JP7768795B2 - Synthetic resin container lid - Google Patents

Description

The present invention relates to a synthetic resin container lid.

The present invention relates to a synthetic resin container lid in which a locking means consisting of multiple locking protrusions extending circumferentially or a continuously extending annular locking ridge is formed on the inner peripheral surface of the tamper-evident bottom portion of the skirt wall.

As is well known, a widely used container lid for a container made of glass, synthetic resin, or sheet metal has a cylindrical neck portion with a male thread on the outer peripheral surface and a locking jaw located below the male thread. The container lid has a circular top wall and a cylindrical skirt wall depending from the periphery of the top wall. The skirt wall has a circumferentially extending fracture line formed therein, which is composed of circumferentially extending slits spaced apart along the periphery and bridging portions between the slits. The skirt wall is divided into a main skirt portion above the fracture line and a tamper-evident skirt portion below the fracture line. An internal thread is formed on the inner peripheral surface of the main skirt portion, and a locking means is formed on the inner peripheral surface of the tamper-evident skirt portion. The locking means consists of multiple locking projections that project radially inward and extend circumferentially, or an annular locking ridge that projects radially inward and extends continuously circumferentially. The upper surface of the main part of the locking means has an upper fitting surface whose inner diameter gradually increases upward and connects to the inner peripheral surface of the tamper-evident hem. The lower surface of the main part of the locking means slopes radially outward downward and connects to the inner peripheral surface of the tamper-evident hem.

When sealing the neck of a container filled with contents, the container lid is fitted onto the neck and rotated in the closing direction, and the female thread of the lid is screwed onto the male thread of the neck. When the container lid is thus attached to the neck as required, the locking means of the container lid elastically overcomes the locking jaw of the neck and positions itself below it. When the locking means elastically overcomes the locking jaw, the underside of the locking means is inclined downward and radially outward, allowing the tamper-evident skirt to be smoothly elastically deformed. When the neck is opened to consume the contents of the container, the container lid is rotated in the opening direction. As a result, the container lid is raised relative to the neck as the male thread and female thread disengage. When the container lid is raised slightly, the locking means on the container lid locks into the locking jaws on the neck portion, thereby preventing the tamper-evident bottom from rising. When the locking means locks into the locking jaws, the locking means is firmly held to the locking jaws by the presence of the mating upper surface. When the container lid continues to rotate in the opening direction, the circumferential tear line formed in the skirt wall breaks, and the tamper-evident bottom is separated from the main skirt portion (or, if an axial tear line is formed in the tamper-evident bottom, the axial tear line breaks and the tamper-evident bottom is expanded from an endless ring shape into a band with ends, and the tamper-evident bottom remains connected to the main skirt portion along part of the circumferential direction without being completely separated from the main skirt portion). If the container lid continues to be rotated in the opening direction, the container lid (or the entire container lid including the tamper-evident hem) will be detached from the neck portion, leaving the tamper-evident hem behind, and the neck portion will be opened.

In recent years, there has been a demand to reduce the amount of material used to manufacture container lids in order to reduce environmental impact and manufacturing costs. Patent Document 1 below discloses an example of a container lid that reduces material usage by providing multiple lightening holes at intervals around the circumference on the mating upper surface of the locking means.

Japanese Patent Application Laid-Open No. 2020-70031

However, even with the container lid disclosed in Patent Document 1, the reduction in material usage is insufficient, and further reduction is required.

However, providing a lightening portion in the locking means to reduce the amount of material used to form the locking means reduces the rigidity of the locking means, which can lead to the following problems. First, when the container lid is released from the molding die, the locking means protruding radially inward is forcibly removed from the molding die. Therefore, if the locking means has low rigidity, there is a risk of the locking means suffering from molding defects such as sagging. Second, when the neck portion is opened, the locking means must be engaged with the locking jaw portion of the neck portion to reliably prevent the tamper-evident bottom from rising. Therefore, if the locking means has low rigidity, there is a risk that the locking means will elastically deform and slip over the locking jaw portion, resulting in a slip-out. Therefore, even if a lightening portion is provided in the locking means to reduce the amount of material used to form the locking means, the locking means must still maintain sufficient rigidity.

