Double container assembly and manufacturing method therefor
Provided is a manufacturing method for a double container that allows easy manufacturing with a molding device not significantly different from conventional devices and that can, at a lower cost than the processing cost of conventional technology, very easily and reliably form, in a comparatively rigid outer container and in a double container that allows, inside the outer container, capacity to be varied with respect to the amount of content, an opening for allowing external air to enter. When a pair of partial molds are brought near each other in order to form a split mold, at least part of the mating faces of the pair of partial molds forms a projection by sandwiching a small outer diameter portion of a parison, a gap that passes between the double container is created by cutting off the projection, and the gap is opened and expanded by screwing on a cap.
1. A method for manufacturing a double container assembly comprising a double container and a threaded cap, wherein the double container is molded, using a split mold as a combination of a pair of partial molds, from a parison comprising at least two layers of an inner layer and an outer layer forming, respectively, a rigid outer container layer and a flexible inner container layer which are separable from each other after molding, the double container being configured to introduce external air into a space between the rigid outer container layer and the flexible inner container layer to enable a capacity of the flexible inner container layer to be reduced, while retaining a shape of the rigid outer container layer, the method comprising:
a step A of: forming a large-outer-diameter region having a given outer diameter, in a cap-receiving threaded portion or a container body portion of the double container or a portion of the double container therebetween, and a small-outer-diameter region having an outer diameter less than that of the large-outer-diameter region, in a portion of the double container between the large-outer-diameter region and the cap-receiving threaded portion; and, during a course of moving the pair of partial molds to come close to each other so as to combine them together to make up the split mold, clamping a portion of the parison corresponding to the small-outer-diameter region by at least respective parts of mating surfaces of the pair of partial molds, to thereby form a clearance-caused burr;
a step B of removing the clearance-caused burr formed in the step A; and
a step C of forming the threaded cap such that, when the threaded cap is threadingly engaged with the cap-receiving threaded portion, it applies a tension to the small-outer-diameter region from which the clearance-caused burr has been removed, in a direction causing the cap-receiving threaded portion and the large-outer-diameter region to be pulled away from each other.
2. The method as recited in claim 1 , wherein the at least respective parts of the mating surfaces of the pair of partial molds clamp the parison at two horizontally opposed lateral positions.
3. The method as recited in claim 1 , wherein the at least respective parts of the mating surfaces of the pair of partial molds clamp the parison at a single position.
4. The method as recited in claim 1 , which comprises forming a protruding tub piece from the parison, at a position outward of a portion of the parison clamped by the at least respective parts of the mating surfaces of the pair of partial molds.
5. The method as recited in claim 1 , wherein a portion of the parison clamped by the at least respective parts of the mating surfaces of the pair of partial molds corresponds to a neck-shoulder portion of the double container.
6. The method as recited in claim 1 , wherein a portion of the parison clamped by the at least respective parts of the mating surfaces of the pair of partial molds corresponds to a mouth portion of the double container.
7. The double container manufacturing method as recited in claim 1 , wherein a portion of the parison clamped by the at least respective parts of the mating surfaces of the pair of partial molds corresponds to the cap-receiving threaded portion of the double container.