JP7754733B2 - Synthetic resin container lid - Google Patents

Description

The present invention relates to a container lid comprising a lid body and a top cover connected to the lid body via hinge means and rotatable between a closed position that covers the lid body and an open position that exposes the lid body.

Patent Document 1 listed below discloses an example of a container lid comprising a lid body and a top lid connected to the lid body via hinge means and rotatable between a closed position that covers the top surface of the lid body and an open position that exposes the top surface of the lid body. The lid body includes a closing wall and a cylindrical mounting wall that hangs down from the periphery of the closing wall, and the top lid includes a top wall and a skirt wall that hangs down from the periphery of the top wall. The skirt wall is provided with a locking piece that extends downward via a breakable bridging portion, and the mounting wall is provided with a locking piece that locks with the locking piece when the top lid is rotated to the closed position. When the top lid is rotated from the closed position to the open position, the breakable bridging portion breaks and the locking piece is separated from the skirt wall. With such a container lid, when the breakable bridge breaks and the locking piece separates from the skirt wall, it is clearly visible to the lid body that the top lid has been opened (tamper-evident function).

Patent No. 5847649

However, with the container lid shown in Patent Document 1, the locking piece is completely separated from the container lid after the breakable bridge is broken, making it difficult for the user to notice the existence of the locking piece itself, and there is a risk that the tamper-evident function will not be fully realized.

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 allows the user to clearly recognize that the top lid has been opened relative to the lid body.

After extensive research, the inventors discovered that the above-mentioned main technical problem could be solved by tilting the engaging piece downward toward one side in the circumferential direction along the outer surface of the mounting wall at a position spaced radially outward from the outer surface of the mounting wall, so that when the breakable bridge portion breaks, the engaging piece moves downward toward one side in the circumferential direction along the engaging piece.

That is, according to the present invention, a synthetic resin container lid that solves the above-mentioned main technical problem comprises a lid body, and a top lid that is connected to the lid body via hinge means and can be rotated between a closed position that covers the top surface of the lid body and an open position that exposes the top surface of the lid body,
the lid body includes a closing wall and a cylindrical mounting wall depending from the periphery of the closing wall, and the upper lid includes a top wall and a skirt wall depending from the periphery of the top wall,
a locking piece extending downward via a breakable bridge portion is disposed on the skirt wall, and a locking piece to which the locking piece is locked is disposed on the mounting wall when the top lid is turned to the closed position, and when the top lid is turned from the closed position to the open position, the breakable bridge portion is broken and the locking piece is separated from the skirt wall;
the locking piece has a flange portion extending radially outward below the breakable bridge portion, and the locked piece is inclined downward toward one side in the circumferential direction along the outer surface of the mounting wall at a position spaced radially outward from the outer surface of the mounting wall,
A synthetic resin container lid is provided, characterized in that when the breakable bridge portion is broken, the lower surface of the flange portion of the locking piece is locked to the upper surface of the locked piece, and the locking piece is moved downward toward one side in the circumferential direction along the locked piece.

Preferably, the one circumferential side is the direction approaching the hinge means. The upper surface of the engaging piece is preferably divided into a relatively short upper horizontal portion located on the other circumferential side and a relatively long upper inclined portion that slopes downward from one circumferential end of the upper horizontal portion toward the one circumferential side. A recess with an open top is formed at the upper end of the outer peripheral surface of the mounting wall, and the engaging piece is disposed in the recess. The outer peripheral surface of the engaging piece is preferably located on the same circumferential plane as the outer peripheral surface of the mounting wall or radially inward therefrom. In this case, both circumferential ends of the engaging piece are preferably connected to the mounting wall at side surfaces that define both circumferential end surfaces of the recess. Preferably, at least one indicia is disposed on the outer surface of the mounting wall, and the indicia is selectively visible depending on the circumferential position of the engaging piece. Preferably, the locking piece has a flange portion extending radially outward below the breakable bridge portion, with the radially outer end of the flange portion located radially outward from the outer circumferential surface of the skirt wall, and the lower surface of the flange portion forms a support lower surface that is supported by the upper surface of the locked piece after the breakable bridge portion is broken. The locking pieces are preferably provided on both sides of a diameter perpendicular to a diameter passing through the circumferential central angular position of the hinge means in a plan view. A removal region is defined in the closing wall by an endless thin-walled breakable line, and a connecting post extending upward is disposed on the upper surface of the removal region, with a tension ring connected to the upper end of the connecting post.

