Lid with pressure-absorbing structure

Abstract

To provide a lid body which can be re-sealed and which has a pressure absorption structure capable of absorbing an inner pressure change generated by hot filling and the like.SOLUTION: A lid body having a drop-in lid-like shape comprises a flange part, a side wall part extending downward from an inner peripheral edge of the flange part, and a top surface positioned inside the side wall part, and a fitting part with a container trunk part inside surface is formed at a side wall part outside surface side. The top surface at least includes an annular flat surface part extending inward from a position below the fitting part of the side wall part, and a central top surface part positioned inside the annular flat surface part, and positioned below the fitting part of the side wall part, and has a pressure absorption structure which can absorb an inner pressure change after filling a content and sealing.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a drop lid-shaped lid having a sealing property, and more particularly to a lid having a pressure absorption structure and capable of effectively suppressing plastic deformation caused by a change in the internal pressure of a container when subjected to heat sterilization or the like.

Background Art

[0002] A container with a lid formed by applying a drop lid-shaped lid made of a resin sheet by thermoforming is widely used. Even in such a container with a lid, depending on the contents, it may be subjected to hot filling, retort sterilization, or the like. However, since such a container with a lid has a high sealing property by heat-sealing the lid, an internal pressure change occurs due to hot filling or the like, and depending on the material of the container or the lid, the lid may be damaged or greatly deformed, impairing the appearance characteristics and sealing performance.

[0003] In order to solve such problems, Patent Document 1 below proposes a lid for a hot pack container formed by molding a laminate in which an aluminum foil and a heat-sealing layer are sequentially provided on the inner surface of a synthetic resin stretched film into a shape having irregularities or dome-shaped portions of a size capable of absorbing volume contraction due to decompression inside the container. Further, Patent Document 2 below proposes a pressure-resistant lid characterized in that, in a lid made of a thermoplastic resin for sealing a container, the top plate shape of the lid has a step near the peripheral wall and is convex downward.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] The lid described in Patent Document 1 above is a lid that deforms in response to changes in internal pressure and is capable of absorbing internal pressure, while the lid described in Patent Document 2 above is a lid that deforms very little in response to changes in internal pressure. These lids do not have a mechanism for resealing after being opened. In other words, even in containers with lids sealed by heat sealing, it is desirable that they be resealable after initial opening. However, the lids used in such resealable containers require a fitting part to secure the lid to the container during resealing. A particularly suitable fitting form is a screw engagement, but this is prone to deformation due to changes in internal pressure, making it difficult to ensure airtightness after resealing.

[0006] Therefore, the object of the present invention is to provide a lid that is resealable and has a pressure-absorbing structure that can absorb changes in internal pressure caused by hot filling or the like without causing deformation of the lid. [Means for solving the problem]

[0007] According to the present invention, a lid in the shape of a drop-in lid comprises a flange portion, a side wall portion extending downward from the inner peripheral edge of the flange portion, and a top surface located inside the side wall portion, wherein a fitting portion with the inner surface of the container body is formed on the outer surface side of the side wall portion, wherein the top surface comprises at least an annular planar portion extending inward from a position below the fitting portion of the side wall portion, and a central top surface portion located inside the annular planar portion and below the fitting portion of the side wall portion. Between the annular planar portion and the central top portion, an annular vertical portion or an annular inclined portion that slopes downward toward the center is formed, and the engaging projection formed on the outer surface of the side wall portion consists of a plurality of protrusions that are intermittently connected in the circumferential direction. It is characterized by having a pressure absorption structure that can absorb changes in internal pressure after the contents have been filled and sealed. First A lid is provided. The present invention also provides a lid in the shape of a drop-in lid, comprising a flange portion, a side wall portion extending downward from the inner peripheral edge of the flange portion, and a top surface located inside the side wall portion, wherein a fitting portion with the inner surface of the container body is formed on the outer surface side of the side wall portion, wherein the top surface comprises at least an annular planar portion extending inward from a position below the fitting portion of the side wall portion, and a central top surface portion located inside the annular planar portion and below the fitting portion of the side wall portion, wherein an annular vertical portion or an annular inclined portion sloping downward toward the center is formed between the annular planar portion and the central top surface portion, and has an annular outer wall hanging down from the outer peripheral edge of the flange portion, with an engaging projection formed on the inner surface of the annular outer wall that can engage with the container, and the fitting portion formed on the outer surface of the side wall portion extending downward from the inner peripheral edge of the flange portion has a tapered shape in which its outer diameter increases as it goes downward from the side wall portion, and has a pressure absorbing structure that can absorb changes in internal pressure after filling and sealing the contents.

