Manufacturing method for packaging containers for frozen foods

Abstract

The present invention provides a manufacturing method for a frozen food packaging container in which both airtight sealability and ease of opening a lid member are achieved. This manufacturing method for a frozen food packaging container including a container and a lid member comprises a sealing step in which the container and the lid member are joined by heating. At the sealing step, heat-sealing is performed multiple times at predetermined positions in the same pattern using a heater having the same pattern shape over the entire periphery of the outer edge portion of the container, whereby the container and the lid member are joined by heating.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a packaging container for frozen foods having a container and a lid material, and particularly to a method for manufacturing a packaging container for frozen foods that achieves both airtightness and easy opening of the lid material.

Background Art

[0002] Currently, a packaging container having a container for storing various foods or beverages, etc. and a lid material for sealing the container so as to block outside air is used. The container is made of plastic or the like and has various shapes such as a cup shape or a tray shape. For example, after storing food or the like in the container, the packaging container is sealed by covering the container with a lid material and heat-sealing the container and the lid material. Various methods for manufacturing the packaging container have been proposed.

[0003] The sealing method of the container in Patent Document 1 is a sealing method of a container in which a lid material is heat-bonded and sealed to an annular flange portion of the container body. The step of heat-bonding and sealing the flange portion and the lid material is composed of a sealing step in which at least two sealing portions overlap by a sealing head having an annular convex portion. On the other hand, at least one of these at least two sealing steps is composed of a sealing step by a sealing head having concavo-convex portions on the inner and outer peripheral edges of the annular convex portion. In Patent Document 1, in order to facilitate opening of the lid material, a portion where no heat-sealing is performed at all is formed at the corner portion of the outer peripheral edge portion of the flange portion, and opening can be started from this portion.

[0004] Patent Document 2 describes a partial lid double-sealing method in which when heat-sealing a lid to the upper end surface of the mouth edge portion of a formed container, the lid is placed on the upper end surface, and the entire circumference of the outer peripheral edge of the lid is heat-sealed at a relatively low temperature from the upper surface of the lid along the upper end surface portion, and then a part of the outer peripheral edge of the lid is heat-sealed again at a temperature higher than the temperature at the time of the first heat-sealing.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Patent No. 4135334 [Patent Document 2] Special Publication No. 7-098530 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] As packaging containers, high airtightness is required to enhance the preservation of contents by preventing the lid from peeling off and the contents from leaking out during distribution, storage, and sales processes. On the other hand, for convenience when removing the stored food or other items, the lid must be easily peeled off. If the contents of the packaging are frozen food, the frozen food is placed in the container in a low-temperature environment of -18°C or below, the lid and container are sealed, and then the container is stored again in a low-temperature environment of -18°C or below. Furthermore, the low-temperature environment is maintained during the distribution process, and each packaging container is heated in a microwave oven. Thus, in the case of frozen foods, the temperature change is significant because the food is heated using a microwave oven from a low temperature of -18°C or below. Packaging containers for frozen foods are required to be airtight and able to withstand low temperatures and large temperature changes.

[0007] However, as mentioned above, in Patent Document 1, in order to facilitate the opening of the lid, a portion that is not heat-sealed at all is formed at the corner of the outer edge of the flange portion, allowing the lid to be opened from this portion. As a result, there is a risk that the sealing performance may not be sufficient at low temperatures or when there are large temperature changes. Furthermore, Patent Document 2 partially seals twice, with some parts being sealed only once. With a single seal, there is a risk that foreign matter may enter the sealed area, or that air bubbles may form in the sealed area, resulting in insufficient airtightness at low temperatures and during large temperature changes. Thus, currently, there are no packaging containers for frozen foods that achieve both airtightness and ease of opening the lid.

[0008] The object of the present invention is to provide a method for manufacturing a packaging container for frozen foods that achieves both airtightness and ease of opening of the lid. [Means for solving the problem]

[0009] To achieve the above objective, one aspect of the present invention provides a method for manufacturing a frozen food packaging container having a container and a lid, comprising a sealing step for heat-joining the container and the lid, wherein the sealing step involves performing heat sealing multiple times at predetermined positions with the same pattern using a heater with the same pattern shape around the entire circumference of the outer edge of the container, thereby heat-joining the container and the lid.

