Abstract: An agitator mill is provided with a separate grinding-stock/auxiliary-grinding-body separator device, which comprises a rotor, drivable to rotate, for the separation of the auxiliary grinding bodies from the treated grinding stock. The auxiliary grinding bodies and untreated grinding stock are returned to the agitator mill. The separator device and the agitor mill and the lines connecting these two form a closed system.

Abstract: A process for producing a curable resin liquid comprising: (a) at least one cyanate ester compound and (b) at least one polyfunctional maleimide compound, characterized in that the process comprises:(A) reacting at least one said maleimide compound with said diamine in the presence of a diluent at a temperature of 60.degree.-200.degree. C., the ratio of the maleimide group to the amine group being in the range of from 1:0.0015 to 1:0.3 to form a preliminary reaction product substantially free from amine group; and(B) mixing said preliminary reaction product with at least one cyanate ester compound ratio by weight of said preliminary reaction product to said cyanate ester compound is disclosed.