A pre-formed container, tray or pot can be
sealed with either a film, foil or paper lid. This lid can either
be pre-cut or fed from a reel of the material. The lidding material
is laid over the open face of the container and is heat sealed to
the container. Sealant layers on the tray and lid cause a bond to
form during the heat sealing process.
Heat sealing is a process which uses three variables: heat, force
and time. It describes the process of transferring heat by means of
conduction through a material at a given force for a period of time.
Different seal strengths can be achieved by:
Modifying the sealant layer of material (tray and film)
By increasing or decreasing any of the three variables (time,
temperature and seal force)
Different seal strengths include:
Weld (film cannot be peeled away from tray at all)
Cold peel (film can be peeled away from tray when it is cold)
Cold weld/hot peel (film peels easily when the tray and film
have been heated e.g. after cooking but forms a hermetic seal
when cold)
And any variety of strengths in between these
However, it is always worth considering the impact of contamination
(e.g. food or oil) on the tray or film – this will have an impact
on the seal strength achieved. If contamination is present it may
be necessary to increase any of the three variables.