[0010] The container has an opening, and a flange portion that protrudes along the outer edge of the opening to the opposite side of the opening. The sealing process preferably involves heat-bonding the lid material to the flange portion of the container. The sealing process preferably involves two heat bonding steps. It is preferable that a continuous linear seal portion is formed around the entire circumference of the outer edge of the container during the sealing process. The sealing process uses a heater, which has a curved surface that contacts the lid material, and preferably the radius of the curved surface is smaller than the width of the sealed portion formed in the sealing process. The sealing portion preferably has a projection that protrudes outward at its outer edge. It is preferable that the surface layer of the container is made of a polyolefin resin film with a thickness of 200 to 1000 μm. The lid material has a sealant layer on the container side, and it is preferable that the sealant layer is made of a polyethylene film with a thickness of 10 to 50 μm. In the sealing process, it is preferable that the seal strength after multiple heat seals is lower than the seal strength after the initial heat seal. [Effects of the Invention]

[0011] According to the present invention, a packaging container for frozen foods is obtained that achieves both airtightness and ease of opening of the lid.

Brief Description of the Drawings

[0012] [Figure 1] It is a graph for explaining the unsealing property of the lid material of the packaging container for frozen foods of the present invention. [Figure 2] It is a graph showing the seal strength indicating the sealing property at each position of the packaging container for frozen foods of the present invention. [Figure 3] It is a schematic diagram showing the positions where the seal strength indicating the sealing property of the packaging container for frozen foods of the present invention was measured. [Figure 4] It is a schematic perspective view showing an example of a method for manufacturing a packaging container for frozen foods according to an embodiment of the present invention. [Figure 5] It is a schematic perspective view showing an example of a packaging container for frozen foods according to an embodiment of the present invention. [Figure 6] It is a schematic diagram showing a partial enlargement of an example of a seal portion of a packaging container for frozen foods according to an embodiment of the present invention. [Figure 7] It is a schematic diagram for explaining an example of a method for manufacturing a packaging container for frozen foods according to an embodiment of the present invention. [Figure 8] It is a schematic enlarged view for explaining an example of a method for manufacturing a packaging container for frozen foods according to an embodiment of the present invention. [Figure 9] It is a schematic perspective view showing another example of the container of a packaging container for frozen foods according to an embodiment of the present invention. [Figure 10] It is a graph showing the seal strength indicating the sealing property at each position of the packaging container for frozen foods of Example 1.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, based on the preferred embodiments shown in the accompanying drawings, the method for manufacturing a packaging container for frozen foods of the present invention will be described in detail. Hereinafter, an example of the method for manufacturing a packaging container for frozen foods of the present invention will be described. However, the drawings described below are illustrative for explaining the present invention, and the present invention is not limited to the drawings shown below.

[0014] As mentioned above, there is a need for packaging containers for frozen foods that achieve both airtightness and ease of opening the lid. We investigated the ease of opening the lid of a frozen food packaging container manufactured by heat-sealing the container and lid together, specifically whether the lid can be opened with minimal force. Specifically, we evaluated the ease of opening the lid when heat-sealing was performed once and when heat-sealing was performed twice. Note that heat-sealing twice means performing heat-sealing twice in the same pattern and at the same position (a predetermined position). Here, Figure 1 is a graph illustrating the ease of opening the lid material of the frozen food packaging container of the present invention. As shown in Figure 1, with a single heat seal (see symbol α), the seal strength increases as the heat seal bar temperature rises up to 190°C. On the other hand, with two heat seals (see symbol β), the seal strength becomes approximately constant at temperatures of 160°C or higher. The seal strength refers to the seal strength at the outwardly protruding portion 11a (see Figure 3), which will be described later. Thus, we found that by performing multiple heat sealing cycles during heat bonding, the seal strength does not increase above a certain temperature. In other words, by performing multiple heat sealing cycles, we found that the force required to open the lid can be reduced even if the heat sealing bar temperature is high. The seal bar temperature refers to the set temperature during heat sealing.