In the container lid of the present invention, the engaging piece is inclined downward toward one side in the circumferential direction along the outer surface of the mounting wall at a position spaced radially outward from the outer surface of the mounting wall. When the breakable bridge portion is broken, the engaging piece is caused to move downward toward one side in the circumferential direction along the engaging piece, allowing the user to clearly recognize that the top lid has been opened relative to the lid body, providing good tamper-evident properties.

1 is a plan view of a top cover of a synthetic resin container lid constructed in accordance with the present invention in an open position; 2 is a bottom view of the container lid shown in FIG. 1 with the top cover in an open position. FIG. 2 is a front view of the container lid shown in FIG. 1 in a state where the top lid is in an open position. 2 is a cross-sectional view taken along line AA in FIG. 1; 2 is a left side view of the container lid shown in FIG. 1 with the top lid omitted in a state where the top lid is in an open position. FIG. 2 is a right side view of the container lid shown in FIG. 1 with the top lid in an open position, with the lid body omitted. FIG. FIG. 2 is a front view of the container lid shown in FIG. 1 with the top lid in a closed position. 8 is a cross-sectional view taken along line AA in FIG. 7 . 2 is a front view showing an initial stage of a process in which the top cover of the container lid shown in FIG. 1 is pivoted from a closed position to an open position. 2 is a front view of the container lid shown in FIG. 1 with the top lid pivoted from a closed position to an open position.

The following provides a more detailed explanation of a preferred embodiment of a synthetic resin container lid constructed in accordance with the present invention, with reference to the accompanying drawings. Unless otherwise specified, the up-down direction in this specification refers to the state in which the top lid is in the closed position, which will be described later. Therefore, when the top lid is in the open position, which will be described later, the up-down direction is reversed.

Referring to Figures 1 to 4, the synthetic resin container lid, generally designated by the numeral 2, comprises a lid body 4 and a top lid 6, which are connected via a hinge means 8.

Referring to Figures 1 to 3 as well as Figure 4, the lid body 4 includes a circular closing wall 10 in plan view and a cylindrical mounting wall 12 that hangs down from the periphery of the closing wall 10. The closing wall 10 is divided into a central portion 14 that is shaped like a downwardly concave bowl and a substantially annular outer peripheral portion 16 that surrounds the central portion 14. The central portion 14 is positioned slightly displaced from the center of the closing wall 10, diametrically opposite the hinge means 8. A removal area 20 is defined in the central portion 14 of the closing wall 10 by an endless thin-wall breakable line 18. The endless thin-wall breakable line 18 consists of a so-called score formed by locally reducing the thickness of the closing wall 10. A connecting post 22 extending upward is disposed on the upper surface of the removal area 20, and a tension ring 24 is connected to the upper end of the connecting post 22. A cylindrical pouring guide wall 26 is formed at the boundary between the central portion 14 and the outer peripheral portion 16, extending upward from the upper surface of the closing wall 10. The extending end, i.e., the upper end, of the pouring guide wall 26 is curved radially outward and forms a lip shape. A cylindrical engagement wall 28 extending upward and radially outward is provided on the upper surface of the outer peripheral portion 16, more specifically, on the outer peripheral edge of the upper surface of the closing wall 10, and an engagement ridge 30 protruding radially outward is formed at the upper end of the outer peripheral surface of the engagement wall 28. A roughly cylindrical sealing wall 32 hanging downward is formed on the lower surface of the outer peripheral portion 16.

