  The effects induced by the quantum vacuum fluctuations of one massless real
scalar field on a configuration of two partially transparent plates are
investigated. The physical properties of the infinitely thin plates are
simulated by means of Dirac-$\delta-\delta^\prime$ point interactions. It is
shown that the distortion caused on the fluctuations by this external
background gives rise to a generalization of Robin boundary conditions. The
$T$-operator for potentials concentrated on points with non defined parity is
computed with total generality. The quantum vacuum interaction energy between
the two plates is computed using the $TGTG$ formula to find positive, negative,
and zero Casimir energies. The parity properties of the $\delta-\delta^\prime$
potential allow repulsive quantum vacuum force between identical plates.