[0008] In the lid of the present invention That was, The central top surface is flat. , is preferable . Furthermore, in the first lid mentioned above, (1) The outer surface of the side wall portion is formed with an engaging projection that can engage with the inner surface of the container body portion. ( 2 The engaging projection formed on the outer surface of the side wall portion consists of a plurality of protrusions that are intermittently connected in the circumferential direction. and, This is preferable. Furthermore, in the second lid mentioned above, It is preferable that the engaging projection formed on the inner surface of the annular outer wall consists of a plurality of protrusions that are intermittently connected in the circumferential direction.

[0009] According to the present invention, the above First A sealed container is provided, comprising a lid and a container, wherein the container consists of a bottom portion and a body portion, a flange portion is formed at the upper end of the body portion, an engaging portion is formed on the upper inner surface of the body portion that can engage with an engaging projection formed on the outer surface of the side wall portion of the lid, and the flange portion of the lid and the flange portion of the container are heat-sealed so as to be removable.

[0010] According to the present invention, further, second A second embodiment of a sealed container is provided, comprising a lid and a container, wherein the container consists of a bottom and a body, a flange is formed at the upper end of the body, an annular side wall is formed hanging down from the outer peripheral edge of the flange, an engaging portion is formed on the outer surface of the annular side wall that can engage with an engaging projection formed on the inner surface of the annular outer wall of the lid, and the flange of the lid and the flange of the container are heat-sealed so as to be removable. In the sealed container of the second embodiment described above, it is preferable that the side wall portion of the lid has a taper in which its inner diameter increases as it goes downward, and that a taper is formed on the upper part of the body of the container that can be pressed against the taper of the lid. [Effects of the Invention]

[0011] In the lid of the present invention, even when a pressure change occurs in the container after filling and sealing by hot filling, retort sterilization, etc., the internal pressure change can be reliably absorbed by the deformation caused by the vertical movement of the central top surface portion. Also, the central top surface portion is connected to the side wall portion via an annular flat surface portion, and both the annular flat surface portion and the central top surface portion are located below the fitting portion, so that the influence of the pressure acting on the central top surface portion on the fitting portion can be reduced, and excellent sealing performance is ensured. Further, since the deformation due to this internal pressure change is within a recoverable range, not only the appearance of the lid after the internal pressure change is not impaired, but excellent sealing performance can also be maintained.

Brief Description of the Drawings

[0012] [Figure 1] It is a perspective view showing an example of the lid of the present invention and an example of a container to which this lid is applied. [Figure 2] It is a schematic cross-sectional view showing the states before and after the increase in internal pressure for an example of the lid of the present invention (Example 1). [Figure 3] It is a schematic cross-sectional view showing the states before and after the increase in internal pressure for another example of the lid of the present invention (Example 2). [Figure 4] It is a schematic cross-sectional view showing the states before and after the increase in internal pressure for the lid of Comparative Example 1. [Figure 5] It is a schematic cross-sectional view showing the states before and after the increase in internal pressure for the lid of Comparative Example 2. [Figure 6] It is a schematic cross-sectional view showing the states before and after the increase in internal pressure for the lid of Comparative Example 3. [Figure 7] It is a perspective view showing another example of the lid of the present invention and another example of a container to which this lid is applied. [Figure 8] It is a schematic cross-sectional view showing a state where another example of the lid of the present invention is applied to a container. [Figure 9] It is a diagram for explaining a method of measuring the opening force. [Figure 10] It is a diagram showing the restraint conditions and boundary conditions for the analysis and evaluation in the examples.

Modes for Carrying Out the Invention

[0013] The lid of the present invention comprises a flange portion, a side wall portion extending downward from the inner peripheral edge of the flange portion, and a top surface located inside the side wall portion, and is a drop-in lid shaped lid in which a fitting portion with the inner surface of the container body is formed on the outer surface side of the side wall portion, wherein the top surface (1) Having an annular planar portion that extends inward from a position below the fitting portion of the side wall. (2) It has at least a central top surface that is located inward from the annular planar portion and below the fitting portion of the side wall portion. This is a key feature, and the top surface of the lid having such a structure allows it to function as a pressure-absorbing structure capable of absorbing changes in internal pressure after the contents have been filled and sealed.

