Airtight container and sealing method

Abstract

The present invention provides a sealed container and a sealing method thereof, in which a lid material is heat-sealed to a container body having a flange portion, without causing the edges to peel, and which combines both excellent ease of opening and airtightness. [Solution] A sealed container comprising a container body having a flange portion and a lid material welded to the flange portion by heat sealing, wherein the container flange portion and the lid material are welded at the inner circumferential welding portion and the outer circumferential welding portion of the flange portion, the outer circumferential welding portion is an easily peelable welding portion formed by a distributed region consisting of a sealed portion and an unsealed portion, a resin mass is partially formed on the outer circumferential edge of the inner circumferential welding portion, and the outer circumferential edge of the inner circumferential welding portion and the inner circumferential edge of the outer circumferential welding portion are in close contact at least at the opening start portion.

Description

Technical Field

[0001] The present invention relates to a sealed container comprising a container having a flange portion and a lid material welded to the flange portion by heat sealing. More specifically, the present invention relates to a sealed container excellent in airtightness and easy opening property, and in which the turning up of the end portion of the lid material is effectively prevented, and a method for sealing the same.

Background Art

[0002] A sealed container formed by heat-sealing a flexible lid material to a flange portion is widely used for food and beverages, etc. as a container excellent in the preservation of contents due to its high airtightness. In such a sealed container, when opening the container, it is necessary to have an easy opening property that allows the lid material to be easily peeled off and removed, and an airtightness that is not impaired even when subjected to heat sterilization treatment such as retort sterilization, when the internal pressure increases, or when subjected to a dropping impact, etc. It is required to have contradictory performances of an easy opening property that allows easy start of opening from the outside of the container and a high airtightness that does not easily peel off from the inside of the container.

[0003] As such a sealed container, for example, in Patent Document 1 below, an easy-opening container is formed by heat-sealing a lid body provided with a heat-sealing layer on the inner surface, with the heat-sealing layer facing the peripheral edge portion of the opening of the container body. A sealing material is adhered to the upper surface of the peripheral edge portion of the opening so that an unadhered portion or a weakly adhered portion is formed on the inner side of the container, and the heat-sealing layer of the lid body and the sealing material are adhered with an adhesion strength weaker than the adhesion strength of the portion of the sealing material and the peripheral edge portion excluding the unadhered portion or the weakly adhered portion. An easy-opening container characterized by heat-sealing the lid body to the peripheral edge portion of the opening is described.

[0004] In addition, in a sealed container formed by heat-sealing a container and a lid, the opening property is improved by adjusting the pressing conditions during heat-sealing to form a resin pool made of a heat-sealing resin at the end portion of the heat-sealing portion (Patent Document 2, etc.).

Prior Art Documents

[0005] [Patent Document 1] Japanese Patent Publication No. 2006-160353 [Patent Document 2] Japanese Patent Publication No. 2021-066479 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, as described in Patent Document 1 above, if an unbonded or weakly bonded portion is provided on the outer edge of the flange portion, in the case of a lid material made of flexible film, peeling may occur from the outer edge of the lid material, causing the end of the lid material to break or curl, which may impair the appearance of the product or allow foreign matter to enter between the flange and the lid material. Furthermore, if such peeling occurs, there is a risk of unintended opening from a point other than the opening point, or opening by misidentifying the opening point, making it impossible to open properly. Furthermore, as described in Patent Document 2, if a resin deposit (resin lump) is formed at the end of the heat-sealed portion, the resin lump may detach from the heat-sealed portion when opened, potentially contaminating the contents as foreign matter.

[0007] Therefore, the object of the present invention is to provide a sealed container and a sealing method thereof in which a lid material, which is heat-sealed to a container body having a flange portion, does not peel off at the edges, possesses both excellent ease of opening and sealing properties, and in which the resin mass formed at the end of the heat-seal portion does not detach from the heat-seal portion when opened. [Means for solving the problem]

[0008] According to the present invention, a sealed container is provided comprising a container body having a flange portion and a lid material welded to the flange portion by heat sealing, wherein the container flange portion and the lid material are welded at an inner circumferential weld portion and an outer circumferential weld portion of the flange portion, the outer circumferential weld portion is an easily peelable weld portion formed by a distributed region consisting of a sealed portion and an unsealed portion, a resin mass is partially formed on the outer circumferential edge of the inner circumferential weld portion, and the outer circumferential edge of the inner circumferential weld portion and the inner circumferential edge of the outer circumferential weld portion are in close contact at least at the opening start portion.

