Foamed molded container for top seal

Abstract

To provide a foam-molded container for a top seal excellent in strength of a flange portion even when the flange portion is formed wide in the foam-molded container, and not easily bent or broken, and also excellent in peelability when a top film is peeled off because of high shape holding force.SOLUTION: The foam-molded container for a top seal has a bottom portion, a side wall portion extending upward from the outer edge of the bottom portion, and a flange extending outward from the upper end of the side wall portion through a connection portion, and has a curved thick portion 5 having a flat portion on the upper surface of the flange, the connection portion forming a curved surface on the surface of the content side, and having a thickness (t2) in the perpendicular direction at a midpoint Rm of the cross sectional view arc on the curved surface larger than a flange thickness (t1) in the flat portion.SELECTED DRAWING: Figure 4

Description

Technical Field

[0001] The present invention relates to a foamed molded container suitable for top seal applications.

Background Art

[0002] Foamed molded containers formed by vacuum thermoforming or pressure-air thermoforming of polystyrene resin foamed sheets are widely used in supermarkets, convenience stores, etc. as food packaging containers for selling bento boxes and prepared foods.

[0003] Regarding such foamed molded containers, in recent years, from the perspective of reducing the environmental load, reducing the usage amount of plastic containers has become a social demand. Furthermore, there is an increasing need to extend the shelf life of food and reduce food loss, and from the point that the freshness of the stored food can be maintained at a high level, a so-called top seal type lid material is used, and after the food is stored in the container body, a foamed molded container of the type in which the lid material is heat-sealed to the flange of the container body has been widely used.

[0004] However, although such top-seal type foamed molded containers can maintain the freshness of food and reduce the usage amount of plastic materials, it is difficult to achieve uniform seal strength on the flange surface extending over the entire circumference of the container body, and there may be partially insufficient strength sites.

[0005] Therefore, conventionally, as a method for achieving uniform seal strength in a top-seal type foamed molded container, for example, Patent Document 1 discloses a foamed molded container in which a wide flange having a flat width of 4 mm or more is provided over the entire circumference of the opening of the container body to improve the uniformity of seal strength during sealing.

[0006] However, although the uniformity of the seal strength described in Patent Document 1 can be improved to some extent, the width of the flange becomes wider, resulting in inferior strength of the flange portion. As a result, the flange portion is likely to bend or the root of the flange is likely to break due to an external force. In addition, when peeling the top seal, the shape retention force of the flange is weak, so the flange follows and bends in the peeling direction, making it difficult to peel the top film. If forced to peel, a so-called bagging phenomenon is likely to occur, in which the laminate film located on the inner surface layer of the container is also peeled off together. On the other hand, although the strength of the flange portion can be improved by increasing the flange thickness to some extent, in this case, the depth of penetration by the seal mold during heat fusion becomes large, resulting in uneven seal strength.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] Therefore, the problem to be solved by the present invention is to provide a foamed molded container that has excellent strength in the flange portion even when the flange portion is formed wide in a top-seal foamed molded container, does not easily bend or break, and also has excellent peelability during top film peeling due to its high shape retention force.

Means for Solving the Problems

[0009] As a result of intensive studies to solve the above problems, the inventors of the present invention have found that by increasing the thickness of the joint portion between the back surface of the flange and the side wall of the container body on the back surface of the flange extending outward from the peripheral edge of the opening of the foamed molded body, the mechanical strength of the flange can be dramatically increased even for a thin and wide flange, and thus the present invention has been completed.

[0010] That is, the present invention relates to a foam-molded body for a top seal, which has a bottom portion, a side wall portion extending upward from the outer edge of the bottom portion, and a flange extending outward from the upper end of the side wall portion via a connecting portion, wherein the upper surface of the flange has a flat portion, the connecting portion forms a curved surface on the surface side of the content, and the thickness in the vertical direction at the midpoint of the circular arc in the cross-sectional view of the curved surface is larger than the flange thickness in the flat portion, and the outer surface has a thick portion constituting a curved surface.

Effects of the Invention

[0011] According to the present invention, even when the flange portion is widely formed in the foam-molded container for a top seal, the strength of the flange portion is excellent, and it does not easily bend or break. Also, since the shape retention force is high, a foam-molded container excellent in peelability at the time of peeling the top film can be provided.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Modes for Carrying Out the Invention

[0013] As described above, the foamed molded container of the present invention is a foamed molded body for top sealing having a bottom portion, a side wall portion extending upward from the outer edge of the bottom portion, and a flange extending outward from the upper end of the side wall portion via a connecting portion. The upper surface of the flange has a flat portion, the connecting portion forms a curved surface on the surface on the content side, and the thickness in the vertical direction at the midpoint of the circular arc in the cross-sectional view of the curved surface is larger than the flange thickness in the flat portion. It is characterized in that the outer surface having a curved shape has a thick portion.

[0014] Here, the "midpoint of the circular arc in the cross-sectional view of the curved surface" means the midpoint that equally bisects the cross-sectional circular arc composed of the same curvature. For example, in FIG. 4, from the contact point x between the straight line and the circular arc along the inner wall in the cross-sectional view to the contact point y between the straight line and the circular arc along the flat portion of the upper surface of the flange, it has a curvature Ra, and it can be represented by the midpoint Rm of the arc length.