[0014] The lid of the present invention will be described below with reference to the attached drawings. Figure 1 is a perspective view showing an example of a lid of the present invention and an example of a container to which this lid is applied, and Figure 2 is a schematic cross-sectional view of a part of the lid shown in Figure 1. As shown in Figures 1 and 2, the lid, represented as 1 in whole, generally consists of a flange portion 11, a side wall portion 12 hanging down from the inner peripheral edge of the flange portion 11, and a top surface located inside the side wall portion 12. On the outer surface of the side wall portion 12, intermittently connected protrusions (engaging projections) 13, 13... are formed in the circumferential direction. In the specific example shown in Figure 1, the top surface located inside the lid beyond the side wall portion 12 consists of an annular planar portion 14 extending inward from the lower end of the side wall portion 12, an annular inclined portion 15 extending diagonally downward and toward the center of the lid from the inner peripheral edge 14a of the annular planar portion 14, and a central top surface portion 16 extending toward the center of the lid from the lower end of the annular inclined portion 15 and covering the central part. As is clear from Figure 1, the central top surface 16 is located below the position of the protruding portion (engaging projection) 13 of the side wall portion 12, and in the specific example shown in the figure, the central top surface 16 is formed in a planar shape. Furthermore, a gripping piece 3 for opening is formed on the flange portion 11.

[0015] Furthermore, the container, which is shown as a whole in Figure 2, generally consists of a bottom portion 21, a body portion 22, and a flange portion 23 extending outward from the upper end of the body portion 22. In the specific example shown in Figure 1, the body portion 22 consists of a lower body portion 22a and an upper body portion 22b separated by a stepped portion 24. The upper body portion 22b has engaging portions 25, 25... formed therein for engaging with the protruding portions (engaging projections) 13, 13... of the lid 1 described above to fix the lid to the container. This engaging portion 25 extends axially downward from the upper end of the container flange portion 23 and consists of an axial recess 25a that is recessed radially outward from the inner surface of the container, and a circumferential recess 25b that extends circumferentially from the lowest point of this axial recess 25a. The lid 1 and the container 2 are sealed by joining the lid flange portion 11 and the container flange portion 23 in a detachable manner using heat sealing or the like. At this time, the engaging projection 13 of the lid and the axial recess 25a of the container are joined in a position that is aligned axially, so that the lid 2 can be pulled upward and the lid can be easily removed from the container. Furthermore, when resealing, the engaging projection 13 of the lid is fitted to the lowest point of the axial recess 25a of the container, and then the lid 1 is rotated to engage the engaging projection 13 of the lid with the circumferential recess 25b of the container, thereby enabling resealing.

[0016] In a sealed container that has been filled with contents and sealed by heat sealing or the like, when subjected to hot filling or retort sterilization, upward pressure is applied from inside the container, centered on the top surface 16 of the lid. As a result, the top surface deforms into a convex dome shape, starting from its outer edge. Similarly, in the lid of the present invention shown in Figures 1 and 2 above, upward pressure is applied to the central top surface 16 from below, causing the central top surface 16 to deform into an upwardly convex dome shape. However, in the lid shown in Figures 1 and 2, as shown by the dotted line in Figure 2, the central top surface 16 is connected to the side wall 12 via the annular planar portion 14 and the annular inclined portion 15. Therefore, it deforms into a dome shape starting from the inner peripheral edge 15a of the annular inclined portion 15 to absorb the pressure. As a result, in the lid of the present invention, not only the joint portion of the flange but also the side wall 12 is hardly affected by deformation due to changes in internal pressure. This ensures sealing performance, prevents damage to the fitting portion with the container, and ensures airtightness during resealing. Furthermore, the deformation when internal pressure is applied, as shown by the dotted lines in Figure 2 and Figures 3-6 described later, was obtained by simulation using structural analysis software, as shown in the examples described later. This simulation more clearly shows the difference in deformation when internal pressure is applied due to differences in the configuration than the actual amount of deformation.