[0009] In the sealed container of the present invention, (1) The distribution region is a distribution region in which unsealed portions are distributed within a continuous seal portion, or a distribution region in which sealed portions are distributed within a continuous unsealed portion. (2) A resin mass is partially formed on the inner edge of the inner circumferential welding portion. (3) At least the uppermost surface of the flange portion of the container body is made of an easily peelable, heat-sealable resin phase. This is preferable.

[0010] According to the present invention, a sealing method for a sealed container comprising a container body having a flange portion and a lid material, wherein the lid material is welded to the flange portion by an inner circumferential welding portion and an outer circumferential welding portion, is provided, wherein after placing the lid material on the flange portion, a first welding step is made to form an inner circumferential welding portion, and then a second welding step is made to form an outer circumferential welding portion, wherein in the first welding step, an inner circumferential welding portion is formed and a resin mass is formed at least on the outer side of the inner circumferential welding portion, and in the second welding step, an outer circumferential welding portion is formed by pressing with a heating tool capable of forming a welded portion formed by a distribution area consisting of a sealed portion and an unsealed portion, and a resin mass is partially formed on the outer side of the inner circumferential welding portion by crushing the resin mass outside the inner circumferential welding portion.

[0011] In the sealing method of the present invention, it is preferable that in the first welding step, a resin mass is also formed on the inner side of the inner circumferential welding portion, and in the second welding step, the outer circumferential welding portion is formed by pressing with the heating tool to a position further inward than the inner edge of the inner circumferential welding portion formed in the first welding step, and at the same time, a resin mass is partially formed on the inner side of the inner circumferential welding portion by crushing the resin mass on the inside of the inner circumferential welding portion. [Effects of the Invention]

[0012] In the sealed container of the present invention, the welded portion, which is the joint portion with the lid material formed on the upper surface of the container flange portion, is welded at two locations: an inner circumference welded portion and an outer circumference welded portion of the flange portion. As a result, airtightness is ensured at the inner circumference welded portion, and the outer circumference welded portion, which has a distributed area consisting of a sealed portion and an unsealed portion, effectively prevents the edges of the lid material from peeling, while also providing easy opening. Furthermore, the resin mass formed on the outer edge of the inner circumferential welding portion is crushed by the sealing portion of the outer circumferential welding portion, and remains continuous with the outer circumferential welding portion. This prevents the resin mass from detaching, and during opening, the peeling from the outer circumferential welding portion to the inner circumferential welding portion proceeds smoothly. Combined with the easy-open properties of the outer circumferential welding portion having the above-mentioned distribution area, this results in even better ease of opening. Furthermore, the formation of a resin mass on the inner edge of the inner circumferential weld increases the pressure resistance. If this resin mass is partially crushed during the second welding process, it becomes easier to release the internal pressure when it rises due to microwave heating, etc. Combined with the fact that the outer circumferential weld has an unsealed area, it becomes possible to slowly release the steam generated during microwave heating to the outside of the container.

[0013] Furthermore, according to the sealing method for sealed containers of the present invention, partial crushing of the resin mass can be performed simultaneously with the formation of the outer peripheral welding portion, making it possible to efficiently manufacture sealed containers that possess both the ease of opening and the airtightness described above. [Brief explanation of the drawing]

[0014] [Figure 1] This is a perspective view of an example of a sealed container of the present invention. [Figure 2] This diagram illustrates the welded portion in section X of the sealed container shown in Figure 1. [Figure 3] This is a schematic cross-sectional view showing the YY section in Figure 2. [Figure 4] This diagram illustrates an example of a heat seal head used for forming the inner circumferential welded portion. [Modes for carrying out the invention]

