Synthetic resin container lid

Abstract

To provide a new synthetic resin container lid which prevents flow marks from forming on an upper edge of an inner surface of a skirt wall.SOLUTION: The upper edge of the inner surface of a skirt wall 6 (the part indicated by number 30) is finished with a pear-skin texture.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a synthetic resin container lid, and more specifically to a synthetic resin container lid having a circular top wall and a cylindrical skirt wall hanging down from the outer peripheral edge of the top wall, with a female thread formed in the middle of the inner peripheral surface of the skirt wall in the vertical direction. [Background technology]

[0002] A typical example of the synthetic resin container lid of the above-mentioned form is shown in the following Patent Document 1. When such a synthetic resin container lid is attached to the mouth and neck of a container, the container lid is fitted onto the mouth and neck and then rotated in the plugging direction relative to it, and is lowered relative to the mouth and neck until the lower surface of the top wall abuts against the top surface of the mouth and neck by the male thread formed on the outer circumferential surface of the mouth and neck and the female thread formed on the inner circumferential surface of the skirt wall screwing together. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 4098797 Summary of the Invention [Problem to be solved by the invention]

[0004] In the synthetic resin container lid of the above-mentioned form, when the lower surface of the top wall comes into contact with the top surface of the mouth and neck part and is then rotated further in the plugging direction relative to the mouth and neck part, the skirt wall tries to descend relative to the mouth and neck part due to the above-mentioned screw engagement, but the top wall is prevented from descending relative to the mouth and neck part by the top surface of the mouth and neck part, so that tensile stress acts on the skirt wall. At this time, because the female thread is formed on the inner peripheral surface of the skirt wall, the skirt wall is pulled downward at a slight radial inward incline, so that the load is concentrated on the upper end of the inner peripheral surface of the skirt wall.

[0005] Meanwhile, grooves with a peculiar pattern called flow marks, which are a type of molding defect, may be formed on the surface of the synthetic resin container lid (here, "surface" refers to the surface that comes into contact with air, and includes not only the outer surface of the container lid but also the inner surface). According to the experience of the present inventors, one of the parts where such flow marks are likely to occur is the upper end of the inner peripheral surface of the skirt wall. Normally, during molding, the softened synthetic resin material moves from the space that defines the top wall to the space that defines the skirt wall in the molding die. When the softened synthetic resin material enters the space that defines the skirt wall from the space that defines the top wall, the flow of the softened synthetic resin material is bent by approximately 90 degrees. At this time, since the softened synthetic resin material is a fluid, the speed of the fluid in the bent part is faster on the inside than on the outside when viewed in the flow direction. This is because the pressure is lower on the inside than on the outside. When the pressure of the fluid is reduced, the density, i.e., the amount of resin per unit space, also decreases, so molding defects, i.e., flow marks, are likely to be formed on the inside of the bent part. Therefore, flow marks are likely to occur at the upper end of the inner peripheral surface of the skirt wall. Although flow marks mostly occur during injection molding, they may also occur during compression molding depending on the molding conditions.

[0006] In the synthetic resin container lid of the above-mentioned configuration, if a flow mark occurs at the upper end of the inner surface of the skirt wall, when load is concentrated at the upper end of the inner surface of the skirt wall as described above, there is a risk that a crack will occur starting from the groove, which is the flow mark.

[0007] The present invention has been made in consideration of the above-mentioned facts, and its main technical object is to provide a new and improved synthetic resin container lid which prevents the occurrence of flow marks at the upper end of the inner surface of the skirt wall, thereby preventing the occurrence of cracks at the upper end of the inner surface of the skirt wall, even if the lower surface of the top wall abuts against the top surface of the mouth and neck portion when the lid is closed and then the lid is further rotated in the closing direction relative to the mouth and neck portion. [Means for solving the problem]

[0008] As a result of extensive investigation, the present inventors have found that the above-mentioned main technical problem can be solved by forming the upper end of the inner peripheral surface of the skirt wall into a matte finish.