The present invention was made in light of the above facts, and its main technical objective is to provide a new and improved synthetic resin container lid that uses even less material than the container lid disclosed in Patent Document 1 while maintaining sufficient rigidity in the locking means.

After extensive research, the inventors discovered that the above-mentioned main technical problem could be solved by making the inner peripheral edge of the main portion of the locking means continuous in the circumferential direction and parallel to the inner peripheral surface of the tamper-evident bottom, and by forming multiple lightening holes at intervals in the circumferential direction on not only the upper mating surface but also the lower mating surface of the main portion.

That is, according to the present invention, a synthetic resin container closure that solves the above-mentioned main technical problem comprises a circular top wall and a cylindrical skirt wall hanging down from the periphery of the top wall, the skirt wall having a circumferentially extending fracture line formed thereon, the circumferentially extending fracture line being made up of a plurality of circumferentially extending slits spaced apart in the circumferential direction and a plurality of bridging portions existing between the slits, the skirt wall being divided into a main skirt portion above the fracture line and a tamper-evident skirt portion below the fracture line, and the inner peripheral surface of the main skirt portion having a female a threaded rib is formed, and a locking means is arranged on the inner peripheral surface of the tamper-evident bottom portion, the locking means consisting of a plurality of locking projections that protrude radially inward and extend circumferentially or an annular locking ridge that protrudes radially inward and extends continuously circumferentially, the upper surface of the main part of the locking means is provided with a fitting upper surface whose inner diameter gradually increases upward and which is connected to the inner peripheral surface of the tamper-evident bottom portion, and the lower surface of the main part is inclined radially outward and downward and is connected to the inner peripheral surface of the tamper-evident bottom portion,
The inner peripheral edge of the main portion is continuous in the circumferential direction parallel to the inner peripheral surface of the tamper-evident bottom portion, and a plurality of recesses are formed at intervals in the circumferential direction on the upper and lower mating surfaces of the main portion.

Preferably, the circumferential width and number of the lightening holes formed on the upper mating surface are equal to the circumferential width and number of the lightening holes formed on the lower surface, and the lightening holes formed on the upper mating surface and the lower surface are aligned in the circumferential direction. Furthermore, the circumferential centers of the lightening holes formed on the upper mating surface and the lower surface may be alternately positioned in the circumferential direction. When the locking means is composed of a plurality of locking protrusions, the inner peripheral edges of the circumferential ends of the locking protrusions preferably slope radially outward from the circumferential end of the inner peripheral edge of the main portion toward the circumferential outside and connect to the inner peripheral surface of the tamper-evident hem. In this case, the upper surface of the end may preferably be provided with an upper reinforcement portion whose inner diameter gradually increases upward and which is connected to the inner peripheral surface of the tamper-evident hem. Additionally, a lower reinforcing section may be provided on the underside of the end portion, the inner diameter of which gradually increases downward and which is connected to the inner peripheral surface of the tamper-evident bottom portion.

According to the present invention, multiple recesses are formed not only on the upper mating surface but also on the lower surface of the main portion of the locking means, allowing the container lid to be manufactured using less material. Furthermore, according to the present invention, the inner peripheral edge of the main portion of the locking means is circumferentially continuous and parallel to the inner peripheral surface of the tamper-evident bottom. Therefore, when the locking means is forcibly removed from the molding die during the process of releasing the container lid from the molding die, the entire inner peripheral edge of the main portion of the locking means abuts against the molding die. When the locking means is engaged with the locking jaw during the process of opening the neck, the entire upper surface of the inner peripheral edge of the main portion of the locking means abuts against the lower surface of the locking jaw. This makes the locking means less likely to deform, i.e., the locking means has sufficient rigidity. Therefore, despite being manufactured using less material, the container lid of the present invention maintains sufficient rigidity, preventing deformation of the tamper-evident bottom even when an external force is applied to the locking means. Furthermore, in the present invention, multiple lightening holes are provided on both the upper and lower surfaces of the locking means, increasing the surface area of the locking means. This reduces the difference in cooling rate between the upper and lower surfaces of the locking means and allows the container lid to be cooled efficiently after molding, improving manufacturing efficiency.

