Preform assembly, double container, and method of manufacturing double container

A double container comprising:

• an outer layer body that includes a tubular outer mouth portion and a bottomed tubular barrel portion connected to the outer mouth portion via a shoulder portion and in which a thin wall portion or thick wall portion extending in a vertical direction is provided in the shoulder portion;
• and
• an inner layer body that includes a tubular inner mouth portion and a volume-reduction deformable containing portion connected to the inner mouth portion and separably laminated on an inner surface of each of the shoulder portion and the barrel portion,
• wherein an outside air introduction port communicating with a part between the outer layer body and the inner layer body is provided in a mouth portion composed of the outer mouth portion and the inner mouth portion located on an inner side of the outer mouth portion.

A method of manufacturing a double container, comprising:

• a preform formation step of forming each of an outer preform that includes a tubular outer mouth portion and a stretch portion connected to the outer mouth portion and in which a recess or ridge extending in a vertical direction is provided on an inner surface of the stretch portion and an inner preform that includes a tubular inner mouth portion and a stretch portion connected to the inner mouth portion, and incorporating the inner preform inside the outer preform to form a preform assembly in which an outside air introduction port communicating with a part between the outer preform and the inner preform is provided in a mouth portion composed of the outer mouth portion and the inner mouth portion located on an inner side of the outer mouth portion;
• and
• a blow molding step of heating the preform assembly to a temperature at which stretching is possible and blow molding the preform assembly into a double container including:
• an outer layer body that includes the outer mouth portion and a bottomed tubular barrel portion connected to the outer mouth portion via a shoulder portion and in which a thin wall portion or thick wall portion extending in the vertical direction is provided in the shoulder portion;
• and an inner layer body that includes the inner mouth portion and a volume-reduction deformable containing portion connected to the inner mouth portion and separably laminated on an inner surface of each of the shoulder portion and the barrel portion, wherein an outside air introduction port communicating with a part between the outer layer body and the inner layer body is provided in a mouth portion composed of the outer mouth portion and the inner mouth portion located on the inner side of the outer mouth portion.