Sealant film, multilayer film including same, packaging bag and packaging container, and method for producing sealant film

A method for producing a sealant film comprising a polyester layer containing polyester as a main ingredient,

• wherein the production method of the sealant film comprises an extrusion step of extruding a resin constituting the polyester layer, by an inflation method,
• a temperature in the extrusion step is 180° C. or more and 260° C. or less,
• the polyester is made of a structural unit derived from ethylene glycol, a structural unit derived from terephthalic acid and a structural unit derived from isophthalic acid,
• a ratio of the structural unit derived from isophthalic acid is 3.0 mol % or more and 15 mol % or less relative to ratios of the structural unit derived from terephthalic acid and the structural unit derived from isophthalic acid constituting the polyester, and
• a content rate of an oligomer contained in the polyester layer is less than 2.0% by mass.