1 is a view showing a preferred embodiment of a synthetic resin container lid constructed according to the present invention, partially in cross section; FIG. 2 is a bottom view of the container lid shown in FIG. 1 . 2 is a partially enlarged view of the container lid shown in FIG. 1 and the neck of the container to which the lid is attached. FIG. 2 is a developed view showing the inner peripheral surface of the tamper-evident bottom portion of the container lid shown in FIG. 1 . FIG. 10 is a diagram showing an expanded view of the inner peripheral surface of the tamper-evident bottom portion in a first modified example of a container lid configured according to the present invention. FIG. FIG. 10 is a developed view showing the inner peripheral surface of the tamper-evident bottom portion in a second modified example of a container lid configured according to the present invention. FIG. 10 is a developed view showing the inner peripheral surface of the tamper-evident bottom portion in a third modified example of a container lid configured according to the present invention. FIG. 10 is a developed view showing the inner peripheral surface of the tamper-evident bottom portion in a fourth modified example of a container lid configured according to the present invention. FIG. 10 is a developed view showing the inner peripheral surface of the tamper-evident bottom portion in a fifth modified example of a container lid configured according to the present invention.

The present invention will now be described in further detail with reference to the accompanying drawings, which show a preferred embodiment of a synthetic resin container lid constructed in accordance with the present invention.

Referring to Figures 1 and 2, the container lid 2, which can be injection molded or compression molded from a suitable synthetic resin such as polyethylene or polypropylene, has a circular top wall 4 and a cylindrical skirt wall 6 depending from the periphery of the top wall 4. A relatively long, tubular inner seal piece 8 and a relatively short, tubular outer seal piece 10 depending downward are formed on the inner peripheral edge of the top wall 4. A small, annular rib 12 is also formed between the inner seal piece 8 and the outer seal piece, protruding slightly downward from the inner surface of the top wall 4.

A circumferentially extending fracture line 14 is formed on the skirt wall 6, and the skirt wall 6 is divided into a main skirt portion 16 above the fracture line 14 and a tamper-evident hem portion 18 below the fracture line 14. The fracture line 14 is composed of a plurality of circumferentially extending slits (kerfs) 20 spaced apart in the circumferential direction and a plurality of bridging portions 22 between the slits 20, and the tamper-evident hem portion 18 is connected to the main skirt portion 16 via the plurality of bridging portions 22.

Anti-slip knurling 24 consisting of alternating concave and convex shapes is formed on the outer peripheral surface of the skirt main portion 16 when viewed circumferentially. A female thread 26 is formed on the inner peripheral surface of the skirt main portion 16 of the skirt wall 6. The female thread 26 has multiple notches 28 spaced circumferentially.

