Note: Descriptions are shown in the official language in which they were submitted.
~ 32~ 2i~ i
Historically, interference pigments are an
outgrowth of nacreous pigments, that is, pigments which
simulate the effect of natural pearls. The pigments
are composed of thin platelets which are transparent in
the visible region of the spectrum. The platelets are
very smooth and part of the light which strikes the
platelets is reflected and part is transmitted through
the platelet. That part of the light which is trans-
mitted is subsequently reflected by other layers of
platelets. The result is that there are multiple re-
flections from many layers and it is this which gives
rise to a depth of sheen since the eye cannot focus on
one particular layer.
The reflection which takes place is specular
in that the angle of incidence equals the angle of
- reflection. The amount of light reflected at non-
specular angles is small and the amount of light re-
flected diminishes very quickly as the specular angle
-2- 1 3 2 1 2 ~3 i
is passed. The result is that nacreous pigments are
extremely sensitive to the angle of vie~ing. In order
for the maximum amount of light to be reflected, the
platelets must be extremely smooth. Any surface rough-
ness causes light to be scattered in a non-specular
manner and diminishes the lustrous effect.
The platelets must be aligned parallel to
each other and to the substrate for maximum
reflectivity. If not so aligned, light will be re-
flected randomly and again, luster will diminish. Theamount of light which is reflected depends on the index
of refraction of the platelets. The greater the index
of refraction, the greater the amount of light reflect-
ed. Since in most cases, the platelets are imbedded in
film forming medi~ms which have an index of refraction
of ap~roximately 1.5, it is necessary that the index of
refraction of the platelets be considerably greater
than 1.5.
In the case of the natural pearl, the layers
of reflecting material are composed of calcium carbon-
ate interspersed between layers of an organic material.
- Synthetic nacreous pigments have been made by growing
crystals of basic lead carbonate and bismuth oxy-
chloride. Both of these substances can be grown into
crystals which are extremely smooth and flat. More
recently, titanium dioxide, which per se has not been
grown into flat crystals has been coated on thin smooth
platelets of mica which act as ~ carrier. The ~ica
platelets are ideally from 5 to 50 microns in length.
The coatings of titanium dioxide which are applied
~32'~ 2~1
generally range from 60 nanometers to 160 nanometers in
thickness.
It is found that with a coating of 60
nanometers of titanium dioxide on mica, a pearl or
white lustrous pigment results. As the thickness of
the titanium dioxide is increased, interference of
,~,i~
light results and the colors of the rainbow are pro-
duced. Thus, it is possible to produce color using
only a transparent layer of titanium dioxide. The
colors seen from an oil slick or from a soap bubble are
examples of interference colors. The colors from an
oil slick or from a soap bubble disappear when the S02p
bubble collapses or the oil slick disappears. The
colors from the interference pigments, howaver, are
permanent and can be incorporated into film-forming
mediums to impart color. Interference pigments not
- only impart color but because of the~r constitution,
also impart luster.
Other substances besides titanium dioxide can
be used as the coating on mica. These include ZrO2,
2' ~ Fe2O3, Cr2O3, V2O5 and the hydrous forms
thereof. The oxides can be present in various crystal-
line forms. For example, Tio2 can be anatase or rutile
or mixtures of the two. Combinations of oxides of two
or more metals can be used as can their different crys-
talline forms.
Interference pigments, if composed of the
correct thickness, can reflect any color of the visible
spectrum. These colors can range from a yellow to a
red to a blue and a green. Shadings between these are
132 ~2 1 i
also possible. Because the reflected colors are pro-
duced by an interference effec~, the complementary
colors are produced by transmission. Thus if a red
color is produced by reflection from an interference
pigment, a green color will be seen if the pigment is
viewed in transmission.
If interference pigments are incorporated
into film formers and coated on white backgrounds, then
two colors can be seen depending on the angle of view-
ing. At near specular angles, the reflected color canbe observed. At other angles, the transmission color
can be observed.