[0015] In the present invention, it is preferable that the thickness (t1) of the flat portion of the flange is in the range of 0.5 to 3 mm. That is, in order to increase the flange strength and the seal strength due to the pushing-in of the seal mold during heat sealing, generally, the greater the thickness (t1), the better. However, on the other hand, the pushing-in width during heat sealing also becomes larger, and seal marks such as partial weakening of the strength occur easily over the entire circumference of the flange. On the other hand, when the thickness (t1) is reduced, although the seal marks are improved, the strength of the flange portion is weakened. The foamed molded container of the present invention has the characteristics that by increasing the thickness of the flange root portion and forming a thick portion with a curved surface on the outside of the container, the strength of the flange portion can be improved even with a thin flange, there are few seal marks, and the flange strength is excellent. That is, in the present invention, by making the thickness (t2) larger than the thickness (t1), it is possible to reduce seal marks and improve strength. However, if the thickness (t2) becomes too large, the fit of the bucket surface supporting the back surface of the flange during heat sealing deteriorates.

[0016] From such a perspective, when the thickness in the perpendicular direction at the midpoint of the arc in the cross-section view on the curved surface is t2, it is preferable that t1 is 0.5 to 3 mm and t2 / t1 is 1.5 to 3.

[0017] The shape of the curved thick part of the flange root portion constituting the thickness (t2) is not particularly limited, but it may be a shape that bulges outward in a cross-section view arc shape (shape pattern 1: for example, the cross-sectional shape shown in FIG. 4), or a shape that is curved toward the flange content side in a cross-section view arc shape (shape pattern 2: for example, the cross-sectional shape shown in FIG. 7). In the case of the latter shape pattern 2, the inner surface curvature Ra' of the flange root portion on the content side and the outer curvature Rc' of the flange root portion satisfy the following relationship Ra’ < Rc’ By this, the shape is such that the flange root becomes thickened.

[0018] In the present invention, in either case of shape pattern 1 and shape pattern 2, at the flange root portion, that is, at the connection portion between the side wall and the flange, both the content side and the outer side are constituted by curved surfaces. In particular, from the viewpoint of the mechanical strength of the flange portion, it is preferable that the outer shape does not have an acute or obtuse bending portion in the cross-section view and is constituted by a straight line and a curve. Here, at the root portion of the flange, when there is an acute or obtuse bending portion, specifically, a bent portion with a curvature radius of 0.2 mm or less, the force applied when peeling the top seal film or the external force directly applied to the flange portion when the product drops cannot disperse the force when acting on the bent portion, and it is likely to break at this portion. Therefore, in the present invention, except for the straight line portions in the cross-section view of the upper and lower surfaces of the flange in the flange portion, that is, it is preferable that the flange root portion is curved both inside and outside so that external forces and the like can be appropriately dispersed.

[0019] Specifically, in the shape pattern 1, the radius of curvature (Ra) of the curved surface extending from the flat portion on the upper surface of the flange to the inner wall surface of the content is 2 to 6 mm, the radius of curvature (Rb) of the curved surface extending from the flat portion on the upper surface of the flange to the outer skirt wall surface is 1 to 4 mm, and the radii of curvature (Re), (Rc), and (Rf) of the corrugated curved surface extending from the back surface of the flange to the container body wall surface are such that the radius of curvature (Re) is 0.3 to 1 mm, the radius of curvature (Rc) is 1 to 4 mm, and the radius of curvature (Rf) is 0.3 to 1 mm, respectively. Also, it is preferable that the radius of curvature (Rd) of the curved surface extending from the flat portion on the back surface of the flange to the inner wall surface of the outer skirt portion is 0.5 to 2 mm.

[0020] On the other hand, in the shape pattern 2, the radius of curvature (Ra') of the curved surface extending from the flat portion on the upper surface of the flange to the inner wall surface of the content is 2 to 6 mm, the radius of curvature (Rb') of the curved surface extending from the flat portion on the upper surface of the flange to the outer skirt wall surface is 1 to 4 mm, the radius of curvature (Rc') of the corrugated curved surface extending from the back surface of the flange to the container body wall surface is 3 to 10 mm (provided that Ra' < Rc'), and it is preferable that the radius of curvature (Rd') of the curved surface extending from the flat portion on the back surface of the flange to the inner wall surface of the outer skirt portion is 0.5 to 2 mm.

[0021] Also, the width of the flat portion at the upper part of the flange (for example, the width F in FIGS. 4 or 7) is preferably 3 to 20 mm. Here, the width of the flat portion at the upper part of the flange means, in the case of the shape pattern 1, for example, in FIG. 4, the length F from the contact point y between the arc of the radius of curvature Ra and the straight line along the flat portion on the upper surface of the flange to the contact point z between the arc of the radius of curvature Ra and the straight line along the flat portion on the upper surface of the flange, and in the case of the shape pattern 2, for example, in FIG. 7, the length F from the contact point y between the arc of the radius of curvature Ra' and the straight line along the flat portion on the upper surface of the flange to the contact point z between the arc of the radius of curvature Ra' and the straight line along the flat portion on the upper surface of the flange.