A locking means 34 is disposed at the lower end of the inner peripheral surface of the mounting wall 12. In the illustrated embodiment, as shown in FIG. 2, the locking means 34 consists of a plurality of (six in the illustrated embodiment) arcuate ridges spaced apart and extending circumferentially. If desired, the locking means can also consist of a continuous annular ridge. As can be seen by referring to FIGS. 1 and 5 in addition to FIG. 4, an arcuate notch 36 is formed in the upper portion of the outer peripheral surface of the mounting wall 12, diametrically opposite the hinge means 8, and a shallow arcuate recess 38 is also formed below the notch 36. As shown in FIG. 3, a locking piece 40 is also disposed at a required location on the outer surface of the mounting wall 12. The locking piece 40 will be described later. As shown in Figure 1, the mounting wall 12 is provided with a known separation mechanism including a bottomed annular groove 42 with an open top and an axial slit 44 (see also Figures 3 and 4). After the container lid 2 is attached to the mouth and neck of a container (described below) and used, the container lid 2 can be separated from the mouth and neck and discarded by performing the required operation. For details of this separation mechanism, see, for example, Japanese Patent No. 6326472, which was filed by the applicant of the present application prior to this application and has already been granted a patent. A cylindrical thin-walled wall 45 that hangs downward continuously in the circumferential direction is attached to the outer peripheral edge of the lower surface of the mounting wall 12.

Continuing the explanation with reference to Figures 1 to 3 as well as Figure 4, the top cover 6 includes a circular top wall 46 and a cylindrical skirt wall 48 depending from the periphery of the top wall 46. The lower end of the outer periphery of the skirt wall 48 is connected to the upper end of the outer periphery of the mounting wall 12 of the lid body 4 via hinge means 8, allowing the top cover 6 to freely pivot between a closed position in which it covers the upper surface of the closing wall 10 of the lid body 4 and an open position in which it exposes the upper surface of the closing wall 10 of the lid body 4. The underside of the top wall 46 is also formed with an inner cylindrical wall 50 and an outer cylindrical wall 52 depending downward, and two annular shallow grooves 54 are formed between the inner cylindrical wall 50 and the outer cylindrical wall 52. As shown in Figure 3, a downwardly extending locking piece 56 is disposed at a required position on the underside of the skirt wall 48. The locking piece 56 will be described later together with the lockable piece 40. As can be seen by referring to Figures 1 and 6 as well as Figure 4, a flange 58 protruding radially outward is disposed at the lower end of the outer peripheral surface of the skirt wall 48, on the diametrically opposite side of the hinge means 8, and a finger can be hooked onto the flange 58 when pivoting the top cover 6 open or closed. A thin, arc-shaped protruding piece 60 protruding downward is formed at the diametrically opposite side of the underside of the skirt wall 48 from the hinge means 8. An annular engaged ridge 62 is disposed at the lower end of the inner peripheral surface of the skirt wall 48. An annular abutting ridge 64 is also disposed on the inner peripheral surface of the skirt wall 48, above the annular engaged ridge 62.

Next, we will explain the locked pieces 40 arranged on the mounting wall 12 of the lid main body 4 and the locking pieces 56 arranged on the skirt wall 48 of the top lid 6. First, regarding the locking pieces 56, in the illustrated embodiment, the locking pieces 56 are arranged on both sides of a diameter perpendicular to a diameter passing through the circumferential central angular position of the hinge means 8 in a plan view (i.e., Figure 1). As shown in Figure 3, in the circumferential portion where the locking pieces 56 are provided, the lower surface of the skirt wall 48 is slightly displaced upward, forming a rectangular notch 66 extending circumferentially at the lower end of the skirt wall 48. At this notch 66, the upper end surface of the locking piece 56 is connected to the lower surface of the skirt wall 48 via a pair of breakable bridges 68. Referring to Figures 3 and 6, the locking piece 56 has a flange portion 70 that extends radially outward below the breakable bridge portion 68. The radially outer end of the flange portion 70 is located radially outward from the outer peripheral surface of the skirt wall 48, and a substantially horizontal support lower surface 72 is formed on the underside of the flange portion 70. A protrusion 74 is provided at the lower end of the locking piece 56. This protrusion 74 has an upper locking surface 76 that extends substantially horizontally radially outward and an inclined lower surface 78 that extends radially inward from the radially outer end of the upper locking surface 76 downward, with the circumferential width of the protrusion 74 gradually decreasing downward. A required amount of clearance exists between the upper locking surface 76 and the support lower surface 72 of the flange portion 70.

