Plastic cap and production method thereof

1. A plastic cap that securely maintains a sealed state of a container that has a mouth having an opening defined therein and sealed with a sealing member, the plastic cap comprising:

a cap main body formed of first plastic resin;

a cover portion formed of second plastic resin;

at least one bridge portion; and

at least one protuberance having a bore therein,

wherein the cover portion is integrated with the cap main body via integral fusion-bonding provided by the at least one bridge portion,

the cap main body, the cover portion, and the bridge portion are formed as different components from each other,

the cap main body has a base portion, which is configured so as to surround the mouth of the container to which the cap is applied, and a top wall integrally arranged so as to be continuous to the base portion,

the cover portion is arranged facing the top wall of the cap main body,

the at least one bridge portion is formed of third plastic resin, which is a synthetic thermoplastic resin, filled in at least one fusion-bonding hole and in the bore, which is continuous to the at least one fusion-bonding hole,

both the at least one fusion-bonding hole and the at least one protuberance having the bore are present together in only one of the cap main body and the cover portion,

wherein the at least one protuberance is formed on an upper surface of the top wall of the cap main body or a lower surface of the cover portion, and the lower surface of the cover potion is facing the upper surface of the top wall of the cap main body,

the at least one bridge portion is in a shape corresponding to a combined shape of the at least one fusion-bonding hole and the bore in the at least one protuberance,

the integral fusion-bonding between the cap main body and the cover portion is provided at an interface between an end surface of the bridge portion, which is an end surface of the bore of the at least one protuberance, and one of the lower surface of the cover portion and the upper surface of the cap main body, which is facing the protuberance and in which the at least one fusion-bonding hole and the at least one protuberance are not formed,

the at least one fusion-bonding hole has a diameter in a range from 0.3 to 3 mm and is arranged extending through the only one of the cap main body and the cover portion such that the cap main body and the cover portion are integrally fusion-bonded by the at least one bridge portion,

the cover portion is separable from the cap main body by separating by hand the at least one bridge portion formed in one of the cover portion and the cap main body from other one of the cover portion and the cap main body in which the at least one bridge portion is not formed, and

a standard deviation of pull force required to separate the cover portion from the cap main body of the plastic cap is smaller than a standard deviation of pull force required to separate a cover portion from a cap main body of a same plastic cap except that the cover portion and the cap main body are integrated by ultrasonic welding of the at least one protuberances, the ultrasonic welding being applied at 20.0 Ws, an amplitude of 18 μm, and a pressure of 0.01 MPa for 2.0 seconds, where the pull force is measured with 10 each of the plastic caps produced in a same way by pulling the cover portion from the cap main body at a pulling rate of 100 mm/min.

2. The plastic cap according to claim 1 , the plastic cap further comprising at least one recessed portion or at least one fixing portion, on the upper surface of the top wall of the cap main body or the lower surface of the cover portion, and at a location opposite to the at least one protuberance,

wherein the at least one recessed portion fixes the protuberance, and the at least one fixing portion is configured so as to fit on an outer circumference of the protuberance.

3. The plastic cap according to claim 1 , wherein the plastic cap has the bridge portions as defined in claim 1 in a number from three to five portions, wherein the bridge portions are arranged with angular intervals therebetween.

4. The plastic cap according to claim 1 , the plastic cap further comprising:

at least one component selected from the group consisting of a land portion and a claw portion; and

a window portion,

wherein the at least one component is arranged on an inner wall of the base portion of the cap main body and engages with an annular lip arranged on an outer circumference of the mouth of the container,

the window portion is centrally arranged through the top wall of the cap main body, and

the cover portion is configured so as to cover at least the window portion.

5. The plastic cap according to claim 1 ,

wherein the plastic cap further comprises the sealing member so that the sealing member is placed between the opening of the mouth of the container and the top wall of the cap main body upon capping of the mouth of the container.

