Several techniques may be used for forming a colored interference filter
coating on a substrate such as polyester film. The interference filter has
two metal reflective films, at least one of which is semi-transparent. A
layer of transparent acrylate polymer dielectric between the metal layers
completes the interference filter, which may be sandwiched between
protective layers. The dielectric is formed by evaporating an acrylate
monomer having a molecular weight in the range of from 150 to 600.
Preferably the acrylate monomer has a molecular weight to acrylate group
ratio in the range of from 150 to 400. The acrylate condenses on the
substrate and is polymerized in situ for forming a monolithic film with a
sufficient thickness to produce an interference color. In several
embodiments different areas of the film have different thicknesses for
producing different interference colors. The thickness of the dielectric
can be controlled by the amount of monomer condensed, by either
controlling the temperature of the condensation surface or controlling the
amount of monomer evaporated adjacent a predetermined area of the
substrate. Thickness may also be controlled by condensing a uniform layer
of monomer and polymerizing the monomer to different degrees for varying
the shrinkage of the film and hence the thickness of the film and color.