1 and 2, as well as 3 and 4, a locking means is disposed on the inner peripheral surface of the tamper-evident hem 18. In the illustrated embodiment, the locking means is composed of a plurality of (five in the illustrated embodiment) locking protrusions 32 that protrude radially inward and extend circumferentially. The locking protrusions 32 are divided into a main portion 34 whose inner peripheral edge is circumferentially continuous and parallel to the inner peripheral surface of the tamper-evident hem 18, and end portions 36 located on both circumferential sides of the main portion 34, whose inner peripheral edges are inclined radially outward from the circumferential end of the inner peripheral edge of the main portion 34 toward the outside in the circumferential direction and connected to the inner peripheral surface of the tamper-evident hem 18. As shown in FIG. 3 , the upper surface of the main portion 34 of the locking projection 32 is divided into an upper locking surface 38 located radially inward and extending substantially horizontally, and an upper mating surface 40 located radially outward and having an inner diameter that gradually increases upward and connects to the inner peripheral surface of the tamper-evident hem portion 18. In the illustrated embodiment, the vertical cross-sectional shape of the upper mating surface 40 extends linearly upward and then slopes radially outward. Meanwhile, the lower surface 42 of the main portion 34 of the locking projection 32 slopes radially outward and connects to the inner peripheral surface of the tamper-evident hem portion 18. As can be understood by referring to FIGS. 1 and 4 , a plurality of recesses 44 are formed at circumferential intervals on each of the upper mating surface 40 and the lower mating surface 42 of the main portion 34. The recessed portions 44 are formed by cutting out the upper and lower mating surfaces 40 and 42 so as to expose the inner circumferential surface of the tamper-evident bottom portion 18. A circumferentially extending protrusion 46 remains at the corners of the recessed portions 44 formed on the upper mating surface 40. The vertical cross-sectional shape of the protrusion 46 is concave arc-shaped, and its radially inner edge is continuously connected to the radially outer edge of the upper locking surface 38. The concave arc-shaped vertical cross-sectional shape of the protrusion 46 reduces the removal resistance when the container lid 2 is removed from the molding die, thereby suppressing deformation of the locking protrusion 32. Meanwhile, the lower surface of the cutout portion of the lower surface 42 is substantially horizontal. Referring to FIG. 4 , in the illustrated embodiment, the number of recessed portions 44 formed on the upper mating surface 40 and the lower surface 42 is equal, four each. The cutouts 44 all have the same circumferential width, and are spaced equally apart in the circumferential direction. Therefore, in the illustrated embodiment, the cutouts 44 formed on the upper mating surface 40 and the lower mating surface 42 are aligned in the circumferential direction. The circumferential width of each cutout 44 is wider than the circumferential width of a remaining portion 50 between two adjacent cutouts 44, and the remaining portion 50 is rib-shaped. The upper surface of the end 36 of the locking projection 32 is provided with an upper reinforcement portion 52a whose inner diameter gradually increases upward and is connected to the inner circumferential surface of the tamper-evident hem 18; the upper reinforcement portion 52a is not cut out. The lower surface of the end 36 is provided with a lower reinforcement portion 52b whose inner diameter gradually increases downward and is connected to the inner circumferential surface of the tamper-evident hem 18; the lower reinforcement portion 52b is also not cut out. In the illustrated embodiment, the inner diameter of the lower reinforcement portion 52b gradually increases in the radial direction away from the main portion 34. The lower edge of the lower surface of the end portion 36 is gradually inclined upward toward the circumferential outside. The inner peripheral surface of the tamper-evident bottom portion 18 also has a ridge 54 that extends continuously in the circumferential direction between two circumferentially adjacent locking projections 32. The cross-sectional shape and vertical height of the ridge 54 are the same as those of the ridge 46, and both circumferential ends of the ridge 54 are connected to the circumferential end faces of the locking projections 32.

In Figure 1, the container neck 100 is shown by a two-dot chain line along with the container lid 2. The container neck 100, which can be formed from a suitable synthetic resin such as polyethylene terephthalate, glass, or thin metal plate, is cylindrical overall, and the outer surface of the neck 100 is formed with a male thread 102 and a locking jaw 104 located below the male thread 102. The locking jaw 104 has an arcuate upper surface whose outer diameter gradually increases downward, a cylindrical outer surface, and a lower surface that extends substantially horizontally. A support ring 106 (such a support ring 106 is used for transporting the container, as is well known to those skilled in the art) is also arranged on the outer surface of the neck 100 and located below the locking jaw 104.

After the contents are filled into the container, the container lid 2 is fitted onto the neck portion 100 and rotated in the closing direction (clockwise as viewed from above in Figure 1) to thread the female thread 26 of the container lid 2 onto the male thread 102 of the neck portion 100. When the female thread 26 is threaded onto the male thread 102 to the state shown in Figure 1, the inner seal piece 8 of the container lid 2 enters the neck portion 100 and is tightly contacted with the inner peripheral surface of the neck portion 100, the outer seal piece 10 is tightly or closely adjacent to the outer peripheral surface of the neck portion 100, and the annular micro-ridge 12 is tightly contacted with the top surface of the neck portion 100, thus sealing the neck portion 100. The locking protrusion 32 disposed on the inner peripheral surface of the tamper-evident skirt 18 elastically overcomes the locking jaw 104 of the mouth and neck portion 100 (i.e., by elastic deformation or displacement of the tamper-evident skirt 18) and is positioned below the locking jaw 104. When the locking protrusion 32 elastically overcomes the locking jaw 104 of the mouth and neck portion 100, the lower surface 42 of the locking protrusion 32 is inclined downward and radially outward, allowing the tamper-evident skirt 18 to be smoothly elastically deformed. In this state, as can be understood by referring to Figures 3 together with Figure 1, the mating upper surface 40 of the locking protrusion 32 comes into contact with or is in close contact with the lower end of the outer peripheral surface of the locking jaw 104 of the mouth and neck portion 100.