[0022] The width F of the flat portion at the upper part of the flange is usually larger for the shape pattern 2 than for the shape pattern 1. The larger the width F of the flat portion is, the wider the seal width can be, resulting in excellent fusion properties and seal strength. From this perspective, it is preferable that the width F of the flat portion in the shape pattern 1 is in the range of 3 to 20 mm, and the width F of the flat portion in the shape pattern 2 is in the range of 4 to 25 mm.

[0023] On the other hand, a back surface horizontal portion substantially parallel to the flat portion at the upper part of the flange is formed on the back surface of the flange. Such a back surface horizontal portion refers to the length from one contact point to the other contact point of the back surface horizontal portion and the curved portion in a cross-sectional view. For example, in the shape pattern 1, it is represented by the length L in FIG. 4, and in the shape pattern 2, it is represented by the length L in FIG. 7. In the present invention, the longer the width L of the back surface horizontal portion of the flange is, the more stably the flange is fixed by the bucket and the indicating member provided at the upper end of the bucket during heat sealing, resulting in excellent reproducibility of the heat seal width and seal strength of the heat-sealed product. From this perspective, the shape pattern 1 is preferable to the shape pattern 2 in terms of being able to ensure a larger width L of the back surface horizontal portion. Specifically, it is preferable that the width L of the back surface horizontal portion of the shape pattern 1 is 2 to 18 mm, and the width F of the back surface horizontal portion of the shape pattern 2 is 2 to 18 mm.

[0024] The thick portions represented by the above-described shape pattern 1 and shape pattern 2 may be provided over the entire circumference of the flange root portion, or may be intermittently provided at the periphery of the flange root portion. In particular, it is preferable that they are provided over the entire circumference of the flange root portion from the viewpoint that the effect of improving the flange strength in the thick portion becomes remarkable.

[0025] Also, in the present invention, it is preferable to have a region of a continuous fine concavo-convex shape (hereinafter, may be abbreviated as "continuous fine concavo-convex shape region") on the outer edge side of at least one place on the upper surface of the flange. That is, by providing at least one location on the upper surface of the flange with a fine concavo-convex shape that is continuous outward when viewed from the content side, when the top seal film is heat-sealed, the area of the fine concavo-convex shape can be weakened, and after cooking, when lifting and opening the top seal film by hand, it can be reliably peeled off from this weakened area. As a result, when the adhesion between the laminated film laminated on the inner surface of the foamed molded body and the top film is high, during opening, a so-called bagging phenomenon may occur where peeling occurs between the laminated film and the foamed base material layer and the contents cannot be taken out. However, such a bagging phenomenon can be well prevented.

[0026] Furthermore, when a continuous fine concavo-convex shape area is provided only at the outer edge of the flange corner part, the area on the content side connected from the continuous fine concavo-convex shape area will be continuously connected to the other upper surface of the flange. As a result, when viewed from the contents, the seal part of the flange will be in a uniformly heat-sealed form, and the seal strength of the entire container is ensured.

[0027] Specific shapes of the continuous fine concavo-convex shape area include those in which linear concavo-convex shapes are arranged continuously, a continuous lattice shape, or those having a plurality of dot-shaped recesses, etc. Among these, in particular, linear concavo-convex shapes or lattice-shaped concavo-convex shapes are preferable in terms of good peelability. Especially when the opening shape of the foamed container is substantially square, it is preferable in terms of the workability of opening that a continuous fine concavo-convex shape area is provided at at least one corner part. At this time, the lattice shape is preferably a lattice shape with the long side direction and the short side direction of the container as sides, as represented by the lattice-shaped recess 9 in FIG. 8, because peeling starts from the lattice vertex part during peeling and can be reliably opened with a smaller force.

[0028] Here, when the continuous fine concavo-convex shape region is composed of a lattice shape, the size of the lattice shape, that is, the length between the centers of the convex portions in adjacent convex portions parallel to one side thereof (for example, the length P between the centers of the convex portions in FIG. 9), is in the range of 0.2 to 5 mm, particularly preferably in the range of 0.7 to 2.5 mm, from the viewpoint of being able to achieve weak adhesion while ensuring appropriate adhesion to the top seal film.

[0029] Furthermore, when the continuous fine concavo-convex shape region is in a lattice shape, the distance (α) of one side of the bottom surface of the concave portion (for example, α in FIG. 9) is preferably in the range of 0.5 to 2 mm, particularly preferably in the range of 0.7 to 1.5 mm, from the viewpoint of the balance between the adhesion and peelability to the top seal film.

[0030] The depth (d) of the concave portion formed on the flange surface (for example, the depth d of the concave portion in FIG. 9) is preferably in the range of 0.2 to 1 mm, from the viewpoint that the strength improvement effect by disposing the concavo-convex portions is sufficiently exhibited and the effect of weakening the adhesion of the seal portion can also be effectively obtained.

[0031] The shape of the opening of the foamed molded container of the present invention may be circular, elliptical, or rectangular in plan view, and may be appropriately selected according to the contents, but is preferably rectangular, particularly substantially square, from the viewpoint of being easily opened by hand. In the case of a rectangular shape in plan view, the bottom surface portion and the opening portion may be formed with rounded corners.

[0032] Further, the flange in the present invention preferably has a structure having a skirt portion extending downward and outward from the outer end of the flange and a thin wall portion extending outward from the lower end of the skirt portion, from the viewpoint that the strength of the flange becomes better.