Next, regarding the engaging pieces 40, in a plan view (i.e., Figure 1), one engaging piece 40 is provided on each of the front and back surfaces of the mounting wall 12. As will be described later, when the top cover 6 is pivoted to the closed position, the engaging pieces 56 disposed on the top cover 6 are elastically engaged with the engaging pieces 40, and therefore the circumferential positions of the engaging pieces 40 correspond to the circumferential positions of the engaging pieces 56. The positions of the engaging pieces 40 will be discussed further below. In a container cover constructed in accordance with the present invention, it is important that the engaging pieces 40 are positioned radially outward from the outer surface of the mounting wall 12 and slope downward toward one circumferential side along the outer surface. As can be understood by referring to Figure 3, in the illustrated embodiment, the one circumferential side is the direction approaching the hinge means 8. The upper surface of the locking piece 40 is divided into a relatively short upper horizontal portion 80 located on the other circumferential side and a relatively long upper inclined portion 82 that slopes downward from one circumferential end of the upper horizontal portion 80 toward one circumferential side. The lower surface of the locking piece 40 is divided into a lower horizontal portion 84 located on the other circumferential side and a lower inclined portion 86 that slopes downward from one circumferential end of the lower horizontal portion 84 toward one circumferential side. The circumferential lengths of the lower horizontal portion 84 and the lower inclined portion 86 are approximately the same. The upper inclined portion 82 and the lower inclined portion 86 are parallel. If desired, the upper and lower surfaces of the locking piece 40 may be entirely inclined downward toward one circumferential side. As shown in FIG. 8 , the upper surface of the locking piece 40 is entirely inclined downward toward the radially inward direction to form a guide surface 88. The "outer surface" of the mounting wall 12 will be mentioned later.

Continuing the explanation with reference to Figures 1, 3, 5, and 8, in the illustrated embodiment, an open-top recess 90 is formed at the upper end of the outer peripheral surface of the mounting wall 12, and the engaging piece 40 is disposed in the recess 90. Therefore, in the above statement, "The engaging piece 40 slopes downward toward one circumferential side along the outer peripheral surface of the mounting wall 12 at a position spaced radially outward from the outer peripheral surface," the "outer peripheral surface" of the mounting wall 12 refers to the bottom surface 91 of the recess 90 in the illustrated embodiment. The outer peripheral surface of the engaging piece 40 is located on the same circumferential plane as the outer peripheral surface of the mounting wall 12, and both circumferential ends of the engaging piece 40 are connected to the mounting wall 12 by side surfaces 92 that define both circumferential end surfaces of the recess 90. The side surfaces 92 extend linearly in the vertical direction. The lower surface 94 of the recess 90 extends somewhat horizontally from the other circumferential end toward one side in the circumferential direction and then slopes downward toward that side along the upper surface inclined portion 82 and the lower surface inclined portion 86 of the engaging piece 40. As shown in FIG. 3 , at least one marking is provided on the outer surface of the mounting wall 12 at the recess 90. In the illustrated embodiment, the markings are the Chinese characters "開" (designated by reference numeral 96a) and "摂" (designated by reference numeral 96b), which are printed by an appropriate printing method on the outer surface of the mounting wall 12 after the container lid 2 is molded. Both the markings 96a and 96b are located below the engaging piece 40, with the marking 96a located at the other circumferential end of the recess 90 and the marking 96b located at one circumferential end of the recess 90, and the markings 96a and 96b are spaced apart in the circumferential direction.

