  The near threshold "soft breakdown" measurements of PVC films conductivity
are investigated. In a wide range of external electric field strength for
various rather thick (>20 mkm) PVC films the resistance shows strong
nonlinearity and seems to enter high conductive state close to the breakdown
threshold. For our "thick" films boundary conditions electrode surface
specifics should not be so important as in thin polymer films experiments. Both
fast, instant mechanisms of nonlinearity, and effects of accumulation and delay
responce were observed. The phenomena corresponding to reversible transitions
in a state with rather high conductivity, seems to be similar to ones
registered earlier in thin layers of some broad-bandgap polymers. In a range of
relatively low field intensity, far from a threshold breakdown, as a result of
reversible switches between normal and high resistivity states a polymer film
in a standard measuring cell formed a relaxation generator giving a loud enough
sound signal with frequency increasing with the increase of external field.
