Double container assembly and manufacturing method therefor

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.