[0017] Furthermore, in Figure 3, which shows another embodiment of the lid of the present invention, the configuration is the same as in Figure 2 in that it has an annular planar portion 14 and an annular inclined portion 15, but in this embodiment, it consists of an upwardly convex frustoconical central top portion 16, via a second annular planar portion 17 from the inner peripheral edge 15a of the annular inclined portion 15. In this embodiment of the lid, when upward pressure is applied from below to the frustoconical central top surface 16, the upper base portion 16a of the frustoconical deforms upward into a convex dome shape, as shown by the dotted line in Figure 3, starting from the outer edge of the upper base 16a, thereby absorbing the pressure. As a result, in this embodiment, even if the second annular planar portion 17 moves slightly upward starting from the inner edge of the annular inclined portion 15, the joint portion of the flange and the side wall portion 12 are hardly affected by deformation due to changes in internal pressure, thus ensuring sealing performance and resealability.

[0018] In contrast, if the top surface of the lid does not have the characteristics described in (1) and / or (2) above, the lid may deform excessively due to changes in internal pressure, undergoing plastic deformation and being unable to return to its original shape, or the central top surface may not be able to adequately absorb the pressure, impairing the fit between the container and the lid, making it difficult to ensure airtightness and resealability. In other words, the embodiment shown in Figure 4 has the same configuration as Figures 1 to 3 described above in that it has a flange portion 11, a side wall portion 12 on which an engaging projection 13 is formed, and an annular planar portion 14. However, in this embodiment, a dome-shaped central top surface portion 16 that is convex downward is formed via an inclined portion 18 that extends diagonally upward and toward the center of the lid from the inner peripheral edge 14a of the annular planar portion 14, and therefore does not satisfy (2) above (Comparative Example 1 described later). In this embodiment, when an upward pressure is applied to the central top surface portion 16 from below due to a change in internal pressure, the central top surface portion 16 hardly changes its position, as shown by the dotted line in Figure 4, and therefore cannot sufficiently absorb the internal pressure. As a result, the pressure acting on the inner surface of the lid also acts on the boundary portion between the inner surface of the container body and the outer surface of the side wall portion of the lid, which may cause damage to the fitting portion (engaging projection) formed on the side wall portion, or the lid may come off if the joint strength at the flange portion is weak.

[0019] The embodiment shown in Figure 5 also has the same configuration as in Figures 1 to 3 described above, in that it has a flange portion 11, a side wall portion 12 on which an engaging projection 13 is formed, and an annular planar portion 14. However, in the embodiment shown in Figure 5, a central top surface portion 16 that is convex upward is formed directly from the inner peripheral edge 14a of the annular planar portion 14, and therefore does not satisfy (2) above (Comparative Example 2 described later). In this embodiment, when an upward pressure is applied to the central top surface portion 16 from below due to a change in internal pressure, the central top surface portion 16 deforms significantly into a dome shape, as shown by the dotted line in Figure 5, starting from the inner peripheral edge 14a of the annular planar portion 14 (the outer peripheral edge of the lower base of the frustocone). Furthermore, since the starting point of the deformation is the inner peripheral edge 14a of the annular planar portion 14, the annular planar portion 14 itself is also pulled upward starting from the outer peripheral edge 14b. As a result, the pressure acting on the inner surface of the lid also acts on the boundary between the inner surface of the container body and the outer surface of the lid's side wall. This can lead to damage to the fitting portion (engaging projection) formed on the side wall, or the lid may come off if the joint strength at the flange is weak.

[0020] Furthermore, even if the embodiment shown in Figure 6 has the same configuration as Figures 1-3 described above in that it has a flange portion 11 and a side wall portion 12 on which engaging projections 13 are formed, the central top surface portion 16 is entirely flat inside the side wall portion 12, and therefore does not satisfy both (1) and (2) above (Comparative Example 3 described later). In this embodiment, when an upward pressure is applied to the central top surface portion 16 from below due to a change in internal pressure, the central top surface portion 16 deforms greatly into a dome shape, as shown by the dotted line in Figure 6, starting from its outer peripheral edge and the inner surface of the side wall portion 12. Also, since the starting point of the deformation is the outer peripheral edge of the central top surface portion 16 and the inner surface of the side wall portion 12, the pressure acting on the inner surface of the lid acts directly on the boundary between the inner surface of the container body and the outer surface of the lid side wall portion, which may damage the engaging projections formed on the side wall portion or cause the lid to come off if the joint strength at the flange portion is weak.

