The process of sealing two or more layers of
material by means of the introduction of a high
frequency voltage field between two electrodes.
The electrodes conduct the high frequency current
through the material and also bring the surfaces
in close contact, thus ensuring an efficient weld.
When power is applied, the agitation of the
molecules within the plastic causes a rapid rise
in temperature until the softening point is
reached, whereupon the plastic sheets fuse along
the seam of the electrodes. Because the line of
fusing must be outside the area of the document
being sealed, it is necessary to cut the plastic
sheets somewhat larger than the document. (276 )