[0033] Also, the inclination angle of the side wall, specifically, the inclination angle with respect to the vertical direction, is preferably such that its maximum value is in the range of 30 to 60°, particularly preferably in the range of 35 to 50°, from the viewpoint that the strength of the container body becomes excellent.

[0034] In the present invention, the larger the inclination angle of the side wall described above, the stronger the toughness against external forces and impacts from the horizontal direction can be exhibited. Also, the smaller the inclination angle, the better the resistance to impacts and loads from above the container. In the present invention, while achieving this balance, since the side wall is composed of a curved surface, when an external force or impact is applied, the force can be propagated and dispersed without concentrating at a specific location, resulting in a foam-formed container for a top seal that is excellent in toughness.

[0035] Further, it is preferable that the central portion of the bottom surface portion has an upper bottom surface from the viewpoint of heating efficiency in a microwave oven. In this case, along the periphery of the upper bottom surface, it is preferable to form a bulging leg portion (for example, the bulging leg portion 7 in FIG. 1) that bulges downward from the periphery, and to have a side wall that extends upward from the outer edge end of the bulging leg portion.

[0036] Also, it is preferable that the side wall further has a stepped portion, for example, the stepped portion 8 in FIGS. 1 to 4, or the stepped portion 8' in FIGS. 5 to 7. By providing the stepped portion, the stackability when stacking the containers can be exhibited. When having such a stepped portion, the upper part of the stepped portion becomes a second side wall portion. Also, it is preferable from the viewpoint of stackability that the inclination angle of the second side wall portion with respect to the vertical is 5° to 20°.

[0037] The height H of the container body may be appropriately selected so as to ensure the wall surface angle, and for example, it can be selected from the range of 30 to 70 mm.

[0038] The foam-formed container for a top seal of the present invention described in detail above has a foam base material layer and a single-layer or multi-layer thermoplastic film layer on its surface, and the thermoplastic film layer constitutes the inner surface of the container bottom surface, the inner surface of the side wall, and the surface of the flange.

[0039] Here, the foam base material layer may be various foam-molded bodies such as a polystyrene-based foam, a polyethylene-based foam, a polypropylene-based foam, and a polyester-based foam. However, it is preferably a polystyrene-based foam particularly from the viewpoint of excellent balance between strength and moldability.

[0040] Here, the polystyrene foam is a foam-molded body made of a styrene resin composition. Examples of the styrene resin composition include a styrene homopolymer (GPPS), high-impact polystyrene (HIPS), multi-branched polystyrene, a styrene-acrylic copolymer, a mixed resin having a styrene homopolymer (GPPS) and polyphenylene ether as essential components, or a mixture thereof. Among these, a mixed resin having a styrene homopolymer (GPPS) and polyphenylene ether as essential components is preferable. Furthermore, it is preferable to contain the HIPS in the mixed resin because, in addition to good heat resistance, it has particularly good impact resistance. Here, in the case of a mixed resin having a styrene homopolymer (GPPS) and polyphenylene ether as essential components, it is preferable to contain polyphenylene ether in a proportion of 1 to 40% by mass.

[0041] The expansion ratio of the polystyrene foam base material layer is preferably in the range of 2 to 40 times. Particularly in the case of a highly foamed sheet that requires high heat resistance, the expansion ratio of the polystyrene resin foam layer is preferably 10 to 40 times.

[0042] In the present invention, it is preferable that the expansion ratio of the flange is 2 to 15 times and the expansion ratio at the thick part at the base of the flange is 5 to 25 times from the viewpoint of excellent flange strength.

[0043] Next, the single-layer or multi-layer thermoplastic film layer is formed by laminating an unfoamed thermoplastic film on the foam sheet used for the foam base material layer and molding it into a desired shape. Such single-layer or multi-layer thermoplastic films include unfoamed films such as styrene resin films, olefin resin films, and gas barrier films, and multi-layer films formed by laminating a plurality of these. Among these, olefin resin films are preferable because of their excellent gloss on the surface and strength on the inner surface.

[0044] Next, the single-layer or multi-layer thermoplastic film layer is formed by laminating various thermoplastic films on the foamed sheet and thermoforming as described above. Specifically, Structure 1: A structure in which a styrene-based resin film is thermally laminated alone on a foamed sheet and then formed; Structure 2: A structure in which an olefin-based resin film is laminated on a foamed sheet via an adhesive and then formed; Structure 3: A structure in which a styrene-based resin film is laminated on an olefin-based resin film via a dry lamination adhesive, the styrene-based resin film side is thermally laminated on a foamed sheet, and then formed; Structure 4: A structure in which the second olefin-based resin layer of a laminated film obtained by co-extruding a first olefin-based resin, a resin constituting a gas barrier layer, and a second olefin-based resin is laminated on a foamed sheet via an adhesive and then formed; Structure 5: A laminated film obtained by co-extruding a first olefin-based resin, a resin constituting a gas barrier layer, and a second olefin-based resin is obtained. Then, a styrene-based resin film is dry laminated on the second olefin-based resin layer side of the obtained laminated film, the surface of the styrene-based resin film is thermally laminated on a foamed sheet, and then formed may be mentioned.

[0045] Among these, when the foam base material is a foam of a styrene homopolymer, the above Structure 1: The structure obtained by thermally laminating a styrene-based resin film alone on the foam base material is preferable in terms of the smoothness of the surface of the molded body and the ease of recovering the foam molded body and recycling it again into a food tray.