[0021] The lid of the present invention is not limited to the specific examples shown in Figures 2 and 3, and various modifications are possible. In other words, in the embodiments shown in Figures 2 and 3, an annular inclined portion is formed between the annular planar portion and the central top portion, which slopes downward toward the center. This allows the central top portion to be positioned below the fitting portion of the side wall while enabling smooth vertical movement of the central top portion. However, if the proportion of the top surface occupied by the central top portion is large, or if the internal pressure rise is low, the inclined surface of the annular inclined portion can be replaced with an annular vertical surface. Furthermore, while the central top surface was flat in the embodiment shown in Figure 2 and truncated cone-shaped in the embodiment shown in Figure 3, the invention is not limited to these, and the central top surface may be dome-shaped or the like, convex upward or downward, as long as conditions (1) and (2) above are satisfied.

[0022] Furthermore, in the embodiments shown in Figures 1 to 3, an engaging projection consisting of multiple circumferentially intermittently connected protrusions is formed on the outer surface of the side wall of the lid as the fitting portion between the lid and the container. This engaging projection engages with an engaging portion consisting of an axial recess recessed radially outward and a circumferential recess on the inner surface of the container body to form the fitting portion, but the invention is not limited to this. For example, as shown in Figure 7, the engaging portion formed on the container body consists of an engaging portion 25 consisting of multiple circumferentially intermittently connected protrusions that protrude radially inward from the container. When resealing, the lid 1 is rotated until the lid flange portion 11 and the container flange portion 23 are in contact, and then fitted onto the container 2. The lid's engaging projection 13 and the container's engaging portion 25 are then engaged to reseal the container.

[0023] Furthermore, as shown in Figure 8, the fitting portion between the lid and the container may not have engaging protrusions, and the fitting portion may be formed by the compression between the outer surface of the lid's side wall and the inner surface of the container body. That is, the lid in the embodiment shown in Figure 8 has a flange portion 11, a side wall portion 12 extending downward from the inner peripheral edge of the flange portion 11, an annular planar portion 14, and a central top surface portion 16, similar to the lids shown in Figures 1 and 2, but it also has an annular outer wall 19 hanging down from the outer peripheral edge of the flange portion 11, and engaging protrusions 20 that can engage with the container are formed on the inner surface of this annular outer wall 19. In addition, the joint surface (outer surface of the side wall portion) of the side wall portion 12 extending downward from the inner peripheral edge of the flange portion 11 with the inner surface of the container body is formed as a tapered surface in which the outer diameter of the side wall portion increases as it goes downward. In a container to which the lid shown in Figure 8 is applied, similar to the container shown in Figure 1, it has a bottom portion 21 and a body portion 22, a flange portion 23 extending outward from the upper end of the body portion 22, and an annular side wall 26 hanging down from the outer peripheral edge of the flange portion 23. An engaging portion 27 that can engage with the engaging projection 20 of the lid is formed on the outer surface of this annular side wall 26. In addition, the joint surface (inner surface of the upper body portion) of the upper body portion 22b that faces the outer surface of the side wall portion 12 of the lid 1 and the lid side wall portion 12 is formed as a tapered surface in which the inner diameter of the upper body portion increases as it goes downward. In the embodiment shown in Figure 8, in the sealed state after filling with contents, the lid 1 and the container 2 are detachably fixed at the flange portion by heat sealing or the like, and the lid side wall portion 12 and the upper body portion 22b of the container are firmly fitted together by tapered surfaces. Therefore, even if a change in internal pressure occurs, it is possible to absorb the change in internal pressure without impairing the airtightness or appearance, similar to the embodiments shown in Figures 1 to 3 described above. In this embodiment as well, the engaging projection 20 formed on the inner surface of the annular outer wall 19 of the lid consists of a plurality of protrusions that are intermittently connected in the circumferential direction, as shown in Figure 1. It engages with the engaging portion 27 formed on the outer surface of the annular side wall 26 of the container, allowing the lid to be fixed to the container when resealing. Combined with the tapered fit between the lid side wall portion 12 and the upper body portion 22b of the container, it is possible to maintain excellent airtightness even after opening.