When opening the neck portion 100 to consume the contents, the container lid 2 is rotated in the opening direction, i.e., counterclockwise when viewed from above in Figure 1. This gradually disengages the male thread 102 from the female thread 26, and the tamper-evident skirt portion 18, along with the skirt main portion 16, is raised relative to the neck portion 100 as the rotation proceeds. At this time, as can be seen from Figure 2, the upper mating surface 40 of the locking projection 32 on the tamper-evident skirt portion 18 is brought into close contact with the lower end of the outer circumferential surface of the locking jaw portion 104 of the neck portion 100, gradually increasing the frictional resistance torque. When the container lid 2 is raised a predetermined amount relative to the neck portion 100, the upper locking surface 38 of the locking projection 32 locks against the lower surface of the locking jaw 104, preventing the tamper-evident hem 18 from moving upward in the axial direction. At this time, the upper mating surface 40 of the locking projection 32 is also in close contact with the lower end of the outer circumferential surface of the locking jaw 104 of the neck portion 100, so that the tamper-evident hem 18 is held by the locking jaw 104. Then, because the tamper-evident hem 18 is prevented from moving upward in the axial direction, stress is generated in the bridging portion 22 of the break line 14, causing the bridging portion 22 to break, and the tamper-evident hem 18 is separated from the main skirt portion 16. After the break line 14 is broken, the tamper-evident bottom 18 remains in the neck portion 100, and the top wall 4 of the container lid 2 and the main skirt portion 16 of the skirt wall 6 are rotated and freely moved axially upward, separating them from the neck portion 100, thereby opening the neck portion 100. If desired, an axial break line can be formed in the tamper-evident bottom 18, so that when the neck portion 100 of the container is opened, the axial break line is broken, while a portion of the circumferentially extending break line 14 remains unbroken, causing the tamper-evident bottom 18 to expand from an endless annular shape into an ended annular shape, allowing the entire container lid 2 to be separated from the neck portion 100 together with the tamper-evident bottom 18.

According to the present invention, multiple recesses 44 are formed not only on the upper mating surface 40 but also on the lower surface 42 of the main portion 34 of the locking protrusion 32, enabling the manufacture of a container lid using less material. Furthermore, according to the present invention, the inner peripheral edge of the main portion 34 of the locking protrusion 32 is circumferentially continuous and parallel to the inner peripheral surface of the tamper-evident bottom portion 18. Therefore, when the locking protrusion 32 is forcibly removed from the molding die during the process of releasing the container lid from the molding die, the entire inner peripheral edge of the main portion 34 of the locking protrusion 32 abuts against the molding die. When the locking protrusion 32 is engaged with the locking jaw 104 during the process of opening the neck portion 100, the entire upper surface of the inner peripheral edge of the main portion 34 of the locking protrusion 32 abuts against the lower surface of the locking jaw 104. This makes the locking protrusion 32 less likely to deform, i.e., the locking protrusion 32 has sufficient rigidity. Therefore, the container lid of the present invention can be manufactured using less material, yet the rigidity of the locking protrusion 32 is maintained sufficiently, preventing deformation of the tamper-evident bottom portion 18 even when an external force is applied to the locking protrusion 32. Furthermore, in the present invention, multiple lightening holes 44 are provided on the upper and lower surfaces of the locking protrusion 32, increasing the surface area of the locking protrusion 32. This reduces the difference in cooling rate between the upper and lower surfaces of the locking protrusion 32 and enables the container lid to be cooled efficiently after molding, improving manufacturing efficiency. Furthermore, by providing an upper reinforcing portion 52a on the upper surface of the end 36 of the locking protrusion 32 and a lower reinforcing portion 52b on the lower surface, the rigidity of the locking protrusion 32 is maintained satisfactorily.