[0046] Also, when gas substitution is performed inside with an inert gas or the like when top-sealing the top-seal film, it is preferable to provide a gas barrier layer. In that case, the above Structures 4 and 5 are preferable. In particular, in the case of Structure 5, it is preferable because the adhesion between the foam base material and the laminated film is high and the effect of preventing bagging is remarkable.

[0047] Also, when the foam base material is a mixed resin having a styrene homopolymer (GPPS) and polyphenylene ether as essential components, The structure 2: A structure in which an olefin resin film is laminated to the foam base material via an adhesive; The structure 3: A structure in which a styrene resin film is laminated to an olefin resin film via a dry lamination adhesive, and the styrene resin film side is thermally laminated to the foam base material; The structure 4: A structure in which the second olefin resin layer of a laminated film obtained by co-extruding a first olefin resin, a resin constituting a gas barrier layer, and a second olefin resin is laminated to the foam base material via an adhesive; The structure 5: A structure in which a styrene resin film is laminated to the second olefin resin layer side of a laminated film obtained by co-extruding a first olefin resin, a resin constituting a gas barrier layer, and a second olefin resin via a dry lamination adhesive, and the surface of the styrene resin film is thermally laminated to the foam base material. The structure 3 and the structure 5 in which an olefin resin film or a co-extruded film containing the same is laminated to the foam base material via a styrene resin film are particularly preferable because the gloss and oil resistance of the molded product surface are good, and excellent impact resistance can be exhibited even in a freezing environment.

[0048] In the case of a structure having an olefin resin film such as Structures 2 to 5 as the surface layer, although it becomes a food container excellent in oil resistance, since the heat seal temperature requires a high temperature condition of 120°C or higher, it is desirable from the viewpoint of seal strength that the temperature condition be higher. On the other hand, sealing at a high temperature reduces productivity, such as by increasing the cooling time after sealing. On the other hand, when sealing under relatively low temperature conditions, high-speed sealing becomes possible and productivity is improved, but it is difficult to obtain sufficient seal strength. This problem of seal strength can be improved by ensuring a wide seal width. In particular, in the case of a foamed molded container, if the adhesive strength per unit area with the top film is too strong, there is a risk of a so-called bagging phenomenon occurring, where the top film and the laminated film are peeled off while fused together when the top film is peeled off. Therefore, it is important to ensure the seal strength as a whole by sealing widely while suppressing the adhesive strength per unit area within an appropriate range. However, when the seal width is thus expanded, the flange strength will decrease accordingly. Therefore, by adopting the flange structure of the present invention, even when an olefin resin film is used as the surface layer, a container excellent in heat seal productivity and having high strength can be obtained.

[0049] Here, examples of the polystyrene resin constituting the polystyrene resin film include polystyrene homopolymer (GPPS), high-impact polystyrene (HIPS), multi-branched polystyrene, syndiotactic polystyrene (SPS), styrene-acrylonitrile copolymer, styrene-butadiene-acrylonitrile copolymer, styrene-acrylic acid copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-maleic anhydride copolymer, styrene-α-methylstyrene copolymer, etc. In particular, it is preferably a polystyrene homopolymer (GPPS), and particularly preferably biaxially stretched polystyrene.

[0050] Next, examples of the olefin resin constituting the olefin resin film include polyethylene, polypropylene, a propylene-ethylene random copolymer having an ethylene polymerization amount of 5% by mass or less, or a mixture of a propylene homopolymer and a propylene-ethylene random copolymer having an ethylene polymerization amount of 5% by mass or less. Among these, polyethylene and polypropylene are preferable, and particularly when the olefin resin film is located on the surface layer, polypropylene is preferable from the viewpoints of oil resistance and heat resistance. Further, from the viewpoint of excellent formability into a container, non-stretched polypropylene is particularly preferable.

[0051] The gas barrier layer may be any layer having low permeability to inert gas, oxygen, water vapor, etc., and examples include ethylene-vinyl alcohol copolymer and polyamide.

[0052] For example, in the case of the structure 1, the thickness of the styrene resin film layer in the layer composed of these thermoplastic non-foamed films is preferably in the range of 5 to 100 μm from the viewpoints of good surface smoothness and gloss.

[0053] In the case of the structure 2, the thickness of the olefin resin film layer is preferably in the range of 5 to 100 μm from the viewpoints of good surface smoothness and gloss.

[0054] In the case of the structure 3, the thickness of the olefin resin film layer is preferably in the range of 15 to 100 μm.

[0055] That is, by setting it to 15 μm or more, a container excellent in oil resistance can be obtained. Further, by setting it to 100 μm or less, good adhesion to the foam base material can be achieved. Particularly, from the viewpoint of excellent balance of these performances, the range of 20 to 50 μm is preferable. On the other hand, the thickness of the polystyrene resin film layer is preferably in the range of 10 to 40 μm, particularly in the range of 10 to 17 μm, from the viewpoint of excellent balance between adhesion to the foam base material and surface smoothness.