[0015] In the measurement of seal strength shown in Figure 1, a polypropylene container was used. The container dimensions were 151 mm × 205.5 mm × 42.0 mm (height), and the thickness was 575 μm. A laminated film of nylon / nylon / polyethylene / sealant layer was used as the lid material. The material of the sealant layer was polyethylene, the thickness of the sealant layer was 30 μm, and the total thickness of the lid material including the sealant layer was 85 μm. A heater with a width of 5 mm and a tip radius of 4 mm was used for heat sealing. The sealing time was set to 0.9 seconds. The pressure applied by the sealing bar during heat sealing was set to 250 kgf (2.45 kN). The second heat sealing was performed before the temperature of the container and lid material returned to room temperature after the first heat sealing. The seal strength indicating ease of opening is the strength required to peel the lid material from the outside of the container, and was measured in accordance with JIS S0021-2:2018 (Packaging - Accessible design - Ease of opening).

[0016] This study investigated the airtightness of frozen food packaging containers manufactured by heat-sealing a container and a lid. Specifically, it examined the force required to separate the lid from the container from the inside. The seal strength at various points on the frozen food packaging container was evaluated for both single-heat sealing and double-heat sealing. Figure 2 is a graph showing the seal strength at various positions of the frozen food packaging container of the present invention, and Figure 3 is a schematic diagram showing the positions where the seal strength of the frozen food packaging container of the present invention was measured. As shown in Figure 2, it has been found that at positions A to D of the frozen food packaging container, the seal bar temperature is 160°C or higher, and the seal strength, which indicates the airtightness of the container, becomes approximately constant. Moreover, the seal strength is sufficient to maintain the airtightness of the container. This ensures the shelf life of the frozen food stored inside the container. In this way, by performing multiple heat sealing steps during the heat bonding process, it is possible to achieve both airtightness and ease of opening of the lid material in packaging containers for frozen foods.

[0017] Figure 3 shows the seal portion 11. The seal portion 11 is a continuous, straight line formed by heat bonding. As shown in Figure 3, the frozen food packaging container 10 is rectangular in plan view. Position A is the long side portion 10a of the frozen food packaging container 10, and position B is the short side portion 10b of the frozen food packaging container 10. Position C is the corner portion 10c of the frozen food packaging container 10. Position D is the corner portion 10d diagonally opposite position C of the frozen food packaging container 10, and the seal portion 11 has a protruding portion 11a that extends outward. The seal strength, which indicates airtightness, is the strength required to peel the lid material from the inside of the container at each position A to D, and was measured according to JIS Z 0238:1998. The following provides a detailed explanation of packaging containers for frozen foods and methods for manufacturing these packaging containers.

[0018] (Frozen food packaging containers) Figure 4 is a schematic perspective view showing an example of a method for manufacturing a frozen food packaging container according to an embodiment of the present invention, and Figure 5 is a schematic perspective view showing an example of a frozen food packaging container according to an embodiment of the present invention. Figure 6 is a schematic diagram showing an enlarged portion of an example of the sealing part of a frozen food packaging container according to an embodiment of the present invention. In Figures 4 to 6, the same components shown in Figure 3 are denoted by the same reference numerals, and their detailed descriptions are omitted. The frozen food packaging container 10 shown in Figure 4 has a container 12 and a lid material 14. The container 12 has a bottom surface 20b and a side surface 20c that is continuously provided around the periphery of the bottom surface 20b. The side surface 20c forms an opening 20a opposite the bottom surface 20b. For example, the side surface 20c is made up of a slope. The side surface 20c extends from the bottom surface 20b toward the opening 20a, and the area of ​​the opening 20a is larger than that of the bottom surface 20b. Note that the side surface 20c is not limited to being made up of a slope, but may be made up of a surface perpendicular to the bottom surface 20b. The container body 20 is made up of the bottom surface 20b and the side surface 20c. The space made up of the bottom surface 20b and the side surface 20c is the storage section 20e. That is, the internal space of the container body 20 is the storage section 20e.

