Method for flushing pigments in the form of water-containing cakes

A method for flushing pigments in the form of a water-containing pigment cake by replacing the water with a suitable organic vehicle, comprising the steps of:

• feeding the pigment cake and the organic vehicle into a horizontally mounted mixing cylinder provided with an inlet opening and a lower closable outlet opening, said cylinder having a single coaxial mixing shaft therein, said shaft being provided with a plurality of projecting mixing tools, each of said mixing tools being connected to said shaft by means of a support rod which supports said mixing tool in the vicinity of the inside wall of said mixing cylinder;
• driving said mixing shaft at a speed such that substantially all of a mass of viscous pigment-vehicle paste formed from said vehicle and the pigment of said cake, within said cylinder, forms on and is wound up on said mixing shaft, thereby causing said water to be separated from said mass, said speed being a subcritical speed, wherein critical speed is calculated in rpm as 42.3 divided by the square root of the diameter of the mixing cylinder in meters;
• and
• draining the separated water which collects in the space between the wound-up pigment-vehicle paste and the inside wall of said mixing cylinder through said lower outlet opening, during said driving step.