[0056] In the case of the above-mentioned Structures 4 and 5, the thickness of the first olefin resin film layer is preferably in the range of 20 to 150 μm based on the total thickness of the coextruded film layer. Further, in the case of Structure 5, the thickness of the styrene resin film layer is preferably in the range of 10 to 40 μm, particularly preferably in the range of 10 to 17 μm, from the viewpoint of excellent balance between adhesion to the foam substrate and surface smoothness.

[0057] In addition, when a non-foamed thermoplastic film is used, the upper surface of the flange of the foam-formed container becomes moderately excellent in smoothness, and its surface roughness (Ra) is preferably 3 μm or less. Here, the surface roughness (Ra) refers to the arithmetic mean roughness in the reference length. For example, the inner surface of the bottom surface of the formed container is measured at a magnification of 1000 times using a Keyence laser microscope (VK-X200 series) in accordance with JIS B0601-2013, and the evaluation length is 2000 μm, the cut-off λs is 2.5 μm, and the cut-off λc is 0.25 mm, and it can be calculated.

[0058] The above-mentioned foam-formed container can be obtained through Step 1 of laminating a polystyrene-based foam sheet and a single-layer film of a thermoplastic non-foamed film or a multi-layer film containing the same (hereinafter abbreviated as "non-foamed film") to form a composite sheet, and then Step 2 of shaping the obtained composite sheet into a predetermined shape to obtain a molded body.

[0059] As means for laminating the polystyrene foam sheet and the non-foamed film in Step 1, there are methods such as thermal lamination, dry lamination, or extrusion lamination in which the polystyrene resin is foam-extruded into a sheet shape and laminated simultaneously. Next, Step 2 is a step of shaping the composite sheet obtained in Step 1 into a desired container shape by thermoforming. The forming method may be a standard method. For example, it can be formed by single-sided vacuum forming or double-sided vacuum forming, but double-sided forming is preferred to increase the flat portion of the flange surface. Also, by performing a knurling process with a predetermined shape on the flange forming portion of the upper convex mold used during vacuum forming, a foam-formed container with a desired shape can be obtained.

[0060] Furthermore, the basis weight of the polystyrene resin foam sheet is preferably 90 to 400 g / m 2 and more preferably 100 to 350 g / m 2 .

[0061] The thickness of the polystyrene resin foam sheet is preferably 0.5 to 4 mm, and more preferably in the range of 1 to 3 mm.

[0062] The foam-formed container for top seal of the present invention described in detail above can be used for food packaging by heat-sealing a top seal film after containing the food as the content. At this time, as described above, when a gas barrier layer is provided in the foam-formed container, it is possible to replace the inside with gas and perform top sealing after containing the food.

[0063] As the top seal film used here, any of an interface peeling type, an interlayer peeling type, and an aggregation peeling type may be used, but an interlayer peeling type or an aggregation peeling type is preferred in terms of excellent adhesion and sealing properties to the surface of the foam-formed container.

[0064] Such delamination type and agglomeration delamination type top seal films may specifically be those having an agglomeration delamination layer or a delamination layer on a base film, and may have a multilayer structure of at least two or more layers. Among them, a multilayer film laminated in the order of base film / support film / agglomeration delamination layer (or delamination layer) is preferably used.

[0065] Here, as the base film, various styrene resins, nylon resins, and polyester resins can be used. Among them, nylon resins and polyester resins are preferable especially from the viewpoint of rigidity. The thickness of the base film is, for example, in the range of 5 to 20 μm.

[0066] As the support film, a resin material having high affinity with the agglomeration delamination layer or the delamination layer can be appropriately selected. For example, polyethylene, high-density polyethylene, polypropylene, propylene block copolymer, etc. can be mentioned. The thickness of such a support film is preferably in the range of 20 to 60 μm when used in one layer, and a total of 20 to 60 μm when used in two layers.

[0067] The foamed formed container described in detail above and the top seal film can be arbitrarily combined and used. However, as the foamed base material, a mixture of a styrene homopolymer (GPPS) and polyphenylene ether is used as a polystyrene-based foamed base material layer, and the structure 3 (a structure in which a styrene-based resin film is laminated on an olefin-based resin film via a dry lamination adhesive, and the styrene-based resin film side is thermally laminated to a foamed sheet and then molded) is used. And when a multilayer film having an agglomeration delamination layer is used as the top seal film, it is preferable because it has excellent impact strength in a low temperature environment.

[0068] As a method of heat-sealing a top-sealing film to a foamed molded container, after the food is contained in the foamed molded container, the top-sealing film is covered so that the release layer side contacts the flange of the foamed molded container, the flat portion on the back surface of the flange is supported at the upper end of the bucket, and a hot plate is pressed from above the flange to obtain heat-sealing. In the present invention, when having the flange shape of the above-described shape pattern 1, it is preferable because the position between the upper end of the bucket and the flange is stable and problems such as displacement of the seal portion can be avoided.

[0069] Here, the seal width during heat-sealing is not particularly limited, but can be appropriately selected according to the size of the upper surface of the flange of the foamed molded container. In the case of shape pattern 1, it is preferably in the range of 3.5 to 20 mm, and in the case of shape pattern 2, it is preferably in the range of 4.5 to 25 mm.