In order to enhance the reflection color,
absorption pigments have been added to interference
pigments. In most cases, the absorption pigments have
been precipitated onto the interf~rence pigments so
that they form an integral part OI the platelets.
) Thus, for example, if Fe2O3 which has a yellow to red
color depending on its particle size is precipitated
upon a yellow interference color, an enhancement of the
yellow color will be produced. The yellow of the Fe2O3
adds to the yellow of the interference color producing
a rich lustrous yellow color. Those pigments which
have an absorption pigment added to an interference
pigment resulting in enhanced color intensity are
called combination pigments.
Other colorants besides Fe2O3 have been used.
In order to enhance the red interference color, car-
mine, an Grganic red colorant, is added to a red inter-
ference pigment. In order to enhance the blue, iron ~
~5~ 13~ 2
blue is added, and in order to enhance the green, Cr2O3is added.
If a colored oxide is used for the coating on
mica, that color will combine with the added colorant
and will modify the final absorption color. If a col-
orless oxide is used for the coating on mica, the ab-
~' sorption color will not be modified.
The concentration of the absorption pigmen'sis adjusted so that the color intensity produced is of
the same order of magnitude as the interference colors.
If the concentration of the colorants is too great, the
absorption colorant will obscure the interference color
and no enhancement will ta~e place. In order for this
enhancement to take place, the colorants are added at a
concentration between about 2~ and 5% in the case or
Tio2 coa.ed mica pigments, based upon the weight of
~ titanium dioxide coated mica.
- Not only can the absorption pigment of the
same color as the interference color be added but dif-
ferent absorption colorants can be added to different
interference~ colors. Thus, for example, it is possi-
ble to add a red absorption pigment (carmine) to a blue
interference pigment.
When absorption colorants differ in color
from the interference color, interesting color effects
are produced depending on the background and the angle
of viewing. Since the concentration of the colorants
is quite low, when the combination pigments are dis-
played over a blac~ bac~ground, the black absorbs the
color of the colorant and only the reflection color of
-6- 1 32 ~2L`~L
the interference is observed. This is true whether the
pigments are observed at the normal angle or the graz-
ing angle.
When the combination pigments are dispersed
in a film-forming medium and coated over a white back-
ground, two distinct colors can be observed depending
( ~ on the angle of viewing. At the normal angle of view-
ing, the reflection color of the interference pigment
is seen. At the difruse angle or the gra~ing angle,
the reflection color of the interference pigment is no
longer observed and the color of the absorpticn pigment
is now seen. Thus by chan~ing the angle of viewing
from the normal to a grazing angle, the color changes
from the reflection color of the interference to the
color of the absorption pigment. Very beautiful and
esthetically pleasing color effects can be seen.
Combination pigments have been used in
applicaLions such as coating on white, grey or black
substrates or incorporating them into formulations used
for cosmetic applications such as eye shadow, etc.
where such color changes would be desirable.
It has now been discovered that there is a
third color which is formed and that is the subject of
this invention. If the known combination pigments are
incorporated into a transparent film-forming medium and
coated on a transparent substrate such as glass, acryl-
ic sheet etc. a third color can be seen. This third
color is difrerent in color from both the reflection
color and the color of the absorption pigment. The
third color is formed from the mixing of the transmis-
~32~2il
sion color of the interference pigment with the color
o~ the absorption pigment. These third colors have,
heretofore, not been seen because combination pigments
are not used on transparent substrates.
In order to demonstrate the colors which are
formed, interference pigments made ~rom titanium diox-
ide coated mica were used as base substrates. Four
interference colors were used. They were yellow, red,
blue and green. The absorption pigments which were
used were a yellow (Fe2O3), a red (carmine), a blue
(iron blue) and a green (Cr2O3). ~ach of the absorp-
tion colorants was precipitated upon the interference
pigments forming a total of 16 samples. The concentra-
tion of the colorants ranged be~ween 2% and 5%. Other
colorants may be used in place of the colorants speci-
fied in these examples.
After appropriate processing, the combination
pigmants were incorporated at 3% concentration into a
nitrocellulose lacquer having a solids content of 9.5%.