[0015] The sealed container of the present invention will be described with reference to the attached drawings. Figure 1 is a perspective view showing an example of a sealed container of the present invention, Figure 2 is a schematic diagram showing an enlarged view of the X portion of Figure 1, and Figure 3 is a schematic diagram showing an enlarged view of the YY cross-section of Figure 2. As is clear from Figure 1, the sealed container of the present invention consists of a container and a lid material 10, which are represented as a whole by 1. The container 1 consists of a bottom portion 2 and a side wall 3, and a flange portion 4 extending horizontally from the upper end of the side wall 3. At least the uppermost surface of the flange portion 4 has a heat-sealable heat-seal layer 5a that can be heat-sealed with the heat-seal layer of the lid material 10, which will be described later. In the specific example shown in Figure 3, at least an easily peelable heat-seal layer 5a and a base resin layer 5b are provided. As a result, when opening the sealed container, cohesive failure occurs in the easily peelable heat-seal layer 5a or interfacial delamination occurs between it and the base resin layer 5b, making it easy to open. The lid material 10 consists of a laminate having at least a heat-seal layer 11a on the side facing the flange portion of the container 1. In the specific example shown in the figure, the laminate constituting the lid material 10 has a two-layer structure with a flexible base film 11b, but is of course not limited to this.

[0016] In the sealed container of the present invention, as is clear from FIGS. 2 and 3, the welded portion of the flange portion 4 and the lid member 10 is composed of two welded portions: an inner peripheral side welded portion 20 located on the inner peripheral side of the flange portion 4 and an outer peripheral side welded portion 21 having an inner peripheral edge that coincides with the outer peripheral edge of the inner peripheral side weld 20. In addition to the inner peripheral side welded portion 20 for securely welding the lid member 10 to the container flange portion 4 to ensure the sealing performance of the sealed container, an outer peripheral side welded portion 21 is formed that welds to the vicinity of the outer peripheral edge of the flange portion 4 on the outer peripheral side of the inner peripheral side welded portion 20, thereby effectively preventing the curling of the lid member end portion. Since this outer peripheral side welded portion 21 is formed by a distribution region composed of a sealed portion 21a and an unsealed portion 21b, it is firmly welded compared to the case where the entire outer peripheral side welded portion 21 is welded as a sealed portion with a weak adhesive force. On the other hand, since it has an unsealed portion 21b, its adhesive force is weaker than that of the inner peripheral side welded portion 20, and it can effectively prevent the curling from the above-mentioned end portion without impairing the easy opening property. Further, even when the internal pressure rises due to microwave heating, the sealed portion 21a can easily peel off toward the outer peripheral end of the flange, making it possible to easily release the internal pressure.

[0017] Also, in the portion where the outer peripheral side welded portion 21 is not formed up to the outer peripheral edge of the flange portion 4, since the flange portion 4 and the lid member 10 are in a non-adhesive state, it is possible to easily grip only the lid member 10, which becomes the opening start portion 22. The opening start portion 22 may be a gripping portion that protrudes outward from the flange portion 4. In the present invention, it is important that the outer peripheral edge of the inner peripheral side welding portion 20 and the inner peripheral edge of the outer peripheral side welding portion 21 are in close contact with each other at least at the position of the unsealing start portion 22. As a result, as will be described later, when unsealing, the progress of peeling from the outer peripheral side welding portion 21 to the inner peripheral side welding portion 20 becomes easy, and easy unsealing property is ensured. Of course, by the outer peripheral edge of the inner peripheral side welding portion 20 and the inner peripheral edge of the outer peripheral side welding portion 21 being in close contact with each other at locations other than the unsealing start portion 22, the easy unsealing property is further improved. Further, a non-adhesive portion (space) may be formed between the inner peripheral edge of the outer peripheral side welding portion 21 and the outer peripheral edge of the inner peripheral side welding portion 20 at a position other than the unsealing start portion 22. By the formation of the non-adhesive portion (space), even when the vapor generated due to the increase in the internal pressure leaks from the inner peripheral side welding portion 20, this vapor is temporarily accommodated in the non-adhesive portion, and since the seal portion 21a of the outer peripheral side welding portion 21 can be easily peeled off to form an internal pressure release path, the rupture of the container can be effectively prevented.

