August 10, 2005

Interference Pigment
● Patent No. U.S. 6,500,251 B1
This patent, awarded to Merck
Patent Gesellschaft, Darmstadt,
Germany, covers a multilayer interference
pigment. The pigment is comprised
of a platelet shaped titanium
dioxide as carrier material, coated
with alternating layers of metal oxides
of low refractive index and colorless
non-absorbing metal oxides of high
refractive index, each layer having a
thickness of from 20 to 500 nm, the
difference in the refractive indices
being at least 0.1, which is obtained by
solidification and hydrolysis of an
aqueous solution of a thermally
hydrolyzable inorganic titanium compound
on a continuous belt, detachment
of the resulting coat, whereby a
platelet shaped titanium dioxide pigment
is formed, coating of the resulting
titanium dioxide platelets, with or
without drying in between, by a wet
method with, alternately, a metal
oxide hydrate of low refractive index
and a colorless non-absorbing metal
oxide hydrate of high refractive index
by hydrolysis of the corresponding,
water soluble inorganic metal compounds,
separation, drying and,
optionally, calcining of the material