[0019] The container 12 has an opening 20a and a flange portion 22 that extends along the outer edge of the opening 20a and protrudes on the opposite side of the opening 20a. The container body 20 and the flange portion 22 are integral. The flange portion 22 is, for example, flat, and its surface 22a is planar. A lid material 14 is joined to the flange portion 22. The outer edge of the opening 20a of the container 12 is the same as the outer edge portion 20d of the container 12. The contents 16 are stored in the storage compartment 20e of the container 12. The contents 16 are frozen food. Preferably, the frozen food is one that can be heated in a microwave oven along with the frozen food packaging container 10. The frozen food may remain solid after heating, become liquid, or be a mixture of solid and liquid. The frozen food is not particularly limited and examples include noodles such as udon, soba, and pasta, hamburgers, shumai, or soup. Furthermore, the frozen food may be packaged individually, or, for example, only the side dishes may be packaged, or multiple meals may be packaged together.

[0020] The lid material 14 seals the opening 20a of the container 12, blocking the inside of the container 12 from the outside air and sealing the container 12. The lid material 14 is made of, for example, a film-like material. The packaging container 10 for frozen foods may, for example, have its lid 14 opened to a predetermined position to form a steam release vent in order to release steam generated by heating when the frozen food is heated in a microwave oven.

[0021] (Method of manufacturing packaging containers for frozen foods) The manufacturing method for a frozen food packaging container involves storing the contents 16 in the storage section 20e of the container 12 through the opening 20a of the container 12. Next, the lid material 14 is positioned and placed over the flange portion 22 from above the opening 20a of the container 12. The surface 22a of the flange portion 22 and the back surface 14b of the cover material 14 are in contact. Next, a sealing process is performed to heat-bond the container 12 and the lid material 14.

[0022] The sealing process involves performing heat sealing multiple times at predetermined positions along the entire circumference of the outer edge 20d of the container 12, thereby heat-joining the container 12 and the lid material 14. This makes it possible to obtain a frozen food packaging container that achieves both airtightness and ease of opening of the lid material. Performing multiple heat seals at predetermined locations means using a heater with the same pattern shape to perform heat sealing at the same location (predetermined location) with the same pattern each time, and that the seal marks formed by each heat seal are identical. "Identical seal marks" includes positional errors during the heat sealing process and does not necessarily mean that the seal marks are perfectly identical. As shown in Figure 5, the sealing process forms a continuous linear sealing portion 11 around the entire circumference of the outer edge 20d of the container 12. In the sealing process, for example, the lid material 14 is heat-bonded to the flat surface 22a of the flange portion 22.

[0023] The sealing portion 11 preferably has a protrusion 11a that extends outward from the container 12, as shown in Figure 6. By providing the protrusion 11a, the force required to open the lid 14 is more easily applied to the tip of the protrusion 11a when opening the container. As a result, the lid 14 can be opened with less force. Even when the protrusion 11a is provided, the airtightness of the lid 14 is maintained. The protruding portion 11a is not particularly limited as long as it protrudes outward from the container 12. For example, the protruding portion 11a can be V-shaped, U-shaped, or W-shaped, protruding outward from the container 12.

[0024] <Sealing process> As described above, heat sealing is used in the sealing process. Known methods can be used for heat sealing. For example, a heater can be used for heat sealing. Here, Figure 7 is a schematic diagram illustrating an example of a method for manufacturing a frozen food packaging container according to an embodiment of the present invention, and Figure 8 is a schematic enlarged view illustrating an example of a method for manufacturing a frozen food packaging container according to an embodiment of the present invention. In Figures 7 and 8, the same components shown in Figures 4 to 6 are denoted by the same reference numerals, and their detailed descriptions are omitted. The sealing process is carried out using a sealing bar 30 and a receiving member 34, for example, as shown in Figure 7. The sealing bar 30 is provided with a heater 32 that forms a sealing portion 11 including a protruding portion 11a, as shown in Figure 5. The heater 32 has a curved surface 32a, which contacts the lid material 14. The heater 32 also has the same pattern shape as the plan view shape of the sealing portion 11 shown in Figure 5. With this configuration, if the heater 32 is pressed against the lid material 14 at a predetermined position, heat sealing is performed in the same pattern and at the same position, and even if heat sealing is performed multiple times, one sealing portion 11 is formed. Plane view means viewing the lid material 14 from a direction perpendicular to the surface 14a. The receiving member 34 is a flat plate-shaped member and has an opening 34a into which the container body 20 of the container 12 is fitted. When the container 12 is fitted into the opening 34a of the receiving member 34, the receiving member 34 supports the back surface 22b of the flange portion 22. For example, in the sealing process, the container 12 is fitted into the opening 34a of the receiving member 34, and the back surface 22b of the flange portion 22 is supported by the receiving member 34.