[0018] In the sealed container of the present invention, the heat seal welding of the lid material 10 to the container flange portion 4 is such that the inner peripheral side welding portion 20 is a full-surface welding, the outer peripheral side welding portion 21 is a welding having a distribution region, and since they have welding portions of different patterns, it is desirable to form them in separate steps under different heat seal conditions. Generally, at the time of heat seal, since it is performed by pressing and heating with a heat seal head (not shown) from the lid material side with the lid material 10 placed on the flange 4, as shown in FIG. 3, the upper surface of the inner peripheral side welding portion 20 is recessed downward, and on the inner peripheral side end portion and the outer peripheral side end portion of the inner peripheral side welding portion 20, inner peripheral side resin masses 20a and outer peripheral side resin masses 20b of the resin that has flowed due to pressing are formed. In other words, the inner circumferential resin mass 20a has the container-side heat seal layer 5a and the lid-side heat seal layer 11a bonded together as one unit, so when the internal pressure rises, the lid material 10 moves in the vertical direction and cohesive failure of the easily peelable heat seal layer 5a is suppressed, thus improving pressure resistance. On the other hand, the outer circumferential resin mass 20b has the container-side heat seal layer 5a and the lid-side heat seal layer 11a bonded together as one unit, so when opened, the lid material 10 moves together in the flange direction and follows, so it is possible to promote cohesive failure of the easily peelable heat seal layer 5a, improving ease of opening. In particular, in the present invention, as will be described later, the outer resin mass 20b of the inner circumferential welding portion 20 is crushed and partially present, and there is a portion where the outer edge of the inner circumferential welding portion 20 and the inner edge of the outer circumferential welding portion 21 are integrated, which further improves ease of opening.

[0019] In the sealed container of the present invention, the outer peripheral welded portion 21 forms a distributed region having a sealed portion 21a and an unsealed portion 21b. Since the outer peripheral welded portion 21 has an unsealed portion 21b, the sealing force is reduced, and the sealing force of the entire welded portion is weaker than that of the inner peripheral welded portion 20, and as mentioned above, ease of opening is not impaired. Furthermore, since the sealed portion 21a of the outer peripheral welded portion 21 does not have a weak adhesive force as in the conventional technology, by forming the sealed portion 21a to the edge of the flange portion 4, it is possible to effectively prevent the lid material 10 from peeling off from the edge. Furthermore, in the pattern shown in Figure 2, if the unsealed portion 21b forms a continuous phase and the sealed portion 21a is formed within this continuous phase, an internal pressure release path is formed in the outer peripheral welded portion 21, allowing for easy release of internal pressure. In addition to the patterns shown in the figure, if, for example, the sealed portion 21a forms a continuous phase and the unsealed portion 21b is formed within this continuous phase, when the internal pressure rises and pressure is applied to the boundary portion of the outer peripheral welded portion 21, the pressure is transmitted to the unsealed portion 21b, and an internal pressure release path is easily formed in the outer peripheral welded portion 21. As a result, the steam generated inside the container can be slowly released from the flange edge, effectively preventing the container from rupturing.

[0020] In the present invention, during heat sealing to form the outer peripheral welded portion 21, the outer peripheral resin mass 20b of the previously formed inner peripheral welded portion 20 is partially crushed by a knurling tool having an uneven surface used for heat sealing the outer peripheral welded portion 21. As a result, the inner peripheral welded portion 20 and the outer peripheral welded portion 21 are partially continuous at the crushed locations, while the outer peripheral resin mass 20b of the inner peripheral welded portion 20 remains partially present. This makes it possible to quickly separate the inner peripheral welded portion 20 from the outer peripheral welded portion 21 at the locations where the inner peripheral welded portion 20 and the outer peripheral welded portion 21 are continuous, thus facilitating opening. Furthermore, the partially formed resin lumps (corresponding to the unsealed areas and remaining uncrushed) are sandwiched between the continuous welded sections, preventing them from falling off during opening and effectively preventing them from becoming foreign objects in the container.

