Patent ID: 12187496

MODE FOR CARRYING OUT THE INVENTION

For the plastic cap of the present invention, the following are important features: The outer ring has a shape inclined toward the interior of the cap. In the closed state, sealability is maintained at least by the outer ring. The seal point of the inner ring after the seal by the outer ring is released is located above the starting point of the screw of the container mouth.

As stated earlier, the inner surface of the container mouth, which corresponds to parts where notches are formed in the screw of the container mouth for the purpose of forming a vent in the screw, may be formed with irregularities. According to the present invention, however, even if the inner ring contacts the inner surface portion of the container mouth where the irregularities may occur, sealability is ensured by the outer ring. After sealing by the outer ring is released, on the other hand, a seal point is produced by the inner ring which lies at a position above the starting point of the screw of the container mouth, namely, at a position on the inner surface of the container mouth where there is no risk of irregularity formation. Hence, even if irregularities are formed on the inner surface of the container mouth corresponding to the parts where the notches are formed in the screw, reliable sealability is ensured.

The present invention will be described below based on the accompanying drawings.

FIG.1is a side view showing an example of the mouth of a resin container to which the plastic cap of the present invention is applied. A screw2of the mouth1of the container has notches3a,3bprovided in a threaded part2aat an upper level and a threaded part2bat a lower level, respectively, to form a vent3A extending axially. Here, the mouth of the container has two vents (not shown) except for the illustrated vents3A,3B, and the four vents in total are formed. In the container mouth of this configuration, protrusions ascribed to the threaded parts and depressions ascribed to the notches are formed on the outer surface of the container mouth simultaneously with the molding of the container. The container mouth corresponding to the protrusions of the threaded parts is thick-walled and has large sink marks, and the inner surface of the container mouth tends to have a large inner diameter. In contrast, the container mouth corresponding to the depressions of the notches, as compared with the protrusions, is thin-walled and has small sink marks, and the inner surface of the container mouth tends to have a small inner diameter. Thus, irregularities tend to occur in the neighborhood of the inner surface of the container mouth corresponding to the notches.

A step5associated with a parting line produced during container molding is formed on an outer surface near the leading end of the container mouth.

An engaging projection6for engagement with flap pieces formed on the inner surface of the TE band of the cap is formed in a lower part of the container mouth.

FIG.2is a view showing an example of the plastic cap according to the present invention, the right half of the view being a side view, and the left half of the view being a side sectional view.

The plastic cap of the present invention, indicated entirely at10, comprises a cap body10acomposed of a top plate section11, and a skirt section12suspending from the peripheral edge of the top plate section11; and a TE band20molded integrally with the cap body10avia a weakened portion17. The top plate section11is formed with an inner ring13for contacting the inner surface1aof the container mouth1to ensure sealability; an outer ring14for contacting the outer surface1bof the container mouth; and a contact ring15formed between the inner ring13and the outer ring14, and located outwardly of the base of the inner ring13, for making contact with the leading end1cof the container mouth. In the skirt section12, a screw16is formed for engaging the screw2formed in the container mouth. On the inner surface of the TE band20, a plurality of flap pieces21extending upward from the lower end are formed.

FIG.3is a side sectional view showing a state in which the plastic cap shown inFIG.2is applied to the container mouth shown inFIG.1.

In the present invention, the inner surface of the outer ring14has a shape inclined toward the interior of the cap. As shown inFIG.3, therefore, the inner surface and the outer surface of the outer ring14are in pressure contact with the outer surface1bof the container mouth as if embracing the outer surface1bfrom outside, so that an innermost diameter portion at the lower end of the inner surface of the outer ring14serves as a seal point P1. In a closed state, sealability between the container mouth1and the cap10is ensured by the seal point P1ascribed to the outer ring14.

