Synthetic resin-made container, preform, and method of manufacturing synthetic resin-made container

A preform that is made of a synthetic resin, has an outer body and an inner body laminated on an inner surface of the outer body, and is used in stretch blow molding, the preform comprising:

• a tubular mouth portion;
• a barrel portion located below the mouth portion;
• and
• a bottom portion closing a lower end of the barrel portion,
• wherein the mouth portion has an outside air introduction hole formed through the outer body,
• the inner body is made of a crystalline resin, and has, in at least a part of the mouth portion in the inner body, a crystallized region having a higher degree of crystallinity than other regions,
• an air passage rib extending in a vertical direction is formed on an outer circumferential surface in at least a part of the crystallized region, and
• the air passage rib extends from above the outside air introduction hole to the crystallized region.

A method of manufacturing a synthetic resin-made container by stretch blow molding a preform that has an outer body and an inner body laminated on an inner surface of the outer body, the preform including:

• a tubular mouth portion;
• a barrel portion located below the mouth portion;
• and a bottom portion closing a lower end of the barrel portion, wherein the mouth portion has an outside air introduction hole formed through the outer body, the method comprising:
• molding the outer body and the inner body that is made of a crystalline resin;
• reheating and cooling at least a part of the mouth portion in the inner body, to form a crystallized region having a higher degree of crystallinity than other regions;
• fitting the inner body having the crystallized region onto an inner circumferential surface of the outer body, to form a preform;
• and
• stretch blow molding the preform to form a synthetic resin-made container,
• wherein the synthetic resin-made container includes a shoulder portion located below a mouth portion corresponding to the mouth portion of the preform, above a barrel portion corresponding to the barrel portion of the preform, and increasing in diameter downward,
• the shoulder portion has a vertical rib extending in a vertical direction, the vertical rib being concave or convex,
• a groove depth of the vertical rib that is concave or a projection height of the vertical rib that is convex is smaller in at least one of an upper end and a lower end of the vertical rib than in a center of the vertical rib, and
• the upper end of the vertical rib is an end nearer to the mouth portion of the synthetic resin-made container, the lower end of the vertical rib is an end nearer to the barrel portion of the synthetic resin-made container, and the center of the vertical rib is between the upper end and the lower end.