An antigraviton is the hypothetical antipartner of a graviton.

This hypothetical particle is the graviton.

nope. thats more for carnivals

In physics, the graviton is a hypothetical elementary particle (or wave) that mediates the force of gravitation in the framework of quantum field theory. If it exists, the graviton is expected to be massless. Two things to consider is that 1. gravitational attraction requires mass (either positive or negative, by formula), and 2. graviton interaction at a quantum level may be independent of any matter (e.g. parent atomic structure) similar to "spooky action at a distance."

Therefore insomuch as there is no evidence to support the graviton hypothesis, its quantum theoretical nature does not allow for its capture within a black hole; ergo, its does not have to escape.