In this state, moreover, a seal point Q1of an outermost diameter portion of the outer side surface of the inner ring13makes intimate contact with the inner surface1aof the container mouth downwardly of the seal point P1of the outer ring14and in the neighborhood of the threaded part2aat the upper level in the container mouth (concretely, at a position on the inner surface of the container mouth corresponding to the notch3aformed first in a path beginning at a starting point4of the screw of the container mouth1shown inFIG.1and heading in the direction of threading). The location of the inner surface1aof the container mouth intimately contacted by the seal point Q1of the inner ring13is in the vicinity of the threaded part2a. Thus, there is a possibility for the occurrence of irregularities at this location of the surface. In the cap of the present invention, as mentioned above, the inner surface of the outer ring14has a shape inclined inward. Even if the sealability by the seal point Q1of the inner ring13fails to be ensured, therefore, the sealability is ensured by the seal point P1of the outer ring14. Furthermore, the contact ring15also makes intimate contact with the leading end1cof the container mouth. Consequently, the cap intimately contacts the container mouth at least at the two points of the outer ring14and the contact ring15, thereby ensuring the sealability.

FIG.4is a side sectional view showing a state in which the cap is turned in an unsealing direction from the closed state shown inFIG.3, whereby the seal by the outer ring14is released.

When the cap10is turned for unsealing, and begins to

move upward, the contact ring15first leaves the leading end1cof the container mouth. Then, the pressure contact between the seal point P1of the outer ring14and the outer surface1bof the container mouth is released. In this state, the seal point Q1of the inner ring13is in pressure contact with the inner surface1aof the container mouth above the starting point4of the threaded part2aof the container mouth. That is, the seal point Q1of the inner ring13maintains the intimate contact state while moving upward, during the unsealing step beginning in the closed state ofFIG.3and ending in the state of release of seal by the outer ring14inFIG.4. In the state ofFIG.4, moreover, the seal point Q1makes pressure contact with a thread-free region located above the inner surface region, where irregularities may have been generated, in the inner surface1aof the container mouth. Hence, reliable sealability by the inner ring13is ensured.

The inner ring13also has a straight-line portion13asuspending from the top plate section11, and the outer surface of the inner ring13bulges out in an arcuate form, whereby the seal point Q1makes intimate contact with the form of the inner surface1aof the container mouth. Thus, the straight-line portion13aelastically deforms in accordance with the seal point Q1.

FIG.5is a side sectional view showing a state in which the cap10is further turned in the unsealing direction from the state of release of the sealing by the outer ring14shown inFIG.4, whereby the weakened portion17connecting the cap body10aand the TE band20together is broken (bridge break). That is, as the turning of the cap for unsealing proceeds, the TE band20, whose flap pieces21are in engagement with the engaging projection6of the container mouth, cannot follow the ascent of the cap body10a. Thus, the breakable weakened portion17is broken (bridge break). In this state, the outer ring14does not contact the container mouth, but the seal point Q1of the inner ring13is in pressure contact with the thread-free region where no thread of the container mouth is formed, namely, the site of the inner surface1aof the container mouth where no irregularities are formed. Thus, reliable sealability is maintained.

FIG.6is a side sectional view showing a state in which the cap is further turned in the unsealing direction from the state of division of the weakened portion17of the TE band20shown inFIG.5, whereby the seal point Q1of the inner ring13is separated from the inner surface1aof the container mouth (seal break). The seal point Q1of the inner ring13makes no contact any more with the site of the inner surface1aof the container mouth corresponding to the thread-free region. At this very point of time, the sealability of the container is released (seal break).

With the plastic cap of the present invention, it is important that in the closed state, the outer ring be capable of ensuring sealability. The length of the outer ring that fulfills this condition varies with the shape of the mouth of the container to which the cap is to be applied. Preferably, however, the outer ring has a length of 1.0 to 1.6 mm. The angle of inclination of the inner surface of the outer ring toward the interior of the cap (the angle with respect to the axial direction) is preferably 10° or less, especially 4 to 10°.

For the container mouth according to the present invention, the turning angle of the cap during initial unsealing varies with the pitch or the like of the screws of the container mouth and the cap. In the case of a resin container of a generally distributed size, the turning angle is 120 to 180 degrees, and the vertical axial height is 0.3 to 0.6 mm, for a turn from the closed state ofFIG.3to the state ofFIG.4; the turning angle is 190 to 230 degrees, and the vertical axial height is 1.0 to 1.4 mm, for a turn from the state ofFIG.3to the state ofFIG.5; and the turning angle is 270 to 310 degrees, and the vertical axial height is 1.8 to 2.2 mm, for a turn from the state ofFIG.3to the state of seal break inFIG.6.