[0021] In the sealed container of the present invention, as described above, it is preferable for a resin mass to be formed on the inner side of the inner circumferential welding portion to improve the pressure resistance of the container. However, from the viewpoint of preventing the resin mass from falling out when the container is opened, it is preferable for the inner circumferential resin mass to be crushed in the same way as the outer circumferential resin mass. In this case, by welding almost the entire surface of the flange portion with a knurling tool used to form the outer circumferential welding portion, it is possible to partially crush the inner circumferential resin mass of the inner circumferential welding portion as well. As mentioned above, this also effectively prevents the resin chunks from falling off when the container is opened and from becoming mixed into the container as foreign matter.

[0022] In the sealed container of the present invention, the inner and outer circumferential welded portions formed on the flange portion are preferably in the range of 5-40% and 10-95% of the flange portion, respectively, when the opening shape of the container is rectangular, based on the width of the flange portion excluding the corners. This makes it possible to obtain both reliable sealing (pressure resistance) and easy opening performance for the sealed container. There are no particular restrictions on the widths of the inner circumferential welded portion, the non-adhesive portion, and the outer circumferential welded portion. However, in order to allow steam to escape slowly from the container, it is preferable that the width of the outer circumferential welded portion be larger than that of the inner circumferential welded portion, and that the width of the non-adhesive portion be larger than that of the inner circumferential welded portion. There are no particular restrictions on the relationship between the width of the outer circumferential welded portion and the width of the non-adhesive portion. Preferably, at the corners of the flange, the width of the outer circumferential welded portion is larger than that of the non-adhesive portion. This configuration effectively prevents the rupture of the sealed container even if internal pressure is locally concentrated at the corners due to deformation of the container.

[0023] Furthermore, the inner and outer resin lumps formed in the inner circumferential welding portion mentioned above can be formed by pressing a heat seal head from above onto the area that will become the inner circumferential welding portion. However, by using a heat seal head 30 with a curved inner circumferential corner portion 31 and a pressing surface 32 that slopes upward toward the outer circumference, as shown in Figure 4, it becomes possible to form an inner circumferential resin lump that is larger than the outer resin lump. The formation of a larger resin lump on the inner circumferential side makes the heat seal layer less susceptible to cohesive failure, thus improving pressure resistance, while the formation of a smaller resin lump on the outer circumference improves ease of opening. Preferably, the height of the smaller resin lump on the outer circumference is 100 μm or more.

[0024] In the specific example shown in the figure, the sealed and unsealed portions formed in the outer circumferential welded portion had a knurled pattern in which the unsealed portion was a continuous phase and the sealed portion was a dispersed phase. However, this is not limited to this as long as the pattern can partially crush the resin mass of the inner circumferential welded portion. As mentioned above, the sealed portion may be a continuous phase and the unsealed portion a dispersed phase, or various distribution areas can be formed, such as a pattern in which the sealed and unsealed portions are formed alternately radially, or a checkerboard pattern. The area ratio of the sealed portion to the unsealed portion in the outer peripheral welded portion varies depending on the seal strength of the outer peripheral welded portion and cannot be specified in general terms. However, it is preferable that the area ratio of the sealed portion to the outer peripheral welded portion (seal area ratio) is in the range of 0.5 to 95%, and particularly 1 to 50%.

[0025] In the sealed container of the present invention, it is preferable that the seal strength of the inner circumferential welded portion is in the range of 5 to 40 N / 15 mm, and the seal strength of the outer circumferential welded portion is in the range of 2 to 30 N / 15 mm. This makes it possible to achieve both airtightness (pressure resistance) and ease of opening of the sealed container.

[0026] (container) In the sealed container of the present invention, the container is a flanged container in which a flange is formed around the entire circumference of the opening, and its shape is not limited to that of a tray with a rectangular opening as shown in the figure, but can also be a cup with a circular opening or various other shapes of containers. Furthermore, the method of molding the container is not particularly limited. While a flanged container can be easily integrally molded by thermoforming such as plug-assisted pressure forming using a resin sheet, the method is not limited to this. Conventional known flanged containers, such as a cup-shaped container with a flange attached separately, can also be used. Furthermore, while there are no material limitations for the container as long as a heat-seal layer is formed on at least the uppermost surface of the flange, it is preferable that the container be made of a laminate comprising a heat-seal layer, a base resin layer, a gas barrier layer, and an oxygen-absorbing layer, in order to particularly improve the preservation of the contents.

