Sealing method using a thin flexible lid to hermetically close a wide opening, delimited by an inner flange, of a container

A method of sealing a container at an annular end thereof, the method comprising the following steps:

• providing a hollow body, comprising a side wall extending around a longitudinal axis and a flange connected to an annular top of the side wall, the flange surrounding an axial opening of the container and being an internal flange protruding radially inward from the annular top as far as an annular inner rim;
• thermosealing a flexible lid onto the flange to close the opening, by axially contacting, pushing and heating the flexible lid with a ring portion of the flange;
• wherein the flange has a radial extension superior or equal to 2.0 mm and inferior or equal to 5.0 mm, measured between the annular inner rim and an annular outer rim adjacent to the annular top of the side wall,
• and wherein the annular inner rim extends perpendicular to the longitudinal axis and the flange is tapering upwardly at least before the thermosealing of the flexible lid, so as to form a slope angle between 5° and 20° to a plane perpendicular to the longitudinal axis, at the ring portion.