Patent ID: 8245869

Claim:
A process for manufacturing a packaging container for a microwave oven which is hermetically sealed by heat-sealing a lid to a periphery of a flange part of a container body made of a synthetic resin, comprising at least one steam releasing seal part having a weakened part inside a peripheral seal part of the flange part at a position separated from the peripheral seal part, wherein the steam releasing seal part is provided in the flange part and comprises an outer seal part, a buffer part adjacent to the outer seal part, and a weakened part made of a through-hole formed in the flange part of the buffer part, and wherein a convex part is provided at a position corresponding to the outer seal part of the steam releasing seal part of the flange part, and the outer seal part of the steam releasing seal part is formed by heat-sealing the convex part to the lid, said process comprising: forming a convex part and a through-hole as a weakened part both provided in a flange part simultaneously, when a packaging container body is manufactured by processing a plastic sheet.