Films of the combination pigments dispersed in the
nitrocellulose lacqler were formed on glass slides
using a Bird Film Applicator. This formed a wet film
of approximately 0.003 inch. The films were allowed to
dry so that the platelets were aligned parallel to the
film.
The dried films were viewed visually in
daylight by observing the specular reflection color at
-8- 1 3 ~
normal incidence, by observing the color at a diffuse
or grazing angle and finally by observing the color by
tr2nsmission, The observer stood with daylight at his
back and the slide held so that the light struck the
surface and was specularly reflected back to the ob-
server, For diffuse reflection, the slide was held
toward the light so that the light fell upon the sur-
~ace at a grazing angle and then was reflected to the
orserver. For tr-nsmission, the slides were held to
the light. The colors which were observed were record-
ed and the results of these observations are shown in
Table I. For comparison, the observations made on the
interference pigments which contained no absorption
pisments are also set forth. The combinations which
lS exhibited the most distinct three-color effects are
indicated by an asterisk.
These examples demonstrate that when the
) color of the absorption pigment is difrerent from the
reflecting color of the interference pigment or its
complement (the transmission color), a new color is
formed. Thus, a red colorant precipitated on a yellow
interference pigment (transmission color blue) formed a
third color, purple, by transmission. A green colorant
on the same yellow interference pigment formed a blue-
green color by transmission.
From the foregoing, it can be seen that --
various shades are possible depending on the identity
and conceniration OL absorption colorant used. A
greater concentrat;on of colorant will tend to shade
the color in the direction of the colorant. If too
~L 3 2 L d
great a concentration o~ colorant is used, the trans-
m ssion color will be masked and obscured and only the
absorption colorant will be seen. The concentration of
the absorption colorant is therefore determined by the
intensity of the transmission color. For the commer-
cially available interference pigments, a concentration
of absorption pigment varying between 2% and 5% has
been found to produce interesting third colors.
The combination pigments which have been used
in the Table to demonstrate third color ef ects had the
absorption pisments precipitated directly on tne sur-
faces. Similar results can be achieved by dispersing
the absorption colorants and the interference pigments
separately in the film former. In this case, tne ab-
sorption colorant is dispersed throughout the filmrather than being concentrated upon each platelet.
Similar, though not exactly equivalent, resulis are
( ~ produced. As can be expected, different concentrations
of colorant will be needed and these can be easily
determined by a few routine experiments.
Any object which is transparent or semi-
transparent and which will allow some of the light to
pass through and which can be coated with the combina-
tion pigments or have them incorporated therein can be
used. This includes glass bottles, glass sheets,
- sheets of transparent acrylic, polyester, etc.
Exam~le 1
A combination pigment of a yellow absorption
29 colorant and a red interference pigment was dispersed
--10--
~ L
in a water base acrylic polymer emulsion. The disper-
sion waS made by taking 3.0 9 of the combination pig-
ment, adding approximately 3 9 of the emulsion and
stirring in thorouqhly. Then 94 9 of the emul~ion was
slowly added with stirring to form a 3% concentration
of the combination pigment in the emulsion. This pig-
mented emulsion was then applied by brush to a clear
transparent acrylic sheet, one quarter inch in thick-
ness, and the emulsion allowed to dry. Small sections
were then cut from this sheet. Each of the sections
when viewed at the specular angle showed a red inter-
ference color, a yellow color at the glancing angle and
by transmission, a yellow-green color.
Similar sections were made using different
combination pigments. The sections were mounted on a
large acrylic panel to simulate a stained glass effect
depicting various scenes.
Examle 2
A combination pigment of a red absorption
colorant on a blue interference pigment was dispersed
in a clear thermosetting acrylic enamel (AT56~ Rohm &
Haas Co.) and diluted in a ratio of 2:1 with xylene.
The dispersion was made by taking 3.0 9 of the combina-
tion pigment and adding approximately 3 9 of the
thermosetting acrylic which was stirred in thoroughly.