[0025] Next, the back surface 14b of the lid material 14 is brought into contact with the surface 22a of the flange portion 22. In this state, the curved surface 32a of the heater 32, which is held at the sealing bar temperature, is pressed against a predetermined position on the surface 14a of the lid material 14 to perform heat sealing. After a predetermined time has elapsed, the curved surface 32a of the heater 32 is removed from the lid material 14. Next, the curved surface 32a of the heater 32, which is held at the sealing bar temperature, is pressed again against a predetermined position on the surface 14a of the lid material 14 to perform a heat seal. As a result, a seal portion 11 is formed around the entire circumference of the outer edge 20d of the container 12, as shown in Figure 5.

[0026] As described above, in the sealing process, heat sealing is performed multiple times at predetermined positions, but all heat sealing is performed using the same heater pattern shape and by pressing the heater 32 against the same position. The multiple heat sealing may be performed at the same position without changing the position of the container, or it may be performed with the container in a different position. That is, the heat sealing may be performed multiple times with the container 12 fitted into a single receiving member 34, or multiple receiving members 34 may be prepared and the receiving member 34 may be changed for each heat sealing. In addition, although the same heater pattern shape is used for all heat sealing, the heater with the same pattern shape may be the same heater, or a different heater may be used for each heat sealing. Furthermore, as described above, in the sealing process, by performing heat sealing multiple times at predetermined positions, the airtightness of the contents 16 is maintained, and damage such as peeling off of the lid material during the distribution, storage, and sales processes of the frozen food packaging container 10 can be suppressed. In addition, the lid material 14 can be peeled off with little force.

[0027] The sealing process does not have a particularly high upper limit on the number of heat seals performed. However, since a large number of heat seals increases the time required for the sealing process, it is preferable to perform fewer heat seals. For this reason, it is preferable to perform heat sealing twice. Performing heat sealing twice maintains the airtightness of the lid material 14 while also ensuring that the lid material 14 can be opened with minimal force. Furthermore, in the sealing process, it is preferable that the seal strength after multiple heat seals is lower than the seal strength after the first heat seal. For example, as shown in Figure 1, if the number of heat seals is two, it can be utilized that the seal strength of the second seal will be lower than the seal strength of the first seal when the seal bar temperature exceeds 155°C. By making the seal strength after multiple heat seals lower than the seal strength after the first heat seal, the force required to open the lid can be reduced.

[0028] In the sealing process, a heater 32 having a curved surface 32a is used, and during heat sealing, the curved surface 32a is pressed against the surface 14a of the lid material 14, so that the lowest end of the curved surface 32a makes contact first, and then the area around the lowest end is pressed. Therefore, even if there is debris between the lid material 14 and the flange portion 22, the debris is pushed out to the periphery, and the lid material 14 and the flange portion 22 can be sealed in close contact. For this reason, it is preferable that the heater 32 has a curved surface 32a. The diameter of the curved surface 32a of the heater 32 is preferably larger than the width of the heater 32 and less than three times the width of the heater 32. Furthermore, the width th of the heater 32 (see Figure 8) is preferably 3 to 10 mm. If the width th of the heater 32 (see Figure 8) is 3 to 10 mm, the seal strength is sufficient without becoming too high, and the ease of opening is not compromised. Moreover, even if there is debris between the lid material 14 and the flange portion 22, the debris can be pushed out to the surroundings. Furthermore, as shown in Figure 8, the radius r of the curved surface 32a of the heater 32 may be smaller than the width d of the sealing portion 11. This helps to suppress variations in heat sealing. Furthermore, the seal width of the seal portion is determined by the width of the heater 32, the radius of the curved surface of the heater, or the width of the flange portion 22, and is approximately 3 to 10 mm. In the sealing process, heat sealing is performed multiple times, but each heat sealing is performed at, for example, the same sealing bar temperature. The same sealing bar temperature means that the set temperature during heat sealing is the same, and this includes temperature errors of equipment such as heaters.

