Preform, double container and method of manufacturing thereof

A double container comprising a container body including an inner bag and an outer shell, wherein

• the container body includes a mouth part and a body part and a bottom part,
• the mouth part is a tubular portion having an open end,
• the body part is arranged adjacent to the mouth part on a side farther from the open end than the mouth part, and has a larger outer diameter than the mouth part,
• the bottom part is configured to close a lower end of the body part,
• the body part includes a shoulder part that increases in outer diameter as it moves away from the mouth part,
• the shoulder part is provided in each of the inner bag and the outer shell,
• a concave-convex shape that reduces a contact area between an outer surface of the inner bag and an inner surface of the outer shell is provided in each of the outer surface of the inner bag and the inner surface of the outer shell in the shoulder part of the container body,
• the outer surface of the inner bag and the inner surface of the outer shell contact each other at a convex part of the concave-convex shape and do not contact each other at a concave part of the concave-convex shape, and
• the container body is a biaxial stretch blow-molded article of a preform that is configured by covering an inner preform that becomes the inner bag with an outer preform that becomes the outer shell.

A double container comprising a container body including an inner bag and an outer shell, wherein

• the double container is configured such that a mouth part of the inner bag moves in a direction to escape from the outer shell by rotating the inner bag relative to the outer shell,
• the inner bag is configured to be able to move in the direction by a cam mechanism,
• the cam mechanism is realized by an engagement structure having direct contact between the outer shell and the inner bag,
• the container body is a biaxial stretch blow-molded article of a preform that is configured by covering an inner preform that becomes the inner bag with an outer preform that becomes the outer shell,
• the body part of the outer shell includes a shoulder part of the outer shell that increases in outer diameter as it moves away from the mouth part of the outer shell, and
• the body part of the inner bag includes a shoulder part of the inner bag that increases in outer diameter as it moves away from the mouth part of the inner bag.