Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-10-24
2004-02-10
Koslow, C. Melissa (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S417000, C106S418000, C106S425000, C106S428000, C106S431000, C106S436000, C106S439000
Reexamination Certificate
active
06689205
ABSTRACT:
The invention relates to multilayer interference pigments consisting of a transparent carrier material coated with alternating layers of a metal oxide of low refractive index and a metal oxide of high refractive index.
Multilayer pigments of low transparency and with a similar layer structure are known. The metal oxide layers are prepared either in a wet process, by precipitating the metal oxide hydrates from a metal salt solution onto a carrier material, or by vapour deposition or sputtering in a vacuum. In general, the vapour deposition processes are too complex and costly for mass production of pigments. Thus U.S. Pat. No. 4,434,010 describes a multilayer interference pigment consisting of a central layer of a reflecting material (aluminium) and alternating layers of two transparent, dielectric materials of high and low refractive index, for example titanium dioxide and silicon dioxide, either side of the central aluminium layer. This pigment is employed for the printing of securities.
JP H7-759 (Kokoku) describes a multilayer interference pigment with a metallic lustre. It consists of a substrate coated with alternating layers of titanium dioxide and silicon dioxide. The substrate is formed from flakes of aluminium, gold or silver or from platelets of mica and glass which are coated with metals. Accordingly, it is a typical metallic pigment. This pigment is of high opacity. For applications where a high level of transparency of the pigmented material is required, as for example for agricultural films, the pigment is unsuitable. Furthermore, it has the disadvantage that the depth effect typical of interference pigments is not produced since, owing to the high reflection of light at the metal layer which forms the core, pigment particles lying deeper in the application medium are unable to contribute to the optical appearance. The interference effect therefore remains limited to the layers located on the metal layer.
The object of the invention is to provide an essentially transparent interference pigment having strong interference colours and/or a strong angular dependency of the interference colours. Furthermore, the object of the invention is to provide pigments having specific spectral characteristics in the visible region and in the infrared region.
This object is achieved in accordance with the invention by a multilayer interference pigment consisting of a transparent carrier material coated with alternating layers of metal oxides of low and high refractive index, the difference in the refractive indices being at least 0.1, which is obtainable by alternate coating of the transparent carrier material with a metal oxide of high refractive index and with a metal oxide of low refractive index in a wet process by hydrolysis of the corresponding water-soluble metal compounds, separation, drying and, if desired, calcination of the resulting pigment.
The transparent carrier material is mica, a different phyllosilicate, glass flakes, PbCO
3
×Pb(OH)
2
and BiOCl in platelet form, or platelet like silicon dioxide prepared by the process described in WO 93/08237.
The metal oxide of high refractive index can be an oxide or mixtures of oxides with or without absorbing properties, such as TiO
2
, ZrO
2
, Fe
2
O
3
, Fe
3
O
4
, Cr
2
O
3
, or ZnO, for example, or a compound of high refractive index, for example iron titanates, iron oxide hydrates and titanium suboxides, or mixtures and/or mixed phases of these compounds with one another or with other metal oxides.
The metal oxide of low refractive index is SiO
2
, Al
2
O
3
, AlOOH, B
2
O
3
or a mixture thereof and can likewise have absorbing or nonabsorbing properties. If desired, the oxide layer of low refractive index may include alkali metal oxides and alkaline earth metal oxides as constituents.
This object is additionally achieved in accordance with the invention by a process for the preparation of the novel pigments, in which the transparent carrier material is suspended in water and coated in alternation with a metal oxide hydrate of high refractive index and with a metal oxide hydrate of low refractive index by addition and hydrolysis of the corresponding water-soluble metal compounds, the pH necessary for the precipitation of the respective metal oxide hydrate being established and held constant by simultaneous addition of acid or base, and then the coated carrier material is separated off from the aqueous suspension, dried and, if desired, calcined.
The invention additionally relates to the use of the novel pigments for pigmenting paints, printing inks, plastics, glazes for ceramics and glass, cosmetics and, in particular, for the production of agricultural films.
For this purpose they can be employed as mixtures with customary commercial pigments, for example inorganic and organic absorption pigments, metallic pigments and LCP pigments.
The thickness of the layers of the metal oxides of high and low refractive index is critical for the optical properties of the pigment. Since a product with powerful interference colours is desired, the thicknesses of the layers must be adjusted relative to one another. If n is the refractive index of a layer and d its thickness, the interference colour of a thin layer is the product of n and d, i.e. the optical thickness. The colours of such a film, as produced with normal incidence of light in reflected light, result from an intensification of the light of wavelength &lgr;=(4/2N−1) ·nd and by attenuation of light of wavelength &lgr;=(2/N) ·nd, where N is a positive integer. The variation in colour which takes place as the thickness of the film increases results from the intensification or attenuation of particular wavelengths of the light by interference. For example, a 115 nm film of titanium dioxide of refractive index 1.94 has an optical thickness of 115×1.94=223 nm, and light of wavelength 2×223 nm=446 nm (blue) is attenuated in the course of reflection, with the result that the reflected light is yellow. In the case of multilayer pigments, the interference colour is determined by the intensification of specific wavelengths and, if two or more layers in a multilayer pigment possess the same optical thickness, the colour of the reflected light becomes more intense and full as the number of layers increases. Moreover, by a suitable choice of the layer thicknesses it is possible to achieve a particularly marked variation of colour in dependency on the viewing angle. A pronounced colour flop develops, which may be desirable for the pigments according to the invention. The thickness of the individual metal oxide layers, independently of their refractive index, is therefore from 20 to 500 nm, preferably from 50 to 300 nm.
The number and thickness of the layers is dependent on the desired effect and on the substrate used. On mica, the desired effects are achieved if the 3-coat system TiO
2
/SiO
2
/TiO
2
is built up and if the thicknesses of the individual layers are matched optically to one another. When using optically relatively thin TiO
2
and SiC
2
layers (layer thickness <100 nm) it is possible, for example, to produce pigments with a blue interference colour which, with a substantially smaller TiO
2
content, are stronger in colour and more transparent than pure TiO
2
-mica pigments. The saving in terms of TiO
2
is up to 50% by weight.
By means of the precipitation of thick SiO
2
layers (layer thickness >100 nm), pigments having a strongly pronounced angular dependency of the interference colour are obtained.
By precipitating further TiO
2
and SiO
2
layers it is also possible to obtain 5-layer and higher systems, but then the number of layers is limited by the economics of the pigment.
However, if SiO
2
platelets of uniform layer thickness are used as substrate instead of mica, then further, particularly well-defined interference effects can be achieved.
In this case, covering the substrate with, for example, 3 layers of the abovementioned structure produces an interference system comprising 7 thin layers of sharply define
Brückner Hans-Dieter
Heyland Andrea
Schank Christina
Schmidt Christoph
Seibel Claudia
Koslow C. Melissa
Merck Patent Gesellschaft
Millen White Zelano & Branigan P.C.
LandOfFree
Multilayer interference pigments does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Multilayer interference pigments, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multilayer interference pigments will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3289875