[0029] (container) Container 12 is used to store the contents 16 as described above. Furthermore, container 12 can also serve as tableware. That is, after heating the frozen food packaging container 10 in a microwave oven, the lid 14 can be removed and the container can be used as tableware. <Container shape> The shape of the container 12 is not particularly limited and is determined appropriately according to the shape of the contents 16 and their form after thawing. As mentioned above, it may also have a design that allows it to be used as tableware. The size of the container 12 is determined appropriately according to the type and quantity of the contents 16 to be contained. The container body 20 of the container 12 is, for example, cup-shaped or tray-shaped. The shape of the opening 20a is not particularly limited, and examples include a square, rectangular, circular, or elliptical shape in plan view. The shape of the outer edge of the flange portion 22 may be similar to the shape of the opening 20a. Also, depending on the design, the shape of the outer edge of the flange portion may differ from the shape of the opening 20a.

[0030] Here, Figure 9 is a schematic perspective view showing another example of a container for frozen food packaging according to an embodiment of the present invention. In the container 12 shown in Figure 9, the same components as those shown in the container 12 in Figure 4 are denoted by the same reference numerals, and detailed descriptions are omitted. In container 12, the number of container bodies 20 is not limited to one as shown in Figure 4, but may be multiple. For example, container 12 may have a configuration in which multiple container bodies 20 are connected by connecting the outer edges of the flange portions 22 of the container bodies 20 shown in Figure 4. Alternatively, it may have a configuration with four container bodies 20, as shown in container 12a in Figure 9. In container 12a, a seal portion 11 (see Figure 5) is formed on the surface 22a of the flange portion 22 surrounding the opening 20a.

[0031] Furthermore, the number of container bodies 20 is not limited to the four shown in Figure 9; the number of container bodies 20 can be two or more, depending on the intended use. In container 12, if there are multiple container bodies 20, the size of each container body 20 may be the same or different depending on the intended use. Similarly, the size of the openings of the container bodies 20 may be the same or different depending on the intended use. When there are multiple container bodies 20, there are no particular restrictions on their arrangement; for example, they may be arranged side by side.

[0032] Furthermore, if there are multiple container bodies 20, the sealing portion is formed around the entire circumference of the outer edge of the container. In addition, the sealing portion may also be formed around the opening 20a of each container body 20, as described above. Even if there are multiple container bodies 20, the sealing portion may be formed only around the outer edge of the container, without forming a sealing portion around each of the openings 20a of the multiple container bodies 20. The sealing portion may have a protrusion 11a (see Figure 5). The protrusion 11a may be provided for each container body 20, or one may be provided for each container 12, and the number of protrusions 11a is not particularly limited. Furthermore, if there are multiple container bodies 20, each container body 20 may be configured to be separable from one another by providing, for example, a separation portion (not shown) at the boundary portion 25 (see Figure 9) of each container body 20. The separation portion is formed, for example, by intermittently cutting perforations at the boundary portion of each container body 20.

[0033] <Container material> The materials used to construct the container are not particularly limited as long as they are materials commonly used in the manufacture of packaging containers. For example, known olefin resins such as low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, propylene-ethylene copolymer, ethylene-vinyl acetate copolymer, and olefin resins graft-modified with ethylene-based unsaturated carboxylic acids or their anhydrides; polyamide or copolyamide resins with relatively low melting points or low softening points; polyester or copolyester resins; polycarbonate resins; and other plastic materials such as paper materials can also be used. Furthermore, the thickness of the container is preferably 200 to 1000 μm, and more preferably 400 to 700 μm, from the standpoint of self-supporting stability during heat sealing and impact resistance during distribution.

[0034] Furthermore, the material used in the container 12 is preferably water-resistant and highly flexible. It is even more preferable if it is easily permeable to microwaves, as this allows for efficient heating by microwave oven. It is even more preferable if it is made of a material with low thermal conductivity, as this prevents the temperature from becoming too high when the packaging container is removed from the microwave oven after heating. Examples of materials that satisfy the above conditions include polypropylene resin, polyethylene resin, mixed resin of polypropylene resin and polyethylene resin, polyethylene terephthalate resin, polystyrene resin, and polylactic acid resin.