[0024] In the lid of the present invention, the top surface inside the side wall portion is provided with at least an annular planar portion and a central top surface portion. As described above, the annular planar portion and the central top surface portion are located below the fitting portion, allowing for internal pressure absorption without affecting the sealing performance of the fitting portion. However, in order to perform this function more efficiently, the annular planar portion is preferably 5 to 30% of the diameter of the top surface (inner diameter of the side wall portion), and the central top surface portion is preferably 50 to 80% of the diameter of the top surface. Furthermore, in order to efficiently manage vertical movement due to changes in internal pressure at the central top surface, it is desirable that the thickness of this portion be in the range of 100 to 500 μm, although this depends on the size of the central top surface.

[0025] The container to which the lid of the present invention can be applied is preferably a cup shape having a circular opening that can be screwed into, but is not limited to this, and may also be tray-shaped or bottle-shaped. Since the lid of the present invention is a lid that can be used for hot filling, boiling sterilization, retort sterilization, etc., it is desirable that the lid has heat resistance, flexibility, and heat sealability. Therefore, it is preferable, though not limited to, that the lid be made of a heat-resistant thermoplastic resin, but polyolefin resins such as polyethylene resin and polypropylene resin, polyester resins such as polyethylene terephthalate, etc. can be suitably used. Furthermore, while the container material may be metal or glass if the flange is joined by means other than heat sealing, it is preferable to use resin, similar to the lid, from the viewpoint of flexibility, heat sealability, and moldability. Polyolefin resins such as polyethylene resin and polypropylene resin, and polyester resins such as polyethylene terephthalate can be suitably used.

[0026] Furthermore, as mentioned above, in a sealed container formed by applying the lid of the present invention to a container, it is preferable to have a joint made by a peelable heat seal in order to ensure reliable sealing until the initial opening. Since such a heat seal must be able to reliably maintain a sealed state and be easily peelable during the initial opening operation, it is preferable to adjust the adhesive strength by the combination of resins that make up the container and the lid. As shown in Figure 9, a suitable adhesive strength that satisfies both sealing performance and easy opening performance is preferably in the range of 0.3 to 3.0 kgf, and more preferably in the range of 0.5 to 2.5 kgf, when the opening force (peel strength) is measured by attaching a push-pull gauge to the gripping part of the lid and pulling it up at a 45-degree angle to the lid. The peeling properties are not particularly limited, and resin materials of the cohesive peeling, interfacial peeling, or interlayer peeling type may be used. As for such resin combinations, two or more thermoplastic resins that have heat-sealing properties but are incompatible can be appropriately combined.

[0027] For example, when the container is made of polypropylene resin, the lid can be made of a blend of polyethylene resin and polypropylene resin to ensure airtightness while maintaining easy opening, and the peel strength can be adjusted by appropriately changing the blending ratio of the blended materials. Examples of the above-mentioned polypropylene resins include homopolypropylene, block copolymers or random copolymers of propylene with ethylene or other α-olefins, such as 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, etc. Examples of the above-mentioned polyethylene resins 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, 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 polyethylene terephthalate isophthalate copolymer, as well as polycarbonate resins, polyacrylonitrile resins, and the olefin polymers mentioned above. When using polypropylene resin and polyethylene resin as a blend, in order for the flange member made of the blend to exhibit good release properties from the container body made of polypropylene resin, it is preferable to use a blend of polypropylene resin and polyethylene resin in a weight ratio of 5:5 to 9.5:0.5. Furthermore, the lid or container may be a single-layer structure of the above-mentioned resin, but it may also be a multi-layer structure with a gas barrier intermediate layer, as long as the portion that becomes the heat-seal part satisfies the above-mentioned conditions.

[0028] The lid of the present invention and the container to which this lid is applied can be manufactured by various methods such as injection molding, compression molding, and thermoforming, as long as they have the above-described configuration. In particular, it is desirable to integrally mold the resin sheet from thermoforming methods such as vacuum pressure forming and plug-assisted pressure forming, as this facilitates the molding process. Furthermore, by thermoforming from a resin sheet, multilayer containers or multilayer lids can be easily formed using multilayer sheets. For example, but not limited to, a flexible laminate comprising an inner layer and an outer layer made of the thermoplastic resin described above, and a gas barrier intermediate layer, etc., can be mentioned. Examples of materials constituting the gas barrier intermediate layer include metal foil such as aluminum foil, inorganic vapor-deposited film, and gas barrier resin such as ethylene vinyl alcohol copolymer. [Examples]

