A search for inverse beta decay electron antineutrinos has been carried out
using the 825 days sample of solar data obtained at SK. The absence of a
significant signal, that is, contributions to the total SK background and their
angular variations has set upper bounds on a) the absolute flux of solar
antineutrinos originated from 8B neutrinos ΦνΛβ(8B)=<1.8Γ105cmβ2sβ1 which is equivalent to an averaged conversion
probability bound of P<3.5% (SSM-BP98 model) and b) their differential energy
spectrum, the conversion probability is smaller than 8% for all Ee,visβ>6.5
MeV going down the 5% level above Ee,visββ10 MeV. It is shown that
an antineutrino flux would have the net effect of enhancing the SK signal at
{\em hep} neutrino energies. The magnitude of this enhancement would highly
depend on the, otherwise rather uncertain, steepness of the solar neutrino
spectrum at these energies.Comment: 5 pages, 3 ps figure