[0035] As a material for constructing the container, it is preferable to use a heat-sealable plastic material for the container surface layer that comes into contact with the lid. Examples of heat-sealable plastic materials include known low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, polypropylene, propylene-ethylene copolymer, ethylene-vinyl acetate copolymer, olefin resins such as olefin resins graft-modified with ethylene-based unsaturated carboxylic acids or their anhydrides; polyamide or copolyamide resins with relatively low melting points or low softening points; polyester or copolyester resins; and polycarbonate resins. In particular, using polypropylene as the surface layer of the container that comes into contact with the lid material results in even better sealing and opening properties. Furthermore, the thickness of the surface layer of the container is preferably 200 to 1000 μm, and more preferably 400 to 700 μm, from the viewpoint of airtightness and ease of opening. For this reason, the surface layer of the container is preferably made of a polyolefin resin film such as polyethylene film or polypropylene film with a thickness of 200 to 1000 μm.

[0036] The container 12 can also be constructed from a laminate. A suitable layer configuration for the laminate is, for example, a laminate of polypropylene. An example of a laminate is one in which, from the inside out, the container 12 is constructed from biaxially oriented polypropylene and unoriented polypropylene (CPP).

[0037] (lid material) As described above, the lid material 14 seals the container 12 by blocking the inside of the container 12 from the outside air. The lid material 14 is a film-like component, and is made of, for example, a heat-sealable film. The lid material 14 is not particularly limited as long as at least the portion in contact with the container 12 is heat-sealable, and may consist of a single component or a multi-layered component. Furthermore, similar to the container 12, it is preferable that the lid material 14 is easily permeable to microwaves, as this allows for more efficient heating by microwave oven.

[0038] <Material of the lid> For example, the lid material can be made from polyester resin, polyamide resin, polyethylene resin, polyethylene terephthalate resin, polypropylene resin, polystyrene resin, polylactic acid resin, polyvinyl chloride resin, polyvinylidene chloride resin, or polycarbonate resin. Furthermore, the lid material may have a laminated structure, for example, nylon / nylon / polyethylene in order from the surface (outside) of the lid material. The lid material may also have a sealant layer on the back side (inside) that faces the container. The sealant layer may be composed of, for example, a polyolefin resin such as polyethylene or polypropylene. The sealant layer may be composed of, for example, a polyolefin resin film such as polyethylene film or polypropylene film. Furthermore, a resin with easy-peel properties can be used for the sealant layer. Examples of resins with easy-peel properties include VMX®, LMX®, and SMX® manufactured by J-Film Co., Ltd. The thickness of the lid material is preferably 40 to 120 μm, and more preferably 60 to 100 μm, from the viewpoint of ease of opening and impact resistance during distribution. Furthermore, the thickness of the sealant layer is preferably 10 to 50 μm, and more preferably 20 to 40 μm, from the viewpoint of ease of opening and sealing. For this reason, the sealant layer is preferably composed of a polyethylene film with a thickness of 10 to 50 μm.

[0039] The present invention is basically configured as described above. Although the method for manufacturing a packaging container for frozen foods of the present invention has been described in detail above, the present invention is not limited to the embodiments described above, and various improvements or modifications may be made without departing from the spirit of the present invention. [Examples]

[0040] The features of the present invention will be further described in detail below with reference to examples. The materials, reagents, amounts and proportions of substances, and procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the following examples. In this example, the seal strength at each position of the packaging container of Example 1 was measured. The results are shown in Figure 10.

[0041] Example 1 used a container with a laminated structure consisting of a polypropylene film and an unoriented polypropylene (CPP) film, in that order from the inside. The thickness of the container was 575 μm, and the thickness of the polypropylene film, which is the surface layer of the container in contact with the lid material, was 550 μm. A laminated film of nylon / nylon / polyethylene / sealant layer (manufactured by Tomowa Sangyo Co., Ltd.) was used for the lid material. An easy-peel polyethylene film (manufactured by J-Film Co., Ltd.) was used for the sealant layer. The thickness of the lid material was 85 μm, and the thickness of the sealant layer was 30 μm. In Example 1, the container dimensions were 151 mm × 205.5 mm × 42.0 mm (height).