[0070] The temperature conditions during heat-sealing can be appropriately selected from the range of 100 to 200 °C to obtain a desired seal strength. That is, in food packaging applications, where a desired seal strength is required according to the application, usually, as the seal temperature increases, the seal strength also increases. Therefore, within the above temperature range, the seal temperature can be set at the required seal strength. From the viewpoint of adjusting such seal strength, a top-sealing lid material having an agglomerating release layer is particularly preferable because it has excellent followability of the seal strength with respect to seal temperature changes and a high degree of design freedom.

[0071] Hereinafter, embodiments of the foamed molded container of the present invention will be described based on the drawings.

[0072] <Embodiment 1> This embodiment is represented by the container body 1 in FIG. 1, and is a foam molded body having a bottom portion 2 that is rectangular in plan view, a side wall portion 3 that extends upward from the outer peripheral edge of the bottom portion 2, a stepped portion 8 that continues from the side wall portion, a side wall portion that continues from the stepped portion 8, and a flange 4 that extends outward from the upper end thereof. Here, the center of the bottom portion 2 is formed with an upper bottom portion to enhance the thermal conductivity when heating with a microwave oven, and a bulging leg portion 7 that bulges downward from the periphery is formed along the periphery of the upper bottom portion.

[0073] FIG. 3 is a cross-sectional view taken along line A-A in FIG. 2, and the upper surface of the flange 4 is formed in a flat shape. By forming the upper surface of the flange in a flat shape in this way, the sealing strength with the top seal film is good.

[0074] FIG. 4 is an enlarged end face view of the portion surrounded by the dotted line in FIG. 3. The upper part of the flange has a flat portion, and at the portion where the flange is joined to the container side wall, there is a thick portion 5 that bulges outward and forms a curved surface on the outside. Further, it hangs downward further outward from the flat portion of the flange, and a thin portion 6 is formed at its edge. The back surface of the flange also has a horizontal portion parallel to the upper flat portion, and is joined to the thick portion 6. As shown in FIG. 4, the end face shape of the thick portion 6 is composed of an arc shape with a radius of curvature Re facing the content side from the flat portion of the back surface of the flange, an arc shape with a radius of curvature Rc facing the outside following this, and an arc shape with a radius of curvature Rf facing the content side following this.

[0075] Here, the shortest length between the flat portion of the upper part of the flange and the flat portion of the back surface of the flange is the flange thickness t1. Also, in this embodiment, it hangs downward in an arc shape with a radius of curvature Ra toward the content side from the flat portion of the upper part of the flange. This arc with a radius of curvature Ra continues from the contact point y with the upper plane of the flange to the contact point x with the straight line along the inner wall of the container, and the intermediate point of the arc shape is Rm. The length passing through the perpendicular of the tangent passing through Rm is the thickness t2 of the thick portion. Furthermore, on the back surface of the flange, it is connected to an arc shape in a cross-sectional view with a radius of curvature Rd from the outer edge end of the flat portion of the back surface.

[0076] In this embodiment, the flange thickness t1 is 1.5 mm, the thick part thickness t2 is 3.5 mm, the width F of the flat part at the upper part of the flange is 7.4 mm, the width L of the flat part on the back surface of the flange is 5.0 mm, the radius of curvature Ra is 3.5 mm, the radius of curvature Rb is 2 mm, the radius of curvature Re is 0.5 mm, the radius of curvature Rc is 2 mm, the radius of curvature Rf is 0.5 mm, and the radius of curvature Rd is 1 mm.

[0077] Further, the container body 1 is a foam of a mixed resin of polystyrene and polyphenylene ether, and on the inner surface of the foam, a polystyrene film is dry laminated to an unstretched polypropylene film (CPP), and the structure has a thermally laminated polystyrene film side.

[0078] <Embodiment 2> This embodiment is represented by the container body 1' in the plan view of FIG. 5, and is a foam-molded body having a bottom part 2' having a rectangular shape in plan view, a side wall part 3' extending upward from the outer peripheral edge of the bottom part 2', and a flange 4' extending outward from the upper end of the side wall part. Here, the center of the bottom part 2' forms a raised bottom, and a bulging leg part 7' bulging downward from the peripheral edge is formed along the peripheral edge of the raised bottom.

[0079] FIG. 6 is a cross-sectional view taken along line B-B in FIG. 5, and the upper surface of the flange 4' is formed in a flat shape. By forming the upper surface of the flange in a flat shape in this way, the sealing strength with the top seal film is good.

[0080] FIG. 7 is an enlarged end view of the portion surrounded by the dotted line in FIG. 6. The upper part of the flange has a flat part, and the part where the flange and the container side wall are joined has a thick part 5' bulging outward. Further, it hangs downward from the flat part of the flange toward the outside, and a thin part 6 is formed at the edge thereof. The back surface of the flange also has a horizontal part parallel to the upper flat part, and is joined to the thick part 6. As shown in Fig. 7, the end face shape of the thick part 6’ is composed of an arc shape facing the content side with a radius of curvature Rc’ from the flat part on the back of the flange. Here, the shortest length between the flat part at the upper part of the flange and the flat part on the back of the flange is the flange thickness t1. Also, in this embodiment, it hangs down toward the content side in an arc shape with a radius of curvature Ra’ from the flat part at the upper part of the flange. The length passing through the perpendicular of the tangent line at the midpoint of the arc shape with the radius of curvature Ra’ is the thickness t2 of the thick part. Furthermore, on the back of the flange, it is connected to an arc shape in cross-sectional view with a radius of curvature Rd’ from the outer edge end of the flat part on the back.

