Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-02-15
2003-06-17
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S417000, C106S418000, C106S430000, C106S436000
Reexamination Certificate
active
06579355
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to interference pigments, preferably strong interference pigments, based on multiply-coated platelet-shaped substrates.
BACKGROUND OF THE INVENTION
Luster or effect pigments are widely used in industry, especially in automotive coatings, decorative coating, plastic, paints, printing inks and cosmetic formulations.
Luster pigments with an angle-dependent color change between a number of interference colors exhibit a color interplay which makes them particularly useful for automotive coatings and anti-counterfeit applications. Pigments of this type which are based on multiply-coated platelet-shaped substrates are known for example from U.S. Pat. No. 4,434,010, JP H7-759, U.S. Pat. No. 3,438,796, U.S. Pat. No. 5,135,812, DE 44 05 494, DE 44 37 753, DE 195 16 181 and DE 195 15 988.
WO 93/12182 discloses luster pigments based on transparent platelet-shaped substrates without a harsh metallic luster. Mica platelets are coated with a high refractive index metal oxide layer, for example TiO
2
and a non-selectively absorbing layer. These pigments have in plan view a certain interference color which depends on the TiO
2
layer thickness and which increasingly weakens with increasing skewness of viewing angle and finally flops off into grey or black. The interference color does not change, but there is a noticeable decrease in the saturation.
JP 1992/93206 teaches luster pigments based on glass platelets or mica platelets coated with an opaque metal layer and alternating SiO
2
and TiO
2
layers.
EP 0 753 545 A2 discloses goniochromatic luster pigments based on multiply-coated, high refractive index, nonmetallic, platelet-shaped substrates which are at least partially transparent to visible light, comprising at least one layer packet of a colorless coating having a low refractive index and a reflecting, selectively or non-selectively absorbing coating. The production process described in EP 0 753 545 A2 involves coating the pigment substrate via chemical vapour deposition (CVD) in a fluidized bed reactor. The substrate, for example finely divided mica, is fluidized in a stream of an inert carrier gas. The reagents required to form the oxide layers are supplied via the inert gas stream or further inert gas inlets. Owing to the large density difference between mica/pigment and carrier gas, however, an essential problem of this process is a uniform distribution of the solid particles and hence a uniform coating. Disadvantages of this invention are accordingly the technically very complicated and cost-intensive production process and the frequently immense difficulty of reproducing the pigments in the desired product quality.
EP 0 768 343 A2 discloses goniochromatic luster pigments comprising a silicon-containing coating and based on multiply-coated platelet-shaped metallic substrates.
Prior art multilayer pigments all possess insufficient color strength and comparatively poor hiding power. In addition, some of the pigments are very difficult to produce or reproduce.
SUMMARY OF THE INVENTION
It is a feature of the present invention to provide hiding gold and reddish orange interference pigments of high color strength which have advantageous application properties and are simple to produce.
Surprisingly, there have now been found gold and reddish orange pigments based on multiply-coated platelet-shaped substrates which contain a certain arrangement of optically functional layers, whereby particular visual effects are obtained.
The strong interference pigments of the invention are notable for their extremely high color strength or chroma C, their very high hiding power and a very pronounced luster featuring a glitter effect. Unlike gold-colored pearl luster pigments as disclosed in EP 0 211 351 B1, for example, the gold-colored interference pigments of the invention possess significantly higher color strength and a higher hiding power. The gold pigments of the invention are equivalent to existing metal bronzes—superior with regard to luster and color strength—in intaglio printing on textiles in particular.
Unlike goniochromatic pigments, the pigments of the invention provide a color effect which has little if any angle dependence.
The present invention accordingly provides a strong interference pigment based on multiply-coated platelet-shaped substrates, comprising at least one layer sequence of
(A) a high refractive index coating comprising a mixture of TiO
2
and Fe
2
O
3
in a ratio of about 10:1 to about 1:3 and optionally one or more metal oxides in amounts of ≲ about 20% by weight based on the layer (A),
(B) a colorless coating having a refractive index n ≲ about 1.8, and optionally
(C) an outer protective layer.
The invention further provides for the use of the pigments of the invention in paints, coatings, printing inks, plastics, ceramic materials, glasses, cosmetic formulations, for laser marking paper and plastics, especially in printing inks. The pigments of the invention are further useful for producing pigment preparations and also for producing dry products, for example granules, chips, pellets, briquettes, etc. The dry products are particularly useful for coatings and printing inks.
Useful base substrates for the multilayer pigments of the invention are opaque platelet-shaped substrates and transparent platelet-shaped substrates. Preferred substrates are sheet-silicates and also platelet-shaped materials with metal oxides. Of particular usefulness are natural and synthetic micas, talc, kaolin, platelet-shaped iron or aluminium oxides, glass, SiO
2
, TiO
2
or synthetic ceramic platelets, synthetic carrier-free platelets, liquid crystal polymers (LCPs), holographic pigments, BiOCl, metal platelets, for example aluminium platelets, aluminium bronzes, brass bronzes, zinc bronzes, titanium bronzes or other comparable materials.
The size of the base substrates is not critical per se and can be adapted to the particular end use. In general, the platelet-shaped substrates are between about 0.1 and about 5 &mgr;m, especially between about 0.2 and about 4.5 &mgr;m, in thickness. In the other two dimensions they usually extend between about 1 and about 250 &mgr;m, preferably between about 2 and about 200 &mgr;m, especially between about 5 and about 60 &mgr;m.
The thickness on the base substrate of the individual layers having a high refractive index (pseudobrookite, for example) and a low refractive index is essential for the optical properties of the pigment. To obtain a pigment providing intensive interference colors, the thicknesses of the individual layers have to be accurately adjusted with respect to one another.
If n is the refractive index of a thin layer and d its thickness, the interference color of this layer is determined by the product n•d (n•d=optical thickness). The colors of such a film which are produced in the reflected light of light of normal incidence result from an amplification of the light of the wavelength
λ
=
4
2
N
-
1
·
n
·
d
and through weakening of the light of the wavelength
λ
=
2
N
·
n
·
d
where N is a positive integer.
The variation in color resulting with increasing film thickness is the result of interference causing some wavelengths of the light to be amplified or attenuated. If a plurality of layers in a multilayer pigment have the same optical thickness, the color of the reflected light will increase in intensity as the number of layers increases. But, given a suitable choice with regard to layer thicknesses, very attractive interference pigments can also be obtained with layers having different optical thicknesses. The thickness of any one metal oxide layer—independent of the refractive index—is generally within the range from about 10 to about 1000 nm, preferably within the range from about 15 to about 800 nm, especially within the range about 20—about 600 nm, depending on the intended application.
The interference pigments of the invention include an alternating arrangement of a high refractive index coating
Bernhardt Klaus
Heinz Dieter
Schmidt Christoph
Bell Mark L.
Hailey Patricia L.
Merck Patent Gesellschaft mit Beschraenkter Haftung
Millen White Zelano & Branigan
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