Method and apparatus for characterizing magnetic coating compositions as well as improving magnetic particle dispersions

Method for improving the degree of dispersion of a magnetic coating composition consisting of a dispersion of magnetic particles in a liquid resin solvent mixture comprising the steps of:

• exposing said magnetic coating composition to an alternating magnetic field;
• exposing said coating composition, in addition to said alternating magnetic field, to a constant magnetic field for a time duration greater than the relaxation time of the rotation of magnetic particles in the liquid resin solvent;
• said constant magnetic field is applied perpendicular to the direction of said alternating magnetic field and has a field strength greater than the coercivity of the magnetic particles so that in the magnetic coating composition the degree of dispersion is improved;
• successively exposiong portions of said magnetic coating composition to said alternating and constant magnetic fields.

Apparatus for characterizing the degree of magnetic particle dispersion in a magnetic coating composition, said apparatus comprising:

• means for generating an alternating magnetic field through said magnetic coating composition;
• means for generating for a predetermined time duration a a constant magnetic field perpendicular to said alternating magnetic field in said magnetic coating composition;
• said time duration exceeds the relaxation time of the magnetic coating composition;
• means for measuring the changes in the magnetic field surrounding said magnetic composition when said constant magnetic field is switched on and off whereby the degree of dispersion of magnetic particles in the coating composition may be characterized from the measured changes.