[0009] That is, according to the present invention, there is provided a synthetic resin container lid that solves the above-mentioned main technical problem, comprising a circular top wall and a cylindrical skirt wall that hangs down from the outer periphery of the top wall, and a female thread is formed in the vertical middle part of the inner periphery of the skirt wall, The upper end of the inner peripheral surface of the skirt wall is matte-finished, thereby providing a synthetic resin container lid.

[0010] Preferably, it is formed by injection molding. The upper end of the inner peripheral surface of the skirt wall extends downward from the outer peripheral edge of the lower surface of the top wall at an inclination radially outward and then extends vertically downward. Preferably, the maximum cross-sectional height (surface roughness) defined in JIS B 0601 at the upper end of the inner peripheral surface of the skirt wall is 2.0 to 12.0 μm. The skirt wall is formed with a fracture line extending in the circumferential direction, and the skirt wall is divided into a main portion above the fracture line and a tamper-evident bottom portion below the fracture line, and the female thread is formed on the inner peripheral surface of the main portion of the skirt wall, and a locking means is disposed on the inner peripheral surface of the tamper-evident bottom portion. Effect of the Invention

[0011] In the synthetic resin container closure of the present invention, the upper end of the inner peripheral surface of the skirt wall is matte, in other words, the portion defining the upper end of the inner peripheral surface of the skirt wall in the mold for forming the synthetic resin container closure of the present invention is matte, so that the softened synthetic resin material flowing in the mold during molding is decelerated in the vicinity of the portion. This increases the pressure of the synthetic resin material flowing in the vicinity of the portion during molding, preventing molding defects, i.e., flow marks consisting of grooves, from occurring in the portion. Therefore, even if the lower surface of the top wall comes into contact with the top surface of the neck portion during plugging and is then further rotated in the plugging direction relative to the neck portion, cracks are prevented from occurring in the upper end of the inner peripheral surface of the skirt wall. [Brief description of the drawings]

[0012] [Figure 1] 1 is a half cross-sectional view showing a preferred embodiment of a synthetic resin container lid constructed according to the present invention. [Diagram 2] 2 is an enlarged cross-sectional view showing the vicinity of the upper end portion of the inner peripheral surface of the skirt wall of the synthetic resin container lid shown in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a synthetic resin container lid according to an embodiment of the present invention; FIG.

[0014] Referring to FIG. 1, a container lid, generally designated by the numeral 2, which can be integrally molded from a suitable synthetic resin, has a circular top wall 4 and a cylindrical skirt wall 6 that hangs down from the outer periphery of the top wall 4. In the illustrated embodiment, the container lid 2 is formed by injection molding using a required mold. The inner periphery of the top wall 4 is formed with an annular protrusion 12 located between the inner seal piece 8 and the outer seal piece 10 as viewed in the radial direction, together with a cylindrical inner seal piece 8 and an outer seal piece 10 that are concentrically arranged. The skirt wall 6 is provided with a circumferentially extending circumferential break line 14, and the skirt wall 6 is divided into a main portion 16 above the circumferential break line 14 and a tamper-evident bottom portion 18 below the circumferential break line 14. The circumferential break line 14 is composed of a plurality of slits 20 that extend linearly in the circumferential direction at intervals in the circumferential direction and a plurality of breakable bridges 22 located between the slits 20. The circumferential breaking line 14 has a required width in the vertical direction, and at required circumferential positions in the slit 20, a plurality of protrusions 23 are formed, which protrude downward from the lower surface of the main portion 16 or upward from the upper surface of the tamper-evident hem portion 18. On the outer peripheral surface of the main portion 16 of the skirt wall 6, a knurl 24 is formed, which is formed of an uneven shape to prevent a finger from slipping when placed thereon. Also, a female thread 26 is formed on the inner peripheral surface of the main portion 16. A locking means 28 is disposed on the inner peripheral surface of the tamper-evident hem portion 18. In the illustrated embodiment, the locking means 28 is composed of a plurality of flap pieces arranged at intervals in the circumferential direction.