In the embodiment described above, the circumferential width and number of the lightening holes 44 formed on the upper mating surface 40 of the locking projection 32 are equal to the circumferential width and number of the lightening holes 44 formed on the lower surface 42, and the lightening holes 44 formed on the upper mating surface 40 and the lower surface 42 are aligned in the circumferential direction. However, as in the modified examples shown in Figures 5 to 8, the circumferential width, number, and circumferential positions of the lightening holes formed on the upper mating surface and the lower surface may be changed as appropriate. In the following description, parts that are the same as those in the embodiment described above are designated by the same numbers, with the letters a to e added in the first to fourth modified examples, respectively.

In the first modified example shown in Figure 5, the number of lightening holes 44a formed on the upper mating surface 40a of the locking projection 32a is equal to the number of lightening holes 44a formed on the lower surface 42a, but the circumferential width of the lightening holes 44a formed on the upper mating surface 40a is slightly wider than the circumferential width of the lightening holes 44a formed on the lower surface 42a, and the circumferential center positions of the lightening holes 44a formed on the upper mating surface 40a and the lightening holes 44a formed on the lower surface 42a are alternately arranged in the circumferential direction with respect to the circumferential center position.

In the second modified example shown in Figure 6, the number of lightening holes 44b formed on the upper mating surface 40b of the locking projection 32b is equal to the number of lightening holes 44b formed on the lower surface 42b, but the circumferential width of the lightening holes 44b formed on the upper mating surface 40b is slightly narrower than the circumferential width of the lightening holes 44b formed on the lower surface 42b. In this modified example, the circumferential width of the remaining portions 50b left on the upper mating surface 40b is wider than the circumferential width of the remaining portions 50b left on the lower surface 42b, and the circumferential centers of the remaining portions 50b left on the upper mating surface 40b and the remaining portions 50b left on the lower surface 42b are aligned circumferentially.

In the third modified example shown in Figure 7, the number of lightening holes 44c formed on the upper mating surface 40c of the locking projection 32c is four, while the number of lightening holes 44c formed on the lower surface 42c is three, and the circumferential width of the lightening holes 44c formed on the upper mating surface 40c is wider than the circumferential width of the lightening holes 44c formed on the lower surface 42c. In this modified example, the circumferential width and circumferential center position of the remaining portion 50c left on the upper mating surface 40c correspond to the circumferential width and circumferential center position of the lightening holes 44c formed on the lower surface 42c.

In the fourth modified example shown in Figure 8, the number of lightening holes 44d formed on the upper mating surface 40d of the locking projection 32d is four, while the number of lightening holes 44d formed on the lower surface 42d is three. However, the circumferential width of the lightening holes 44d formed on the upper mating surface 40d is approximately the same as the circumferential width of the lightening holes 44c formed on the lower surface 42d, the circumferential width of the remaining portions 50d left on the upper mating surface 40d is approximately the same as the circumferential width of the remaining portions 50d left on the lower surface 42d, and the circumferential center positions of the remaining portions 50d left on the upper mating surface 40c and the circumferential center positions of the lightening holes 44d formed on the lower surface 42d are aligned.

For example, as in the third and fourth modified examples, when the lightening holes 44c, 44d formed on the upper mating surfaces 40c, 40d and the lightening holes 44c, 44d formed on the lower surfaces 42c, 42d are arranged alternately in the circumferential direction, it is possible to avoid, as much as possible, lightening holes being formed at the same circumferential positions on both the upper mating surfaces 40c, 40d and the lower surfaces 42c, 42d, and therefore the rigidity of the locking protrusions 32c, 32d is further improved compared to the rigidity of the locking protrusions 32 in the embodiment shown in Figures 1 to 3.

