Method of sealing containers and lids by melt adhesion by laser

A method of sealing a container and a lid by melt adhesion by a laser beam, wherein

• said container is a cup type container having a bottom portion, a body portion and a flange portion, said lid is a lid formed in a dented shape, said container comprising a thermoplastic resin that permits the laser beam to transmit therethrough, said lid comprising a resin composition of the thermoplastic resin containing a heat-generating substance that generates heat upon absorbing the laser beam;
• the method comprising applying the laser beam to a contacting surface of the flange portion and a circumferential portion of the lid from a lower side of the container in a state where the container and the lid are being pushed and closely contacted to each other by use of a pushing jig, wherein
• said laser beam is capable of applying a rectangular beam having a uniform intensity distribution,
• an upper-limit of temperature that is elevated by the application of the laser beam lies in a range of not lower than a melting point of said thermoplastic resin but lower than a thermal decomposition start temperature thereof in a melt adhesion interface between said container and said lid, and
• the temperature reaches said upper-limit in a heating time t (msec) represented by the following formula (1),
• t (msec)=L/S (1)
• wherein L is the length (mm) of the rectangular beam in the scanning direction, and S is the rate of laser scanning (mm/msec) of not higher than 1.65 mm/msec.