the thickness direction from the surface (corresponding to the interface A) on the surface opposite to the surface on which the film B of the foam layer was laminated. The measurement target was decided.

The average value ( _{ABS) of the cross-sectional area of the bubbles existing in the portion from the interface B to 50 μm in the thickness direction specifies the measurement target and the specified bubbles are found in the same manner as the measurement of the average value (AAS )} . The area occupied and the number of the bubbles were measured, and the average value ( _ABS ) was obtained. In Comparative Example 4, air bubbles existing in a portion up to 50 μm in the thickness direction from the surface (corresponding to the interface B) opposite to the surface of the foam layer on which the resin layer A was laminated were measured.

The average value (A _W ) of the cross-sectional area of the bubbles in the entire laminated foam sheet is an enlarged photograph of the TD cross section (magnification: 100) as described above using the "VHX-6000 (lens: VH-Z20R)" manufactured by Keyence. ~ 200x) was photographed, and as described above, the cross-sectional area per bubble was calculated using "CAD software: JwCAD", and this measurement was performed at 10 randomly selected laminated foam sheets. The average value of the measured values calculated in each measurement was taken as the average value ( _AW ).
The length of the foamed sheet in the line drawing in the width direction was set to 2.0 mm in actual size.

The average thickness of the container was measured as described above.

The overall apparent density of the container was determined as described above. As the measurement sample, a test piece having a “50 mm × 50 mm × container thickness” cut out from a flat portion other than the flange portion and the specially shaped portion of the foam container was used.

The average thickness of the resin layer A and the film B in the container was measured as described above.

The average value ( _AAS ), the average value ( _ABS ), and the average value ( _AW ) in the container were measured as described above.

The compressive strength in the horizontal direction of the container and the amount of deflection at the time of compression failure were measured as follows using "TENSILON universal tester RTG-1310 manufactured by ORIENTEC".
As shown in FIG. 1, the container 1 can be sandwiched between the upper jig 2 and the lower jig 3 so as to have an initial load of 0.2 N, and can be compressed in the horizontal direction of the container (direction perpendicular to the height direction of the container). As such, the container was attached to the measuring device. The container was compressed in the horizontal direction of the container with an initial load of 0.2 N and a compression rate of 500 mm / min, and the change in the compressive strength of the container with respect to the displacement due to the compression until the container buckled was measured. In this measurement, the displacement at the time when the container buckled was defined as the amount of deflection at the time of compression fracture, and the strength at the time when the container buckled was defined as the compressive strength. Further, the compressive strength of the container at the time when the displacement became 10 mm was set to 10 mm compressive strength.
In the above measurement, the container was attached so that the direction of compressing the container was perpendicular to the extrusion direction of the laminated foam sheet constituting the container. Further, the above measurement was performed at N = 5, and these arithmetic mean values were adopted.

In the above measurement, the case where all of the following criteria were satisfied was regarded as acceptable.
10 mm compressive strength: 5.5 N or more Compressive strength in the horizontal direction of the container: 16 N or more Deflection during compression failure in the horizontal direction of the container: 30 mm or more If the 10 mm compressive strength is 5.5 N or more, the container has excellent stiffness. It becomes.

1 Container 2 Upper jig 3 Lower jig

Claims (7)

Polystyrene resin foam layer and
A polystyrene-based resin layer A laminated and adhered to one surface of the foam layer by coextrusion,
A polystyrene-based resin laminated foam sheet having a thermoplastic resin film B laminated and adhered to the other surface of the foam layer.
The polystyrene-based resin laminated foam sheet has an overall apparent density of 0.05 to 0.14 g / cm ³ , an overall basis weight of 100 to 200 g / m ² , and an average thickness of 0.5 to 3.0 mm. ,
The polystyrene-based resin layer A has a basis weight of 3 to 18 g / m ² .
The basis weight of the thermoplastic resin film B is 14 g / m ² or more, and the basis weight is 14 g / m 2.
Breakage per bubble for bubbles existing in a portion up to 50 μm in the thickness direction from the interface between the foam layer and the polystyrene resin layer A in a cross section perpendicular to the extrusion direction of the polystyrene resin foam layer. A polystyrene-based resin laminated foam sheet having an average area value ( _AAS ) of 7000 μm ² / piece or more.
Claim 1 is characterized in that the apparent density of the surface layer portion B, which is a portion of the laminated foam sheet from the surface of the thermoplastic resin film B to 200 μm in the thickness direction, is 0.20 g / cm ³ or more. The polystyrene-based resin laminated foam sheet described in 1.
The average value (A _W ) of the cross-sectional area per bubble for the bubbles in the entire foam layer in the cross section perpendicular to the extrusion direction of the polystyrene-based resin foam layer is 20000 to 60,000 μm ² / piece. The invention according to claim 1 or 2, wherein the ratio (A _AS / A _W ) of the average value A _AS of the cross section to the average value A _W of the cross section is 0.3 or more and 0.5 or less. Polystyrene resin laminated foam sheet.
The polystyrene-based resin laminated foam sheet according to any one of claims 1 to 3, wherein the thermoplastic resin film B is laminated and adhered to the polystyrene-based resin foamed layer by thermal lamination.
Breakage per bubble for bubbles existing in a portion up to 50 μm in the thickness direction from the interface between the foam layer and the thermoplastic resin film B in a cross section perpendicular to the extrusion direction of the polystyrene-based resin foam layer. The polystyrene-based resin laminated foam sheet according to any one of claims 1 to 4, wherein the average value ( _ABS ) of the area is 4000 μm ² / piece or more and less than 7000 μm ² / piece.
The average value (A _W ) of the cross-sectional area per bubble for the bubbles in the entire foam layer in the cross section perpendicular to the extrusion direction of the polystyrene-based resin foam layer is 20000 to 60,000 μm ² / piece. The polystyrene according to claim 5, wherein the ratio (A _BS / A _W ) of the average value A _BS of the cross section to the average value A _W of the cross section is 0.1 or more and less than 0.3. Polystyrene foam sheet.
A container formed by thermoforming the polystyrene-based resin laminated foam sheet according to any one of claims 1 to 6, wherein the polystyrene-based resin layer A is located outside the container. ..

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