If desired, the outer peripheral surface of the engaging piece 40 may be located radially inward from the outer peripheral surface of the mounting wall 12. Alternatively, the recess 90 may be omitted and the engaging piece 40 may be disposed on the outer peripheral surface of the mounting wall 12, with the outer peripheral surface of the engaging piece 40 located radially outward from the outer peripheral surface of the mounting wall 12. In this case, the engaging piece 56 is connected via the breakable bridge portion 68 to the outer peripheral surface of the skirt wall 48 rather than the underside, and the entire engaging piece 40 is located radially outward from the outer peripheral surface of the skirt wall 48.

The above-described container lid 2 is formed by a molding machine with the top lid 6 in an open position relative to the lid body 4. After the formed container lid 2 is removed from the molding machine, it is completed through a folding process in which the top lid 6 is rotated from the open position to the closed position using a required folding machine. In the final stage of the folding process, the protrusion 74 of the locking piece 56 formed on the top lid 6 elastically overcomes the lockable piece 40 formed on the lid body 4, and the locking piece 56 is thus elastically locked to the lockable piece 40. When the locking piece 56 is locked to the lockable piece 40, the guide surface 88 formed on the upper surface of the lockable piece 40 cooperates with the inclined lower surface 78 formed on the protrusion 74 of the locking piece 56 to allow the protrusion 74 to smoothly clear the lockable piece 40. For details of the folding process, please refer to the specification of Patent Application No. 2021-175414, filed prior to this application by the applicant of this application.

As shown in Figure 7, in the illustrated embodiment, when the locking piece 56 is elastically locked to the locked piece 40, the lower horizontal portion 84 of the locked piece 40 is positioned vertically opposite the upper locking surface 76 of the locking piece 56. The other circumferential end of the locked piece 40 is positioned slightly away from the locking piece 56 on the other circumferential side, while the one circumferential end of the locked piece 40 is positioned sufficiently away from the locking piece 56 on the one circumferential side. The locking piece 56 covers the kanji character "open" 96a arranged on the outer surface of the mounting wall 12, making it invisible, and only the kanji character "close" 96b is visible.

At this time, as shown in Figure 8, the annular engaging ridge 62 of the top lid 6 engages with the outer peripheral surface or underside of the engaging ridge 30 of the lid body 4, the annular abutting ridge 64 of the top lid 6 abuts against the upper surface of the engaging wall 28 of the lid body 4, the outer peripheral surface of the inner cylindrical wall 50 of the top lid 6 is brought into close contact with the inner peripheral surface of the pouring guide wall 26 of the lid body 4, and, as shown in Figure 7, the thin-walled arc-shaped protruding piece 60 of the top lid 6 is positioned in the notch 36 of the lid body 4.

Figures 7 and 8 show, by two-dot chain lines, a container lid 2 constructed in accordance with the present invention, as well as the neck of a container to which such container lid 2 is applied. The container neck 100, which can be formed from an appropriate synthetic resin or glass, has a cylindrical shape with an open top, and a locking ridge 102 is formed on the upper end of its outer periphery. The outer periphery of the neck 100 also has a support ring 104 (used when transporting the container) located below the locking ridge 102.

When the container lid 2 is attached to the neck portion 100 and the neck portion 100 is sealed after the contents have been placed inside the container, the container lid 2 (more specifically, the container lid 2 with the top lid 6 in the closed position relative to the lid body 4) is fitted onto the neck portion 100 and forced downward, elastically deforming the mounting wall 12 of the lid body 4 and causing the locking means 34 formed on the inner surface of the mounting wall 12 to lock beneath the locking ridge 102 on the neck portion 100.