6. A production method of a plastic cap that securely maintains a sealed state of a container that has a mouth having an opening defined therein and sealed with a sealing member, the method comprising:

a step of filling a molten third plastic resin, which is a synthetic thermoplastic resin, in at least one fusion-bonding hole and a bore, which is continuous to the at least one fusion-bonding hole, in at least one protuberance of the plastic cap; and

solidifying the molten synthetic thermoplastic resin,

wherein said plastic cap comprises:

a cap main body formed of first plastic resin; and

a cover portion that is integrated with the cap main body via integral fusion-bonding provided by at least one bridge portion and formed of second plastic resin; and

the at least one protuberance having the bore therein,

the cap main body, the cover portion, and the bridge portion are formed as different components from each other,

said cap main body has a base portion, which is configured so as to surround the mouth of the container to which the cap is applied, and a top wall integrally arranged so as to be continuous to the base portion,

upon integrating, via the at least one bridge portion, the cover portion faces the top wall of the cap main body,

both the at least one fusion-bonding hole and the at least one protuberance having the bore are present together in only one of the cap main body and the cover portion,

wherein the at least one protuberance is formed on an upper surface of the top wall of the cap main body or a lower surface of the cover portion, and the lower surface of the cover potion is facing the upper surface of the top wall of the cap main body,

the at least one bridge portion is in a shape corresponding to a combined shape of the at least one fusion-bonding hole and the bore in the at least one protuberance,

the integral fusion-bonding between the cap main body and the cover portion is provided at an interface between an end surface of the bridge portion, which is an end surface of the bore of the at least one protuberance, and one of the lower surface of the cover portion and the upper surface of the cap main body, which is facing the protuberance and in which the at least one fusion-bonding hole and the at least one protuberance are not formed,

the at least one fusion-bonding hole has a diameter in a range from 0.3 to 3 mm and is arranged extending through only one of the cap main body and the cover portion such that the cap main body and the cover portion are integrally fusion-bonded by the at least one bridge portion,

the cover portion is separable from the cap main body by separating by hand the at least one bridge portion formed in one of the cover portion and the cap main body from other one of the cover portion and the cap main body in which the at least one bridge portion is not formed, and

a standard deviation of pull force required to separate the cover portion from the cap main body of the plastic cap is smaller than a standard deviation of pull force required to separate a cover portion from a cap main body of a same plastic cap except that the cover portion and the cap main body are integrated by ultrasonic welding of the at least one protuberances, the ultrasonic welding being applied at 20.0 Ws, an amplitude of 18 μm, and a pressure of 0.01 MPa for 2.0 seconds, where the pull force is measured with 10 each of the plastic caps produced in a same way by pulling the cover portion from the cap main body at a pulling rate of 100 mm/min.

7. The plastic cap according to claim 1 ,

wherein the cap comprises at least one resin selected from the group consisting of polypropylene, polyethylene, and polycarbonate.

8. The plastic cap according to claim 1 ,

wherein each of the first plastic resin for the cap main body, the second plastic resin for the cover portion, and the third plastic resin for the at least one bridge portion comprises polypropylene.

9. The plastic cap according to claim 1 ,

wherein the first plastic resin for the cap main body and the second plastic resin for the cover portion comprise polypropylene, and the third plastic resin for the at least one bridge portion comprises polyethylene.

10. The plastic cap according to claim 1 ,

wherein the first plastic resin for the cap main body and the third plastic resin for the at least one bridge portion comprise polypropylene, and the second plastic resin for the cover portion comprises polyethylene.

11. The plastic cap according to claim 1 ,

wherein the shape of the at least one bridge portion is a cylindrical shape.

12. The plastic cap according to claim 1 ,

wherein the bore formed in the protuberance has a same dimeter as the diameter of the at least one fusion-bonding hole.

13. The plastic cap according to claim 1 , wherein the at least one bridge portion is retained entirely within the at least one fusion-bonding hole and the bore.