The positive roller creates an electric field that pushes the charge in the "opposite" direction to the circuit. So, what pushes the electrons? Answer: At "2" it is an electric field that causes the electrons to migrate through the air gap. But below point "2", on the moving belt, the electrons are carried against the electric field by the motor that causes the belt to move. Rubber is an insulator, so that the electrons are unable move according to F=qE, but instead are influenced the force that prevents electrons from moving through an insulator.