When the contents of the container are to be consumed, a finger is placed under the flange 58 of the top lid 6, and an upward force is applied to the flange 58 around the hinge means 8, causing the top lid 6 to pivot from the closed position to the open position, i.e., pivot open. Referring to Figure 8, in the initial stage of this pivot open movement, the locking piece 56 on the top lid 6 engages with the lockable piece 40 on the lid body 4. More specifically, the locking upper surface 76 of the protrusion 74 on the locking piece 56 engages with the lower horizontal portion 84 of the lockable piece 40. This upward force exerts a vertical tensile force on the breakable bridge 68 connecting the locking piece 56 and the skirt wall 48, causing it to break. Here, in a container lid constructed according to the present invention, it is important that, when the breakable bridge portion 68 is broken, the locking piece 56 moves downward toward one side in the circumferential direction along the locked piece 40. When the breakable bridge portion 68 is broken, the locking piece 56 separates from the skirt wall 48, and the support lower surface 72 of the locking piece 56 (flange portion 70) engages with the upper inclined portion 82 of the locked piece 40, causing gravity to move (slide) the locking piece 56 toward one side in the circumferential direction along this upper inclined portion 82. Then, when the locking piece 56 slides to one end in the circumferential direction, as shown in Figure 9(c), the locking piece 56 covers the kanji character "close" ("close") indicia 96b arranged on the outer surface of the mounting wall 12, making it invisible, and only the kanji character "open" ("open") indicia 96a becomes visible.

In the container lid of the present invention, the engaging piece 40 is inclined downward toward one side in the circumferential direction along the outer surface at a position spaced radially outward from the outer surface of the mounting wall 12, and when the breakable bridge portion 68 is broken, the engaging piece 56 is caused to move downward toward one side in the circumferential direction along the engaging piece 40, so that the user can clearly recognize that the top lid 6 has been opened relative to the lid body 4, and the container lid has good tamper-evident properties.
After the breakable bridge portion 68 breaks and the locking piece 56 is separated from the top cover 6, the lower surface of the flange portion 70 engages with the upper inclined surface portion 82 of the locking piece 40, restricting downward movement of the locking piece 56 relative to the locking piece 40. Upward movement of the locking piece 56 relative to the locking piece 40 is restricted by the locking upper surface 76 of the locking piece 56 engaging with the lower inclined surface portion 86 of the locking piece 40. Furthermore, circumferential movement of the locking piece 56 relative to the locking piece 40 is restricted by the circumferential side surface of the locking piece 56 abutting against the side surface 92. Therefore, in the container lid of the illustrated embodiment, even if the breakable bridge portion 68 breaks and the locking piece 56 is separated from the top lid 6, the locking piece 56 will not separate from the locked piece 40, i.e., the container lid 2, but will continue to be held by it, so the locking piece 56 itself will not become waste.

After the breakable bridge 68 is broken, the top cover 6 is pivoted open from the closed position to the open position, exposing the upper surface of the closing wall 10 of the cover body 4, as shown in FIG. 10. The pull ring 24 of the cover body 4 is then forced upward with a finger, breaking the endless thin-walled breakable line 18 and removing the removal area 20 from the closing wall 10, thus creating a discharge opening. The contents of the container are then discharged through the discharge opening by tilting the container appropriately. After the contents have been discharged, the top cover 6 is pivoted back to the closed position and reattached to the cover body 4.