[0027] The base resin layer can be made from resins that have been conventionally used as packaging materials, such as olefin resins and polyester resins. Examples include, but are not limited to, polyethylenes such as low-density polyethylene (LDPE), medium-density polyethylene (MDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LLDPE), and linear ultra-low-density polyethylene (LVLDPE); olefin resins such as polypropylene, ethylene-propylene copolymer, polybutene-1, ethylene-butene-1 copolymer, propylene-butene-1 copolymer, ethylene-propylene-butene-1 copolymer, ethylene-vinyl acetate copolymer, and ion-crosslinked olefin copolymer (ionomer); and polyester resins such as polyethylene terephthalate and polybutylene terephthalate. In particular, since it is desirable to have heat resistance that can withstand heat and pressure sterilization treatments such as retort sterilization, polypropylene and polyethylene terephthalate can be suitably used.

[0028] The gas barrier layer can be made of a conventionally known gas barrier resin. Suitable gas barrier resins include ethylene vinyl alcohol copolymer (EVOH) and polyamide resins. Examples of polyamide resins include xylylene group-containing polyamides such as nylon 6, nylon 6,6, nylon 6 / 6,6 copolymer, nylon 6,10, nylon 11, nylon 12, nylon 13, metaxylylene adipamide, and metaxylylene sevacamide, with ethylene vinyl alcohol copolymer being particularly suitable.

[0029] The oxygen-absorbing layer is preferably made of a conventionally known oxygen-absorbing resin composition in which an iron-based oxygen absorbent containing reduced iron is contained in the base resin. The iron-based oxygen absorbent can be one that is known on its own, and one containing reduced iron and metal halides is preferably used. When an iron-based oxygen absorbent is used as the oxygen absorbent layer, it is preferable that the base resin layer contains a white pigment to conceal it.

[0030] The heat seal layer can use any conventionally known heat sealable resin without limitation, as long as it can be heat-sealed with the heat seal layer of the lid material described later. However, as mentioned above, it is preferable that the heat seal layer itself has easy peelability, so a blend made by appropriately combining two or more heat-sealable but mismatched thermoplastic resins can be suitably used. For example, when the base resin layer is made of a propylene polymer, the heat seal layer can be made of a blend of an ethylene polymer and a propylene polymer to ensure airtightness while maintaining easy opening, and the peel strength can be adjusted by appropriately changing the blending ratio of the blended materials.

[0031] Examples of the above-mentioned propylene-based polymers include homopolypropylene, as well as block copolymers and random copolymers of propylene with ethylene or other α-olefins, such as 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene. Examples of the above-mentioned ethylene-based polymers include homopolymers of ethylene such as low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and medium- and high-density polyethylene (MDPE, HDPE), or copolymers of ethylene with other α-olefins such as 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, and 1-octene, or vinyl monomers such as (meth)acrylic acid, ethyl (meth)acrylate, methyl (meth)acrylate, vinyl acetate, and styrene, or ionomers. In addition to combinations of the olefin polymers mentioned above, blends can also be made using thermoplastic polyester resins such as polyethylene terephthalate, polybutylene terephthalate, and copolymers thereof modified with isophthalates, as well as combinations of polycarbonate resins, polyacrylonitrile resins, etc., with the olefin polymers mentioned above.

[0032] To facilitate the layer structure, it is preferable that the heat seal layer itself has easy peelability, but it is not limited to this. Even if the heat seal layer does not have easy peelability, if an easily peelable resin layer capable of exhibiting easy peelability is further formed between the heat seal layer and the base resin layer, the same effects as when the heat seal layer has easy peelability can be achieved.