In addition, in all of the above-described embodiments, the locking means is composed of multiple locking protrusions that protrude radially inward and extend circumferentially. However, as in the fifth modified example shown in Figure 9, the locking means may be composed of a single annular locking ridge 32e that protrudes radially inward and extends continuously circumferentially. When the locking means is composed of an annular locking ridge 32e, the entire annular locking ridge 32e becomes the main portion 34e of the locking means. In this case, too, the number, circumferential width, and circumferential position of the lightening holes 44e formed on each of the upper and lower mating surfaces 40e, 42e may be changed as appropriate.

The above describes in detail a preferred embodiment of the container lid of the present invention with reference to the accompanying drawings, but the present invention is not limited to the above embodiment, and further modifications may be made within the scope of the present invention. For example, in the illustrated embodiment, the upper surface of the locking means is provided with an upper engaging surface whose inner diameter gradually increases upward and which connects to the inner peripheral surface of the tamper-evident bottom portion, as well as an upper engaging surface that extends approximately horizontally. However, the upper engaging surface may be omitted, and the entire upper surface of the locking means may serve as the upper engaging surface. Furthermore, while the shape of the lightening portion 44 is rectangular in the examples and modified examples, it may also be curved, such as connecting the upper ends of the remaining portions together and the lower ends together in an arc-like shape when viewed circumferentially.

2: Container lid 4: Top wall 6: Skirt wall 14: Breaking line 16: Main skirt portion 18: Tamper-evident bottom portion 20: Slit 22: Bridge portion 26: Female thread 32: Locking protrusion (locking means)
34: Main portion (of the locking projection) 40: Fitting upper surface (of the main portion of the locking projection) 42: Lower surface (of the main portion of the locking projection) 44: Lightening portion

Claims (6)

The device comprises a circular top wall and a cylindrical skirt wall hanging down from the periphery of the top wall, and the skirt wall has a circumferentially extending fracture line formed therein, the circumferentially extending fracture line being made up of a plurality of circumferentially extending slits spaced apart from one another and a plurality of bridging portions existing between the slits, the skirt wall being divided into a main skirt portion above the fracture line and a tamper-evident skirt portion below the fracture line, and a female thread is formed on the inner peripheral surface of the main skirt portion, and the tamper-evident skirt portion a locking means is disposed on the inner peripheral surface of the bottom portion, the locking means being composed of a plurality of locking projections that project radially inward and extend circumferentially, or an annular locking ridge that projects radially inward and extends continuously circumferentially, the upper surface of the main portion of the locking means is provided with a fitting upper surface whose inner diameter gradually increases upward and which is connected to the inner peripheral surface of the tamper-evident bottom portion, and the lower surface of the main portion is inclined radially outward downward and is connected to the inner peripheral surface of the tamper-evident bottom portion,
A synthetic resin container lid characterized in that the inner peripheral edge of the main portion is continuous in the circumferential direction parallel to the inner peripheral surface of the tamper-evident bottom portion, and a plurality of recessed portions are formed at intervals in the circumferential direction on the mating upper and lower surfaces of the main portion. The synthetic resin container lid of claim 1, wherein the circumferential width and number of the recessed portions formed on the upper engaging surface are equal to the circumferential width and number of the recessed portions formed on the lower surface, and the recessed portions formed on the upper engaging surface and the recessed portions formed on the lower surface are aligned in the circumferential direction. The synthetic resin container lid according to claim 1, wherein the circumferential centers of the recesses formed on the upper mating surface and the lower mating surface are alternately positioned in the circumferential direction. A synthetic resin container lid according to any one of claims 1 to 3, wherein when the locking means is composed of a plurality of locking projections, the inner peripheral edges of the circumferential ends of the locking projections are connected to the inner peripheral surface of the tamper-evident bottom portion, inclining radially outward from the circumferential end of the inner peripheral edge of the main portion toward the circumferential outside. The synthetic resin container lid according to claim 4, wherein the upper surface of the end portion is provided with an upper reinforcing portion whose inner diameter gradually increases upward and is connected to the inner peripheral surface of the tamper-evident bottom portion. A synthetic resin container lid as described in claim 4 or 5, wherein the underside of the end portion is provided with a lower reinforcing portion whose inner diameter gradually increases downward and is connected to the inner peripheral surface of the tamper-evident bottom portion.