[0029] (Examples 1, 2 and Comparative Examples 1-3) For the lids with the shapes shown in Figures 2-6 (Examples 1 and 2, and Comparative Examples 1, 2, and 3, respectively), resin molds were created using a 3D printer, and the lids were formed by vacuum pressure molding using a polypropylene sheet with a thickness of 0.32 mm and an easy-peel layer on one side. In Examples 1 and 2, an annular inclined section that slopes downward is formed between the annular flat section and the central top section. In Comparative Examples 1 and 2, an annular inclined section that slopes upward is formed between the annular flat section and the central top section. In Comparative Example 3, no annular flat section is formed. Similarly, a container formed from a single layer of polypropylene sheet using vacuum pressure molding was filled with water to create a headspace of 5cc to 15cc, the aforementioned lid was placed on top, and it was heat-sealed using a cup sealer. After that, it was retort sterilized at 121°C for 30 minutes, opened, and evaluated.

[0030] • Evaluation items ◇Appearance of the top surface of the lid (4-point rating scale) 4: Excellent, 3: Good, 2: Slightly Poor, 1: Poor (Significant unevenness / deformation) ◇Deformation of the lid fitting area (3-level evaluation) 3: No deformation, 2: Slight deformation, 1: Significant deformation ◇Can the container and lid fit together? ○: Fits, ×: Not fit

[0031] The evaluation results are shown in Table 1. As shown in Table 1, both Examples 1 and 2 showed good results. In Comparative Example 1, the appearance of the top surface and fitting surface was poor, and the deformation of the fitting surface was significant, making it impossible to fit the container and lid together. In Comparative Examples 2 and 3, the appearance of the top surface and fitting surface was not as good as in Comparative Example 1. However, the deformation of the fitting surface was not as severe, so it was possible to fit the container and lid together.

[0032] [Table 1]

[0033] (Evaluation through analysis) The deformation of the lids with the shapes shown in Figures 2-6 (Examples 1 and 2, and Comparative Examples 1-3) was evaluated using structural analysis software when an internal pressure of 5 kPa was applied. • Analysis software: SOLIDWORKS (trademark registered) Simulation • Analysis conditions: 2D axisymmetric model, linear static analysis • Analysis model • Material: Homopolypropylene ·Lid thickness: 0.4mm The constraint and boundary conditions are shown in Figure 10. • Evaluation items Maximum displacement value (the amount of change at the point that changed the most before and after deformation)

[0034] The analysis results are shown in Figures 2-6 with dotted lines. As shown in Figures 2 and 3, in Examples 1 and 2, the central part of the top surface was the most deformed, with a maximum displacement of 9-10 mm. Also, as shown in Figure 4, in Comparative Example 1, the dome-shaped portion in the center of the top surface had a nearly uniform displacement of about 2 mm, and the overall amount of deformation was small. This suggests that the dome-shaped portion was less prone to deformation, and that the deformation was mainly in the other parts of the top surface. Furthermore, as shown in Figures 5 and 6, in Comparative Examples 2 and 3, the central part of the top surface was the most deformed, with a maximum displacement of 20 mm or more, indicating significant deformation. Furthermore, the above analysis results only evaluate the magnitude of deformation when internal pressure is applied to the lid. In contrast, the actual phenomenon during retort sterilization involves not only an increase in internal pressure but also the effects of heat, and deformation may remain even after the internal pressure returns to its original state after retort sterilization is complete. Therefore, the presence or absence of deformation that cannot be restored has not been evaluated.

[0035] Furthermore, we will consider the correspondence between the experimental results and analytical results obtained using the aforementioned retort sterilization method. In the experiment, the lids of Examples 1 and 2 showed favorable results. The maximum displacement in the analysis results was 9-10 mm, which is intermediate compared to the comparative examples. It is presumed that the top surface deformed moderately without excessive deformation, and that it was able to efficiently absorb the internal pressure within a recoverable range. In contrast, Comparative Example 1 had a maximum displacement of only 2 mm, showing almost no deformation. This meant that the deformation was easily transmitted to the mating part, causing significant deformation in the mating part, and ultimately resulting in residual deformation, which prevented the lid from fitting properly to the container. On the other hand, Comparative Examples 2 and 3 had large maximum displacement values ​​of 20 mm or more. This meant that deformation was particularly likely to remain on the top surface, and the deformation also affected the mating part, resulting in residual deformation. [Industrial applicability]