[0033] (lid material) The lid material can be of any form as long as it is heat-sealed to the container flange. In addition to the sheet-like lid material shown in the figure, conventionally known lid materials such as molded lids with a flange can be used. However, in the sealed container of the present invention, the presence of a welded portion on the outer circumference effectively prevents the edges of the lid material from peeling, so a flexible sheet-like lid material is preferably used as the lid material. The lid material can be made from conventionally known sheets, as long as it has a heat-seal layer on the portion facing the container flange, and can consist of a single layer of heat-sealable resin. However, similar to the container, it is preferable to include a barrier layer or the like from the viewpoint of improving the preservation of the contents. Examples of such a barrier layer include a layer made of the gas barrier resin mentioned above, or a metal foil such as aluminum foil or a vapor-deposited layer.

[0034] (Sealing method) As described above, in the sealing method for the sealed container of the present invention, the welding pattern and seal strength differ between the inner circumferential welding portion and the outer circumferential welding portion, so it is preferable to perform these in separate processes. That is, the sealing method of the present invention has a first welding step of forming the inner circumferential welding portion, followed by a second welding step of forming the outer circumferential welding portion. In the first welding step, an inner circumferential welded portion is formed by heat sealing, and a resin mass is formed at least on the outer circumference side of the inner circumferential welded portion, preferably on both the outer and inner circumference sides. Next, in the second welding step, an outer circumferential welded portion is formed by pressing with a heating tool capable of forming a welded portion formed by a distributed region consisting of a sealed portion and an unsealed portion, and the pressure is applied to at least the outer circumference mass portion of the inner circumferential welded portion, preferably the inner circumferential resin mass portion of the inner circumferential welded portion. As a result, the resin mass pressed on the pressing surface of the heat seal head, where the seal portion is formed, is crushed, leaving areas without resin mass, while resin mass remains in the areas that form the unsealed portion.

[0035] The sealing conditions cannot be defined in general terms, as they depend on the materials of the container and lid used, as well as the thickness and width of the heat seal layer. However, when ethylene propylene copolymer is used as the heat seal layer on the container side and a propylene polymer is used as the heat seal layer on the lid side, the sealing conditions for the inner circumferential weld are preferably 160-240°C with pressure heating for 0.8-3.0 seconds. For the outer circumferential weld, in the knurling pattern shown in Figure 2, the knurling is preferably performed at a peak temperature of 160-240°C for 0.8-3.0 seconds. [Examples]

[0036] (Containers and lids) A multilayer sheet (base resin layer: 470 μm, heat seal layer: 30 μm) was formed by co-extruding polypropylene as the base resin layer and ethylene propylene copolymer as the heat seal layer. A container (flanged tray) of the following dimensions was then formed using a vacuum pressure forming machine with plug assist. Flange outer diameter: Long axis 153mm x Short axis 121mm Caliber: Long axis 137mm x Short axis 105mm Bottom outer diameter: Long axis 90mm x Short axis 57mm Height: 33mm As the lid material, a barrier film (87 μm thick) made by dry laminating silica vapor-deposited film and unoriented polypropylene film was used.

[0037] (Example 1) After filling the above container with water, a lid material was placed and fixed to the flange portion, and heat sealing was performed at 200°C for 1.0 second using the heat sealing head shown in Figure 4 so that the width of the inner circumferential weld portion was 2 mm, forming a resin mass with a height of 100 μm on the outer edge of the inner circumferential weld portion. Then, the inner edge of the outer circumferential weld portion was aligned with the outer edge of the inner circumferential weld portion at the opening start point, and a non-adhesive portion was formed between the inner edge of the outer circumferential weld portion and the outer edge of the inner circumferential weld portion outside the opening start point. A knurling tool with an outer seal area ratio of 4% was used to heat seal at 200°C for 1.0 second to create a sealed container.

[0038] (Comparative Example 1) A sealed container was prepared in the same manner as in Example 1, except that the width of the outer-circumferential welded portion was set to 2 mm from the flange edge so that a non-adhesive portion is formed between the inner edge of the outer-circumferential welded portion and the outer edge of the inner-circumferential welded portion at the opening start point.