[0015] Here, in the container lid 2 constructed according to the present invention, it is important that the upper end portion of the inner peripheral surface of the skirt wall 6 (this portion is designated by the number 30 as a unique portion) is matte. The reason for this will be described later. In the illustrated embodiment, the unique portion 30 extends downward from the outer peripheral edge of the lower surface of the top wall 4, inclining radially outwardly and then extending vertically downward. The maximum cross-sectional height (surface roughness) of the unique portion 30 as defined in JIS B 0601 is preferably 2.0 to 12.0 μm.

[0016] In Fig. 1, the container lid 2 and the mouth and neck of the container to which the container lid 2 is attached are shown by a two-dot chain line. The container mouth and neck 32, which can be made of a suitable synthetic resin such as polyethylene terephthalate or glass, is generally cylindrical in shape and has an open top. On the outer periphery of the mouth and neck 32, there are formed a male thread 34, a locking jaw 36 located below the male thread 34, and a support ring 38 located further below the locking jaw 36. As is well known to those skilled in the art, the support ring 38 is used when the container is transported.

[0017] When the container lid 2 is fitted to the mouth and neck portion 32 to seal the mouth and neck portion 32 after filling the container with contents such as a soft drink, the container lid 2 is fitted onto the mouth and neck portion 32 and rotated in the closing direction, i.e., clockwise as viewed from above in Fig. 1. In this way, the female thread 26 of the container lid 2 is screwed into the male thread 34 of the mouth and neck portion 32, and the container lid 2 is relatively lowered as it rotates. When the container lid 2 is lowered to a required position, i.e., the position shown in Fig. 1, the annular protrusion 12 formed on the inner surface of the top wall 4 of the container lid 2 is brought into contact with the top surface of the mouth and neck portion 32, and the inner seal piece 8 and the outer seal piece 10 formed on the inner surface of the top wall 4 of the container lid 2 are brought into close contact or into contact with the inner and outer peripheral surfaces of the mouth and neck portion 32, respectively, thereby sealing the mouth and neck portion 32. The locking means 28 formed on the inner peripheral surface of the tamper-evident skirt 18 elastically climbs over the locking jaws 36 of the mouth and neck portion 32 and is positioned below them.

[0018] Here, when the container lid 2 is relatively lowered with rotation, if the container lid 2 is further rotated in the closing direction after the annular protrusion 12 formed on the inner surface of the top wall 4 of the container lid 2 is abutted against the top surface of the mouth and neck portion 32, the skirt wall 6 tries to descend toward the mouth and neck portion 32 due to the above-mentioned screwing, but the top wall 4 is prevented from descending toward the mouth and neck portion 32 by the top surface of the mouth and neck portion 32, and tensile stress acts on the skirt wall 6. At this time, since the female thread 26 is formed on the inner peripheral surface of the skirt wall 6, the skirt wall 6 is pulled downward with a slight radial inward inclination, so that the load is concentrated on the upper end of the inner peripheral surface of the skirt wall 6, i.e., the unique portion 30. As described above, this unique portion 30 is a place where flow marks are likely to occur, and if load is concentrated in the state where flow marks have occurred in the unique portion 30, there is a risk that cracks will occur starting from the flow marks.

[0019] However, in the container closure 2 constructed according to the present invention, the unique portion 30, i.e., the upper end of the inner peripheral surface of the skirt wall 6, is matte-finished. In other words, due to the fact that the portion defining the unique portion 30 in the mold for forming the container closure 2 is matte-finished, the softened synthetic resin material flowing in the mold during molding is decelerated in the vicinity of the portion. This increases the pressure of the synthetic resin material flowing in the vicinity of the portion during molding, preventing molding defects, i.e., flow marks consisting of grooves, from occurring in the portion. Therefore, even if the lower surface of the top wall 4 comes into contact with the top surface of the neck portion 32 during plugging and is then further rotated in the plugging direction relative to the neck portion 32, cracks are prevented from occurring in the upper end of the inner peripheral surface of the skirt wall 6. In the illustrated embodiment, the unique portion 30 extends downward from the outer peripheral edge of the lower surface of the top wall 4 at an incline radially outward and then extends vertically downward, so that the softened synthetic resin material during molding can flow smoothly along the surface of the mold from the portion defining the inner surface of the top wall 4 to the portion defining the unique portion 30, thereby avoiding a pressure drop in the synthetic resin material flowing near the portion defining the unique portion 30. If the surface roughness of the unique portion is 12.0 μm or more, the surface roughness of the mold portion becomes excessively large, which is undesirable because there is a risk that the mold portion may damage other portions of the container lid (e.g., the female thread) during demolding.

