  Numerical calculations indicate that by suitably controlling the individual
gate voltages of a capacitively coupled parallel double quantum dot, with each
quantum dot coupled to one of two independent non-magnetic channels, this
system can be set into a spin-orbital Kondo state by applying a magnetic field.
This Kondo regime, closely related to the SU(4) Kondo, flips spin from one to
zero through cotunneling processes that generate almost totally spin-polarized
currents with opposite spin orientation along the two channels. Moreover, by
appropriately changing the gate voltages of both quantum dots, one can
simultaneously flip the spin polarization of the currents in each channel. As a
similar zero magnetic field Kondo effect has been recently observed by Y.
Okazaki {\it et al.} [Phys. Rev. B {\bf 84}, (R)161305 (2011)], we analyze a
range of magnetic field values where this polarization effect seems robust,
suggesting that the setup may be used as an efficient bipolar spin filter,
which can generate electrostatically reversible spatially separated spin
currents with opposite polarizations.