[0042] (Heating bonding conditions) In Example 1, a heater with a width of 5 mm and a tip radius of 4 mm was used for heat sealing. The heat sealing was performed twice, with a sealing time of 0.9 seconds and a sealing bar pressure of 250 kgf (2.45 kN) applied during heat sealing. The second heat sealing was performed before the temperature of the container and lid material returned to room temperature after the first heat sealing. The sealing bar temperatures were set to 140°C, 150°C, 160°C, 170°C, 180°C, 190°C, and 195°C. When the sealing bar temperature was 195°C, the temperature of the container surface at the sealed area immediately after heat sealing was 95°C. The measurement locations for seal strength were positions A to D shown in Figure 3. Furthermore, the seal strength was measured in accordance with JIS Z 0238:1998 ("Test methods for heat-sealable flexible packaging bags and semi-rigid containers").

[0043] In Example 1 shown in Figure 10, it was found that the seal strength becomes nearly constant and airtightness is achieved when the seal bar temperature is 160°C or higher. For Example 1, the seal strength indicating openability was measured. The seal strength indicating openability was measured by peeling the lid material from the protruding portion 11a of the seal portion 11 (see Figure 3) and measured in accordance with JIS S0021-2:2018. In Example 1, at a seal bar temperature of 170°C to 190°C, the seal strength indicating openability was in the range of 15 to 20 N. This prevented the seal strength from becoming excessively high, resulting in good openability. Therefore, Example 1 achieved a balance between airtightness and openability of the lid material. [Explanation of Symbols]

[0044] 10 Packaging containers for frozen foods 10a Long side 10b Short side 10c, 10d corner 11. Seal part 11a Projection 12 containers 14 Lid material 14a, 22a surface 14b, 22b back side 16 Contents 20 Container body 20a opening 20b Bottom part 20c side part 20d Outer edge 20e Storage compartment 22 Flange section 25 Boundary 30 Silver 32 Heater 32a curved surface 34 Receiving member 34a opening r radius

Claims

1. A method for manufacturing a packaging container for frozen foods having a container and a lid, The container and the lid material are sealed by a heat-bonding process, The sealing process involves performing heat sealing multiple times at predetermined positions with the same pattern using a heater with the same pattern shape around the entire circumference of the outer edge of the container, thereby heating and joining the container and the lid material. A method for manufacturing a packaging container for frozen foods, wherein, in the sealing process, the seal strength after multiple heat sealings is lower than the seal strength after the initial heat sealing.

2. The container has an opening, and along the outer edge of the opening, it has a flange portion that protrudes on the opposite side of the opening. The method for manufacturing a packaging container for frozen foods according to claim 1, wherein the sealing step involves heat-bonding the lid material to the flange portion of the container.

3. The method for manufacturing a packaging container for frozen foods according to claim 1 or 2, wherein the sealing step involves performing the heat bonding twice.

4. A method for manufacturing a packaging container for frozen foods according to any one of claims 1 to 3, wherein the sealing step forms a continuous sealing portion around the entire circumference of the outer edge of the container.

5. The sealing process is performed using the heater. The method for manufacturing a packaging container for frozen foods according to any one of claims 1 to 4, wherein the heater has a curved surface that contacts the lid material, and the radius of the curved surface is smaller than the width of the sealed portion formed in the sealing step.

6. The method for manufacturing a packaging container for frozen foods according to claim 4 or 5, wherein the sealing portion has a protrusion that protrudes outward from the outer edge.

7. A method for manufacturing a packaging container for frozen foods according to any one of claims 1 to 6, wherein the surface layer of the container is made of a polyolefin resin film having a thickness of 200 to 1000 μm.

8. A method for manufacturing a packaging container for frozen foods according to any one of claims 1 to 7, wherein the lid material has a sealant layer on the container side, and the sealant layer is made of a polyethylene film with a thickness of 10 to 50 μm.

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