[0081] In this embodiment, the flange thickness t1 is 1.5 mm, the thick part thickness t2 is 3.5 mm, the width F of the flat part at the upper part of the flange is 11.4 mm, the width L of the flat part on the back of the flange is 5.0 mm, the radius of curvature Ra’ is 3.5 mm, the radius of curvature Rb’ is 2 mm, the radius of curvature Rc’ is 7 mm, and the radius of curvature Rd’ is 1 mm.

[0082] Also, the container body 1’ is a foam of a mixed resin of polystyrene and polyphenylene ether, and on the surface on the content side of the foam, a polystyrene film is dry laminated to an unstretched polypropylene film (CPP), and the side of the polystyrene film has a structure heat laminated.

Example

[0083] Example 1 A heat-resistant polystyrene-based resin foam sheet (basis weight 200 g / m 2 , primary thickness 1.95 mm) made of a mixture of GPPS, HIPS, and polyphenylene ether was dry laminated with a polystyrene film to an unstretched polypropylene film (CPP), and the side of the polystyrene film was heat laminated to obtain a multilayer sheet. Using a vacuum forming machine, it was formed into a container having the shape of Embodiment 1 (container size (including flange): 20 mm × 15 mm × 15 mm). After the obtained container was filled with 130 g of a food sample, “CMPS017C” manufactured by Mitsui Chemicals Toagosei Co., Ltd. (thickness: 30 μm) was laminated onto a PET film (thickness: 12 μm), and the “CMPS017C” was arranged so as to be in contact with the formed container, and heat sealing was performed at 120°C to obtain a food-containing container. Eight of these food-containing containers were packed in a cardboard box, and a drop test was conducted under the following conditions in accordance with JIS Z 0202:2017. <Free fall test> · The cardboard box was dropped from a height of 40 cm. · Number of drops: A total of 10 drops, including 1 drop from a corner, 3 drops from each edge, and 6 drops from each surface. · Ambient temperature: 1°C After the drop, when each container was visually inspected, there were no cracks or breaks in the flange, and no bags were torn. Also, the peeling operation of the top film, which is the lid, was easy.

Explanation of reference numerals

[0084] 1 ··· Container body 1’ ··· Container body 2 ··· Bottom 2’ ··· Bottom 3 ··· Side wall 3’ ··· Side wall 4 ··· Flange 4’ ··· Flange 5 ··· Thick part 5’ ··· Thick part 6 ··· Thin part 6’ ··· Thin part 7 ··· Bulging leg 7’ ··· Bulging leg 8 ··· Step 8’ ··· Step 9 ··· Lattice-shaped recess x ··· Contact point of a straight line and an arc y ··· Contact point of a straight line and an arc z ··· Contact point of a straight line and an arc Rm ··· Intermediate point of an arc Ra ··· Radius of curvature Rb ··· Radius of curvature Rc ··· Radius of curvature Ra’ ···Radius of curvature Rb’ ···Radius of curvature Rc’ ···Radius of curvature t1 ···Thickness of flange flat part t2 ···Thickness in the perpendicular direction at the midpoint of the cross-sectional arc on the connecting part surface d ···Depth of recess P ···Length between convex part centers α ···Width of recess

Claims

1. A foamed molded body for a top seal, having a bottom portion, a side wall portion extending upward from the outer edge of the bottom portion, and a flange extending outward from the upper end of the side wall portion via a connecting portion, wherein the upper surface of the flange has a flat portion, the connecting portion forms a curved surface on the surface side of the content, and the thickness in the perpendicular direction at the midpoint of the circular arc in cross-sectional view of the curved surface is larger than the flange thickness in the flat portion, and has a thick portion whose outer surface forms a curved surface. The foamed molded container for a top seal, wherein the shape of the thick portion is a circular arc shape in cross-sectional view bulging outward.

2. A foamed molded body for a top seal, having a bottom portion, a side wall portion extending upward from the outer edge of the bottom portion, and a flange extending outward from the upper end of the side wall portion via a connecting portion, wherein the upper surface of the flange has a flat portion, the connecting portion forms a curved surface on the surface side of the content, and the thickness in the perpendicular direction at the midpoint of the circular arc in cross-sectional view of the curved surface is larger than the flange thickness in the flat portion, and has a thick portion whose outer surface forms a curved surface. The shape of the thick portion is a circular arc shape in cross-sectional view whose outer surface is curved toward the content side of the flange, and the curvature Ra' on the content side surface of the flange root portion and the outer curvature Rc' of the flange root portion satisfy the following relationship Ra' < Rc' The foamed molded container for a top seal.

3. When the thickness of the flat portion is t1 and the thickness in the perpendicular direction at the midpoint of the circular arc in cross-sectional view of the curved surface is t2, t1 is 0.5 to 3 mm, and t2 / t1 is 1.5 to 3. The foamed molded container for a top seal according to Claim 1 or 2.

4. The width of the flat portion is 3 to 20 mm. The foamed molded container for a top seal according to Claim 1 or 2.

5. The foamed molded container for a top seal according to Claim 1 or 2, having a structure in which a styrene-based foamed substrate and a polyolefin-based film layer are laminated on the content side of the styrene-based foamed substrate.

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