Then 94 9 of the acrylic enamel was added with stir- -
ring. The pigmented acrylic enamel was applied to a
large transparent glass bowl approximately 24 inches in
29 diameter. The coating was applied using a conventional
-ll- 13~ ~2
air spray gun. Two layers were applied~ The coating
was then cured in an oven at 120C for 30 minutes.
Viewing the bowl directly a blue reflection color was
seen. The sides of the bowl displayed a red absorption
S color and the rear of the bowl where the transmission
~ color could be seen displayed an orange color. 'rhe
-, colors blended one into the other and a pleasing artis-
tic effect was produced which was a delight to the eye.
Exam~le 2A
The components of the combination pigment of
Example 2 were introduced separately into the acrylic
lac~uer of that example. The red colorant was first
dispersed followed by the blue inte ference pigment.
The color pl2y in the coated bowl was similar to that
seen in Example 2.
(~ Exam~le 3
A combination pigment of a red absorption
pigment on a yellow interference pigment was dispersed
in ~ nitrocellulose lacquer. The dispersion was made
by mixing 3.0 g of the pigment with 3 g of a nitrocel-
lulose lacquer having a solids content of 9.5%. After
thorough mixing, an additional 94 g of the nitrocellu-
lose lacquer was added with stirring. Films of the
dispersed particles in the nitrocellulose lacquer were
formed on glass slides by using a Bird Film Applicator
This formed a wet film of approximately 0.003 inch.
The films were allowed to air dry. The glass slides
28 were then cut into rectangular sections, 2 inches by 3
-12- ~ ~ 2~J rL
inches, and provision made so the slides could be hung
by a wire or string.
Similar slides were made using the
combination pigment of a red colorant on a yellow in-
terference pigment and the combination pigment of ayellow colorant on a red interference pigment. The
slides were then hung from strings as in a mobile and
beautiful color effects could be seen as each slide,
revolving slowly by air currents, alternately showed
various colors by reflection and transmission.
Exam~le g
A combination pigment of a blue colorant and
green interference pigment was dispersed in a low den-
sity polyethylene. 950 g of Tenite 1925F~ made by
Eastman Chemicals was put into a Banbury Mixer. The
plastic was mixed until melted. 50 9 of the combina-
tion pigment were then added slowly to the melted plas-
tic and mixing was continued for 10 minutes. After the
mixing cycle was complete, the pigmented plastic was
dumped into a pan and taken immediately to a Boling
Steward hot roll machine where the pigmented plastic
was pressed between the 2 hot rolls to form a slab ~ to
~ inch in thickness and 10 inches wide. It was scored
with a razor knife, allowed to cool, and broken into
small pieces. It was then granulated in a Cumberland~
Granulator. After granulation, the material was taken
to a Killian~ Extruder where it was extruded from a
sheeting die forming a sheet approximately 4 mils in
29 thickness. A green color was observed at the specular
~. ,,
3 2 ~
angle, a blue color at a glancing angle and by trans-
mission, a purple color was seen. Similar sheets could
be made using different combination pigments and all
could be cut into different patterns and suitably
mounted on a clear substrate (for example between 2
~ pieces of glass) to form an art work which had a myriad
`~ of colors.
From the examples set forth hereinbefore, it
can be seen that the combination pisments can be ap-
plied to a substrate by methods which are ~nown in theart. The coating me~hods include brush, roll, knife,
pressure-roll, engraving roll, dipping, air blade, air
spray, electrostatic spray, airless spray, fluidized
bed and other similar methods. The pigmented plastics
can also be molded by any of the known processes which
include compression molding, injection molding, e~tru-
sion, or blow molding. They may also be cast by vari-
~;) ous processes.
The thermoplastics which can be used include
cellulose acetate, cellulose acetate butyrate, poly-
carbonate, polyethylene, polypropylene, polystyrene,
and similar materials. The thermosetting plastics
include epoxy resins, phenol-formaldehyde acrylic,
polyesters, polystyrene, polyurethanes and similar
products.
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