Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2000-04-17
2003-07-22
Bell, Mark L. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S415000, C106S418000, C106S436000, C106S438000, C106S439000, C106S442000, C428S404000
Reexamination Certificate
active
06596070
ABSTRACT:
The present invention relates to interference pigments based on multiply coated platelet-shaped substrates.
Lustre pigments or special-effect pigments are employed in numerous fields in industry, especially in the sector of automotive finishes, in decorative coating, in plastics, in paints, in printing inks and in cosmetic formulations.
Lustre pigments which exhibit an angle-dependent colour change between two or more interference colours have a play of colour which makes them of particular interest for automotive finishes and in connection with counterfeit-protected documents of value. Pigments of this kind on the basis of multiply coated platelet-shaped substrates are known.
Interference pigments consist generally of platelet-shaped substrates with a thickness of from 200 to 1000 nm which are coated with highly refractive metal oxides or metal oxide mixtures with a thickness of from 50 to 300 nm. The optical properties of these pigments are critically determined by the refractive index of the metal oxide layer. In addition to the possibility of using chemical vapour deposition (CVD) or physical vapour deposition (PVD) techniques to prepare metal oxide layers having high densities and so refractive indices that lie close to the optimum, the deposition of metal oxides on finely divided, platelet-shaped substrates is frequently accomplished by titrating aqueous, usually acidic metal salt solutions against sodium hydroxide solution in the presence of a substrate, as described, for example, in DE 14 67 468 and DE 20 09 566.
A disadvantage of the vapour deposition technique is the high costs it entails. For instance, U.S. Pat. No. 4,434,010 discloses a multilayer interference pigment consisting of a central layer of a reflective metal, such as aluminium, and alternating layers of two transparent dielectric materials of high and low refractive index respectively, such as titanium dioxide and silicon dioxide, for example. This multilayer pigment is used preferably for counterfeit-protected securities.
JP H7-759 discloses a multilayer interference pigment with metallic lustre, for which a substrate is coated with alternate layers of titanium dioxide and silicon dioxide. The substrate comprises flakes of aluminium, gold or silver, or of mica or glass, with a coating of metals. The depth effect which is characteristic of and desired for interference pigments, however, cannot be generated. This is because of the total reflection of the light at the metal layer which forms the core. Consequently, the interference effect remains limited to the layers which are located on the metal layer. Furthermore, the lack of transparency of the substrate greatly restricts the diverse possibilities for combination with further pigments in applications-related formulations.
U.S. Pat. No. 3,438,796 and U.S. Pat. No. 5,135,812 describe, for example, metal lustre pigments having a central opaque aluminium film coated on both sides in alternation with dielectric films of low refractive index, such as silicon dioxide or magnesium fluoride, and with partially transparent metal films, such as films of chromium or aluminium, for example. Owing to the preparation process, the central metal film of these pigments is coated only on the top and bottom sides of the platelets, while the side areas constitute broken edges and lie open towards the medium.
DE 44 05 494, DE 44 37 753, DE 195 16 181 and DE 195 15 988 disclose lustre pigments prepared by coating metal platelets, especially aluminium flakes, with metal oxide layers of low refractive index, such as with a silicon dioxide layer, and with non-selectively absorbing metal oxide layers or metal layers of high refractive index, using CVD or wet-chemical techniques.
Lustre pigments based on metal substrates frequently have good performance properties, including good opacity, but the result on application, such as in the paint, for example, is a “hard” metallic lustre, which is frequently unwanted.
Lustre pigments based on transparent platelet-shaped substrates which do not have this “hard” metallic lustre are the subject of WO 93/12182. Mica flakes are covered with a metal oxide layer of high refractive index, such as TiO
2
, and with a non-selectively absorbing layer. Depending on the thickness of the TiO
2
layer, when viewed straight on these pigments exhibit a particular interference colour which becomes increasingly weaker as the viewing angle becomes more oblique and which finally flips to grey or black. The interference colour does not change, but a decrease is found in the colour saturation.
JP 1992/93206 claims lustre pigments on the basis of glass flakes or mica particles which are covered with an opaque metal layer and with alternating layers of SiO
2
and TiO
2
.
EP 0 753 545 discloses lustre pigments based on multiply coated, nonmetallic, platelet-shaped substrates which are of high refractive index, are at least partially transparent to visible light and have at least one layer assembly comprising a colourless coating of low refractive index and a reflective coating which absorbs selectively or nonselectively. Disadvantages of this invention are the technically very complex and costly preparation process and the frequent difficulty in reproducing the pigments in the desired product quality.
The object of the present invention is to provide an essentially transparent interference pigment having strong interference colours and/or a strong angular dependence of the interference colours which is notable for its advantageous performance properties and which at the same time can be prepared in a simple manner.
Surprisingly, an interference pigment has now been found which is based on multiply coated, platelet-shaped substrates and comprises a particular arrangement of optically functional layers by means of which particular optical effects are achieved.
The invention therefore provides interference pigments on the basis of multiply coated, platelet-shaped substrates which comprise at least one layer sequence comprising
(A) a coating having a refractive index n≧2.0,
(B) a colourless coating having a refractive index n≦1.8, and
(C) a nonabsorbing coating of high refractive index,
and, if desired,
(D) an external protective layer.
The invention also provides for the use of the pigments of the invention in paints, lacquers, printing inks, plastics, ceramic materials, glasses and cosmetic formulations.
Suitable base substrates for the multilayer pigments of the invention are firstly opaque and secondly transparent platelet-shaped substances. Preferred substrates are phyllosilicates and metal oxide-coated, platelet-shaped materials. Of particular suitability are natural and synthetic micas, talc, kaolin, platelet-shaped iron oxides, bismuth oxychloride, flakes of glass, SiO
2
, Al
2
O
3
or TiO
2
, synthetic ceramic flakes, carrier-free synthetic platelets, LCPs or other comparable materials.
The size of the base substrates per se is not critical and can be matched to the particular target application. In general, the platelet-shaped substrates have a thickness of between 0.1 and 5 &mgr;m, in particular between 0.2 and 4.5 &mgr;m. The extent in the two other dimensions is usually between 1 and 250 &mgr;m, preferably between 2 and 200 &mgr;m and, in particular, between 5 and 50 &mgr;m.
The thickness of the individual layers of high and low refractive index on the base substrate is essential for the optical properties of the pigment. For a pigment with intensive interference colours, the thickness of the individual layers must be adjusted precisely with respect to one another.
If n is the refractive index of a thin layer and d its thickness, the interference colour of this layer is defined by the product n·d(n·d=optical thickness). The colours which result from such a film under perpendicular light incidence in reflected light result from an intensification of the light of wavelength
λ
=
4
2
N
-
1
·
n
·
d
and by an attenuation of the light of wavelength
λ
=
2
N
·
n
·
d
where N is a positive
Pfaff Gerhard
Schank Christina
Schmidt Christoph
Schoen Sabine
Bell Mark L.
Hailey Patricia L.
Merck Patent Gesellschaft
Millen White Zelano & Branigan P.C.
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