While the synthetic resin container lid of the present invention has been described in detail above with reference to the accompanying drawings, the present invention is not limited to the above-described embodiment, and various modifications are contemplated within the scope of the present invention. For example, in the illustrated embodiment, the engaging piece 40 is inclined downward toward the hinge means 8, i.e., one circumferential side is in a direction approaching the hinge means. However, by appropriately selecting the inclination angle, the engaging piece can also be inclined downward in a direction away from the hinge means. Also, in the illustrated embodiment, the outer surface of the mounting wall is provided with indicia 96a and indicia 96b, but either or both may be omitted. Furthermore, in the illustrated embodiment, the endless thin-walled breakable line 18 is broken by the tension ring 24 to create a discharge opening in the closure wall 10. However, any suitable method other than the tension ring may be used to create a discharge opening in the closure wall. For example, as shown in Japanese Patent Application No. 2021-137189, filed by the applicant prior to this application, the closing wall of the lid body and the top wall of the upper lid can be connected by an appropriate connecting means, so that the endless thin-walled breakable line breaks at the same time that the upper lid is pivoted open from the closed position.

2: Container lid 4: Lid body 6: Upper lid 8: Hinge means 10: Closing wall 12: Mounting wall 40: Locking piece 46: Top wall 48: Skirt wall 56: Locking piece 68: Breakable bridge portion 70: Flange portion 72: Supporting lower surface

Claims (9)

The container comprises a lid body, and a top lid connected to the lid body via a hinge means and rotatable between a closed position that covers an upper surface of the lid body and an open position that exposes the upper surface of the lid body,
the lid body includes a closing wall and a cylindrical mounting wall depending from the periphery of the closing wall, and the upper lid includes a top wall and a skirt wall depending from the periphery of the top wall,
a locking piece extending downward via a breakable bridge portion is disposed on the skirt wall, and a locking piece to which the locking piece is locked is disposed on the mounting wall when the top lid is turned to the closed position, and when the top lid is turned from the closed position to the open position, the breakable bridge portion is broken and the locking piece is separated from the skirt wall;
the locking piece has a flange portion extending radially outward below the breakable bridge portion, and the locked piece is inclined downward toward one side in the circumferential direction along the outer surface of the mounting wall at a position spaced radially outward from the outer surface of the mounting wall,
A synthetic resin container lid characterized in that, when the breakable bridge portion is broken, the lower surface of the flange portion of the locking piece is locked to the upper surface of the locked piece, and the locking piece is moved downward toward one side in the circumferential direction along the locked piece. The synthetic resin container lid according to claim 1, wherein the one circumferential side is the direction approaching the hinge means. The synthetic resin container lid according to claim 1 or 2, wherein the upper surface of the engaging piece is divided into a relatively short upper horizontal portion located on the other circumferential side, and a relatively long upper inclined portion that slopes downward from one circumferential end of the upper horizontal portion toward that circumferential side. A synthetic resin container lid according to any one of claims 1 to 3, wherein an open recess is formed at the upper end of the outer peripheral surface of the mounting wall, the engaging piece is disposed in the recess, and the outer peripheral surface of the engaging piece is located on the same circumferential plane as the outer peripheral surface of the mounting wall or radially inward therefrom. The synthetic resin container lid of claim 4, wherein both circumferential ends of the engaging piece are connected to the mounting wall at side surfaces that define both circumferential end faces of the recess. A synthetic resin container lid according to any one of claims 1 to 5, wherein at least one marking is disposed on the outer surface of the mounting wall, and the marking is selectively visible depending on the circumferential position of the locking piece. A synthetic resin container lid as described in any one of claims 1 to 6, wherein the locking piece has a flange portion extending radially outward below the breakable bridge portion, the radially outer end of the flange portion being located radially outward from the outer circumferential surface of the skirt wall, and the underside of the flange portion is formed with a support lower surface that is supported by the upper surface of the lockable piece after the breakable bridge portion is broken. A synthetic resin container lid according to any one of claims 1 to 7, wherein the locking pieces are provided on both sides of the diameter perpendicular to a diameter passing through the circumferential central angular position of the hinge means in a plan view. A synthetic resin container lid according to any one of claims 1 to 8, wherein a removal area is defined in the closure wall by an endless thin-walled breakable line, and a connecting post extending upward is disposed on the upper surface of the removal area, and a tension ring is connected to the upper end of the connecting post.