In a PCO-1881 bottle (outer diameter of the mouth: 28 mm, pitch of the screw: 2.7 mm), a general container as a polyester bottle, the turning angle is set to be about 150 degrees for a turn from the sealed state ofFIG.3to the state ofFIG.4, about 60 degrees for a turn from the state ofFIG.4to the state ofFIG.5, and about 80 degrees for a turn from the state ofFIG.5to the state of seal break inFIG.6. By not forming the notch that should be formed in the threaded part at the uppermost level where the vent3A, which is first formed in the path beginning at the starting point of the screw and heading in the direction of threading, is to be formed, the inner surface of the container is smoothly formed at the turning angle after the release of the seal by the outer ring, but before the seal break. Thus, sealing by the inner ring can be performed reliably.

The site of the inner surface of the container mouth, which the inner ring contacts and where the irregularities attributed to the difference in the amount of resin shrinkage occur, is a site 1.7 mm or more below the upper end of the container mouth. In the state ofFIG.3, the inner ring intimately contacts a site 1.8 to 2.2 mm below the upper end of the container mouth. When turned to the state ofFIG.4, the cap10moves upwards by 0.3 to 0.6 mm. During its turn from the state ofFIG.3to the state ofFIG.4, therefore, the seal point Q1of the inner ring13moves to a site with a smaller difference in the wall thickness and a smaller difference in the rate of resin shrinkage in the inner surface of the container, and makes pressure contact with the site. Afterwards, the cap10is turned from the state ofFIG.4until the weakened portion breaks. At this time, the cap10ascends from the state of the closed state ofFIG.3by 1.0 to 1.4 mm. The cap10, i.e., the seal point Q1of the inner ring13, ascends by 1.8 to 2.2 mm from the closed state ofFIG.3until the seal break ofFIG.6.

Let the axial length from the upper end of the above-mentioned site of the inner surface of the container mouth, which the inner ring contacts and where the irregularities attributed to the difference in the amount of resin shrinkage occur (i.e., the upper end of the notch formed in the threaded part at the uppermost level), to the upper end of the container mouth be W; the distance for which the cap10ascends from the closed state ofFIG.3to the state of release of the sealing by the outer ring inFIG.4be X; the distance for which the cap10ascends from the closed state ofFIG.3to the state of breakage of the weakened portion17inFIG.5be Y; and the distance for which the cap10ascends from the closed state ofFIG.3to the state of the seal break inFIG.6be Z. Then, the relationships Y<Z and X>Z−W hold. The distances W, X, Y and Z are shown inFIG.7.

The plastic cap of the present invention uses, for example, a thermoplastic resin, such as low, medium or high density polyethylene, linear low density polyethylene, isotactic polypropylene, syndiotactic polypropylene, poly-1-butene, poly-4-methyl-1-pentene, random or block copolymer of α-olefins such as ethylene, propylene, 1-butene, or 4-methyl-1-pentene, ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-(meth)acrylate copolymer, or ion crosslinked olefin copolymer (ionomer). The plastic cap can be molded, for example, by compression molding or injection molding.

INDUSTRIAL APPLICABILITY

The plastic cap of the present invention can be used for a resin container formed with a vent mechanism, in which a screw and a notch constituting a vent are formed simultaneously with the molding of the mouth of the container, so that irregularities due to molding strain such as sink marks are apt to occur in the inner surface of the mouth of the container.

Such a resin container formed with a vent mechanism is put to a use for filling contents having an autogenous pressure, such as a carbonated beverage, and a use such as aseptic filling or hot packing (hot filling). In the present invention, in particular, the resin container can be put suitably to a use such as aseptic filling using a polyethylene terephthalate bottle having an uncrystallized mouth.

EXPLANATIONS OF LETTERS OR NUMERALS

1container mouth;2screw;3A,3B vents;3a,3bnotches;4starting point of screw;5step;6engaging projection;10cap;11top plate section;12skirt section;13inner ring;14outer ring;15contact ring;16screw;17weakened portion;20TE band;21flap piece.