  The existence problem for {C}ahn--{H}illiard system with dynamic boundary
conditions and time periodic conditions is discussed. We apply the abstract
theory of evolution equations by using viscosity approach and the Schauder
fixed point theorem in the level of approximate ploblem. One of the key point
is the assumption for maximal monotone graphs with respect to their domains.
Thanks to this, we obtain the existence result of the weak solution by using
the passage to the limit.