[0036] The lid of the present invention can absorb changes in the internal pressure of the container and does not deform at the fitting portion, thus ensuring airtightness after resealing. Therefore, it can be suitably used for heat sterilization applications such as hot filling and retort sterilization. [Explanation of Symbols]

[0037] 1 Lid, 2 Container, 11 Flange, 12 Side wall, 13 Engaging projection, 14 Annular flat section, 15 Annular inclined section, 16 Central top section, 17 Annular flat section, 18 Inclined section, 19 Annular outer wall, 20 Engaging projection, 21 Bottom, 22 Body, 23 Flange, 24 Stepped section, 25 Engaging section, 26 Annular side wall, 27 Engaging section.

Claims

1. In a lid body having a drop-in lid shape, comprising a flange portion, a side wall portion extending downward from the inner peripheral edge of the flange portion, and a top surface located inside the side wall portion, a fitting portion with the inner surface of the container body is formed on the outer surface side of the side wall portion, The top surface comprises at least an annular planar portion extending inward from a position below the fitting portion of the side wall, and a central top surface portion located inward from the annular planar portion and below the fitting portion of the side wall. Between the aforementioned annular planar portion and the central top portion, an annular vertical portion or an annular inclined portion that slopes downward toward the center is formed. The engaging projection formed on the outer surface of the side wall consists of a plurality of protrusions that are intermittently connected in the circumferential direction. A lid characterized by having a pressure-absorbing structure capable of absorbing changes in internal pressure after the contents have been filled and sealed.

2. A lid in the shape of a drop-in lid, comprising a flange portion, a side wall portion extending downward from the inner peripheral edge of the flange portion, and a top surface located inside the side wall portion, wherein a fitting portion with the inner surface of the container body is formed on the outer surface side of the side wall portion, The top surface comprises at least an annular planar portion extending inward from a position below the fitting portion of the side wall, and a central top surface portion located inward from the annular planar portion and below the fitting portion of the side wall. Between the aforementioned annular planar portion and the central top portion, an annular vertical portion or an annular inclined portion that slopes downward toward the center is formed. The flange portion has an annular outer wall that hangs down from the outer peripheral edge, and an engaging projection that can engage with a container is formed on the inner surface of the annular outer wall, and the fitting portion formed on the outer surface of the side wall portion that extends downward from the inner peripheral edge of the flange portion has a tapered shape in which its outer diameter increases as it goes downward from the side wall portion. A lid characterized by having a pressure-absorbing structure capable of absorbing changes in internal pressure after the contents have been filled and sealed.

3. The lid according to claim 1 or 2, wherein the central top surface is flat.

4. The lid according to claim 1, wherein an engaging projection capable of engaging with the inner surface of the container body is formed on the outer surface of the side wall portion.

5. The lid according to claim 2, wherein the engaging projection formed on the inner surface of the annular outer wall consists of a plurality of protrusions that are intermittently connected in the circumferential direction.

6. A sealed container comprising a lid and a container as described in claim 1, The container consists of a bottom and a body, with a flange formed at the upper end of the body, and an engaging portion formed above the inner surface of the body that can engage with an engaging projection formed on the outer surface of the side wall of the lid. A sealed container characterized in that the flange portion of the lid and the flange portion of the container are heat-sealed in a way that allows them to be peeled off.

7. A sealed container comprising a lid and a container according to claim 5, The container consists of a bottom portion and a body portion, with a flange portion formed at the upper end of the body portion, and an annular side wall formed hanging down from the outer peripheral edge of the flange portion. The outer surface of the annular side wall has an engaging portion formed which can engage with an engaging projection formed on the inner surface of the annular outer wall of the lid. A sealed container characterized in that the flange portion of the lid and the flange portion of the container are heat-sealed in a way that allows them to be peeled off.

8. The sealed container according to claim 7, wherein the side wall portion of the lid has a taper that increases in outer diameter as it goes downward, and a taper is formed on the upper part of the body of the container that can be pressed against the taper of the lid.

9. A sealed container according to any one of claims 6 to 8, for use in heat sterilization.

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