[0039] (Comparative Example 2) A sealed container was prepared in the same manner as in Example 1, except that a welded portion was not formed on the outer circumference.

[0040] (Example 2) A sealed container was created in the same manner as in Example 1, except that a gripping portion extending outward from the flange portion was formed on the lid material, and the outer circumferential welding portion was heat-sealed at a temperature of 200°C for 1.0 second using a known heat-sealing bar to completely weld the entire surface (100% of the sealed area).

[0041] (Examples 3 and 4) The sealed container obtained in Example 1 was heated in a microwave oven. The container from which steam escaped from the area where the non-adhesive part was formed was designated as Example 3, and the container from which steam escaped from the outer edge of the inner circumferential welded part or from an area where there was no resin mass on the outer edge was designated as Example 4.

[0042] (Evaluation of sealing performance) The resulting sealed containers were evaluated for leakage using the JIS Z 0238 drop strength test. The results are shown in Table 1. ○: Items that were not leaked. ×: Items that were missing

[0043] (Evaluation of ease of opening) The resulting sealed containers were opened by lifting the lid from the opening point, and their ease of opening was evaluated. The results are shown in Table 1. ◎: Easy to open ○: Easy to open △: Somewhat difficult to open ×: Difficult to open

[0044] (Evaluation of lid material curl suppression) The edges of the lid material of the obtained sealed containers were visually evaluated. The results are shown in Table 1. ◎: Best ○: Good △: Partially curled ×: Curly

[0045] [Table 1] [Explanation of symbols]

[0046] 1 container, 2 bottom, 3 side wall, 4 flange, 5a heat seal layer, 5b base resin layer, 10 lid material, 11a heat seal layer, 11b base film, 20 inner circumference welded part, 20a inner circumference resin mass, 20b outer circumference resin mass, 21 outer circumference welded part, 21a sealed part, 21b unsealed part, 22 opening start part.

Claims

1. In a sealed container comprising a container body having a flange portion and a lid material that is heat-sealed to the flange portion, The container flange and the lid material are welded together at the inner and outer circumferential welding portions of the flange. The outer peripheral welded portion is an easily peelable welded portion formed by a distributed region consisting of a sealed portion and an unsealed portion. A resin mass is partially formed on the outer edge of the inner circumferential welding portion. A sealed container characterized in that the outer edge of the inner circumferential welded portion and the inner circumferential edge of the outer circumferential welded portion are in close contact, at least at the opening start portion.

2. The sealed container according to claim 1, wherein the distribution region is a distribution region in which unsealed portions are distributed within a continuous sealed portion, or a distribution region in which sealed portions are distributed within a continuous unsealed portion.

3. The sealed container according to claim 1 or 2, wherein a resin mass is partially formed on the inner edge of the inner circumferential welding portion.

4. The sealed container according to claim 1 or 2, wherein at least the uppermost surface of the flange portion of the container body is made of an easily peelable heat-sealable resin layer.

5. In a method for sealing a sealed container, the container consists of a container body having a flange portion and a lid material, wherein the lid material is welded to the flange portion at an inner circumferential welding portion and an outer circumferential welding portion, After placing the cover material on the flange portion, the welding process includes a first welding step to form the inner circumferential welding portion, followed by a second welding step to form the outer circumferential welding portion. In the first welding process, an inner circumferential welding portion is formed, and a resin mass is formed at least on the outer side of the inner circumferential welding portion. In the second welding step, a sealing method characterized by forming an outer peripheral welded portion by pressing with a heating tool capable of forming a welded portion formed by a distribution area consisting of a sealed portion and an unsealed portion, and partially forming a resin mass on the outer peripheral side of the inner peripheral welded portion by crushing the resin mass outside the inner peripheral welded portion.

6. The sealing method according to claim 5, wherein in the first welding step, a resin mass is also formed on the inner side of the inner circumferential welding portion, and in the second welding step, the heating tool is pressed to a position inward from the inner edge of the inner circumferential welding portion formed in the first welding step, thereby forming an outer circumferential welding portion and crushing the resin mass inside the inner circumferential welding portion, thereby partially forming a resin mass on the inner side of the inner circumferential welding portion.

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