[0020] <Evaluation Results> Using four different required molds, container lids made of high density (0.960 g / cm3) polyethylene resin having the configuration shown in Figures 1 and 2 were injection molded. The four molds were identical in configuration except that the surface roughness of the portion defining the upper end of the inner peripheral surface of the skirt wall was different. In other words, three of the four molds were subjected to a matte finish with a different surface roughness, and the remaining one was not subjected to any particular matte finish. The container lids molded by each of the four molds were designated A1 to A4, and the surface roughness (maximum cross-sectional height defined in JIS B 0601) of the upper end of the inner peripheral surface of the skirt wall of each of the container lids A1 to A4 was measured, and the presence or absence of flow marks at the upper end of the inner peripheral surface of the skirt wall was visually observed. The results are shown in Table 1. The molding conditions were as follows. Melt flow rate (MFR): 6g / 10min Resin temperature during molding: 220℃ Resin pressure during molding: 150MPa

[0021] [Table 1]

[0022] According to the results shown in Table 1, the lower limit of the surface roughness is 2.0 μm or more. Considering the results in Table 1, this lower limit of the surface roughness can be said to be the depth of the groove of the flow mark (the flow mark generated at the upper end of the inner peripheral surface of the skirt wall) generated when molding is performed under the same molding conditions without applying any special matte finish to the molding die. As mentioned above, the upper limit of the surface roughness is preferably about 12.0 μm from the viewpoint of preventing damage to other parts during demolding.

[0023] Although the synthetic resin container lid constructed according to the present invention has been described in detail above with reference to the attached drawings, the present invention is not limited to the above-mentioned embodiment, and appropriate modifications and changes are possible within the scope of the present invention. For example, in the illustrated embodiment, no packing is provided on the underside of the top wall, but depending on the type of contents contained in the container, a packing may be provided on the underside of the top wall. [Explanation of symbols]

[0024] 2: Container lid 4: Top wall 6: Skirt wall 26:Female thread 30: Unique part (the upper end of the inner circumferential surface of the skirt wall, which is made matte)

Claims

1. A synthetic resin container lid having a circular top wall and a cylindrical skirt wall extending downward from an outer periphery of the top wall, the inner periphery of the skirt wall having a female thread formed in a vertically intermediate portion thereof, A synthetic resin container lid, characterized in that the upper end of the inner peripheral surface of the skirt wall is matte-finished.

2. 2. The synthetic resin container lid according to claim 1, which is formed by injection molding.

3. 2. The synthetic resin container lid according to claim 1, wherein the upper end of the inner peripheral surface of the skirt wall extends downward from the outer peripheral edge of the lower surface of the top wall at an inclination radially outward and then extends vertically downward.

4. 2. The synthetic resin container closure according to claim 1, wherein the maximum cross-sectional height (surface roughness) defined in JIS B 0601 at the upper end of the inner peripheral surface of the skirt wall is 2.0 to 12.0 μm.

5. 2. The synthetic resin container lid of claim 1, wherein a circumferentially extending break line is formed in the skirt wall, the skirt wall is divided into a main portion above the break line and a tamper-evident bottom portion below the break line, the female thread is formed on the inner peripheral surface of the main portion of the skirt wall, and a locking means is arranged on the inner peripheral surface of the tamper-evident bottom portion.

Images